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tests/cases/compiler/typePredicatesInUnion3.ts(59,24): error TS2345: Argument of type 'number | null' is not assignable to parameter of type 'number'.
Type 'null' is not assignable to type 'number'.
==== tests/cases/compiler/typePredicatesInUnion3.ts (1 errors) ====
// A union of function types is considered a type predicate if at least one constituent is a type
// predicate and the other constituents are matching type predicates or functions returning `false`.
type P1 = (x: unknown) => x is string;
type P2 = (x: unknown) => x is number;
type F1 = (x: unknown) => false;
type F2 = (x: unknown) => boolean;
type F3 = (x: unknown) => string;
function f1(x: unknown, p: P1 | P2) {
if (p(x)) {
x; // string | number
}
}
function f2(x: unknown, p: P1 | P2 | F1) {
if (p(x)) {
x; // string | number
}
}
function f3(x: unknown, p: P1 | P2 | F2) {
if (p(x)) {
x; // unknown
}
}
function f4(x: unknown, p: P1 | P2 | F3) {
if (p(x)) {
x; // unknown
}
}
// Repro from #54143
type HasAttribute<T> = T & { attribute: number };
class Type1 {
attribute: number | null = null;
predicate(): this is HasAttribute<Type1> {
return true;
}
}
class Type2 {
attribute: number | null = null;
predicate(): boolean {
return true;
}
}
function assertType<T>(_val: T) {
}
declare const val: Type1 | Type2;
if (val.predicate()) {
assertType<number>(val.attribute); // Error
~~~~~~~~~~~~~
!!! error TS2345: Argument of type 'number | null' is not assignable to parameter of type 'number'.
!!! error TS2345: Type 'null' is not assignable to type 'number'.
}
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