Reverse mapped types don't use their constraint types when no candidates are present unlike the regular type parameters

Bắt đầu với bản tái hiện trong Playground và lần theo các đường dẫn kiểm tra kiểu được nêu trong báo cáo: getInferredType, inferReverseMappedType và getTypeFromInference. Điều tra cách các kiểu ràng buộc được xử lý khi suy luận reverse-mapped không có ứng viên; hoàn thành có nghĩa là lệnh gọi thiết lập được cung cấp được suy luận thành công mà không có lỗi ràng buộc được hiển thị.

🔎 Search Terms

reverse mapped constraint inference candidates

🕗 Version & Regression Information

• This is the behavior in every version I tried

⏯ Playground Link

https://www.typescriptlang.org/play?ts=5.3.0-dev.20231028#code/JYOwLgpgTgZghgYwgAgApynAthSVgBeEAJgPIBGAVhAmMgN4BQyyYAngA4QBcyAzmHwgA5gG5myDhmx8A-LwBKNAPZRiAHgFDhAGmQBXEAGsQygO4gAfOIC+jRsRoAbDChiHawZSH659HdQkAFQBhb0gADzAdYIBxfQxiPmQIKIgQJOQlBFUNLVBdNGkcPEISCmpaAG0AIilMLD4agF1kAB8DDIgYUBJLGMsACgB9XiYWdi4+MYkWHPBUsF5Q8MXxFht15GEEtWmGWeQqgGlkUGQjCDZlGGQg+MS+Zt5B+cilu7CFqL16mWWHnsTs0AJTIAC8lmQADdlMBiFtNowbCCAbskuJGPMBMgoBA+PonHRwb4wP5BuNWJx8TMWHNVlFaXT6YYPgBGAAMHJizJsPOQfIkO0eTLmAAsaEYAGLKZQvYZ6ejIGCygVjZWy3j5EQCsGQjXKCHgkk1FXKGr8lhwJxmOBsPhBKD6HjIEZ6qGCZ38wUozF4glE8QAeiDyAAerJ7IwgA

💻 Code

interface ParameterizedObject {
  type: string;
  params?: Record<string, unknown>;
}

declare function setup<
  TContext,
  TGuards extends Record<string, ParameterizedObject["params"] | undefined>,
>(_: {
  types: {
    context: TContext;
  };
  guards: {
    [K in keyof TGuards]: (context: TContext, params: TGuards[K]) => void;
  };
}): TGuards;

const result = setup({
  types: {
    context: {
      count: 100,
    },
  },
  guards: {
    checkFoo: (_, { foo }: { foo: string }) => foo === "foo",
    alwaysTrue: (_) => true,
  },
});

result;
// ^?

🙁 Actual behavior

Type '(_: { count: number; }, { foo }: { foo: string; }) => boolean' is not assignable to type '(context: { count: number; }, params: Record<string, unknown> | undefined) => void'.
  Types of parameters '__1' and 'params' are incompatible.
    Type 'Record<string, unknown> | undefined' is not assignable to type '{ foo: string; }'.
      Type 'undefined' is not assignable to type '{ foo: string; }'.(2322)

🙂 Expected behavior

I'd expect the inference to succeed here

Additional information about the issue

TGuards is inferred as { checkFoo: { foo: string; }; alwaysTrue: unknown; } and thus rejected by the constraint check in getInferredType. alwaysTrue is inferred as unknown because inferReverseMappedType has such a return:

return getTypeFromInference(inference) || unknownType

And getTypeFromInference doesn't attempt to read the type parameter's constraint at all. It simply handles .candidates and .contraCandidates and that's it.