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GeezerVison is showing github.com — Fix getTypeAtLocation for `as const` to not issue a diagnostic by weswigham · Pull Request #36741 · microsoft/TypeScript

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@weswigham

@weswigham Wesley Wigham (weswigham) commented Feb 11, 2020 •
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Fixes #34913

checkAssertion in the normal codepath avoids calling into getTypeFromTypeNode on the const in as const expressions, however the checker getTypeAtLocation API may invoke it directly. Previously, this'd cause as resolution error, as we'd resolve an (entirely unused) variable named const and return its' type. With this change, we instead return the type of the expression associated with the const (which should be more useful to API consumers, I hope, and prevents any spurious errors from being added).

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Wesley Wigham (weswigham) added 3 commits February 11, 2020 14:11
@weswigham
Fix getTypeAtLocation for as const to not issue a diagnostic
015a472
@weswigham
use existing helpers for checks
6feb349
@weswigham
Fix lint
8bcd4f4
@weswigham
Wesley Wigham (weswigham) requested review from Ryan Cavanaugh (RyanCavanaugh), Andrew Casey (amcasey), Nathan Shively-Sanders (sandersn) and Sheetal Nandi (sheetalkamat) February 11, 2020 22:32
sheetalkamat
Sheetal Nandi (sheetalkamat) reviewed Feb 11, 2020
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Comment thread src/compiler/checker.ts
function getTypeFromTypeReference(node: TypeReferenceType): Type {
const links = getNodeLinks(node);
if (!links.resolvedType) {
// handle LS queries on the `const` in `x as const` by resolving to the type of `x`

@sheetalkamat Sheetal Nandi (sheetalkamat) Feb 11, 2020

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Instead of this shouldn't getTypeOfNode just check if it is const of as const expression should forward it to correct node instead?

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@weswigham Wesley Wigham (weswigham) Feb 11, 2020 •
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Ehhhhhh, it could, but I'd rather push the handling to here, to prevent us from ever attempting to resolve the const in as const as a real type reference, however we may get there in the future (plus, by doing it here the result is cached).

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@weswigham
Merge branch 'master' into fix-ls-gettypeatlocation-for-as-const
a85b27c
sandersn
Nathan Shively-Sanders (sandersn) approved these changes Feb 12, 2020
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Wesley Wigham (weswigham) merged commit 2b64731 into microsoft:master Feb 12, 2020
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Wesley Wigham (weswigham) deleted the fix-ls-gettypeatlocation-for-as-const branch February 12, 2020 21:43
@amcasey

Andrew Casey (amcasey) commented Feb 12, 2020

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Is this related to #36490? I believe that PR was also about handling LS requests in larger spans (i.e. not just on identifiers).
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@weswigham

Wesley Wigham (weswigham) commented Feb 12, 2020

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Not as far as I know - this is just about fixing us giving a bogus result (and adding a diagnostic) for the type of const in x as const when the LS requests the type at const.
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@amcasey

Andrew Casey (amcasey) commented Feb 12, 2020

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So it changes from wrong to right, rather than from nothing to something? Makes sense.
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@weswigham Wesley Wigham (weswigham) mentioned this pull request Mar 28, 2022
Prevent looking up symbol for as const from triggering an error #48464
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@microsoft Microsoft (microsoft) locked as resolved and limited conversation to collaborators Oct 21, 2025
@typescript-bot TypeScript Bot (typescript-bot) assigned Wesley Wigham (weswigham) Oct 21, 2025
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Reviewers

@sheetalkamat Sheetal Nandi (sheetalkamat) sheetalkamat left review comments
@sandersn Nathan Shively-Sanders (sandersn) sandersn approved these changes
@amcasey Andrew Casey (amcasey) Awaiting requested review from amcasey
@RyanCavanaugh Ryan Cavanaugh (RyanCavanaugh) Awaiting requested review from RyanCavanaugh

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@weswigham Wesley Wigham (weswigham)

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Successfully merging this pull request may close these issues.

Using getTypeAtLocation on a const type reference creates a TS2304 diagnostic

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4 participants

@weswigham @amcasey @sandersn @sheetalkamat
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