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tests/cases/compiler/unionPropertyOfProtectedAndIntersectionProperty.ts(19,23): error TS2339: Property 'foo' does not exist on type 'Foo | Bar'.
==== tests/cases/compiler/unionPropertyOfProtectedAndIntersectionProperty.ts (1 errors) ====
class Foo {
protected foo = 0;
}
class Bar {
protected foo = 0;
}
type Nothing<V extends Foo> = void;
type Broken<V extends Array<Foo | Bar>> = {
readonly [P in keyof V]: V[P] extends Foo ? Nothing<V[P]> : never;
};
// The issue above, #49517, is fixed very indirectly. Here's some code
// that shows the direct result of the change:
type _3 = (Foo & Bar)['foo']; // Ok
type _4 = (Foo | Bar)['foo']; // Error
~~~~~
!!! error TS2339: Property 'foo' does not exist on type 'Foo | Bar'.
type _5 = (Foo | (Foo & Bar))['foo']; // Prev error, now ok
// V[P] in `Nothing<V[P]>` is the substitution type `V[P] & Foo`. When
// checking if that's assignable to `Foo` in the constraint of `Nothing`,
// it passes the regular assignability check but then goes into intersection
// property checks. To pull `foo` from the substitution type, it gets the
// apparent type, which turns out to be something like `(Foo & Foo') | (Foo & Bar)`
// where `Foo` and `Foo'` are different this-type instantiations of `Foo`.
// Those two instantiations have the same `foo` property, but then `(Foo & Bar)['foo']`
// is a synthesized intersection property with a declaration in `Foo` and a
// declaration in `Bar`. Because the former was marked as protected and the
// latter was a different symbol, we previously thought the two symbols were
// totally unrelated, as in `(Foo | Bar)['foo']`. The fix I implemented is to
// check not that the two property symbols are identical, but that they share
// some common declaration. The change is directly observable by seeing whether
// `(Foo | (Foo & Bar))['foo']` is allowed.
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