Read T[keyof T] as unknown for T bound to an unknown-valued record

packages/compiler/src/frontend/type-mapper.ts

@@ -5139,11 +5139,15 @@ function mapGenericIndexedAccess(type: ts.Type, ctx: TypeMapperCtx): IrType | nu
   const obj = type.getObjectType();
   if (obj === undefined || !(obj.flags & ts.TypeFlags.TypeParameter)) return null;
   const bound = resolveTypeParam(obj);
+  const idx = type.getIndexType();
+  if (idx === undefined) return null;
+  // `T[keyof T]` over a T bound to an unknown-valued record view
+  // (`Record<string, unknown>` maps to the checked-dynamic value, see
+  // mapRecordType): every member reads as unknown.
+  if (bound?.kind === "dyn" && idx.isIndexType() && idx.getTarget() === obj) return DYN;
   if (!bound || bound.kind !== "record") return null;
   const shape = shapes.get(bound.shapeId);
   if (!shape || shape.tuple) return null;
-  const idx = type.getIndexType();
-  if (idx === undefined) return null;
   let covered: IrType[] | null = null;
   if (idx.isStringLiteralType()) {
     const f = shape.fields.find((x) => x.name === idx.value);
@@ -5199,6 +5203,17 @@ function mapBoundKeyofNeverConditional(type: ts.Type, ctx: TypeMapperCtx): IrTyp
   const target = check.getTarget();
   if (!target || !(target.flags & ts.TypeFlags.TypeParameter)) return null;
   const bound = resolveTypeParam(target);
+  // A T bound to the checked-dynamic value (`Record<string, unknown>`, an
+  // unknown-valued record view) has no static key set to decide the
+  // branch, but both branches of the lib's `keyof T extends never ?
+  // unknown : T[keyof T]` read as unknown there: one answer either way.
+  if (bound?.kind === "dyn") {
+    const whenEmpty = type.getTrueType();
+    const otherwise = type.getFalseType();
+    const a = whenEmpty ? mapType(whenEmpty, ctx) : null;
+    const b = otherwise ? mapType(otherwise, ctx) : null;
+    return a && b && typeEquals(a, b) ? a : null;
+  }
   if (bound?.kind !== "record") return null;
   const shape = shapes.get(bound.shapeId);
   if (!shape || shape.tuple) return null;

packages/compiler/test/ts7/baselines/order-parity/tests/corpus/6468-generic-unknown-record-entries.ts.json

@@ -0,0 +1,6 @@
+{
+ "order": [
+  "<repo>/tests/corpus/6468-generic-unknown-record-entries.ts"
+ ],
+ "diags": []
+}

tests/corpus/6468-generic-unknown-record-entries.ts

@@ -0,0 +1,33 @@
+// Inside a generic body, `Object.entries(tags)` over `T extends
+// Record<string, unknown>` reads `[string, T[keyof T]]` elements. An
+// instance whose T is the unknown-valued record view reads every member
+// as unknown; a record instance reads the union of its member types.
+function upper(text: string): string {
+  return text.toUpperCase();
+}
+
+function scrub(text: string): string {
+  return text.replace(/secret/g, "***");
+}
+
+function describe<T extends Record<string, unknown>>(tags: T): string[] {
+  return Object.entries(tags).map(
+    ([key, value]) => `${key}=${typeof value === "string" ? upper(value) : String(value)}`,
+  );
+}
+
+function redact<T extends Record<string, unknown>>(tags: T): T {
+  return Object.fromEntries(
+    Object.entries(tags).map(([key, value]) => [key, typeof value === "string" ? scrub(value) : value]),
+  ) as T;
+}
+
+function flatten(value: unknown): Record<string, unknown> {
+  return typeof value === "object" && value !== null ? (value as Record<string, unknown>) : { value };
+}
+
+console.log(describe(flatten({ b: 1, a: "x", c: true })));
+console.log(describe(flatten(5)));
+console.log(describe({ name: "n", size: 3 }));
+const cleaned = redact(flatten({ token: "secret", count: 2 }));
+console.log(cleaned, Object.keys(cleaned));