Issue #1354, 'in' with splatted arrays.

lib/nodes.js

@@ -1727,7 +1727,18 @@
     In.prototype.children = ['object', 'array'];
     In.prototype.invert = NEGATE;
     In.prototype.compileNode = function(o) {
-      if (this.array instanceof Value && this.array.isArray()) {
+      var isArray, obj, splat, _i, _len, _ref2;
+      isArray = this.array instanceof Value && this.array.isArray();
+      if (isArray) {
+        _ref2 = this.array.base.objects;
+        for (_i = 0, _len = _ref2.length; _i < _len; _i++) {
+          obj = _ref2[_i];
+          if (obj instanceof Splat) {
+            splat = obj;
+          }
+        }
+      }
+      if (isArray && !splat) {
         return this.compileOrTest(o);
       } else {
         return this.compileLoopTest(o);

src/nodes.coffee

@@ -1355,7 +1355,9 @@ exports.In = class In extends Base
   invert: NEGATE
 
   compileNode: (o) ->
-    if @array instanceof Value and @array.isArray()
+    isArray = @array instanceof Value and @array.isArray()
+    splat   = obj for obj in @array.base.objects when obj instanceof Splat if isArray
+    if isArray and not splat
       @compileOrTest o
     else
       @compileLoopTest o

test/operators.coffee

@@ -187,6 +187,10 @@ test "#768: `in` should preserve evaluation order", ->
 test "#1099: empty array after `in` should compile to `false`", ->
   eq 1, [5 in []].length
   eq false, do -> return 0 in []
+  
+test "#1354: optimized `in` checks should not happen when splats are present", ->
+  a = [6, 9]
+  eq 9 in [3, a...], true
 
 
 # Chained Comparison