Fix crash when '^::' is used as a default template argument.

Also fixes an issue for which a qualified-id whose leading component is
a splice could be interpreted as a dependent member expression.

Closes issue llvm#35.

Author: katzdm

clang/lib/Sema/SemaTemplate.cpp

@@ -754,11 +754,14 @@ Sema::ActOnDependentIdExpression(const CXXScopeSpec &SS,
 
   // Check if the nested name specifier is an enum type.
   bool IsEnum = false;
-  if (NestedNameSpecifier *NNS = SS.getScopeRep())
+  bool HasLeadingSplice = false;
+  if (NestedNameSpecifier *NNS = SS.getScopeRep()) {
     IsEnum = isa_and_nonnull<EnumType>(NNS->getAsType());
+    HasLeadingSplice = NNS->getAsSpliceExpr();
+  }
 
   if (!MightBeCxx11UnevalField && !isAddressOfOperand && !IsEnum &&
-      isa<CXXMethodDecl>(DC) &&
+      !HasLeadingSplice && isa<CXXMethodDecl>(DC) &&
       cast<CXXMethodDecl>(DC)->isImplicitObjectMemberFunction()) {
     QualType ThisType = cast<CXXMethodDecl>(DC)->getThisType().getNonReferenceType();
 

clang/lib/Sema/SemaTemplateInstantiate.cpp

@@ -1838,6 +1838,8 @@ getPackSubstitutedTemplateArgument(Sema &S, TemplateArgument Arg) {
 Decl *TemplateInstantiator::TransformDecl(SourceLocation Loc, Decl *D) {
   if (!D)
     return nullptr;
+  if (isa<TranslationUnitDecl>(D))
+    return D;
 
   if (TemplateTemplateParmDecl *TTP = dyn_cast<TemplateTemplateParmDecl>(D)) {
     if (TTP->getDepth() < TemplateArgs.getNumLevels()) {

clang/test/Reflection/lift-operator.cpp

@@ -109,3 +109,12 @@ constexpr info info_nonstructural = ^Nonstructural{42};
 
 namespace ns {}
 constexpr info info_ns = ^ns;
+
+                   // =======================================
+                   // bb_clang_p2996_issue_35_regression_test
+                   // =======================================
+
+namespace bb_clang_p2996_issue_35_regression_test {
+template <auto R = ^::> class S {};
+S s;
+}  // namespace bb_clang_p2996_issue_35_regression_test