[clang] [Clang] Recover GLTemplateParameterList for generic lambdas in RebuildLambdaScopeInfo (PR #118176)

[Erich Keane via cfe-commits]

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@@ -15504,10 +15504,25 @@ LambdaScopeInfo *Sema::RebuildLambdaScopeInfo(CXXMethodDecl *CallOperator) {
   LSI->CallOperator = CallOperator;
   LSI->Lambda = LambdaClass;
   LSI->ReturnType = CallOperator->getReturnType();
-  // This function in calls in situation where the context of the call operator
-  // is not entered, so we set AfterParameterList to false, so that
+  // When this function is called in situation where the context of the call
+  // operator is not entered, we set AfterParameterList to false, so that
   // `tryCaptureVariable` finds explicit captures in the appropriate context.
-  LSI->AfterParameterList = false;
+  //
+  // There is also at least a situation as in FinishTemplateArgumentDeduction(),
+  // where we would set the CurContext to the lambda operator before
+  // substituting into it. In this case the flag needs to be true such that
+  // tryCaptureVariable can correctly handle potential captures thereof.
+  LSI->AfterParameterList = CurContext == CallOperator;
+  // GLTemplateParameterList is necessary for getCurGenericLambda() which is
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erichkeane wrote:

I would like a new-line right above this comment (after the actual source), as it makes it REALLY easy to miss that line of code here.

https://github.com/llvm/llvm-project/pull/118176