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Recursive conditional types (#40002)
* Support recursive conditional types * Accept new API baselines * Accept new baselines * Simplify recursive type tracking in type inference * Accept new baselines * Add tests * Accept new baselines * Revise recursion tracking in type inference * Revise tests * Accept new baselines * Add more tests * Accept new baselines
1 parent 2426eb4 commit cd30534

11 files changed

+1392
-116
lines changed

‎src/compiler/checker.ts

+78-107
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‎src/compiler/types.ts

-2
Original file line numberDiff line numberDiff line change
@@ -5290,8 +5290,6 @@ namespace ts {
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node: ConditionalTypeNode;
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checkType: Type;
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extendsType: Type;
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trueType: Type;
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falseType: Type;
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isDistributive: boolean;
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inferTypeParameters?: TypeParameter[];
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outerTypeParameters?: TypeParameter[];

‎tests/baselines/reference/api/tsserverlibrary.d.ts

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@@ -2605,8 +2605,6 @@ declare namespace ts {
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node: ConditionalTypeNode;
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checkType: Type;
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extendsType: Type;
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trueType: Type;
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falseType: Type;
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isDistributive: boolean;
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inferTypeParameters?: TypeParameter[];
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outerTypeParameters?: TypeParameter[];

‎tests/baselines/reference/api/typescript.d.ts

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@@ -2605,8 +2605,6 @@ declare namespace ts {
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node: ConditionalTypeNode;
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checkType: Type;
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extendsType: Type;
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trueType: Type;
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falseType: Type;
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isDistributive: boolean;
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inferTypeParameters?: TypeParameter[];
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outerTypeParameters?: TypeParameter[];

‎tests/baselines/reference/deeplyNestedConditionalTypes.types

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@@ -108,5 +108,5 @@ type T0 = Foo<99>;
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>T0 : "99"
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type T1 = Foo<any>;
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>T1 : "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9" | "10" | "11" | "12" | "13" | "14" | "15" | "16" | "17" | "18" | "19" | "20" | "21" | "22" | "23" | "24" | "25" | "26" | "27" | "28" | "29" | "30" | "31" | "32" | "33" | "34" | "35" | "36" | "37" | "38" | "39" | "40" | "41" | "42" | "43" | "44" | "45" | "46" | "47" | "48" | "49" | "50" | "51" | "52" | "53" | "54" | "55" | "56" | "57" | "58" | "59" | "60" | "61" | "62" | "63" | "64" | "65" | "66" | "67" | "68" | "69" | "70" | "71" | "72" | "73" | "74" | "75" | "76" | "77" | "78" | "79" | "80" | "81" | "82" | "83" | "84" | "85" | "86" | "87" | "88" | "89" | "90" | "91" | "92" | "93" | "94" | "95" | "96" | "97" | "98" | "99"
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>T1 : "99" | "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9" | "10" | "11" | "12" | "13" | "14" | "15" | "16" | "17" | "18" | "19" | "20" | "21" | "22" | "23" | "24" | "25" | "26" | "27" | "28" | "29" | "30" | "31" | "32" | "33" | "34" | "35" | "36" | "37" | "38" | "39" | "40" | "41" | "42" | "43" | "44" | "45" | "46" | "47" | "48" | "49" | "50" | "51" | "52" | "53" | "54" | "55" | "56" | "57" | "58" | "59" | "60" | "61" | "62" | "63" | "64" | "65" | "66" | "67" | "68" | "69" | "70" | "71" | "72" | "73" | "74" | "75" | "76" | "77" | "78" | "79" | "80" | "81" | "82" | "83" | "84" | "85" | "86" | "87" | "88" | "89" | "90" | "91" | "92" | "93" | "94" | "95" | "96" | "97" | "98"
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‎tests/baselines/reference/promiseTypeInference.types

+2-2
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@@ -22,8 +22,8 @@ declare function convert(s: string): IPromise<number>;
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>s : string
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var $$x = load("something").then(s => convert(s));
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>$$x : CPromise<unknown>
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>load("something").then(s => convert(s)) : CPromise<unknown>
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>$$x : CPromise<number>
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>load("something").then(s => convert(s)) : CPromise<number>
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>load("something").then : <U>(success?: (value: string) => CPromise<U>) => CPromise<U>
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>load("something") : CPromise<string>
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>load : (name: string) => CPromise<string>

‎tests/baselines/reference/recursiveConditionalTypes.errors.txt

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@@ -0,0 +1,195 @@
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tests/cases/compiler/recursiveConditionalTypes.ts(16,11): error TS2589: Type instantiation is excessively deep and possibly infinite.
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tests/cases/compiler/recursiveConditionalTypes.ts(20,5): error TS2322: Type 'Awaited<T>' is not assignable to type 'Awaited<U>'.
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Type 'T' is not assignable to type 'U'.
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'U' could be instantiated with an arbitrary type which could be unrelated to 'T'.
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tests/cases/compiler/recursiveConditionalTypes.ts(21,5): error TS2322: Type 'T' is not assignable to type 'Awaited<T>'.
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tests/cases/compiler/recursiveConditionalTypes.ts(22,5): error TS2322: Type 'Awaited<T>' is not assignable to type 'T'.
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'T' could be instantiated with an arbitrary type which could be unrelated to 'Awaited<T>'.
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Type 'T | (T extends PromiseLike<infer U> ? Awaited<U> : T)' is not assignable to type 'T'.
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'T' could be instantiated with an arbitrary type which could be unrelated to 'T | (T extends PromiseLike<infer U> ? Awaited<U> : T)'.
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Type 'T extends PromiseLike<infer U> ? Awaited<U> : T' is not assignable to type 'T'.
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'T' could be instantiated with an arbitrary type which could be unrelated to 'T extends PromiseLike<infer U> ? Awaited<U> : T'.
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Type 'unknown' is not assignable to type 'T'.
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'T' could be instantiated with an arbitrary type which could be unrelated to 'unknown'.
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tests/cases/compiler/recursiveConditionalTypes.ts(35,11): error TS2589: Type instantiation is excessively deep and possibly infinite.
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tests/cases/compiler/recursiveConditionalTypes.ts(46,12): error TS2589: Type instantiation is excessively deep and possibly infinite.
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tests/cases/compiler/recursiveConditionalTypes.ts(49,5): error TS2322: Type 'TupleOf<number, M>' is not assignable to type 'TupleOf<number, N>'.
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Type 'number extends M ? number[] : _TupleOf<number, M, []>' is not assignable to type 'TupleOf<number, N>'.
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Type 'number[] | _TupleOf<number, M, []>' is not assignable to type 'TupleOf<number, N>'.
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Type 'number[]' is not assignable to type 'TupleOf<number, N>'.
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tests/cases/compiler/recursiveConditionalTypes.ts(50,5): error TS2322: Type 'TupleOf<number, N>' is not assignable to type 'TupleOf<number, M>'.
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Type 'number extends N ? number[] : _TupleOf<number, N, []>' is not assignable to type 'TupleOf<number, M>'.
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Type 'number[] | _TupleOf<number, N, []>' is not assignable to type 'TupleOf<number, M>'.
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Type 'number[]' is not assignable to type 'TupleOf<number, M>'.
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tests/cases/compiler/recursiveConditionalTypes.ts(116,5): error TS2589: Type instantiation is excessively deep and possibly infinite.
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tests/cases/compiler/recursiveConditionalTypes.ts(116,9): error TS2345: Argument of type 'Grow2<[], T>' is not assignable to parameter of type 'Grow1<[], T>'.
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Type '[] | Grow2<[string], T>' is not assignable to type 'Grow1<[], T>'.
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Type '[]' is not assignable to type 'Grow1<[], T>'.
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Type 'Grow2<[string], T>' is not assignable to type 'Grow1<[number], T>'.
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Type '[string] | Grow2<[string, string], T>' is not assignable to type 'Grow1<[number], T>'.
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Type '[string]' is not assignable to type 'Grow1<[number], T>'.
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Type '[string]' is not assignable to type '[number]'.
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Type 'string' is not assignable to type 'number'.
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==== tests/cases/compiler/recursiveConditionalTypes.ts (10 errors) ====
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// Awaiting promises
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type Awaited<T> =
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T extends null | undefined ? T :
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T extends PromiseLike<infer U> ? Awaited<U> :
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T;
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type MyPromise<T> = {
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then<U>(f: ((value: T) => U | PromiseLike<U>) | null | undefined): MyPromise<U>;
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}
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type InfinitePromise<T> = Promise<InfinitePromise<T>>;
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type P0 = Awaited<Promise<string | Promise<MyPromise<number> | null> | undefined>>;
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type P1 = Awaited<any>;
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type P2 = Awaited<InfinitePromise<number>>; // Error
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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!!! error TS2589: Type instantiation is excessively deep and possibly infinite.
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function f11<T, U extends T>(tx: T, ta: Awaited<T>, ux: U, ua: Awaited<U>) {
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ta = ua;
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ua = ta; // Error
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~~
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!!! error TS2322: Type 'Awaited<T>' is not assignable to type 'Awaited<U>'.
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!!! error TS2322: Type 'T' is not assignable to type 'U'.
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!!! error TS2322: 'U' could be instantiated with an arbitrary type which could be unrelated to 'T'.
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ta = tx; // Error
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~~
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!!! error TS2322: Type 'T' is not assignable to type 'Awaited<T>'.
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tx = ta; // Error
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~~
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!!! error TS2322: Type 'Awaited<T>' is not assignable to type 'T'.
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!!! error TS2322: 'T' could be instantiated with an arbitrary type which could be unrelated to 'Awaited<T>'.
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!!! error TS2322: Type 'T | (T extends PromiseLike<infer U> ? Awaited<U> : T)' is not assignable to type 'T'.
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!!! error TS2322: 'T' could be instantiated with an arbitrary type which could be unrelated to 'T | (T extends PromiseLike<infer U> ? Awaited<U> : T)'.
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!!! error TS2322: Type 'T extends PromiseLike<infer U> ? Awaited<U> : T' is not assignable to type 'T'.
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!!! error TS2322: 'T' could be instantiated with an arbitrary type which could be unrelated to 'T extends PromiseLike<infer U> ? Awaited<U> : T'.
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!!! error TS2322: Type 'unknown' is not assignable to type 'T'.
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!!! error TS2322: 'T' could be instantiated with an arbitrary type which could be unrelated to 'unknown'.
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}
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// Flattening arrays
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type Flatten<T extends readonly unknown[]> = T extends unknown[] ? _Flatten<T>[] : readonly _Flatten<T>[];
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type _Flatten<T> = T extends readonly (infer U)[] ? _Flatten<U> : T;
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type InfiniteArray<T> = InfiniteArray<T>[];
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type B0 = Flatten<string[][][]>;
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type B1 = Flatten<string[][] | readonly (number[] | boolean[][])[]>;
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type B2 = Flatten<InfiniteArray<string>>;
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type B3 = B2[0]; // Error
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~~~~~
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!!! error TS2589: Type instantiation is excessively deep and possibly infinite.
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// Repeating tuples
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type TupleOf<T, N extends number> = N extends N ? number extends N ? T[] : _TupleOf<T, N, []> : never;
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type _TupleOf<T, N extends number, R extends unknown[]> = R['length'] extends N ? R : _TupleOf<T, N, [T, ...R]>;
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type TT0 = TupleOf<string, 4>;
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type TT1 = TupleOf<number, 0 | 2 | 4>;
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type TT2 = TupleOf<number, number>;
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type TT3 = TupleOf<number, any>;
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type TT4 = TupleOf<number, 100>; // Depth error
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~~~~~~~~~~~~~~~~~~~~
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!!! error TS2589: Type instantiation is excessively deep and possibly infinite.
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function f22<N extends number, M extends N>(tn: TupleOf<number, N>, tm: TupleOf<number, M>) {
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tn = tm;
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~~
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!!! error TS2322: Type 'TupleOf<number, M>' is not assignable to type 'TupleOf<number, N>'.
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!!! error TS2322: Type 'number extends M ? number[] : _TupleOf<number, M, []>' is not assignable to type 'TupleOf<number, N>'.
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!!! error TS2322: Type 'number[] | _TupleOf<number, M, []>' is not assignable to type 'TupleOf<number, N>'.
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!!! error TS2322: Type 'number[]' is not assignable to type 'TupleOf<number, N>'.
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tm = tn;
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~~
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!!! error TS2322: Type 'TupleOf<number, N>' is not assignable to type 'TupleOf<number, M>'.
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!!! error TS2322: Type 'number extends N ? number[] : _TupleOf<number, N, []>' is not assignable to type 'TupleOf<number, M>'.
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!!! error TS2322: Type 'number[] | _TupleOf<number, N, []>' is not assignable to type 'TupleOf<number, M>'.
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!!! error TS2322: Type 'number[]' is not assignable to type 'TupleOf<number, M>'.
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}
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declare function f23<T>(t: TupleOf<T, 3>): T;
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f23(['a', 'b', 'c']); // string
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// Inference to recursive type
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interface Box<T> { value: T };
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type RecBox<T> = T | Box<RecBox<T>>;
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type InfBox<T> = Box<InfBox<T>>;
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declare function unbox<T>(box: RecBox<T>): T
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type T1 = Box<string>;
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type T2 = Box<T1>;
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type T3 = Box<T2>;
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type T4 = Box<T3>;
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type T5 = Box<T4>;
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type T6 = Box<T5>;
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declare let b1: Box<Box<Box<Box<Box<Box<string>>>>>>;
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declare let b2: T6;
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declare let b3: InfBox<string>;
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declare let b4: { value: { value: { value: typeof b4 }}};
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unbox(b1); // string
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unbox(b2); // string
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unbox(b3); // InfBox<string>
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unbox({ value: { value: { value: { value: { value: { value: 5 }}}}}}); // number
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unbox(b4); // { value: { value: typeof b4 }}
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unbox({ value: { value: { get value() { return this; } }}}); // { readonly value: ... }
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// Inference from nested instantiations of same generic types
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type Box1<T> = { value: T };
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type Box2<T> = { value: T };
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declare function foo<T>(x: Box1<Box1<T>>): T;
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declare let z: Box2<Box2<string>>;
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foo(z); // unknown, but ideally would be string (requires unique recursion ID for each type reference)
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// Intersect tuple element types
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type Intersect<U extends any[], R = unknown> = U extends [infer H, ...infer T] ? Intersect<T, R & H> : R;
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type QQ = Intersect<[string[], number[], 7]>;
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// Infer between structurally identical recursive conditional types
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type Unpack1<T> = T extends (infer U)[] ? Unpack1<U> : T;
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type Unpack2<T> = T extends (infer U)[] ? Unpack2<U> : T;
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function f20<T, U extends T>(x: Unpack1<T>, y: Unpack2<T>) {
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x = y;
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y = x;
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f20(y, x);
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}
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type Grow1<T extends unknown[], N extends number> = T['length'] extends N ? T : Grow1<[number, ...T], N>;
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type Grow2<T extends unknown[], N extends number> = T['length'] extends N ? T : Grow2<[string, ...T], N>;
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function f21<T extends number>(x: Grow1<[], T>, y: Grow2<[], T>) {
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f21(y, x); // Error
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~~~~~~~~~
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!!! error TS2589: Type instantiation is excessively deep and possibly infinite.
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~
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!!! error TS2345: Argument of type 'Grow2<[], T>' is not assignable to parameter of type 'Grow1<[], T>'.
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!!! error TS2345: Type '[] | Grow2<[string], T>' is not assignable to type 'Grow1<[], T>'.
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!!! error TS2345: Type '[]' is not assignable to type 'Grow1<[], T>'.
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!!! error TS2345: Type 'Grow2<[string], T>' is not assignable to type 'Grow1<[number], T>'.
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!!! error TS2345: Type '[string] | Grow2<[string, string], T>' is not assignable to type 'Grow1<[number], T>'.
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!!! error TS2345: Type '[string]' is not assignable to type 'Grow1<[number], T>'.
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!!! error TS2345: Type '[string]' is not assignable to type '[number]'.
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!!! error TS2345: Type 'string' is not assignable to type 'number'.
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}
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