feat(lsp): use trait method docs for trait impl method docs on hover

tooling/lsp/Cargo.toml

@@ -3,7 +3,7 @@ name = "noir_lsp"
 description = "Language server for Noir"
 version.workspace = true
 authors.workspace = true
-edition.workspace = true#
+edition.workspace = true
 rust-version.workspace = true
 license.workspace = true
 
@@ -16,7 +16,7 @@ workspace = true
 acvm.workspace = true
 codespan-lsp.workspace = true
 lsp-types.workspace = true
-nargo.workspace = true
+nargo = { workspace = true, features = ["rpc"] }
 nargo_fmt.workspace = true
 nargo_toml.workspace = true
 noirc_driver.workspace = true

tooling/lsp/src/requests/hover.rs

@@ -410,8 +410,10 @@ fn format_function(id: FuncId, args: &ProcessRequestCallbackArgs) -> String {
         string.push_str("comptime ");
     }
 
+    let func_name = &func_name_definition_id.name;
+
     string.push_str("fn ");
-    string.push_str(&func_name_definition_id.name);
+    string.push_str(func_name);
     format_generics(&func_meta.direct_generics, &mut string);
     string.push('(');
     let parameters = &func_meta.parameters;
@@ -442,7 +444,20 @@ fn format_function(id: FuncId, args: &ProcessRequestCallbackArgs) -> String {
 
     string.push_str(&go_to_type_links(return_type, args.interner, args.files));
 
-    append_doc_comments(args.interner, ReferenceId::Function(id), &mut string);
+    let had_doc_comments =
+        append_doc_comments(args.interner, ReferenceId::Function(id), &mut string);
+    if !had_doc_comments {
+        // If this function doesn't have doc comments, but it's a trait impl method,
+        // use the trait method doc comments.
+        if let Some(trait_impl_id) = func_meta.trait_impl {
+            let trait_impl = args.interner.get_trait_implementation(trait_impl_id);
+            let trait_impl = trait_impl.borrow();
+            let trait_ = args.interner.get_trait(trait_impl.trait_id);
+            if let Some(func_id) = trait_.method_ids.get(func_name) {
+                append_doc_comments(args.interner, ReferenceId::Function(*func_id), &mut string);
+            }
+        }
+    }
 
     string
 }
@@ -776,13 +791,16 @@ fn format_link(name: String, location: lsp_types::Location) -> String {
     )
 }
 
-fn append_doc_comments(interner: &NodeInterner, id: ReferenceId, string: &mut String) {
+fn append_doc_comments(interner: &NodeInterner, id: ReferenceId, string: &mut String) -> bool {
     if let Some(doc_comments) = interner.doc_comments(id) {
         string.push_str("\n\n---\n\n");
         for comment in doc_comments {
             string.push_str(comment);
             string.push('\n');
         }
+        true
+    } else {
+        false
     }
 }
 
@@ -1139,4 +1157,12 @@ mod hover_tests {
     pub fn bar_stuff(self)"
         ));
     }
+
+    #[test]
+    async fn hover_on_trait_impl_method_uses_docs_from_trait_method() {
+        let hover_text =
+            get_hover_text("workspace", "two/src/lib.nr", Position { line: 92, character: 8 })
+                .await;
+        assert!(hover_text.contains("Some docs"));
+    }
 }

tooling/lsp/test_programs/workspace/two/src/lib.nr

@@ -84,3 +84,12 @@ fn bar_stuff() {
     foo.bar_stuff();
 }
 
+trait TraitWithDocs {
+    /// Some docs
+    fn foo();
+}
+
+impl TraitWithDocs for Field {
+    fn foo() {}
+}
+