* regex.c (at_begline_loc_p): Also recognize `(?N:' and correctly

account for preceding backslashes.  (Bug#11663)

2 files changed, 35 insertions, 11 deletions

diff --git a/src/ChangeLog b/src/ChangeLog
index fb8b2a7b956..919dcc10098 100644
--- a/src/ChangeLog
+++ b/src/ChangeLog
@@ -1,3 +1,8 @@
+2012-06-10  Andreas Schwab  <schwab@linux-m68k.org>
+
+        * regex.c (at_begline_loc_p): Also recognize `(?N:' and correctly
+        account for preceding backslashes.  (Bug#11663)
+
 2012-06-09  Chong Yidong  <cyd@gnu.org>
 
         * term.c: Support italics in capable terminals (Bug#9652).
diff --git a/src/regex.c b/src/regex.c
index f9a12a3c2dc..0dd3a187898 100644
--- a/src/regex.c
+++ b/src/regex.c
@@ -3824,18 +3824,37 @@ static boolean
 at_begline_loc_p (const re_char *pattern, const re_char *p, reg_syntax_t syntax)
 {
   re_char *prev = p - 2;
-  boolean prev_prev_backslash = prev > pattern && prev[-1] == '\\';
+  boolean odd_backslashes;
 
-  return
-       /* After a subexpression?  */
-       (*prev == '(' && (syntax & RE_NO_BK_PARENS || prev_prev_backslash))
-       /* After an alternative?  */
-    || (*prev == '|' && (syntax & RE_NO_BK_VBAR || prev_prev_backslash))
-       /* After a shy subexpression?  */
-    || ((syntax & RE_SHY_GROUPS) && prev - 2 >= pattern
-        && prev[-1] == '?' && prev[-2] == '('
-        && (syntax & RE_NO_BK_PARENS
-            || (prev - 3 >= pattern && prev[-3] == '\\')));
+  /* After a subexpression?  */
+  if (*prev == '(')
+    odd_backslashes = (syntax & RE_NO_BK_PARENS) == 0;
+
+  /* After an alternative?  */
+  else if (*prev == '|')
+    odd_backslashes = (syntax & RE_NO_BK_VBAR) == 0;
+
+  /* After a shy subexpression?  */
+  else if (*prev == ':' && (syntax & RE_SHY_GROUPS))
+    {
+      /* Skip over optional regnum.  */
+      while (prev - 1 >= pattern && prev[-1] >= '0' && prev[-1] <= '9')
+        --prev;
+
+      if (!(prev - 2 >= pattern
+            && prev[-1] == '?' && prev[-2] == '('))
+        return false;
+      prev -= 2;
+      odd_backslashes = (syntax & RE_NO_BK_PARENS) == 0;
+    }
+  else
+    return false;
+
+  /* Count the number of preceding backslashes.  */
+  p = prev;
+  while (prev - 1 >= pattern && prev[-1] == '\\')
+    --prev;
+  return (p - prev) & odd_backslashes;
 }