Handle undefined variables in underscore templates

Author: geoffp

core/lib/pattern_engines/engine_underscore.js

@@ -53,10 +53,24 @@
     // render it
     renderPattern: function renderPattern(template, data, partials) {
       var compiled = _.template(template);
-      return compiled(_.extend(data, {
-        _allData: data,
-        _partials: partials
-      }));
+      var renderedHTML;
+
+      // This try-catch is necessary because references to undefined variables
+      // in underscore templates are eval()ed directly as javascript, and as
+      // such will throw very real exceptions that will shatter the whole build
+      // process if we don't handle them.
+      try {
+        renderedHTML = compiled(_.extend(data || {}, {
+          _allData: data,
+          _partials: partials
+        }));
+      } catch (e) {
+        var errorMessage = "WARNING: the underscore template " + template.fileName + " threw an exception; it probably just tried to reference an undefined variable. Is this pattern maybe missing a .json file?";
+        console.log(errorMessage, e);
+        renderedHTML = "<h1>Error in underscore template</h1>" + errorMessage;
+      }
+
+      return renderedHTML;
     },
 
     // registerPartial: function (oPattern) {