Resolve type parameters on arrow-methods

Resolves #2320

CHANGELOG.md

@@ -13,6 +13,7 @@
 
 ### Bug Fixes
 
+-   Type parameters will now be resolved for arrow-methods on classes like regular class methods, #2320.
 -   Methods which return function types no longer have duplicated comments, #2336.
 -   Comments on function-like type aliases will now show up under the type alias, rather than nested within the type declaration, #2372.
 -   Fix crash when converting some complicated union/intersection types, #2451.

src/lib/converter/symbols.ts

@@ -748,10 +748,31 @@ function convertArrowAsMethod(
 
     const rc = context.withScope(reflection);
 
-    const signature = context.checker.getSignatureFromDeclaration(arrow);
-    assert(signature);
+    const locationDeclaration =
+        symbol.parent
+            ?.getDeclarations()
+            ?.find(
+                (d) => ts.isClassDeclaration(d) || ts.isInterfaceDeclaration(d),
+            ) ??
+        symbol.parent?.getDeclarations()?.[0]?.getSourceFile() ??
+        symbol.getDeclarations()?.[0]?.getSourceFile();
+    assert(locationDeclaration, "Missing declaration context");
 
-    createSignature(rc, ReflectionKind.CallSignature, signature, symbol, arrow);
+    const type = context.checker.getTypeOfSymbolAtLocation(
+        symbol,
+        locationDeclaration,
+    );
+
+    const signatures = type.getNonNullableType().getCallSignatures();
+    assert(signatures.length, "Missing signatures");
+
+    createSignature(
+        rc,
+        ReflectionKind.CallSignature,
+        signatures[0],
+        symbol,
+        arrow,
+    );
 }
 
 function convertConstructor(context: Context, symbol: ts.Symbol) {

src/test/converter2/issues/gh2320.ts

@@ -0,0 +1,23 @@
+export type BaseUnionMember = {
+    type: string;
+};
+
+export type Union =
+    | {
+          type: "one";
+      }
+    | {
+          type: "two";
+      };
+
+export class GenericClass<U extends BaseUnionMember> {
+    public arrowFunction = <MemberType extends U["type"]>(
+        member: Extract<U, { type: MemberType }>,
+    ) => {};
+
+    public classFunction<MemberType extends U["type"]>(
+        member: Extract<U, { type: MemberType }>,
+    ) {}
+}
+
+export class ResolvedSubclass extends GenericClass<Union> {}

src/test/issues.c2.test.ts

@@ -1123,6 +1123,13 @@ describe("Issue Tests", () => {
         equal(tp.flags.isConst, true);
     });
 
+    it("Uses type parameters from parent class in arrow-methods, #2320", () => {
+        const project = convert();
+        const arrow = querySig(project, "ResolvedSubclass.arrowFunction");
+
+        equal(arrow.typeParameters![0].type?.toString(), '"one" | "two"');
+    });
+
     it("Handles comments with nested methods #2336", () => {
         const project = convert();