Weird fix

Author: andrewbranch

src/compiler/checker.ts

@@ -20983,7 +20983,16 @@ namespace ts {
             }
             if (contextFlags && contextFlags & ContextFlags.Completion && signature.target) {
                 const baseSignature = getBaseSignature(signature.target);
-                return intersectTypes(getTypeAtPosition(signature, argIndex), getTypeAtPosition(baseSignature, argIndex));
+                // Only consider the type from the base signature for completions
+                // if it actually contributes something. The type from the contextually
+                // instantiated signature is the _real_ type anyway, so we should never
+                // let the base type _remove_ completions from the list.
+                const baseArgumentType = filterType(
+                    getTypeAtPosition(baseSignature, argIndex),
+                    t => !(t.flags & (TypeFlags.AnyOrUnknown | TypeFlags.IndexedAccess)));
+                if (!(baseArgumentType.flags & TypeFlags.Never)) {
+                    return intersectTypes(getTypeAtPosition(signature, argIndex), baseArgumentType);
+                }
             }
             return getTypeAtPosition(signature, argIndex);
         }

tests/cases/fourslash/completionsGenericIndexedAccess1.ts

@@ -0,0 +1,18 @@
+/// <reference path="fourslash.ts" />
+
+// #34825
+
+////interface Sample {
+////  addBook: { name: string, year: number }
+////}
+////
+////export declare function testIt<T>(method: T[keyof T]): any
+////testIt<Sample>({ /**/ });
+
+verify.completions({
+  marker: '',
+  exact: [
+    { name: 'name' },
+    { name: 'year' },
+  ]
+});

tests/cases/fourslash/completionsGenericIndexedAccess2.ts

@@ -0,0 +1,34 @@
+/// <reference path="fourslash.ts" />
+
+// #34825
+
+////export type GetMethodsForType<T, G extends string> = { [K in keyof T]:
+////  T[K] extends () => any ? { name: K, group: G, } : T[K] extends (s: infer U) => any ? { name: K, group: G, payload: U } : never }[keyof T];
+////
+////
+////class Sample {
+////  count = 0;
+////  books: { name: string, year: number }[] = []
+////  increment() {
+////      this.count++
+////      this.count++
+////  }
+////
+////  addBook(book: Sample["books"][0]) {
+////      this.books.push(book)
+////  }
+////}
+////export declare function testIt<T, G extends string>(): (input: any, method: GetMethodsForType<T, G>) => any
+////
+////
+////const t = testIt<Sample, "Sample">()
+////
+////const i = t(null, { name: "addBook", group: "Sample", payload: { /**/ } })
+
+verify.completions({
+  marker: '',
+  exact: [
+    { name: 'name' },
+    { name: 'year' },
+  ]
+});