Auto-import failure: Cannot read property 'length' of undefined

[amcasey]

tsconfig.json

{
    "compilerOptions": {
        "allowJs": true,
        "checkJs": true,
        "noEmit": true,
    }
}

test.js

class Abcde {
    x
}

module.exports = {
    Abcde
};

index.ts

export var foo = 1
declare module "./test" {
    interface Abcde { b: string }
}

Abcde// Invoke completion here to trigger auto-import

Expected: Abcde is imported from test.
Actual:

Exception has occurred: TypeError
TypeError: Cannot read property 'length' of undefined
    at getLocalTypeParametersOfClassOrInterfaceOrTypeAlias (e:\ts_gh\src\compiler\checker.ts:8292:32)
    at typeParametersToTypeParameterDeclarations (e:\ts_gh\src\compiler\checker.ts:5002:62)
    at e:\ts_gh\src\compiler\checker.ts:4098:82
    at withContext (e:\ts_gh\src\compiler\checker.ts:4130:39)
    at Object.symbolToTypeParameterDeclarations (e:\ts_gh\src\compiler\checker.ts:4098:21)
    at e:\ts_gh\src\services\symbolDisplay.ts:634:44
    at Object.mapToDisplayParts (e:\ts_gh\src\services\utilities.ts:2091:13)
    at writeTypeParametersOfSymbol (e:\ts_gh\src\services\symbolDisplay.ts:633:40)
    at Object.getSymbolDisplayPartsDocumentationAndSymbolKind (e:\ts_gh\src\services\symbolDisplay.ts:289:13)
    at E:\ts_gh\built\local\tsserver.js:111800:41
    at Object.runWithCancellationToken (e:\ts_gh\src\compiler\checker.ts:662:28)
    at createCompletionDetailsForSymbol (e:\ts_gh\src\services\completions.ts:678:15)
    at Object.getCompletionEntryDetails (e:\ts_gh\src\services\completions.ts:659:24)
    at Proxy.getCompletionEntryDetails (e:\ts_gh\src\services\services.ts:1476:32)
    at e:\ts_gh\src\server\session.ts:1683:53
    at Object.mapDefined (e:\ts_gh\src\compiler\core.ts:475:32)
    at IOSession.Session.getCompletionEntryDetails (e:\ts_gh\src\server\session.ts:1681:28)
    at Session.handlers.ts.createMapFromTemplate._a.<computed> (e:\ts_gh\src\server\session.ts:2455:51)
    at e:\ts_gh\src\server\session.ts:2665:69
    at IOSession.Session.executeWithRequestId (e:\ts_gh\src\server\session.ts:2655:25)
    at IOSession.Session.executeCommand (e:\ts_gh\src\server\session.ts:2665:29)
    at IOSession.Session.onMessage (e:\ts_gh\src\server\session.ts:2694:23)
    at Interface.<anonymous> (e:\ts_gh\src\tsserver\server.ts:577:22)
    at Interface.emit (events.js:203:13)
    at Interface._onLine (readline.js:316:10)
    at Interface._normalWrite (readline.js:461:12)
    at Socket.ondata (readline.js:172:10)
    at Socket.emit (events.js:203:13)
    at addChunk (_stream_readable.js:295:12)
    at readableAddChunk (_stream_readable.js:276:11)
    at Socket.Readable.push (_stream_readable.js:210:10)
    at Pipe.onStreamRead (internal/stream_base_commons.js:166:17)

TS version: c47aca0

[sandersn]

@andrewbranch if this is a regression it should be high priority. In that case, feel free to hand it off to the person who knows the most about the code that is actually at fault.

[andrewbranch]

I don’t think it’s technically a regression because it looks like we didn’t offer an auto-import here at all before 3.9. But, I’ll be able to fix this prior to the RC regardless.

[andrewbranch]

This doesn’t actually seem like an auto-import bug; this pattern of merging doesn’t type check correctly. Importing Abcde yields an implicit any that doesn’t error with noImplicitAny 😳

[andrewbranch]

Had this automatically close in the wrong PR—#38152 was unrelated.