union type over generics inconsistency

[bluescreen303]

TypeScript Version: 3.5.0-dev.20190508

Search Terms: union generics

Code

type Foo1 = (e: string) => { bar: number, name: string } | { bar: number, label: string }
function t1(foo: Foo1): number {
    return foo("hello").bar + 1
}

type Foo2 = ((e: string) => { bar: number, name: string }) | ((e: string) => { bar: number, label: string })
function t2(foo: Foo2): number {
    return foo("hello").bar + 1
}
type Foo3 = <E>(e: E) => { bar: number, name: E } | { bar: number, label: E }
function t3(foo: Foo3): number {
    return foo("hello").bar + 1
}

type Foo4 = (<E>(e: E) => { bar: number, name: E }) | (<E>(e: E) => { bar: number, label: E })
function t4(foo: Foo4): number {
    return foo("hello").bar + 1
}

Expected behavior:
I would expect t4 to work, because it is just a combination of t2 and t3, which both work.
Clearly, typescript is able to process over function types in a union and isn't blocked by functions that have a generic type parameter.

Actual behavior:

error TS2349: Cannot invoke an expression whose type lacks a call signature. Type 'Foo4' has no compatible call signatures.

[jack-williams]

I think this is a current design limitation. Call signatures are not synthesized for unions of generic functions. See here.

[RyanCavanaugh]

Thanks @jack-williams for link to #7294

[jack-williams]

No problem @RyanCavanaugh!

[typescript-bot]

This issue has been marked as a 'Duplicate' and has seen no recent activity. It has been automatically closed for house-keeping purposes.