Regular expressions does not crash anymore (cont) (#490)

* enhanced type safety on regexp implementation
* fixed memory leak in b2::regex::compiler::regcomp
* fixed crashing of bad regexps, due to attempt to reference a compiled regexp, which has not been compiled due to some error, by b2::regex::program::result_iterator::advance
* added the b2::regex::frame variable for formatting errors when using regexps (especially compilation) and program termination (optional).
* b2::regex::program::result_iterator::operator[] bug on boundary check fixed
* added b2::regex::program::result_iterator::count method, for better regex usability
* better cleanup on abs_workdir.py test
* alternate includes scheme to aid linking
* partially revert of regex include scheme

Author: paolopas

doc/src/history.adoc

@@ -9,6 +9,10 @@
 * *New*: Added test for regular expressions with MATCH builtin rule.
   -- _Paolo Pastori_
 
+* Fix various regexp issues, allowing for mandatory regular expression
+  syntax checking, detailed error messages, and improved MATCH rule.
+  -- _Paolo Pastori_
+
 == Version 5.4.2
 
 Fix detection of Visual Studio 2026 to account for non-native tools being

src/engine/builtins.cpp

@@ -1018,20 +1018,23 @@ LIST * builtin_match( FRAME * frame, int flags )
     b2::list_cref patterns( lol_get( frame->args, 0 ) );
     for ( auto pattern : patterns )
     {
-        b2::regex::program re( pattern->str() );
+        b2::regex::program re;
+        {
+            // compilation errors print a nice error message and exit
+            b2::regex::frame_ctx ctx(frame);
+            re.reset( pattern->str() );
+        }
 
         /* For each text string to match against. */
         b2::list_cref texts( lol_get( frame->args, 1 ) );
         for ( auto text : texts )
         {
             if ( auto re_i = re.search( text->str() ) )
             {
-                /* Find highest parameter */
-                int top = NSUBEXP-1;
-                while ( !re_i[top].begin() ) top -= 1;
-                /* And add all parameters up to highest onto list. */
-                /* Must have parameters to have results! */
-                for ( int i = 1; i <= top ; ++i )
+                /* Find total groups matched */
+                int tot = re_i.count();
+                /* And add all catched matches onto result list. */
+                for ( int i = 1; i <= tot ; ++i )
                 {
                     string_append_range( buf, re_i[i].begin(), re_i[i].end() );
                     result.push_back( object_new( buf->value ) );