P0620 follow-up: deducing `auto` from braced-init-list in new expr

Summary:
This is a side-effect brought in by p0620r0, which allows other placeholder types (derived from `auto` and `decltype(auto)`) to be usable in a `new` expression with a single-clause //braced-init-list// as its initializer (8.3.4 [expr.new]/2).  N3922 defined its semantics.

References:
 http://wg21.link/p0620r0
 http://wg21.link/n3922

Reviewers: rsmith, aaron.ballman

Reviewed By: rsmith

Subscribers: cfe-commits

Differential Revision: https://reviews.llvm.org/D39451

llvm-svn: 320401

1 files changed, 12 insertions, 5 deletions

diff --git a/clang/lib/Sema/SemaExprCXX.cpp b/clang/lib/Sema/SemaExprCXX.cpp
index cd0d7157415..9c842ded1e1 100644
--- a/clang/lib/Sema/SemaExprCXX.cpp
+++ b/clang/lib/Sema/SemaExprCXX.cpp
@@ -1748,20 +1748,27 @@ Sema::BuildCXXNew(SourceRange Range, bool UseGlobal,
     if (AllocType.isNull())
       return ExprError();
   } else if (Deduced) {
+    bool Braced = (initStyle == CXXNewExpr::ListInit);
+    if (NumInits == 1) {
+      if (auto p = dyn_cast_or_null<InitListExpr>(Inits[0])) {
+        Inits = p->getInits();
+        NumInits = p->getNumInits();
+        Braced = true;
+      }
+    }
+
     if (initStyle == CXXNewExpr::NoInit || NumInits == 0)
       return ExprError(Diag(StartLoc, diag::err_auto_new_requires_ctor_arg)
                        << AllocType << TypeRange);
-    if (initStyle == CXXNewExpr::ListInit ||
-        (NumInits == 1 && isa<InitListExpr>(Inits[0])))
-      return ExprError(Diag(Inits[0]->getLocStart(),
-                            diag::err_auto_new_list_init)
-                       << AllocType << TypeRange);
     if (NumInits > 1) {
       Expr *FirstBad = Inits[1];
       return ExprError(Diag(FirstBad->getLocStart(),
                             diag::err_auto_new_ctor_multiple_expressions)
                        << AllocType << TypeRange);
     }
+    if (Braced && !getLangOpts().CPlusPlus17)
+      Diag(Initializer->getLocStart(), diag::ext_auto_new_list_init)
+          << AllocType << TypeRange;
     Expr *Deduce = Inits[0];
     QualType DeducedType;
     if (DeduceAutoType(AllocTypeInfo, Deduce, DeducedType) == DAR_Failed)