Auto merge of #17676 - winstxnhdw:precise-capturing, r=Veykril

feat: add preliminary support for `+ use<..>` `precise_capturing` syntax

## Summary

This PR adds basic support for the following syntax.

```rs
fn captures<'a: 'a, 'b: 'b, T>() -> impl Sized + use<'b, T> {}
//                                  ~~~~~~~~~~~~~~~~~~~~~~~
//                          This opaque type does not capture `'a`.

fn outlives<'o, T: 'o>(_: T) {}

fn caller<'o, 'a, 'b: 'o, T: 'o>() {
    //        ~~
    //        ^ Note that we don't need `'a: 'o`.
    outlives::<'o>(captures::<'a, 'b, T>());
}
```

Related to #17598

crates/hir-def/src/hir/type_ref.rs

@@ -379,6 +379,7 @@ impl TypeBound {
                     None => TypeBound::Error,
                 }
             }
+            ast::TypeBoundKind::Use(_) => TypeBound::Error,
             ast::TypeBoundKind::Lifetime(lifetime) => {
                 TypeBound::Lifetime(LifetimeRef::new(&lifetime))
             }

crates/parser/src/grammar/generic_params.rs

@@ -144,6 +144,12 @@ fn type_bound(p: &mut Parser<'_>) -> bool {
     match p.current() {
         LIFETIME_IDENT => lifetime(p),
         T![for] => types::for_type(p, false),
+        // test precise_capturing
+        // fn captures<'a: 'a, 'b: 'b, T>() -> impl Sized + use<'b, T> {}
+        T![use] => {
+            p.bump_any();
+            generic_param_list(p)
+        }
         T![?] if p.nth_at(1, T![for]) => {
             // test question_for_type_trait_bound
             // fn f<T>() where T: ?for<> Sized {}

crates/parser/test_data/generated/runner.rs

@@ -467,6 +467,10 @@ mod ok {
     #[test]
     fn postfix_range() { run_and_expect_no_errors("test_data/parser/inline/ok/postfix_range.rs"); }
     #[test]
+    fn precise_capturing() {
+        run_and_expect_no_errors("test_data/parser/inline/ok/precise_capturing.rs");
+    }
+    #[test]
     fn pub_parens_typepath() {
         run_and_expect_no_errors("test_data/parser/inline/ok/pub_parens_typepath.rs");
     }

crates/parser/test_data/parser/inline/ok/precise_capturing.rast

@@ -0,0 +1,69 @@
+SOURCE_FILE
+  FN
+    FN_KW "fn"
+    WHITESPACE " "
+    NAME
+      IDENT "captures"
+    GENERIC_PARAM_LIST
+      L_ANGLE "<"
+      LIFETIME_PARAM
+        LIFETIME
+          LIFETIME_IDENT "'a"
+        COLON ":"
+        WHITESPACE " "
+        LIFETIME
+          LIFETIME_IDENT "'a"
+      COMMA ","
+      WHITESPACE " "
+      LIFETIME_PARAM
+        LIFETIME
+          LIFETIME_IDENT "'b"
+        COLON ":"
+        WHITESPACE " "
+        LIFETIME
+          LIFETIME_IDENT "'b"
+      COMMA ","
+      WHITESPACE " "
+      TYPE_PARAM
+        NAME
+          IDENT "T"
+      R_ANGLE ">"
+    PARAM_LIST
+      L_PAREN "("
+      R_PAREN ")"
+    WHITESPACE " "
+    RET_TYPE
+      THIN_ARROW "->"
+      WHITESPACE " "
+      IMPL_TRAIT_TYPE
+        IMPL_KW "impl"
+        WHITESPACE " "
+        TYPE_BOUND_LIST
+          TYPE_BOUND
+            PATH_TYPE
+              PATH
+                PATH_SEGMENT
+                  NAME_REF
+                    IDENT "Sized"
+          WHITESPACE " "
+          PLUS "+"
+          WHITESPACE " "
+          TYPE_BOUND
+            USE_KW "use"
+            GENERIC_PARAM_LIST
+              L_ANGLE "<"
+              LIFETIME_PARAM
+                LIFETIME
+                  LIFETIME_IDENT "'b"
+              COMMA ","
+              WHITESPACE " "
+              TYPE_PARAM
+                NAME
+                  IDENT "T"
+              R_ANGLE ">"
+    WHITESPACE " "
+    BLOCK_EXPR
+      STMT_LIST
+        L_CURLY "{"
+        R_CURLY "}"
+  WHITESPACE "\n"

crates/parser/test_data/parser/inline/ok/precise_capturing.rs

@@ -0,0 +1 @@
+fn captures<'a: 'a, 'b: 'b, T>() -> impl Sized + use<'b, T> {}

crates/syntax/rust.ungram

@@ -629,6 +629,7 @@ TypeBoundList =
 TypeBound =
   Lifetime
 | ('~' 'const' | 'const')? 'async'? '?'? Type
+| 'use' GenericParamList
 
 //************************//
 //        Patterns        //

crates/syntax/src/ast/generated/nodes.rs

@@ -1788,6 +1788,8 @@ pub struct TypeBound {
     pub(crate) syntax: SyntaxNode,
 }
 impl TypeBound {
+    #[inline]
+    pub fn generic_param_list(&self) -> Option<GenericParamList> { support::child(&self.syntax) }
     #[inline]
     pub fn lifetime(&self) -> Option<Lifetime> { support::child(&self.syntax) }
     #[inline]
@@ -1799,6 +1801,8 @@ impl TypeBound {
     #[inline]
     pub fn const_token(&self) -> Option<SyntaxToken> { support::token(&self.syntax, T![const]) }
     #[inline]
+    pub fn use_token(&self) -> Option<SyntaxToken> { support::token(&self.syntax, T![use]) }
+    #[inline]
     pub fn tilde_token(&self) -> Option<SyntaxToken> { support::token(&self.syntax, T![~]) }
 }
 

crates/syntax/src/ast/node_ext.rs

@@ -794,6 +794,8 @@ pub enum TypeBoundKind {
     PathType(ast::PathType),
     /// for<'a> ...
     ForType(ast::ForType),
+    /// use
+    Use(ast::GenericParamList),
     /// 'a
     Lifetime(ast::Lifetime),
 }
@@ -804,6 +806,8 @@ impl ast::TypeBound {
             TypeBoundKind::PathType(path_type)
         } else if let Some(for_type) = support::children(self.syntax()).next() {
             TypeBoundKind::ForType(for_type)
+        } else if let Some(generic_param_list) = self.generic_param_list() {
+            TypeBoundKind::Use(generic_param_list)
         } else if let Some(lifetime) = self.lifetime() {
             TypeBoundKind::Lifetime(lifetime)
         } else {