Hover over property accessed using ?. shows T | undefined

[larsnystrom]

Issue Type: Bug

When I hover an object property, there is a tooltip with the type:

The problem is that the type is not for the property but for the expression. This can get confusing when using optional chaining. In the screenshot above, the type of the filteredFile.reports property is actually just FilteredReport[], which is why there is no red squiggly line warning about it being potentially undefined when accessing the .length property. But the expression filteredFile?.reports has the type FilteredReport[] | undefined because of the optional chaining, which I guess is why that's the type being presented in the tooltip?

So the tooltip says (property) FilteredFile.reports: FilteredReport[] | undefined, even though the type is not for the property but for the expression. I think a better tooltip would be:

(expression) filteredFile?.reports: FilteredReport[] | undefined
(property) FilteredFile.reports: FilteredReport[]

VS Code version: Code 1.43.2 (0ba0ca52957102ca3527cf479571617f0de6ed50, 2020-03-24T07:34:57.037Z)
OS version: Darwin x64 19.4.0
Remote OS version: Linux x64 4.15.0-91-generic
TypeScript version: 3.8.3

[mjbvz]

Please share a complete, self-contained code example that demonstrates the problem

[larsnystrom]

@mjbvz Here is a repo with a repro: https://github.com/larsnystrom/vscode-issue-94348-repro

Open it and hover prop in the expression att?.prop.length and you'll see this:

I know this doesn't really add much additional info to my initial post. Not sure how much more self-contained I can make it though?

[mjbvz]

Playground link: https://www.typescriptlang.org/play/#code/PTAEAkHsDcFMCdQwaANrAdgcwC4AsAoAgY0gwGcdQBDALlAG8kAHHASzOtQH57qMAngG0AuqAC+oALyNxBagDpIrDhi4L02fKBCgAynkgB3cqAwBXALYAjBPKUrOPDZlx5QOsOUMmzV24gAPqDmGAAmsABmbBiwYUA

[RyanCavanaugh]

We show the symbol and the type as it exists in the current expression - this can be influenced by narrowing, for example:

so in this case a?.p.length can produce undefined as part of the expression context its in, so undefined is intentionally included

[larsnystrom]

Sorry, if I knew the message came from TypeScript and not VSCode I would have provided a TypeScript playground link myself. The code submitted by mjbvz does not describe the problem here.

@RyanCavanaugh Please look at this playground link instead. The problem here is that when you hover arr in a?.arr.length , the message says (property) A.arr: string[] | undefined but the type is not for (property) A.arr but for (expression) a?.arr. The distinction is important in this case because if the property has the type string[] | undefined then TypeScript should not allow me to write a?.arr.length but I should instead have to write a?.arr?.length.

https://www.typescriptlang.org/play/?ssl=1&ssc=1&pln=12&pc=1#code/PTAEAkHsDcFMCdQAMCG95NASwHbJQPwB0a8RANrDgOYAuAFpijgCba2gDuW55oAzigCeAKBCgJACgAO8SNIS0hASlABBEugBcA2vFzUA2gF1QAH1ABXVrABmuWCzFgAQpY4bSoAMbMckDgAjWCsbexxHIhERXFoEWxRvELVQAG8RCQlSHX49AxMAbhEAX2jba29aLEg8ONzJQh01ZRy8mjSMzPhYWkt4PEJNMkoaBlACUAAiNUnQHUmXSaLSoA

[typescript-bot]

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