[PATCH] Canonicalize the variadic template alias with multiple ellipsis.

[Logan Chien]

Ping?

This patch tries to fix an assertion failure related to the template alias
with two (or more) parameter packs.  For example,

template <typename... T> struct tuple;
template <typename... T> struct extract_;
template <typename... T> using extract = typename extract_<T...>::type;
template <typename... A, typename... B>
inline auto test(tuple<A...>&& xs, B&&... ys) -> extract<A&&..., B...> { }

Please have a look, and feel free to let me know if there is any problem.
Thanks!

Sincerely,
Logan


On Mon, Jun 30, 2014 at 1:10 AM, Logan Chien <tzuhsiang.chien at gmail.com>
wrote:

> Hi rsmith,
>
> If the template has two variadic formal parameters, then the type
> might not be canonical.  We have call ASTContext.getCanonicalType()
> to canonicalize the type; otherwise, an assertion failure will be
> raised.
>
> This patch fix this issue by adding getCanonicalType() in
> TransformTemplateTypeParmType.
>
> http://reviews.llvm.org/D4343
>
> Files:
>   lib/Sema/SemaTemplateInstantiate.cpp
>   test/SemaTemplate/alias-templates.cpp
>
> Index: lib/Sema/SemaTemplateInstantiate.cpp
> ===================================================================
> --- lib/Sema/SemaTemplateInstantiate.cpp
> +++ lib/Sema/SemaTemplateInstantiate.cpp
> @@ -1376,7 +1376,7 @@
>      assert(Arg.getKind() == TemplateArgument::Type &&
>             "Template argument kind mismatch");
>
> -    QualType Replacement = Arg.getAsType();
> +    QualType Replacement =
> getSema().Context.getCanonicalType(Arg.getAsType());
>
>      // TODO: only do this uniquing once, at the start of instantiation.
>      QualType Result
> Index: test/SemaTemplate/alias-templates.cpp
> ===================================================================
> --- test/SemaTemplate/alias-templates.cpp
> +++ test/SemaTemplate/alias-templates.cpp
> @@ -201,3 +201,17 @@
>    template <typename T, typename U, typename V>
>    using derived2 = ::PR16904::base<T, U>::template derived<V>; //
> expected-error {{expected a type}} expected-error {{expected ';'}}
>  }
> +
> +namespace VariadicTemplateAlias {
> +  template <typename... T> struct tuple;
> +  template <typename... T> struct extract_;
> +
> +  // Note: Both the template alias and the concatenation of variadic
> template
> +  // arguments A and B are required to trigger the assertion failure.
> +
> +  template <typename... T>
> +  using extract = typename extract_<T...>::type;
> +
> +  template <typename... A, typename... B>
> +  inline auto test(tuple<A...>&& xs, B&&... ys) -> extract<A&&..., B...>
> { }
> +}
>
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