Errors not reported when signature help is active

[DanielRosenwasser]

declare function printValue(str: string): void;
declare function printValue(num: number, maxFractionDigits?: number): void

printValue("hello"/*$*/)

At /*$*/, type in , 123. Notice that you're not getting any errors.

Now try dismissing signature help and making a small edit like erasing 3 or inserting 4. An error will appear.

signatureHelpPoisoningTypeCheckerCache.webm

What are the mechanics here that're making this happen? If you're using VS Code, that initial , will start a signature help session. Every subsequent character will likey be used as a retrigger for signature help prior to requesting diagnostics. And so signature help, which I recall is checked in a specific way to handle overloads that differ slightly in arity, keeps getting requested for a specific expression before the rest of the type-checker gets to walk over it to report errors.

I believe that because signature help gets checked in a special way, it is likely poisoning the type-checker state we use for reporting errors as well.

[andrewbranch]

Duplicate of #49624

[typescript-bot]

This issue has been marked as a 'Duplicate' and has seen no recent activity. It has been automatically closed for house-keeping purposes.