1 files changed, 12 insertions, 0 deletions
diff --git a/lib/Sema/SemaExpr.cpp b/lib/Sema/SemaExpr.cpp
index 60dbdc14be..2acbe5961e 100644
--- a/lib/Sema/SemaExpr.cpp
+++ b/lib/Sema/SemaExpr.cpp
@@ -55,6 +55,12 @@ bool Sema::CanUseDecl(NamedDecl *D) {
   if (FunctionDecl *FD = dyn_cast<FunctionDecl>(D)) {
     if (FD->isDeleted())
       return false;
+
+    // If the function has a deduced return type, and we can't deduce it,
+    // then we can't use it either.
+    if (getLangOpts().CPlusPlus1y && FD->getResultType()->isUndeducedType() &&
+        DeduceReturnType(FD, SourceLocation(), /*Diagnose*/false))
+      return false;
   }
 
   // See if this function is unavailable.
@@ -278,6 +284,12 @@ bool Sema::DiagnoseUseOfDecl(NamedDecl *D, SourceLocation Loc,
       NoteDeletedFunction(FD);
       return true;
     }
+
+    // If the function has a deduced return type, and we can't deduce it,
+    // then we can't use it either.
+    if (getLangOpts().CPlusPlus1y && FD->getResultType()->isUndeducedType() &&
+        DeduceReturnType(FD, Loc))
+      return true;
   }
   DiagnoseAvailabilityOfDecl(*this, D, Loc, UnknownObjCClass);