From 86a48d83a7caf38c553000a250ed1359c235f55e Mon Sep 17 00:00:00 2001
From: Tony Cook <tony@develop-help.com>
Date: Thu, 19 Oct 2017 10:46:04 +1100
Subject: [PATCH] (perl #132245) don't try to process a char range with no
 preceding char
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A range like \N{}-0 eventually results in compilation failing, but
before that, get_and_check_backslash_N_name() attempts to treat
the memory before the empty output of \N{} as a character.

Petr Písař: Ported to 5.24.3.

Signed-off-by: Petr Písař <ppisar@redhat.com>
---
 t/lib/warnings/toke | 5 +++++
 toke.c              | 4 ++--
 2 files changed, 7 insertions(+), 2 deletions(-)

diff --git a/t/lib/warnings/toke b/t/lib/warnings/toke
index 493c8a2..4a521e0 100644
--- a/t/lib/warnings/toke
+++ b/t/lib/warnings/toke
@@ -1509,3 +1509,8 @@ my $v = 𝛃 - 5;
 EXPECT
 OPTION regex
 (Wide character.*\n)?Warning: Use of "𝛃" without parentheses is ambiguous
+########
+# NAME tr/// range with empty \N{} at the start
+tr//\N{}-0/;
+EXPECT
+Unknown charname '' is deprecated at - line 1.
diff --git a/toke.c b/toke.c
index f2310cc..3d93fac 100644
--- a/toke.c
+++ b/toke.c
@@ -2906,8 +2906,8 @@ S_scan_const(pTHX_ char *start)
                  * at least one character, then see if this next one is a '-',
                  * indicating the previous one was the start of a range.  But
                  * don't bother if we're too close to the end for the minus to
-                 * mean that. */
-                if (*s != '-' || s >= send - 1 || s == start) {
+                 * mean that, or if we haven't output any characters yet. */
+                if (*s != '-' || s >= send - 1 || s == start || d == SvPVX(sv)) {
 
                     /* A regular character.  Process like any other, but first
                      * clear any flags */
-- 
2.13.6