Re: [PATCH] [PR86747] tsubst friend tpl ctxt before looking it up for dupes

[Jason Merrill <jason@redhat.com>]

On 11/16/18 5:32 PM, Alexandre Oliva wrote:
> When a member template is redeclared as a friend, we enter the context
> of the member before looking it up, and then we check that the decls
> are compatible.  However, when the member template references template
> types of the enclosing context, say an enclosing template class, the
> compare fails because the friend decl is already tsubsted, whereas the
> looked up name isn't.
> 
> The problem is that the enclosing context is taken from the friend
> declaration before tsubsting it, so we look up in the context of the
> generic template instead of that of the tsubsted one we're
> specializing.  The solution is to tsubst the enclosing context when
> it's a non-namespace scope.
> 
> Regstrapped on i686- and x86_64-linux-gnu.  Ok to install?

OK.

> 
> 
> for  gcc/cp/ChangeLog
> 
> 	PR c++/86747
> 	* pt.c (tsubst_friend_class): Enter tsubsted class context.
> 
> for  gcc/testsuite/ChangeLog
> 
> 	PR c++/86747
> 	* g++.dg/pr86747.C: New.
> ---
>   gcc/cp/pt.c                    |    5 ++++-
>   gcc/testsuite/g++.dg/pr86747.C |    8 ++++++++
>   2 files changed, 12 insertions(+), 1 deletion(-)
>   create mode 100644 gcc/testsuite/g++.dg/pr86747.C
> 
> diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c
> index 83d0a74b209f..82c8019431b8 100644
> --- a/gcc/cp/pt.c
> +++ b/gcc/cp/pt.c
> @@ -10568,7 +10568,10 @@ tsubst_friend_class (tree friend_tmpl, tree args)
>     if (TREE_CODE (context) == NAMESPACE_DECL)
>       push_nested_namespace (context);
>     else
> -    push_nested_class (context);
> +    {
> +      context = tsubst (context, args, tf_error, NULL_TREE);
> +      push_nested_class (context);
> +    }
>   
>     tmpl = lookup_name_real (DECL_NAME (friend_tmpl), /*prefer_type=*/false,
>   			   /*non_class=*/false, /*block_p=*/false,
> diff --git a/gcc/testsuite/g++.dg/pr86747.C b/gcc/testsuite/g++.dg/pr86747.C
> new file mode 100644
> index 000000000000..5b0a0bb95146
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/pr86747.C
> @@ -0,0 +1,8 @@
> +// { dg-do compile }
> +
> +template <typename T> class A {
> +  template <void (A::*p)()> class C; // #1
> +  template <void (A::*q)()> friend class C; // #2
> +};
> +
> +A<double> a;
>