Intersections have order dependent behavior

[marcusdarmstrong]

// @flow
type Foo = {
  foo: string,
};

type Bar = {
  bar: string,
} & Foo;

type Baz = Foo & {
  baz: string,
};

const bat = (foo: Foo) => foo.foo;

export const invalid = ({ bar, ...baz }: Bar) => bar && bat(baz);
export const valid = ({ baz, ...bar }: Baz) => baz && bat(bar);

yields

src/components/test.js:15
 15: export const invalid = ({ bar, ...baz }: Bar) => bar && bat(baz);
                                                             ^^^^^^^^ function call
 14: const bat = (foo: Foo) => foo.foo;
                       ^^^ property `foo`. Property not found in
 15: export const invalid = ({ bar, ...baz }: Bar) => bar && bat(baz);
                                                                 ^^^ object pattern spread property


Found 1 error

Apologies if the names are confusing, I was trying to reduce the problem to a minimal case. But the point is, Bar and Baz are, in practice, the same type, however, the intersection operator handles them very differently. I expect this is the root cause of issues such as #1511, #1118, #824, and #1462.

[avikchaudhuri]

Spread has a bunch of problems right now, independent of union/intersection bugs.

[chris-lock]

+1