The generic type cannot be successfully inferred.

[LiST-GIT]

🔎 Search Terms

The generic type cannot be successfully inferred.

🕗 Version & Regression Information

5.3

⏯ Playground Link

https://www.typescriptlang.org/play?#code/C4TwDgpgBMEM7APoCMA8AVANFAwugGgHxQC8U6UEAHrAHYAmcUA3gL5QD8LUA2gNJQAlrSgBrCCAD2AM3IBdAFzl+cyjQgMmACgDGwKkoCGtENklhgcIyewA6e4YBOAcytDa0iI6gAFAJSkxMKe3gBKnFC6+kp4+GYWbsxioqJKtACuALbIXlCsdg4ubv6BUOFpEABuuexKAEwA3ABQ0um0eoKSIoY9hqgAItjohFrASkn0HEqDUNJT5FAAPjDwSGhY3HBbaVk53qzErAFJrE29hlrMTVA3UAD0d1D041BbbgCMdQDMedgPuJJMpkNMBhM4YAALQRMAA2wmgknSwCgAHdBDCYVAQIIIDD6E9BNIQiCoI54OkYZZbNdbtJxjTbrcLnoqPFLNhescGYyeSzbG9uYz8oLbsgoqyoOZ2VBOSwRTyoHyBQqbsKVYrxWy4Byelz1YylVt5b9jW8lAByAACCCcwHNmG5wqOQA

💻 Code

type test_b<T, CTX> = T extends {} ? { [K in keyof T]: T[K] extends (ctx: any, opts: any, ...args: infer P) => infer R ? (ctx: CTX, opts: { kkk: number }, ...args: P) => R : never } : 2;
function aaaa<D, T>(t: { d?: D, f?: T | test_b<T, { sss: number }> }) { }
aaaa({
    // d: { sss: 123 }, // Commenting this line out will yield different results.
    f: {
        a(ctx, opts, aaa) {
            ctx.sss
        },
        b(ctx, opts, aaa) {
            ctx.sss
        },
        c(ctx, opts, aaa) {
            ctx.sss
        },
        sss: '@start',
    },
})

🙁 Actual behavior

The error occurred after set d.

🙂 Expected behavior

It should always converge successfully.

Additional information about the issue

No response

[Andarist]

This is an interesting example of #47599

The problem here is that when u add ur d property you make the whole object "partially inferrable" and the inference algorithm successfully infers { sss: number; }. At the same time, the other part of the object is non-inferrable (due to the presence of context-sensitive functions). Judging by the observable results the parameter types are pulled before inferences for this reverse mapped type (T) can be made (maybe before a candidate for that T can even be created).

When the property is not included no inferences are made in the first pass~ and the reverse mapped type and TS avoids pulling the parameter types. In the second pass~ the candidate for T can finally be created and it resolves much better in your case.

Or something like that 😉

[typescript-bot]

This issue has been marked as "Duplicate" and has seen no recent activity. It has been automatically closed for house-keeping purposes.