Fix handling of global matching in pcre2test when a lookbehind assertion

contains \K.

ChangeLog

@@ -70,6 +70,9 @@ lookbehind assertion. This bug was discovered by the LLVM fuzzer.
 17. The use of \K in a positive lookbehind assertion in a non-anchored pattern
 (e.g. /(?<=\Ka)/) could make pcre2grep loop.
 
+18. There was a similar problem to 17 in pcre2test for global matches, though
+the code there did catch the loop.
+
 
 Version 10.10 06-March-2015
 ---------------------------

src/pcre2test.c

@@ -5684,20 +5684,20 @@ else for (gmatched = 0;; gmatched++)
 
   ovector = FLD(match_data, ovector);
 
-  /* After the first time round a global loop, save the current ovector[0,1] so
-  that we can check that they do change each time. Otherwise a matching bug
-  that returns the same string causes an infinite loop. It has happened! */
+  /* After the first time round a global loop, for a normal global (/g)
+  iteration, save the current ovector[0,1] so that we can check that they do
+  change each time. Otherwise a matching bug that returns the same string
+  causes an infinite loop. It has happened! */
 
-  if (gmatched > 0)
+  if (gmatched > 0 && (dat_datctl.control & CTL_GLOBAL) != 0)
     {
     ovecsave[0] = ovector[0];
     ovecsave[1] = ovector[1];
     }
 
-  /* Set the variables on the first iteration, just to stop a compiler warning
-  when ovecsave[] is referenced below. */
+  /* For altglobal (or first time round the loop), set an "unset" value. */
 
-  else ovecsave[0] = ovecsave[1] = 0;
+  else ovecsave[0] = ovecsave[1] = PCRE2_UNSET;
 
   /* Fill the ovector with junk to detect elements that do not get set
   when they should be. */
@@ -6169,13 +6169,48 @@ else for (gmatched = 0;; gmatched++)
       if (end_offset == ulen) break;      /* End of subject */
       g_notempty = PCRE2_NOTEMPTY_ATSTART | PCRE2_ANCHORED;
       }
-    else g_notempty = 0;
 
-    /* For /g, update the start offset, leaving the rest alone */
+    /* However, even after matching a non-empty string, there is still one
+    tricky case. If a pattern contains \K within a lookbehind assertion at the
+    start, the end of the matched string can be at the offset where the match
+    started. In the case of a normal /g iteration without special action, this
+    leads to a loop that keeps on returning the same substring. The loop would
+    be caught above, but we really want to move on to the next match. */
 
-    if ((dat_datctl.control & CTL_GLOBAL) != 0) dat_datctl.offset = end_offset;
+    else
+      {
+      g_notempty = 0;   /* Set for a "normal" repeat */
+      if ((dat_datctl.control & CTL_GLOBAL) != 0)
+        {
+        PCRE2_SIZE startchar;
+        PCRE2_GET_STARTCHAR(startchar, match_data);
+        if (end_offset <= startchar)
+          {
+          if (startchar >= ulen) break;       /* End of subject */
+          end_offset = startchar + 1;
+          if (utf && test_mode != PCRE32_MODE)
+            {
+            if (test_mode == PCRE8_MODE)
+              {
+              for (; end_offset < ulen; end_offset++)
+                if ((((PCRE2_SPTR8)pp)[end_offset] & 0xc0) != 0x80) break;
+              }
+            else  /* 16-bit mode */
+              {
+              for (; end_offset < ulen; end_offset++)
+                if ((((PCRE2_SPTR16)pp)[end_offset] & 0xfc00) != 0xdc00) break;
+              }
+            }
+          }
+        }
+      }
 
-    /* For /G, update the pointer and length */
+    /* For /g (global), update the start offset, leaving the rest alone. */
+
+    if ((dat_datctl.control & CTL_GLOBAL) != 0)
+      dat_datctl.offset = end_offset;
+
+    /* For altglobal, just update the pointer and length. */
 
     else
       {

testdata/testinput2

@@ -4255,4 +4255,12 @@ a random value. /Ix
 
 ";(?<=()((?3))((?2)))"
 
+# Perl loops on this (PCRE2 used to!)
+
+/(?<=\Ka)/g,aftertext
+    aaaaa
+
+/(?<=\Ka)/altglobal,aftertext
+    aaaaa
+
 # End of testinput2 

testdata/testinput5

@@ -1641,4 +1641,10 @@
 /[A-`]/iB,utf
     abcdefghijklmno
 
+/(?<=\K\x{17f})/g,utf,aftertext
+    \x{17f}\x{17f}\x{17f}\x{17f}\x{17f}
+
+/(?<=\K\x{17f})/altglobal,utf,aftertext
+    \x{17f}\x{17f}\x{17f}\x{17f}\x{17f}
+
 # End of testinput5 

testdata/testoutput2

@@ -14260,4 +14260,32 @@ Failed: error 115 at offset 15: reference to non-existent subpattern
 ";(?<=()((?3))((?2)))"
 Failed: error 125 at offset 20: lookbehind assertion is not fixed length
 
+# Perl loops on this (PCRE2 used to!)
+
+/(?<=\Ka)/g,aftertext
+    aaaaa
+ 0: a
+ 0+ aaaa
+ 0: a
+ 0+ aaa
+ 0: a
+ 0+ aa
+ 0: a
+ 0+ a
+ 0: a
+ 0+ 
+
+/(?<=\Ka)/altglobal,aftertext
+    aaaaa
+ 0: a
+ 0+ aaaa
+ 0: a
+ 0+ aaa
+ 0: a
+ 0+ aa
+ 0: a
+ 0+ a
+ 0: a
+ 0+ 
+
 # End of testinput2 

testdata/testoutput5

@@ -4019,4 +4019,30 @@ Failed: error 140 at offset 11: recursion could loop indefinitely
     abcdefghijklmno
  0: a
 
+/(?<=\K\x{17f})/g,utf,aftertext
+    \x{17f}\x{17f}\x{17f}\x{17f}\x{17f}
+ 0: \x{17f}
+ 0+ \x{17f}\x{17f}\x{17f}\x{17f}
+ 0: \x{17f}
+ 0+ \x{17f}\x{17f}\x{17f}
+ 0: \x{17f}
+ 0+ \x{17f}\x{17f}
+ 0: \x{17f}
+ 0+ \x{17f}
+ 0: \x{17f}
+ 0+ 
+
+/(?<=\K\x{17f})/altglobal,utf,aftertext
+    \x{17f}\x{17f}\x{17f}\x{17f}\x{17f}
+ 0: \x{17f}
+ 0+ \x{17f}\x{17f}\x{17f}\x{17f}
+ 0: \x{17f}
+ 0+ \x{17f}\x{17f}\x{17f}
+ 0: \x{17f}
+ 0+ \x{17f}\x{17f}
+ 0: \x{17f}
+ 0+ \x{17f}
+ 0: \x{17f}
+ 0+ 
+
 # End of testinput5