Internal error in tsc: "TypeError: Cannot read properties of undefined (reading 'flags')"

[GaurangTandon]

🔎 Search Terms

TypeError: Cannot read properties of undefined (reading 'flags')

🕗 Version & Regression Information

• This is the behavior in every version I tried, and I reviewed the FAQ for entries about unhandled TypeScript errors

⏯ Repository Link

https://github.com/GaurangTandon/tsc-issue-repro

💻 Code

const UPDATE_MARKER_FUNC = 'updateMarkerPosition';
window[UPDATE_MARKER_FUNC] = (coordinates, color = 'red') => {};

🙁 Actual behavior

/Users/blazegt/test-tsc/node_modules/typescript/lib/_tsc.js:122142
      throw e;
      ^

TypeError: Cannot read properties of undefined (reading 'flags')
    at getMembersOfSymbol (/Users/blazegt/test-tsc/node_modules/typescript/lib/_tsc.js:56777:19)
    at getLateBoundSymbol (/Users/blazegt/test-tsc/node_modules/typescript/lib/_tsc.js:56787:11)
    at getSymbolOfDeclaration (/Users/blazegt/test-tsc/node_modules/typescript/lib/_tsc.js:49588:43)
    at getSymbolOfNode (/Users/blazegt/test-tsc/node_modules/typescript/lib/_tsc.js:49591:34)
    at getFunctionExpressionParentSymbolOrSymbol (/Users/blazegt/test-tsc/node_modules/typescript/lib/_tsc.js:49598:198)
    at getResolvedMembersOrExportsOfSymbol (/Users/blazegt/test-tsc/node_modules/typescript/lib/_tsc.js:56742:27)
    at getExportsOfSymbol (/Users/blazegt/test-tsc/node_modules/typescript/lib/_tsc.js:49486:61)
    at resolveAnonymousTypeMembers (/Users/blazegt/test-tsc/node_modules/typescript/lib/_tsc.js:57350:19)
    at resolveStructuredTypeMembers (/Users/blazegt/test-tsc/node_modules/typescript/lib/_tsc.js:57698:11)
    at getSignaturesOfStructuredType (/Users/blazegt/test-tsc/node_modules/typescript/lib/_tsc.js:58389:24)

Node.js v20.18.3

🙂 Expected behavior

Internal TypeScript errors should not be thrown.

Additional information about the issue

No response

[RyanCavanaugh]

Shorter repo (JS file)

const UPDATE_MARKER_FUNC = 'updateMarkerPosition';
window[UPDATE_MARKER_FUNC] = () => { };

Run with --allowJs --noEmit

Workaround

const UPDATE_MARKER_FUNC = 'updateMarkerPosition';
window[UPDATE_MARKER_FUNC.toString()] = () => { };

Longer stack trace

_tsc.js:122168
      throw e;
      ^

TypeError: Cannot read properties of undefined (reading 'flags')
    at getMembersOfSymbol (C:\Users\ryanca\AppData\Roaming\npm\node_modules\typescript\lib\_tsc.js:56780:19)
    at getLateBoundSymbol (C:\Users\ryanca\AppData\Roaming\npm\node_modules\typescript\lib\_tsc.js:56790:11)
    at getSymbolOfDeclaration (C:\Users\ryanca\AppData\Roaming\npm\node_modules\typescript\lib\_tsc.js:49591:43)
    at getSymbolOfNode (C:\Users\ryanca\AppData\Roaming\npm\node_modules\typescript\lib\_tsc.js:49594:34)
    at getFunctionExpressionParentSymbolOrSymbol (C:\Users\ryanca\AppData\Roaming\npm\node_modules\typescript\lib\_tsc.js:49601:198)
    at getResolvedMembersOrExportsOfSymbol (C:\Users\ryanca\AppData\Roaming\npm\node_modules\typescript\lib\_tsc.js:56745:27)
    at getExportsOfSymbol (C:\Users\ryanca\AppData\Roaming\npm\node_modules\typescript\lib\_tsc.js:49489:61)
    at resolveAnonymousTypeMembers (C:\Users\ryanca\AppData\Roaming\npm\node_modules\typescript\lib\_tsc.js:57353:19)
    at resolveStructuredTypeMembers (C:\Users\ryanca\AppData\Roaming\npm\node_modules\typescript\lib\_tsc.js:57701:11)
    at getSignaturesOfStructuredType (C:\Users\ryanca\AppData\Roaming\npm\node_modules\typescript\lib\_tsc.js:58392:24)
    at getSignaturesOfType (C:\Users\ryanca\AppData\Roaming\npm\node_modules\typescript\lib\_tsc.js:58398:20)
    at contextuallyCheckFunctionExpressionOrObjectLiteralMethod (C:\Users\ryanca\AppData\Roaming\npm\node_modules\typescript\lib\_tsc.js:78068:44)
    at checkFunctionExpressionOrObjectLiteralMethod (C:\Users\ryanca\AppData\Roaming\npm\node_modules\typescript\lib\_tsc.js:78059:5)
    at checkExpressionWorker (C:\Users\ryanca\AppData\Roaming\npm\node_modules\typescript\lib\_tsc.js:79990:16)
    at checkExpression (C:\Users\ryanca\AppData\Roaming\npm\node_modules\typescript\lib\_tsc.js:79880:32)
    at maybeCheckExpression (C:\Users\ryanca\AppData\Roaming\npm\node_modules\typescript\lib\_tsc.js:78830:28)
    at BinaryExpressionStateMachine.onRight (C:\Users\ryanca\AppData\Roaming\npm\node_modules\typescript\lib\_tsc.js:78794:16)
    at Array.right (C:\Users\ryanca\AppData\Roaming\npm\node_modules\typescript\lib\_tsc.js:27760:30)
    at trampoline (C:\Users\ryanca\AppData\Roaming\npm\node_modules\typescript\lib\_tsc.js:27847:42)
    at C:\Users\ryanca\AppData\Roaming\npm\node_modules\typescript\lib\_tsc.js:78722:22
    at checkExpressionWorker (C:\Users\ryanca\AppData\Roaming\npm\node_modules\typescript\lib\_tsc.js:80015:16)
    at checkExpression (C:\Users\ryanca\AppData\Roaming\npm\node_modules\typescript\lib\_tsc.js:79880:32)
    at checkExpressionStatement (C:\Users\ryanca\AppData\Roaming\npm\node_modules\typescript\lib\_tsc.js:82458:5)
    at checkSourceElementWorker (C:\Users\ryanca\AppData\Roaming\npm\node_modules\typescript\lib\_tsc.js:85523:16)
    at checkSourceElement (C:\Users\ryanca\AppData\Roaming\npm\node_modules\typescript\lib\_tsc.js:85375:7)
    at forEach (C:\Users\ryanca\AppData\Roaming\npm\node_modules\typescript\lib\_tsc.js:32:22)
    at checkSourceFileWorker (C:\Users\ryanca\AppData\Roaming\npm\node_modules\typescript\lib\_tsc.js:85781:7)
    at checkSourceFile (C:\Users\ryanca\AppData\Roaming\npm\node_modules\typescript\lib\_tsc.js:85741:69)

[sandersn]

The binder forgets to check that there is a parent symbol when late-binding assignment declarations, even though late-binding currently requires a parent symbol. More explanation at the PR with a fix: #61593

[TechQuery]

typescript@~5.9 throws the same error on Class fields, but typescript@~5.8 works fine:

// A library
export abstract class A {
    async *someLoader() {
    }

    [Symbol.asyncIterator] = this.someLoader;
}

// B library
export function BMixin(AClass: new (...data: any[]) => A) {
    return abstract class B extends AClass {
    };
}

tsc will throws:

node_modules/.pnpm/typescript@5.9.3/node_modules/typescript/lib/_tsc.js:123168
      throw e;
      ^

TypeError: Cannot read properties of undefined (reading 'flags')
    at addPropertyToElementList (node_modules/.pnpm/typescript@5.9.3/node_modules/typescript/lib/_tsc.js:52170:67)
    at createTypeNodesFromResolvedType (node_modules/.pnpm/typescript@5.9.3/node_modules/typescript/lib/_tsc.js:52103:11)
    at createTypeNodeFromObjectType (node_modules/.pnpm/typescript@5.9.3/node_modules/typescript/lib/_tsc.js:51831:25)
    at visitAndTransformType (node_modules/.pnpm/typescript@5.9.3/node_modules/typescript/lib/_tsc.js:51754:24)   
    at createAnonymousTypeNode (node_modules/.pnpm/typescript@5.9.3/node_modules/typescript/lib/_tsc.js:51694:20) 
    at typeReferenceToTypeNode (node_modules/.pnpm/typescript@5.9.3/node_modules/typescript/lib/_tsc.js:51880:18) 
    at typeToTypeNodeWorker (node_modules/.pnpm/typescript@5.9.3/node_modules/typescript/lib/_tsc.js:51393:83)    
    at typeToTypeNodeHelper (node_modules/.pnpm/typescript@5.9.3/node_modules/typescript/lib/_tsc.js:51214:24)    
    at serializeInferredReturnTypeForSignature (node_modules/.pnpm/typescript@5.9.3/node_modules/typescript/lib/_tsc.js:53463:186)
    at Object.serializeReturnTypeForSignature (node_modules/.pnpm/typescript@5.9.3/node_modules/typescript/lib/_tsc.js:50721:16)