Fixed regexp compilation of patterns with escaped '[' characters.

[xeioex]

This fixes #934 issue on Github.

[VadimZhestikov]

It would be nice fix bug in processing regexp /[[]/ as well:

>> /[[]/
Thrown:
SyntaxError: pcre_compile2("[(?!)") failed: missing terminating ] for character class at "" in shell:1
>> /[[^]/
/[[\s\S]/
>>

It could be something like this before your fix:

diff --git a/external/njs_regex.c b/external/njs_regex.c
index a118666b..59e864be 100644
--- a/external/njs_regex.c
+++ b/external/njs_regex.c
@@ -112,18 +112,29 @@ njs_regex_escape(njs_mp_t *mp, njs_str_t *text)
     anychars = 0;
     nomatches = 0;

+    njs_bool_t in;
+
+    in  = 0;
+
     for (p = start; p < end; p++) {
         switch (*p) {
         case '[':
-            if (p + 1 < end && p[1] == ']') {
-                p += 1;
-                nomatches += 1;
-
-            } else if (p + 2 < end && p[1] == '^' && p[2] == ']') {
-                p += 2;
-                anychars += 1;
+            if (!in) {
+                if (p + 1 < end && p[1] == ']') {
+                    p += 1;
+                    nomatches += 1;
+                    break;
+
+                } else if (p + 2 < end && p[1] == '^' && p[2] == ']') {
+                    p += 2;
+                    anychars += 1;
+                    break;
+                }
             }
-
+            in = 1;
+            break;
+        case ']':
+            in = 0;
             break;
         }
     }
@@ -143,20 +154,29 @@ njs_regex_escape(njs_mp_t *mp, njs_str_t *text)

     dst = text->start;

+    in = 0;
+
     for (p = start; p < end; p++) {

         switch (*p) {
         case '[':
-            if (p + 1 < end && p[1] == ']') {
-                p += 1;
-                dst = njs_cpymem(dst, "(?!)", 4);
-                continue;
-
-            } else if (p + 2 < end && p[1] == '^' && p[2] == ']') {
-                p += 2;
-                dst = njs_cpymem(dst, "[\\s\\S]", 6);
-                continue;
+            if (!in) {
+                if (p + 1 < end && p[1] == ']') {
+                    p += 1;
+                    dst = njs_cpymem(dst, "(?!)", 4);
+                    continue;
+
+                } else if (p + 2 < end && p[1] == '^' && p[2] == ']') {
+                    p += 2;
+                    dst = njs_cpymem(dst, "[\\s\\S]", 6);
+                    continue;
+                }
             }
+            in = 1;
+            break;
+        case ']':
+            in = 0;
+            break;
         }

         *dst++ = *p;

[VadimZhestikov]

Looks good