microsoft / microsoft/TypeScript

Common fields of union not resolved for generic conditional with `any` branch

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Bug Domain: Conditional Types Help Wanted
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Description

### 🔎 Search Terms

"conditional generics with any branch in union", "union with generic conditional branch"

### 🕗 Version & Regression Information

This is the behavior in every version I tried, and I reviewed the FAQ for entries about conditional generics used in unions but didn't find anything that seemed relevant.

### ⏯ Playground Link

https://www.typescriptlang.org/play/?ts=5.9.2#code/C4TwDgpgBAkgdgYQPYFsVLlAvFA3gY1XTgC4oBnYAJwEs4BzAXwG4AoV0SKZOAExuA0MAQwA2AHgDSUCAA9gEPuQrU69KAB8ocAK4oARhCoA+bFGlyFS7XsNUoAfjwYIZXQaOMoZAEoRCVLzilLQMADRQOnAA1nBIAO5wxmyc0ACqcEJwAOoCABZ+9DqiwlQ8-IIiEhbyirzKIWqaNh4mZvDIaBjNABTlAlliUqYAZLCIRBgAlGwAZlH4lZhywihgohAZWbnABRBFJVRSMrXWjQzN7nbGPdEQIGSSU3isUG9QhHCUkZkYO3sHUr9JZiMy4LzCZRbP75QrFIEYCqDarJV7vAD06KguxoyniSCo0WUkJOkEWEF4aLeUW2sP28LKiIGVQAdIQunA2Ix2KluEyQaJ-gBBOAgY6WOoNVQXLRXIymHA1Kz1Fp2RxQYSi7xQPwBILnegRKKxBJJFLgdK-HL5EUgYHI8WnFUGy62eXtCYc3r2qrC0XDKBjDqTOAzVjzOCLLInVbrTZWv1ipWSlShdSyt0mW73R7PXBUj4Yb40mG7W0+uCgnDgjVQhM20UVoaSVHvKCY7F5XFQPIk4TYi0yKhUAlQWajgAG7OIE+0SGAJ1xggu3QnTcFDaTo3GnRnBZL1rLjf5yLZIbYbYLHf0OgXu0Une7ACpeEgIOQn1B8YSC59vmARzARN1zBCFlD6E9fU3AMg09YgwzbACkCAzd1zPDkuVYIA

### 💻 Code

```ts
type InCommon = {common: string};

type Conditional = K extends number ? {one: number} : Record;
type UnionWithRegularConditional = InCommon | (Conditional & InCommon);
function exampleUnionWithRegular(key: K) {
const unionWithRegularConditional = {} as UnionWithRegularConditional;
// this works as expected
unionWithRegularConditional.common;
}

type ConditionalWithAny = K extends number ? any : Record;
type UnionWithAnyConditional = InCommon | (ConditionalWithAny & InCommon);
function exampleUnionWithAny(key: K) {
const unionWithAnyConditional = {} as UnionWithAnyConditional;
// this has a type error for `common` not existing on `ConditionalWithAny & InCommon`
unionWithAnyConditional.common;

// but then this *does* work
const propWithAnyConditional = {} as (ConditionalWithAny & InCommon);
propWithAnyConditional.common;
}
```

### 🙁 Actual behavior

When a union type contains a conditional generic whose branch is `any`, the common fields of the union are not being correctly recognized.

This is illustrated above when TS is unable to recognize that `common` is a field on `unionWithAnyConditional`.

### 🙂 Expected behavior

The expected behavior here is that common fields of the union should be correctly resolved.

From the above example, the expectation is that `unionWithAnyConditional.common` would not have a "does not exist on type" error.

### Additional information about the issue

_No response_

Guide de contribution

Ouvrir le guide de contribution

Piste de recherche

Commencez par le repro TypeScript Playground lié et confirmez la différence entre le conditionnel normal et le conditionnel avec une branche `any`. Suivez la manière dont le compilateur traite les propriétés communes de l’union résultante, puis ajoutez une couverture pour `unionWithAnyConditional.common`. C’est terminé lorsque l’accès attendu ne signale plus que `common` est manquant.

Rédigé par le modèle d'indexation à partir du texte de l'issue.

Évaluation

Stack technique
typescript
Domaine
compilers
Type d'issue
Bug
Difficulté
4/5
Temps estimé
3-5 jours
Activité
À l'abandon
Clarté
Plutôt claire
Accessibilité débutants
45/100

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