[gcc r13-1841] c++: ICE with erroneous template redeclaration [PR106311]

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

https://gcc.gnu.org/g:2333b58c9892667545d0c2c3ecd2d7b947197511

commit r13-1841-g2333b58c9892667545d0c2c3ecd2d7b947197511
Author: Marek Polacek <polacek@redhat.com>
Date:   Fri Jul 15 09:51:50 2022 -0400

    c++: ICE with erroneous template redeclaration [PR106311]
    
    Here we ICE trying to get DECL_SOURCE_LOCATION of the parm that happens
    to be error_mark_node in this ill-formed test.  I kept running into this
    while reducing code, so it'd be good to have it fixed.
    
            PR c++/106311
    
    gcc/cp/ChangeLog:
    
            * pt.cc (redeclare_class_template): Check DECL_P before accessing
            DECL_SOURCE_LOCATION.
    
    gcc/testsuite/ChangeLog:
    
            * g++.dg/template/redecl5.C: New test.

Diff:
---
 gcc/cp/pt.cc                            | 5 ++++-
 gcc/testsuite/g++.dg/template/redecl5.C | 5 +++++
 2 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
index c415db304c9..6c581fe0fb7 100644
--- a/gcc/cp/pt.cc
+++ b/gcc/cp/pt.cc
@@ -6377,7 +6377,10 @@ redeclare_class_template (tree type, tree parms, tree cons)
 	{
 	  auto_diagnostic_group d;
 	  error ("template parameter %q+#D", tmpl_parm);
-	  inform (DECL_SOURCE_LOCATION (parm), "redeclared here as %q#D", parm);
+	  if (DECL_P (parm))
+	    inform (DECL_SOURCE_LOCATION (parm), "redeclared here as %q#D", parm);
+	  else
+	    inform (input_location, "redeclared here");
 	  return false;
 	}
 
diff --git a/gcc/testsuite/g++.dg/template/redecl5.C b/gcc/testsuite/g++.dg/template/redecl5.C
new file mode 100644
index 00000000000..fb2d698e6bc
--- /dev/null
+++ b/gcc/testsuite/g++.dg/template/redecl5.C
@@ -0,0 +1,5 @@
+// PR c++/106311
+// { dg-do compile }
+
+template <typename, long> struct array; // { dg-error "template parameter" }
+template <typename, size_t X> struct array { }; // { dg-error "declared" }