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1//! Eager expansion related utils
2//!
3//! Here is a dump of a discussion from Vadim Petrochenkov about Eager Expansion and
4//! Its name resolution :
5//!
6//! > Eagerly expanded macros (and also macros eagerly expanded by eagerly expanded macros,
7//! > which actually happens in practice too!) are resolved at the location of the "root" macro
8//! > that performs the eager expansion on its arguments.
9//! > If some name cannot be resolved at the eager expansion time it's considered unresolved,
10//! > even if becomes available later (e.g. from a glob import or other macro).
11//!
12//! > Eagerly expanded macros don't add anything to the module structure of the crate and
13//! > don't build any speculative module structures, i.e. they are expanded in a "flat"
14//! > way even if tokens in them look like modules.
15//!
16//! > In other words, it kinda works for simple cases for which it was originally intended,
17//! > and we need to live with it because it's available on stable and widely relied upon.
18//!
19//!
20//! See the full discussion : https://rust-lang.zulipchat.com/#narrow/stream/131828-t-compiler/topic/Eager.20expansion.20of.20built-in.20macros
21
22use crate::{
23 ast::{self, AstNode},
24 db::AstDatabase,
25 EagerCallLoc, EagerMacroId, InFile, MacroCallId, MacroCallKind, MacroDefId, MacroDefKind,
26};
27
28use base_db::CrateId;
29use parser::FragmentKind;
30use std::sync::Arc;
31use syntax::{algo::SyntaxRewriter, SyntaxNode};
32
33pub fn expand_eager_macro(
34 db: &dyn AstDatabase,
35 krate: CrateId,
36 macro_call: InFile<ast::MacroCall>,
37 def: MacroDefId,
38 resolver: &dyn Fn(ast::Path) -> Option<MacroDefId>,
39) -> Option<EagerMacroId> {
40 let args = macro_call.value.token_tree()?;
41 let parsed_args = mbe::ast_to_token_tree(&args)?.0;
42
43 // Note:
44 // When `lazy_expand` is called, its *parent* file must be already exists.
45 // Here we store an eager macro id for the argument expanded subtree here
46 // for that purpose.
47 let arg_id = db.intern_eager_expansion({
48 EagerCallLoc {
49 def,
50 fragment: FragmentKind::Expr,
51 subtree: Arc::new(parsed_args.clone()),
52 krate,
53 file_id: macro_call.file_id,
54 }
55 });
56 let arg_file_id: MacroCallId = arg_id.into();
57
58 let parsed_args = mbe::token_tree_to_syntax_node(&parsed_args, FragmentKind::Expr).ok()?.0;
59 let result = eager_macro_recur(
60 db,
61 InFile::new(arg_file_id.as_file(), parsed_args.syntax_node()),
62 krate,
63 resolver,
64 )?;
65 let subtree = to_subtree(&result)?;
66
67 if let MacroDefKind::BuiltInEager(eager) = def.kind {
68 let (subtree, fragment) = eager.expand(db, arg_id, &subtree).ok()?;
69 let eager = EagerCallLoc {
70 def,
71 fragment,
72 subtree: Arc::new(subtree),
73 krate,
74 file_id: macro_call.file_id,
75 };
76
77 Some(db.intern_eager_expansion(eager))
78 } else {
79 None
80 }
81}
82
83fn to_subtree(node: &SyntaxNode) -> Option<tt::Subtree> {
84 let mut subtree = mbe::syntax_node_to_token_tree(node)?.0;
85 subtree.delimiter = None;
86 Some(subtree)
87}
88
89fn lazy_expand(
90 db: &dyn AstDatabase,
91 def: &MacroDefId,
92 macro_call: InFile<ast::MacroCall>,
93 krate: CrateId,
94) -> Option<InFile<SyntaxNode>> {
95 let ast_id = db.ast_id_map(macro_call.file_id).ast_id(&macro_call.value);
96
97 let id: MacroCallId =
98 def.as_lazy_macro(db, krate, MacroCallKind::FnLike(macro_call.with_value(ast_id))).into();
99
100 db.parse_or_expand(id.as_file()).map(|node| InFile::new(id.as_file(), node))
101}
102
103fn eager_macro_recur(
104 db: &dyn AstDatabase,
105 curr: InFile<SyntaxNode>,
106 krate: CrateId,
107 macro_resolver: &dyn Fn(ast::Path) -> Option<MacroDefId>,
108) -> Option<SyntaxNode> {
109 let original = curr.value.clone();
110
111 let children = curr.value.descendants().filter_map(ast::MacroCall::cast);
112 let mut rewriter = SyntaxRewriter::default();
113
114 // Collect replacement
115 for child in children {
116 let def: MacroDefId = macro_resolver(child.path()?)?;
117 let insert = match def.kind {
118 MacroDefKind::BuiltInEager(_) => {
119 let id: MacroCallId = expand_eager_macro(
120 db,
121 krate,
122 curr.with_value(child.clone()),
123 def,
124 macro_resolver,
125 )?
126 .into();
127 db.parse_or_expand(id.as_file())?
128 }
129 MacroDefKind::Declarative
130 | MacroDefKind::BuiltIn(_)
131 | MacroDefKind::BuiltInDerive(_)
132 | MacroDefKind::CustomDerive(_) => {
133 let expanded = lazy_expand(db, &def, curr.with_value(child.clone()), krate)?;
134 // replace macro inside
135 eager_macro_recur(db, expanded, krate, macro_resolver)?
136 }
137 };
138
139 rewriter.replace(child.syntax(), &insert);
140 }
141
142 let res = rewriter.rewrite(&original);
143 Some(res)
144}