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fix(jest-mock): tweak typings to allow jest.replaceProperty() replace methods #14008

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Apr 9, 2023
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1 change: 1 addition & 0 deletions CHANGELOG.md
Original file line number Diff line number Diff line change
Expand Up @@ -7,6 +7,7 @@
- `[jest-config]` Handle frozen config object ([#14054](https://github.com/facebook/jest/pull/14054))
- `[jest-environment-jsdom, jest-environment-node]` Fix assignment of `customExportConditions` via `testEnvironmentOptions` when custom env subclass defines a default value ([#13989](https://github.com/facebook/jest/pull/13989))
- `[jest-matcher-utils]` Fix copying value of inherited getters ([#14007](https://github.com/facebook/jest/pull/14007))
- `[jest-mock]` Tweak typings to allow `jest.replaceProperty()` replace methods ([#14008](https://github.com/facebook/jest/pull/14008))
- `[jest-snapshot]` Fix a potential bug when not using prettier and improve performance ([#14036](https://github.com/facebook/jest/pull/14036))
- `[@jest/transform]` Do not instrument `.json` modules ([#14048](https://github.com/facebook/jest/pull/14048))

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23 changes: 14 additions & 9 deletions packages/jest-mock/__typetests__/mock-functions.test.ts
Original file line number Diff line number Diff line change
Expand Up @@ -497,20 +497,25 @@ expectError(

// replaceProperty + Replaced

const obj = {
fn: () => {},

const replaceObject = {
method: () => {},
property: 1,
};

expectType<Replaced<number>>(replaceProperty(obj, 'property', 1));
expectType<void>(replaceProperty(obj, 'property', 1).replaceValue(1).restore());
expectType<Replaced<number>>(replaceProperty(replaceObject, 'property', 1));
expectType<Replaced<() => void>>(
replaceProperty(replaceObject, 'method', () => {}),
);
expectType<void>(
replaceProperty(replaceObject, 'property', 1).replaceValue(1).restore(),
);

expectError(replaceProperty(obj, 'invalid', 1));
expectError(replaceProperty(obj, 'property', 'not a number'));
expectError(replaceProperty(obj, 'fn', () => {}));
expectError(replaceProperty(replaceObject, 'invalid', 1));
expectError(replaceProperty(replaceObject, 'property', 'not a number'));

expectError(replaceProperty(obj, 'property', 1).replaceValue('not a number'));
expectError(
replaceProperty(replaceObject, 'property', 1).replaceValue('not a number'),
);

interface ComplexObject {
numberOrUndefined: number | undefined;
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24 changes: 10 additions & 14 deletions packages/jest-mock/src/index.ts
Original file line number Diff line number Diff line change
Expand Up @@ -177,17 +177,13 @@ export interface Replaced<T = unknown> {
* Restore property to its original value known at the time of mocking.
*/
restore(): void;

/**
* Change the value of the property.
*/
replaceValue(value: T): this;
}

type ReplacedPropertyRestorer<
T extends object,
K extends PropertyLikeKeys<T>,
> = {
type ReplacedPropertyRestorer<T extends object, K extends keyof T> = {
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I think that this should align with:

function replaceProperty<T, K extends keyof T>(obj: T, key: K, value: T[K]): ReplaceProperty<T[K]>;

in the types packages.

Currently (without this change) getting a typescript error:

node_modules/@jest/environment/build/index.d.ts:401:26 - error TS2430: Interface 'JestImportMeta' incorrectly extends interface 'ImportMeta'.
  The types of 'jest.replaceProperty' are incompatible between these types.
    Type '<T extends object, K extends Exclude<keyof T, keyof { [K in keyof T as Required<T>[K] extends ClassLike ? K : never]: T[K]; } | keyof { [K in keyof T as Required<T>[K] extends FunctionLike ? K : never]: T[K]; }>, V extends T[K]>(object: T, propertyKey: K, value: V) => Replaced<...>' is not assignable to type '<T, K extends keyof T>(obj: T, key: K, value: T[K]) => ReplaceProperty<T[K]>'.
      Types of parameters 'object' and 'obj' are incompatible.
        Type 'T' is not assignable to type 'object'.

401 export declare interface JestImportMeta extends ImportMeta {
                             ~~~~~~~~~~~~~~

  node_modules/@types/jest/index.d.ts:331:30
    331     function replaceProperty<T, K extends keyof T>(obj: T, key: K, value: T[K]): ReplaceProperty<T[K]>;
                                     ~
    This type parameter might need an `extends object` constraint.

So basically one of the issues is fixed here by not using PropertyLikeKeys anymore but T extends object is still incompatible with T so should likely also become just T here.

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Hm.. I think it would be better to have T extends object in @types/jest. It looks right to have a constrain here.

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As long as it's aligned I guess. But I don't think object is a good choice because object means "all non-primitive" types. So any class instances would also match that, for example. I don't know jest well enough to suggest what it should be but perhaps Record<.., ..> would be a better fit?

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If all non-primitive types are objects and if objects can have properties, I think it is alright to assume that these objects can have properties and that these properties might get replaced. Sometimes people add extra properties on arrays or functions. For instance, expect() has expect.not.stringContaining() which is the property of that function.

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(): void;
object: T;
property: K;
Expand Down Expand Up @@ -995,10 +991,10 @@ export class ModuleMocker {
/**
* Check whether the given property of an object has been already replaced.
*/
private _findReplacedProperty<
T extends object,
K extends PropertyLikeKeys<T>,
>(object: T, propertyKey: K): ReplacedPropertyRestorer<T, K> | undefined {
private _findReplacedProperty<T extends object, K extends keyof T>(
object: T,
propertyKey: K,
): ReplacedPropertyRestorer<T, K> | undefined {
for (const {restore} of this._spyState) {
if (
'object' in restore &&
Expand Down Expand Up @@ -1328,11 +1324,11 @@ export class ModuleMocker {
return descriptor[accessType] as Mock;
}

replaceProperty<
T extends object,
K extends PropertyLikeKeys<T>,
V extends T[K],
>(object: T, propertyKey: K, value: V): Replaced<T[K]> {
replaceProperty<T extends object, K extends keyof T>(
object: T,
propertyKey: K,
value: T[K],
): Replaced<T[K]> {
if (object === undefined || object == null) {
throw new Error(
`replaceProperty could not find an object on which to replace ${String(
Expand Down