Provide class member completions for classes implementing types with dynamically generated members

src/services/completions.ts

@@ -5239,7 +5239,7 @@ function getCompletionData(
      * @returns Symbols to be suggested in an class element depending on existing memebers and symbol flags
      */
     function filterClassMembersList(baseSymbols: readonly Symbol[], existingMembers: readonly ClassElement[], currentClassElementModifierFlags: ModifierFlags): Symbol[] {
-        const existingMemberNames = new Set<__String>();
+        const existingMemberNames = new Set(["prototype" as __String]); // always exclude 'prototype' from completions
         for (const m of existingMembers) {
             // Ignore omitted expressions for missing members
             if (
@@ -5274,7 +5274,6 @@ function getCompletionData(
 
         return baseSymbols.filter(propertySymbol =>
             !existingMemberNames.has(propertySymbol.escapedName) &&
-            !!propertySymbol.declarations &&
             !(getDeclarationModifierFlagsFromSymbol(propertySymbol) & ModifierFlags.Private) &&
             !(propertySymbol.valueDeclaration && isPrivateIdentifierClassElementDeclaration(propertySymbol.valueDeclaration))
         );

tests/cases/fourslash/completionListClassMembersImplementingDynamicallyCreatedType1.ts

@@ -0,0 +1,34 @@
+/// <reference path="fourslash.ts" />
+
+//// type Base = {
+////   [K in "foo" | "bar"]: K;
+//// };
+////
+//// class Cls implements Base { /*1*/ }
+
+verify.completions({
+  marker: "1",
+  includes: ["foo", "bar"],
+  isNewIdentifierLocation: true,
+});
+
+verify.completions({
+  marker: "1",
+  includes: [
+    {
+      name: "foo",
+      insertText: `foo: "foo";`,
+      filterText: "foo",
+    },
+    {
+      name: "bar",
+      insertText: `bar: "bar";`,
+      filterText: "bar",
+    },
+  ],
+  isNewIdentifierLocation: true,
+  preferences: {
+    includeCompletionsWithClassMemberSnippets: true,
+    includeCompletionsWithInsertText: true,
+  },
+});

tests/cases/fourslash/completionListClassMembersImplementingDynamicallyCreatedType2.ts

@@ -0,0 +1,86 @@
+/// <reference path="fourslash.ts" />
+
+// https://github.com/microsoft/TypeScript/issues/62689
+
+//// type EventType = "start" | "foo" | "bar" | "fooBar" | "end";
+////
+//// type EventDataType<T extends EventType> = T extends "fooBar"
+////   ? { foo: string; bar: number }
+////   : T extends "foo"
+////   ? { foo: string }
+////   : T extends "bar"
+////   ? { bar: number }
+////   : T extends EventType
+////   ? Record<string, any>
+////   : never;
+////
+//// type ListenerFunction<T extends EventType> = (
+////   context: any,
+////   data: EventDataType<T>,
+//// ) => void | Promise<void>;
+////
+//// type EvtListenerMethods = {
+////   [K in EventType as `on${Capitalize<K>}`]?: ListenerFunction<K>;
+//// };
+////
+//// class A implements EvtListenerMethods {
+////   onFoo(context: any, data: EventDataType<"foo">) {}
+////   onBar(context: any, data: { abcd: any }) {}
+////   /*1*/
+//// }
+////
+//// interface EvtListener extends EvtListenerMethods {}
+////
+//// class B implements EvtListener {
+////   onFoo(context: any, data: EventDataType<"foo">) {}
+////   onBar(context: any, data: { abcd: any }) {}
+////   /*2*/
+//// }
+////
+//// interface EvtListenerHardcoded {
+////   onStart?: ListenerFunction<"start">;
+////   onFooBar?: ListenerFunction<"fooBar">;
+////   onFoo?: ListenerFunction<"foo">;
+////   onBar?: ListenerFunction<"bar">;
+////   onEnd?: ListenerFunction<"end">;
+//// }
+////
+//// class C implements EvtListenerHardcoded {
+////   onFoo(context: any, data: EventDataType<"foo">) {}
+////   onBar(context: any, data: { abcd: any }) {}
+////   /*3*/
+//// }
+
+verify.completions({
+  marker: ["1", "2", "3"],
+  includes: ["onStart", "onEnd", "onFooBar"],
+  excludes: ["onFoo", "onBar"],
+  isNewIdentifierLocation: true,
+});
+
+verify.completions({
+  marker: ["1", "2", "3"],
+  includes: [
+    {
+      name: "onStart",
+      insertText: `onStart?: ListenerFunction<"start">;`,
+      filterText: "onStart",
+    },
+    {
+      name: "onEnd",
+      insertText: `onEnd?: ListenerFunction<"end">;`,
+      filterText: "onEnd",
+    },
+    {
+      name: "onFooBar",
+      insertText: `onFooBar?: ListenerFunction<"fooBar">;`,
+      filterText: "onFooBar",
+    },
+  ],
+  excludes: ["onFoo", "onBar"],
+  isNewIdentifierLocation: true,
+  preferences: {
+    includeCompletionsWithClassMemberSnippets: true,
+    includeCompletionsWithInsertText: true,
+  },
+});