Translate (( n++ )) to sh-expr ' n++ '.

With tests.  Now everything in oil/ should translate.

osh/cmd_parse.py

@@ -1181,10 +1181,17 @@ def ParseDBracket(self):

  def ParseDParen(self):
    maybe_error_word = self.cur_word
    left_spid = word.LeftMostSpanForWord(self.cur_word)

    self._Next()  # skip ((
    anode = self.w_parser.ReadDParen()
    anode, right_spid = self.w_parser.ReadDParen()
    assert anode is not None
    return ast.DParen(anode)

    node = ast.DParen(anode)
    node.spids.append(left_spid)
    node.spids.append(right_spid)

    return node

  def ParseCommand(self):
    """

osh/word_parse.py

@@ -840,7 +840,7 @@ def ReadDParen(self):
            self.cur_token.val, token=self.cur_token)
    self._Next(lex_mode_e.OUTER)

    return anode
    return anode, self.cur_token.span_id

  def _NextNonSpace(self):
    """Same logic as _ReadWord, but for ReadForExpresion."""

test/osh2oil.sh

@@ -966,6 +966,16 @@ echo $<[echo hi] $>[echo hi]
OIL
}

dparen() {
  osh0-oil3 << 'OSH' 3<< 'OIL'
(( n++ ))
echo done
OSH
sh-expr ' n++ '
echo done
OIL
}

arith-sub() {
  # NOTE: This probably needs double quotes?
  osh0-oil3 << 'OSH' 3<< 'OIL'
@@ -981,7 +991,6 @@ echo $[  1+ 2 ]
OSH
echo $(  1+ 2 )
OIL

}

arith-ops() {
@@ -1169,6 +1178,7 @@ readonly -a PASSING=(
  here-doc
  pipeline
  and-or
  dparen

  # Word stuff
  escaped-literal

tools/osh2oil.py

@@ -666,15 +666,17 @@ def DoCommand(self, node, local_symbols, at_top_level=False):
      self.f.write('}')

    elif node.tag == command_e.DParen:
      # TODO: (( a == 0 )) is sh-expr ' a == 0 '
      # (( a == 0 )) is sh-expr ' a == 0 '
      #
      # NOTE: I have a (( n++ )) in one script.  That can be 'set n++' or
      # 'set n += 1'.
      #
      # Auto-translation is:
      #
      # sh-expr 'n++'
      raise NotImplementedError('DParen')
      # NOTE: (( n++ )) is auto-translated to sh-expr 'n++', but could be set
      # n++.
      left_spid, right_spid = node.spids
      self.cursor.PrintUntil(left_spid)
      self.cursor.SkipUntil(left_spid + 1)
      self.f.write("sh-expr '")
      self.cursor.PrintUntil(right_spid - 1)  # before ))
      self.cursor.SkipUntil(right_spid + 1)  # after )) -- each one is a token
      self.f.write("'")

    elif node.tag == command_e.DBracket:
      # [[ 1 -eq 2 ]] to (1 == 2)