From 6332aa1101ab84ec973e393fb046571e535c03a9 Mon Sep 17 00:00:00 2001
From: "Philip.Hazel" <Philip.Hazel@gmail.com>
Date: Wed, 11 Jan 2017 17:02:27 +0000
Subject: [PATCH] Fix pcre2test mishandling "end before start" return with
 POSIX interface.

---
 ChangeLog             |  4 ++++
 src/pcre2test.c       | 21 +++++++++++++++------
 testdata/testinput18  |  3 +++
 testdata/testoutput18 |  6 ++++++
 4 files changed, 28 insertions(+), 6 deletions(-)

diff --git a/ChangeLog b/ChangeLog
index cd7a470..096928a 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -317,6 +317,10 @@ just wastes time. In the UTF case it can also produce redundant entries in
 XCLASS lists caused by characters with multiple other cases and pairs of
 characters in the same "not-x" sublists.
 
+49. A pattern such as /(?=(a\K))/ can report the end of the match being before 
+its start; pcre2test was not handling this correctly when using the POSIX 
+interface (it was OK with the native interface).
+
 
 Version 10.22 29-July-2016
 --------------------------
diff --git a/src/pcre2test.c b/src/pcre2test.c
index d9c8ed8..5ea245d 100644
--- a/src/pcre2test.c
+++ b/src/pcre2test.c
@@ -6184,18 +6184,27 @@ if ((pat_patctl.control & CTL_POSIX) != 0)
       {
       if (pmatch[i].rm_so >= 0)
         {
+        PCRE2_SIZE start = pmatch[i].rm_so;
+        PCRE2_SIZE end = pmatch[i].rm_eo;
+        if (start > end)
+          {
+          start = pmatch[i].rm_eo;
+          end = pmatch[i].rm_so;
+          fprintf(outfile, "Start of matched string is beyond its end - "
+            "displaying from end to start.\n");
+          }
         fprintf(outfile, "%2d: ", (int)i);
-        PCHARSV(pp, pmatch[i].rm_so,
-          pmatch[i].rm_eo - pmatch[i].rm_so, utf, outfile);
+        PCHARSV(pp, start, end - start, utf, outfile);
         fprintf(outfile, "\n");
+
         if ((i == 0 && (dat_datctl.control & CTL_AFTERTEXT) != 0) ||
             (dat_datctl.control & CTL_ALLAFTERTEXT) != 0)
           {
           fprintf(outfile, "%2d+ ", (int)i);
-          PCHARSV(pp, pmatch[i].rm_eo, len - pmatch[i].rm_eo,
-            utf, outfile);
-          fprintf(outfile, "\n");
-          }
+          /* Note: don't use the start/end variables here because we want to
+          show the text from what is reported as the end. */
+          PCHARSV(pp, pmatch[i].rm_eo, len - pmatch[i].rm_eo, utf, outfile);
+          fprintf(outfile, "\n"); }
         }
       }
     }
diff --git a/testdata/testinput18 b/testdata/testinput18
index ea47a4d..bd1c6ad 100644
--- a/testdata/testinput18
+++ b/testdata/testinput18
@@ -106,4 +106,7 @@
 //posix_nosub
     \=offset=70000
 
+/(?=(a\K))/
+    a
+     
 # End of testdata/testinput18
diff --git a/testdata/testoutput18 b/testdata/testoutput18
index 51c7d21..fd6fac3 100644
--- a/testdata/testoutput18
+++ b/testdata/testoutput18
@@ -162,4 +162,10 @@ Failed: POSIX code 4: ? * + invalid at offset 1000001
 ** Ignored with POSIX interface: offset
 Matched with REG_NOSUB
 
+/(?=(a\K))/
+    a
+Start of matched string is beyond its end - displaying from end to start.
+ 0: a
+ 1: a
+     
 # End of testdata/testinput18