Re: [PATCH] c++: Fix ICE with -Wmismatched-tags [PR105725]

[Jason Merrill <jason@redhat.com>]

On 5/27/22 11:46, Marek Polacek wrote:
> Here we ICE with -Wmismatched-tags on something like
> 
>    template <class T>
>    bool B<T, enable_if_t<is_class_v<class T::foo>>>;
> 
> Specifically, the "class T::foo" bit.  There, class_decl_loc_t::add gets
> a TYPENAME_TYPE as TYPE, rather than a class/union type, so checking
> TYPE_BEING_DEFINED will crash.  I think it's OK to allow a TYPENAME_TYPE to
> slip into that function; we just shouldn't consider the 'class' tag redundant
> (which works as a 'typename').  In fact, every other compiler *requires* it.
> 
> Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?

OK.

> 	PR c++/105725
> 
> gcc/cp/ChangeLog:
> 
> 	* parser.cc (class_decl_loc_t::add): Check CLASS_TYPE_P.
> 
> gcc/testsuite/ChangeLog:
> 
> 	* g++.dg/warn/Wmismatched-tags-10.C: New test.
> ---
>   gcc/cp/parser.cc                                |  5 +++--
>   gcc/testsuite/g++.dg/warn/Wmismatched-tags-10.C | 10 ++++++++++
>   2 files changed, 13 insertions(+), 2 deletions(-)
>   create mode 100644 gcc/testsuite/g++.dg/warn/Wmismatched-tags-10.C
> 
> diff --git a/gcc/cp/parser.cc b/gcc/cp/parser.cc
> index 4b9859543ed..9a9f859974a 100644
> --- a/gcc/cp/parser.cc
> +++ b/gcc/cp/parser.cc
> @@ -33666,7 +33666,8 @@ class_decl_loc_t::add (cp_parser *parser, location_t key_loc,
>     bool key_redundant = (!def_p && !decl_p
>   			&& (decl == type_decl
>   			    || TREE_CODE (decl) == TEMPLATE_DECL
> -			    || TYPE_BEING_DEFINED (type)));
> +			    || (CLASS_TYPE_P (type)
> +				&& TYPE_BEING_DEFINED (type))));
>   
>     if (key_redundant
>         && class_key != class_type
> @@ -33704,7 +33705,7 @@ class_decl_loc_t::add (cp_parser *parser, location_t key_loc,
>   	}
>         else
>   	{
> -	  /* TYPE was previously defined in some unknown precompiled hdeader.
> +	  /* TYPE was previously defined in some unknown precompiled header.
>   	     Simply add a record of its definition at an unknown location and
>   	     proceed below to add a reference to it at the current location.
>   	     (Declarations in precompiled headers that are not definitions
> diff --git a/gcc/testsuite/g++.dg/warn/Wmismatched-tags-10.C b/gcc/testsuite/g++.dg/warn/Wmismatched-tags-10.C
> new file mode 100644
> index 00000000000..d7e10743bb4
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/warn/Wmismatched-tags-10.C
> @@ -0,0 +1,10 @@
> +// PR c++/105725
> +// { dg-do compile { target c++14 } }
> +// { dg-options "-Wall -Wmismatched-tags" }
> +
> +template <bool> struct enable_if;
> +template <bool Cond> using enable_if_t = typename enable_if<Cond>::type;
> +template <typename> bool is_class_v;
> +template <class, class> bool B;
> +template <class T>
> +bool B<T, enable_if_t<is_class_v<class T::foo>>>;
> 
> base-commit: de57440858591a88e8fd7ba2505ca54546c86021