Related to PR11848 and core-21989: switch ContainsUnexpandedParameterPack from

being a property of a canonical type to being a property of the fully-sugared
type. This should only make a difference in the case where an alias template
ignores one of its parameters, and that parameter is an unexpanded parameter
pack.

llvm-svn: 160244

clang/lib/AST/ASTContext.cpp

@@ -2892,10 +2892,17 @@ QualType ASTContext::getPackExpansionType(QualType Pattern,
 
   QualType Canon;
   if (!Pattern.isCanonical()) {
-    Canon = getPackExpansionType(getCanonicalType(Pattern), NumExpansions);
+    Canon = getCanonicalType(Pattern);
+    // The canonical type might not contain an unexpanded parameter pack, if it
+    // contains an alias template specialization which ignores one of its
+    // parameters.
+    if (Canon->containsUnexpandedParameterPack()) {
+      Canon = getPackExpansionType(getCanonicalType(Pattern), NumExpansions);
 
-    // Find the insert position again.
-    PackExpansionTypes.FindNodeOrInsertPos(ID, InsertPos);
+      // Find the insert position again, in case we inserted an element into
+      // PackExpansionTypes and invalidated our insert position.
+      PackExpansionTypes.FindNodeOrInsertPos(ID, InsertPos);
+    }
   }
 
   T = new (*this) PackExpansionType(Pattern, Canon, NumExpansions);

clang/lib/AST/Type.cpp

@@ -1862,8 +1862,7 @@ TemplateSpecializationType(TemplateName T,
          Canon.isNull()? T.isDependent() 
                        : Canon->isInstantiationDependentType(),
          false,
-         Canon.isNull()? T.containsUnexpandedParameterPack()
-                       : Canon->containsUnexpandedParameterPack()),
+         T.containsUnexpandedParameterPack()),
     Template(T), NumArgs(NumArgs), TypeAlias(!AliasedType.isNull()) {
   assert(!T.getAsDependentTemplateName() && 
          "Use DependentTemplateSpecializationType for dependent template-name");
@@ -1888,6 +1887,8 @@ TemplateSpecializationType(TemplateName T,
     // arguments is. Given:
     //   template<typename T> using U = int;
     // U<T> is always non-dependent, irrespective of the type T.
+    // However, U<Ts> contains an unexpanded parameter pack, even though
+    // its expansion (and thus its desugared type) doesn't.
     if (Canon.isNull() && Args[Arg].isDependent())
       setDependent();
     else if (Args[Arg].isInstantiationDependent())
@@ -1896,7 +1897,7 @@ TemplateSpecializationType(TemplateName T,
     if (Args[Arg].getKind() == TemplateArgument::Type &&
         Args[Arg].getAsType()->isVariablyModifiedType())
       setVariablyModified();
-    if (Canon.isNull() && Args[Arg].containsUnexpandedParameterPack())
+    if (Args[Arg].containsUnexpandedParameterPack())
       setContainsUnexpandedParameterPack();
 
     new (&TemplateArgs[Arg]) TemplateArgument(Args[Arg]);

clang/test/SemaTemplate/alias-templates.cpp

@@ -73,19 +73,38 @@ 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}}
+  void f1(U<T> i, U<Ts> ...is) { // expected-note 2{{couldn't infer template argument 'T'}}
+    return i + f1<Ts...>(is...);
+  }
+
+  // FIXME: This note is technically correct, but could be better. We
+  // should really say that we couldn't infer template argument 'Ts'.
+  template<typename ...Ts>
+  void f2(U<Ts> ...is) { } // expected-note {{requires 0 arguments, but 1 was provided}}
+
+  template<typename...> struct type_tuple {};
+  template<typename ...Ts>
+  void f3(type_tuple<Ts...>, U<Ts> ...is) {} // expected-note {{requires 4 arguments, but 3 were provided}}
+
+  void g() {
+    f1(U<void>()); // expected-error {{no match}}
+    f1(1, 2, 3, 4, 5); // expected-error {{no match}}
+    f2(); // ok
+    f2(1); // expected-error {{no match}}
+    f3(type_tuple<>());
+    f3(type_tuple<void, void, void>(), 1, 2); // expected-error {{no match}}
+    f3(type_tuple<void, void, void>(), 1, 2, 3);
   }
 
   template<typename ...Ts>
   struct S {
-    S(U<Ts>...ts); // expected-error {{does not contain any unexpanded parameter packs}}
+    S(U<Ts>...ts);
   };
 
   template<typename T>
   struct Hidden1 {
     template<typename ...Ts>
-    Hidden1(typename T::template U<Ts> ...ts); // expected-error{{type 'typename Hide::U<Ts>' (aka 'int') of function parameter pack does not contain any unexpanded parameter packs}}
+    Hidden1(typename T::template U<Ts> ...ts);
   };
 
   template<typename T, typename ...Ts>
@@ -97,10 +116,28 @@ namespace PR11848 {
     template<typename T> using U = int;
   };
 
-  Hidden1<Hide> h1;  // expected-note{{in instantiation of template class 'PR11848::Hidden1<PR11848::Hide>' requested here}}
+  Hidden1<Hide> h1;
   Hidden2<Hide, double, char> h2(1, 2);
 }
 
+namespace Core22036 {
+  struct X {};
+  void h(...);
+  template<typename T> using Y = X;
+  template<typename T, typename ...Ts> struct S {
+    void f1(Y<T> a) { h(g(a)); } // expected-error {{undeclared identifier 'g'}}
+    // FIXME: We should reject this too: 'as' has non-dependent type 'X', so
+    //        ADL should be performed at the point of definition of the
+    //        template.
+    void f2(Y<Ts>...as) { h(g(as)...); }
+  };
+  int g(X);
+  void test() {
+    S<int, int>().f1({});
+    S<int, int>().f2({});
+  }
+}
+
 namespace PR13243 {
   template<typename A> struct X {};
   template<int I> struct C {};
@@ -126,5 +163,6 @@ namespace PR13136 {
   int main() {
     foo(1, NumberTuple<unsigned int, 0, 1>());
     bar(1, NumberTuple<unsigned int, 0, 1>());
+    return 0;
   }
 }