From 95aaa99312d19e5d7fac866dead4d484b000131b Mon Sep 17 00:00:00 2001
From: Avital Oliver <avital@thewe.net>
Date: Sat, 19 Apr 2014 00:21:01 -0700
Subject: [PATCH] Fix {{#with}} over a data context that is mutated

In `Spacebars.With` we embox the data context. This commit makes
that emboxing happen modulo `safeEquals`. So now if you
{{#with}} over a helper that returns an object, any time
that helper gets invalidated we re-run the computations in the block.

Fixes #2046 (though notably that example mutates the data context
from within a helper, which could lead to other types of unintended
behavior; it's probably in this particular example -- the data context
just gets added properties)
---
 packages/spacebars-tests/template_tests.html |  6 +++++
 packages/spacebars-tests/template_tests.js   | 23 +++++++++++++++++++-
 packages/spacebars/spacebars-runtime.js      |  2 +-
 packages/ui/builtins.js                      |  4 ++--
 4 files changed, 31 insertions(+), 4 deletions(-)

diff --git a/packages/spacebars-tests/template_tests.html b/packages/spacebars-tests/template_tests.html
index 05256a6bb5..dbec7e2fbb 100644
--- a/packages/spacebars-tests/template_tests.html
+++ b/packages/spacebars-tests/template_tests.html
@@ -712,3 +712,9 @@ Hi there!
     {{bar}}
   --}}
 </template>
+
+<template name="spacebars_test_with_mutated_data_context">
+  {{#with foo}}
+    {{value}}
+  {{/with}}
+</template>
diff --git a/packages/spacebars-tests/template_tests.js b/packages/spacebars-tests/template_tests.js
index e6b570e6fb..93f1b646ff 100644
--- a/packages/spacebars-tests/template_tests.js
+++ b/packages/spacebars-tests/template_tests.js
@@ -1877,7 +1877,7 @@ Tinytest.add(
   }
 );
 
-Tinytest.add("spacebars - templates - UI.toHTML", function (test) {
+Tinytest.add("spacebars - template - UI.toHTML", function (test) {
   // run once, verifying that autoruns are stopped
   var once = function (tmplToRender, tmplForHelper, helper, val) {
     var count = 0;
@@ -1919,3 +1919,24 @@ Tinytest.add(
     test.equal(canonicalizeHtml(div.innerHTML), '');
   }
 );
+
+// Originally reported at https://github.com/meteor/meteor/issues/2046
+Tinytest.add(
+  "spacebars - template - {{#with}} with mutated data context",
+  function (test) {
+    var tmpl = Template.spacebars_test_with_mutated_data_context;
+    var foo = {value: 0};
+    var dep = new Deps.Dependency;
+    tmpl.foo = function () {
+      dep.depend();
+      return foo;
+    };
+
+    var div = renderToDiv(tmpl);
+    test.equal(canonicalizeHtml(div.innerHTML), '0');
+
+    foo.value = 1;
+    dep.changed();
+    Deps.flush();
+    test.equal(canonicalizeHtml(div.innerHTML), '1');
+  });
diff --git a/packages/spacebars/spacebars-runtime.js b/packages/spacebars/spacebars-runtime.js
index 120356753b..59c2f37a47 100644
--- a/packages/spacebars/spacebars-runtime.js
+++ b/packages/spacebars/spacebars-runtime.js
@@ -216,7 +216,7 @@ Spacebars.dot = function (value, id1/*, id2, ...*/) {
 Spacebars.With = function (argFunc, contentBlock, elseContentBlock) {
   return UI.Component.extend({
     init: function () {
-      this.v = UI.emboxValue(argFunc);
+      this.v = UI.emboxValue(argFunc, UI.safeEquals);
     },
     render: function () {
       return UI.If(this.v, UI.With(this.v, contentBlock), elseContentBlock);
diff --git a/packages/ui/builtins.js b/packages/ui/builtins.js
index a97bead067..2ba0da6f48 100644
--- a/packages/ui/builtins.js
+++ b/packages/ui/builtins.js
@@ -38,7 +38,7 @@ UI.Unless = function (argFunc, contentBlock, elseContentBlock) {
 // (Because then, they may be equal references to an object that was mutated,
 // and we'll never know.  We save only a reference to the old object; we don't
 // do any deep-copying or diffing.)
-var safeEquals = function (a, b) {
+UI.safeEquals = function (a, b) {
   if (a !== b)
     return false;
   else
@@ -67,7 +67,7 @@ UI.With = function (argFunc, contentBlock) {
   };
 
   block.init = function () {
-    this.data = UI.emboxValue(argFunc, safeEquals);
+    this.data = UI.emboxValue(argFunc, UI.safeEquals);
   };
 
   block.materialized = function () {