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fix(common): preserve literal key union in KeyValuePipe.transform() #70200

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fix(common): preserve literal key union in KeyValuePipe.transform() #70200

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27 changes: 18 additions & 9 deletions packages/common/src/pipes/keyvalue_pipe.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -75,14 +75,23 @@ export class KeyValuePipe implements PipeTransform {
input: ReadonlyMap<K, V>,
compareFn?: ((a: KeyValue<K, V>, b: KeyValue<K, V>) => number) | null,
): Array<KeyValue<K, V>>;
transform<K extends number, V>(
input: Record<K, V>,
compareFn?: ((a: KeyValue<string, V>, b: KeyValue<string, V>) => number) | null,
): Array<KeyValue<string, V>>;
// TypeScript tries overloads top-to-bottom and stops at the first match. A
// plain object with string-literal keys (e.g. `Record<'a' | 'b', V>`) also
// happens to satisfy the more general `K extends number` overload below once
// inference falls back to its constraint — so if that overload is checked
// first, it wins by accident and silently widens `key` from `'a' | 'b'` to
// plain `string`. Putting the string overload first means it claims
// string-keyed input before the number overload ever gets a chance, while
// genuinely numeric-keyed input (which fails `K extends string`) still falls
// through to the number overload exactly as before.
transform<K extends string, V>(
input: Record<K, V> | ReadonlyMap<K, V>,
compareFn?: ((a: KeyValue<K, V>, b: KeyValue<K, V>) => number) | null,
): Array<KeyValue<K, V>>;
transform<K extends number, V>(
input: Record<K, V>,
compareFn?: ((a: KeyValue<string, V>, b: KeyValue<string, V>) => number) | null,
): Array<KeyValue<string, V>>;
transform(
input: null | undefined,
compareFn?: ((a: KeyValue<unknown, unknown>, b: KeyValue<unknown, unknown>) => number) | null,
Expand All @@ -91,16 +100,16 @@ export class KeyValuePipe implements PipeTransform {
input: ReadonlyMap<K, V> | null | undefined,
compareFn?: ((a: KeyValue<K, V>, b: KeyValue<K, V>) => number) | null,
): Array<KeyValue<K, V>> | null;
transform<K extends number, V>(
input: Record<K, V> | null | undefined,
compareFn?: ((a: KeyValue<string, V>, b: KeyValue<string, V>) => number) | null,
): Array<KeyValue<string, V>> | null;

transform<K extends string, V>(
input: Record<K, V> | ReadonlyMap<K, V> | null | undefined,
compareFn?: ((a: KeyValue<K, V>, b: KeyValue<K, V>) => number) | null,
): Array<KeyValue<K, V>> | null;

transform<K extends number, V>(
input: Record<K, V> | null | undefined,
compareFn?: ((a: KeyValue<string, V>, b: KeyValue<string, V>) => number) | null,
): Array<KeyValue<string, V>> | null;

transform<T>(
input: T,
compareFn?: T extends object ? (a: T[keyof T], b: T[keyof T]) => number : never,
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32 changes: 32 additions & 0 deletions packages/common/test/pipes/keyvalue_pipe_spec.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -100,6 +100,38 @@ describe('KeyValuePipe', () => {
expect(pipe.transform(value)).toEqual(null);
});

it('should preserve a literal key union instead of widening it to string', () => {
const pipe = new KeyValuePipe(defaultKeyValueDiffers);
const input: Record<'a' | 'b', number> = {a: 1, b: 2};
const result = pipe.transform(input);

// Compile-time check: if `key` had widened back to plain `string`, this
// assignment would fail to compile — that's the actual bug from #43883.
const key: 'a' | 'b' = result[0].key;

expect(key).toBe('a');
expect(result).toEqual([
{key: 'a', value: 1},
{key: 'b', value: 2},
]);
});

it('should still collapse a numerically-keyed object to string keys', () => {
const pipe = new KeyValuePipe(defaultKeyValueDiffers);
const input: Record<1 | 2, string> = {1: 'one', 2: 'two'};
const result = pipe.transform(input);

// Numeric keys become strings at runtime (Object.keys() always returns
// strings), so `key` should stay `string`, not narrow to `1 | 2`.
const key: string = result[0].key;

expect(key).toBe('1');
expect(result).toEqual([
{key: '1', value: 'one'},
{key: '2', value: 'two'},
]);
});

it('should accept an object with optional keys', () => {
interface MyInterface {
one: string;
Expand Down
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