conditionalTypes1.errors.txt

tests/cases/conformance/types/conditional/conditionalTypes1.ts(12,5): error TS2322: Type 'T' is not assignable to type 'NonNullable<T>'.
tests/cases/conformance/types/conditional/conditionalTypes1.ts(17,5): error TS2322: Type 'T' is not assignable to type 'NonNullable<T>'.
  Type 'string | undefined' is not assignable to type 'NonNullable<T>'.
    Type 'undefined' is not assignable to type 'NonNullable<T>'.
tests/cases/conformance/types/conditional/conditionalTypes1.ts(18,9): error TS2322: Type 'T' is not assignable to type 'string'.
  Type 'string | undefined' is not assignable to type 'string'.
    Type 'undefined' is not assignable to type 'string'.
tests/cases/conformance/types/conditional/conditionalTypes1.ts(24,5): error TS2322: Type 'T[keyof T] | undefined' is not assignable to type 'NonNullable<Partial<T>[keyof T]>'.
  Type 'undefined' is not assignable to type 'NonNullable<Partial<T>[keyof T]>'.
tests/cases/conformance/types/conditional/conditionalTypes1.ts(29,5): error TS2322: Type 'T["x"]' is not assignable to type 'NonNullable<T["x"]>'.
  Type 'string | undefined' is not assignable to type 'NonNullable<T["x"]>'.
    Type 'undefined' is not assignable to type 'NonNullable<T["x"]>'.
tests/cases/conformance/types/conditional/conditionalTypes1.ts(30,9): error TS2322: Type 'T["x"]' is not assignable to type 'string'.
  Type 'string | undefined' is not assignable to type 'string'.
    Type 'undefined' is not assignable to type 'string'.
tests/cases/conformance/types/conditional/conditionalTypes1.ts(103,5): error TS2322: Type 'Pick<T, { [K in keyof T]: T[K] extends Function ? K : never; }[keyof T]>' is not assignable to type 'T'.
  'Pick<T, { [K in keyof T]: T[K] extends Function ? K : never; }[keyof T]>' is assignable to the constraint of type 'T', but 'T' could be instantiated with a different subtype of constraint '{}'.
tests/cases/conformance/types/conditional/conditionalTypes1.ts(104,5): error TS2322: Type 'Pick<T, { [K in keyof T]: T[K] extends Function ? never : K; }[keyof T]>' is not assignable to type 'T'.
  'Pick<T, { [K in keyof T]: T[K] extends Function ? never : K; }[keyof T]>' is assignable to the constraint of type 'T', but 'T' could be instantiated with a different subtype of constraint '{}'.
tests/cases/conformance/types/conditional/conditionalTypes1.ts(106,5): error TS2322: Type 'Pick<T, { [K in keyof T]: T[K] extends Function ? never : K; }[keyof T]>' is not assignable to type 'Pick<T, { [K in keyof T]: T[K] extends Function ? K : never; }[keyof T]>'.
  Type 'T[keyof T] extends Function ? keyof T : never' is not assignable to type 'T[keyof T] extends Function ? never : keyof T'.
tests/cases/conformance/types/conditional/conditionalTypes1.ts(108,5): error TS2322: Type 'Pick<T, { [K in keyof T]: T[K] extends Function ? K : never; }[keyof T]>' is not assignable to type 'Pick<T, { [K in keyof T]: T[K] extends Function ? never : K; }[keyof T]>'.
  Type 'T[keyof T] extends Function ? never : keyof T' is not assignable to type 'T[keyof T] extends Function ? keyof T : never'.
tests/cases/conformance/types/conditional/conditionalTypes1.ts(114,5): error TS2322: Type 'keyof T' is not assignable to type 'T[keyof T] extends Function ? keyof T : never'.
  Type 'string | number | symbol' is not assignable to type 'T[keyof T] extends Function ? keyof T : never'.
    Type 'string' is not assignable to type 'T[keyof T] extends Function ? keyof T : never'.
tests/cases/conformance/types/conditional/conditionalTypes1.ts(115,5): error TS2322: Type 'T[keyof T] extends Function ? never : keyof T' is not assignable to type 'T[keyof T] extends Function ? keyof T : never'.
  Type 'keyof T' is not assignable to type 'never'.
    Type 'string | number | symbol' is not assignable to type 'never'.
      Type 'string' is not assignable to type 'never'.
tests/cases/conformance/types/conditional/conditionalTypes1.ts(116,5): error TS2322: Type 'keyof T' is not assignable to type 'T[keyof T] extends Function ? never : keyof T'.
  Type 'string | number | symbol' is not assignable to type 'T[keyof T] extends Function ? never : keyof T'.
    Type 'string' is not assignable to type 'T[keyof T] extends Function ? never : keyof T'.
tests/cases/conformance/types/conditional/conditionalTypes1.ts(117,5): error TS2322: Type 'T[keyof T] extends Function ? keyof T : never' is not assignable to type 'T[keyof T] extends Function ? never : keyof T'.
  Type 'keyof T' is not assignable to type 'never'.
tests/cases/conformance/types/conditional/conditionalTypes1.ts(134,10): error TS2540: Cannot assign to 'id' because it is a read-only property.
tests/cases/conformance/types/conditional/conditionalTypes1.ts(135,5): error TS2542: Index signature in type 'DeepReadonlyArray<Part>' only permits reading.
tests/cases/conformance/types/conditional/conditionalTypes1.ts(136,22): error TS2540: Cannot assign to 'id' because it is a read-only property.
tests/cases/conformance/types/conditional/conditionalTypes1.ts(137,10): error TS2339: Property 'updatePart' does not exist on type 'DeepReadonlyObject<Part>'.
tests/cases/conformance/types/conditional/conditionalTypes1.ts(159,5): error TS2322: Type 'ZeroOf<T>' is not assignable to type 'T'.
  'ZeroOf<T>' is assignable to the constraint of type 'T', but 'T' could be instantiated with a different subtype of constraint 'string | number'.
    Type '0 | (T extends string ? "" : false)' is not assignable to type 'T'.
      Type '0' is not assignable to type 'T'.
        '0' is assignable to the constraint of type 'T', but 'T' could be instantiated with a different subtype of constraint 'string | number'.
          Type '"" | 0' is not assignable to type 'T'.
            '"" | 0' is assignable to the constraint of type 'T', but 'T' could be instantiated with a different subtype of constraint 'string | number'.
              Type '""' is not assignable to type 'T'.
                '""' is assignable to the constraint of type 'T', but 'T' could be instantiated with a different subtype of constraint 'string | number'.
tests/cases/conformance/types/conditional/conditionalTypes1.ts(160,5): error TS2322: Type 'T' is not assignable to type 'ZeroOf<T>'.
  Type 'string | number' is not assignable to type 'ZeroOf<T>'.
    Type 'string' is not assignable to type 'ZeroOf<T>'.
tests/cases/conformance/types/conditional/conditionalTypes1.ts(263,9): error TS2403: Subsequent variable declarations must have the same type.  Variable 'z' must be of type 'T1', but here has type 'Foo<T & U>'.
tests/cases/conformance/types/conditional/conditionalTypes1.ts(288,43): error TS2322: Type 'T95<U>' is not assignable to type 'T94<U>'.
  Type 'boolean' is not assignable to type 'true'.


==== tests/cases/conformance/types/conditional/conditionalTypes1.ts (22 errors) ====
    type T00 = Exclude<"a" | "b" | "c" | "d", "a" | "c" | "f">;  // "b" | "d"
    type T01 = Extract<"a" | "b" | "c" | "d", "a" | "c" | "f">;  // "a" | "c"
    
    type T02 = Exclude<string | number | (() => void), Function>;  // string | number
    type T03 = Extract<string | number | (() => void), Function>;  // () => void
    
    type T04 = NonNullable<string | number | undefined>;  // string | number
    type T05 = NonNullable<(() => string) | string[] | null | undefined>;  // (() => string) | string[]
    
    function f1<T>(x: T, y: NonNullable<T>) {
        x = y;
        y = x;  // Error
        ~
!!! error TS2322: Type 'T' is not assignable to type 'NonNullable<T>'.
    }
    
    function f2<T extends string | undefined>(x: T, y: NonNullable<T>) {
        x = y;
        y = x;  // Error
        ~
!!! error TS2322: Type 'T' is not assignable to type 'NonNullable<T>'.
!!! error TS2322:   Type 'string | undefined' is not assignable to type 'NonNullable<T>'.
!!! error TS2322:     Type 'undefined' is not assignable to type 'NonNullable<T>'.
        let s1: string = x;  // Error
            ~~
!!! error TS2322: Type 'T' is not assignable to type 'string'.
!!! error TS2322:   Type 'string | undefined' is not assignable to type 'string'.
!!! error TS2322:     Type 'undefined' is not assignable to type 'string'.
        let s2: string = y;
    }
    
    function f3<T>(x: Partial<T>[keyof T], y: NonNullable<Partial<T>[keyof T]>) {
        x = y;
        y = x;  // Error
        ~
!!! error TS2322: Type 'T[keyof T] | undefined' is not assignable to type 'NonNullable<Partial<T>[keyof T]>'.
!!! error TS2322:   Type 'undefined' is not assignable to type 'NonNullable<Partial<T>[keyof T]>'.
    }
    
    function f4<T extends { x: string | undefined }>(x: T["x"], y: NonNullable<T["x"]>) {
        x = y;
        y = x;  // Error
        ~
!!! error TS2322: Type 'T["x"]' is not assignable to type 'NonNullable<T["x"]>'.
!!! error TS2322:   Type 'string | undefined' is not assignable to type 'NonNullable<T["x"]>'.
!!! error TS2322:     Type 'undefined' is not assignable to type 'NonNullable<T["x"]>'.
        let s1: string = x;  // Error
            ~~
!!! error TS2322: Type 'T["x"]' is not assignable to type 'string'.
!!! error TS2322:   Type 'string | undefined' is not assignable to type 'string'.
!!! error TS2322:     Type 'undefined' is not assignable to type 'string'.
        let s2: string = y;
    }
    
    type Options = { k: "a", a: number } | { k: "b", b: string } | { k: "c", c: boolean };
    
    type T10 = Exclude<Options, { k: "a" | "b" }>;  // { k: "c", c: boolean }
    type T11 = Extract<Options, { k: "a" | "b" }>;  // { k: "a", a: number } | { k: "b", b: string }
    
    type T12 = Exclude<Options, { k: "a" } | { k: "b" }>;  // { k: "c", c: boolean }
    type T13 = Extract<Options, { k: "a" } | { k: "b" }>;  // { k: "a", a: number } | { k: "b", b: string }
    
    type T14 = Exclude<Options, { q: "a" }>;  // Options
    type T15 = Extract<Options, { q: "a" }>;  // never
    
    declare function f5<T extends Options, K extends string>(p: K): Extract<T, { k: K }>;
    let x0 = f5("a");  // { k: "a", a: number }
    
    type OptionsOfKind<K extends Options["k"]> = Extract<Options, { k: K }>;
    
    type T16 = OptionsOfKind<"a" | "b">;  // { k: "a", a: number } | { k: "b", b: string }
    
    type Select<T, K extends keyof T, V extends T[K]> = Extract<T, { [P in K]: V }>;
    
    type T17 = Select<Options, "k", "a" | "b">;  // // { k: "a", a: number } | { k: "b", b: string }
    
    type TypeName<T> =
        T extends string ? "string" :
        T extends number ? "number" :
        T extends boolean ? "boolean" :
        T extends undefined ? "undefined" :
        T extends Function ? "function" :
        "object";
    
    type T20 = TypeName<string | (() => void)>;  // "string" | "function"
    type T21 = TypeName<any>;  // "string" | "number" | "boolean" | "undefined" | "function" | "object"
    type T22 = TypeName<never>;  // never
    type T23 = TypeName<{}>;  // "object"
    
    type KnockoutObservable<T> = { object: T };
    type KnockoutObservableArray<T> = { array: T };
    
    type KnockedOut<T> = T extends any[] ? KnockoutObservableArray<T[number]> : KnockoutObservable<T>;
    
    type KnockedOutObj<T> = {
        [P in keyof T]: KnockedOut<T[P]>;
    }
    
    interface Item {
        id: number;
        name: string;
        subitems: string[];
    }
    
    type KOItem = KnockedOutObj<Item>;
    
    interface Part {
        id: number;
        name: string;
        subparts: Part[];
        updatePart(newName: string): void;
    }
    
    type FunctionPropertyNames<T> = { [K in keyof T]: T[K] extends Function ? K : never }[keyof T];
    type FunctionProperties<T> = Pick<T, FunctionPropertyNames<T>>;
    
    type NonFunctionPropertyNames<T> = { [K in keyof T]: T[K] extends Function ? never : K }[keyof T];
    type NonFunctionProperties<T> = Pick<T, NonFunctionPropertyNames<T>>;
    
    type T30 = FunctionProperties<Part>;
    type T31 = NonFunctionProperties<Part>;
    
    function f7<T>(x: T, y: FunctionProperties<T>, z: NonFunctionProperties<T>) {
        x = y;  // Error
        ~
!!! error TS2322: Type 'Pick<T, { [K in keyof T]: T[K] extends Function ? K : never; }[keyof T]>' is not assignable to type 'T'.
!!! error TS2322:   'Pick<T, { [K in keyof T]: T[K] extends Function ? K : never; }[keyof T]>' is assignable to the constraint of type 'T', but 'T' could be instantiated with a different subtype of constraint '{}'.
        x = z;  // Error
        ~
!!! error TS2322: Type 'Pick<T, { [K in keyof T]: T[K] extends Function ? never : K; }[keyof T]>' is not assignable to type 'T'.
!!! error TS2322:   'Pick<T, { [K in keyof T]: T[K] extends Function ? never : K; }[keyof T]>' is assignable to the constraint of type 'T', but 'T' could be instantiated with a different subtype of constraint '{}'.
        y = x;
        y = z;  // Error
        ~
!!! error TS2322: Type 'Pick<T, { [K in keyof T]: T[K] extends Function ? never : K; }[keyof T]>' is not assignable to type 'Pick<T, { [K in keyof T]: T[K] extends Function ? K : never; }[keyof T]>'.
!!! error TS2322:   Type 'T[keyof T] extends Function ? keyof T : never' is not assignable to type 'T[keyof T] extends Function ? never : keyof T'.
        z = x;
        z = y;  // Error
        ~
!!! error TS2322: Type 'Pick<T, { [K in keyof T]: T[K] extends Function ? K : never; }[keyof T]>' is not assignable to type 'Pick<T, { [K in keyof T]: T[K] extends Function ? never : K; }[keyof T]>'.
!!! error TS2322:   Type 'T[keyof T] extends Function ? never : keyof T' is not assignable to type 'T[keyof T] extends Function ? keyof T : never'.
    }
    
    function f8<T>(x: keyof T, y: FunctionPropertyNames<T>, z: NonFunctionPropertyNames<T>) {
        x = y;
        x = z;
        y = x;  // Error
        ~
!!! error TS2322: Type 'keyof T' is not assignable to type 'T[keyof T] extends Function ? keyof T : never'.
!!! error TS2322:   Type 'string | number | symbol' is not assignable to type 'T[keyof T] extends Function ? keyof T : never'.
!!! error TS2322:     Type 'string' is not assignable to type 'T[keyof T] extends Function ? keyof T : never'.
        y = z;  // Error
        ~
!!! error TS2322: Type 'T[keyof T] extends Function ? never : keyof T' is not assignable to type 'T[keyof T] extends Function ? keyof T : never'.
!!! error TS2322:   Type 'keyof T' is not assignable to type 'never'.
!!! error TS2322:     Type 'string | number | symbol' is not assignable to type 'never'.
!!! error TS2322:       Type 'string' is not assignable to type 'never'.
        z = x;  // Error
        ~
!!! error TS2322: Type 'keyof T' is not assignable to type 'T[keyof T] extends Function ? never : keyof T'.
!!! error TS2322:   Type 'string | number | symbol' is not assignable to type 'T[keyof T] extends Function ? never : keyof T'.
!!! error TS2322:     Type 'string' is not assignable to type 'T[keyof T] extends Function ? never : keyof T'.
        z = y;  // Error
        ~
!!! error TS2322: Type 'T[keyof T] extends Function ? keyof T : never' is not assignable to type 'T[keyof T] extends Function ? never : keyof T'.
!!! error TS2322:   Type 'keyof T' is not assignable to type 'never'.
    }
    
    type DeepReadonly<T> =
        T extends any[] ? DeepReadonlyArray<T[number]> :
        T extends object ? DeepReadonlyObject<T> :
        T;
    
    interface DeepReadonlyArray<T> extends ReadonlyArray<DeepReadonly<T>> {}
    
    type DeepReadonlyObject<T> = {
        readonly [P in NonFunctionPropertyNames<T>]: DeepReadonly<T[P]>;
    };
    
    function f10(part: DeepReadonly<Part>) {
        let name: string = part.name;
        let id: number = part.subparts[0].id;
        part.id = part.id;  // Error
             ~~
!!! error TS2540: Cannot assign to 'id' because it is a read-only property.
        part.subparts[0] = part.subparts[0];  // Error
        ~~~~~~~~~~~~~~~~
!!! error TS2542: Index signature in type 'DeepReadonlyArray<Part>' only permits reading.
        part.subparts[0].id = part.subparts[0].id;  // Error
                         ~~
!!! error TS2540: Cannot assign to 'id' because it is a read-only property.
        part.updatePart("hello");  // Error
             ~~~~~~~~~~
!!! error TS2339: Property 'updatePart' does not exist on type 'DeepReadonlyObject<Part>'.
    }
    
    type ZeroOf<T extends number | string | boolean> = T extends number ? 0 : T extends string ? "" : false;
    
    function zeroOf<T extends number | string | boolean>(value: T) {
        return <ZeroOf<T>>(typeof value === "number" ? 0 : typeof value === "string" ? "" : false);
    }
    
    function f20<T extends string>(n: number, b: boolean, x: number | boolean, y: T) {
        zeroOf(5);  // 0
        zeroOf("hello");  // ""
        zeroOf(true);  // false
        zeroOf(n);  // 0
        zeroOf(b);  // False
        zeroOf(x);  // 0 | false
        zeroOf(y);  // ZeroOf<T>
    }
    
    function f21<T extends number | string>(x: T, y: ZeroOf<T>) {
        let z1: number | string = y;
        let z2: 0 | "" = y;
        x = y;  // Error
        ~
!!! error TS2322: Type 'ZeroOf<T>' is not assignable to type 'T'.
!!! error TS2322:   'ZeroOf<T>' is assignable to the constraint of type 'T', but 'T' could be instantiated with a different subtype of constraint 'string | number'.
!!! error TS2322:     Type '0 | (T extends string ? "" : false)' is not assignable to type 'T'.
!!! error TS2322:       Type '0' is not assignable to type 'T'.
!!! error TS2322:         '0' is assignable to the constraint of type 'T', but 'T' could be instantiated with a different subtype of constraint 'string | number'.
!!! error TS2322:           Type '"" | 0' is not assignable to type 'T'.
!!! error TS2322:             '"" | 0' is assignable to the constraint of type 'T', but 'T' could be instantiated with a different subtype of constraint 'string | number'.
!!! error TS2322:               Type '""' is not assignable to type 'T'.
!!! error TS2322:                 '""' is assignable to the constraint of type 'T', but 'T' could be instantiated with a different subtype of constraint 'string | number'.
        y = x;  // Error
        ~
!!! error TS2322: Type 'T' is not assignable to type 'ZeroOf<T>'.
!!! error TS2322:   Type 'string | number' is not assignable to type 'ZeroOf<T>'.
!!! error TS2322:     Type 'string' is not assignable to type 'ZeroOf<T>'.
    }
    
    type T35<T extends { a: string, b: number }> = T[];
    type T36<T> = T extends { a: string } ? T extends { b: number } ? T35<T> : never : never;
    type T37<T> = T extends { b: number } ? T extends { a: string } ? T35<T> : never : never;
    type T38<T> = [T] extends [{ a: string }] ? [T] extends [{ b: number }] ? T35<T> : never : never;
    
    type Extends<T, U> = T extends U ? true : false;
    type If<C extends boolean, T, F> = C extends true ? T : F;
    type Not<C extends boolean> = If<C, false, true>;
    type And<A extends boolean, B extends boolean> = If<A, B, false>;
    type Or<A extends boolean, B extends boolean> = If<A, true, B>;
    
    type IsString<T> = Extends<T, string>;
    
    type Q1 = IsString<number>;  // false
    type Q2 = IsString<"abc">;  // true
    type Q3 = IsString<any>;  // boolean
    type Q4 = IsString<never>;  // never
    
    type N1 = Not<false>;  // true
    type N2 = Not<true>;  // false
    type N3 = Not<boolean>;  // boolean
    
    type A1 = And<false, false>;  // false
    type A2 = And<false, true>;  // false
    type A3 = And<true, false>;  // false
    type A4 = And<true, true>;  // true
    type A5 = And<boolean, false>;  // false
    type A6 = And<false, boolean>;  // false
    type A7 = And<boolean, true>;  // boolean
    type A8 = And<true, boolean>;  // boolean
    type A9 = And<boolean, boolean>;  // boolean
    
    type O1 = Or<false, false>;  // false
    type O2 = Or<false, true>;  // true
    type O3 = Or<true, false>;  // true
    type O4 = Or<true, true>;  // true
    type O5 = Or<boolean, false>;  // boolean
    type O6 = Or<false, boolean>;  // boolean
    type O7 = Or<boolean, true>;  // true
    type O8 = Or<true, boolean>;  // true
    type O9 = Or<boolean, boolean>;  // boolean
    
    type T40 = never extends never ? true : false;  // true
    type T41 = number extends never ? true : false;  // false
    type T42 = never extends number ? true : false;  // true
    
    type IsNever<T> = [T] extends [never] ? true : false;
    
    type T50 = IsNever<never>;  // true
    type T51 = IsNever<number>;  // false
    type T52 = IsNever<any>;  // false
    
    function f22<T>(x: T extends (infer U)[] ? U[] : never) {
        let e = x[0];  // {}
    }
    
    function f23<T extends string[]>(x: T extends (infer U)[] ? U[] : never) {
        let e = x[0];  // string
    }
    
    // Repros from #21664
    
    type Eq<T, U> = T extends U ? U extends T ? true : false : false;
    type T60 = Eq<true, true>;  // true
    type T61 = Eq<true, false>;  // false
    type T62 = Eq<false, true>;  // false
    type T63 = Eq<false, false>;  // true
    
    type Eq1<T, U> = Eq<T, U> extends false ? false : true;
    type T70 = Eq1<true, true>;  // true
    type T71 = Eq1<true, false>;  // false
    type T72 = Eq1<false, true>;  // false
    type T73 = Eq1<false, false>;  // true
    
    type Eq2<T, U> = Eq<T, U> extends true ? true : false;
    type T80 = Eq2<true, true>;  // true
    type T81 = Eq2<true, false>;  // false
    type T82 = Eq2<false, true>;  // false
    type T83 = Eq2<false, false>;  // true
    
    // Repro from #21756
    
    type Foo<T> = T extends string ? boolean : number;
    type Bar<T> = T extends string ? boolean : number;
    const convert = <U>(value: Foo<U>): Bar<U> => value;
    
    type Baz<T> = Foo<T>;
    const convert2 = <T>(value: Foo<T>): Baz<T> => value;
    
    function f31<T>() {
        type T1 = T extends string ? boolean : number;
        type T2 = T extends string ? boolean : number;
        var x: T1;
        var x: T2;
    }
    
    function f32<T, U>() {
        type T1 = T & U extends string ? boolean : number;
        type T2 = Foo<T & U>;
        var z: T1;
        var z: T2;  // Error, T2 is distributive, T1 isn't
            ~
!!! error TS2403: Subsequent variable declarations must have the same type.  Variable 'z' must be of type 'T1', but here has type 'Foo<T & U>'.
    }
    
    function f33<T, U>() {
        type T1 = Foo<T & U>;
        type T2 = Bar<T & U>;
        var z: T1;
        var z: T2;
    }
    
    // Repro from #21823
    
    type T90<T> = T extends 0 ? 0 : () => 0;
    type T91<T> = T extends 0 ? 0 : () => 0;
    const f40 = <U>(a: T90<U>): T91<U> => a;
    const f41 = <U>(a: T91<U>): T90<U> => a;
    
    type T92<T> = T extends () => 0 ? () => 1 : () => 2;
    type T93<T> = T extends () => 0 ? () => 1 : () => 2;
    const f42 = <U>(a: T92<U>): T93<U> => a;
    const f43 = <U>(a: T93<U>): T92<U> => a;
    
    type T94<T> = T extends string ? true : 42;
    type T95<T> = T extends string ? boolean : number;
    const f44 = <U>(value: T94<U>): T95<U> => value;
    const f45 = <U>(value: T95<U>): T94<U> => value;  // Error
                                              ~~~~~
!!! error TS2322: Type 'T95<U>' is not assignable to type 'T94<U>'.
!!! error TS2322:   Type 'boolean' is not assignable to type 'true'.
    
    // Repro from #21863
    
    function f50() {
        type Eq<T, U> = T extends U ? U extends T ? true : false : false;
        type If<S, T, U> = S extends false ? U : T;
        type Omit<T extends object> = { [P in keyof T]: If<Eq<T[P], never>, never, P>; }[keyof T];
        type Omit2<T extends object, U = never> = { [P in keyof T]: If<Eq<T[P], U>, never, P>; }[keyof T];
        type A = Omit<{ a: void; b: never; }>;  // 'a'
        type B = Omit2<{ a: void; b: never; }>;  // 'a'
    }
    
    // Repro from #21862
    
    type OldDiff<T extends keyof any, U extends keyof any> = (
        & { [P in T]: P; }
        & { [P in U]: never; }
        & { [x: string]: never; }
    )[T];
    type NewDiff<T, U> = T extends U ? never : T;
    interface A {
        a: 'a';
    }
    interface B1 extends A {
        b: 'b';
        c: OldDiff<keyof this, keyof A>;
    }
    interface B2 extends A {
        b: 'b';
        c: NewDiff<keyof this, keyof A>;
    }
    type c1 = B1['c']; // 'c' | 'b'
    type c2 = B2['c']; // 'c' | 'b'
    
    // Repro from #21929
    
    type NonFooKeys1<T extends object> = OldDiff<keyof T, 'foo'>;
    type NonFooKeys2<T extends object> = Exclude<keyof T, 'foo'>;
    
    type Test1 = NonFooKeys1<{foo: 1, bar: 2, baz: 3}>;  // "bar" | "baz"
    type Test2 = NonFooKeys2<{foo: 1, bar: 2, baz: 3}>;  // "bar" | "baz"
    
    // Repro from #21729
    
    interface Foo2 { foo: string; }
    interface Bar2 { bar: string; }
    type FooBar = Foo2 | Bar2;
    declare interface ExtractFooBar<FB extends FooBar> { }
    
    type Extracted<Struct> = {
        [K in keyof Struct]: Struct[K] extends FooBar ? ExtractFooBar<Struct[K]> : Struct[K];
    }
    
    // Repro from #22985
    
    type RecursivePartial<T> = {
      [P in keyof T]?: T[P] extends Array<any> ? {[index: number]: RecursivePartial<T[P][0]>} :
        T[P] extends object ? RecursivePartial<T[P]> : T[P];
    };
    
    declare function assign<T>(o: T, a: RecursivePartial<T>): void;
    
    var a = {o: 1, b: 2, c: [{a: 1, c: '213'}]}
    assign(a, {o: 2, c: {0: {a: 2, c: '213123'}}})
    
    // Repros from #23843
    
    type Weird1 = (<U extends boolean>(a: U) => never) extends 
        (<U extends true>(a: U) => never) ? never : never;
    
    type Weird2 = (<U extends boolean>(a: U) => U) extends 
        (<U extends true>(a: U) => infer T) ? T : never;