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ConditionalPickDeep / SimplifyDeep: Prevent mapping over built-ins#1293

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sindresorhus merged 6 commits intosindresorhus:mainfrom
ryangoree:main
Nov 10, 2025
Merged

ConditionalPickDeep / SimplifyDeep: Prevent mapping over built-ins#1293
sindresorhus merged 6 commits intosindresorhus:mainfrom
ryangoree:main

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@ryangoree ryangoree commented Nov 7, 2025 •
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IsPlainObject currently returns true for Promise, WeakMap, and WeakSet types, and returns never for never. This affects types like ConditionalPickDeep that rely on it for deciding when to map over a type's fields.

This PR fixes the behavior by ensuring IsPlainObject returns false for these types.

type Example = {
	a: string;
	b: Promise<string>;
	c: WeakMap<WeakKey, string>;
	d: WeakSet<WeakKey>;
};

type Current = ConditionalPickDeep<Example, string>;
//=> {
//   a: string;
//   b: {
//     readonly [Symbol.toStringTag]: string;
//   };
//   c: {
//     readonly [Symbol.toStringTag]: string;
//   };
//   d: {
//     readonly [Symbol.toStringTag]: string;
//   };
// };

type Fixed = ConditionalPickDeep<Example, string>;
//=> {a: string;}

never example:

type Example = {
	a: string;
	b: never;
};

type Current = ConditionalPickDeep<Example, string, {condition: 'equality'}>;
//=> {a: string; b: never}

type Fixed = ConditionalPickDeep<Example, string, {condition: 'equality'}>;
//=> {a: string;}

This PR also fixes the SimplifyDeep type:

type Example = {
	a: string;
} & {
	b: Promise<string>;
	c: ReadonlySet<string>;
	d: WeakSet<WeakKey>;
	e: ReadonlyMap<string, string>;
	f: WeakMap<WeakKey, string>;
};

type Current = SimplifyDeep<Example>;
//=> {
//   a: string;
//   b: {
//     ...;
//   };
//   c: {
//     ...;
//   };
//   d: {
//     ...;
//   };
//   e: {
//     ...;
//   };
//   f: {
//     ...;
//   };
// };

type Fixed = SimplifyDeep<Example>;
//=> {
//   a: string;
//   b: Promise<string>;
//   c: ReadonlySet<string>;
//   d: WeakSet<WeakKey>;
//   e: ReadonlyMap<string, string>;
//   f: WeakMap<WeakKey, string>;
// };

@ryangoree ryangoree changed the title ConditionalPickDeep: Fix behavior with Promise, WeakMap, and WeakSet ConditionalPickDeep: Fix behavior with Promise, WeakMap, WeakSet, never Nov 7, 2025
@ryangoree ryangoree changed the title ConditionalPickDeep: Fix behavior with Promise, WeakMap, WeakSet, never ConditionalPickDeep / SimplifyDeep: Prevent mapping over built-ins Nov 8, 2025
som-sm
som-sm approved these changes Nov 10, 2025
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LGTM!

@sindresorhus sindresorhus merged commit f14a75a into sindresorhus:main Nov 10, 2025
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@Andyuu Andyuu mentioned this pull request Jan 26, 2026
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@som-sm som-sm mentioned this pull request Jan 27, 2026
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@ryangoree @som-sm @sindresorhus