diff options
author | bors[bot] <26634292+bors[bot]@users.noreply.github.com> | 2021-06-04 18:45:37 +0100 |
---|---|---|
committer | GitHub <[email protected]> | 2021-06-04 18:45:37 +0100 |
commit | 98395f29a417b37a5969594f0cac5ae23585da85 (patch) | |
tree | 3a13913003723f3da843dae8580287b9d33c68eb /crates/ide_completion/src | |
parent | 92d91050c4aa48732e7af3bf979aa7ed5aed924d (diff) | |
parent | ae1c63fcdd0caf34f41fba62b04e3d868a589f1d (diff) |
Merge #9138
9138: feat: Implement hover for lints r=Veykril a=Veykril
fixes https://github.com/rust-analyzer/rust-analyzer/issues/8857, fixes https://github.com/rust-analyzer/rust-analyzer/issues/3941

We also generate the default lints(and lint groups 🎉) instead now by invoking `rustc -W help` and parsing the output from that.
Co-authored-by: Lukas Wirth <[email protected]>
Diffstat (limited to 'crates/ide_completion/src')
-rw-r--r-- | crates/ide_completion/src/completions/attribute.rs | 5 | ||||
-rw-r--r-- | crates/ide_completion/src/completions/attribute/lint.rs | 127 | ||||
-rw-r--r-- | crates/ide_completion/src/generated_lint_completions.rs | 6380 | ||||
-rw-r--r-- | crates/ide_completion/src/lib.rs | 1 |
4 files changed, 4 insertions, 6509 deletions
diff --git a/crates/ide_completion/src/completions/attribute.rs b/crates/ide_completion/src/completions/attribute.rs index c48bb9e66..f80d7eec3 100644 --- a/crates/ide_completion/src/completions/attribute.rs +++ b/crates/ide_completion/src/completions/attribute.rs | |||
@@ -3,20 +3,19 @@ | |||
3 | //! This module uses a bit of static metadata to provide completions | 3 | //! This module uses a bit of static metadata to provide completions |
4 | //! for built-in attributes. | 4 | //! for built-in attributes. |
5 | 5 | ||
6 | use ide_db::helpers::generated_lints::{CLIPPY_LINTS, DEFAULT_LINTS, FEATURES}; | ||
6 | use once_cell::sync::Lazy; | 7 | use once_cell::sync::Lazy; |
7 | use rustc_hash::{FxHashMap, FxHashSet}; | 8 | use rustc_hash::{FxHashMap, FxHashSet}; |
8 | use syntax::{algo::non_trivia_sibling, ast, AstNode, Direction, NodeOrToken, SyntaxKind, T}; | 9 | use syntax::{algo::non_trivia_sibling, ast, AstNode, Direction, NodeOrToken, SyntaxKind, T}; |
9 | 10 | ||
10 | use crate::{ | 11 | use crate::{ |
11 | context::CompletionContext, | 12 | context::CompletionContext, |
12 | generated_lint_completions::{CLIPPY_LINTS, FEATURES}, | ||
13 | item::{CompletionItem, CompletionItemKind, CompletionKind}, | 13 | item::{CompletionItem, CompletionItemKind, CompletionKind}, |
14 | Completions, | 14 | Completions, |
15 | }; | 15 | }; |
16 | 16 | ||
17 | mod derive; | 17 | mod derive; |
18 | mod lint; | 18 | mod lint; |
19 | pub(crate) use self::lint::LintCompletion; | ||
20 | 19 | ||
21 | pub(crate) fn complete_attribute(acc: &mut Completions, ctx: &CompletionContext) -> Option<()> { | 20 | pub(crate) fn complete_attribute(acc: &mut Completions, ctx: &CompletionContext) -> Option<()> { |
22 | let attribute = ctx.attribute_under_caret.as_ref()?; | 21 | let attribute = ctx.attribute_under_caret.as_ref()?; |
@@ -25,7 +24,7 @@ pub(crate) fn complete_attribute(acc: &mut Completions, ctx: &CompletionContext) | |||
25 | "derive" => derive::complete_derive(acc, ctx, token_tree), | 24 | "derive" => derive::complete_derive(acc, ctx, token_tree), |
26 | "feature" => lint::complete_lint(acc, ctx, token_tree, FEATURES), | 25 | "feature" => lint::complete_lint(acc, ctx, token_tree, FEATURES), |
27 | "allow" | "warn" | "deny" | "forbid" => { | 26 | "allow" | "warn" | "deny" | "forbid" => { |
28 | lint::complete_lint(acc, ctx, token_tree.clone(), lint::DEFAULT_LINT_COMPLETIONS); | 27 | lint::complete_lint(acc, ctx, token_tree.clone(), DEFAULT_LINTS); |
29 | lint::complete_lint(acc, ctx, token_tree, CLIPPY_LINTS); | 28 | lint::complete_lint(acc, ctx, token_tree, CLIPPY_LINTS); |
30 | } | 29 | } |
31 | _ => (), | 30 | _ => (), |
diff --git a/crates/ide_completion/src/completions/attribute/lint.rs b/crates/ide_completion/src/completions/attribute/lint.rs index 403630dce..b486c9093 100644 --- a/crates/ide_completion/src/completions/attribute/lint.rs +++ b/crates/ide_completion/src/completions/attribute/lint.rs | |||
@@ -1,4 +1,5 @@ | |||
1 | //! Completion for lints | 1 | //! Completion for lints |
2 | use ide_db::helpers::generated_lints::Lint; | ||
2 | use syntax::ast; | 3 | use syntax::ast; |
3 | 4 | ||
4 | use crate::{ | 5 | use crate::{ |
@@ -11,7 +12,7 @@ pub(super) fn complete_lint( | |||
11 | acc: &mut Completions, | 12 | acc: &mut Completions, |
12 | ctx: &CompletionContext, | 13 | ctx: &CompletionContext, |
13 | derive_input: ast::TokenTree, | 14 | derive_input: ast::TokenTree, |
14 | lints_completions: &[LintCompletion], | 15 | lints_completions: &[Lint], |
15 | ) { | 16 | ) { |
16 | if let Some(existing_lints) = super::parse_comma_sep_input(derive_input) { | 17 | if let Some(existing_lints) = super::parse_comma_sep_input(derive_input) { |
17 | for lint_completion in lints_completions | 18 | for lint_completion in lints_completions |
@@ -29,130 +30,6 @@ pub(super) fn complete_lint( | |||
29 | } | 30 | } |
30 | } | 31 | } |
31 | 32 | ||
32 | pub(crate) struct LintCompletion { | ||
33 | pub(crate) label: &'static str, | ||
34 | pub(crate) description: &'static str, | ||
35 | } | ||
36 | |||
37 | #[rustfmt::skip] | ||
38 | pub(super) const DEFAULT_LINT_COMPLETIONS: &[LintCompletion] = &[ | ||
39 | LintCompletion { label: "absolute_paths_not_starting_with_crate", description: r#"fully qualified paths that start with a module name instead of `crate`, `self`, or an extern crate name"# }, | ||
40 | LintCompletion { label: "anonymous_parameters", description: r#"detects anonymous parameters"# }, | ||
41 | LintCompletion { label: "box_pointers", description: r#"use of owned (Box type) heap memory"# }, | ||
42 | LintCompletion { label: "deprecated_in_future", description: r#"detects use of items that will be deprecated in a future version"# }, | ||
43 | LintCompletion { label: "elided_lifetimes_in_paths", description: r#"hidden lifetime parameters in types are deprecated"# }, | ||
44 | LintCompletion { label: "explicit_outlives_requirements", description: r#"outlives requirements can be inferred"# }, | ||
45 | LintCompletion { label: "indirect_structural_match", description: r#"pattern with const indirectly referencing non-structural-match type"# }, | ||
46 | LintCompletion { label: "keyword_idents", description: r#"detects edition keywords being used as an identifier"# }, | ||
47 | LintCompletion { label: "macro_use_extern_crate", description: r#"the `#[macro_use]` attribute is now deprecated in favor of using macros via the module system"# }, | ||
48 | LintCompletion { label: "meta_variable_misuse", description: r#"possible meta-variable misuse at macro definition"# }, | ||
49 | LintCompletion { label: "missing_copy_implementations", description: r#"detects potentially-forgotten implementations of `Copy`"# }, | ||
50 | LintCompletion { label: "missing_crate_level_docs", description: r#"detects crates with no crate-level documentation"# }, | ||
51 | LintCompletion { label: "missing_debug_implementations", description: r#"detects missing implementations of Debug"# }, | ||
52 | LintCompletion { label: "missing_docs", description: r#"detects missing documentation for public members"# }, | ||
53 | LintCompletion { label: "missing_doc_code_examples", description: r#"detects publicly-exported items without code samples in their documentation"# }, | ||
54 | LintCompletion { label: "non_ascii_idents", description: r#"detects non-ASCII identifiers"# }, | ||
55 | LintCompletion { label: "private_doc_tests", description: r#"detects code samples in docs of private items not documented by rustdoc"# }, | ||
56 | LintCompletion { label: "single_use_lifetimes", description: r#"detects lifetime parameters that are only used once"# }, | ||
57 | LintCompletion { label: "trivial_casts", description: r#"detects trivial casts which could be removed"# }, | ||
58 | LintCompletion { label: "trivial_numeric_casts", description: r#"detects trivial casts of numeric types which could be removed"# }, | ||
59 | LintCompletion { label: "unaligned_references", description: r#"detects unaligned references to fields of packed structs"# }, | ||
60 | LintCompletion { label: "unreachable_pub", description: r#"`pub` items not reachable from crate root"# }, | ||
61 | LintCompletion { label: "unsafe_code", description: r#"usage of `unsafe` code"# }, | ||
62 | LintCompletion { label: "unsafe_op_in_unsafe_fn", description: r#"unsafe operations in unsafe functions without an explicit unsafe block are deprecated"# }, | ||
63 | LintCompletion { label: "unstable_features", description: r#"enabling unstable features (deprecated. do not use)"# }, | ||
64 | LintCompletion { label: "unused_crate_dependencies", description: r#"crate dependencies that are never used"# }, | ||
65 | LintCompletion { label: "unused_extern_crates", description: r#"extern crates that are never used"# }, | ||
66 | LintCompletion { label: "unused_import_braces", description: r#"unnecessary braces around an imported item"# }, | ||
67 | LintCompletion { label: "unused_lifetimes", description: r#"detects lifetime parameters that are never used"# }, | ||
68 | LintCompletion { label: "unused_qualifications", description: r#"detects unnecessarily qualified names"# }, | ||
69 | LintCompletion { label: "unused_results", description: r#"unused result of an expression in a statement"# }, | ||
70 | LintCompletion { label: "variant_size_differences", description: r#"detects enums with widely varying variant sizes"# }, | ||
71 | LintCompletion { label: "array_into_iter", description: r#"detects calling `into_iter` on arrays"# }, | ||
72 | LintCompletion { label: "asm_sub_register", description: r#"using only a subset of a register for inline asm inputs"# }, | ||
73 | LintCompletion { label: "bare_trait_objects", description: r#"suggest using `dyn Trait` for trait objects"# }, | ||
74 | LintCompletion { label: "bindings_with_variant_name", description: r#"detects pattern bindings with the same name as one of the matched variants"# }, | ||
75 | LintCompletion { label: "cenum_impl_drop_cast", description: r#"a C-like enum implementing Drop is cast"# }, | ||
76 | LintCompletion { label: "clashing_extern_declarations", description: r#"detects when an extern fn has been declared with the same name but different types"# }, | ||
77 | LintCompletion { label: "coherence_leak_check", description: r#"distinct impls distinguished only by the leak-check code"# }, | ||
78 | LintCompletion { label: "confusable_idents", description: r#"detects visually confusable pairs between identifiers"# }, | ||
79 | LintCompletion { label: "dead_code", description: r#"detect unused, unexported items"# }, | ||
80 | LintCompletion { label: "deprecated", description: r#"detects use of deprecated items"# }, | ||
81 | LintCompletion { label: "ellipsis_inclusive_range_patterns", description: r#"`...` range patterns are deprecated"# }, | ||
82 | LintCompletion { label: "exported_private_dependencies", description: r#"public interface leaks type from a private dependency"# }, | ||
83 | LintCompletion { label: "illegal_floating_point_literal_pattern", description: r#"floating-point literals cannot be used in patterns"# }, | ||
84 | LintCompletion { label: "improper_ctypes", description: r#"proper use of libc types in foreign modules"# }, | ||
85 | LintCompletion { label: "improper_ctypes_definitions", description: r#"proper use of libc types in foreign item definitions"# }, | ||
86 | LintCompletion { label: "incomplete_features", description: r#"incomplete features that may function improperly in some or all cases"# }, | ||
87 | LintCompletion { label: "inline_no_sanitize", description: r#"detects incompatible use of `#[inline(always)]` and `#[no_sanitize(...)]`"# }, | ||
88 | LintCompletion { label: "intra_doc_link_resolution_failure", description: r#"failures in resolving intra-doc link targets"# }, | ||
89 | LintCompletion { label: "invalid_codeblock_attributes", description: r#"codeblock attribute looks a lot like a known one"# }, | ||
90 | LintCompletion { label: "invalid_value", description: r#"an invalid value is being created (such as a NULL reference)"# }, | ||
91 | LintCompletion { label: "irrefutable_let_patterns", description: r#"detects irrefutable patterns in if-let and while-let statements"# }, | ||
92 | LintCompletion { label: "late_bound_lifetime_arguments", description: r#"detects generic lifetime arguments in path segments with late bound lifetime parameters"# }, | ||
93 | LintCompletion { label: "mixed_script_confusables", description: r#"detects Unicode scripts whose mixed script confusables codepoints are solely used"# }, | ||
94 | LintCompletion { label: "mutable_borrow_reservation_conflict", description: r#"reservation of a two-phased borrow conflicts with other shared borrows"# }, | ||
95 | LintCompletion { label: "non_camel_case_types", description: r#"types, variants, traits and type parameters should have camel case names"# }, | ||
96 | LintCompletion { label: "non_shorthand_field_patterns", description: r#"using `Struct { x: x }` instead of `Struct { x }` in a pattern"# }, | ||
97 | LintCompletion { label: "non_snake_case", description: r#"variables, methods, functions, lifetime parameters and modules should have snake case names"# }, | ||
98 | LintCompletion { label: "non_upper_case_globals", description: r#"static constants should have uppercase identifiers"# }, | ||
99 | LintCompletion { label: "no_mangle_generic_items", description: r#"generic items must be mangled"# }, | ||
100 | LintCompletion { label: "overlapping_patterns", description: r#"detects overlapping patterns"# }, | ||
101 | LintCompletion { label: "path_statements", description: r#"path statements with no effect"# }, | ||
102 | LintCompletion { label: "private_in_public", description: r#"detect private items in public interfaces not caught by the old implementation"# }, | ||
103 | LintCompletion { label: "proc_macro_derive_resolution_fallback", description: r#"detects proc macro derives using inaccessible names from parent modules"# }, | ||
104 | LintCompletion { label: "redundant_semicolons", description: r#"detects unnecessary trailing semicolons"# }, | ||
105 | LintCompletion { label: "renamed_and_removed_lints", description: r#"lints that have been renamed or removed"# }, | ||
106 | LintCompletion { label: "safe_packed_borrows", description: r#"safe borrows of fields of packed structs were erroneously allowed"# }, | ||
107 | LintCompletion { label: "stable_features", description: r#"stable features found in `#[feature]` directive"# }, | ||
108 | LintCompletion { label: "trivial_bounds", description: r#"these bounds don't depend on an type parameters"# }, | ||
109 | LintCompletion { label: "type_alias_bounds", description: r#"bounds in type aliases are not enforced"# }, | ||
110 | LintCompletion { label: "tyvar_behind_raw_pointer", description: r#"raw pointer to an inference variable"# }, | ||
111 | LintCompletion { label: "uncommon_codepoints", description: r#"detects uncommon Unicode codepoints in identifiers"# }, | ||
112 | LintCompletion { label: "unconditional_recursion", description: r#"functions that cannot return without calling themselves"# }, | ||
113 | LintCompletion { label: "unknown_lints", description: r#"unrecognized lint attribute"# }, | ||
114 | LintCompletion { label: "unnameable_test_items", description: r#"detects an item that cannot be named being marked as `#[test_case]`"# }, | ||
115 | LintCompletion { label: "unreachable_code", description: r#"detects unreachable code paths"# }, | ||
116 | LintCompletion { label: "unreachable_patterns", description: r#"detects unreachable patterns"# }, | ||
117 | LintCompletion { label: "unstable_name_collisions", description: r#"detects name collision with an existing but unstable method"# }, | ||
118 | LintCompletion { label: "unused_allocation", description: r#"detects unnecessary allocations that can be eliminated"# }, | ||
119 | LintCompletion { label: "unused_assignments", description: r#"detect assignments that will never be read"# }, | ||
120 | LintCompletion { label: "unused_attributes", description: r#"detects attributes that were not used by the compiler"# }, | ||
121 | LintCompletion { label: "unused_braces", description: r#"unnecessary braces around an expression"# }, | ||
122 | LintCompletion { label: "unused_comparisons", description: r#"comparisons made useless by limits of the types involved"# }, | ||
123 | LintCompletion { label: "unused_doc_comments", description: r#"detects doc comments that aren't used by rustdoc"# }, | ||
124 | LintCompletion { label: "unused_features", description: r#"unused features found in crate-level `#[feature]` directives"# }, | ||
125 | LintCompletion { label: "unused_imports", description: r#"imports that are never used"# }, | ||
126 | LintCompletion { label: "unused_labels", description: r#"detects labels that are never used"# }, | ||
127 | LintCompletion { label: "unused_macros", description: r#"detects macros that were not used"# }, | ||
128 | LintCompletion { label: "unused_must_use", description: r#"unused result of a type flagged as `#[must_use]`"# }, | ||
129 | LintCompletion { label: "unused_mut", description: r#"detect mut variables which don't need to be mutable"# }, | ||
130 | LintCompletion { label: "unused_parens", description: r#"`if`, `match`, `while` and `return` do not need parentheses"# }, | ||
131 | LintCompletion { label: "unused_unsafe", description: r#"unnecessary use of an `unsafe` block"# }, | ||
132 | LintCompletion { label: "unused_variables", description: r#"detect variables which are not used in any way"# }, | ||
133 | LintCompletion { label: "warnings", description: r#"mass-change the level for lints which produce warnings"# }, | ||
134 | LintCompletion { label: "where_clauses_object_safety", description: r#"checks the object safety of where clauses"# }, | ||
135 | LintCompletion { label: "while_true", description: r#"suggest using `loop { }` instead of `while true { }`"# }, | ||
136 | LintCompletion { label: "ambiguous_associated_items", description: r#"ambiguous associated items"# }, | ||
137 | LintCompletion { label: "arithmetic_overflow", description: r#"arithmetic operation overflows"# }, | ||
138 | LintCompletion { label: "conflicting_repr_hints", description: r#"conflicts between `#[repr(..)]` hints that were previously accepted and used in practice"# }, | ||
139 | LintCompletion { label: "const_err", description: r#"constant evaluation detected erroneous expression"# }, | ||
140 | LintCompletion { label: "ill_formed_attribute_input", description: r#"ill-formed attribute inputs that were previously accepted and used in practice"# }, | ||
141 | LintCompletion { label: "incomplete_include", description: r#"trailing content in included file"# }, | ||
142 | LintCompletion { label: "invalid_type_param_default", description: r#"type parameter default erroneously allowed in invalid location"# }, | ||
143 | LintCompletion { label: "macro_expanded_macro_exports_accessed_by_absolute_paths", description: r#"macro-expanded `macro_export` macros from the current crate cannot be referred to by absolute paths"# }, | ||
144 | LintCompletion { label: "missing_fragment_specifier", description: r#"detects missing fragment specifiers in unused `macro_rules!` patterns"# }, | ||
145 | LintCompletion { label: "mutable_transmutes", description: r#"mutating transmuted &mut T from &T may cause undefined behavior"# }, | ||
146 | LintCompletion { label: "no_mangle_const_items", description: r#"const items will not have their symbols exported"# }, | ||
147 | LintCompletion { label: "order_dependent_trait_objects", description: r#"trait-object types were treated as different depending on marker-trait order"# }, | ||
148 | LintCompletion { label: "overflowing_literals", description: r#"literal out of range for its type"# }, | ||
149 | LintCompletion { label: "patterns_in_fns_without_body", description: r#"patterns in functions without body were erroneously allowed"# }, | ||
150 | LintCompletion { label: "pub_use_of_private_extern_crate", description: r#"detect public re-exports of private extern crates"# }, | ||
151 | LintCompletion { label: "soft_unstable", description: r#"a feature gate that doesn't break dependent crates"# }, | ||
152 | LintCompletion { label: "unconditional_panic", description: r#"operation will cause a panic at runtime"# }, | ||
153 | LintCompletion { label: "unknown_crate_types", description: r#"unknown crate type found in `#[crate_type]` directive"# }, | ||
154 | ]; | ||
155 | |||
156 | #[cfg(test)] | 33 | #[cfg(test)] |
157 | mod tests { | 34 | mod tests { |
158 | 35 | ||
diff --git a/crates/ide_completion/src/generated_lint_completions.rs b/crates/ide_completion/src/generated_lint_completions.rs deleted file mode 100644 index 0d405350d..000000000 --- a/crates/ide_completion/src/generated_lint_completions.rs +++ /dev/null | |||
@@ -1,6380 +0,0 @@ | |||
1 | //! Generated file, do not edit by hand, see `xtask/src/codegen` | ||
2 | |||
3 | use crate::completions::attribute::LintCompletion; | ||
4 | pub(super) const FEATURES: &[LintCompletion] = &[ | ||
5 | LintCompletion { | ||
6 | label: "plugin_registrar", | ||
7 | description: r##"# `plugin_registrar` | ||
8 | |||
9 | The tracking issue for this feature is: [#29597] | ||
10 | |||
11 | [#29597]: https://github.com/rust-lang/rust/issues/29597 | ||
12 | |||
13 | This feature is part of "compiler plugins." It will often be used with the | ||
14 | [`plugin`] and `rustc_private` features as well. For more details, see | ||
15 | their docs. | ||
16 | |||
17 | [`plugin`]: plugin.md | ||
18 | |||
19 | ------------------------ | ||
20 | "##, | ||
21 | }, | ||
22 | LintCompletion { | ||
23 | label: "inline_const", | ||
24 | description: r##"# `inline_const` | ||
25 | |||
26 | The tracking issue for this feature is: [#76001] | ||
27 | |||
28 | ------ | ||
29 | |||
30 | This feature allows you to use inline constant expressions. For example, you can | ||
31 | turn this code: | ||
32 | |||
33 | ```rust | ||
34 | # fn add_one(x: i32) -> i32 { x + 1 } | ||
35 | const MY_COMPUTATION: i32 = 1 + 2 * 3 / 4; | ||
36 | |||
37 | fn main() { | ||
38 | let x = add_one(MY_COMPUTATION); | ||
39 | } | ||
40 | ``` | ||
41 | |||
42 | into this code: | ||
43 | |||
44 | ```rust | ||
45 | #![feature(inline_const)] | ||
46 | |||
47 | # fn add_one(x: i32) -> i32 { x + 1 } | ||
48 | fn main() { | ||
49 | let x = add_one(const { 1 + 2 * 3 / 4 }); | ||
50 | } | ||
51 | ``` | ||
52 | |||
53 | You can also use inline constant expressions in patterns: | ||
54 | |||
55 | ```rust | ||
56 | #![feature(inline_const)] | ||
57 | |||
58 | const fn one() -> i32 { 1 } | ||
59 | |||
60 | let some_int = 3; | ||
61 | match some_int { | ||
62 | const { 1 + 2 } => println!("Matched 1 + 2"), | ||
63 | const { one() } => println!("Matched const fn returning 1"), | ||
64 | _ => println!("Didn't match anything :("), | ||
65 | } | ||
66 | ``` | ||
67 | |||
68 | [#76001]: https://github.com/rust-lang/rust/issues/76001 | ||
69 | "##, | ||
70 | }, | ||
71 | LintCompletion { | ||
72 | label: "auto_traits", | ||
73 | description: r##"# `auto_traits` | ||
74 | |||
75 | The tracking issue for this feature is [#13231] | ||
76 | |||
77 | [#13231]: https://github.com/rust-lang/rust/issues/13231 | ||
78 | |||
79 | ---- | ||
80 | |||
81 | The `auto_traits` feature gate allows you to define auto traits. | ||
82 | |||
83 | Auto traits, like [`Send`] or [`Sync`] in the standard library, are marker traits | ||
84 | that are automatically implemented for every type, unless the type, or a type it contains, | ||
85 | has explicitly opted out via a negative impl. (Negative impls are separately controlled | ||
86 | by the `negative_impls` feature.) | ||
87 | |||
88 | [`Send`]: https://doc.rust-lang.org/std/marker/trait.Send.html | ||
89 | [`Sync`]: https://doc.rust-lang.org/std/marker/trait.Sync.html | ||
90 | |||
91 | ```rust,ignore (partial-example) | ||
92 | impl !Trait for Type {} | ||
93 | ``` | ||
94 | |||
95 | Example: | ||
96 | |||
97 | ```rust | ||
98 | #![feature(negative_impls)] | ||
99 | #![feature(auto_traits)] | ||
100 | |||
101 | auto trait Valid {} | ||
102 | |||
103 | struct True; | ||
104 | struct False; | ||
105 | |||
106 | impl !Valid for False {} | ||
107 | |||
108 | struct MaybeValid<T>(T); | ||
109 | |||
110 | fn must_be_valid<T: Valid>(_t: T) { } | ||
111 | |||
112 | fn main() { | ||
113 | // works | ||
114 | must_be_valid( MaybeValid(True) ); | ||
115 | |||
116 | // compiler error - trait bound not satisfied | ||
117 | // must_be_valid( MaybeValid(False) ); | ||
118 | } | ||
119 | ``` | ||
120 | |||
121 | ## Automatic trait implementations | ||
122 | |||
123 | When a type is declared as an `auto trait`, we will automatically | ||
124 | create impls for every struct/enum/union, unless an explicit impl is | ||
125 | provided. These automatic impls contain a where clause for each field | ||
126 | of the form `T: AutoTrait`, where `T` is the type of the field and | ||
127 | `AutoTrait` is the auto trait in question. As an example, consider the | ||
128 | struct `List` and the auto trait `Send`: | ||
129 | |||
130 | ```rust | ||
131 | struct List<T> { | ||
132 | data: T, | ||
133 | next: Option<Box<List<T>>>, | ||
134 | } | ||
135 | ``` | ||
136 | |||
137 | Presuming that there is no explicit impl of `Send` for `List`, the | ||
138 | compiler will supply an automatic impl of the form: | ||
139 | |||
140 | ```rust | ||
141 | struct List<T> { | ||
142 | data: T, | ||
143 | next: Option<Box<List<T>>>, | ||
144 | } | ||
145 | |||
146 | unsafe impl<T> Send for List<T> | ||
147 | where | ||
148 | T: Send, // from the field `data` | ||
149 | Option<Box<List<T>>>: Send, // from the field `next` | ||
150 | { } | ||
151 | ``` | ||
152 | |||
153 | Explicit impls may be either positive or negative. They take the form: | ||
154 | |||
155 | ```rust,ignore (partial-example) | ||
156 | impl<...> AutoTrait for StructName<..> { } | ||
157 | impl<...> !AutoTrait for StructName<..> { } | ||
158 | ``` | ||
159 | |||
160 | ## Coinduction: Auto traits permit cyclic matching | ||
161 | |||
162 | Unlike ordinary trait matching, auto traits are **coinductive**. This | ||
163 | means, in short, that cycles which occur in trait matching are | ||
164 | considered ok. As an example, consider the recursive struct `List` | ||
165 | introduced in the previous section. In attempting to determine whether | ||
166 | `List: Send`, we would wind up in a cycle: to apply the impl, we must | ||
167 | show that `Option<Box<List>>: Send`, which will in turn require | ||
168 | `Box<List>: Send` and then finally `List: Send` again. Under ordinary | ||
169 | trait matching, this cycle would be an error, but for an auto trait it | ||
170 | is considered a successful match. | ||
171 | |||
172 | ## Items | ||
173 | |||
174 | Auto traits cannot have any trait items, such as methods or associated types. This ensures that we can generate default implementations. | ||
175 | |||
176 | ## Supertraits | ||
177 | |||
178 | Auto traits cannot have supertraits. This is for soundness reasons, as the interaction of coinduction with implied bounds is difficult to reconcile. | ||
179 | "##, | ||
180 | }, | ||
181 | LintCompletion { | ||
182 | label: "ffi_const", | ||
183 | description: r##"# `ffi_const` | ||
184 | |||
185 | The tracking issue for this feature is: [#58328] | ||
186 | |||
187 | ------ | ||
188 | |||
189 | The `#[ffi_const]` attribute applies clang's `const` attribute to foreign | ||
190 | functions declarations. | ||
191 | |||
192 | That is, `#[ffi_const]` functions shall have no effects except for its return | ||
193 | value, which can only depend on the values of the function parameters, and is | ||
194 | not affected by changes to the observable state of the program. | ||
195 | |||
196 | Applying the `#[ffi_const]` attribute to a function that violates these | ||
197 | requirements is undefined behaviour. | ||
198 | |||
199 | This attribute enables Rust to perform common optimizations, like sub-expression | ||
200 | elimination, and it can avoid emitting some calls in repeated invocations of the | ||
201 | function with the same argument values regardless of other operations being | ||
202 | performed in between these functions calls (as opposed to `#[ffi_pure]` | ||
203 | functions). | ||
204 | |||
205 | ## Pitfalls | ||
206 | |||
207 | A `#[ffi_const]` function can only read global memory that would not affect | ||
208 | its return value for the whole execution of the program (e.g. immutable global | ||
209 | memory). `#[ffi_const]` functions are referentially-transparent and therefore | ||
210 | more strict than `#[ffi_pure]` functions. | ||
211 | |||
212 | A common pitfall involves applying the `#[ffi_const]` attribute to a | ||
213 | function that reads memory through pointer arguments which do not necessarily | ||
214 | point to immutable global memory. | ||
215 | |||
216 | A `#[ffi_const]` function that returns unit has no effect on the abstract | ||
217 | machine's state, and a `#[ffi_const]` function cannot be `#[ffi_pure]`. | ||
218 | |||
219 | A `#[ffi_const]` function must not diverge, neither via a side effect (e.g. a | ||
220 | call to `abort`) nor by infinite loops. | ||
221 | |||
222 | When translating C headers to Rust FFI, it is worth verifying for which targets | ||
223 | the `const` attribute is enabled in those headers, and using the appropriate | ||
224 | `cfg` macros in the Rust side to match those definitions. While the semantics of | ||
225 | `const` are implemented identically by many C and C++ compilers, e.g., clang, | ||
226 | [GCC], [ARM C/C++ compiler], [IBM ILE C/C++], etc. they are not necessarily | ||
227 | implemented in this way on all of them. It is therefore also worth verifying | ||
228 | that the semantics of the C toolchain used to compile the binary being linked | ||
229 | against are compatible with those of the `#[ffi_const]`. | ||
230 | |||
231 | [#58328]: https://github.com/rust-lang/rust/issues/58328 | ||
232 | [ARM C/C++ compiler]: http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.dui0491c/Cacgigch.html | ||
233 | [GCC]: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-const-function-attribute | ||
234 | [IBM ILE C/C++]: https://www.ibm.com/support/knowledgecenter/fr/ssw_ibm_i_71/rzarg/fn_attrib_const.htm | ||
235 | "##, | ||
236 | }, | ||
237 | LintCompletion { | ||
238 | label: "external_doc", | ||
239 | description: r##"# `external_doc` | ||
240 | |||
241 | The tracking issue for this feature is: [#44732] | ||
242 | |||
243 | The `external_doc` feature allows the use of the `include` parameter to the `#[doc]` attribute, to | ||
244 | include external files in documentation. Use the attribute in place of, or in addition to, regular | ||
245 | doc comments and `#[doc]` attributes, and `rustdoc` will load the given file when it renders | ||
246 | documentation for your crate. | ||
247 | |||
248 | With the following files in the same directory: | ||
249 | |||
250 | `external-doc.md`: | ||
251 | |||
252 | ```markdown | ||
253 | # My Awesome Type | ||
254 | |||
255 | This is the documentation for this spectacular type. | ||
256 | ``` | ||
257 | |||
258 | `lib.rs`: | ||
259 | |||
260 | ```no_run (needs-external-files) | ||
261 | #![feature(external_doc)] | ||
262 | |||
263 | #[doc(include = "external-doc.md")] | ||
264 | pub struct MyAwesomeType; | ||
265 | ``` | ||
266 | |||
267 | `rustdoc` will load the file `external-doc.md` and use it as the documentation for the `MyAwesomeType` | ||
268 | struct. | ||
269 | |||
270 | When locating files, `rustdoc` will base paths in the `src/` directory, as if they were alongside the | ||
271 | `lib.rs` for your crate. So if you want a `docs/` folder to live alongside the `src/` directory, | ||
272 | start your paths with `../docs/` for `rustdoc` to properly find the file. | ||
273 | |||
274 | This feature was proposed in [RFC #1990] and initially implemented in PR [#44781]. | ||
275 | |||
276 | [#44732]: https://github.com/rust-lang/rust/issues/44732 | ||
277 | [RFC #1990]: https://github.com/rust-lang/rfcs/pull/1990 | ||
278 | [#44781]: https://github.com/rust-lang/rust/pull/44781 | ||
279 | "##, | ||
280 | }, | ||
281 | LintCompletion { | ||
282 | label: "box_patterns", | ||
283 | description: r##"# `box_patterns` | ||
284 | |||
285 | The tracking issue for this feature is: [#29641] | ||
286 | |||
287 | [#29641]: https://github.com/rust-lang/rust/issues/29641 | ||
288 | |||
289 | See also [`box_syntax`](box-syntax.md) | ||
290 | |||
291 | ------------------------ | ||
292 | |||
293 | Box patterns let you match on `Box<T>`s: | ||
294 | |||
295 | |||
296 | ```rust | ||
297 | #![feature(box_patterns)] | ||
298 | |||
299 | fn main() { | ||
300 | let b = Some(Box::new(5)); | ||
301 | match b { | ||
302 | Some(box n) if n < 0 => { | ||
303 | println!("Box contains negative number {}", n); | ||
304 | }, | ||
305 | Some(box n) if n >= 0 => { | ||
306 | println!("Box contains non-negative number {}", n); | ||
307 | }, | ||
308 | None => { | ||
309 | println!("No box"); | ||
310 | }, | ||
311 | _ => unreachable!() | ||
312 | } | ||
313 | } | ||
314 | ``` | ||
315 | "##, | ||
316 | }, | ||
317 | LintCompletion { | ||
318 | label: "abi_c_cmse_nonsecure_call", | ||
319 | description: r##"# `abi_c_cmse_nonsecure_call` | ||
320 | |||
321 | The tracking issue for this feature is: [#81391] | ||
322 | |||
323 | [#81391]: https://github.com/rust-lang/rust/issues/81391 | ||
324 | |||
325 | ------------------------ | ||
326 | |||
327 | The [TrustZone-M | ||
328 | feature](https://developer.arm.com/documentation/100690/latest/) is available | ||
329 | for targets with the Armv8-M architecture profile (`thumbv8m` in their target | ||
330 | name). | ||
331 | LLVM, the Rust compiler and the linker are providing | ||
332 | [support](https://developer.arm.com/documentation/ecm0359818/latest/) for the | ||
333 | TrustZone-M feature. | ||
334 | |||
335 | One of the things provided, with this unstable feature, is the | ||
336 | `C-cmse-nonsecure-call` function ABI. This ABI is used on function pointers to | ||
337 | non-secure code to mark a non-secure function call (see [section | ||
338 | 5.5](https://developer.arm.com/documentation/ecm0359818/latest/) for details). | ||
339 | |||
340 | With this ABI, the compiler will do the following to perform the call: | ||
341 | * save registers needed after the call to Secure memory | ||
342 | * clear all registers that might contain confidential information | ||
343 | * clear the Least Significant Bit of the function address | ||
344 | * branches using the BLXNS instruction | ||
345 | |||
346 | To avoid using the non-secure stack, the compiler will constrain the number and | ||
347 | type of parameters/return value. | ||
348 | |||
349 | The `extern "C-cmse-nonsecure-call"` ABI is otherwise equivalent to the | ||
350 | `extern "C"` ABI. | ||
351 | |||
352 | <!-- NOTE(ignore) this example is specific to thumbv8m targets --> | ||
353 | |||
354 | ``` rust,ignore | ||
355 | #![no_std] | ||
356 | #![feature(abi_c_cmse_nonsecure_call)] | ||
357 | |||
358 | #[no_mangle] | ||
359 | pub fn call_nonsecure_function(addr: usize) -> u32 { | ||
360 | let non_secure_function = | ||
361 | unsafe { core::mem::transmute::<usize, extern "C-cmse-nonsecure-call" fn() -> u32>(addr) }; | ||
362 | non_secure_function() | ||
363 | } | ||
364 | ``` | ||
365 | |||
366 | ``` text | ||
367 | $ rustc --emit asm --crate-type lib --target thumbv8m.main-none-eabi function.rs | ||
368 | |||
369 | call_nonsecure_function: | ||
370 | .fnstart | ||
371 | .save {r7, lr} | ||
372 | push {r7, lr} | ||
373 | .setfp r7, sp | ||
374 | mov r7, sp | ||
375 | .pad #16 | ||
376 | sub sp, #16 | ||
377 | str r0, [sp, #12] | ||
378 | ldr r0, [sp, #12] | ||
379 | str r0, [sp, #8] | ||
380 | b .LBB0_1 | ||
381 | .LBB0_1: | ||
382 | ldr r0, [sp, #8] | ||
383 | push.w {r4, r5, r6, r7, r8, r9, r10, r11} | ||
384 | bic r0, r0, #1 | ||
385 | mov r1, r0 | ||
386 | mov r2, r0 | ||
387 | mov r3, r0 | ||
388 | mov r4, r0 | ||
389 | mov r5, r0 | ||
390 | mov r6, r0 | ||
391 | mov r7, r0 | ||
392 | mov r8, r0 | ||
393 | mov r9, r0 | ||
394 | mov r10, r0 | ||
395 | mov r11, r0 | ||
396 | mov r12, r0 | ||
397 | msr apsr_nzcvq, r0 | ||
398 | blxns r0 | ||
399 | pop.w {r4, r5, r6, r7, r8, r9, r10, r11} | ||
400 | str r0, [sp, #4] | ||
401 | b .LBB0_2 | ||
402 | .LBB0_2: | ||
403 | ldr r0, [sp, #4] | ||
404 | add sp, #16 | ||
405 | pop {r7, pc} | ||
406 | ``` | ||
407 | "##, | ||
408 | }, | ||
409 | LintCompletion { | ||
410 | label: "member_constraints", | ||
411 | description: r##"# `member_constraints` | ||
412 | |||
413 | The tracking issue for this feature is: [#61997] | ||
414 | |||
415 | [#61997]: https://github.com/rust-lang/rust/issues/61997 | ||
416 | |||
417 | ------------------------ | ||
418 | |||
419 | The `member_constraints` feature gate lets you use `impl Trait` syntax with | ||
420 | multiple unrelated lifetime parameters. | ||
421 | |||
422 | A simple example is: | ||
423 | |||
424 | ```rust | ||
425 | #![feature(member_constraints)] | ||
426 | |||
427 | trait Trait<'a, 'b> { } | ||
428 | impl<T> Trait<'_, '_> for T {} | ||
429 | |||
430 | fn foo<'a, 'b>(x: &'a u32, y: &'b u32) -> impl Trait<'a, 'b> { | ||
431 | (x, y) | ||
432 | } | ||
433 | |||
434 | fn main() { } | ||
435 | ``` | ||
436 | |||
437 | Without the `member_constraints` feature gate, the above example is an | ||
438 | error because both `'a` and `'b` appear in the impl Trait bounds, but | ||
439 | neither outlives the other. | ||
440 | "##, | ||
441 | }, | ||
442 | LintCompletion { | ||
443 | label: "allocator_internals", | ||
444 | description: r##"# `allocator_internals` | ||
445 | |||
446 | This feature does not have a tracking issue, it is an unstable implementation | ||
447 | detail of the `global_allocator` feature not intended for use outside the | ||
448 | compiler. | ||
449 | |||
450 | ------------------------ | ||
451 | "##, | ||
452 | }, | ||
453 | LintCompletion { | ||
454 | label: "cfg_sanitize", | ||
455 | description: r##"# `cfg_sanitize` | ||
456 | |||
457 | The tracking issue for this feature is: [#39699] | ||
458 | |||
459 | [#39699]: https://github.com/rust-lang/rust/issues/39699 | ||
460 | |||
461 | ------------------------ | ||
462 | |||
463 | The `cfg_sanitize` feature makes it possible to execute different code | ||
464 | depending on whether a particular sanitizer is enabled or not. | ||
465 | |||
466 | ## Examples | ||
467 | |||
468 | ```rust | ||
469 | #![feature(cfg_sanitize)] | ||
470 | |||
471 | #[cfg(sanitize = "thread")] | ||
472 | fn a() { | ||
473 | // ... | ||
474 | } | ||
475 | |||
476 | #[cfg(not(sanitize = "thread"))] | ||
477 | fn a() { | ||
478 | // ... | ||
479 | } | ||
480 | |||
481 | fn b() { | ||
482 | if cfg!(sanitize = "leak") { | ||
483 | // ... | ||
484 | } else { | ||
485 | // ... | ||
486 | } | ||
487 | } | ||
488 | ``` | ||
489 | "##, | ||
490 | }, | ||
491 | LintCompletion { | ||
492 | label: "cfg_panic", | ||
493 | description: r##"# `cfg_panic` | ||
494 | |||
495 | The tracking issue for this feature is: [#77443] | ||
496 | |||
497 | [#77443]: https://github.com/rust-lang/rust/issues/77443 | ||
498 | |||
499 | ------------------------ | ||
500 | |||
501 | The `cfg_panic` feature makes it possible to execute different code | ||
502 | depending on the panic strategy. | ||
503 | |||
504 | Possible values at the moment are `"unwind"` or `"abort"`, although | ||
505 | it is possible that new panic strategies may be added to Rust in the | ||
506 | future. | ||
507 | |||
508 | ## Examples | ||
509 | |||
510 | ```rust | ||
511 | #![feature(cfg_panic)] | ||
512 | |||
513 | #[cfg(panic = "unwind")] | ||
514 | fn a() { | ||
515 | // ... | ||
516 | } | ||
517 | |||
518 | #[cfg(not(panic = "unwind"))] | ||
519 | fn a() { | ||
520 | // ... | ||
521 | } | ||
522 | |||
523 | fn b() { | ||
524 | if cfg!(panic = "abort") { | ||
525 | // ... | ||
526 | } else { | ||
527 | // ... | ||
528 | } | ||
529 | } | ||
530 | ``` | ||
531 | "##, | ||
532 | }, | ||
533 | LintCompletion { | ||
534 | label: "ffi_pure", | ||
535 | description: r##"# `ffi_pure` | ||
536 | |||
537 | The tracking issue for this feature is: [#58329] | ||
538 | |||
539 | ------ | ||
540 | |||
541 | The `#[ffi_pure]` attribute applies clang's `pure` attribute to foreign | ||
542 | functions declarations. | ||
543 | |||
544 | That is, `#[ffi_pure]` functions shall have no effects except for its return | ||
545 | value, which shall not change across two consecutive function calls with | ||
546 | the same parameters. | ||
547 | |||
548 | Applying the `#[ffi_pure]` attribute to a function that violates these | ||
549 | requirements is undefined behavior. | ||
550 | |||
551 | This attribute enables Rust to perform common optimizations, like sub-expression | ||
552 | elimination and loop optimizations. Some common examples of pure functions are | ||
553 | `strlen` or `memcmp`. | ||
554 | |||
555 | These optimizations are only applicable when the compiler can prove that no | ||
556 | program state observable by the `#[ffi_pure]` function has changed between calls | ||
557 | of the function, which could alter the result. See also the `#[ffi_const]` | ||
558 | attribute, which provides stronger guarantees regarding the allowable behavior | ||
559 | of a function, enabling further optimization. | ||
560 | |||
561 | ## Pitfalls | ||
562 | |||
563 | A `#[ffi_pure]` function can read global memory through the function | ||
564 | parameters (e.g. pointers), globals, etc. `#[ffi_pure]` functions are not | ||
565 | referentially-transparent, and are therefore more relaxed than `#[ffi_const]` | ||
566 | functions. | ||
567 | |||
568 | However, accessing global memory through volatile or atomic reads can violate the | ||
569 | requirement that two consecutive function calls shall return the same value. | ||
570 | |||
571 | A `pure` function that returns unit has no effect on the abstract machine's | ||
572 | state. | ||
573 | |||
574 | A `#[ffi_pure]` function must not diverge, neither via a side effect (e.g. a | ||
575 | call to `abort`) nor by infinite loops. | ||
576 | |||
577 | When translating C headers to Rust FFI, it is worth verifying for which targets | ||
578 | the `pure` attribute is enabled in those headers, and using the appropriate | ||
579 | `cfg` macros in the Rust side to match those definitions. While the semantics of | ||
580 | `pure` are implemented identically by many C and C++ compilers, e.g., clang, | ||
581 | [GCC], [ARM C/C++ compiler], [IBM ILE C/C++], etc. they are not necessarily | ||
582 | implemented in this way on all of them. It is therefore also worth verifying | ||
583 | that the semantics of the C toolchain used to compile the binary being linked | ||
584 | against are compatible with those of the `#[ffi_pure]`. | ||
585 | |||
586 | |||
587 | [#58329]: https://github.com/rust-lang/rust/issues/58329 | ||
588 | [ARM C/C++ compiler]: http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.dui0491c/Cacigdac.html | ||
589 | [GCC]: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-pure-function-attribute | ||
590 | [IBM ILE C/C++]: https://www.ibm.com/support/knowledgecenter/fr/ssw_ibm_i_71/rzarg/fn_attrib_pure.htm | ||
591 | "##, | ||
592 | }, | ||
593 | LintCompletion { | ||
594 | label: "repr128", | ||
595 | description: r##"# `repr128` | ||
596 | |||
597 | The tracking issue for this feature is: [#56071] | ||
598 | |||
599 | [#56071]: https://github.com/rust-lang/rust/issues/56071 | ||
600 | |||
601 | ------------------------ | ||
602 | |||
603 | The `repr128` feature adds support for `#[repr(u128)]` on `enum`s. | ||
604 | |||
605 | ```rust | ||
606 | #![feature(repr128)] | ||
607 | |||
608 | #[repr(u128)] | ||
609 | enum Foo { | ||
610 | Bar(u64), | ||
611 | } | ||
612 | ``` | ||
613 | "##, | ||
614 | }, | ||
615 | LintCompletion { | ||
616 | label: "generators", | ||
617 | description: r##"# `generators` | ||
618 | |||
619 | The tracking issue for this feature is: [#43122] | ||
620 | |||
621 | [#43122]: https://github.com/rust-lang/rust/issues/43122 | ||
622 | |||
623 | ------------------------ | ||
624 | |||
625 | The `generators` feature gate in Rust allows you to define generator or | ||
626 | coroutine literals. A generator is a "resumable function" that syntactically | ||
627 | resembles a closure but compiles to much different semantics in the compiler | ||
628 | itself. The primary feature of a generator is that it can be suspended during | ||
629 | execution to be resumed at a later date. Generators use the `yield` keyword to | ||
630 | "return", and then the caller can `resume` a generator to resume execution just | ||
631 | after the `yield` keyword. | ||
632 | |||
633 | Generators are an extra-unstable feature in the compiler right now. Added in | ||
634 | [RFC 2033] they're mostly intended right now as a information/constraint | ||
635 | gathering phase. The intent is that experimentation can happen on the nightly | ||
636 | compiler before actual stabilization. A further RFC will be required to | ||
637 | stabilize generators/coroutines and will likely contain at least a few small | ||
638 | tweaks to the overall design. | ||
639 | |||
640 | [RFC 2033]: https://github.com/rust-lang/rfcs/pull/2033 | ||
641 | |||
642 | A syntactical example of a generator is: | ||
643 | |||
644 | ```rust | ||
645 | #![feature(generators, generator_trait)] | ||
646 | |||
647 | use std::ops::{Generator, GeneratorState}; | ||
648 | use std::pin::Pin; | ||
649 | |||
650 | fn main() { | ||
651 | let mut generator = || { | ||
652 | yield 1; | ||
653 | return "foo" | ||
654 | }; | ||
655 | |||
656 | match Pin::new(&mut generator).resume(()) { | ||
657 | GeneratorState::Yielded(1) => {} | ||
658 | _ => panic!("unexpected value from resume"), | ||
659 | } | ||
660 | match Pin::new(&mut generator).resume(()) { | ||
661 | GeneratorState::Complete("foo") => {} | ||
662 | _ => panic!("unexpected value from resume"), | ||
663 | } | ||
664 | } | ||
665 | ``` | ||
666 | |||
667 | Generators are closure-like literals which can contain a `yield` statement. The | ||
668 | `yield` statement takes an optional expression of a value to yield out of the | ||
669 | generator. All generator literals implement the `Generator` trait in the | ||
670 | `std::ops` module. The `Generator` trait has one main method, `resume`, which | ||
671 | resumes execution of the generator at the previous suspension point. | ||
672 | |||
673 | An example of the control flow of generators is that the following example | ||
674 | prints all numbers in order: | ||
675 | |||
676 | ```rust | ||
677 | #![feature(generators, generator_trait)] | ||
678 | |||
679 | use std::ops::Generator; | ||
680 | use std::pin::Pin; | ||
681 | |||
682 | fn main() { | ||
683 | let mut generator = || { | ||
684 | println!("2"); | ||
685 | yield; | ||
686 | println!("4"); | ||
687 | }; | ||
688 | |||
689 | println!("1"); | ||
690 | Pin::new(&mut generator).resume(()); | ||
691 | println!("3"); | ||
692 | Pin::new(&mut generator).resume(()); | ||
693 | println!("5"); | ||
694 | } | ||
695 | ``` | ||
696 | |||
697 | At this time the main intended use case of generators is an implementation | ||
698 | primitive for async/await syntax, but generators will likely be extended to | ||
699 | ergonomic implementations of iterators and other primitives in the future. | ||
700 | Feedback on the design and usage is always appreciated! | ||
701 | |||
702 | ### The `Generator` trait | ||
703 | |||
704 | The `Generator` trait in `std::ops` currently looks like: | ||
705 | |||
706 | ```rust | ||
707 | # #![feature(arbitrary_self_types, generator_trait)] | ||
708 | # use std::ops::GeneratorState; | ||
709 | # use std::pin::Pin; | ||
710 | |||
711 | pub trait Generator<R = ()> { | ||
712 | type Yield; | ||
713 | type Return; | ||
714 | fn resume(self: Pin<&mut Self>, resume: R) -> GeneratorState<Self::Yield, Self::Return>; | ||
715 | } | ||
716 | ``` | ||
717 | |||
718 | The `Generator::Yield` type is the type of values that can be yielded with the | ||
719 | `yield` statement. The `Generator::Return` type is the returned type of the | ||
720 | generator. This is typically the last expression in a generator's definition or | ||
721 | any value passed to `return` in a generator. The `resume` function is the entry | ||
722 | point for executing the `Generator` itself. | ||
723 | |||
724 | The return value of `resume`, `GeneratorState`, looks like: | ||
725 | |||
726 | ```rust | ||
727 | pub enum GeneratorState<Y, R> { | ||
728 | Yielded(Y), | ||
729 | Complete(R), | ||
730 | } | ||
731 | ``` | ||
732 | |||
733 | The `Yielded` variant indicates that the generator can later be resumed. This | ||
734 | corresponds to a `yield` point in a generator. The `Complete` variant indicates | ||
735 | that the generator is complete and cannot be resumed again. Calling `resume` | ||
736 | after a generator has returned `Complete` will likely result in a panic of the | ||
737 | program. | ||
738 | |||
739 | ### Closure-like semantics | ||
740 | |||
741 | The closure-like syntax for generators alludes to the fact that they also have | ||
742 | closure-like semantics. Namely: | ||
743 | |||
744 | * When created, a generator executes no code. A closure literal does not | ||
745 | actually execute any of the closure's code on construction, and similarly a | ||
746 | generator literal does not execute any code inside the generator when | ||
747 | constructed. | ||
748 | |||
749 | * Generators can capture outer variables by reference or by move, and this can | ||
750 | be tweaked with the `move` keyword at the beginning of the closure. Like | ||
751 | closures all generators will have an implicit environment which is inferred by | ||
752 | the compiler. Outer variables can be moved into a generator for use as the | ||
753 | generator progresses. | ||
754 | |||
755 | * Generator literals produce a value with a unique type which implements the | ||
756 | `std::ops::Generator` trait. This allows actual execution of the generator | ||
757 | through the `Generator::resume` method as well as also naming it in return | ||
758 | types and such. | ||
759 | |||
760 | * Traits like `Send` and `Sync` are automatically implemented for a `Generator` | ||
761 | depending on the captured variables of the environment. Unlike closures, | ||
762 | generators also depend on variables live across suspension points. This means | ||
763 | that although the ambient environment may be `Send` or `Sync`, the generator | ||
764 | itself may not be due to internal variables live across `yield` points being | ||
765 | not-`Send` or not-`Sync`. Note that generators do | ||
766 | not implement traits like `Copy` or `Clone` automatically. | ||
767 | |||
768 | * Whenever a generator is dropped it will drop all captured environment | ||
769 | variables. | ||
770 | |||
771 | ### Generators as state machines | ||
772 | |||
773 | In the compiler, generators are currently compiled as state machines. Each | ||
774 | `yield` expression will correspond to a different state that stores all live | ||
775 | variables over that suspension point. Resumption of a generator will dispatch on | ||
776 | the current state and then execute internally until a `yield` is reached, at | ||
777 | which point all state is saved off in the generator and a value is returned. | ||
778 | |||
779 | Let's take a look at an example to see what's going on here: | ||
780 | |||
781 | ```rust | ||
782 | #![feature(generators, generator_trait)] | ||
783 | |||
784 | use std::ops::Generator; | ||
785 | use std::pin::Pin; | ||
786 | |||
787 | fn main() { | ||
788 | let ret = "foo"; | ||
789 | let mut generator = move || { | ||
790 | yield 1; | ||
791 | return ret | ||
792 | }; | ||
793 | |||
794 | Pin::new(&mut generator).resume(()); | ||
795 | Pin::new(&mut generator).resume(()); | ||
796 | } | ||
797 | ``` | ||
798 | |||
799 | This generator literal will compile down to something similar to: | ||
800 | |||
801 | ```rust | ||
802 | #![feature(arbitrary_self_types, generators, generator_trait)] | ||
803 | |||
804 | use std::ops::{Generator, GeneratorState}; | ||
805 | use std::pin::Pin; | ||
806 | |||
807 | fn main() { | ||
808 | let ret = "foo"; | ||
809 | let mut generator = { | ||
810 | enum __Generator { | ||
811 | Start(&'static str), | ||
812 | Yield1(&'static str), | ||
813 | Done, | ||
814 | } | ||
815 | |||
816 | impl Generator for __Generator { | ||
817 | type Yield = i32; | ||
818 | type Return = &'static str; | ||
819 | |||
820 | fn resume(mut self: Pin<&mut Self>, resume: ()) -> GeneratorState<i32, &'static str> { | ||
821 | use std::mem; | ||
822 | match mem::replace(&mut *self, __Generator::Done) { | ||
823 | __Generator::Start(s) => { | ||
824 | *self = __Generator::Yield1(s); | ||
825 | GeneratorState::Yielded(1) | ||
826 | } | ||
827 | |||
828 | __Generator::Yield1(s) => { | ||
829 | *self = __Generator::Done; | ||
830 | GeneratorState::Complete(s) | ||
831 | } | ||
832 | |||
833 | __Generator::Done => { | ||
834 | panic!("generator resumed after completion") | ||
835 | } | ||
836 | } | ||
837 | } | ||
838 | } | ||
839 | |||
840 | __Generator::Start(ret) | ||
841 | }; | ||
842 | |||
843 | Pin::new(&mut generator).resume(()); | ||
844 | Pin::new(&mut generator).resume(()); | ||
845 | } | ||
846 | ``` | ||
847 | |||
848 | Notably here we can see that the compiler is generating a fresh type, | ||
849 | `__Generator` in this case. This type has a number of states (represented here | ||
850 | as an `enum`) corresponding to each of the conceptual states of the generator. | ||
851 | At the beginning we're closing over our outer variable `foo` and then that | ||
852 | variable is also live over the `yield` point, so it's stored in both states. | ||
853 | |||
854 | When the generator starts it'll immediately yield 1, but it saves off its state | ||
855 | just before it does so indicating that it has reached the yield point. Upon | ||
856 | resuming again we'll execute the `return ret` which returns the `Complete` | ||
857 | state. | ||
858 | |||
859 | Here we can also note that the `Done` state, if resumed, panics immediately as | ||
860 | it's invalid to resume a completed generator. It's also worth noting that this | ||
861 | is just a rough desugaring, not a normative specification for what the compiler | ||
862 | does. | ||
863 | "##, | ||
864 | }, | ||
865 | LintCompletion { | ||
866 | label: "non_ascii_idents", | ||
867 | description: r##"# `non_ascii_idents` | ||
868 | |||
869 | The tracking issue for this feature is: [#55467] | ||
870 | |||
871 | [#55467]: https://github.com/rust-lang/rust/issues/55467 | ||
872 | |||
873 | ------------------------ | ||
874 | |||
875 | The `non_ascii_idents` feature adds support for non-ASCII identifiers. | ||
876 | |||
877 | ## Examples | ||
878 | |||
879 | ```rust | ||
880 | #![feature(non_ascii_idents)] | ||
881 | |||
882 | const ε: f64 = 0.00001f64; | ||
883 | const Î : f64 = 3.14f64; | ||
884 | ``` | ||
885 | |||
886 | ## Changes to the language reference | ||
887 | |||
888 | > **<sup>Lexer:<sup>**\ | ||
889 | > IDENTIFIER :\ | ||
890 | > XID_start XID_continue<sup>\*</sup>\ | ||
891 | > | `_` XID_continue<sup>+</sup> | ||
892 | |||
893 | An identifier is any nonempty Unicode string of the following form: | ||
894 | |||
895 | Either | ||
896 | |||
897 | * The first character has property [`XID_start`] | ||
898 | * The remaining characters have property [`XID_continue`] | ||
899 | |||
900 | Or | ||
901 | |||
902 | * The first character is `_` | ||
903 | * The identifier is more than one character, `_` alone is not an identifier | ||
904 | * The remaining characters have property [`XID_continue`] | ||
905 | |||
906 | that does _not_ occur in the set of [strict keywords]. | ||
907 | |||
908 | > **Note**: [`XID_start`] and [`XID_continue`] as character properties cover the | ||
909 | > character ranges used to form the more familiar C and Java language-family | ||
910 | > identifiers. | ||
911 | |||
912 | [`XID_start`]: http://unicode.org/cldr/utility/list-unicodeset.jsp?a=%5B%3AXID_Start%3A%5D&abb=on&g=&i= | ||
913 | [`XID_continue`]: http://unicode.org/cldr/utility/list-unicodeset.jsp?a=%5B%3AXID_Continue%3A%5D&abb=on&g=&i= | ||
914 | [strict keywords]: ../../reference/keywords.md#strict-keywords | ||
915 | "##, | ||
916 | }, | ||
917 | LintCompletion { | ||
918 | label: "compiler_builtins", | ||
919 | description: r##"# `compiler_builtins` | ||
920 | |||
921 | This feature is internal to the Rust compiler and is not intended for general use. | ||
922 | |||
923 | ------------------------ | ||
924 | "##, | ||
925 | }, | ||
926 | LintCompletion { | ||
927 | label: "or_patterns", | ||
928 | description: r##"# `or_patterns` | ||
929 | |||
930 | The tracking issue for this feature is: [#54883] | ||
931 | |||
932 | [#54883]: https://github.com/rust-lang/rust/issues/54883 | ||
933 | |||
934 | ------------------------ | ||
935 | |||
936 | The `or_pattern` language feature allows `|` to be arbitrarily nested within | ||
937 | a pattern, for example, `Some(A(0) | B(1 | 2))` becomes a valid pattern. | ||
938 | |||
939 | ## Examples | ||
940 | |||
941 | ```rust,no_run | ||
942 | #![feature(or_patterns)] | ||
943 | |||
944 | pub enum Foo { | ||
945 | Bar, | ||
946 | Baz, | ||
947 | Quux, | ||
948 | } | ||
949 | |||
950 | pub fn example(maybe_foo: Option<Foo>) { | ||
951 | match maybe_foo { | ||
952 | Some(Foo::Bar | Foo::Baz) => { | ||
953 | println!("The value contained `Bar` or `Baz`"); | ||
954 | } | ||
955 | Some(_) => { | ||
956 | println!("The value did not contain `Bar` or `Baz`"); | ||
957 | } | ||
958 | None => { | ||
959 | println!("The value was `None`"); | ||
960 | } | ||
961 | } | ||
962 | } | ||
963 | ``` | ||
964 | "##, | ||
965 | }, | ||
966 | LintCompletion { | ||
967 | label: "negative_impls", | ||
968 | description: r##"# `negative_impls` | ||
969 | |||
970 | The tracking issue for this feature is [#68318]. | ||
971 | |||
972 | [#68318]: https://github.com/rust-lang/rust/issues/68318 | ||
973 | |||
974 | ---- | ||
975 | |||
976 | With the feature gate `negative_impls`, you can write negative impls as well as positive ones: | ||
977 | |||
978 | ```rust | ||
979 | #![feature(negative_impls)] | ||
980 | trait DerefMut { } | ||
981 | impl<T: ?Sized> !DerefMut for &T { } | ||
982 | ``` | ||
983 | |||
984 | Negative impls indicate a semver guarantee that the given trait will not be implemented for the given types. Negative impls play an additional purpose for auto traits, described below. | ||
985 | |||
986 | Negative impls have the following characteristics: | ||
987 | |||
988 | * They do not have any items. | ||
989 | * They must obey the orphan rules as if they were a positive impl. | ||
990 | * They cannot "overlap" with any positive impls. | ||
991 | |||
992 | ## Semver interaction | ||
993 | |||
994 | It is a breaking change to remove a negative impl. Negative impls are a commitment not to implement the given trait for the named types. | ||
995 | |||
996 | ## Orphan and overlap rules | ||
997 | |||
998 | Negative impls must obey the same orphan rules as a positive impl. This implies you cannot add a negative impl for types defined in upstream crates and so forth. | ||
999 | |||
1000 | Similarly, negative impls cannot overlap with positive impls, again using the same "overlap" check that we ordinarily use to determine if two impls overlap. (Note that positive impls typically cannot overlap with one another either, except as permitted by specialization.) | ||
1001 | |||
1002 | ## Interaction with auto traits | ||
1003 | |||
1004 | Declaring a negative impl `impl !SomeAutoTrait for SomeType` for an | ||
1005 | auto-trait serves two purposes: | ||
1006 | |||
1007 | * as with any trait, it declares that `SomeType` will never implement `SomeAutoTrait`; | ||
1008 | * it disables the automatic `SomeType: SomeAutoTrait` impl that would otherwise have been generated. | ||
1009 | |||
1010 | Note that, at present, there is no way to indicate that a given type | ||
1011 | does not implement an auto trait *but that it may do so in the | ||
1012 | future*. For ordinary types, this is done by simply not declaring any | ||
1013 | impl at all, but that is not an option for auto traits. A workaround | ||
1014 | is that one could embed a marker type as one of the fields, where the | ||
1015 | marker type is `!AutoTrait`. | ||
1016 | |||
1017 | ## Immediate uses | ||
1018 | |||
1019 | Negative impls are used to declare that `&T: !DerefMut` and `&mut T: !Clone`, as required to fix the soundness of `Pin` described in [#66544](https://github.com/rust-lang/rust/issues/66544). | ||
1020 | |||
1021 | This serves two purposes: | ||
1022 | |||
1023 | * For proving the correctness of unsafe code, we can use that impl as evidence that no `DerefMut` or `Clone` impl exists. | ||
1024 | * It prevents downstream crates from creating such impls. | ||
1025 | "##, | ||
1026 | }, | ||
1027 | LintCompletion { | ||
1028 | label: "cmse_nonsecure_entry", | ||
1029 | description: r##"# `cmse_nonsecure_entry` | ||
1030 | |||
1031 | The tracking issue for this feature is: [#75835] | ||
1032 | |||
1033 | [#75835]: https://github.com/rust-lang/rust/issues/75835 | ||
1034 | |||
1035 | ------------------------ | ||
1036 | |||
1037 | The [TrustZone-M | ||
1038 | feature](https://developer.arm.com/documentation/100690/latest/) is available | ||
1039 | for targets with the Armv8-M architecture profile (`thumbv8m` in their target | ||
1040 | name). | ||
1041 | LLVM, the Rust compiler and the linker are providing | ||
1042 | [support](https://developer.arm.com/documentation/ecm0359818/latest/) for the | ||
1043 | TrustZone-M feature. | ||
1044 | |||
1045 | One of the things provided, with this unstable feature, is the | ||
1046 | `cmse_nonsecure_entry` attribute. This attribute marks a Secure function as an | ||
1047 | entry function (see [section | ||
1048 | 5.4](https://developer.arm.com/documentation/ecm0359818/latest/) for details). | ||
1049 | With this attribute, the compiler will do the following: | ||
1050 | * add a special symbol on the function which is the `__acle_se_` prefix and the | ||
1051 | standard function name | ||
1052 | * constrain the number of parameters to avoid using the Non-Secure stack | ||
1053 | * before returning from the function, clear registers that might contain Secure | ||
1054 | information | ||
1055 | * use the `BXNS` instruction to return | ||
1056 | |||
1057 | Because the stack can not be used to pass parameters, there will be compilation | ||
1058 | errors if: | ||
1059 | * the total size of all parameters is too big (for example more than four 32 | ||
1060 | bits integers) | ||
1061 | * the entry function is not using a C ABI | ||
1062 | |||
1063 | The special symbol `__acle_se_` will be used by the linker to generate a secure | ||
1064 | gateway veneer. | ||
1065 | |||
1066 | <!-- NOTE(ignore) this example is specific to thumbv8m targets --> | ||
1067 | |||
1068 | ``` rust,ignore | ||
1069 | #![feature(cmse_nonsecure_entry)] | ||
1070 | |||
1071 | #[no_mangle] | ||
1072 | #[cmse_nonsecure_entry] | ||
1073 | pub extern "C" fn entry_function(input: u32) -> u32 { | ||
1074 | input + 6 | ||
1075 | } | ||
1076 | ``` | ||
1077 | |||
1078 | ``` text | ||
1079 | $ rustc --emit obj --crate-type lib --target thumbv8m.main-none-eabi function.rs | ||
1080 | $ arm-none-eabi-objdump -D function.o | ||
1081 | |||
1082 | 00000000 <entry_function>: | ||
1083 | 0: b580 push {r7, lr} | ||
1084 | 2: 466f mov r7, sp | ||
1085 | 4: b082 sub sp, #8 | ||
1086 | 6: 9001 str r0, [sp, #4] | ||
1087 | 8: 1d81 adds r1, r0, #6 | ||
1088 | a: 460a mov r2, r1 | ||
1089 | c: 4281 cmp r1, r0 | ||
1090 | e: 9200 str r2, [sp, #0] | ||
1091 | 10: d30b bcc.n 2a <entry_function+0x2a> | ||
1092 | 12: e7ff b.n 14 <entry_function+0x14> | ||
1093 | 14: 9800 ldr r0, [sp, #0] | ||
1094 | 16: b002 add sp, #8 | ||
1095 | 18: e8bd 4080 ldmia.w sp!, {r7, lr} | ||
1096 | 1c: 4671 mov r1, lr | ||
1097 | 1e: 4672 mov r2, lr | ||
1098 | 20: 4673 mov r3, lr | ||
1099 | 22: 46f4 mov ip, lr | ||
1100 | 24: f38e 8800 msr CPSR_f, lr | ||
1101 | 28: 4774 bxns lr | ||
1102 | 2a: f240 0000 movw r0, #0 | ||
1103 | 2e: f2c0 0000 movt r0, #0 | ||
1104 | 32: f240 0200 movw r2, #0 | ||
1105 | 36: f2c0 0200 movt r2, #0 | ||
1106 | 3a: 211c movs r1, #28 | ||
1107 | 3c: f7ff fffe bl 0 <_ZN4core9panicking5panic17h5c028258ca2fb3f5E> | ||
1108 | 40: defe udf #254 ; 0xfe | ||
1109 | ``` | ||
1110 | "##, | ||
1111 | }, | ||
1112 | LintCompletion { | ||
1113 | label: "plugin", | ||
1114 | description: r##"# `plugin` | ||
1115 | |||
1116 | The tracking issue for this feature is: [#29597] | ||
1117 | |||
1118 | [#29597]: https://github.com/rust-lang/rust/issues/29597 | ||
1119 | |||
1120 | |||
1121 | This feature is part of "compiler plugins." It will often be used with the | ||
1122 | [`plugin_registrar`] and `rustc_private` features. | ||
1123 | |||
1124 | [`plugin_registrar`]: plugin-registrar.md | ||
1125 | |||
1126 | ------------------------ | ||
1127 | |||
1128 | `rustc` can load compiler plugins, which are user-provided libraries that | ||
1129 | extend the compiler's behavior with new lint checks, etc. | ||
1130 | |||
1131 | A plugin is a dynamic library crate with a designated *registrar* function that | ||
1132 | registers extensions with `rustc`. Other crates can load these extensions using | ||
1133 | the crate attribute `#![plugin(...)]`. See the | ||
1134 | `rustc_driver::plugin` documentation for more about the | ||
1135 | mechanics of defining and loading a plugin. | ||
1136 | |||
1137 | In the vast majority of cases, a plugin should *only* be used through | ||
1138 | `#![plugin]` and not through an `extern crate` item. Linking a plugin would | ||
1139 | pull in all of librustc_ast and librustc as dependencies of your crate. This is | ||
1140 | generally unwanted unless you are building another plugin. | ||
1141 | |||
1142 | The usual practice is to put compiler plugins in their own crate, separate from | ||
1143 | any `macro_rules!` macros or ordinary Rust code meant to be used by consumers | ||
1144 | of a library. | ||
1145 | |||
1146 | # Lint plugins | ||
1147 | |||
1148 | Plugins can extend [Rust's lint | ||
1149 | infrastructure](../../reference/attributes/diagnostics.md#lint-check-attributes) with | ||
1150 | additional checks for code style, safety, etc. Now let's write a plugin | ||
1151 | [`lint-plugin-test.rs`](https://github.com/rust-lang/rust/blob/master/src/test/ui-fulldeps/auxiliary/lint-plugin-test.rs) | ||
1152 | that warns about any item named `lintme`. | ||
1153 | |||
1154 | ```rust,ignore (requires-stage-2) | ||
1155 | #![feature(plugin_registrar)] | ||
1156 | #![feature(box_syntax, rustc_private)] | ||
1157 | |||
1158 | extern crate rustc_ast; | ||
1159 | |||
1160 | // Load rustc as a plugin to get macros | ||
1161 | extern crate rustc_driver; | ||
1162 | #[macro_use] | ||
1163 | extern crate rustc_lint; | ||
1164 | #[macro_use] | ||
1165 | extern crate rustc_session; | ||
1166 | |||
1167 | use rustc_driver::plugin::Registry; | ||
1168 | use rustc_lint::{EarlyContext, EarlyLintPass, LintArray, LintContext, LintPass}; | ||
1169 | use rustc_ast::ast; | ||
1170 | declare_lint!(TEST_LINT, Warn, "Warn about items named 'lintme'"); | ||
1171 | |||
1172 | declare_lint_pass!(Pass => [TEST_LINT]); | ||
1173 | |||
1174 | impl EarlyLintPass for Pass { | ||
1175 | fn check_item(&mut self, cx: &EarlyContext, it: &ast::Item) { | ||
1176 | if it.ident.name.as_str() == "lintme" { | ||
1177 | cx.lint(TEST_LINT, |lint| { | ||
1178 | lint.build("item is named 'lintme'").set_span(it.span).emit() | ||
1179 | }); | ||
1180 | } | ||
1181 | } | ||
1182 | } | ||
1183 | |||
1184 | #[plugin_registrar] | ||
1185 | pub fn plugin_registrar(reg: &mut Registry) { | ||
1186 | reg.lint_store.register_lints(&[&TEST_LINT]); | ||
1187 | reg.lint_store.register_early_pass(|| box Pass); | ||
1188 | } | ||
1189 | ``` | ||
1190 | |||
1191 | Then code like | ||
1192 | |||
1193 | ```rust,ignore (requires-plugin) | ||
1194 | #![feature(plugin)] | ||
1195 | #![plugin(lint_plugin_test)] | ||
1196 | |||
1197 | fn lintme() { } | ||
1198 | ``` | ||
1199 | |||
1200 | will produce a compiler warning: | ||
1201 | |||
1202 | ```txt | ||
1203 | foo.rs:4:1: 4:16 warning: item is named 'lintme', #[warn(test_lint)] on by default | ||
1204 | foo.rs:4 fn lintme() { } | ||
1205 | ^~~~~~~~~~~~~~~ | ||
1206 | ``` | ||
1207 | |||
1208 | The components of a lint plugin are: | ||
1209 | |||
1210 | * one or more `declare_lint!` invocations, which define static `Lint` structs; | ||
1211 | |||
1212 | * a struct holding any state needed by the lint pass (here, none); | ||
1213 | |||
1214 | * a `LintPass` | ||
1215 | implementation defining how to check each syntax element. A single | ||
1216 | `LintPass` may call `span_lint` for several different `Lint`s, but should | ||
1217 | register them all through the `get_lints` method. | ||
1218 | |||
1219 | Lint passes are syntax traversals, but they run at a late stage of compilation | ||
1220 | where type information is available. `rustc`'s [built-in | ||
1221 | lints](https://github.com/rust-lang/rust/blob/master/src/librustc_session/lint/builtin.rs) | ||
1222 | mostly use the same infrastructure as lint plugins, and provide examples of how | ||
1223 | to access type information. | ||
1224 | |||
1225 | Lints defined by plugins are controlled by the usual [attributes and compiler | ||
1226 | flags](../../reference/attributes/diagnostics.md#lint-check-attributes), e.g. | ||
1227 | `#[allow(test_lint)]` or `-A test-lint`. These identifiers are derived from the | ||
1228 | first argument to `declare_lint!`, with appropriate case and punctuation | ||
1229 | conversion. | ||
1230 | |||
1231 | You can run `rustc -W help foo.rs` to see a list of lints known to `rustc`, | ||
1232 | including those provided by plugins loaded by `foo.rs`. | ||
1233 | "##, | ||
1234 | }, | ||
1235 | LintCompletion { | ||
1236 | label: "intrinsics", | ||
1237 | description: r##"# `intrinsics` | ||
1238 | |||
1239 | The tracking issue for this feature is: None. | ||
1240 | |||
1241 | Intrinsics are never intended to be stable directly, but intrinsics are often | ||
1242 | exported in some sort of stable manner. Prefer using the stable interfaces to | ||
1243 | the intrinsic directly when you can. | ||
1244 | |||
1245 | ------------------------ | ||
1246 | |||
1247 | |||
1248 | These are imported as if they were FFI functions, with the special | ||
1249 | `rust-intrinsic` ABI. For example, if one was in a freestanding | ||
1250 | context, but wished to be able to `transmute` between types, and | ||
1251 | perform efficient pointer arithmetic, one would import those functions | ||
1252 | via a declaration like | ||
1253 | |||
1254 | ```rust | ||
1255 | #![feature(intrinsics)] | ||
1256 | # fn main() {} | ||
1257 | |||
1258 | extern "rust-intrinsic" { | ||
1259 | fn transmute<T, U>(x: T) -> U; | ||
1260 | |||
1261 | fn offset<T>(dst: *const T, offset: isize) -> *const T; | ||
1262 | } | ||
1263 | ``` | ||
1264 | |||
1265 | As with any other FFI functions, these are always `unsafe` to call. | ||
1266 | "##, | ||
1267 | }, | ||
1268 | LintCompletion { | ||
1269 | label: "rustc_attrs", | ||
1270 | description: r##"# `rustc_attrs` | ||
1271 | |||
1272 | This feature has no tracking issue, and is therefore internal to | ||
1273 | the compiler, not being intended for general use. | ||
1274 | |||
1275 | Note: `rustc_attrs` enables many rustc-internal attributes and this page | ||
1276 | only discuss a few of them. | ||
1277 | |||
1278 | ------------------------ | ||
1279 | |||
1280 | The `rustc_attrs` feature allows debugging rustc type layouts by using | ||
1281 | `#[rustc_layout(...)]` to debug layout at compile time (it even works | ||
1282 | with `cargo check`) as an alternative to `rustc -Z print-type-sizes` | ||
1283 | that is way more verbose. | ||
1284 | |||
1285 | Options provided by `#[rustc_layout(...)]` are `debug`, `size`, `align`, | ||
1286 | `abi`. Note that it only works on sized types without generics. | ||
1287 | |||
1288 | ## Examples | ||
1289 | |||
1290 | ```rust,compile_fail | ||
1291 | #![feature(rustc_attrs)] | ||
1292 | |||
1293 | #[rustc_layout(abi, size)] | ||
1294 | pub enum X { | ||
1295 | Y(u8, u8, u8), | ||
1296 | Z(isize), | ||
1297 | } | ||
1298 | ``` | ||
1299 | |||
1300 | When that is compiled, the compiler will error with something like | ||
1301 | |||
1302 | ```text | ||
1303 | error: abi: Aggregate { sized: true } | ||
1304 | --> src/lib.rs:4:1 | ||
1305 | | | ||
1306 | 4 | / pub enum T { | ||
1307 | 5 | | Y(u8, u8, u8), | ||
1308 | 6 | | Z(isize), | ||
1309 | 7 | | } | ||
1310 | | |_^ | ||
1311 | |||
1312 | error: size: Size { raw: 16 } | ||
1313 | --> src/lib.rs:4:1 | ||
1314 | | | ||
1315 | 4 | / pub enum T { | ||
1316 | 5 | | Y(u8, u8, u8), | ||
1317 | 6 | | Z(isize), | ||
1318 | 7 | | } | ||
1319 | | |_^ | ||
1320 | |||
1321 | error: aborting due to 2 previous errors | ||
1322 | ``` | ||
1323 | "##, | ||
1324 | }, | ||
1325 | LintCompletion { | ||
1326 | label: "const_fn", | ||
1327 | description: r##"# `const_fn` | ||
1328 | |||
1329 | The tracking issue for this feature is: [#57563] | ||
1330 | |||
1331 | [#57563]: https://github.com/rust-lang/rust/issues/57563 | ||
1332 | |||
1333 | ------------------------ | ||
1334 | |||
1335 | The `const_fn` feature enables additional functionality not stabilized in the | ||
1336 | [minimal subset of `const_fn`](https://github.com/rust-lang/rust/issues/53555) | ||
1337 | "##, | ||
1338 | }, | ||
1339 | LintCompletion { | ||
1340 | label: "abi_thiscall", | ||
1341 | description: r##"# `abi_thiscall` | ||
1342 | |||
1343 | The tracking issue for this feature is: [#42202] | ||
1344 | |||
1345 | [#42202]: https://github.com/rust-lang/rust/issues/42202 | ||
1346 | |||
1347 | ------------------------ | ||
1348 | |||
1349 | The MSVC ABI on x86 Windows uses the `thiscall` calling convention for C++ | ||
1350 | instance methods by default; it is identical to the usual (C) calling | ||
1351 | convention on x86 Windows except that the first parameter of the method, | ||
1352 | the `this` pointer, is passed in the ECX register. | ||
1353 | "##, | ||
1354 | }, | ||
1355 | LintCompletion { | ||
1356 | label: "trait_alias", | ||
1357 | description: r##"# `trait_alias` | ||
1358 | |||
1359 | The tracking issue for this feature is: [#41517] | ||
1360 | |||
1361 | [#41517]: https://github.com/rust-lang/rust/issues/41517 | ||
1362 | |||
1363 | ------------------------ | ||
1364 | |||
1365 | The `trait_alias` feature adds support for trait aliases. These allow aliases | ||
1366 | to be created for one or more traits (currently just a single regular trait plus | ||
1367 | any number of auto-traits), and used wherever traits would normally be used as | ||
1368 | either bounds or trait objects. | ||
1369 | |||
1370 | ```rust | ||
1371 | #![feature(trait_alias)] | ||
1372 | |||
1373 | trait Foo = std::fmt::Debug + Send; | ||
1374 | trait Bar = Foo + Sync; | ||
1375 | |||
1376 | // Use trait alias as bound on type parameter. | ||
1377 | fn foo<T: Foo>(v: &T) { | ||
1378 | println!("{:?}", v); | ||
1379 | } | ||
1380 | |||
1381 | pub fn main() { | ||
1382 | foo(&1); | ||
1383 | |||
1384 | // Use trait alias for trait objects. | ||
1385 | let a: &Bar = &123; | ||
1386 | println!("{:?}", a); | ||
1387 | let b = Box::new(456) as Box<dyn Foo>; | ||
1388 | println!("{:?}", b); | ||
1389 | } | ||
1390 | ``` | ||
1391 | "##, | ||
1392 | }, | ||
1393 | LintCompletion { | ||
1394 | label: "lang_items", | ||
1395 | description: r##"# `lang_items` | ||
1396 | |||
1397 | The tracking issue for this feature is: None. | ||
1398 | |||
1399 | ------------------------ | ||
1400 | |||
1401 | The `rustc` compiler has certain pluggable operations, that is, | ||
1402 | functionality that isn't hard-coded into the language, but is | ||
1403 | implemented in libraries, with a special marker to tell the compiler | ||
1404 | it exists. The marker is the attribute `#[lang = "..."]` and there are | ||
1405 | various different values of `...`, i.e. various different 'lang | ||
1406 | items'. | ||
1407 | |||
1408 | For example, `Box` pointers require two lang items, one for allocation | ||
1409 | and one for deallocation. A freestanding program that uses the `Box` | ||
1410 | sugar for dynamic allocations via `malloc` and `free`: | ||
1411 | |||
1412 | ```rust,ignore (libc-is-finicky) | ||
1413 | #![feature(lang_items, box_syntax, start, libc, core_intrinsics, rustc_private)] | ||
1414 | #![no_std] | ||
1415 | use core::intrinsics; | ||
1416 | use core::panic::PanicInfo; | ||
1417 | |||
1418 | extern crate libc; | ||
1419 | |||
1420 | #[lang = "owned_box"] | ||
1421 | pub struct Box<T>(*mut T); | ||
1422 | |||
1423 | #[lang = "exchange_malloc"] | ||
1424 | unsafe fn allocate(size: usize, _align: usize) -> *mut u8 { | ||
1425 | let p = libc::malloc(size as libc::size_t) as *mut u8; | ||
1426 | |||
1427 | // Check if `malloc` failed: | ||
1428 | if p as usize == 0 { | ||
1429 | intrinsics::abort(); | ||
1430 | } | ||
1431 | |||
1432 | p | ||
1433 | } | ||
1434 | |||
1435 | #[lang = "box_free"] | ||
1436 | unsafe fn box_free<T: ?Sized>(ptr: *mut T) { | ||
1437 | libc::free(ptr as *mut libc::c_void) | ||
1438 | } | ||
1439 | |||
1440 | #[start] | ||
1441 | fn main(_argc: isize, _argv: *const *const u8) -> isize { | ||
1442 | let _x = box 1; | ||
1443 | |||
1444 | 0 | ||
1445 | } | ||
1446 | |||
1447 | #[lang = "eh_personality"] extern fn rust_eh_personality() {} | ||
1448 | #[lang = "panic_impl"] extern fn rust_begin_panic(info: &PanicInfo) -> ! { unsafe { intrinsics::abort() } } | ||
1449 | #[no_mangle] pub extern fn rust_eh_register_frames () {} | ||
1450 | #[no_mangle] pub extern fn rust_eh_unregister_frames () {} | ||
1451 | ``` | ||
1452 | |||
1453 | Note the use of `abort`: the `exchange_malloc` lang item is assumed to | ||
1454 | return a valid pointer, and so needs to do the check internally. | ||
1455 | |||
1456 | Other features provided by lang items include: | ||
1457 | |||
1458 | - overloadable operators via traits: the traits corresponding to the | ||
1459 | `==`, `<`, dereferencing (`*`) and `+` (etc.) operators are all | ||
1460 | marked with lang items; those specific four are `eq`, `ord`, | ||
1461 | `deref`, and `add` respectively. | ||
1462 | - stack unwinding and general failure; the `eh_personality`, | ||
1463 | `panic` and `panic_bounds_check` lang items. | ||
1464 | - the traits in `std::marker` used to indicate types of | ||
1465 | various kinds; lang items `send`, `sync` and `copy`. | ||
1466 | - the marker types and variance indicators found in | ||
1467 | `std::marker`; lang items `covariant_type`, | ||
1468 | `contravariant_lifetime`, etc. | ||
1469 | |||
1470 | Lang items are loaded lazily by the compiler; e.g. if one never uses | ||
1471 | `Box` then there is no need to define functions for `exchange_malloc` | ||
1472 | and `box_free`. `rustc` will emit an error when an item is needed | ||
1473 | but not found in the current crate or any that it depends on. | ||
1474 | |||
1475 | Most lang items are defined by `libcore`, but if you're trying to build | ||
1476 | an executable without the standard library, you'll run into the need | ||
1477 | for lang items. The rest of this page focuses on this use-case, even though | ||
1478 | lang items are a bit broader than that. | ||
1479 | |||
1480 | ### Using libc | ||
1481 | |||
1482 | In order to build a `#[no_std]` executable we will need libc as a dependency. | ||
1483 | We can specify this using our `Cargo.toml` file: | ||
1484 | |||
1485 | ```toml | ||
1486 | [dependencies] | ||
1487 | libc = { version = "0.2.14", default-features = false } | ||
1488 | ``` | ||
1489 | |||
1490 | Note that the default features have been disabled. This is a critical step - | ||
1491 | **the default features of libc include the standard library and so must be | ||
1492 | disabled.** | ||
1493 | |||
1494 | ### Writing an executable without stdlib | ||
1495 | |||
1496 | Controlling the entry point is possible in two ways: the `#[start]` attribute, | ||
1497 | or overriding the default shim for the C `main` function with your own. | ||
1498 | |||
1499 | The function marked `#[start]` is passed the command line parameters | ||
1500 | in the same format as C: | ||
1501 | |||
1502 | ```rust,ignore (libc-is-finicky) | ||
1503 | #![feature(lang_items, core_intrinsics, rustc_private)] | ||
1504 | #![feature(start)] | ||
1505 | #![no_std] | ||
1506 | use core::intrinsics; | ||
1507 | use core::panic::PanicInfo; | ||
1508 | |||
1509 | // Pull in the system libc library for what crt0.o likely requires. | ||
1510 | extern crate libc; | ||
1511 | |||
1512 | // Entry point for this program. | ||
1513 | #[start] | ||
1514 | fn start(_argc: isize, _argv: *const *const u8) -> isize { | ||
1515 | 0 | ||
1516 | } | ||
1517 | |||
1518 | // These functions are used by the compiler, but not | ||
1519 | // for a bare-bones hello world. These are normally | ||
1520 | // provided by libstd. | ||
1521 | #[lang = "eh_personality"] | ||
1522 | #[no_mangle] | ||
1523 | pub extern fn rust_eh_personality() { | ||
1524 | } | ||
1525 | |||
1526 | #[lang = "panic_impl"] | ||
1527 | #[no_mangle] | ||
1528 | pub extern fn rust_begin_panic(info: &PanicInfo) -> ! { | ||
1529 | unsafe { intrinsics::abort() } | ||
1530 | } | ||
1531 | ``` | ||
1532 | |||
1533 | To override the compiler-inserted `main` shim, one has to disable it | ||
1534 | with `#![no_main]` and then create the appropriate symbol with the | ||
1535 | correct ABI and the correct name, which requires overriding the | ||
1536 | compiler's name mangling too: | ||
1537 | |||
1538 | ```rust,ignore (libc-is-finicky) | ||
1539 | #![feature(lang_items, core_intrinsics, rustc_private)] | ||
1540 | #![feature(start)] | ||
1541 | #![no_std] | ||
1542 | #![no_main] | ||
1543 | use core::intrinsics; | ||
1544 | use core::panic::PanicInfo; | ||
1545 | |||
1546 | // Pull in the system libc library for what crt0.o likely requires. | ||
1547 | extern crate libc; | ||
1548 | |||
1549 | // Entry point for this program. | ||
1550 | #[no_mangle] // ensure that this symbol is called `main` in the output | ||
1551 | pub extern fn main(_argc: i32, _argv: *const *const u8) -> i32 { | ||
1552 | 0 | ||
1553 | } | ||
1554 | |||
1555 | // These functions are used by the compiler, but not | ||
1556 | // for a bare-bones hello world. These are normally | ||
1557 | // provided by libstd. | ||
1558 | #[lang = "eh_personality"] | ||
1559 | #[no_mangle] | ||
1560 | pub extern fn rust_eh_personality() { | ||
1561 | } | ||
1562 | |||
1563 | #[lang = "panic_impl"] | ||
1564 | #[no_mangle] | ||
1565 | pub extern fn rust_begin_panic(info: &PanicInfo) -> ! { | ||
1566 | unsafe { intrinsics::abort() } | ||
1567 | } | ||
1568 | ``` | ||
1569 | |||
1570 | In many cases, you may need to manually link to the `compiler_builtins` crate | ||
1571 | when building a `no_std` binary. You may observe this via linker error messages | ||
1572 | such as "```undefined reference to `__rust_probestack'```". | ||
1573 | |||
1574 | ## More about the language items | ||
1575 | |||
1576 | The compiler currently makes a few assumptions about symbols which are | ||
1577 | available in the executable to call. Normally these functions are provided by | ||
1578 | the standard library, but without it you must define your own. These symbols | ||
1579 | are called "language items", and they each have an internal name, and then a | ||
1580 | signature that an implementation must conform to. | ||
1581 | |||
1582 | The first of these functions, `rust_eh_personality`, is used by the failure | ||
1583 | mechanisms of the compiler. This is often mapped to GCC's personality function | ||
1584 | (see the [libstd implementation][unwind] for more information), but crates | ||
1585 | which do not trigger a panic can be assured that this function is never | ||
1586 | called. The language item's name is `eh_personality`. | ||
1587 | |||
1588 | [unwind]: https://github.com/rust-lang/rust/blob/master/src/libpanic_unwind/gcc.rs | ||
1589 | |||
1590 | The second function, `rust_begin_panic`, is also used by the failure mechanisms of the | ||
1591 | compiler. When a panic happens, this controls the message that's displayed on | ||
1592 | the screen. While the language item's name is `panic_impl`, the symbol name is | ||
1593 | `rust_begin_panic`. | ||
1594 | |||
1595 | Finally, a `eh_catch_typeinfo` static is needed for certain targets which | ||
1596 | implement Rust panics on top of C++ exceptions. | ||
1597 | |||
1598 | ## List of all language items | ||
1599 | |||
1600 | This is a list of all language items in Rust along with where they are located in | ||
1601 | the source code. | ||
1602 | |||
1603 | - Primitives | ||
1604 | - `i8`: `libcore/num/mod.rs` | ||
1605 | - `i16`: `libcore/num/mod.rs` | ||
1606 | - `i32`: `libcore/num/mod.rs` | ||
1607 | - `i64`: `libcore/num/mod.rs` | ||
1608 | - `i128`: `libcore/num/mod.rs` | ||
1609 | - `isize`: `libcore/num/mod.rs` | ||
1610 | - `u8`: `libcore/num/mod.rs` | ||
1611 | - `u16`: `libcore/num/mod.rs` | ||
1612 | - `u32`: `libcore/num/mod.rs` | ||
1613 | - `u64`: `libcore/num/mod.rs` | ||
1614 | - `u128`: `libcore/num/mod.rs` | ||
1615 | - `usize`: `libcore/num/mod.rs` | ||
1616 | - `f32`: `libstd/f32.rs` | ||
1617 | - `f64`: `libstd/f64.rs` | ||
1618 | - `char`: `libcore/char.rs` | ||
1619 | - `slice`: `liballoc/slice.rs` | ||
1620 | - `str`: `liballoc/str.rs` | ||
1621 | - `const_ptr`: `libcore/ptr.rs` | ||
1622 | - `mut_ptr`: `libcore/ptr.rs` | ||
1623 | - `unsafe_cell`: `libcore/cell.rs` | ||
1624 | - Runtime | ||
1625 | - `start`: `libstd/rt.rs` | ||
1626 | - `eh_personality`: `libpanic_unwind/emcc.rs` (EMCC) | ||
1627 | - `eh_personality`: `libpanic_unwind/gcc.rs` (GNU) | ||
1628 | - `eh_personality`: `libpanic_unwind/seh.rs` (SEH) | ||
1629 | - `eh_catch_typeinfo`: `libpanic_unwind/emcc.rs` (EMCC) | ||
1630 | - `panic`: `libcore/panicking.rs` | ||
1631 | - `panic_bounds_check`: `libcore/panicking.rs` | ||
1632 | - `panic_impl`: `libcore/panicking.rs` | ||
1633 | - `panic_impl`: `libstd/panicking.rs` | ||
1634 | - Allocations | ||
1635 | - `owned_box`: `liballoc/boxed.rs` | ||
1636 | - `exchange_malloc`: `liballoc/heap.rs` | ||
1637 | - `box_free`: `liballoc/heap.rs` | ||
1638 | - Operands | ||
1639 | - `not`: `libcore/ops/bit.rs` | ||
1640 | - `bitand`: `libcore/ops/bit.rs` | ||
1641 | - `bitor`: `libcore/ops/bit.rs` | ||
1642 | - `bitxor`: `libcore/ops/bit.rs` | ||
1643 | - `shl`: `libcore/ops/bit.rs` | ||
1644 | - `shr`: `libcore/ops/bit.rs` | ||
1645 | - `bitand_assign`: `libcore/ops/bit.rs` | ||
1646 | - `bitor_assign`: `libcore/ops/bit.rs` | ||
1647 | - `bitxor_assign`: `libcore/ops/bit.rs` | ||
1648 | - `shl_assign`: `libcore/ops/bit.rs` | ||
1649 | - `shr_assign`: `libcore/ops/bit.rs` | ||
1650 | - `deref`: `libcore/ops/deref.rs` | ||
1651 | - `deref_mut`: `libcore/ops/deref.rs` | ||
1652 | - `index`: `libcore/ops/index.rs` | ||
1653 | - `index_mut`: `libcore/ops/index.rs` | ||
1654 | - `add`: `libcore/ops/arith.rs` | ||
1655 | - `sub`: `libcore/ops/arith.rs` | ||
1656 | - `mul`: `libcore/ops/arith.rs` | ||
1657 | - `div`: `libcore/ops/arith.rs` | ||
1658 | - `rem`: `libcore/ops/arith.rs` | ||
1659 | - `neg`: `libcore/ops/arith.rs` | ||
1660 | - `add_assign`: `libcore/ops/arith.rs` | ||
1661 | - `sub_assign`: `libcore/ops/arith.rs` | ||
1662 | - `mul_assign`: `libcore/ops/arith.rs` | ||
1663 | - `div_assign`: `libcore/ops/arith.rs` | ||
1664 | - `rem_assign`: `libcore/ops/arith.rs` | ||
1665 | - `eq`: `libcore/cmp.rs` | ||
1666 | - `ord`: `libcore/cmp.rs` | ||
1667 | - Functions | ||
1668 | - `fn`: `libcore/ops/function.rs` | ||
1669 | - `fn_mut`: `libcore/ops/function.rs` | ||
1670 | - `fn_once`: `libcore/ops/function.rs` | ||
1671 | - `generator_state`: `libcore/ops/generator.rs` | ||
1672 | - `generator`: `libcore/ops/generator.rs` | ||
1673 | - Other | ||
1674 | - `coerce_unsized`: `libcore/ops/unsize.rs` | ||
1675 | - `drop`: `libcore/ops/drop.rs` | ||
1676 | - `drop_in_place`: `libcore/ptr.rs` | ||
1677 | - `clone`: `libcore/clone.rs` | ||
1678 | - `copy`: `libcore/marker.rs` | ||
1679 | - `send`: `libcore/marker.rs` | ||
1680 | - `sized`: `libcore/marker.rs` | ||
1681 | - `unsize`: `libcore/marker.rs` | ||
1682 | - `sync`: `libcore/marker.rs` | ||
1683 | - `phantom_data`: `libcore/marker.rs` | ||
1684 | - `discriminant_kind`: `libcore/marker.rs` | ||
1685 | - `freeze`: `libcore/marker.rs` | ||
1686 | - `debug_trait`: `libcore/fmt/mod.rs` | ||
1687 | - `non_zero`: `libcore/nonzero.rs` | ||
1688 | - `arc`: `liballoc/sync.rs` | ||
1689 | - `rc`: `liballoc/rc.rs` | ||
1690 | "##, | ||
1691 | }, | ||
1692 | LintCompletion { | ||
1693 | label: "doc_spotlight", | ||
1694 | description: r##"# `doc_spotlight` | ||
1695 | |||
1696 | The tracking issue for this feature is: [#45040] | ||
1697 | |||
1698 | The `doc_spotlight` feature allows the use of the `spotlight` parameter to the `#[doc]` attribute, | ||
1699 | to "spotlight" a specific trait on the return values of functions. Adding a `#[doc(spotlight)]` | ||
1700 | attribute to a trait definition will make rustdoc print extra information for functions which return | ||
1701 | a type that implements that trait. For example, this attribute is applied to the `Iterator`, | ||
1702 | `io::Read`, `io::Write`, and `Future` traits in the standard library. | ||
1703 | |||
1704 | You can do this on your own traits, like this: | ||
1705 | |||
1706 | ``` | ||
1707 | #![feature(doc_spotlight)] | ||
1708 | |||
1709 | #[doc(spotlight)] | ||
1710 | pub trait MyTrait {} | ||
1711 | |||
1712 | pub struct MyStruct; | ||
1713 | impl MyTrait for MyStruct {} | ||
1714 | |||
1715 | /// The docs for this function will have an extra line about `MyStruct` implementing `MyTrait`, | ||
1716 | /// without having to write that yourself! | ||
1717 | pub fn my_fn() -> MyStruct { MyStruct } | ||
1718 | ``` | ||
1719 | |||
1720 | This feature was originally implemented in PR [#45039]. | ||
1721 | |||
1722 | [#45040]: https://github.com/rust-lang/rust/issues/45040 | ||
1723 | [#45039]: https://github.com/rust-lang/rust/pull/45039 | ||
1724 | "##, | ||
1725 | }, | ||
1726 | LintCompletion { | ||
1727 | label: "c_variadic", | ||
1728 | description: r##"# `c_variadic` | ||
1729 | |||
1730 | The tracking issue for this feature is: [#44930] | ||
1731 | |||
1732 | [#44930]: https://github.com/rust-lang/rust/issues/44930 | ||
1733 | |||
1734 | ------------------------ | ||
1735 | |||
1736 | The `c_variadic` language feature enables C-variadic functions to be | ||
1737 | defined in Rust. The may be called both from within Rust and via FFI. | ||
1738 | |||
1739 | ## Examples | ||
1740 | |||
1741 | ```rust | ||
1742 | #![feature(c_variadic)] | ||
1743 | |||
1744 | pub unsafe extern "C" fn add(n: usize, mut args: ...) -> usize { | ||
1745 | let mut sum = 0; | ||
1746 | for _ in 0..n { | ||
1747 | sum += args.arg::<usize>(); | ||
1748 | } | ||
1749 | sum | ||
1750 | } | ||
1751 | ``` | ||
1752 | "##, | ||
1753 | }, | ||
1754 | LintCompletion { | ||
1755 | label: "intra_doc_pointers", | ||
1756 | description: r##"# `intra-doc-pointers` | ||
1757 | |||
1758 | The tracking issue for this feature is: [#80896] | ||
1759 | |||
1760 | [#80896]: https://github.com/rust-lang/rust/issues/80896 | ||
1761 | |||
1762 | ------------------------ | ||
1763 | |||
1764 | Rustdoc does not currently allow disambiguating between `*const` and `*mut`, and | ||
1765 | raw pointers in intra-doc links are unstable until it does. | ||
1766 | |||
1767 | ```rust | ||
1768 | #![feature(intra_doc_pointers)] | ||
1769 | //! [pointer::add] | ||
1770 | ``` | ||
1771 | "##, | ||
1772 | }, | ||
1773 | LintCompletion { | ||
1774 | label: "box_syntax", | ||
1775 | description: r##"# `box_syntax` | ||
1776 | |||
1777 | The tracking issue for this feature is: [#49733] | ||
1778 | |||
1779 | [#49733]: https://github.com/rust-lang/rust/issues/49733 | ||
1780 | |||
1781 | See also [`box_patterns`](box-patterns.md) | ||
1782 | |||
1783 | ------------------------ | ||
1784 | |||
1785 | Currently the only stable way to create a `Box` is via the `Box::new` method. | ||
1786 | Also it is not possible in stable Rust to destructure a `Box` in a match | ||
1787 | pattern. The unstable `box` keyword can be used to create a `Box`. An example | ||
1788 | usage would be: | ||
1789 | |||
1790 | ```rust | ||
1791 | #![feature(box_syntax)] | ||
1792 | |||
1793 | fn main() { | ||
1794 | let b = box 5; | ||
1795 | } | ||
1796 | ``` | ||
1797 | "##, | ||
1798 | }, | ||
1799 | LintCompletion { | ||
1800 | label: "unsized_locals", | ||
1801 | description: r##"# `unsized_locals` | ||
1802 | |||
1803 | The tracking issue for this feature is: [#48055] | ||
1804 | |||
1805 | [#48055]: https://github.com/rust-lang/rust/issues/48055 | ||
1806 | |||
1807 | ------------------------ | ||
1808 | |||
1809 | This implements [RFC1909]. When turned on, you can have unsized arguments and locals: | ||
1810 | |||
1811 | [RFC1909]: https://github.com/rust-lang/rfcs/blob/master/text/1909-unsized-rvalues.md | ||
1812 | |||
1813 | ```rust | ||
1814 | #![allow(incomplete_features)] | ||
1815 | #![feature(unsized_locals, unsized_fn_params)] | ||
1816 | |||
1817 | use std::any::Any; | ||
1818 | |||
1819 | fn main() { | ||
1820 | let x: Box<dyn Any> = Box::new(42); | ||
1821 | let x: dyn Any = *x; | ||
1822 | // ^ unsized local variable | ||
1823 | // ^^ unsized temporary | ||
1824 | foo(x); | ||
1825 | } | ||
1826 | |||
1827 | fn foo(_: dyn Any) {} | ||
1828 | // ^^^^^^ unsized argument | ||
1829 | ``` | ||
1830 | |||
1831 | The RFC still forbids the following unsized expressions: | ||
1832 | |||
1833 | ```rust,compile_fail | ||
1834 | #![feature(unsized_locals)] | ||
1835 | |||
1836 | use std::any::Any; | ||
1837 | |||
1838 | struct MyStruct<T: ?Sized> { | ||
1839 | content: T, | ||
1840 | } | ||
1841 | |||
1842 | struct MyTupleStruct<T: ?Sized>(T); | ||
1843 | |||
1844 | fn answer() -> Box<dyn Any> { | ||
1845 | Box::new(42) | ||
1846 | } | ||
1847 | |||
1848 | fn main() { | ||
1849 | // You CANNOT have unsized statics. | ||
1850 | static X: dyn Any = *answer(); // ERROR | ||
1851 | const Y: dyn Any = *answer(); // ERROR | ||
1852 | |||
1853 | // You CANNOT have struct initialized unsized. | ||
1854 | MyStruct { content: *answer() }; // ERROR | ||
1855 | MyTupleStruct(*answer()); // ERROR | ||
1856 | (42, *answer()); // ERROR | ||
1857 | |||
1858 | // You CANNOT have unsized return types. | ||
1859 | fn my_function() -> dyn Any { *answer() } // ERROR | ||
1860 | |||
1861 | // You CAN have unsized local variables... | ||
1862 | let mut x: dyn Any = *answer(); // OK | ||
1863 | // ...but you CANNOT reassign to them. | ||
1864 | x = *answer(); // ERROR | ||
1865 | |||
1866 | // You CANNOT even initialize them separately. | ||
1867 | let y: dyn Any; // OK | ||
1868 | y = *answer(); // ERROR | ||
1869 | |||
1870 | // Not mentioned in the RFC, but by-move captured variables are also Sized. | ||
1871 | let x: dyn Any = *answer(); | ||
1872 | (move || { // ERROR | ||
1873 | let y = x; | ||
1874 | })(); | ||
1875 | |||
1876 | // You CAN create a closure with unsized arguments, | ||
1877 | // but you CANNOT call it. | ||
1878 | // This is an implementation detail and may be changed in the future. | ||
1879 | let f = |x: dyn Any| {}; | ||
1880 | f(*answer()); // ERROR | ||
1881 | } | ||
1882 | ``` | ||
1883 | |||
1884 | ## By-value trait objects | ||
1885 | |||
1886 | With this feature, you can have by-value `self` arguments without `Self: Sized` bounds. | ||
1887 | |||
1888 | ```rust | ||
1889 | #![feature(unsized_fn_params)] | ||
1890 | |||
1891 | trait Foo { | ||
1892 | fn foo(self) {} | ||
1893 | } | ||
1894 | |||
1895 | impl<T: ?Sized> Foo for T {} | ||
1896 | |||
1897 | fn main() { | ||
1898 | let slice: Box<[i32]> = Box::new([1, 2, 3]); | ||
1899 | <[i32] as Foo>::foo(*slice); | ||
1900 | } | ||
1901 | ``` | ||
1902 | |||
1903 | And `Foo` will also be object-safe. | ||
1904 | |||
1905 | ```rust | ||
1906 | #![feature(unsized_fn_params)] | ||
1907 | |||
1908 | trait Foo { | ||
1909 | fn foo(self) {} | ||
1910 | } | ||
1911 | |||
1912 | impl<T: ?Sized> Foo for T {} | ||
1913 | |||
1914 | fn main () { | ||
1915 | let slice: Box<dyn Foo> = Box::new([1, 2, 3]); | ||
1916 | // doesn't compile yet | ||
1917 | <dyn Foo as Foo>::foo(*slice); | ||
1918 | } | ||
1919 | ``` | ||
1920 | |||
1921 | One of the objectives of this feature is to allow `Box<dyn FnOnce>`. | ||
1922 | |||
1923 | ## Variable length arrays | ||
1924 | |||
1925 | The RFC also describes an extension to the array literal syntax: `[e; dyn n]`. In the syntax, `n` isn't necessarily a constant expression. The array is dynamically allocated on the stack and has the type of `[T]`, instead of `[T; n]`. | ||
1926 | |||
1927 | ```rust,ignore (not-yet-implemented) | ||
1928 | #![feature(unsized_locals)] | ||
1929 | |||
1930 | fn mergesort<T: Ord>(a: &mut [T]) { | ||
1931 | let mut tmp = [T; dyn a.len()]; | ||
1932 | // ... | ||
1933 | } | ||
1934 | |||
1935 | fn main() { | ||
1936 | let mut a = [3, 1, 5, 6]; | ||
1937 | mergesort(&mut a); | ||
1938 | assert_eq!(a, [1, 3, 5, 6]); | ||
1939 | } | ||
1940 | ``` | ||
1941 | |||
1942 | VLAs are not implemented yet. The syntax isn't final, either. We may need an alternative syntax for Rust 2015 because, in Rust 2015, expressions like `[e; dyn(1)]` would be ambiguous. One possible alternative proposed in the RFC is `[e; n]`: if `n` captures one or more local variables, then it is considered as `[e; dyn n]`. | ||
1943 | |||
1944 | ## Advisory on stack usage | ||
1945 | |||
1946 | It's advised not to casually use the `#![feature(unsized_locals)]` feature. Typical use-cases are: | ||
1947 | |||
1948 | - When you need a by-value trait objects. | ||
1949 | - When you really need a fast allocation of small temporary arrays. | ||
1950 | |||
1951 | Another pitfall is repetitive allocation and temporaries. Currently the compiler simply extends the stack frame every time it encounters an unsized assignment. So for example, the code | ||
1952 | |||
1953 | ```rust | ||
1954 | #![feature(unsized_locals)] | ||
1955 | |||
1956 | fn main() { | ||
1957 | let x: Box<[i32]> = Box::new([1, 2, 3, 4, 5]); | ||
1958 | let _x = {{{{{{{{{{*x}}}}}}}}}}; | ||
1959 | } | ||
1960 | ``` | ||
1961 | |||
1962 | and the code | ||
1963 | |||
1964 | ```rust | ||
1965 | #![feature(unsized_locals)] | ||
1966 | |||
1967 | fn main() { | ||
1968 | for _ in 0..10 { | ||
1969 | let x: Box<[i32]> = Box::new([1, 2, 3, 4, 5]); | ||
1970 | let _x = *x; | ||
1971 | } | ||
1972 | } | ||
1973 | ``` | ||
1974 | |||
1975 | will unnecessarily extend the stack frame. | ||
1976 | "##, | ||
1977 | }, | ||
1978 | LintCompletion { | ||
1979 | label: "arbitrary_enum_discriminant", | ||
1980 | description: r##"# `arbitrary_enum_discriminant` | ||
1981 | |||
1982 | The tracking issue for this feature is: [#60553] | ||
1983 | |||
1984 | [#60553]: https://github.com/rust-lang/rust/issues/60553 | ||
1985 | |||
1986 | ------------------------ | ||
1987 | |||
1988 | The `arbitrary_enum_discriminant` feature permits tuple-like and | ||
1989 | struct-like enum variants with `#[repr(<int-type>)]` to have explicit discriminants. | ||
1990 | |||
1991 | ## Examples | ||
1992 | |||
1993 | ```rust | ||
1994 | #![feature(arbitrary_enum_discriminant)] | ||
1995 | |||
1996 | #[allow(dead_code)] | ||
1997 | #[repr(u8)] | ||
1998 | enum Enum { | ||
1999 | Unit = 3, | ||
2000 | Tuple(u16) = 2, | ||
2001 | Struct { | ||
2002 | a: u8, | ||
2003 | b: u16, | ||
2004 | } = 1, | ||
2005 | } | ||
2006 | |||
2007 | impl Enum { | ||
2008 | fn tag(&self) -> u8 { | ||
2009 | unsafe { *(self as *const Self as *const u8) } | ||
2010 | } | ||
2011 | } | ||
2012 | |||
2013 | assert_eq!(3, Enum::Unit.tag()); | ||
2014 | assert_eq!(2, Enum::Tuple(5).tag()); | ||
2015 | assert_eq!(1, Enum::Struct{a: 7, b: 11}.tag()); | ||
2016 | ``` | ||
2017 | "##, | ||
2018 | }, | ||
2019 | LintCompletion { | ||
2020 | label: "unboxed_closures", | ||
2021 | description: r##"# `unboxed_closures` | ||
2022 | |||
2023 | The tracking issue for this feature is [#29625] | ||
2024 | |||
2025 | See Also: [`fn_traits`](../library-features/fn-traits.md) | ||
2026 | |||
2027 | [#29625]: https://github.com/rust-lang/rust/issues/29625 | ||
2028 | |||
2029 | ---- | ||
2030 | |||
2031 | The `unboxed_closures` feature allows you to write functions using the `"rust-call"` ABI, | ||
2032 | required for implementing the [`Fn*`] family of traits. `"rust-call"` functions must have | ||
2033 | exactly one (non self) argument, a tuple representing the argument list. | ||
2034 | |||
2035 | [`Fn*`]: https://doc.rust-lang.org/std/ops/trait.Fn.html | ||
2036 | |||
2037 | ```rust | ||
2038 | #![feature(unboxed_closures)] | ||
2039 | |||
2040 | extern "rust-call" fn add_args(args: (u32, u32)) -> u32 { | ||
2041 | args.0 + args.1 | ||
2042 | } | ||
2043 | |||
2044 | fn main() {} | ||
2045 | ``` | ||
2046 | "##, | ||
2047 | }, | ||
2048 | LintCompletion { | ||
2049 | label: "custom_test_frameworks", | ||
2050 | description: r##"# `custom_test_frameworks` | ||
2051 | |||
2052 | The tracking issue for this feature is: [#50297] | ||
2053 | |||
2054 | [#50297]: https://github.com/rust-lang/rust/issues/50297 | ||
2055 | |||
2056 | ------------------------ | ||
2057 | |||
2058 | The `custom_test_frameworks` feature allows the use of `#[test_case]` and `#![test_runner]`. | ||
2059 | Any function, const, or static can be annotated with `#[test_case]` causing it to be aggregated (like `#[test]`) | ||
2060 | and be passed to the test runner determined by the `#![test_runner]` crate attribute. | ||
2061 | |||
2062 | ```rust | ||
2063 | #![feature(custom_test_frameworks)] | ||
2064 | #![test_runner(my_runner)] | ||
2065 | |||
2066 | fn my_runner(tests: &[&i32]) { | ||
2067 | for t in tests { | ||
2068 | if **t == 0 { | ||
2069 | println!("PASSED"); | ||
2070 | } else { | ||
2071 | println!("FAILED"); | ||
2072 | } | ||
2073 | } | ||
2074 | } | ||
2075 | |||
2076 | #[test_case] | ||
2077 | const WILL_PASS: i32 = 0; | ||
2078 | |||
2079 | #[test_case] | ||
2080 | const WILL_FAIL: i32 = 4; | ||
2081 | ``` | ||
2082 | "##, | ||
2083 | }, | ||
2084 | LintCompletion { | ||
2085 | label: "abi_msp430_interrupt", | ||
2086 | description: r##"# `abi_msp430_interrupt` | ||
2087 | |||
2088 | The tracking issue for this feature is: [#38487] | ||
2089 | |||
2090 | [#38487]: https://github.com/rust-lang/rust/issues/38487 | ||
2091 | |||
2092 | ------------------------ | ||
2093 | |||
2094 | In the MSP430 architecture, interrupt handlers have a special calling | ||
2095 | convention. You can use the `"msp430-interrupt"` ABI to make the compiler apply | ||
2096 | the right calling convention to the interrupt handlers you define. | ||
2097 | |||
2098 | <!-- NOTE(ignore) this example is specific to the msp430 target --> | ||
2099 | |||
2100 | ``` rust,ignore | ||
2101 | #![feature(abi_msp430_interrupt)] | ||
2102 | #![no_std] | ||
2103 | |||
2104 | // Place the interrupt handler at the appropriate memory address | ||
2105 | // (Alternatively, you can use `#[used]` and remove `pub` and `#[no_mangle]`) | ||
2106 | #[link_section = "__interrupt_vector_10"] | ||
2107 | #[no_mangle] | ||
2108 | pub static TIM0_VECTOR: extern "msp430-interrupt" fn() = tim0; | ||
2109 | |||
2110 | // The interrupt handler | ||
2111 | extern "msp430-interrupt" fn tim0() { | ||
2112 | // .. | ||
2113 | } | ||
2114 | ``` | ||
2115 | |||
2116 | ``` text | ||
2117 | $ msp430-elf-objdump -CD ./target/msp430/release/app | ||
2118 | Disassembly of section __interrupt_vector_10: | ||
2119 | |||
2120 | 0000fff2 <TIM0_VECTOR>: | ||
2121 | fff2: 00 c0 interrupt service routine at 0xc000 | ||
2122 | |||
2123 | Disassembly of section .text: | ||
2124 | |||
2125 | 0000c000 <int::tim0>: | ||
2126 | c000: 00 13 reti | ||
2127 | ``` | ||
2128 | "##, | ||
2129 | }, | ||
2130 | LintCompletion { | ||
2131 | label: "impl_trait_in_bindings", | ||
2132 | description: r##"# `impl_trait_in_bindings` | ||
2133 | |||
2134 | The tracking issue for this feature is: [#63065] | ||
2135 | |||
2136 | [#63065]: https://github.com/rust-lang/rust/issues/63065 | ||
2137 | |||
2138 | ------------------------ | ||
2139 | |||
2140 | The `impl_trait_in_bindings` feature gate lets you use `impl Trait` syntax in | ||
2141 | `let`, `static`, and `const` bindings. | ||
2142 | |||
2143 | A simple example is: | ||
2144 | |||
2145 | ```rust | ||
2146 | #![feature(impl_trait_in_bindings)] | ||
2147 | |||
2148 | use std::fmt::Debug; | ||
2149 | |||
2150 | fn main() { | ||
2151 | let a: impl Debug + Clone = 42; | ||
2152 | let b = a.clone(); | ||
2153 | println!("{:?}", b); // prints `42` | ||
2154 | } | ||
2155 | ``` | ||
2156 | |||
2157 | Note however that because the types of `a` and `b` are opaque in the above | ||
2158 | example, calling inherent methods or methods outside of the specified traits | ||
2159 | (e.g., `a.abs()` or `b.abs()`) is not allowed, and yields an error. | ||
2160 | "##, | ||
2161 | }, | ||
2162 | LintCompletion { | ||
2163 | label: "cfg_version", | ||
2164 | description: r##"# `cfg_version` | ||
2165 | |||
2166 | The tracking issue for this feature is: [#64796] | ||
2167 | |||
2168 | [#64796]: https://github.com/rust-lang/rust/issues/64796 | ||
2169 | |||
2170 | ------------------------ | ||
2171 | |||
2172 | The `cfg_version` feature makes it possible to execute different code | ||
2173 | depending on the compiler version. | ||
2174 | |||
2175 | ## Examples | ||
2176 | |||
2177 | ```rust | ||
2178 | #![feature(cfg_version)] | ||
2179 | |||
2180 | #[cfg(version("1.42"))] | ||
2181 | fn a() { | ||
2182 | // ... | ||
2183 | } | ||
2184 | |||
2185 | #[cfg(not(version("1.42")))] | ||
2186 | fn a() { | ||
2187 | // ... | ||
2188 | } | ||
2189 | |||
2190 | fn b() { | ||
2191 | if cfg!(version("1.42")) { | ||
2192 | // ... | ||
2193 | } else { | ||
2194 | // ... | ||
2195 | } | ||
2196 | } | ||
2197 | ``` | ||
2198 | "##, | ||
2199 | }, | ||
2200 | LintCompletion { | ||
2201 | label: "link_cfg", | ||
2202 | description: r##"# `link_cfg` | ||
2203 | |||
2204 | This feature is internal to the Rust compiler and is not intended for general use. | ||
2205 | |||
2206 | ------------------------ | ||
2207 | "##, | ||
2208 | }, | ||
2209 | LintCompletion { | ||
2210 | label: "infer_static_outlives_requirements", | ||
2211 | description: r##"# `infer_static_outlives_requirements` | ||
2212 | |||
2213 | The tracking issue for this feature is: [#54185] | ||
2214 | |||
2215 | [#54185]: https://github.com/rust-lang/rust/issues/54185 | ||
2216 | |||
2217 | ------------------------ | ||
2218 | The `infer_static_outlives_requirements` feature indicates that certain | ||
2219 | `'static` outlives requirements can be inferred by the compiler rather than | ||
2220 | stating them explicitly. | ||
2221 | |||
2222 | Note: It is an accompanying feature to `infer_outlives_requirements`, | ||
2223 | which must be enabled to infer outlives requirements. | ||
2224 | |||
2225 | For example, currently generic struct definitions that contain | ||
2226 | references, require where-clauses of the form T: 'static. By using | ||
2227 | this feature the outlives predicates will be inferred, although | ||
2228 | they may still be written explicitly. | ||
2229 | |||
2230 | ```rust,ignore (pseudo-Rust) | ||
2231 | struct Foo<U> where U: 'static { // <-- currently required | ||
2232 | bar: Bar<U> | ||
2233 | } | ||
2234 | struct Bar<T: 'static> { | ||
2235 | x: T, | ||
2236 | } | ||
2237 | ``` | ||
2238 | |||
2239 | |||
2240 | ## Examples: | ||
2241 | |||
2242 | ```rust,ignore (pseudo-Rust) | ||
2243 | #![feature(infer_outlives_requirements)] | ||
2244 | #![feature(infer_static_outlives_requirements)] | ||
2245 | |||
2246 | #[rustc_outlives] | ||
2247 | // Implicitly infer U: 'static | ||
2248 | struct Foo<U> { | ||
2249 | bar: Bar<U> | ||
2250 | } | ||
2251 | struct Bar<T: 'static> { | ||
2252 | x: T, | ||
2253 | } | ||
2254 | ``` | ||
2255 | "##, | ||
2256 | }, | ||
2257 | LintCompletion { | ||
2258 | label: "marker_trait_attr", | ||
2259 | description: r##"# `marker_trait_attr` | ||
2260 | |||
2261 | The tracking issue for this feature is: [#29864] | ||
2262 | |||
2263 | [#29864]: https://github.com/rust-lang/rust/issues/29864 | ||
2264 | |||
2265 | ------------------------ | ||
2266 | |||
2267 | Normally, Rust keeps you from adding trait implementations that could | ||
2268 | overlap with each other, as it would be ambiguous which to use. This | ||
2269 | feature, however, carves out an exception to that rule: a trait can | ||
2270 | opt-in to having overlapping implementations, at the cost that those | ||
2271 | implementations are not allowed to override anything (and thus the | ||
2272 | trait itself cannot have any associated items, as they're pointless | ||
2273 | when they'd need to do the same thing for every type anyway). | ||
2274 | |||
2275 | ```rust | ||
2276 | #![feature(marker_trait_attr)] | ||
2277 | |||
2278 | #[marker] trait CheapToClone: Clone {} | ||
2279 | |||
2280 | impl<T: Copy> CheapToClone for T {} | ||
2281 | |||
2282 | // These could potentially overlap with the blanket implementation above, | ||
2283 | // so are only allowed because CheapToClone is a marker trait. | ||
2284 | impl<T: CheapToClone, U: CheapToClone> CheapToClone for (T, U) {} | ||
2285 | impl<T: CheapToClone> CheapToClone for std::ops::Range<T> {} | ||
2286 | |||
2287 | fn cheap_clone<T: CheapToClone>(t: T) -> T { | ||
2288 | t.clone() | ||
2289 | } | ||
2290 | ``` | ||
2291 | |||
2292 | This is expected to replace the unstable `overlapping_marker_traits` | ||
2293 | feature, which applied to all empty traits (without needing an opt-in). | ||
2294 | "##, | ||
2295 | }, | ||
2296 | LintCompletion { | ||
2297 | label: "doc_masked", | ||
2298 | description: r##"# `doc_masked` | ||
2299 | |||
2300 | The tracking issue for this feature is: [#44027] | ||
2301 | |||
2302 | ----- | ||
2303 | |||
2304 | The `doc_masked` feature allows a crate to exclude types from a given crate from appearing in lists | ||
2305 | of trait implementations. The specifics of the feature are as follows: | ||
2306 | |||
2307 | 1. When rustdoc encounters an `extern crate` statement annotated with a `#[doc(masked)]` attribute, | ||
2308 | it marks the crate as being masked. | ||
2309 | |||
2310 | 2. When listing traits a given type implements, rustdoc ensures that traits from masked crates are | ||
2311 | not emitted into the documentation. | ||
2312 | |||
2313 | 3. When listing types that implement a given trait, rustdoc ensures that types from masked crates | ||
2314 | are not emitted into the documentation. | ||
2315 | |||
2316 | This feature was introduced in PR [#44026] to ensure that compiler-internal and | ||
2317 | implementation-specific types and traits were not included in the standard library's documentation. | ||
2318 | Such types would introduce broken links into the documentation. | ||
2319 | |||
2320 | [#44026]: https://github.com/rust-lang/rust/pull/44026 | ||
2321 | [#44027]: https://github.com/rust-lang/rust/pull/44027 | ||
2322 | "##, | ||
2323 | }, | ||
2324 | LintCompletion { | ||
2325 | label: "abi_ptx", | ||
2326 | description: r##"# `abi_ptx` | ||
2327 | |||
2328 | The tracking issue for this feature is: [#38788] | ||
2329 | |||
2330 | [#38788]: https://github.com/rust-lang/rust/issues/38788 | ||
2331 | |||
2332 | ------------------------ | ||
2333 | |||
2334 | When emitting PTX code, all vanilla Rust functions (`fn`) get translated to | ||
2335 | "device" functions. These functions are *not* callable from the host via the | ||
2336 | CUDA API so a crate with only device functions is not too useful! | ||
2337 | |||
2338 | OTOH, "global" functions *can* be called by the host; you can think of them | ||
2339 | as the real public API of your crate. To produce a global function use the | ||
2340 | `"ptx-kernel"` ABI. | ||
2341 | |||
2342 | <!-- NOTE(ignore) this example is specific to the nvptx targets --> | ||
2343 | |||
2344 | ``` rust,ignore | ||
2345 | #![feature(abi_ptx)] | ||
2346 | #![no_std] | ||
2347 | |||
2348 | pub unsafe extern "ptx-kernel" fn global_function() { | ||
2349 | device_function(); | ||
2350 | } | ||
2351 | |||
2352 | pub fn device_function() { | ||
2353 | // .. | ||
2354 | } | ||
2355 | ``` | ||
2356 | |||
2357 | ``` text | ||
2358 | $ xargo rustc --target nvptx64-nvidia-cuda --release -- --emit=asm | ||
2359 | |||
2360 | $ cat $(find -name '*.s') | ||
2361 | // | ||
2362 | // Generated by LLVM NVPTX Back-End | ||
2363 | // | ||
2364 | |||
2365 | .version 3.2 | ||
2366 | .target sm_20 | ||
2367 | .address_size 64 | ||
2368 | |||
2369 | // .globl _ZN6kernel15global_function17h46111ebe6516b382E | ||
2370 | |||
2371 | .visible .entry _ZN6kernel15global_function17h46111ebe6516b382E() | ||
2372 | { | ||
2373 | |||
2374 | |||
2375 | ret; | ||
2376 | } | ||
2377 | |||
2378 | // .globl _ZN6kernel15device_function17hd6a0e4993bbf3f78E | ||
2379 | .visible .func _ZN6kernel15device_function17hd6a0e4993bbf3f78E() | ||
2380 | { | ||
2381 | |||
2382 | |||
2383 | ret; | ||
2384 | } | ||
2385 | ``` | ||
2386 | "##, | ||
2387 | }, | ||
2388 | LintCompletion { | ||
2389 | label: "profiler_runtime", | ||
2390 | description: r##"# `profiler_runtime` | ||
2391 | |||
2392 | The tracking issue for this feature is: [#42524](https://github.com/rust-lang/rust/issues/42524). | ||
2393 | |||
2394 | ------------------------ | ||
2395 | "##, | ||
2396 | }, | ||
2397 | LintCompletion { | ||
2398 | label: "crate_visibility_modifier", | ||
2399 | description: r##"# `crate_visibility_modifier` | ||
2400 | |||
2401 | The tracking issue for this feature is: [#53120] | ||
2402 | |||
2403 | [#53120]: https://github.com/rust-lang/rust/issues/53120 | ||
2404 | |||
2405 | ----- | ||
2406 | |||
2407 | The `crate_visibility_modifier` feature allows the `crate` keyword to be used | ||
2408 | as a visibility modifier synonymous to `pub(crate)`, indicating that a type | ||
2409 | (function, _&c._) is to be visible to the entire enclosing crate, but not to | ||
2410 | other crates. | ||
2411 | |||
2412 | ```rust | ||
2413 | #![feature(crate_visibility_modifier)] | ||
2414 | |||
2415 | crate struct Foo { | ||
2416 | bar: usize, | ||
2417 | } | ||
2418 | ``` | ||
2419 | "##, | ||
2420 | }, | ||
2421 | LintCompletion { | ||
2422 | label: "doc_cfg", | ||
2423 | description: r##"# `doc_cfg` | ||
2424 | |||
2425 | The tracking issue for this feature is: [#43781] | ||
2426 | |||
2427 | ------ | ||
2428 | |||
2429 | The `doc_cfg` feature allows an API be documented as only available in some specific platforms. | ||
2430 | This attribute has two effects: | ||
2431 | |||
2432 | 1. In the annotated item's documentation, there will be a message saying "This is supported on | ||
2433 | (platform) only". | ||
2434 | |||
2435 | 2. The item's doc-tests will only run on the specific platform. | ||
2436 | |||
2437 | In addition to allowing the use of the `#[doc(cfg)]` attribute, this feature enables the use of a | ||
2438 | special conditional compilation flag, `#[cfg(doc)]`, set whenever building documentation on your | ||
2439 | crate. | ||
2440 | |||
2441 | This feature was introduced as part of PR [#43348] to allow the platform-specific parts of the | ||
2442 | standard library be documented. | ||
2443 | |||
2444 | ```rust | ||
2445 | #![feature(doc_cfg)] | ||
2446 | |||
2447 | #[cfg(any(windows, doc))] | ||
2448 | #[doc(cfg(windows))] | ||
2449 | /// The application's icon in the notification area (a.k.a. system tray). | ||
2450 | /// | ||
2451 | /// # Examples | ||
2452 | /// | ||
2453 | /// ```no_run | ||
2454 | /// extern crate my_awesome_ui_library; | ||
2455 | /// use my_awesome_ui_library::current_app; | ||
2456 | /// use my_awesome_ui_library::windows::notification; | ||
2457 | /// | ||
2458 | /// let icon = current_app().get::<notification::Icon>(); | ||
2459 | /// icon.show(); | ||
2460 | /// icon.show_message("Hello"); | ||
2461 | /// ``` | ||
2462 | pub struct Icon { | ||
2463 | // ... | ||
2464 | } | ||
2465 | ``` | ||
2466 | |||
2467 | [#43781]: https://github.com/rust-lang/rust/issues/43781 | ||
2468 | [#43348]: https://github.com/rust-lang/rust/issues/43348 | ||
2469 | "##, | ||
2470 | }, | ||
2471 | LintCompletion { | ||
2472 | label: "unsized_tuple_coercion", | ||
2473 | description: r##"# `unsized_tuple_coercion` | ||
2474 | |||
2475 | The tracking issue for this feature is: [#42877] | ||
2476 | |||
2477 | [#42877]: https://github.com/rust-lang/rust/issues/42877 | ||
2478 | |||
2479 | ------------------------ | ||
2480 | |||
2481 | This is a part of [RFC0401]. According to the RFC, there should be an implementation like this: | ||
2482 | |||
2483 | ```rust,ignore (partial-example) | ||
2484 | impl<..., T, U: ?Sized> Unsized<(..., U)> for (..., T) where T: Unsized<U> {} | ||
2485 | ``` | ||
2486 | |||
2487 | This implementation is currently gated behind `#[feature(unsized_tuple_coercion)]` to avoid insta-stability. Therefore you can use it like this: | ||
2488 | |||
2489 | ```rust | ||
2490 | #![feature(unsized_tuple_coercion)] | ||
2491 | |||
2492 | fn main() { | ||
2493 | let x : ([i32; 3], [i32; 3]) = ([1, 2, 3], [4, 5, 6]); | ||
2494 | let y : &([i32; 3], [i32]) = &x; | ||
2495 | assert_eq!(y.1[0], 4); | ||
2496 | } | ||
2497 | ``` | ||
2498 | |||
2499 | [RFC0401]: https://github.com/rust-lang/rfcs/blob/master/text/0401-coercions.md | ||
2500 | "##, | ||
2501 | }, | ||
2502 | LintCompletion { | ||
2503 | label: "no_sanitize", | ||
2504 | description: r##"# `no_sanitize` | ||
2505 | |||
2506 | The tracking issue for this feature is: [#39699] | ||
2507 | |||
2508 | [#39699]: https://github.com/rust-lang/rust/issues/39699 | ||
2509 | |||
2510 | ------------------------ | ||
2511 | |||
2512 | The `no_sanitize` attribute can be used to selectively disable sanitizer | ||
2513 | instrumentation in an annotated function. This might be useful to: avoid | ||
2514 | instrumentation overhead in a performance critical function, or avoid | ||
2515 | instrumenting code that contains constructs unsupported by given sanitizer. | ||
2516 | |||
2517 | The precise effect of this annotation depends on particular sanitizer in use. | ||
2518 | For example, with `no_sanitize(thread)`, the thread sanitizer will no longer | ||
2519 | instrument non-atomic store / load operations, but it will instrument atomic | ||
2520 | operations to avoid reporting false positives and provide meaning full stack | ||
2521 | traces. | ||
2522 | |||
2523 | ## Examples | ||
2524 | |||
2525 | ``` rust | ||
2526 | #![feature(no_sanitize)] | ||
2527 | |||
2528 | #[no_sanitize(address)] | ||
2529 | fn foo() { | ||
2530 | // ... | ||
2531 | } | ||
2532 | ``` | ||
2533 | "##, | ||
2534 | }, | ||
2535 | LintCompletion { | ||
2536 | label: "try_blocks", | ||
2537 | description: r##"# `try_blocks` | ||
2538 | |||
2539 | The tracking issue for this feature is: [#31436] | ||
2540 | |||
2541 | [#31436]: https://github.com/rust-lang/rust/issues/31436 | ||
2542 | |||
2543 | ------------------------ | ||
2544 | |||
2545 | The `try_blocks` feature adds support for `try` blocks. A `try` | ||
2546 | block creates a new scope one can use the `?` operator in. | ||
2547 | |||
2548 | ```rust,edition2018 | ||
2549 | #![feature(try_blocks)] | ||
2550 | |||
2551 | use std::num::ParseIntError; | ||
2552 | |||
2553 | let result: Result<i32, ParseIntError> = try { | ||
2554 | "1".parse::<i32>()? | ||
2555 | + "2".parse::<i32>()? | ||
2556 | + "3".parse::<i32>()? | ||
2557 | }; | ||
2558 | assert_eq!(result, Ok(6)); | ||
2559 | |||
2560 | let result: Result<i32, ParseIntError> = try { | ||
2561 | "1".parse::<i32>()? | ||
2562 | + "foo".parse::<i32>()? | ||
2563 | + "3".parse::<i32>()? | ||
2564 | }; | ||
2565 | assert!(result.is_err()); | ||
2566 | ``` | ||
2567 | "##, | ||
2568 | }, | ||
2569 | LintCompletion { | ||
2570 | label: "transparent_unions", | ||
2571 | description: r##"# `transparent_unions` | ||
2572 | |||
2573 | The tracking issue for this feature is [#60405] | ||
2574 | |||
2575 | [#60405]: https://github.com/rust-lang/rust/issues/60405 | ||
2576 | |||
2577 | ---- | ||
2578 | |||
2579 | The `transparent_unions` feature allows you mark `union`s as | ||
2580 | `#[repr(transparent)]`. A `union` may be `#[repr(transparent)]` in exactly the | ||
2581 | same conditions in which a `struct` may be `#[repr(transparent)]` (generally, | ||
2582 | this means the `union` must have exactly one non-zero-sized field). Some | ||
2583 | concrete illustrations follow. | ||
2584 | |||
2585 | ```rust | ||
2586 | #![feature(transparent_unions)] | ||
2587 | |||
2588 | // This union has the same representation as `f32`. | ||
2589 | #[repr(transparent)] | ||
2590 | union SingleFieldUnion { | ||
2591 | field: f32, | ||
2592 | } | ||
2593 | |||
2594 | // This union has the same representation as `usize`. | ||
2595 | #[repr(transparent)] | ||
2596 | union MultiFieldUnion { | ||
2597 | field: usize, | ||
2598 | nothing: (), | ||
2599 | } | ||
2600 | ``` | ||
2601 | |||
2602 | For consistency with transparent `struct`s, `union`s must have exactly one | ||
2603 | non-zero-sized field. If all fields are zero-sized, the `union` must not be | ||
2604 | `#[repr(transparent)]`: | ||
2605 | |||
2606 | ```rust | ||
2607 | #![feature(transparent_unions)] | ||
2608 | |||
2609 | // This (non-transparent) union is already valid in stable Rust: | ||
2610 | pub union GoodUnion { | ||
2611 | pub nothing: (), | ||
2612 | } | ||
2613 | |||
2614 | // Error: transparent union needs exactly one non-zero-sized field, but has 0 | ||
2615 | // #[repr(transparent)] | ||
2616 | // pub union BadUnion { | ||
2617 | // pub nothing: (), | ||
2618 | // } | ||
2619 | ``` | ||
2620 | |||
2621 | The one exception is if the `union` is generic over `T` and has a field of type | ||
2622 | `T`, it may be `#[repr(transparent)]` even if `T` is a zero-sized type: | ||
2623 | |||
2624 | ```rust | ||
2625 | #![feature(transparent_unions)] | ||
2626 | |||
2627 | // This union has the same representation as `T`. | ||
2628 | #[repr(transparent)] | ||
2629 | pub union GenericUnion<T: Copy> { // Unions with non-`Copy` fields are unstable. | ||
2630 | pub field: T, | ||
2631 | pub nothing: (), | ||
2632 | } | ||
2633 | |||
2634 | // This is okay even though `()` is a zero-sized type. | ||
2635 | pub const THIS_IS_OKAY: GenericUnion<()> = GenericUnion { field: () }; | ||
2636 | ``` | ||
2637 | |||
2638 | Like transarent `struct`s, a transparent `union` of type `U` has the same | ||
2639 | layout, size, and ABI as its single non-ZST field. If it is generic over a type | ||
2640 | `T`, and all its fields are ZSTs except for exactly one field of type `T`, then | ||
2641 | it has the same layout and ABI as `T` (even if `T` is a ZST when monomorphized). | ||
2642 | |||
2643 | Like transparent `struct`s, transparent `union`s are FFI-safe if and only if | ||
2644 | their underlying representation type is also FFI-safe. | ||
2645 | |||
2646 | A `union` may not be eligible for the same nonnull-style optimizations that a | ||
2647 | `struct` or `enum` (with the same fields) are eligible for. Adding | ||
2648 | `#[repr(transparent)]` to `union` does not change this. To give a more concrete | ||
2649 | example, it is unspecified whether `size_of::<T>()` is equal to | ||
2650 | `size_of::<Option<T>>()`, where `T` is a `union` (regardless of whether or not | ||
2651 | it is transparent). The Rust compiler is free to perform this optimization if | ||
2652 | possible, but is not required to, and different compiler versions may differ in | ||
2653 | their application of these optimizations. | ||
2654 | "##, | ||
2655 | }, | ||
2656 | LintCompletion { | ||
2657 | label: "const_eval_limit", | ||
2658 | description: r##"# `const_eval_limit` | ||
2659 | |||
2660 | The tracking issue for this feature is: [#67217] | ||
2661 | |||
2662 | [#67217]: https://github.com/rust-lang/rust/issues/67217 | ||
2663 | |||
2664 | The `const_eval_limit` allows someone to limit the evaluation steps the CTFE undertakes to evaluate a `const fn`. | ||
2665 | "##, | ||
2666 | }, | ||
2667 | LintCompletion { | ||
2668 | label: "link_args", | ||
2669 | description: r##"# `link_args` | ||
2670 | |||
2671 | The tracking issue for this feature is: [#29596] | ||
2672 | |||
2673 | [#29596]: https://github.com/rust-lang/rust/issues/29596 | ||
2674 | |||
2675 | ------------------------ | ||
2676 | |||
2677 | You can tell `rustc` how to customize linking, and that is via the `link_args` | ||
2678 | attribute. This attribute is applied to `extern` blocks and specifies raw flags | ||
2679 | which need to get passed to the linker when producing an artifact. An example | ||
2680 | usage would be: | ||
2681 | |||
2682 | ```rust,no_run | ||
2683 | #![feature(link_args)] | ||
2684 | |||
2685 | #[link_args = "-foo -bar -baz"] | ||
2686 | extern "C" {} | ||
2687 | # fn main() {} | ||
2688 | ``` | ||
2689 | |||
2690 | Note that this feature is currently hidden behind the `feature(link_args)` gate | ||
2691 | because this is not a sanctioned way of performing linking. Right now `rustc` | ||
2692 | shells out to the system linker (`gcc` on most systems, `link.exe` on MSVC), so | ||
2693 | it makes sense to provide extra command line arguments, but this will not | ||
2694 | always be the case. In the future `rustc` may use LLVM directly to link native | ||
2695 | libraries, in which case `link_args` will have no meaning. You can achieve the | ||
2696 | same effect as the `link_args` attribute with the `-C link-args` argument to | ||
2697 | `rustc`. | ||
2698 | |||
2699 | It is highly recommended to *not* use this attribute, and rather use the more | ||
2700 | formal `#[link(...)]` attribute on `extern` blocks instead. | ||
2701 | "##, | ||
2702 | }, | ||
2703 | LintCompletion { | ||
2704 | label: "internal_output_capture", | ||
2705 | description: r##"# `internal_output_capture` | ||
2706 | |||
2707 | This feature is internal to the Rust compiler and is not intended for general use. | ||
2708 | |||
2709 | ------------------------ | ||
2710 | "##, | ||
2711 | }, | ||
2712 | LintCompletion { | ||
2713 | label: "windows_handle", | ||
2714 | description: r##"# `windows_handle` | ||
2715 | |||
2716 | This feature is internal to the Rust compiler and is not intended for general use. | ||
2717 | |||
2718 | ------------------------ | ||
2719 | "##, | ||
2720 | }, | ||
2721 | LintCompletion { | ||
2722 | label: "asm", | ||
2723 | description: r##"# `asm` | ||
2724 | |||
2725 | The tracking issue for this feature is: [#72016] | ||
2726 | |||
2727 | [#72016]: https://github.com/rust-lang/rust/issues/72016 | ||
2728 | |||
2729 | ------------------------ | ||
2730 | |||
2731 | For extremely low-level manipulations and performance reasons, one | ||
2732 | might wish to control the CPU directly. Rust supports using inline | ||
2733 | assembly to do this via the `asm!` macro. | ||
2734 | |||
2735 | # Guide-level explanation | ||
2736 | [guide-level-explanation]: #guide-level-explanation | ||
2737 | |||
2738 | Rust provides support for inline assembly via the `asm!` macro. | ||
2739 | It can be used to embed handwritten assembly in the assembly output generated by the compiler. | ||
2740 | Generally this should not be necessary, but might be where the required performance or timing | ||
2741 | cannot be otherwise achieved. Accessing low level hardware primitives, e.g. in kernel code, may also demand this functionality. | ||
2742 | |||
2743 | > **Note**: the examples here are given in x86/x86-64 assembly, but other architectures are also supported. | ||
2744 | |||
2745 | Inline assembly is currently supported on the following architectures: | ||
2746 | - x86 and x86-64 | ||
2747 | - ARM | ||
2748 | - AArch64 | ||
2749 | - RISC-V | ||
2750 | - NVPTX | ||
2751 | - Hexagon | ||
2752 | - MIPS32r2 and MIPS64r2 | ||
2753 | - wasm32 | ||
2754 | |||
2755 | ## Basic usage | ||
2756 | |||
2757 | Let us start with the simplest possible example: | ||
2758 | |||
2759 | ```rust,allow_fail | ||
2760 | # #![feature(asm)] | ||
2761 | unsafe { | ||
2762 | asm!("nop"); | ||
2763 | } | ||
2764 | ``` | ||
2765 | |||
2766 | This will insert a NOP (no operation) instruction into the assembly generated by the compiler. | ||
2767 | Note that all `asm!` invocations have to be inside an `unsafe` block, as they could insert | ||
2768 | arbitrary instructions and break various invariants. The instructions to be inserted are listed | ||
2769 | in the first argument of the `asm!` macro as a string literal. | ||
2770 | |||
2771 | ## Inputs and outputs | ||
2772 | |||
2773 | Now inserting an instruction that does nothing is rather boring. Let us do something that | ||
2774 | actually acts on data: | ||
2775 | |||
2776 | ```rust,allow_fail | ||
2777 | # #![feature(asm)] | ||
2778 | let x: u64; | ||
2779 | unsafe { | ||
2780 | asm!("mov {}, 5", out(reg) x); | ||
2781 | } | ||
2782 | assert_eq!(x, 5); | ||
2783 | ``` | ||
2784 | |||
2785 | This will write the value `5` into the `u64` variable `x`. | ||
2786 | You can see that the string literal we use to specify instructions is actually a template string. | ||
2787 | It is governed by the same rules as Rust [format strings][format-syntax]. | ||
2788 | The arguments that are inserted into the template however look a bit different then you may | ||
2789 | be familiar with. First we need to specify if the variable is an input or an output of the | ||
2790 | inline assembly. In this case it is an output. We declared this by writing `out`. | ||
2791 | We also need to specify in what kind of register the assembly expects the variable. | ||
2792 | In this case we put it in an arbitrary general purpose register by specifying `reg`. | ||
2793 | The compiler will choose an appropriate register to insert into | ||
2794 | the template and will read the variable from there after the inline assembly finishes executing. | ||
2795 | |||
2796 | Let us see another example that also uses an input: | ||
2797 | |||
2798 | ```rust,allow_fail | ||
2799 | # #![feature(asm)] | ||
2800 | let i: u64 = 3; | ||
2801 | let o: u64; | ||
2802 | unsafe { | ||
2803 | asm!( | ||
2804 | "mov {0}, {1}", | ||
2805 | "add {0}, {number}", | ||
2806 | out(reg) o, | ||
2807 | in(reg) i, | ||
2808 | number = const 5, | ||
2809 | ); | ||
2810 | } | ||
2811 | assert_eq!(o, 8); | ||
2812 | ``` | ||
2813 | |||
2814 | This will add `5` to the input in variable `i` and write the result to variable `o`. | ||
2815 | The particular way this assembly does this is first copying the value from `i` to the output, | ||
2816 | and then adding `5` to it. | ||
2817 | |||
2818 | The example shows a few things: | ||
2819 | |||
2820 | First, we can see that `asm!` allows multiple template string arguments; each | ||
2821 | one is treated as a separate line of assembly code, as if they were all joined | ||
2822 | together with newlines between them. This makes it easy to format assembly | ||
2823 | code. | ||
2824 | |||
2825 | Second, we can see that inputs are declared by writing `in` instead of `out`. | ||
2826 | |||
2827 | Third, one of our operands has a type we haven't seen yet, `const`. | ||
2828 | This tells the compiler to expand this argument to value directly inside the assembly template. | ||
2829 | This is only possible for constants and literals. | ||
2830 | |||
2831 | Fourth, we can see that we can specify an argument number, or name as in any format string. | ||
2832 | For inline assembly templates this is particularly useful as arguments are often used more than once. | ||
2833 | For more complex inline assembly using this facility is generally recommended, as it improves | ||
2834 | readability, and allows reordering instructions without changing the argument order. | ||
2835 | |||
2836 | We can further refine the above example to avoid the `mov` instruction: | ||
2837 | |||
2838 | ```rust,allow_fail | ||
2839 | # #![feature(asm)] | ||
2840 | let mut x: u64 = 3; | ||
2841 | unsafe { | ||
2842 | asm!("add {0}, {number}", inout(reg) x, number = const 5); | ||
2843 | } | ||
2844 | assert_eq!(x, 8); | ||
2845 | ``` | ||
2846 | |||
2847 | We can see that `inout` is used to specify an argument that is both input and output. | ||
2848 | This is different from specifying an input and output separately in that it is guaranteed to assign both to the same register. | ||
2849 | |||
2850 | It is also possible to specify different variables for the input and output parts of an `inout` operand: | ||
2851 | |||
2852 | ```rust,allow_fail | ||
2853 | # #![feature(asm)] | ||
2854 | let x: u64 = 3; | ||
2855 | let y: u64; | ||
2856 | unsafe { | ||
2857 | asm!("add {0}, {number}", inout(reg) x => y, number = const 5); | ||
2858 | } | ||
2859 | assert_eq!(y, 8); | ||
2860 | ``` | ||
2861 | |||
2862 | ## Late output operands | ||
2863 | |||
2864 | The Rust compiler is conservative with its allocation of operands. It is assumed that an `out` | ||
2865 | can be written at any time, and can therefore not share its location with any other argument. | ||
2866 | However, to guarantee optimal performance it is important to use as few registers as possible, | ||
2867 | so they won't have to be saved and reloaded around the inline assembly block. | ||
2868 | To achieve this Rust provides a `lateout` specifier. This can be used on any output that is | ||
2869 | written only after all inputs have been consumed. | ||
2870 | There is also a `inlateout` variant of this specifier. | ||
2871 | |||
2872 | Here is an example where `inlateout` *cannot* be used: | ||
2873 | |||
2874 | ```rust,allow_fail | ||
2875 | # #![feature(asm)] | ||
2876 | let mut a: u64 = 4; | ||
2877 | let b: u64 = 4; | ||
2878 | let c: u64 = 4; | ||
2879 | unsafe { | ||
2880 | asm!( | ||
2881 | "add {0}, {1}", | ||
2882 | "add {0}, {2}", | ||
2883 | inout(reg) a, | ||
2884 | in(reg) b, | ||
2885 | in(reg) c, | ||
2886 | ); | ||
2887 | } | ||
2888 | assert_eq!(a, 12); | ||
2889 | ``` | ||
2890 | |||
2891 | Here the compiler is free to allocate the same register for inputs `b` and `c` since it knows they have the same value. However it must allocate a separate register for `a` since it uses `inout` and not `inlateout`. If `inlateout` was used, then `a` and `c` could be allocated to the same register, in which case the first instruction to overwrite the value of `c` and cause the assembly code to produce the wrong result. | ||
2892 | |||
2893 | However the following example can use `inlateout` since the output is only modified after all input registers have been read: | ||
2894 | |||
2895 | ```rust,allow_fail | ||
2896 | # #![feature(asm)] | ||
2897 | let mut a: u64 = 4; | ||
2898 | let b: u64 = 4; | ||
2899 | unsafe { | ||
2900 | asm!("add {0}, {1}", inlateout(reg) a, in(reg) b); | ||
2901 | } | ||
2902 | assert_eq!(a, 8); | ||
2903 | ``` | ||
2904 | |||
2905 | As you can see, this assembly fragment will still work correctly if `a` and `b` are assigned to the same register. | ||
2906 | |||
2907 | ## Explicit register operands | ||
2908 | |||
2909 | Some instructions require that the operands be in a specific register. | ||
2910 | Therefore, Rust inline assembly provides some more specific constraint specifiers. | ||
2911 | While `reg` is generally available on any architecture, these are highly architecture specific. E.g. for x86 the general purpose registers `eax`, `ebx`, `ecx`, `edx`, `ebp`, `esi`, and `edi` | ||
2912 | among others can be addressed by their name. | ||
2913 | |||
2914 | ```rust,allow_fail,no_run | ||
2915 | # #![feature(asm)] | ||
2916 | let cmd = 0xd1; | ||
2917 | unsafe { | ||
2918 | asm!("out 0x64, eax", in("eax") cmd); | ||
2919 | } | ||
2920 | ``` | ||
2921 | |||
2922 | In this example we call the `out` instruction to output the content of the `cmd` variable | ||
2923 | to port `0x64`. Since the `out` instruction only accepts `eax` (and its sub registers) as operand | ||
2924 | we had to use the `eax` constraint specifier. | ||
2925 | |||
2926 | Note that unlike other operand types, explicit register operands cannot be used in the template string: you can't use `{}` and should write the register name directly instead. Also, they must appear at the end of the operand list after all other operand types. | ||
2927 | |||
2928 | Consider this example which uses the x86 `mul` instruction: | ||
2929 | |||
2930 | ```rust,allow_fail | ||
2931 | # #![feature(asm)] | ||
2932 | fn mul(a: u64, b: u64) -> u128 { | ||
2933 | let lo: u64; | ||
2934 | let hi: u64; | ||
2935 | |||
2936 | unsafe { | ||
2937 | asm!( | ||
2938 | // The x86 mul instruction takes rax as an implicit input and writes | ||
2939 | // the 128-bit result of the multiplication to rax:rdx. | ||
2940 | "mul {}", | ||
2941 | in(reg) a, | ||
2942 | inlateout("rax") b => lo, | ||
2943 | lateout("rdx") hi | ||
2944 | ); | ||
2945 | } | ||
2946 | |||
2947 | ((hi as u128) << 64) + lo as u128 | ||
2948 | } | ||
2949 | ``` | ||
2950 | |||
2951 | This uses the `mul` instruction to multiply two 64-bit inputs with a 128-bit result. | ||
2952 | The only explicit operand is a register, that we fill from the variable `a`. | ||
2953 | The second operand is implicit, and must be the `rax` register, which we fill from the variable `b`. | ||
2954 | The lower 64 bits of the result are stored in `rax` from which we fill the variable `lo`. | ||
2955 | The higher 64 bits are stored in `rdx` from which we fill the variable `hi`. | ||
2956 | |||
2957 | ## Clobbered registers | ||
2958 | |||
2959 | In many cases inline assembly will modify state that is not needed as an output. | ||
2960 | Usually this is either because we have to use a scratch register in the assembly, | ||
2961 | or instructions modify state that we don't need to further examine. | ||
2962 | This state is generally referred to as being "clobbered". | ||
2963 | We need to tell the compiler about this since it may need to save and restore this state | ||
2964 | around the inline assembly block. | ||
2965 | |||
2966 | ```rust,allow_fail | ||
2967 | # #![feature(asm)] | ||
2968 | let ebx: u32; | ||
2969 | let ecx: u32; | ||
2970 | |||
2971 | unsafe { | ||
2972 | asm!( | ||
2973 | "cpuid", | ||
2974 | // EAX 4 selects the "Deterministic Cache Parameters" CPUID leaf | ||
2975 | inout("eax") 4 => _, | ||
2976 | // ECX 0 selects the L0 cache information. | ||
2977 | inout("ecx") 0 => ecx, | ||
2978 | lateout("ebx") ebx, | ||
2979 | lateout("edx") _, | ||
2980 | ); | ||
2981 | } | ||
2982 | |||
2983 | println!( | ||
2984 | "L1 Cache: {}", | ||
2985 | ((ebx >> 22) + 1) * (((ebx >> 12) & 0x3ff) + 1) * ((ebx & 0xfff) + 1) * (ecx + 1) | ||
2986 | ); | ||
2987 | ``` | ||
2988 | |||
2989 | In the example above we use the `cpuid` instruction to get the L1 cache size. | ||
2990 | This instruction writes to `eax`, `ebx`, `ecx`, and `edx`, but for the cache size we only care about the contents of `ebx` and `ecx`. | ||
2991 | |||
2992 | However we still need to tell the compiler that `eax` and `edx` have been modified so that it can save any values that were in these registers before the asm. This is done by declaring these as outputs but with `_` instead of a variable name, which indicates that the output value is to be discarded. | ||
2993 | |||
2994 | This can also be used with a general register class (e.g. `reg`) to obtain a scratch register for use inside the asm code: | ||
2995 | |||
2996 | ```rust,allow_fail | ||
2997 | # #![feature(asm)] | ||
2998 | // Multiply x by 6 using shifts and adds | ||
2999 | let mut x: u64 = 4; | ||
3000 | unsafe { | ||
3001 | asm!( | ||
3002 | "mov {tmp}, {x}", | ||
3003 | "shl {tmp}, 1", | ||
3004 | "shl {x}, 2", | ||
3005 | "add {x}, {tmp}", | ||
3006 | x = inout(reg) x, | ||
3007 | tmp = out(reg) _, | ||
3008 | ); | ||
3009 | } | ||
3010 | assert_eq!(x, 4 * 6); | ||
3011 | ``` | ||
3012 | |||
3013 | ## Symbol operands | ||
3014 | |||
3015 | A special operand type, `sym`, allows you to use the symbol name of a `fn` or `static` in inline assembly code. | ||
3016 | This allows you to call a function or access a global variable without needing to keep its address in a register. | ||
3017 | |||
3018 | ```rust,allow_fail | ||
3019 | # #![feature(asm)] | ||
3020 | extern "C" fn foo(arg: i32) { | ||
3021 | println!("arg = {}", arg); | ||
3022 | } | ||
3023 | |||
3024 | fn call_foo(arg: i32) { | ||
3025 | unsafe { | ||
3026 | asm!( | ||
3027 | "call {}", | ||
3028 | sym foo, | ||
3029 | // 1st argument in rdi, which is caller-saved | ||
3030 | inout("rdi") arg => _, | ||
3031 | // All caller-saved registers must be marked as clobberred | ||
3032 | out("rax") _, out("rcx") _, out("rdx") _, out("rsi") _, | ||
3033 | out("r8") _, out("r9") _, out("r10") _, out("r11") _, | ||
3034 | out("xmm0") _, out("xmm1") _, out("xmm2") _, out("xmm3") _, | ||
3035 | out("xmm4") _, out("xmm5") _, out("xmm6") _, out("xmm7") _, | ||
3036 | out("xmm8") _, out("xmm9") _, out("xmm10") _, out("xmm11") _, | ||
3037 | out("xmm12") _, out("xmm13") _, out("xmm14") _, out("xmm15") _, | ||
3038 | ) | ||
3039 | } | ||
3040 | } | ||
3041 | ``` | ||
3042 | |||
3043 | Note that the `fn` or `static` item does not need to be public or `#[no_mangle]`: | ||
3044 | the compiler will automatically insert the appropriate mangled symbol name into the assembly code. | ||
3045 | |||
3046 | ## Register template modifiers | ||
3047 | |||
3048 | In some cases, fine control is needed over the way a register name is formatted when inserted into the template string. This is needed when an architecture's assembly language has several names for the same register, each typically being a "view" over a subset of the register (e.g. the low 32 bits of a 64-bit register). | ||
3049 | |||
3050 | By default the compiler will always choose the name that refers to the full register size (e.g. `rax` on x86-64, `eax` on x86, etc). | ||
3051 | |||
3052 | This default can be overriden by using modifiers on the template string operands, just like you would with format strings: | ||
3053 | |||
3054 | ```rust,allow_fail | ||
3055 | # #![feature(asm)] | ||
3056 | let mut x: u16 = 0xab; | ||
3057 | |||
3058 | unsafe { | ||
3059 | asm!("mov {0:h}, {0:l}", inout(reg_abcd) x); | ||
3060 | } | ||
3061 | |||
3062 | assert_eq!(x, 0xabab); | ||
3063 | ``` | ||
3064 | |||
3065 | In this example, we use the `reg_abcd` register class to restrict the register allocator to the 4 legacy x86 register (`ax`, `bx`, `cx`, `dx`) of which the first two bytes can be addressed independently. | ||
3066 | |||
3067 | Let us assume that the register allocator has chosen to allocate `x` in the `ax` register. | ||
3068 | The `h` modifier will emit the register name for the high byte of that register and the `l` modifier will emit the register name for the low byte. The asm code will therefore be expanded as `mov ah, al` which copies the low byte of the value into the high byte. | ||
3069 | |||
3070 | If you use a smaller data type (e.g. `u16`) with an operand and forget the use template modifiers, the compiler will emit a warning and suggest the correct modifier to use. | ||
3071 | |||
3072 | ## Memory address operands | ||
3073 | |||
3074 | Sometimes assembly instructions require operands passed via memory addresses/memory locations. | ||
3075 | You have to manually use the memory address syntax specified by the respectively architectures. | ||
3076 | For example, in x86/x86_64 and intel assembly syntax, you should wrap inputs/outputs in `[]` | ||
3077 | to indicate they are memory operands: | ||
3078 | |||
3079 | ```rust,allow_fail | ||
3080 | # #![feature(asm, llvm_asm)] | ||
3081 | # fn load_fpu_control_word(control: u16) { | ||
3082 | unsafe { | ||
3083 | asm!("fldcw [{}]", in(reg) &control, options(nostack)); | ||
3084 | |||
3085 | // Previously this would have been written with the deprecated `llvm_asm!` like this | ||
3086 | llvm_asm!("fldcw $0" :: "m" (control) :: "volatile"); | ||
3087 | } | ||
3088 | # } | ||
3089 | ``` | ||
3090 | |||
3091 | ## Options | ||
3092 | |||
3093 | By default, an inline assembly block is treated the same way as an external FFI function call with a custom calling convention: it may read/write memory, have observable side effects, etc. However in many cases, it is desirable to give the compiler more information about what the assembly code is actually doing so that it can optimize better. | ||
3094 | |||
3095 | Let's take our previous example of an `add` instruction: | ||
3096 | |||
3097 | ```rust,allow_fail | ||
3098 | # #![feature(asm)] | ||
3099 | let mut a: u64 = 4; | ||
3100 | let b: u64 = 4; | ||
3101 | unsafe { | ||
3102 | asm!( | ||
3103 | "add {0}, {1}", | ||
3104 | inlateout(reg) a, in(reg) b, | ||
3105 | options(pure, nomem, nostack), | ||
3106 | ); | ||
3107 | } | ||
3108 | assert_eq!(a, 8); | ||
3109 | ``` | ||
3110 | |||
3111 | Options can be provided as an optional final argument to the `asm!` macro. We specified three options here: | ||
3112 | - `pure` means that the asm code has no observable side effects and that its output depends only on its inputs. This allows the compiler optimizer to call the inline asm fewer times or even eliminate it entirely. | ||
3113 | - `nomem` means that the asm code does not read or write to memory. By default the compiler will assume that inline assembly can read or write any memory address that is accessible to it (e.g. through a pointer passed as an operand, or a global). | ||
3114 | - `nostack` means that the asm code does not push any data onto the stack. This allows the compiler to use optimizations such as the stack red zone on x86-64 to avoid stack pointer adjustments. | ||
3115 | |||
3116 | These allow the compiler to better optimize code using `asm!`, for example by eliminating pure `asm!` blocks whose outputs are not needed. | ||
3117 | |||
3118 | See the reference for the full list of available options and their effects. | ||
3119 | |||
3120 | # Reference-level explanation | ||
3121 | [reference-level-explanation]: #reference-level-explanation | ||
3122 | |||
3123 | Inline assembler is implemented as an unsafe macro `asm!()`. | ||
3124 | The first argument to this macro is a template string literal used to build the final assembly. | ||
3125 | The following arguments specify input and output operands. | ||
3126 | When required, options are specified as the final argument. | ||
3127 | |||
3128 | The following ABNF specifies the general syntax: | ||
3129 | |||
3130 | ```text | ||
3131 | dir_spec := "in" / "out" / "lateout" / "inout" / "inlateout" | ||
3132 | reg_spec := <register class> / "<explicit register>" | ||
3133 | operand_expr := expr / "_" / expr "=>" expr / expr "=>" "_" | ||
3134 | reg_operand := dir_spec "(" reg_spec ")" operand_expr | ||
3135 | operand := reg_operand / "const" const_expr / "sym" path | ||
3136 | option := "pure" / "nomem" / "readonly" / "preserves_flags" / "noreturn" / "nostack" / "att_syntax" | ||
3137 | options := "options(" option *["," option] [","] ")" | ||
3138 | asm := "asm!(" format_string *("," format_string) *("," [ident "="] operand) ["," options] [","] ")" | ||
3139 | ``` | ||
3140 | |||
3141 | The macro will initially be supported only on ARM, AArch64, Hexagon, x86, x86-64 and RISC-V targets. Support for more targets may be added in the future. The compiler will emit an error if `asm!` is used on an unsupported target. |