Self-referencing spread recursive loop

[sandersn]

Fixes #12735

Use checkExpression in checkSpreadExpression, not checkExpressionCached. checkExpressionCached ignores ongoing control flow analysis, which causes the following loop to make the compiler recur infinitely:

// @noImplicitAny: true
let a = []
for (const x of []) {
    a = [...a]
}

An alternate fix would make checkExpressionCached not ignore control flow analysis in some situations, but that's a much more complicated fix, I think. @ahejlsberg, do you have an opinion on whether that or some other fix is feasible?

[DanielRosenwasser]

Does checkExpressionCached document that it doesn't respect control flow analysis? Maybe it should be renamed so that other people don't incorrectly use it.

[sandersn]

checkExpressionCached also interacts with contextual typing. Both interactions are documented in the function's comments, but not in its name. I can't think of a good name anyway ... checkExpressionCachedWithContextualTypingAndFreshControlFlow?

[sandersn]

Oops, this fixes #12735. I got the bug number wrong initially.

[mhegazy]

@sandersn please port this change to release-2.1 as well.

[sandersn]

Ok, I ported it.

[mhegazy]

never mind. i have a port already up: #12864

[sandersn]

Sorry, I didn't see it until after I pushed . I wondered why I did t have merge conflicts with the new commits...