[PATCH] D21030: [Sema] Fix rejects-valid where parameter pack was not expanded in type alias

[Erik Pilkington via cfe-commits]

erik.pilkington updated this revision to Diff 60908.
erik.pilkington added a comment.

This new patch replaces the call to `RebuildPackExpansion` with a direct call to `getPackExpansionType`. Also use `None` instead of `NumExpansions` as argument.

As far as the `assert(*NumExpansions == 1)`, I don't believe that is always the case. Consider:

  template<class T> struct Foo {};
  template<class... Ts> using FooAlias = Foo<void(Ts...)>;
  template<class... Us> using FooAliasAlias = FooAlias<Us..., Us...>;

Here, the `Ts` in `FooAlias` are expanded into 2 `Us` in `FooAliasAlias`, meaning that there are 2 expansions that need to be separately rebuilt. I added this case to the test file.

Thanks for the review!


http://reviews.llvm.org/D21030

Files:
  lib/Sema/TreeTransform.h
  test/CXX/temp/temp.decls/temp.variadic/p5.cpp

Index: test/CXX/temp/temp.decls/temp.variadic/p5.cpp
===================================================================
--- test/CXX/temp/temp.decls/temp.variadic/p5.cpp
+++ test/CXX/temp/temp.decls/temp.variadic/p5.cpp
@@ -437,3 +437,35 @@
   template void g<>();
   template void g<1, 2, 3>();
 }
+
+template <class... Ts>
+int var_expr(Ts... ts);
+
+template <class... Ts>
+auto a_function(Ts... ts) -> decltype(var_expr(ts...));
+
+template <class T>
+using partial = decltype(a_function<int, T>);
+
+int use_partial() { partial<char> n; }
+
+namespace PR26017 {
+template <class T>
+struct Foo {};
+template <class... Ts>
+using FooAlias = Foo<void(Ts...)>;
+
+template <class... Ts>
+using FooAliasAlias = FooAlias<void(Ts..., Ts...)>;
+
+template <class... Ts>
+void bar(const FooAlias<Ts...> &) {}
+
+int fn() {
+  FooAlias<> a;
+  bar(a);
+
+  FooAlias<int> b;
+  bar(b);
+}
+}
Index: lib/Sema/TreeTransform.h
===================================================================
--- lib/Sema/TreeTransform.h
+++ lib/Sema/TreeTransform.h
@@ -3310,8 +3310,6 @@
         if (Out.isInvalid())
           return true;
 
-        // FIXME: Can this happen? We should not try to expand the pack
-        // in this case.
         if (Out.get()->containsUnexpandedParameterPack()) {
           Out = getDerived().RebuildPackExpansion(
               Out.get(), Expansion->getEllipsisLoc(), OrigNumExpansions);
@@ -4780,6 +4778,14 @@
           if (NewType.isNull())
             return true;
 
+          if (NewType->containsUnexpandedParameterPack()) {
+            NewType =
+                getSema().getASTContext().getPackExpansionType(NewType, None);
+
+            if (NewType.isNull())
+              return true;
+          }
+
           if (ParamInfos)
             PInfos.set(OutParamTypes.size(), ParamInfos[i]);
           OutParamTypes.push_back(NewType);


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