From 8b2c642df1d3d7e348afd20e4656152fe79ed907 Mon Sep 17 00:00:00 2001
From: David Greenspan <dgreenspan@alum.mit.edu>
Date: Wed, 1 Apr 2015 15:36:04 -0700
Subject: [PATCH] Fix #4097: error when View invalidated immediately

Bug introduced in 28c760e
---
 packages/blaze/view.js                       |  4 +++-
 packages/spacebars-tests/template_tests.html |  4 ++++
 packages/spacebars-tests/template_tests.js   | 24 ++++++++++++++++++++
 3 files changed, 31 insertions(+), 1 deletion(-)

diff --git a/packages/blaze/view.js b/packages/blaze/view.js
index b5c105c6e9..63d32083de 100644
--- a/packages/blaze/view.js
+++ b/packages/blaze/view.js
@@ -354,7 +354,9 @@ Blaze._materializeView = function (view, parentView, _workStack, _intoArray) {
       // helpers in the DOM tree to be replaced might be scheduled
       // to re-run before we have a chance to stop them.
       Tracker.onInvalidate(function () {
-        domrange.destroyMembers();
+        if (domrange) {
+          domrange.destroyMembers();
+        }
       });
     }, undefined, 'materialize');
 
diff --git a/packages/spacebars-tests/template_tests.html b/packages/spacebars-tests/template_tests.html
index 6ff3a5582a..d5260e05c1 100644
--- a/packages/spacebars-tests/template_tests.html
+++ b/packages/spacebars-tests/template_tests.html
@@ -32,6 +32,10 @@
   {{/if}}
 </template>
 
+<template name="spacebars_template_test_bracketed_foo">
+  [{{foo}}]
+</template>
+
 <!-- -->
 
 
diff --git a/packages/spacebars-tests/template_tests.js b/packages/spacebars-tests/template_tests.js
index b68a491bc0..436ba072e8 100644
--- a/packages/spacebars-tests/template_tests.js
+++ b/packages/spacebars-tests/template_tests.js
@@ -2749,6 +2749,30 @@ Tinytest.add('spacebars-tests - template_tests - current view in event handler',
 });
 
 
+Tinytest.add('spacebars-tests - template_tests - helper invalidates self', function (test) {
+  var tmpl = Template.spacebars_template_test_bracketed_foo;
+
+  var count = new ReactiveVar(0);
+
+  tmpl.helpers({
+    // It's unusual for a helper to have side effects, but it's possible
+    // and people do it.  Regression test for #4097.
+    foo: function () {
+      // Make count odd and return it.
+      var c = count.get();
+      if ((c % 2) === 0) {
+        count.set(c+1);
+      }
+      return c;
+    }
+  });
+
+  var div = renderToDiv(tmpl);
+  divRendersTo(test, div, '[1]');
+  count.set(2);
+  divRendersTo(test, div, '[3]');
+});
+
 Tinytest.add(
   "spacebars-tests - template_tests - textarea attrs", function (test) {
     var tmplNoContents = {