Skip lifetime elision on fn pointers and fn trait types

crates/hir-ty/src/infer/expr.rs

@@ -334,6 +334,7 @@ fn infer_expr_inner(&mut self, tgt_expr: ExprId, expected: &Expectation) -> Ty {
                 let (param_tys, ret_ty) = match res {
                     Some(res) => {
                         let adjustments = auto_deref_adjust_steps(&derefs);
+                        // FIXME: Handle call adjustments for Fn/FnMut
                         self.write_expr_adj(*callee, adjustments);
                         res
                     }

crates/ide-assists/src/handlers/add_explicit_type.rs

@@ -47,7 +47,10 @@ pub(crate) fn add_explicit_type(acc: &mut Assists, ctx: &AssistContext<'_>) -> O
     // Don't enable the assist if there is a type ascription without any placeholders
     if let Some(ty) = &ascribed_ty {
         let mut contains_infer_ty = false;
-        walk_ty(ty, &mut |ty| contains_infer_ty |= matches!(ty, ast::Type::InferType(_)));
+        walk_ty(ty, &mut |ty| {
+            contains_infer_ty |= matches!(ty, ast::Type::InferType(_));
+            false
+        });
         if !contains_infer_ty {
             cov_mark::hit!(add_explicit_type_not_applicable_if_ty_already_specified);
             return None;

crates/ide-assists/src/handlers/extract_type_alias.rs

@@ -108,7 +108,8 @@ fn find_lifetime(text: &str) -> impl Fn(&&ast::GenericParam) -> bool + '_ {
     }
 
     let mut generics = Vec::new();
-    walk_ty(ty, &mut |ty| match ty {
+    walk_ty(ty, &mut |ty| {
+        match ty {
             ast::Type::PathType(ty) => {
                 if let Some(path) = ty.path() {
                     if let Some(name_ref) = path.as_single_name_ref() {
@@ -156,7 +157,8 @@ fn find_lifetime(text: &str) -> impl Fn(&&ast::GenericParam) -> bool + '_ {
                 }
             }
             ast::Type::RefType(ref_) => generics.extend(
-            ref_.lifetime().and_then(|lt| known_generics.iter().find(find_lifetime(&lt.text()))),
+                ref_.lifetime()
+                    .and_then(|lt| known_generics.iter().find(find_lifetime(&lt.text()))),
             ),
             ast::Type::ArrayType(ar) => {
                 if let Some(expr) = ar.expr() {
@@ -178,6 +180,8 @@ fn find_lifetime(text: &str) -> impl Fn(&&ast::GenericParam) -> bool + '_ {
                 }
             }
             _ => (),
+        };
+        false
     });
     // stable resort to lifetime, type, const
     generics.sort_by_key(|gp| match gp {

crates/ide-db/src/syntax_helpers/node_ext.rs

@@ -173,7 +173,8 @@ pub fn walk_pat(pat: &ast::Pat, cb: &mut dyn FnMut(ast::Pat)) {
 }
 
 /// Preorder walk all the type's sub types.
-pub fn walk_ty(ty: &ast::Type, cb: &mut dyn FnMut(ast::Type)) {
+// FIXME: Make the control flow more proper
+pub fn walk_ty(ty: &ast::Type, cb: &mut dyn FnMut(ast::Type) -> bool) {
     let mut preorder = ty.syntax().preorder();
     while let Some(event) = preorder.next() {
         let node = match event {
@@ -184,10 +185,12 @@ pub fn walk_ty(ty: &ast::Type, cb: &mut dyn FnMut(ast::Type)) {
         match ast::Type::cast(node) {
             Some(ty @ ast::Type::MacroType(_)) => {
                 preorder.skip_subtree();
-                cb(ty)
+                cb(ty);
             }
             Some(ty) => {
-                cb(ty);
+                if cb(ty) {
+                    preorder.skip_subtree();
+                }
             }
             // skip const args
             None if ast::ConstArg::can_cast(kind) => {

crates/ide/src/inlay_hints/fn_lifetime_fn.rs

@@ -59,9 +59,14 @@ pub(super) fn hints(
                         r.amp_token(),
                         lifetime,
                         is_elided,
-                    ))
+                    ));
+                    false
                 }
-                _ => (),
+                ast::Type::FnPtrType(_) => true,
+                ast::Type::PathType(t) => {
+                    t.path().and_then(|it| it.segment()).and_then(|it| it.param_list()).is_some()
+                }
+                _ => false,
             })
         });
         acc
@@ -146,8 +151,13 @@ pub(super) fn hints(
                         is_trivial = false;
                         acc.push(mk_lt_hint(amp, output_lt.to_string()));
                     }
+                    false
                 }
-                _ => (),
+                ast::Type::FnPtrType(_) => true,
+                ast::Type::PathType(t) => {
+                    t.path().and_then(|it| it.segment()).and_then(|it| it.param_list()).is_some()
+                }
+                _ => false,
             })
         }
     }
@@ -295,6 +305,20 @@ fn foo(&self, a: &()) -> &() {}
     // ^^^<'0, '1>
         // ^'0       ^'1     ^'0
 }
+"#,
+        );
+    }
+
+    #[test]
+    fn hints_lifetimes_skip_fn_likes() {
+        check_with_config(
+            InlayHintsConfig {
+                lifetime_elision_hints: LifetimeElisionHints::Always,
+                ..TEST_CONFIG
+            },
+            r#"
+fn fn_ptr(a: fn(&()) -> &()) {}
+fn fn_trait<>(a: impl Fn(&()) -> &()) {}
 "#,
         );
     }