Fixed #24257 -- Corrected i18n handling of percent signs.

Refactored tests to use a sample project.

Updated extraction:
* Removed special handling of single percent signs.
* When extracting messages from template text, doubled all percent signs
  so they are not interpreted by gettext as string format flags. All
  strings extracted by gettext, if containing a percent sign, will now
  be labeled "#, python-format".

Updated translation:
* Used "%%" for "%" in template text before calling gettext.
* Updated {% trans %} rendering to restore "%" from "%%".

2 files changed, 19 insertions, 0 deletions

diff --git a/tests/template_tests/syntax_tests/test_basic.py b/tests/template_tests/syntax_tests/test_basic.py
index b72d6e6414..da45fe2839 100644
--- a/tests/template_tests/syntax_tests/test_basic.py
+++ b/tests/template_tests/syntax_tests/test_basic.py
@@ -323,3 +323,12 @@ class BasicSyntaxTests(SimpleTestCase):
         msg = "Unclosed tag 'if'. Looking for one of: elif, else, endif."
         with self.assertRaisesMessage(TemplateSyntaxError, msg):
             self.engine.render_to_string('template')
+
+    @setup({'tpl-str': '%s', 'tpl-percent': '%%', 'tpl-weird-percent': '% %s'})
+    def test_ignores_strings_that_look_like_format_interpolation(self):
+        output = self.engine.render_to_string('tpl-str')
+        self.assertEqual(output, '%s')
+        output = self.engine.render_to_string('tpl-percent')
+        self.assertEqual(output, '%%')
+        output = self.engine.render_to_string('tpl-weird-percent')
+        self.assertEqual(output, '% %s')
diff --git a/tests/template_tests/syntax_tests/test_i18n.py b/tests/template_tests/syntax_tests/test_i18n.py
index 6013251366..4fbbfffd78 100644
--- a/tests/template_tests/syntax_tests/test_i18n.py
+++ b/tests/template_tests/syntax_tests/test_i18n.py
@@ -511,3 +511,13 @@ class I18nTagTests(SimpleTestCase):
         msg = "The 'noop' option was specified more than once."
         with self.assertRaisesMessage(TemplateSyntaxError, msg):
             self.engine.render_to_string('template')
+
+    @setup({'template': '{% load i18n %}{% trans "%s" %}'})
+    def test_trans_tag_using_a_string_that_looks_like_str_fmt(self):
+        output = self.engine.render_to_string('template')
+        self.assertEqual(output, '%s')
+
+    @setup({'template': '{% load i18n %}{% blocktrans %}%s{% endblocktrans %}'})
+    def test_blocktrans_tag_using_a_string_that_looks_like_str_fmt(self):
+        output = self.engine.render_to_string('template')
+        self.assertEqual(output, '%s')