PR18401: Fix assert by implementing the current proposed direction of core

issue 1430. Don't allow a pack expansion to be used as an argument to an alias
template unless the corresponding parameter is a parameter pack.

llvm-svn: 198833

2 files changed, 20 insertions, 17 deletions

diff --git a/clang/lib/Sema/SemaTemplate.cpp b/clang/lib/Sema/SemaTemplate.cpp
index b468e31f097..97137184c29 100644
--- a/clang/lib/Sema/SemaTemplate.cpp
+++ b/clang/lib/Sema/SemaTemplate.cpp
@@ -1975,17 +1975,15 @@ QualType Sema::CheckTemplateIdType(TemplateName Name,
   // Check that the template argument list is well-formed for this
   // template.
   SmallVector<TemplateArgument, 4> Converted;
-  bool ExpansionIntoFixedList = false;
   if (CheckTemplateArgumentList(Template, TemplateLoc, TemplateArgs,
-                                false, Converted, &ExpansionIntoFixedList))
+                                false, Converted))
     return QualType();
 
   QualType CanonType;
 
   bool InstantiationDependent = false;
-  TypeAliasTemplateDecl *AliasTemplate = 0;
-  if (!ExpansionIntoFixedList &&
-      (AliasTemplate = dyn_cast<TypeAliasTemplateDecl>(Template))) {
+  if (TypeAliasTemplateDecl *AliasTemplate =
+          dyn_cast<TypeAliasTemplateDecl>(Template)) {
     // Find the canonical type for this type alias template specialization.
     TypeAliasDecl *Pattern = AliasTemplate->getTemplatedDecl();
     if (Pattern->isInvalidDecl())
@@ -2590,11 +2588,10 @@ Sema::CheckVarTemplateId(VarTemplateDecl *Template, SourceLocation TemplateLoc,
 
   // Check that the template argument list is well-formed for this template.
   SmallVector<TemplateArgument, 4> Converted;
-  bool ExpansionIntoFixedList = false;
   if (CheckTemplateArgumentList(
           Template, TemplateNameLoc,
           const_cast<TemplateArgumentListInfo &>(TemplateArgs), false,
-          Converted, &ExpansionIntoFixedList))
+          Converted))
     return true;
 
   // Find the variable template specialization declaration that
@@ -3549,11 +3546,7 @@ bool Sema::CheckTemplateArgumentList(TemplateDecl *Template,
                                      SourceLocation TemplateLoc,
                                      TemplateArgumentListInfo &TemplateArgs,
                                      bool PartialTemplateArgs,
-                          SmallVectorImpl<TemplateArgument> &Converted,
-                                     bool *ExpansionIntoFixedList) {
-  if (ExpansionIntoFixedList)
-    *ExpansionIntoFixedList = false;
-
+                          SmallVectorImpl<TemplateArgument> &Converted) {
   TemplateParameterList *Params = Template->getTemplateParameters();
 
   SourceLocation RAngleLoc = TemplateArgs.getRAngleLoc();
@@ -3606,6 +3599,20 @@ bool Sema::CheckTemplateArgumentList(TemplateDecl *Template,
                                 ArgumentPack.size(), Converted))
         return true;
 
+      if (TemplateArgs[ArgIdx].getArgument().isPackExpansion() &&
+          isa<TypeAliasTemplateDecl>(Template) &&
+          !(Param + 1 == ParamEnd && (*Param)->isTemplateParameterPack() &&
+            !getExpandedPackSize(*Param))) {
+        // Core issue 1430: we have a pack expansion as an argument to an
+        // alias template, and it's not part of a final parameter pack. This
+        // can't be canonicalized, so reject it now.
+        Diag(TemplateArgs[ArgIdx].getLocation(),
+             diag::err_alias_template_expansion_into_fixed_list)
+          << TemplateArgs[ArgIdx].getSourceRange();
+        Diag((*Param)->getLocation(), diag::note_template_param_here);
+        return true;
+      }
+
       // We're now done with this argument.
       ++ArgIdx;
 
@@ -3652,9 +3659,6 @@ bool Sema::CheckTemplateArgumentList(TemplateDecl *Template,
                                              ArgumentPack.data(),
                                              ArgumentPack.size()));
           ArgumentPack.clear();
-        } else if (ExpansionIntoFixedList) {
-          // We have expanded a pack into a fixed list.
-          *ExpansionIntoFixedList = true;
         }
 
         return false;
diff --git a/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp b/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
index 8c988f07edf..22f13d7d2f7 100644
--- a/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
+++ b/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
@@ -2480,11 +2480,10 @@ Decl *TemplateDeclInstantiator::VisitVarTemplateSpecializationDecl(
 
   // Check that the template argument list is well-formed for this template.
   SmallVector<TemplateArgument, 4> Converted;
-  bool ExpansionIntoFixedList = false;
   if (SemaRef.CheckTemplateArgumentList(
           VarTemplate, VarTemplate->getLocStart(),
           const_cast<TemplateArgumentListInfo &>(VarTemplateArgsInfo), false,
-          Converted, &ExpansionIntoFixedList))
+          Converted))
     return 0;
 
   // Find the variable template specialization declaration that