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