Also allow /\N{}/

See 4cbd7e223 and ticket #123417.

If a charnames handler returns the empty string for a particular name,
then the regular expression stringifies with an empty \N{} in it.
This needs to round-trip properly (eval "/$qr/"), just like \N{U+...}.

2 files changed, 9 insertions, 0 deletions

diff --git a/t/re/pat_advanced.t b/t/re/pat_advanced.t
index ea8974129b..c210e2e06e 100644
--- a/t/re/pat_advanced.t
+++ b/t/re/pat_advanced.t
@@ -2356,6 +2356,12 @@ EOP
         "afoot" =~ eval "qr/$qr/";
         is "$1" || $@, "foo", 'multichar \N{...} stringified and retoked';
     }
+    {   # empty \N{...} tripping roundly
+        BEGIN { $^H{charnames} = sub { "" } }
+        my $qr = qr$(a\N{foo}t)$;
+        "at" =~ eval "qr/$qr/";
+        is "$1" || $@, "at", 'empty \N{...} stringified and retoked';
+    }
 
 
     #
diff --git a/toke.c b/toke.c
index c47e2c2dae..06ec26ab51 100644
--- a/toke.c
+++ b/toke.c
@@ -2492,6 +2492,9 @@ S_get_and_check_backslash_N_name(pTHX_ const char* s, const char* const e)
 
     PERL_ARGS_ASSERT_GET_AND_CHECK_BACKSLASH_N_NAME;
 
+    if (!SvCUR(res))
+        return res;
+
     if (UTF && ! is_utf8_string_loc((U8 *) backslash_ptr,
                                      e - backslash_ptr,
                                      &first_bad_char_loc))