[clang] Reapply "[Clang][CWG1815] Support lifetime extension of temporary created by aggregate initialization using a default member initializer" (PR #92527)

[Erich Keane via cfe-commits]

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@@ -5695,19 +5694,35 @@ ExprResult Sema::BuildCXXDefaultInitExpr(SourceLocation Loc, FieldDecl *Field) {
   ImmediateCallVisitor V(getASTContext());
   if (!NestedDefaultChecking)
     V.TraverseDecl(Field);
-  if (V.HasImmediateCalls) {
+
+  // CWG1815
+  // Support lifetime extension of temporary created by aggregate
+  // initialization using a default member initializer. We should always rebuild
+  // the initializer if it contains any temporaries (if the initializer
+  // expression is an ExprWithCleanups). Then make sure the normal lifetime
+  // extension code recurses into the default initializer and does lifetime
+  // extension when warranted.
+  bool ContainsAnyTemporaries =
+      isa_and_present<ExprWithCleanups>(Field->getInClassInitializer());
+  if (V.HasImmediateCalls || InLifetimeExtendingContext ||
+      ContainsAnyTemporaries) {
     ExprEvalContexts.back().DelayedDefaultInitializationContext = {Loc, Field,
                                                                    CurContext};
     ExprEvalContexts.back().IsCurrentlyCheckingDefaultArgumentOrInitializer =
         NestedDefaultChecking;
-
+    // Pass down lifetime extending flag, and collect temporaries in
+    // CreateMaterializeTemporaryExpr when we rewrite the call argument.
+    keepInLifetimeExtendingContext();
     EnsureImmediateInvocationInDefaultArgs Immediate(*this);
     ExprResult Res;
+
+    // Rebuild CXXDefaultInitExpr might cause diagnostics.
+    SFINAETrap Trap(*this);
----------------
erichkeane wrote:

I'm not sure I get the question?  The SFINAETrap IS suppressing at least some diagnostics.  

We can see if there are already errors pre-transformation via `containsError` (or if it is nullptr, depending on RecoveryExpr).  So if there was  previously detected error, one of those should catch it.



https://github.com/llvm/llvm-project/pull/92527