Fix GH #17278

This was an assertion failure in regexec.c under rare circumstances.  A
reduction of the fuzzed test case is now in pat_advanced.t

The root cause of this was that the pattern being compiled was encoded in
UTF-8 and 'use locale' was in effect, equivalent to the /l charset, and
then the charset was reset inside the pattern, to /d.  But /d in a UTF-8
patterns is illegal, hence the later assertion failure.

The solution is to reset instead to /u when the pattern is UTF-8.

1 files changed, 14 insertions, 0 deletions

diff --git a/t/re/pat_advanced.t b/t/re/pat_advanced.t
index b8de776ae5..c469d5c59b 100644
--- a/t/re/pat_advanced.t
+++ b/t/re/pat_advanced.t
@@ -2562,6 +2562,20 @@ EOF
                          {}, "GH #17734");
     }
 
+    {   # GH $17278 assertion fails
+        fresh_perl_is('use locale;
+                       my $A_grave = "\N{LATIN CAPITAL LETTER A WITH GRAVE}";
+                       utf8::encode($A_grave);
+                       my $a_grave = "\N{LATIN SMALL LETTER A WITH GRAVE}";
+                       utf8::encode($a_grave);
+
+                       my $z="q!$a_grave! =~ m!(?^i)[$A_grave]!";
+                       utf8::decode($z);
+                       print eval $z, "\n";',
+                       1,
+                       {}, "GH #17278");
+    }
+
 
     # !!! NOTE that tests that aren't at all likely to crash perl should go
     # a ways above, above these last ones.  There's a comment there that, like