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3.5 regression: union type as property accessor break function parameter inference #32038
Description
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)
Related Issues:
Activity
fregante commentedon Jun 22, 2019
This is probably due to #30769
But the types of
window.resizeToandwindow.resizeByare identical so there shouldn't be any difference or ambiguity.You can find a real-life example here: refined-github/refined-github#2164
ahejlsberg commentedon Jun 23, 2019
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.
fregante commentedon Jun 23, 2019
Great!
fregante commentedon Jul 1, 2019
I can confirm that this was fixed and works as expected in 3.6.0-dev.20190701
Thank you!