Optional chaining control flow refinements missing

[ahejlsberg]

TypeScript Version: 3.7.x-dev.20191017

Code

In the comments on #33736, several issues related to control flow analysis of optional chaining constructs are mentioned. Specifically:

#33736 (comment) -- No narrowing in switch statement.
#33736 (comment) -- No narrowing following assertion.
#33736 (comment) -- No narrowing in false branch of if statement.

Expected behavior:

Proper narrowing as indicated in the examples.

Actual behavior:

No narrowing.