[clang] [Clang] Rebuild lambda captures in default member initializers while skipping body (PR #196597)

[Eli Friedman via cfe-commits]

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@@ -5723,16 +5728,51 @@ struct ImmediateCallVisitor : DynamicRecursiveASTVisitor {
 
 struct EnsureImmediateInvocationInDefaultArgs
     : TreeTransform<EnsureImmediateInvocationInDefaultArgs> {
+  using Base = TreeTransform<EnsureImmediateInvocationInDefaultArgs>;
+
   EnsureImmediateInvocationInDefaultArgs(Sema &SemaRef)
       : TreeTransform(SemaRef) {}
 
   bool AlwaysRebuild() { return true; }
+  bool ReplacingOriginal() { return true; }
+
+  // Lambda bodies are not subexpressions of the enclosing default initializer,
+  // but init-capture expressions are evaluated in the enclosing context. Keep
+  // the existing closure type and capture declarations so the existing body
+  // still refers to the right declarations.
+  ExprResult TransformLambdaExpr(LambdaExpr *E) {
+    SmallVector<Expr *, 4> CaptureInits(E->capture_inits());
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efriedma-quic wrote:

I suspect we want to refactor this to use it in other places, but I guess that can go in a followup.

https://github.com/llvm/llvm-project/pull/196597