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
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
|
tests/cases/compiler/recursiveConditionalTypes.ts(16,11): error TS2589: Type instantiation is excessively deep and possibly infinite.
tests/cases/compiler/recursiveConditionalTypes.ts(20,5): error TS2322: Type '__Awaited<T>' is not assignable to type '__Awaited<U>'.
Type 'T' is not assignable to type 'U'.
'U' could be instantiated with an arbitrary type which could be unrelated to 'T'.
tests/cases/compiler/recursiveConditionalTypes.ts(21,5): error TS2322: Type 'T' is not assignable to type '__Awaited<T>'.
tests/cases/compiler/recursiveConditionalTypes.ts(22,5): error TS2322: Type '__Awaited<T>' is not assignable to type 'T'.
'T' could be instantiated with an arbitrary type which could be unrelated to '__Awaited<T>'.
tests/cases/compiler/recursiveConditionalTypes.ts(35,11): error TS2589: Type instantiation is excessively deep and possibly infinite.
tests/cases/compiler/recursiveConditionalTypes.ts(47,12): error TS2589: Type instantiation is excessively deep and possibly infinite.
tests/cases/compiler/recursiveConditionalTypes.ts(50,5): error TS2322: Type 'TupleOf<number, M>' is not assignable to type 'TupleOf<number, N>'.
Type 'number extends M ? number[] : _TupleOf<number, M, []>' is not assignable to type 'TupleOf<number, N>'.
Type 'number[] | _TupleOf<number, M, []>' is not assignable to type 'TupleOf<number, N>'.
Type 'number[]' is not assignable to type 'TupleOf<number, N>'.
tests/cases/compiler/recursiveConditionalTypes.ts(51,5): error TS2322: Type 'TupleOf<number, N>' is not assignable to type 'TupleOf<number, M>'.
Type 'number extends N ? number[] : _TupleOf<number, N, []>' is not assignable to type 'TupleOf<number, M>'.
Type 'number[] | _TupleOf<number, N, []>' is not assignable to type 'TupleOf<number, M>'.
Type 'number[]' is not assignable to type 'TupleOf<number, M>'.
tests/cases/compiler/recursiveConditionalTypes.ts(117,9): error TS2345: Argument of type 'Grow2<[], T>' is not assignable to parameter of type 'Grow1<[], T>'.
Type '[] | Grow2<[string], T>' is not assignable to type 'Grow1<[], T>'.
Type '[]' is not assignable to type 'Grow1<[], T>'.
Type 'Grow2<[string], T>' is not assignable to type 'Grow1<[number], T>'.
Type '[string] | Grow2<[string, string], T>' is not assignable to type 'Grow1<[number], T>'.
Type '[string]' is not assignable to type 'Grow1<[number], T>'.
Type '[string]' is not assignable to type '[number]'.
Type 'string' is not assignable to type 'number'.
tests/cases/compiler/recursiveConditionalTypes.ts(169,5): error TS2322: Type 'number' is not assignable to type 'Enumerate<T["length"]>'.
==== tests/cases/compiler/recursiveConditionalTypes.ts (10 errors) ====
// Awaiting promises
type __Awaited<T> =
T extends null | undefined ? T :
T extends PromiseLike<infer U> ? __Awaited<U> :
T;
type MyPromise<T> = {
then<U>(f: ((value: T) => U | PromiseLike<U>) | null | undefined): MyPromise<U>;
}
type InfinitePromise<T> = Promise<InfinitePromise<T>>;
type P0 = __Awaited<Promise<string | Promise<MyPromise<number> | null> | undefined>>;
type P1 = __Awaited<any>;
type P2 = __Awaited<InfinitePromise<number>>; // Error
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
!!! error TS2589: Type instantiation is excessively deep and possibly infinite.
function f11<T, U extends T>(tx: T, ta: __Awaited<T>, ux: U, ua: __Awaited<U>) {
ta = ua;
ua = ta; // Error
~~
!!! error TS2322: Type '__Awaited<T>' is not assignable to type '__Awaited<U>'.
!!! error TS2322: Type 'T' is not assignable to type 'U'.
!!! error TS2322: 'U' could be instantiated with an arbitrary type which could be unrelated to 'T'.
!!! related TS2208 tests/cases/compiler/recursiveConditionalTypes.ts:18:14: This type parameter might need an `extends U` constraint.
ta = tx; // Error
~~
!!! error TS2322: Type 'T' is not assignable to type '__Awaited<T>'.
tx = ta; // Error
~~
!!! error TS2322: Type '__Awaited<T>' is not assignable to type 'T'.
!!! error TS2322: 'T' could be instantiated with an arbitrary type which could be unrelated to '__Awaited<T>'.
}
// Flattening arrays
type Flatten<T extends readonly unknown[]> = T extends unknown[] ? _Flatten<T>[] : readonly _Flatten<T>[];
type _Flatten<T> = T extends readonly (infer U)[] ? _Flatten<U> : T;
type InfiniteArray<T> = InfiniteArray<T>[];
type B0 = Flatten<string[][][]>;
type B1 = Flatten<string[][] | readonly (number[] | boolean[][])[]>;
type B2 = Flatten<InfiniteArray<string>>;
type B3 = B2[0]; // Error
~~~~~
!!! error TS2589: Type instantiation is excessively deep and possibly infinite.
// Repeating tuples
type TupleOf<T, N extends number> = N extends N ? number extends N ? T[] : _TupleOf<T, N, []> : never;
type _TupleOf<T, N extends number, R extends unknown[]> = R['length'] extends N ? R : _TupleOf<T, N, [T, ...R]>;
type TT0 = TupleOf<string, 4>;
type TT1 = TupleOf<number, 0 | 2 | 4>;
type TT2 = TupleOf<number, number>;
type TT3 = TupleOf<number, any>;
type TT4 = TupleOf<number, 100>;
type TT5 = TupleOf<number, 1000>; // Depth error
~~~~~~~~~~~~~~~~~~~~~
!!! error TS2589: Type instantiation is excessively deep and possibly infinite.
function f22<N extends number, M extends N>(tn: TupleOf<number, N>, tm: TupleOf<number, M>) {
tn = tm;
~~
!!! error TS2322: Type 'TupleOf<number, M>' is not assignable to type 'TupleOf<number, N>'.
!!! error TS2322: Type 'number extends M ? number[] : _TupleOf<number, M, []>' is not assignable to type 'TupleOf<number, N>'.
!!! error TS2322: Type 'number[] | _TupleOf<number, M, []>' is not assignable to type 'TupleOf<number, N>'.
!!! error TS2322: Type 'number[]' is not assignable to type 'TupleOf<number, N>'.
tm = tn;
~~
!!! error TS2322: Type 'TupleOf<number, N>' is not assignable to type 'TupleOf<number, M>'.
!!! error TS2322: Type 'number extends N ? number[] : _TupleOf<number, N, []>' is not assignable to type 'TupleOf<number, M>'.
!!! error TS2322: Type 'number[] | _TupleOf<number, N, []>' is not assignable to type 'TupleOf<number, M>'.
!!! error TS2322: Type 'number[]' is not assignable to type 'TupleOf<number, M>'.
}
declare function f23<T>(t: TupleOf<T, 3>): T;
f23(['a', 'b', 'c']); // string
// Inference to recursive type
interface Box<T> { value: T };
type RecBox<T> = T | Box<RecBox<T>>;
type InfBox<T> = Box<InfBox<T>>;
declare function unbox<T>(box: RecBox<T>): T
type T1 = Box<string>;
type T2 = Box<T1>;
type T3 = Box<T2>;
type T4 = Box<T3>;
type T5 = Box<T4>;
type T6 = Box<T5>;
declare let b1: Box<Box<Box<Box<Box<Box<string>>>>>>;
declare let b2: T6;
declare let b3: InfBox<string>;
declare let b4: { value: { value: { value: typeof b4 }}};
unbox(b1); // string
unbox(b2); // string
unbox(b3); // InfBox<string>
unbox({ value: { value: { value: { value: { value: { value: 5 }}}}}}); // number
unbox(b4); // { value: { value: typeof b4 }}
unbox({ value: { value: { get value() { return this; } }}}); // { readonly value: ... }
// Inference from nested instantiations of same generic types
type Box1<T> = { value: T };
type Box2<T> = { value: T };
declare function foo<T>(x: Box1<Box1<T>>): T;
declare let z: Box2<Box2<string>>;
foo(z); // unknown, but ideally would be string (requires unique recursion ID for each type reference)
// Intersect tuple element types
type Intersect<U extends any[], R = unknown> = U extends [infer H, ...infer T] ? Intersect<T, R & H> : R;
type QQ = Intersect<[string[], number[], 7]>;
// Infer between structurally identical recursive conditional types
type Unpack1<T> = T extends (infer U)[] ? Unpack1<U> : T;
type Unpack2<T> = T extends (infer U)[] ? Unpack2<U> : T;
function f20<T, U extends T>(x: Unpack1<T>, y: Unpack2<T>) {
x = y;
y = x;
f20(y, x);
}
type Grow1<T extends unknown[], N extends number> = T['length'] extends N ? T : Grow1<[number, ...T], N>;
type Grow2<T extends unknown[], N extends number> = T['length'] extends N ? T : Grow2<[string, ...T], N>;
function f21<T extends number>(x: Grow1<[], T>, y: Grow2<[], T>) {
f21(y, x); // Error
~
!!! error TS2345: Argument of type 'Grow2<[], T>' is not assignable to parameter of type 'Grow1<[], T>'.
!!! error TS2345: Type '[] | Grow2<[string], T>' is not assignable to type 'Grow1<[], T>'.
!!! error TS2345: Type '[]' is not assignable to type 'Grow1<[], T>'.
!!! error TS2345: Type 'Grow2<[string], T>' is not assignable to type 'Grow1<[number], T>'.
!!! error TS2345: Type '[string] | Grow2<[string, string], T>' is not assignable to type 'Grow1<[number], T>'.
!!! error TS2345: Type '[string]' is not assignable to type 'Grow1<[number], T>'.
!!! error TS2345: Type '[string]' is not assignable to type '[number]'.
!!! error TS2345: Type 'string' is not assignable to type 'number'.
}
// Repros from #41756
type ParseSuccess<R extends string> = { rest: R };
type ParseManyWhitespace<S extends string> =
S extends ` ${infer R0}` ?
ParseManyWhitespace<R0> extends ParseSuccess<infer R1> ? ParseSuccess<R1> : null :
ParseSuccess<S>;
type TP1 = ParseManyWhitespace<" foo">;
type ParseManyWhitespace2<S extends string> =
S extends ` ${infer R0}` ?
Helper<ParseManyWhitespace2<R0>> :
ParseSuccess<S>;
type Helper<T> = T extends ParseSuccess<infer R> ? ParseSuccess<R> : null
type TP2 = ParseManyWhitespace2<" foo">;
// Repro from #46183
type NTuple<N extends number, Tup extends unknown[] = []> =
Tup['length'] extends N ? Tup : NTuple<N, [...Tup, unknown]>;
type Add<A extends number, B extends number> =
[...NTuple<A>, ...NTuple<B>]['length'];
let five: Add<2, 3>;
// Repro from #46316
type _PrependNextNum<A extends Array<unknown>> = A['length'] extends infer T
? [T, ...A] extends [...infer X]
? X
: never
: never;
type _Enumerate<A extends Array<unknown>, N extends number> = N extends A['length']
? A
: _Enumerate<_PrependNextNum<A>, N> & number;
type Enumerate<N extends number> = number extends N
? number
: _Enumerate<[], N> extends (infer E)[]
? E
: never;
function foo2<T extends unknown[]>(value: T): Enumerate<T['length']> {
return value.length; // Error
~~~~~~~~~~~~~~~~~~~~
!!! error TS2322: Type 'number' is not assignable to type 'Enumerate<T["length"]>'.
}
|
