From: Ben Darnell <ben@bendarnell.com>
Date: Mon, 27 Aug 2012 01:03:12 +0000 (-0700)
Subject: Fix template errors with empty blocks.
X-Git-Tag: v2.4.0~14
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=54d91d5e1312eb2e3d0c9ae0b7f5c8333a4ac50e;p=thirdparty%2Ftornado.git

Fix template errors with empty blocks.

Emits a "pass" statement in every generated block whether it's empty or not;
I verified with the disassembler that the unnecessary pass statements
don't generate extra bytecodes.

Closes #546.
---

diff --git a/tornado/template.py b/tornado/template.py
index 13eb78081..14306d9a5 100644
--- a/tornado/template.py
+++ b/tornado/template.py
@@ -501,6 +501,8 @@ class _ControlBlock(_Node):
         writer.write_line("%s:" % self.statement, self.line)
         with writer.indent():
             self.body.generate(writer)
+            # Just in case the body was empty
+            writer.write_line("pass", self.line)
 
 
 class _IntermediateControlBlock(_Node):
@@ -509,6 +511,8 @@ class _IntermediateControlBlock(_Node):
         self.line = line
 
     def generate(self, writer):
+        # In case the previous block was empty
+        writer.write_line("pass", self.line)
         writer.write_line("%s:" % self.statement, self.line, writer.indent_size() - 1)
 
 
diff --git a/tornado/test/template_test.py b/tornado/test/template_test.py
index a4b9453b7..6e14abb92 100644
--- a/tornado/test/template_test.py
+++ b/tornado/test/template_test.py
@@ -101,6 +101,10 @@ class TemplateTest(LogTrapTestCase):
         self.assertEqual(template.generate(x=5), b("yes"))
         self.assertEqual(template.generate(x=3), b("no"))
 
+    def test_if_empty_body(self):
+        template = Template(utf8("{% if True %}{% else %}{% end %}"))
+        self.assertEqual(template.generate(), b(""))
+
     def test_try(self):
         template = Template(utf8("""{% try %}
 try{% set y = 1/x %}