Reapply "[Clang][CWG1815] Support lifetime extension of temporary created by aggregate initialization using a default member initializer" (#97308)

The PR reapply https://github.com/llvm/llvm-project/pull/92527.
Implemented CWG1815 and fixed the bugs mentioned in the comments of
https://github.com/llvm/llvm-project/pull/92527 and
https://github.com/llvm/llvm-project/pull/87933.

The reason why the original PR was reverted was that errors might occur
during the rebuild.

---------

Signed-off-by: yronglin <yronglin777@gmail.com>

1 files changed, 16 insertions, 6 deletions

diff --git a/clang/lib/Sema/SemaInit.cpp b/clang/lib/Sema/SemaInit.cpp
index 7dc1718..de2686e 100644
--- a/clang/lib/Sema/SemaInit.cpp
+++ b/clang/lib/Sema/SemaInit.cpp
@@ -750,8 +750,20 @@ void InitListChecker::FillInEmptyInitForField(unsigned Init, FieldDecl *Field,
     if (Field->hasInClassInitializer()) {
       if (VerifyOnly)
         return;
-
-      ExprResult DIE = SemaRef.BuildCXXDefaultInitExpr(Loc, Field);
+      ExprResult DIE;
+      {
+        // Enter a default initializer rebuild context, then we can support
+        // lifetime extension of temporary created by aggregate initialization
+        // using a default member initializer.
+        // CWG1815 (https://wg21.link/CWG1815).
+        EnterExpressionEvaluationContext RebuildDefaultInit(
+            SemaRef, Sema::ExpressionEvaluationContext::PotentiallyEvaluated);
+        // Just copy previous record, make sure we haven't forget anything.
+        SemaRef.currentEvaluationContext() = SemaRef.parentEvaluationContext();
+        SemaRef.currentEvaluationContext().RebuildDefaultArgOrDefaultInit =
+            true;
+        DIE = SemaRef.BuildCXXDefaultInitExpr(Loc, Field);
+      }
       if (DIE.isInvalid()) {
         hadError = true;
         return;
@@ -7521,10 +7533,8 @@ Sema::CreateMaterializeTemporaryExpr(QualType T, Expr *Temporary,
   // are done in both CreateMaterializeTemporaryExpr and MaybeBindToTemporary,
   // but there may be a chance to merge them.
   Cleanup.setExprNeedsCleanups(false);
-  if (isInLifetimeExtendingContext()) {
-    auto &Record = ExprEvalContexts.back();
-    Record.ForRangeLifetimeExtendTemps.push_back(MTE);
-  }
+  if (isInLifetimeExtendingContext())
+    currentEvaluationContext().ForRangeLifetimeExtendTemps.push_back(MTE);
   return MTE;
 }