Fix PR11848: decree that an alias template contains an unexpanded parameter pack

iff its substitution contains an unexpanded parameter pack. This has the effect
that we now reject declarations such as this (which we used to crash when
expanding):

  template<typename T> using Int = int;
  template<typename ...Ts> void f(Int<Ts> ...ints);

The standard is inconsistent on how this case should be treated.

llvm-svn: 148905

clang/lib/AST/Type.cpp

@@ -1889,7 +1889,9 @@ TemplateSpecializationType(TemplateName T,
          Canon.isNull()? T.isDependent() : Canon->isDependentType(),
          Canon.isNull()? T.isDependent() 
                        : Canon->isInstantiationDependentType(),
-         false, T.containsUnexpandedParameterPack()),
+         false,
+         Canon.isNull()? T.containsUnexpandedParameterPack()
+                       : Canon->containsUnexpandedParameterPack()),
     Template(T), NumArgs(NumArgs) {
   assert(!T.getAsDependentTemplateName() && 
          "Use DependentTemplateSpecializationType for dependent template-name");
@@ -1922,7 +1924,7 @@ TemplateSpecializationType(TemplateName T,
     if (Args[Arg].getKind() == TemplateArgument::Type &&
         Args[Arg].getAsType()->isVariablyModifiedType())
       setVariablyModified();
-    if (Args[Arg].containsUnexpandedParameterPack())
+    if (Canon.isNull() && Args[Arg].containsUnexpandedParameterPack())
       setContainsUnexpandedParameterPack();
 
     new (&TemplateArgs[Arg]) TemplateArgument(Args[Arg]);

clang/lib/Sema/SemaTemplateInstantiate.cpp

@@ -1510,7 +1510,7 @@ ParmVarDecl *Sema::SubstParmVarDecl(ParmVarDecl *OldParm,
   // FIXME: When OldParm is a parameter pack and NewParm is not a parameter
   // pack, we actually have a set of instantiated locations. Maintain this set!
   if (OldParm->isParameterPack() && !NewParm->isParameterPack()) {
-    // Add the new parameter to 
+    // Add the new parameter to the instantiated parameter pack.
     CurrentInstantiationScope->InstantiatedLocalPackArg(OldParm, NewParm);
   } else {
     // Introduce an Old -> New mapping

clang/test/SemaTemplate/alias-templates.cpp

@@ -68,3 +68,36 @@ itt::thing ith(itr);
 
 itt::rebind<bool> btr;
 itt::rebind_thing<bool> btt(btr);
+
+namespace PR11848 {
+  template<typename T> using U = int;
+
+  template<typename T, typename ...Ts>
+  void f(U<T> i, U<Ts> ...is) { // expected-error {{type 'U<Ts>' (aka 'int') of function parameter pack does not contain any unexpanded parameter packs}}
+    return i + f<Ts...>(is...); // expected-error {{pack expansion does not contain any unexpanded parameter packs}}
+  }
+
+  template<typename ...Ts>
+  struct S {
+    S(U<Ts>...ts); // expected-error {{does not contain any unexpanded parameter packs}}
+  };
+
+  template<typename T>
+  struct Hidden1 {
+    template<typename ...Ts>
+    Hidden1(typename T::template U<Ts> ...ts);
+  };
+
+  template<typename T, typename ...Ts>
+  struct Hidden2 {
+    Hidden2(typename T::template U<Ts> ...ts);
+  };
+
+  struct Hide {
+    template<typename T> using U = int;
+  };
+
+  // FIXME: This case crashes clang at the moment.
+  //Hidden1<Hide> h1;
+  Hidden2<Hide, double, char> h2(1, 2);
+}