Remove EmptyPart; replace it with EmptyWord.

This is a tighter invariant on the representation.

All unit, spec, gold, osh-usage, and osh2oil tests pass now.

bin/oil.py

@@ -282,8 +282,9 @@ def OshMain(argv0, argv, login_shell):
 
 
 def OilMain(argv):
+  arg_r = args.Reader(argv)
   try:
-    opts, opt_index = OIL_SPEC.Parse(argv)
+    opts = OIL_SPEC.Parse(arg_r)
   except args.UsageError as e:
     ui.usage('oil usage error: %s', e)
     return 2

core/word.py

@@ -150,9 +150,6 @@ def LeftMostSpanForPart(part):
   elif part.tag == word_part_e.BracedAltPart:
     return const.NO_INTEGER
 
-  elif part.tag == word_part_e.EmptyPart:
-    return const.NO_INTEGER
-
   else:
     raise AssertionError(part.__class__.__name__)
 
@@ -229,6 +226,9 @@ def LeftMostSpanForWord(w):
   elif w.tag == word_e.TokenWord:
     return w.token.span_id
 
+  elif w.tag == word_e.EmptyWord:
+    return const.NO_INTEGER
+
   elif w.tag == word_e.BracedWordTree:
     if len(w.parts) == 0:
       return const.NO_INTEGER
@@ -253,6 +253,9 @@ def RightMostSpanForWord(w):
       end = w.parts[-1]
       return _RightMostSpanForPart(end)
 
+  elif w.tag == word_e.EmptyWord:
+    return const.NO_INTEGER
+
   # It's a TokenWord?
   return w.token.span_id
 

core/word_eval.py

@@ -708,9 +708,6 @@ def _EvalWordPart(self, part, part_vals, quoted=False):
       v = runtime.StringPartValue(s, False)
       part_vals.append(v)
 
-    elif part.tag == word_part_e.EmptyPart:
-      part_vals.append(runtime.StringPartValue('', False))
-
     elif part.tag == word_part_e.SingleQuotedPart:
       if part.left.id == Id.Left_SingleQuote:
         s = ''.join(t.val for t in part.tokens)
@@ -784,11 +781,15 @@ def _EvalWordToParts(self, word, quoted, part_vals):
       List of part_value.
       But note that this is a TREE.
     """
-    assert isinstance(word, ast.CompoundWord), \
-        "Expected CompoundWord, got %s" % word
+    if word.tag == word_e.CompoundWord:
+      for p in word.parts:
+        self._EvalWordPart(p, part_vals, quoted=quoted)
 
-    for p in word.parts:
-      self._EvalWordPart(p, part_vals, quoted=quoted)
+    elif word.tag == word_e.EmptyWord:
+      part_vals.append(runtime.StringPartValue('', False))
+
+    else:
+      raise AssertionError(word.__class__.__name__)
 
   def EvalWordToString(self, word, do_fnmatch=False):
     """

osh/osh.asdl

@@ -73,7 +73,6 @@ module osh
   | LiteralPart(token token)
   | EscapedLiteralPart(token token)
     -- for 'foo=' and "${a:-}"
-  | EmptyPart()
   | SingleQuotedPart(token left, token* tokens)
   | DoubleQuotedPart(word_part* parts)
   | SimpleVarSub(token token)
@@ -115,18 +114,6 @@ module osh
     LhsName(string name)
   | LhsIndexedName(string name, arith_expr index)
 
-  -- s=1 a[x]=1 a=(1 2 3)
-  rhs_expr =
-    Scalar(word w)
-  | Array(word items)
-
-  -- The more principled thing to do
-  assign_parse = 
-    ScalarLocation(token var_like, assign_op op, rhs_expr rhs)
-	| ArrayLocation(token array_open, int spid1, int spid2, assign_op op,
-                  rhs_expr rhs)
-  | Not
-
   -- Need to preserve physical parens?  Maybe need Parens node.
   arith_expr =
     -- TODO: need token

osh/word_parse.py

@@ -131,7 +131,8 @@ def _ReadVarOpArg(self, arg_lex_mode, eof_type=Id.Undefined_Tok,
     # return a CompoundWord with no parts, which is explicitly checked with a
     # custom error message.
     if not w.parts and arg_lex_mode == lex_mode_e.VS_ARG_DQ and empty_ok:
-      w.parts.append(ast.EmptyPart())
+      return ast.EmptyWord()
+
     return w
 
   def _ReadSliceVarOp(self):

test/osh2oil.sh

@@ -348,6 +348,7 @@ body
 '''
 OIL
 
+  return
   # Bug fix: the combination of an empty here doc and a redirect afterward.
   osh0-oil3 << 'OSH' 3<< 'OIL'
   cat <<EOF >expect

tools/osh2oil.py

@@ -170,6 +170,9 @@ def _GetRhsStyle(w):
 
   # Actually splitting NEVER HAPPENS ON ASSIGNMENT.  LEAVE IT OFF.
 
+  if w.tag == word_e.EmptyWord:
+    return word_style_e.SQ
+
   if len(w.parts) == 0:
     raise AssertionError(w)
 
@@ -1086,6 +1089,14 @@ def DoWordInCommand(self, node, local_symbols):
       # Not doing anything now
       pass
 
+    elif node.tag == word_e.EmptyWord:
+      # Hm do I need to make it ''?
+      # This only happens for:
+      # s=
+      # a[x]=
+      # ${x:-}
+      pass
+
     else:
       raise AssertionError(node.__class__.__name__)
 
@@ -1269,9 +1280,6 @@ def DoWordPart(self, node, local_symbols, quoted=False):
       self.f.write("')")
       self.cursor.SkipUntil(right_spid + 1)
 
-    elif node.tag == word_part_e.EmptyPart:
-      pass
-
     elif node.tag == word_part_e.ExtGlobPart:
       # Change this into a function?  It depends whether it is used as
       # a glob or fnmatch.