Prettify error messages in the BoolParser.

There is less detail now, but the messages look better.  We don't have a
great way to print an arbitrary word, so we just point to a position.

Addresses issue #27 and #103.

osh/bool_parse.py

@@ -43,6 +43,7 @@

lex_mode_e = types.lex_mode_e
log = util.log
p_die = util.p_die


class BoolParser(object):
@@ -125,9 +126,8 @@ def Parse(self):

    node = self.ParseExpr()
    if self.op_id != Id.Lit_DRightBracket:
      self.AddErrorContext("Unexpected extra word %r", self.cur_word,
                           word=self.cur_word)
      return None
      #p_die("Expected ]], got %r", self.cur_word, word=self.cur_word)
      p_die('Expected ]]', word=self.cur_word)
    return node

  def _TestAtEnd(self):
@@ -247,8 +247,7 @@ def ParseFactor(self):

          # doesn't contain $foo, etc.
          if ok and not libc.regex_parse(regex_str):
            self.AddErrorContext("Invalid regex: %r" % regex_str, word=right)
            return None
            p_die("Invalid regex: %r" % regex_str, word=right)

        if not self._Next(): return None
        return ast.BoolBinary(op, left, right)
@@ -268,7 +267,5 @@ def ParseFactor(self):
      if not self._Next(): return None
      return node

    # TODO: A proper error, e.g. for [[ && ]] or [[ ]]
    self.AddErrorContext(
        'Unexpected token: %s' % self.cur_word, word=self.cur_word)
    return None
    # It's not WORD, UNARY_OP, or '('
    p_die('Unexpected token in boolean expression', word=self.cur_word)

osh/cmd_parse.py

@@ -1219,7 +1219,6 @@ def ParseDBracket(self):
    if not bnode:
      error_stack = b_parser.Error()
      self.error_stack.extend(error_stack)
      self.AddErrorContext("Error parsing [[", word=maybe_error_word)
      return None
    return ast.DBracket(bnode)