René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Inference regression (5.0.4 vs 4.9.5) with nullable enum function parameter","articleBody":"# Bug Report\r\n\r\n\u003c!--\r\n  Please fill in each section completely. Thank you!\r\n--\u003e\r\n\r\n### 🔎 Search Terms\r\n\r\ninference string null function parameter \r\n\r\n### 🕗 Version \u0026 Regression Information\r\n\r\n- This changed between versions 4.9.5 and 5.0.4\r\n\r\n### ⏯ Playground Link\r\n\r\n[Playground link with relevant code](https://www.typescriptlang.org/play?ts=5.0.4#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-HaHVBizAXRX0kwwZCbAB+YwjqxQ-gTktOehQLb5QolMoVdp1I+fVqvzrNgGDYaYMYph7Jg+wDCRri4cUTFWc8bGjSd-QTVoZwkOdcCXLYPF4CAIBeTorhqPpeBYL8yHMXg63YaEoFwiAyIkYZeA5Fpvg6P5en6P9gSAsFIl2boJlsNB12MLdaCcJc+IE8Z4OvJggA)\r\n\r\n### 💻 Code\r\n\r\n```ts\r\nenum Thing { a = 'a', b = 'b', };\r\n\r\nfunction f(\r\n    registrationStatusOptions: SelectOptions\u003cThing\u003e,\r\n    onChange: (status: Thing | null) =\u003e void, // \u003c-- Remove the `| null` and the error goes away.\r\n): void {\r\n    select({ // \u003c-- Add an explicit type argument `Thing` and the error goes away.\r\n        options: registrationStatusOptions,\r\n        onChange: onChange, // ERROR in v5.0.4 but not in v4.9.5: Type '(status: Thing | null) =\u003e void' is not assignable to type '(key: string) =\u003e void'.\r\n    });\r\n}\r\n\r\nexport function select\u003cKeyT extends string\u003e(props: SelectProps\u003cKeyT\u003e): void {\r\n    throw new Error('hello');\r\n}\r\n\r\nexport type SelectProps\u003cKeyT extends string\u003e = {\r\n    onChange: (key: KeyT) =\u003e void;\r\n    options?: SelectOptions\u003cKeyT\u003e; // \u003c-- Remove the `?` and the error goes away.\r\n};\r\n\r\nexport type SelectOptions\u003cKeyT extends string\u003e =\r\n    // Comment either of the below union members out and the error goes away.\r\n    | Array\u003c{key: KeyT}\u003e\r\n    | Array\u003cKeyT\u003e;\r\n```\r\n\r\n### 🙁 Actual behavior\r\n\r\n1. Got a type error; see \"ERROR\" comment above. Looks like the type argument to `select(...)` is being inferred incorrectly.\r\n2. Minor perturbations of the code cause the error to go away; see other comments above.\r\n\r\nThis was extracted from some React UI code.\r\n\r\n### 🙂 Expected behavior\r\n\r\nTypeScript 4.9.5 infers the type argument I wanted. I was hoping TypeScript 5.0.4 would do the same.","author":{"url":"https://github.com/cakoose","@type":"Person","name":"cakoose"},"datePublished":"2023-04-25T07:58:21.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":3},"url":"https://github.com/54005/TypeScript/issues/54005"}