René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Wrong type inference, returns the base class type instead of the child class type","articleBody":"### 🔎 Search Terms\r\n\r\nNone\r\n\r\n### 🕗 Version \u0026 Regression Information\r\n\r\n- This is the behavior in every version I tried, and I reviewed the FAQ for entries about _________\r\n\r\n### ⏯ Playground Link\r\n\r\n[Playground Link](https://www.typescriptlang.org/play?ts=5.4.0-dev.20240204#code/N4WAUAkAxgNghgZwQAgEKIKbNJCBzDAF2QQxgDMAKASgC41NtkAnIgV2YDtlCALASxQBfcBBGRYiFAGEBMACbIMAD0IZO8lOlLZREAPYA3DM2b95WAsVIUa9WfwVNWhDtz6Dk4iNDmKAvDzMbBgA3KLiouRsnFCE-PrcUInGzIQAPAAqSqrqmgykAHyUABr0mdRMAPRVyPwAtgAOMPxQ-IQwAJ4s7FxamADaAEQ25EMAunWcCGpwivrkyJnDoxN6Lm7IJQB0o+GQkRKJM8iGcDAhyIHJnKmElMicGADuyA4KNMjU+xA1OY0YOIYeT0QidAELU7nS6Bd7ybaiP54fSEUHgjCQs4XLCBbQYBFgKIxOIJJIpEyEABMWRyag0-SKpXKdCWKzIY0mwGQfwazVa7S6PVcfQKGDZFAmUxmGDmyEhyxG7LWuA2XC2u3ZP0O0GOxCxIUpV2QNzulIeT1ecM+30RtTBEMW+pxbz8BPEOGg8CQoukXoQ6QAaoVdLhGswUYC1IpyHAANYYOzIANMPjh14W5AAUVM+mYlCGQ0q3m1km9AGk-YHgyo6fk8b6pFWPb5HAEgiEteBRPasNJdcE4rn0gAFWl5BkYBtIdKcNj1ABGJkKwcCGc+-mDw5+Pam5BMmQwMyyK6WY-pb37bEHzHS-E4e+YyGHwYA-E-kLQnql9t30cgAKpGneD4HkefbTIQA6EEOFaNrOC5Lsu3K1IBgSwdO8GLswhTgO6oilhOU7+kGIY+GGEZAtGcYJiyyZcqm+jpi8WY5nmBZFhEXYSH6yDocR1a5Oe9aVkGzZQH4RqQR2nGEpAO7gTMUFDgGAA0741uOPoiUhq7Meum7bn+wH7oeGSqUsJ7ZBp54KVJ16BmpxmPs+yBvqOn4YN+XEQDuqG7iZR6YSYam2UpN5Bcwal8TOc5YcuwZ-H5wlwbFS64UAA)\r\n\r\n### 💻 Code\r\n\r\n```ts\r\n// BUG1:\r\n{\r\n\tclass Base {\r\n\t\tget self(): Base { return this }\r\n\t}\r\n\tclass Child extends Base {\r\n\t\toverride get self(): Child { return this }\r\n\t\tchild = true;\r\n\t}\r\n\r\n\tfunction convert\u003cT extends Base\u003e(X: T) { // implicitly returns Base[\"self\"] instead of T[\"self\"]\r\n\t\treturn X.self;\r\n\t}\r\n\r\n\tconst value = convert( new Child() );\r\n\t// expected: typeof value = Child.\r\n\t// got: typeof value = Base.\r\n\t\r\n\t\r\n\tfunction convert2\u003cT extends Base\u003e(X: T): T[\"self\"] {\r\n\t\treturn X.self;\r\n\t}\r\n\r\n\tconst value2 = convert2( new Child() );\r\n\t// typeof value = Child.\r\n}\r\n\r\n// BUG2:\r\n{\r\n\tclass BaseClass\u003cV\u003e {\r\n\t\tprotected fake(): V { throw new Error(\"\") }\r\n\t}\r\n\r\n\tclass Klass\u003cV\u003e extends BaseClass\u003cV\u003e{\r\n\t\tchild = true;\r\n    }\r\n\r\n\ttype Constructor\u003cP extends BaseClass\u003cnumber\u003e\u003e = new () =\u003e P;\r\n\ttype inferTest\u003cT\u003e = T extends Constructor\u003cinfer P\u003e ? P :never;\r\n\r\n\ttype U = inferTest\u003cConstructor\u003cKlass\u003cnumber\u003e\u003e\u003e // U = Klass\u003cnumber\u003e\r\n}\r\n{\r\n\tclass BaseClass\u003cV\u003e {\r\n\t\tprotected fake(): V { throw new Error(\"\") }\r\n\t}\r\n\r\n\tclass Klass\u003cV\u003e extends BaseClass\u003cV\u003e{\r\n\t\tchild = true;\r\n    }\r\n\r\n\ttype Constructor\u003cV, P extends BaseClass\u003cV\u003e\u003e = new () =\u003e P;\r\n\ttype inferTest\u003cV, T\u003e = T extends Constructor\u003cV, infer P\u003e ? P :never;\r\n\r\n\ttype U = inferTest\u003cnumber, Constructor\u003cnumber, Klass\u003cnumber\u003e\u003e\u003e\r\n\t// got: U = BaseClass\u003cnumber\u003e\r\n\t//expected: U = Klass\u003cnumber\u003e\r\n}\r\n```\r\n\r\n\r\n### 🙁 Actual behavior\r\n\r\nBug1: It seems that when calling methods in generic function `foo\u003cT extends Base\u003e(t: T)` :\r\n```typescript\r\nt.foo() // viewed as method Base.foo()\r\n// instead of being viewed as T.foo() with T extends Base.\r\n```\r\n\r\nBug2: For type inference, it seems that adding a generic parameters confuses TS.\r\n\r\n### 🙂 Expected behavior\r\n\r\nCf code.\r\n\r\n### Additional information about the issue\r\n\r\nRelated to issue #57102","author":{"url":"https://github.com/denis-migdal","@type":"Person","name":"denis-migdal"},"datePublished":"2024-02-04T16:37:13.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":3},"url":"https://github.com/57286/TypeScript/issues/57286"}