c++: Error recovery in merge_default_template_args [PR108206]

We ICE on the following testcase during error recovery, both new_parm
and old_parm are error_mark_node, the ICE is on
          error ("redefinition of default argument for %q+#D", new_parm);
          inform (DECL_SOURCE_LOCATION (old_parm),
                  "original definition appeared here");
where we don't print anything useful for new_parm and ICE trying to
access DECL_SOURCE_LOCATION of old_parm.  I think we shouldn't diagnose
anything when either of the parms is erroneous, GCC 11 before
merge_default_template_args has been added was doing
      if (TREE_VEC_ELT (tmpl_parms, i) == error_mark_node
          || TREE_VEC_ELT (parms, i) == error_mark_node)
        continue;

      tmpl_parm = TREE_VALUE (TREE_VEC_ELT (tmpl_parms, i));
      if (error_operand_p (tmpl_parm))
        return false;
in redeclare_class_template.

2023-01-04  Jakub Jelinek  <jakub@redhat.com>

	PR c++/108206
	* decl.cc (merge_default_template_args): Return false if either
	new_parm or old_parm are erroneous.

	* g++.dg/template/pr108206.C: New test.

(cherry picked from commit fc349931adcf1024ee95e0a0cd98cf4a41996093)

diff --git a/gcc/cp/decl.cc b/gcc/cp/decl.cc
index ed47d262078718b1be8f6efa2e62827e5f7f6e2c..64fba7fafac7470ba230c7a55eb9ac6fda0c2f26 100644 (file)
--- a/gcc/cp/decl.cc
+++ b/gcc/cp/decl.cc
@@ -1490,6 +1490,8 @@ merge_default_template_args (tree new_parms, tree old_parms, bool class_p)
       tree old_parm = TREE_VALUE (TREE_VEC_ELT (old_parms, i));
       tree& new_default = TREE_PURPOSE (TREE_VEC_ELT (new_parms, i));
       tree& old_default = TREE_PURPOSE (TREE_VEC_ELT (old_parms, i));
+      if (error_operand_p (new_parm) || error_operand_p (old_parm))
+       return false;
       if (new_default != NULL_TREE && old_default != NULL_TREE)
        {
          auto_diagnostic_group d;

diff --git a/gcc/testsuite/g++.dg/template/pr108206.C b/gcc/testsuite/g++.dg/template/pr108206.C
new file mode 100644 (file)
index 0000000..9362d26
--- /dev/null
+++ b/gcc/testsuite/g++.dg/template/pr108206.C
@@ -0,0 +1,5 @@
+// PR c++/108206
+// { dg-do compile { target c++11 } }
+
+template <X x, typename T1> void foo (T1);     // { dg-error "'X' has not been declared" }
+template <X x, typename T2> void foo (T2);     // { dg-error "'X' has not been declared" }