C++ PATCH to fix ICE with suggestions (PR c++/84537)

[Marek Polacek]

Here error_mark_node leaks all the way to edit_distance_traits::get_string
which crashed, so let's not try to give a suggestion for an error node in
the first place.

Bootstrapped/regtested on x86_64-linux, ok for trunk?

2018-02-26  Marek Polacek  <pola...@redhat.com>

        PR c++/84537
        * name-lookup.c (suggest_alternative_in_explicit_scope): Return false
        if name is error node.

        * g++.dg/parse/error60.C: New test.

diff --git gcc/cp/name-lookup.c gcc/cp/name-lookup.c
index 9117e0b30eb..0f00328e96e 100644
--- gcc/cp/name-lookup.c
+++ gcc/cp/name-lookup.c
@@ -5541,6 +5541,10 @@ bool
 suggest_alternative_in_explicit_scope (location_t location, tree name,
                                       tree scope)
 {
+  /* Something went very wrong; don't suggest anything.  */
+  if (name == error_mark_node)
+    return false;
+
   /* Resolve any namespace aliases.  */
   scope = ORIGINAL_NAMESPACE (scope);
 
diff --git gcc/testsuite/g++.dg/parse/error60.C 
gcc/testsuite/g++.dg/parse/error60.C
index e69de29bb2d..38f4e34c59d 100644
--- gcc/testsuite/g++.dg/parse/error60.C
+++ gcc/testsuite/g++.dg/parse/error60.C
@@ -0,0 +1,9 @@
+// PR c++/84537
+// { dg-do compile }
+
+namespace N
+{
+  template<int> struct A {};
+}
+
+N::template A<> a; // { dg-error "" }

        Marek