René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"5.6 regression: Incorrect param type inference for type with all optional props","articleBody":"### 🔎 Search Terms\r\n\r\ninference, param\r\n\r\n### 🕗 Version \u0026 Regression Information\r\n\r\n- This changed between versions 5.5.4 and 5.6.0\r\n\r\n### ⏯ Playground Link\r\n\r\nhttps://www.typescriptlang.org/play/?ts=5.6.0-dev.20240816#code/JYOwLgpgTgZghgYwgAgMoHsC2EAqBPABxQG8AoZC5AeiuQHkRkBWAOgDYWAGAGmQgA8iUYNnDIARnmSY4Aa1ABzZGAAWwAM7ICUdAWRQIARwCuwAwBMW5SsZDATEAAo6CAfgBcydWGEgFAblIAX1JScwgEABs4A2QEdBBvZHRxdU86VOgANzhxSIgAHgxsfCIAPkDSGFsEMGAE5BiFAHEIMHUAdR0-UogACgBKdMyoHLzC4iCy5DJKfTbjKEYU9RYCYCI+sDgCPqbkAF5p2bnKJsDTyhoAPVdrS5pkAFFBCMhzT2LcQhRQZhZWAAWe6nR4AQVqxjgkU8FEmyD+WVYHE4AFpxG04Mp0P8UajwlkWAAmThEwGcAAcAEY2Mg9mBkPk4N4BiCggMBoEQlUanUGk1Wu0AMLoKAGWq9QYzEEGMCLZapNYbfrbXb7I7Sy4Uc4guY3O5a6i0MGRADucDwmniYrebI5XNCoEgsEQKAy6myuXyBRwxxB6yIBTBZT6unSQjgYFFADFefUQD7eMGhvQRmNvcGHU7oPAkMgAKogGJ4WMgWrxxPIABKxzp6nQiyQnhwKar-mQIWzLrzdAjUagpfLCUrNb4-EgIHMmkLxcHfIT7s94x9ZV4i9GXsKNdrnfAOddyAAsgl0L1e9BIzG48PfWOJ1P6H2r2X55Xb8QO2EItFYtUX-HlB2Fc+hAAQwE8PockiYwIGbAZDmmLJ0GAcwU2PEBTx+c8oEvAdrwTX1AiAA\r\n\r\n### 💻 Code\r\n\r\n```ts\r\ninterface SomeType {\r\n    // On 5.6.0, experiment by making this prop required.\r\n    uniqueProp?: string;\r\n}\r\n\r\ndeclare const obs: Observable\u003cSomeType\u003e;\r\n\r\nfunction argGetsWrongType(): Observable\u003c{}\u003e {\r\n    return obs.pipe(tap(arg =\u003e {\r\n        arg;\r\n        //^?\r\n        // Expected: SomeType in 5.5.4\r\n        // Actual:   {} in v5.6.0-beta to 5.6.0-dev.20240816 (at least)\r\n    }));\r\n}\r\n\r\nfunction argGetsCorrectType() {\r\n    return obs.pipe(tap(arg =\u003e {\r\n        arg;\r\n        //^?\r\n        // Always correct\r\n    }));\r\n}\r\n\r\ninterface Observable\u003cT\u003e {\r\n    pipe\u003cA\u003e(op: OperatorFunction\u003cT, A\u003e): Observable\u003cA\u003e;\r\n}\r\ninterface UnaryFunction\u003cT, R\u003e { (source: T): R; }\r\ninterface OperatorFunction\u003cT, R\u003e extends UnaryFunction\u003cObservable\u003cT\u003e, Observable\u003cR\u003e\u003e { }\r\ninterface MonoTypeOperatorFunction\u003cT\u003e extends OperatorFunction\u003cT, T\u003e { }\r\ndeclare function tap\u003cT\u003e(next: (value: T) =\u003e void): MonoTypeOperatorFunction\u003cT\u003e;\r\n```\r\n\r\n### 🙁 Actual behavior\r\n\r\n`arg` is inferred as `{}`\r\n\r\n### 🙂 Expected behavior\r\n\r\n`arg` is inferred as `SomeType` as was consistent in v5.5.4\r\n\r\n### Additional information about the issue\r\n\r\n(Google note: See http://cl/664889390 for local workaround)","author":{"url":"https://github.com/trevorade","@type":"Person","name":"trevorade"},"datePublished":"2024-08-16T17:52:50.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":9},"url":"https://github.com/59656/TypeScript/issues/59656"}