Issue #1703, - --x

lib/coffee-script/nodes.js

@@ -1579,12 +1579,13 @@
       }).addElse(this.second).compile(o);
     };
     Op.prototype.compileUnary = function(o) {
-      var op, parts;
+      var op, parts, plusMinus;
       parts = [op = this.operator];
-      if ((op === 'new' || op === 'typeof' || op === 'delete') || (op === '+' || op === '-') && this.first instanceof Op && this.first.operator === op) {
+      plusMinus = op === '+' || op === '-';
+      if ((op === 'new' || op === 'typeof' || op === 'delete') || plusMinus && this.first instanceof Op && this.first.operator === op) {
         parts.push(' ');
       }
-      if (op === 'new' && this.first.isStatement(o)) {
+      if ((plusMinus && this.first instanceof Op) || (op === 'new' && this.first.isStatement(o))) {
         this.first = new Parens(this.first);
       }
       parts.push(this.first.compile(o, LEVEL_OP));

src/nodes.coffee

@@ -1366,9 +1366,11 @@ exports.Op = class Op extends Base
   # Compile a unary **Op**.
   compileUnary: (o) ->
     parts = [op = @operator]
+    plusMinus = op in ['+', '-']
     parts.push ' ' if op in ['new', 'typeof', 'delete'] or
-                      op in ['+', '-'] and @first instanceof Op and @first.operator is op
-    @first = new Parens @first if op is 'new' and @first.isStatement o
+                      plusMinus and @first instanceof Op and @first.operator is op
+    if (plusMinus && @first instanceof Op) or (op is 'new' and @first.isStatement o)
+      @first = new Parens @first 
     parts.push @first.compile o, LEVEL_OP
     parts.reverse() if @flip
     parts.join ''

test/operators.coffee

@@ -247,3 +247,7 @@ test "#1234: Applying a splat to :: applies the splat to the wrong object", ->
 test "#1102: String literal prevents line continuation", ->
   eq "': '", '' +
      "': '"
+
+test "#1703, ---x is invalid JS", ->
+  x = 2
+  eq (- --x), -1