3.5 regression: union type as property accessor break function parameter inference

TypeScript Version: 3.5.2 (it works with 3.4.4). Also tested on 3.6.0-dev.20190622

Search Terms:

Code (not real-life, just a repro)

const actions = ['resizeTo', 'resizeBy'] as const;
for (const action of actions) {
	window[action] = (x, y) => {
		window[action](x, y);
	}
}

Expected behavior:

x and y are of type number (like in 3.4)

Actual behavior:

x and y are of type any

Playground Link: (enable noImplicitAny, but it seems to be on 3.4)

https://www.typescriptlang.org/play/#src=%0D%0Aconst%20actions%20%3D%20%5B'resizeTo'%2C%20'resizeBy'%5D%20as%20const%3B%0D%0Afor%20(const%20action%20of%20actions)%20%7B%0D%0A%09window%5Baction%5D%20%3D%20(x%2C%20y)%20%3D%3E%20%7B%0D%0A%09%09window%5Baction%5D(x%2C%20y)%3B%0D%0A%09%7D%0D%0A%7D

Related Issues:

#32037

This is probably due to #30769

But the types of window.resizeTo and window.resizeBy are identical so there shouldn't be any difference or ambiguity.

You can find a real-life example here: refined-github/refined-github#2164

Yes, this is caused by #30769. When an indexed access type occurs on the target side of an assignment, we form an intersection instead of a union. When intersecting properties of the same type we just end up with a property of that type, however we don't remove duplicate call/construct signatures. So, in your example the intersection ends up being a type with two (identical) call signatures, at which point we no longer do contextual typing of parameters.

We can fix the issue by removing duplicate call/construct signatures in an intersection.

Great!

I can confirm that this was fixed and works as expected in 3.6.0-dev.20190701

Thank you!

Navigation Menu

Repository navigation

3.5 regression: union type as property accessor break function parameter inference #32038

Metadata

Assignees

Labels

Type

Projects

Milestone

Relationships

Development

3.5 regression: union type as property accessor break function parameter inference #32038

Description

Activity

fregante commented on Jun 22, 2019

ahejlsberg commented on Jun 23, 2019

fregante commented on Jun 23, 2019

fregante commented on Jul 1, 2019

Metadata

Metadata

Assignees

Labels

Type

Projects

Milestone

Relationships

Development

Issue actions