microsoft / microsoft/TypeScript
Common fields of union not resolved for generic conditional with `any` branch
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説明
### 🔎 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_
コントリビューションガイド
調査の方向性
リンクされている TypeScript Playground の再現コードから始め、通常の conditional と `any` ブランチを持つ conditional の違いを確認します。結果の union における共通プロパティをコンパイラーがどのように処理するかを追跡し、その後 `unionWithAnyConditional.common` のカバレッジを追加します。期待されるアクセスで `common` が存在しないという報告が出なくなれば完了です。
索引モデルが issue の本文から書いたものです。
評価
- 技術スタック
- typescript
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- compilers
- issue の種類
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- 難易度
- 4/5
- 見積もり時間
- 3〜5日
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- 停滞
- 明瞭さ
- おおむね明確
- 初心者へのやさしさ
- 45/100