Allow template fragment caching for unlimited time

[MikiSoft]

Apparently, I've discovered that {% cache None name %} doesn't work - it should cache the content wrapped with it forever i.e. until server restarts, but when I specify it like that then it's giving an error for invalid input, and I don't see any other solution to this. So can someone make it to accept None as a parameter for unlimited time, like it is in low-level API?

[Tim Graham]

I didn't test it but it looks like it should work -- the template tag is calling ​cache.set(key, value, timeout). Can you check to be sure that the problem isn't in your project?

[MikiSoft]

Replying to Tim Graham:
Yes, I'm sure that it's not a problem in my project because I've tested my project on this way:
First, I put in a view print(cache.get(make_template_fragment_key('test'))) and in corresponding template {% cache 0 test %}, then I started the server and I opened to that page. It printed me None, even after refreshing the page.
So, I changed the tag to be {% cache 300 test %} and I've opened that page again. And suddenly it started printing content which I put under that cache tag!
Maybe the problem is with make_template_fragment_key method or it has to do with the cache framework itself?

[Tim Graham]

​The documentation says, "Passing in None for timeout will cache the value forever. A timeout of 0 won’t cache the value." So {% cache %} needs to allow None. It looks like this patch does the trick:

django/templatetags/cache.py

@@ -20 +20 @@
             expire_time = self.expire_time_var.resolve(context)
         except VariableDoesNotExist:
             raise TemplateSyntaxError('"cache" tag got an unknown variable: %r' % self.expire_time_var.var)
-        try:
-            expire_time = int(expire_time)
-        except (ValueError, TypeError):
-            raise TemplateSyntaxError('"cache" tag got a non-integer timeout value: %r' % expire_time)
+        if expire_time is not None:
+            try:
+                expire_time = int(expire_time)
+            except (ValueError, TypeError):
+                raise TemplateSyntaxError('"cache" tag got a non-integer timeout value: %r' % expire_time)
         if self.cache_name:
             try:
                 cache_name = self.cache_name.resolve(context)

A test and perhaps a documentation update is also required.

[MikiSoft]

Replying to Tim Graham:
Yes you're right about that, it should be None instead of zero (I've corrected the main post). Thanks for solving it!
I have one more question if you can answer me here (sorry for being a bit off topic) - when can I expect a new Django release with such patch?

[Bo Marchman]

PR is at ​https://github.com/django/django/pull/8120, with a test and doc changes.

[Tim Graham]

I left a few comments for improvement on the PR.

[Bo Marchman]

Requested changes made.

[Tim Graham <timograham@…>]

In 7a7b331c:

Fixed #27882 -- Allowed {% cache %} to cache indefinitely.