[clang] [Sema] Preserve ContainsUnexpandedParameterPack in TransformLambdaExpr (PR #86265)

[Younan Zhang via cfe-commits]

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@@ -4006,6 +4007,37 @@ class TreeTransform {
                                       NumExpansions);
   }
 
+  void RebuildLambdaExprImpl(SourceLocation StartLoc, SourceLocation EndLoc,
+                             LambdaScopeInfo *LSI) {}
+
+  ExprResult RebuildLambdaExpr(SourceLocation StartLoc, SourceLocation EndLoc,
+                               LambdaScopeInfo *LSI) {
+    CXXRecordDecl *Class = LSI->Lambda;
+    CXXMethodDecl *CallOperator = LSI->CallOperator;
+    CallOperator->setLexicalDeclContext(Class);
+    Decl *TemplateOrNonTemplateCallOperatorDecl =
+        CallOperator->getDescribedFunctionTemplate()
+            ? CallOperator->getDescribedFunctionTemplate()
+            : cast<Decl>(CallOperator);
+    // FIXME: Is this really the best choice? Keeping the lexical decl context
+    // set as CurContext seems more faithful to the source.
+    TemplateOrNonTemplateCallOperatorDecl->setLexicalDeclContext(Class);
+
+    getDerived().RebuildLambdaExprImpl(StartLoc, EndLoc, LSI);
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zyn0217 wrote:

@cor3ntin Aha, I've figured out a way to simplify this `RebuildLambdaExpr()` thing: I think it's unnecessary to change the new method decl's lexical context to CurContext (we do so in parsing because we want to align the Scope nesting with the lexical nesting; however this is just what needs to be respected in parsing) and this way, we could just get rid of these setter calls.

https://github.com/llvm/llvm-project/pull/86265