Repository navigation
Non-null assertion doesn't work for mapped types #23849
Description
Activity
Wesley Wigham (@weswigham) can you take a look.
I'm going to guess that when we look at
NonNullable<{ [key in A]: {} | undefined; }[A]>and instantiate with the constraint and simplify toNonNullable<{} | undefined>, the process through which we do so is not creating a distributive conditional type (the original conditional was not distributed, and{} | undefineddoesn't extendundefined, so just passes thru unchanged).Another question is why this is irreproducible in the playground?
Bowen Ni (@bowenni) because as it turns out, this is a regression introduced by #23592, I believe (since, looking at the playground, it clearly worked in 2.8).
Update: Our conditional type constraint comparison logic was incorrect, but not for the stated reason. The distributivity is handled correctly, but how we got the constraint for an indexed access is off. We saw
{[K in A]: {} | undefined}[string]and just...decided not to simplify it and return no constraint because the object type was generic.Thank you Wesley for the explanation!
And I've got a fix up at #23884 😉
- locked and limited conversation to collaborators
on Jul 31, 2018
TypeScript Version:
Reproducible in 2.7.2 and 2.9.0-dev.20180502.
Irreproducible in 2.6.2
Search Terms:
Mapped types, Non-null assertion
Code
Expected behavior:
No errors.
Actual behavior:
In 2.7.2:
error TS2322: Type '{ [key in A]: {} | undefined; }[A]' is not assignable to type '{}'.
Type '{} | undefined' is not assignable to type '{}'.
Type 'undefined' is not assignable to type '{}'.
In 2.9.0-dev.20180502:
error TS2322: Type 'NonNullable<{ [key in A]: {} | undefined; }[A]>' is not assignable to type '{}'.
Type '{} | undefined' is not assignable to type '{}'.
Type 'undefined' is not assignable to type '{}'.
Playground Link:
I cannot reproduce the error in the playground.
From command line, I'm running
node_modules/.bin/tsc -strict test.tsto reproduce it.Related Issues:
#19608
Rado Kirov (@rkirov)