Unexpected circular constraint error (regression)

[falsandtru]

TypeScript Version: master

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Code

type StrictExtract<T, U> = T extends U ? U extends T ? T : never : never;
type StrictExclude<T, U> = T extends StrictExtract<T, U> ? never : T;
type A<T> = { [Q in { [P in keyof T]: P; }[keyof T]]: T[Q]; };
type B<T, V> = A<{ [Q in keyof T]: StrictExclude<B<T[Q], V>, {}>; }>;

Expected behavior:

pass

Actual behavior:

$ node built/local/tsc.js --noEmit index.ts
index.ts:3:21 - error TS2313: Type parameter 'Q' has a circular constraint.

3 type A<T> = { [Q in { [P in keyof T]: P; }[keyof T]]: T[Q]; };
                      ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

  index.ts:4:36
    4 type B<T, V> = A<{ [Q in keyof T]: StrictExclude<B<T[Q], V>, {}>; }>;
                                         ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    Circularity originates in type at this location.


Found 1 error.

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[falsandtru]

Note that this error doesn't appear with the following code:

type B<T, V> = A<{ [Q in keyof T]: B<T[Q], V>; }>;

@ahejlsberg Is this your intended behavior with #30109? I guess non-mapped types shouldn't affect this error.