Catch exceptions thrown from template helpers

packages/blaze/exceptions.js

@@ -1,11 +1,6 @@
-// XXX This is dead code but we should probably still do something like this.
-// Change "Meteor UI" to "Blaze".  Actually, "Exception in Blaze" is cryptic
-// and misleading; better to make it clear the fault is in user code, as in
-// "Exception in 'created' callback" etc.
-
 var debugFunc;
 
-// Meteor UI calls into user code in many places, and it's nice to catch exceptions
+// We call into user code in many places, and it's nice to catch exceptions
 // propagated from user code immediately so that the whole system doesn't just
 // break.  Catching exceptions is easy; reporting them is hard.  This helper
 // reports exceptions.
@@ -22,7 +17,7 @@ var debugFunc;
 //
 // An optional second argument overrides the default message.
 
-reportUIException = function (e, msg) {
+Blaze.reportException = function (e, msg) {
   if (! debugFunc)
     // adapted from Deps
     debugFunc = function () {
@@ -34,5 +29,18 @@ reportUIException = function (e, msg) {
   // In Chrome, `e.stack` is a multiline string that starts with the message
   // and contains a stack trace.  Furthermore, `console.log` makes it clickable.
   // `console.log` supplies the space between the two arguments.
-  debugFunc()(msg || 'Exception in Meteor UI:', e.stack || e.message);
+  debugFunc()(msg || 'Exception caught in template:', e.stack || e.message);
+};
+
+Blaze.wrapCatchingExceptions = function (f, where) {
+  if (typeof f !== 'function')
+    return f;
+
+  return function () {
+    try {
+      return f.apply(this, arguments);
+    } catch (e) {
+      Blaze.reportException(e, 'Exception in ' + where + ':');
+    }
+  };
 };

packages/blaze/lookup.js

@@ -18,6 +18,10 @@ var bindToCurrentDataIfIsFunction = function (x) {
   return x;
 };
 
+var wrapHelper = function (f) {
+  return Blaze.wrapCatchingExceptions(f, 'template helper');
+};
+
 // Implements {{foo}} where `name` is "foo"
 // and `component` is the component the tag is found in
 // (the lexical "self," on which to look for methods).
@@ -37,15 +41,15 @@ Blaze.View.prototype.lookup = function (name, _options) {
     return Blaze._parentData(name.length - 1);
 
   } else if (template && (name in template)) {
-    return bindToCurrentDataIfIsFunction(template[name]);
+    return wrapHelper(bindToCurrentDataIfIsFunction(template[name]));
   } else if (lookupTemplate && Template.__lookup__(name)) {
     return Template.__lookup__(name);
   } else if (UI._globalHelpers[name]) {
-    return bindToCurrentDataIfIsFunction(UI._globalHelpers[name]);
+    return wrapHelper(bindToCurrentDataIfIsFunction(UI._globalHelpers[name]));
   } else {
     var data = Blaze.getCurrentData();
     if (data)
-      return bindIfIsFunction(data[name], data);
+      return wrapHelper(bindIfIsFunction(data[name], data));
   }
   return null;
 };

packages/blaze/package.js

@@ -27,6 +27,7 @@ Package.on_use(function (api) {
 
   // client and server
   api.add_files([
+    'exceptions.js',
     'reactivevar.js',
     'view.js',
     'builtins.js',