make {|/ "" /|} equivalent to {|/ bos eos /|}

Author: zazedd

common/mik_lexer.mll

@@ -99,6 +99,7 @@ rule token = parse
       | None -> IDENT id
     }
   | '\'' { char_literal (Buffer.create 16) lexbuf }
+  | "\"\"" { EMPTY_STR }
   | '"' { string_literal (Buffer.create 16) lexbuf }
   | eof { EOF }
   | _ as c { raise (Error ("Unexpected character: " ^ String.make 1 c)) }

common/mik_parser.mly

@@ -42,7 +42,7 @@ let unclosed_error what startpos endpos =
 
 %token <string> CHAR_LITERAL STRING_LITERAL IDENT MOD_IDENT PREDEFINED_CLASS
 %token <int> INT
-%token SLASH LPAREN RPAREN LBRACKET RBRACKET CARET LBRACE RBRACE
+%token SLASH LPAREN RPAREN LBRACKET RBRACKET CARET LBRACE RBRACE EMPTY_STR
 %token DASH BAR STAR PLUS QUESTION UNDERSCORE COLON EQUAL AS PIPE
 %token INT_CONVERTER FLOAT_CONVERTER EOF
 
@@ -136,6 +136,9 @@ basic_atom:
   | STRING_LITERAL {
       to_pcre_regex $1 $startpos $endpos
     }
+  | EMPTY_STR {
+      to_pcre_regex "^$" $startpos $endpos
+    }
   | UNDERSCORE {
       to_pcre_regex "." $startpos $endpos
     }