[Sema] Ensure an auto non-type template parameter is dependent

The dependent auto was getting stripped away while rebuilding the template
parameter type, so substitute it in.

rdar://41852459

Differential revision: https://reviews.llvm.org/D50088

llvm-svn: 339198

1 files changed, 10 insertions, 1 deletions

diff --git a/clang/lib/Sema/SemaTemplate.cpp b/clang/lib/Sema/SemaTemplate.cpp
index fa002de3f5f..f31f0d4957a 100644
--- a/clang/lib/Sema/SemaTemplate.cpp
+++ b/clang/lib/Sema/SemaTemplate.cpp
@@ -974,7 +974,7 @@ NamedDecl *Sema::ActOnTypeParameter(Scope *S, bool Typename,
 QualType Sema::CheckNonTypeTemplateParameterType(TypeSourceInfo *&TSI,
                                                  SourceLocation Loc) {
   if (TSI->getType()->isUndeducedType()) {
-    // C++1z [temp.dep.expr]p3:
+    // C++17 [temp.dep.expr]p3:
     //   An id-expression is type-dependent if it contains
     //    - an identifier associated by name lookup with a non-type
     //      template-parameter declared with a type that contains a
@@ -9866,6 +9866,15 @@ bool Sema::RebuildTemplateParamsInCurrentInstantiation(
     if (!NewTSI)
       return true;
 
+    if (NewTSI->getType()->isUndeducedType()) {
+      // C++17 [temp.dep.expr]p3:
+      //   An id-expression is type-dependent if it contains
+      //    - an identifier associated by name lookup with a non-type
+      //      template-parameter declared with a type that contains a
+      //      placeholder type (7.1.7.4),
+      NewTSI = SubstAutoTypeSourceInfo(NewTSI, Context.DependentTy);
+    }
+
     if (NewTSI != NTTP->getTypeSourceInfo()) {
       NTTP->setTypeSourceInfo(NewTSI);
       NTTP->setType(NewTSI->getType());