Merge #8124

8124: Add basic lifetime completion r=Veykril a=Veykril

This adds basic lifetime completion, basic in the sense that the completions for lifetimes are only shown when the user enters `'` followed by a char. Showing them when nothing is entered is kind of a pain, as we would want them to only show up where they are useful which in turn requires a lot of tree traversal and cursor position checking to verify whether the position is valid for a lifetime. This in itself doesn't seem too bad as usually when you know you want to write a lifetime putting `'` to ask for lifetime completions seems fine.

~~I'll take a look at whether its possible to lift the restriction of having to put a char after `'`.~~ This actually already works so I guess this is the clients responsibility, in which case VSCode doesn't like it.

![TYH9gIlyVo](https://user-images.githubusercontent.com/3757771/111886437-c9b02f80-89cd-11eb-9bee-340f1536b0de.gif)


Co-authored-by: Lukas Wirth <[email protected]>

5 files changed, 233 insertions, 14 deletions

diff --git a/crates/ide_completion/src/completions.rs b/crates/ide_completion/src/completions.rs
index 09882c4f3..cdac4e41a 100644
--- a/crates/ide_completion/src/completions.rs
+++ b/crates/ide_completion/src/completions.rs
@@ -2,25 +2,27 @@
 
 pub(crate) mod attribute;
 pub(crate) mod dot;
-pub(crate) mod record;
-pub(crate) mod pattern;
+pub(crate) mod flyimport;
 pub(crate) mod fn_param;
 pub(crate) mod keyword;
-pub(crate) mod snippet;
-pub(crate) mod qualified_path;
-pub(crate) mod unqualified_path;
-pub(crate) mod postfix;
+pub(crate) mod lifetime;
 pub(crate) mod macro_in_item_position;
-pub(crate) mod trait_impl;
 pub(crate) mod mod_;
-pub(crate) mod flyimport;
+pub(crate) mod pattern;
+pub(crate) mod postfix;
+pub(crate) mod qualified_path;
+pub(crate) mod record;
+pub(crate) mod snippet;
+pub(crate) mod trait_impl;
+pub(crate) mod unqualified_path;
 
 use std::iter;
 
 use hir::{known, ModPath, ScopeDef, Type};
+use ide_db::SymbolKind;
 
 use crate::{
-    item::Builder,
+    item::{Builder, CompletionKind},
     render::{
         const_::render_const,
         enum_variant::render_variant,
@@ -31,7 +33,7 @@ use crate::{
         type_alias::render_type_alias,
         RenderContext,
     },
-    CompletionContext, CompletionItem,
+    CompletionContext, CompletionItem, CompletionItemKind,
 };
 
 /// Represents an in-progress set of completions being built.
@@ -77,6 +79,13 @@ impl Completions {
         self.add(item);
     }
 
+    pub(crate) fn add_static_lifetime(&mut self, ctx: &CompletionContext) {
+        let mut item =
+            CompletionItem::new(CompletionKind::Reference, ctx.source_range(), "'static");
+        item.kind(CompletionItemKind::SymbolKind(SymbolKind::LifetimeParam));
+        self.add(item.build());
+    }
+
     pub(crate) fn add_resolution(
         &mut self,
         ctx: &CompletionContext,
diff --git a/crates/ide_completion/src/completions/lifetime.rs b/crates/ide_completion/src/completions/lifetime.rs
new file mode 100644
index 000000000..74eb23360
--- /dev/null
+++ b/crates/ide_completion/src/completions/lifetime.rs
@@ -0,0 +1,181 @@
+//! Completes lifetimes.
+use hir::ScopeDef;
+
+use crate::{completions::Completions, context::CompletionContext};
+
+/// Completes lifetimes.
+pub(crate) fn complete_lifetime(acc: &mut Completions, ctx: &CompletionContext) {
+    if !ctx.lifetime_allowed {
+        return;
+    }
+    let param_lifetime = match (
+        &ctx.lifetime_syntax,
+        ctx.lifetime_param_syntax.as_ref().and_then(|lp| lp.lifetime()),
+    ) {
+        (Some(lt), Some(lp)) if lp == lt.clone() => return,
+        (Some(_), Some(lp)) => Some(lp.to_string()),
+        _ => None,
+    };
+
+    ctx.scope.process_all_names(&mut |name, res| {
+        if let ScopeDef::GenericParam(hir::GenericParam::LifetimeParam(_)) = res {
+            if param_lifetime != Some(name.to_string()) {
+                acc.add_resolution(ctx, name.to_string(), &res);
+            }
+        }
+    });
+    if param_lifetime.is_none() {
+        acc.add_static_lifetime(ctx);
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use expect_test::{expect, Expect};
+
+    use crate::{
+        test_utils::{check_edit, completion_list_with_config, TEST_CONFIG},
+        CompletionConfig, CompletionKind,
+    };
+
+    fn check(ra_fixture: &str, expect: Expect) {
+        check_with_config(TEST_CONFIG, ra_fixture, expect);
+    }
+
+    fn check_with_config(config: CompletionConfig, ra_fixture: &str, expect: Expect) {
+        let actual = completion_list_with_config(config, ra_fixture, CompletionKind::Reference);
+        expect.assert_eq(&actual)
+    }
+
+    #[test]
+    fn check_lifetime_edit() {
+        check_edit(
+            "'lifetime",
+            r#"
+fn func<'lifetime>(foo: &'li$0) {}
+"#,
+            r#"
+fn func<'lifetime>(foo: &'lifetime) {}
+"#,
+        );
+    }
+
+    #[test]
+    fn complete_lifetime_in_ref() {
+        check(
+            r#"
+fn foo<'lifetime>(foo: &'a$0 usize) {}
+"#,
+            expect![[r#"
+                lt 'lifetime
+                lt 'static
+            "#]],
+        );
+    }
+
+    #[test]
+    fn complete_lifetime_in_ref_missing_ty() {
+        check(
+            r#"
+fn foo<'lifetime>(foo: &'a$0) {}
+"#,
+            expect![[r#"
+                lt 'lifetime
+                lt 'static
+            "#]],
+        );
+    }
+    #[test]
+    fn complete_lifetime_in_self_ref() {
+        check(
+            r#"
+struct Foo;
+impl<'impl> Foo {
+    fn foo<'func>(&'a$0 self) {}
+}
+"#,
+            expect![[r#"
+                lt 'func
+                lt 'impl
+                lt 'static
+            "#]],
+        );
+    }
+
+    #[test]
+    fn complete_lifetime_in_arg_list() {
+        check(
+            r#"
+struct Foo<'lt>;
+fn foo<'lifetime>(_: Foo<'a$0>) {}
+"#,
+            expect![[r#"
+                lt 'lifetime
+                lt 'static
+            "#]],
+        );
+    }
+
+    #[test]
+    fn complete_lifetime_in_where_pred() {
+        check(
+            r#"
+fn foo2<'lifetime, T>() where 'a$0 {}
+"#,
+            expect![[r#"
+                lt 'lifetime
+                lt 'static
+            "#]],
+        );
+    }
+
+    #[test]
+    fn complete_lifetime_in_ty_bound() {
+        check(
+            r#"
+fn foo2<'lifetime, T>() where T: 'a$0 {}
+"#,
+            expect![[r#"
+                lt 'lifetime
+                lt 'static
+            "#]],
+        );
+        check(
+            r#"
+fn foo2<'lifetime, T>() where T: Trait<'a$0> {}
+"#,
+            expect![[r#"
+                lt 'lifetime
+                lt 'static
+            "#]],
+        );
+    }
+
+    #[test]
+    fn dont_complete_lifetime_in_assoc_ty_bound() {
+        check(
+            r#"
+fn foo2<'lifetime, T>() where T: Trait<Item = 'a$0> {}
+"#,
+            expect![[r#""#]],
+        );
+    }
+
+    #[test]
+    fn complete_lifetime_in_param_list() {
+        check(
+            r#"
+fn foo<'a$0>() {}
+"#,
+            expect![[r#""#]],
+        );
+        check(
+            r#"
+fn foo<'footime, 'lifetime: 'a$0>() {}
+"#,
+            expect![[r#"
+                lt 'footime
+            "#]],
+        );
+    }
+}
diff --git a/crates/ide_completion/src/completions/pattern.rs b/crates/ide_completion/src/completions/pattern.rs
index 476eecff0..b06498e6d 100644
--- a/crates/ide_completion/src/completions/pattern.rs
+++ b/crates/ide_completion/src/completions/pattern.rs
@@ -1,4 +1,4 @@
-//! Completes constats and paths in patterns.
+//! Completes constants and paths in patterns.
 
 use crate::{CompletionContext, Completions};
 
diff --git a/crates/ide_completion/src/context.rs b/crates/ide_completion/src/context.rs
index a60b8b09d..4c2b31084 100644
--- a/crates/ide_completion/src/context.rs
+++ b/crates/ide_completion/src/context.rs
@@ -41,12 +41,15 @@ pub(crate) struct CompletionContext<'a> {
     pub(super) expected_name: Option<NameOrNameRef>,
     pub(super) expected_type: Option<Type>,
     pub(super) name_ref_syntax: Option<ast::NameRef>,
+    pub(super) lifetime_syntax: Option<ast::Lifetime>,
+    pub(super) lifetime_param_syntax: Option<ast::LifetimeParam>,
     pub(super) function_syntax: Option<ast::Fn>,
     pub(super) use_item_syntax: Option<ast::Use>,
     pub(super) record_lit_syntax: Option<ast::RecordExpr>,
     pub(super) record_pat_syntax: Option<ast::RecordPat>,
     pub(super) record_field_syntax: Option<ast::RecordExprField>,
     pub(super) impl_def: Option<ast::Impl>,
+    pub(super) lifetime_allowed: bool,
     /// FIXME: `ActiveParameter` is string-based, which is very very wrong
     pub(super) active_parameter: Option<ActiveParameter>,
     pub(super) is_param: bool,
@@ -139,9 +142,12 @@ impl<'a> CompletionContext<'a> {
             original_token,
             token,
             krate,
+            lifetime_allowed: false,
             expected_name: None,
             expected_type: None,
             name_ref_syntax: None,
+            lifetime_syntax: None,
+            lifetime_param_syntax: None,
             function_syntax: None,
             use_item_syntax: None,
             record_lit_syntax: None,
@@ -244,7 +250,7 @@ impl<'a> CompletionContext<'a> {
     pub(crate) fn source_range(&self) -> TextRange {
         // check kind of macro-expanded token, but use range of original token
         let kind = self.token.kind();
-        if kind == IDENT || kind == UNDERSCORE || kind.is_keyword() {
+        if kind == IDENT || kind == LIFETIME_IDENT || kind == UNDERSCORE || kind.is_keyword() {
             cov_mark::hit!(completes_if_prefix_is_keyword);
             self.original_token.text_range()
         } else {
@@ -390,6 +396,11 @@ impl<'a> CompletionContext<'a> {
         self.expected_name = expected_name;
         self.attribute_under_caret = find_node_at_offset(&file_with_fake_ident, offset);
 
+        if let Some(lifetime) = find_node_at_offset::<ast::Lifetime>(&file_with_fake_ident, offset)
+        {
+            self.classify_lifetime(original_file, lifetime, offset);
+        }
+
         // First, let's try to complete a reference to some declaration.
         if let Some(name_ref) = find_node_at_offset::<ast::NameRef>(&file_with_fake_ident, offset) {
             // Special case, `trait T { fn foo(i_am_a_name_ref) {} }`.
@@ -449,6 +460,23 @@ impl<'a> CompletionContext<'a> {
         }
     }
 
+    fn classify_lifetime(
+        &mut self,
+        original_file: &SyntaxNode,
+        lifetime: ast::Lifetime,
+        offset: TextSize,
+    ) {
+        self.lifetime_syntax =
+            find_node_at_offset(original_file, lifetime.syntax().text_range().start());
+        if lifetime.syntax().parent().map_or(false, |p| p.kind() != syntax::SyntaxKind::ERROR) {
+            self.lifetime_allowed = true;
+        }
+        if let Some(_) = lifetime.syntax().parent().and_then(ast::LifetimeParam::cast) {
+            self.lifetime_param_syntax =
+                self.sema.find_node_at_offset_with_macros(original_file, offset);
+        }
+    }
+
     fn classify_name_ref(
         &mut self,
         original_file: &SyntaxNode,
@@ -456,11 +484,11 @@ impl<'a> CompletionContext<'a> {
         offset: TextSize,
     ) {
         self.name_ref_syntax =
-            find_node_at_offset(&original_file, name_ref.syntax().text_range().start());
+            find_node_at_offset(original_file, name_ref.syntax().text_range().start());
         let name_range = name_ref.syntax().text_range();
         if ast::RecordExprField::for_field_name(&name_ref).is_some() {
             self.record_lit_syntax =
-                self.sema.find_node_at_offset_with_macros(&original_file, offset);
+                self.sema.find_node_at_offset_with_macros(original_file, offset);
         }
 
         self.fill_impl_def();
diff --git a/crates/ide_completion/src/lib.rs b/crates/ide_completion/src/lib.rs
index d9ea7b7ea..7a0eb6a96 100644
--- a/crates/ide_completion/src/lib.rs
+++ b/crates/ide_completion/src/lib.rs
@@ -130,6 +130,7 @@ pub fn completions(
     completions::trait_impl::complete_trait_impl(&mut acc, &ctx);
     completions::mod_::complete_mod(&mut acc, &ctx);
     completions::flyimport::import_on_the_fly(&mut acc, &ctx);
+    completions::lifetime::complete_lifetime(&mut acc, &ctx);
 
     Some(acc)
 }