From bd9920c5714bcfe51f3514d5df7b7b963d846058 Mon Sep 17 00:00:00 2001
From: Tor Andersson <tor.andersson@artifex.com>
Date: Mon, 7 Jan 2019 13:21:36 +0100
Subject: [PATCH] Handle null/undefined in OP_NEXTITER rather than creating
 empty iterator.

Only create an iterator for coercible types in OP_ITERATOR, and then
detect the lack of a real iterator in OP_NEXTITER.
Thus we don't need to allocate and push an empty iterator object for
these cases.
---
 jsproperty.c |  8 --------
 jsrun.c      | 24 ++++++++++++++----------
 jsvalue.h    |  1 -
 3 files changed, 14 insertions(+), 19 deletions(-)

diff --git a/jsproperty.c b/jsproperty.c
index 4aa3a49..a66c433 100644
--- a/jsproperty.c
+++ b/jsproperty.c
@@ -252,14 +252,6 @@ static js_Iterator *itflatten(js_State *J, js_Object *obj)
 	return iter;
 }
 
-js_Object *jsV_emptyiterator(js_State *J)
-{
-	js_Object *io = jsV_newobject(J, JS_CITERATOR, NULL);
-	io->u.iter.target = NULL;
-	io->u.iter.head = NULL;
-	return io;
-}
-
 js_Object *jsV_newiterator(js_State *J, js_Object *obj, int own)
 {
 	char buf[32];
diff --git a/jsrun.c b/jsrun.c
index 68c963e..ac1a1c4 100644
--- a/jsrun.c
+++ b/jsrun.c
@@ -1469,20 +1469,24 @@ static void jsR_run(js_State *J, js_Function *F)
 			break;
 
 		case OP_ITERATOR:
-			if (js_isundefined(J, -1) || js_isnull(J, -1))
-				obj = jsV_emptyiterator(J);
-			else
+			if (js_iscoercible(J, -1)) {
 				obj = jsV_newiterator(J, js_toobject(J, -1), 0);
-			js_pop(J, 1);
-			js_pushobject(J, obj);
+				js_pop(J, 1);
+				js_pushobject(J, obj);
+			}
 			break;
 
 		case OP_NEXTITER:
-			obj = js_toobject(J, -1);
-			str = jsV_nextiterator(J, obj);
-			if (str) {
-				js_pushliteral(J, str);
-				js_pushboolean(J, 1);
+			if (js_isobject(J, -1)) {
+				obj = js_toobject(J, -1);
+				str = jsV_nextiterator(J, obj);
+				if (str) {
+					js_pushliteral(J, str);
+					js_pushboolean(J, 1);
+				} else {
+					js_pop(J, 1);
+					js_pushboolean(J, 0);
+				}
 			} else {
 				js_pop(J, 1);
 				js_pushboolean(J, 0);
diff --git a/jsvalue.h b/jsvalue.h
index 05750c9..09427da 100644
--- a/jsvalue.h
+++ b/jsvalue.h
@@ -173,7 +173,6 @@ js_Property *jsV_setproperty(js_State *J, js_Object *obj, const char *name);
 js_Property *jsV_nextproperty(js_State *J, js_Object *obj, const char *name);
 void jsV_delproperty(js_State *J, js_Object *obj, const char *name);
 
-js_Object *jsV_emptyiterator(js_State *J);
 js_Object *jsV_newiterator(js_State *J, js_Object *obj, int own);
 const char *jsV_nextiterator(js_State *J, js_Object *iter);