[gcc r12-8419] c++: Fix ICE with -Wmismatched-tags [PR105725]

[Marek Polacek <mpolacek@gcc.gnu.org>]

https://gcc.gnu.org/g:2c11a9a380e7af333e19d6e576a889646d699b2a

commit r12-8419-g2c11a9a380e7af333e19d6e576a889646d699b2a
Author: Marek Polacek <polacek@redhat.com>
Date:   Fri May 27 10:51:30 2022 -0400

    c++: Fix ICE with -Wmismatched-tags [PR105725]
    
    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.
    
            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.
    
    (cherry picked from commit d822f4bbd714c6595f70cc68888dcebecfb6662d)

Diff:
---
 gcc/cp/parser.cc                                |  5 +++--
 gcc/testsuite/g++.dg/warn/Wmismatched-tags-10.C | 10 ++++++++++
 2 files changed, 13 insertions(+), 2 deletions(-)

diff --git a/gcc/cp/parser.cc b/gcc/cp/parser.cc
index 2235da10c7c..1173056dc0a 100644
--- a/gcc/cp/parser.cc
+++ b/gcc/cp/parser.cc
@@ -33508,7 +33508,8 @@ 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
@@ -33546,7 +33547,7 @@ 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>>>;