From fd0d7059df45012d513f083c01efb289f870343b Mon Sep 17 00:00:00 2001
From: Douglas Brown <doug.brown@alliants.com>
Date: Fri, 9 Sep 2016 18:05:25 -0400
Subject: [PATCH] Prevent Infinite Loop in m.prop.combine

Passing a non-stream value to combine or merge will result in uncaught
errors that are not descriptive enough to be helpful.
---
 util/stream.js            |  2 ++
 util/tests/test-stream.js | 14 ++++++++++++++
 2 files changed, 16 insertions(+)

diff --git a/util/stream.js b/util/stream.js
index a3833526..526ab1c8 100644
--- a/util/stream.js
+++ b/util/stream.js
@@ -116,6 +116,7 @@ module.exports = function(log) {
 		return initDependency(self, [stream], derive, recover)
 	}
 	function combine(fn, streams) {
+		if (streams.length > streams.filter(valid).length) throw new Error("Ensure that each item passed to m.prop.combine/m.prop.merge is a stream")
 		return initDependency(createStream(), streams, function() {
 			var failed = streams.filter(errored)
 			if (failed.length > 0) throw {__error: failed[0]._state.error}
@@ -177,6 +178,7 @@ module.exports = function(log) {
 	function valueOf() {return this._state.value}
 	function toJSON() {return this._state.value != null && typeof this._state.value.toJSON === "function" ? this._state.value.toJSON() : this._state.value}
 
+	function valid(stream) {return stream._state }
 	function active(stream) {return stream._state.state === 1}
 	function changed(stream) {return stream._state.changed}
 	function notEnded(stream) {return stream._state.state !== 2}
diff --git a/util/tests/test-stream.js b/util/tests/test-stream.js
index bd187d77..fc29e396 100644
--- a/util/tests/test-stream.js
+++ b/util/tests/test-stream.js
@@ -171,6 +171,20 @@ o.spec("stream", function() {
 
 			o(b()).equals(undefined)
 		})
+		o("combine will throw with a helpful error if given non-stream values", function () {
+			var spy = o.spy()
+			var a = Stream(1)
+			var thrown = null;
+			try {
+				var b = Stream.combine(spy, [a, ''])
+			} catch (e) {
+				thrown = e
+			}
+
+			o(thrown).notEquals(null)
+			o(thrown.constructor === TypeError).equals(false)
+			o(spy.callCount).equals(0)
+		})
 	})
 	o.spec("merge", function() {
 		o("transforms an array of streams to an array of values", function() {