Wrong compilation error in type combining intersection of unions

[arnauorriols]

TypeScript Version: typescript@3.5.0-dev.20190523

Search Terms: "intersection of unions"

Code

type Foo = (A | B) & (C | D);

interface A {
	a: true;
}

interface B {
	a: false;
}

interface C {
	b: "foo";
}

interface D {
	b: "bar";
}

const foo: Foo = {
	a: true,
	// b: "foo"
};

Expected behavior: Compilation error:

Property 'b' is missing in type '{ name: string; a: true}' but required in type 'C'.

Actual behavior: Compilation error:

test.ts(19,7): error TS2322: Type '{ a: true; }' is not assignable to type 'Foo'.
Type '{ a: true; }' is not assignable to type 'B & D'.
Type '{ a: true; }' is not assignable to type 'B'.
Types of property 'a' are incompatible.
Type 'true' is not assignable to type 'false'.

If // b: "foo" line is uncommented, code compiles, as expected.

Playground Link: link

Related Issues:

• Using intersection with unions #8896

[RyanCavanaugh]

Works as expected now