[PATCH] c++: Check template parameter number in member class template specialization [PR115716]

[Simon Martin]

We currently ICE upon the following invalid code, because we don't check the
number of template parameters in member class template specializations. This
patch fixes the PR by adding such a check.

=== cut here ===
template <typename T> struct x {
  template <typename U> struct y {
    typedef T result2;
  };
};
template<> template<typename U, typename> struct x<int>::y {
  typedef double result2;
};
int main() {
  x<int>::y<int>::result2 xxx2;
}
=== cut here ===

Successfully tested on x86_64-pc-linux-gnu.

        PR c++/115716

gcc/cp/ChangeLog:

        * pt.cc (maybe_process_partial_specialization): Check number of
        template parameters in specialization.

gcc/testsuite/ChangeLog:

        * g++.dg/template/spec42.C: New test.

---
 gcc/cp/pt.cc                           | 14 ++++++++++++++
 gcc/testsuite/g++.dg/template/spec42.C | 17 +++++++++++++++++
 2 files changed, 31 insertions(+)
 create mode 100644 gcc/testsuite/g++.dg/template/spec42.C

diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
index bc3ad5edcc5..db8c2a3b4de 100644
--- a/gcc/cp/pt.cc
+++ b/gcc/cp/pt.cc
@@ -1173,6 +1173,20 @@ maybe_process_partial_specialization (tree type)
                       type, inst);
            }
 
+         /* Check that the number of template parameters matches the template
+            being specialized.  */
+         gcc_assert (current_template_parms);
+         if (TREE_VEC_LENGTH (INNERMOST_TEMPLATE_ARGS
+                              (CLASSTYPE_TI_ARGS (type)))
+             != TREE_VEC_LENGTH (INNERMOST_TEMPLATE_PARMS
+                                 (current_template_parms)))
+           {
+             error ("wrong number of template parameters for %qT", type);
+             inform (DECL_SOURCE_LOCATION (tmpl), "from definition of %q#D",
+                     tmpl);
+             return error_mark_node;
+           }
+
          /* Mark TYPE as a specialization.  And as a result, we only
             have one level of template argument for the innermost
             class template.  */
diff --git a/gcc/testsuite/g++.dg/template/spec42.C 
b/gcc/testsuite/g++.dg/template/spec42.C
new file mode 100644
index 00000000000..e00a48d12a9
--- /dev/null
+++ b/gcc/testsuite/g++.dg/template/spec42.C
@@ -0,0 +1,17 @@
+// PR c++/115716
+// { dg-do compile }
+template <typename T> struct x {
+  template <typename U> struct y { // { dg-note "from definition" }
+    typedef T result2;
+  };
+};
+
+template<>
+template<typename U, typename>
+struct x<int>::y { // { dg-error "wrong number" }
+  typedef double result2;
+};
+
+int main() {
+  x<int>::y<int>::result2 xxx2;
+}
-- 
2.44.0