c++: Fix ICE on partial specialization redeclaration with mismatched parameters ...

When a partial specialization was redeclared with different template
parameters, maybe_new_partial_specialization was incorrectly treating it
as the same specialization by only comparing template argument lists
without comparing template-heads. This caused an ICE when the
redeclaration had different template parameters.

Per [temp.spec.partial.general]/2, two partial specializations declare
the same entity only if they have equivalent template-heads and
template argument lists.
Fix by comparing template parameter lists (template-heads) in addition
to template argument lists when checking for existing specializations,
and removing flag_concepts to provide diagnostics before c++20 for the
testcase.

	PR c++/122958

gcc/cp/ChangeLog:

	* pt.cc (maybe_new_partial_specialization): Compare template
	parameter lists when checking for existing specializations and
	remove flag_concepts check.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp2a/partial-spec-redecl.C: New test.

Signed-off-by: Egas Ribeiro <egas.g.ribeiro@gmail.com>
Reviewed-by: Jason Merrill <jason@redhat.com>

diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
index ae7429b449c4cb7d1defbbe00eabec1f15e17abf..af2c7a767ab8456f861d108ff0044dbac2192154 100644 (file)
--- a/gcc/cp/pt.cc
+++ b/gcc/cp/pt.cc
@@ -946,7 +946,7 @@ maybe_new_partial_specialization (tree& type)
      Note that we also get here for injected class names and
      late-parsed template definitions. We must ensure that we
      do not create new type declarations for those cases.  */
-  if (flag_concepts && CLASSTYPE_TEMPLATE_SPECIALIZATION (type))
+  if (CLASSTYPE_TEMPLATE_SPECIALIZATION (type))
     {
       tree tmpl = CLASSTYPE_TI_TEMPLATE (type);
       tree args = CLASSTYPE_TI_ARGS (type);
@@ -979,7 +979,12 @@ maybe_new_partial_specialization (tree& type)
           tree spec_tmpl = TREE_VALUE (specs);
           tree spec_args = TREE_PURPOSE (specs);
           tree spec_constr = get_constraints (spec_tmpl);
-          if (comp_template_args (args, spec_args)
+         tree spec_parms = DECL_TEMPLATE_PARMS (spec_tmpl);
+         /* Per [temp.spec.partial.general]/2, two partial specializations
+            declare the same entity if they have equivalent template-heads
+            and template argument lists.  */
+         if (comp_template_args (args, spec_args)
+             && comp_template_parms (spec_parms, current_template_parms)
              && equivalent_constraints (type_constr, spec_constr))
            {
              type = TREE_TYPE (spec_tmpl);

diff --git a/gcc/testsuite/g++.dg/cpp2a/partial-spec-redecl.C b/gcc/testsuite/g++.dg/cpp2a/partial-spec-redecl.C
new file mode 100644 (file)
index 0000000..4340019
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/partial-spec-redecl.C
@@ -0,0 +1,10 @@
+// PR c++/122958
+// { dg-do compile }
+template <class>
+class D;
+
+template <class R, class S>
+class D<R(S)>;
+
+template <class R, class S, class Extra>
+class D<R(S)> {}; // { dg-error "template parameters not deducible" }