c++: Check DECL_TEMPLATE_PARM_P in duplicate_decls [PR97511]

This makes duplicate_decls differentiate a TYPE_DECL for an alias
template from a TYPE_DECL for one of its template parameters.  The
recently added assert in template_parm_to_arg revealed this latent issue
because merging of the two TYPE_DECLs cleared the DECL_TEMPLATE_PARM_P
flag.

With this patch, we now also correctly diagnose the name shadowing in
the below testcase (as required by [temp.local]/6).

gcc/cp/ChangeLog:

	PR c++/97511
	* decl.c (duplicate_decls): Return NULL_TREE if
	DECL_TEMPLATE_PARM_P differ.

gcc/testsuite/ChangeLog:

	PR c++/97511
	* g++.dg/template/shadow3.C: New test.

diff --git a/gcc/cp/decl.c b/gcc/cp/decl.c
index 5f370e60b4e809d7de45f23c697627cb239488f0..2de4e1657fba8fbe07edf5e047b8b4e848e485ca 100644 (file)
--- a/gcc/cp/decl.c
+++ b/gcc/cp/decl.c
@@ -2002,6 +2002,9 @@ duplicate_decls (tree newdecl, tree olddecl, bool hiding, bool was_hidden)
          || DECL_IMPLICIT_TYPEDEF_P (newdecl)))
     return NULL_TREE;
 
+  if (DECL_TEMPLATE_PARM_P (olddecl) != DECL_TEMPLATE_PARM_P (newdecl))
+    return NULL_TREE;
+
   if (!validate_constexpr_redeclaration (olddecl, newdecl))
     return error_mark_node;
 

diff --git a/gcc/testsuite/g++.dg/template/shadow3.C b/gcc/testsuite/g++.dg/template/shadow3.C
new file mode 100644 (file)
index 0000000..a5f2563
--- /dev/null
+++ b/gcc/testsuite/g++.dg/template/shadow3.C
@@ -0,0 +1,4 @@
+// PR c++/97511
+// { dg-do compile { target c++11 } }
+
+template <class Z> using Z = Z; // { dg-error "shadow|declaration" }