Fix issue where sync render would not raise errors in included templates

fixes #1272

CHANGELOG.md

@@ -18,6 +18,9 @@ Changelog
   Merge of [#1276](https://github.com/mozilla/nunjucks/pull/1276); fixes
   [#1198](https://github.com/mozilla/nunjucks/issues/1198). Thanks
   [ogonkov](https://github.com/ogonkovv)!
+* Fix bug that prevented errors in included templates from being raised when
+  rendering templates synchronously. Fixes
+  [#1272](https://github.com/mozilla/nunjucks/pull/1276).
 
 3.2.1 (Mar 17 2020)
 -------------------

nunjucks/src/environment.js

@@ -476,14 +476,15 @@ class Template extends Obj {
     let didError = false;
 
     this.rootRenderFunc(this.env, context, frame, globalRuntime, (err, res) => {
-      if (didError) {
+      // TODO: this is actually a bug in the compiled template (because waterfall
+      // tasks are both not passing errors up the chain of callbacks AND are not
+      // causing a return from the top-most render function). But it will be
+      // easier to rewrite the compiler than to fix that problem.
+      if (didError && cb && typeof res !== 'undefined') {
         // prevent multiple calls to cb
-        if (cb) {
-          return;
-        } else {
-          throw err;
-        }
+        return;
       }
+
       if (err) {
         err = lib._prettifyError(this.path, this.env.opts.dev, err);
         didError = true;

tests/compiler.js

@@ -847,6 +847,25 @@
       });
     }
 
+    it('should throw exceptions from included templates when called synchronously', function() {
+      function templateRender() {
+        render('{% include "broken-import.njk" %}', {str: 'abc'});
+      }
+      expect(templateRender).to.throwException(/template not found: doesnotexist/);
+    });
+
+    it('should pass errors from included templates to callback when async', function(done) {
+      render(
+        '{% include "broken-import.njk" %}',
+        {str: 'abc'},
+        {noThrow: true},
+        function(err, res) {
+          expect(err).to.match(/template not found: doesnotexist/);
+          expect(res).to.be(undefined);
+          done();
+        });
+    });
+
     it('should compile string concatenations with tilde', function(done) {
       equal('{{ 4 ~ \'hello\' }}', '4hello');
       equal('{{ 4 ~ 5 }}', '45');