Bug: [no-non-null-asserted-optional-chain] Rule not working as expected if non-null-assertion is followed by other actions about typescript-eslint HOT 2 CLOSED

If you want to catch this case, use no-unnecessary-type-assertion

from typescript-eslint.

This is working as expected!

In the error case you have an expression that may return undefined - so by using a non-null assertion you are cancelling the undefined and creating a bug vector in the code.

However with the continued chain case the optional chain short-circuits - meaning you may never reach the non-null assertion at all.
Specifically when the non-null assertion is directly chained off it does not apply to the entire expression - instead it applies just to the property it is directly attached to.
I.e. In your "bad" case the non-null assertion is not removing the undefined from the optional chain - instead it's removing the nullishness from the b property.

This is obviously still a bug vector - non-nullish assertions are never truly safe - but it's not a "this is always completely wrong" usage like the former. If you want to prevent this case you can use the no-non-null-assertion lint rule.

from typescript-eslint.