Updating the pull request.

lib.coffee

@@ -21,8 +21,10 @@ Blaze._getTemplateHelper = (template, name, templateInstance) ->
     helper = template.__helpers.get name
     if helper is Blaze._OLDSTYLE_HELPER
       isKnownOldStyleHelper = true
+    else if helper?
+      return wrapHelper bindDataContext(helper), templateInstance
     else
-      return helper
+      return null
 
   # Old-style helper.
   if name of template
@@ -31,31 +33,55 @@ Blaze._getTemplateHelper = (template, name, templateInstance) ->
       template.__helpers.set name, Blaze._OLDSTYLE_HELPER
       unless template._NOWARN_OLDSTYLE_HELPERS
         Blaze._warn "Assigning helper with `" + template.viewName + "." + name + " = ...` is deprecated.  Use `" + template.viewName + ".helpers(...)` instead."
-    return template[name]
+    if template[name]?
+      return wrapHelper bindDataContext(template[name]), templateInstance
+    else
+      return null
 
   return null unless templateInstance
 
   # TODO: Blaze.View::lookup should not introduce any reactive dependencies. Can we simply ignore reactivity here? Can this template instance or parent template instances change without reconstructing the component as well? I don't think so. Only data context is changing and this is why templateInstance or .get() are reactive and we do not care about data context here.
   component = Tracker.nonreactive ->
-    templateInstance = templateInstance()
-    templateInstance.get 'component'
+    templateInstance().get 'component'
 
   # Component.
   if component
     if name of component
-      return wrapHelper component, component[name]
+      return wrapHelper bindComponent(component, component[name]), templateInstance
 
     if mixin = component.getMixinWith null, name
-      return wrapHelper mixin, mixin[name]
+      return wrapHelper bindComponent(mixin, mixin[name]), templateInstance
 
   null
 
-wrapHelper = (component, helper) ->
+bindComponent = (component, helper) ->
   if _.isFunction helper
     _.bind helper, component
   else
     helper
 
+bindDataContext = (helper) ->
+  if _.isFunction helper
+    ->
+      data = Blaze.getData()
+      data ?= {}
+      helper.apply data, arguments
+  else
+    helper
+
+wrapHelper = (f, templateFunc) ->
+  # XXX COMPAT WITH METEOR 1.0.3.2
+  return Blaze._wrapCatchingExceptions f, 'template helper' unless Blaze.Template._withTemplateInstanceFunc
+
+  return f unless _.isFunction f
+
+  ->
+    self = @
+    args = arguments
+
+    Blaze.Template._withTemplateInstanceFunc templateFunc, ->
+      Blaze._wrapCatchingExceptions(f, 'template helper').apply self, args
+
 viewToTemplateInstance = (view) ->
   # We skip contentBlock views which are injected by Meteor when using
   # block helpers (in addition to block helper view). This matches more

lookup.js

@@ -26,8 +26,10 @@ Blaze._getTemplateHelper = function (template, name, templateInstance) {
     var helper = template.__helpers.get(name);
     if (helper === Blaze._OLDSTYLE_HELPER) {
       isKnownOldStyleHelper = true;
+    } else if (helper != null) {
+      return wrapHelper(bindDataContext(helper), templateInstance);
     } else {
-      return helper;
+      return null;
     }
   }
 
@@ -42,7 +44,9 @@ Blaze._getTemplateHelper = function (template, name, templateInstance) {
                     '.helpers(...)` instead.');
       }
     }
-    return template[name];
+    if (template[name] != null) {
+      return wrapHelper(bindDataContext(template[name]), templateInstance);
+    }
   }
 
   return null;
@@ -98,7 +102,7 @@ Blaze.View.prototype.lookup = function (name, _options) {
 
   } else if (template &&
              ((helper = Blaze._getTemplateHelper(template, name, boundTmplInstance)) != null)) {
-    return wrapHelper(bindDataContext(helper), boundTmplInstance);
+    return helper;
   } else if (lookupTemplate &&
              ((foundTemplate = Blaze._getTemplate(name, boundTmplInstance)) != null)) {
     return foundTemplate;