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
|
tests/cases/compiler/conditionalTypeAssignabilityWhenDeferred.ts(28,20): error TS2345: Argument of type 'string' is not assignable to parameter of type 'never'.
tests/cases/compiler/conditionalTypeAssignabilityWhenDeferred.ts(29,21): error TS2345: Argument of type 'string' is not assignable to parameter of type 'never'.
tests/cases/compiler/conditionalTypeAssignabilityWhenDeferred.ts(39,3): error TS2322: Type '{ x: T; y: T; }' is not assignable to type 'T extends T ? { x: T; y: T; } : never'.
tests/cases/compiler/conditionalTypeAssignabilityWhenDeferred.ts(46,3): error TS2322: Type 'string' is not assignable to type 'Foo<T>'.
tests/cases/compiler/conditionalTypeAssignabilityWhenDeferred.ts(63,9): error TS2322: Type '{ a: number; b: number; }' is not assignable to type '[T] extends [[infer U]] ? U : { b: number; }'.
tests/cases/compiler/conditionalTypeAssignabilityWhenDeferred.ts(95,23): error TS2345: Argument of type 'string' is not assignable to parameter of type 'Unwrap<this["prop"]>'.
tests/cases/compiler/conditionalTypeAssignabilityWhenDeferred.ts(106,3): error TS2322: Type 'Q' is not assignable to type 'InferBecauseWhyNot<Q>'.
Type '(arg: any) => any' is not assignable to type 'InferBecauseWhyNot<Q>'.
tests/cases/compiler/conditionalTypeAssignabilityWhenDeferred.ts(116,3): error TS2322: Type 'Q' is not assignable to type 'InferBecauseWhyNotDistributive<Q>'.
Type '(arg: any) => any' is not assignable to type 'InferBecauseWhyNotDistributive<Q>'.
==== tests/cases/compiler/conditionalTypeAssignabilityWhenDeferred.ts (8 errors) ====
export type FilterPropsByType<T, TT> = {
[K in keyof T]: T[K] extends TT ? K : never
}[keyof T];
function select<
T extends string | number,
TList extends object,
TValueProp extends FilterPropsByType<TList, T>
>(property: T, list: TList[], valueProp: TValueProp) {}
export function func<XX extends string>(x: XX, tipos: { value: XX }[]) {
select(x, tipos, "value");
}
declare function onlyNullablePlease<T extends null extends T ? any : never>(
value: T
): void;
declare function onlyNullablePlease2<
T extends [null] extends [T] ? any : never
>(value: T): void;
declare var z: string | null;
onlyNullablePlease(z); // works as expected
onlyNullablePlease2(z); // works as expected
declare var y: string;
onlyNullablePlease(y); // error as expected
~
!!! error TS2345: Argument of type 'string' is not assignable to parameter of type 'never'.
onlyNullablePlease2(y); // error as expected
~
!!! error TS2345: Argument of type 'string' is not assignable to parameter of type 'never'.
function f<T>(t: T) {
var x: T | null = Math.random() > 0.5 ? null : t;
onlyNullablePlease(x); // should work
onlyNullablePlease2(x); // should work
}
function f2<T>(t1: { x: T; y: T }, t2: T extends T ? { x: T; y: T } : never) {
t1 = t2; // OK
t2 = t1; // should fail
~~
!!! error TS2322: Type '{ x: T; y: T; }' is not assignable to type 'T extends T ? { x: T; y: T; } : never'.
}
type Foo<T> = T extends true ? string : "a";
function test<T>(x: Foo<T>, s: string) {
x = "a"; // Currently an error, should be ok
x = s; // Error
~
!!! error TS2322: Type 'string' is not assignable to type 'Foo<T>'.
}
// #26933
type Distributive<T> = T extends { a: number } ? { a: number } : { b: number };
function testAssignabilityToConditionalType<T>() {
const o = { a: 1, b: 2 };
const x: [T] extends [string]
? { y: number }
: { a: number; b: number } = undefined!;
// Simple case: OK
const o1: [T] extends [number] ? { a: number } : { b: number } = o;
// Simple case where source happens to be a conditional type: also OK
const x1: [T] extends [number]
? ([T] extends [string] ? { y: number } : { a: number })
: ([T] extends [string] ? { y: number } : { b: number }) = x;
// Infer type parameters: no good
const o2: [T] extends [[infer U]] ? U : { b: number } = o;
~~
!!! error TS2322: Type '{ a: number; b: number; }' is not assignable to type '[T] extends [[infer U]] ? U : { b: number; }'.
// The next 4 are arguable - if you choose to ignore the `never` distribution case,
// then they're all good. The `never` case _is_ a bit of an outlier - we say distributive types
// look approximately like the sum of their branches, but the `never` case bucks that.
// There's an argument for the result of dumping `never` into a distributive conditional
// being not `never`, but instead the intersection of the branches - a much more precise bound
// on that "impossible" input.
// Distributive where T might instantiate to never: no good
const o3: Distributive<T> = o;
// Distributive where T & string might instantiate to never: also no good
const o4: Distributive<T & string> = o;
// Distributive where {a: T} cannot instantiate to never: OK
const o5: Distributive<{ a: T }> = o;
// Distributive where check type is a conditional which returns a non-never type upon instantiation with `never` but can still return never otherwise: no good
const o6: Distributive<[T] extends [never] ? { a: number } : never> = o;
}
type Wrapped<T> = { ___secret: T };
type Unwrap<T> = T extends Wrapped<infer U> ? U : T;
declare function set<T, K extends keyof T>(
obj: T,
key: K,
value: Unwrap<T[K]>
): Unwrap<T[K]>;
class Foo2 {
prop!: Wrapped<string>;
method() {
set(this, "prop", "hi"); // <-- type error
~~~~
!!! error TS2345: Argument of type 'string' is not assignable to parameter of type 'Unwrap<this["prop"]>'.
}
}
set(new Foo2(), "prop", "hi"); // <-- typechecks
type InferBecauseWhyNot<T> = [T] extends [(p: infer P1) => any]
? P1 | T
: never;
function f3<Q extends (arg: any) => any>(x: Q): InferBecauseWhyNot<Q> {
return x;
~~~~~~~~~
!!! error TS2322: Type 'Q' is not assignable to type 'InferBecauseWhyNot<Q>'.
!!! error TS2322: Type '(arg: any) => any' is not assignable to type 'InferBecauseWhyNot<Q>'.
}
type InferBecauseWhyNotDistributive<T> = T extends (p: infer P1) => any
? P1 | T
: never;
function f4<Q extends (arg: any) => any>(
x: Q
): InferBecauseWhyNotDistributive<Q> {
return x; // should fail
~~~~~~~~~
!!! error TS2322: Type 'Q' is not assignable to type 'InferBecauseWhyNotDistributive<Q>'.
!!! error TS2322: Type '(arg: any) => any' is not assignable to type 'InferBecauseWhyNotDistributive<Q>'.
}
|
