fix: generate delegate methods filters out functions that already exist

on the struct's impls

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

@@ -86,7 +86,8 @@ pub(crate) fn generate_delegate_methods(acc: &mut Assists, ctx: &AssistContext<'
     for method in methods {
         let adt = ast::Adt::Struct(strukt.clone());
         let name = method.name(ctx.db()).to_string();
-        let impl_def = find_struct_impl(ctx, &adt, &[name]).flatten();
+        // if `find_struct_impl` returns None, that means that a function named `name` already exists.
+        let Some(impl_def) = find_struct_impl(ctx, &adt, &[name]) else { continue; };
         acc.add_group(
             &GroupLabel("Generate delegate methods…".to_owned()),
             AssistId("generate_delegate_methods", AssistKind::Generate),
@@ -380,4 +381,26 @@ struct Person {
 }"#,
         )
     }
+
+    #[test]
+    fn test_generate_not_eligible_if_fn_exists() {
+        check_assist_not_applicable(
+            generate_delegate_methods,
+            r#"
+struct Age(u8);
+impl Age {
+    fn age(&self) -> u8 {
+        self.0
+    }
+}
+
+struct Person {
+    ag$0e: Age,
+}
+impl Person {
+    fn age(&self) -> u8 { 0 }
+}
+"#,
+        );
+    }
 }

crates/ide-assists/src/utils.rs

@@ -338,7 +338,12 @@ fn calc_depth(pat: &ast::Pat, depth: usize) -> usize {
 
 /// `find_struct_impl` looks for impl of a struct, but this also has additional feature
 /// where it takes a list of function names and check if they exist inside impl_, if
-/// even one match is found, it returns None
+/// even one match is found, it returns None.
+///
+/// That means this function can have 3 potential return values:
+///  - `None`: an impl exists, but one of the function names within the impl matches one of the provided names.
+///  - `Some(None)`: no impl exists.
+///  - `Some(Some(_))`: an impl exists, with no matching function names.
 pub(crate) fn find_struct_impl(
     ctx: &AssistContext<'_>,
     adt: &ast::Adt,