Passing Jinja2 context to callable instance as first argument when the callable instance has __getattr__ method since Jinja2 2.11.0

[Jun Omae]

From comment:78:ticket:12130

The callable instance is Href instance.

See also

• ​https://github.com/pallets/jinja/blob/2.11.0/src/jinja2/runtime.py#L261
• ​https://github.com/pallets/jinja/blob/2.10.3/jinja2/runtime.py#L235

Jinja2 2.11.0

>>> import jinja2, sys
>>> jinja2.__version__
'2.11.0'
>>> from jinja2 import Template
>>> from trac.web.href import Href
>>> href = Href('/trac.cgi')
>>> Template('{{ href() }}').render(href=href)
"/trac.cgi/%3CContext%20%7B'range'%3A%20%3Cclass%20'range'%3E%2C%20'dict'%3A%20%3Cclass%20'dict'%3E%2C%20'lipsum'%3A%20%3Cfunction%20generate_lorem_ipsum%20at%200x7f0386031310%3E%2C%20'cycler'%3A%20%3Cclass%20'jinja2.utils.Cycler'%3E%2C%20'joiner'%3A%20%3Cclass%20'jinja2.utils.Joiner'%3E%2C%20'namespace'%3A%20%3Cclass%20'jinja2.utils.Namespace'%3E%2C%20'href'%3A%20%3CHref%20'/trac.cgi'%3E%7D%20of%20None%3E"
>>> class Foo(object):
...     def __getattr__(self, name):
...         sys.stderr.write('__getattr__({!r})\n'.format(name))
...         return self
...     def __call__(self, *args, **kwargs):
...         sys.stderr.write('__call__(args={!r}, kwargs={!r})\n'.format(args, kwargs))
...
>>> Template('{{ val() }}').render(val=Foo())
__getattr__('contextfunction')
__call__(args=(<Context {'range': <class 'range'>, 'dict': <class 'dict'>, 'lipsum': <function generate_lorem_ipsum at 0x7f0386031310>, 'cycler': <class 'jinja2.utils.Cycler'>, 'joiner': <class 'jinja2.utils.Joiner'>, 'namespace': <class 'jinja2.utils.Namespace'>, 'val': <__main__.Foo object at 0x7f038a15d160>} of None>,), kwargs={})
'None'

Jinja2 2.10.3

>>> import jinja2, sys
>>> jinja2.__version__
'2.10.3'
>>> from jinja2 import Template
>>> from trac.web.href import Href
>>> href = Href('/trac.cgi')
>>> Template('{{ href() }}').render(href=href)
'/trac.cgi'
>>> class Foo(object):
...     def __getattr__(self, name):
...         sys.stderr.write('__getattr__({!r})\n'.format(name))
...         return self
...     def __call__(self, *args, **kwargs):
...         sys.stderr.write('__call__(args={!r}, kwargs={!r})\n'.format(args, kwargs))
...
>>> Template('{{ val() }}').render(val=Foo())
__call__(args=(), kwargs={})
'None'

[Jun Omae]

Ad hoc patch:

trac/web/href.py

@@ -188 +188 @@
         return href
 
     def __getattr__(self, name):
+        if name in ('contextfunction', 'evalcontextfunction',
+                    'environmentfunction'):
+            raise AttributeError
         if name not in self._derived:
             self._derived[name] = lambda *args, **kw: self(name, *args, **kw)
         return self._derived[name]

[Ryan J Ollos]

Looks similar to ​Jinja2 issue #1139. Relevant change is ​70ea1d3e.

It wouldn't be an issue if Jinja2 tested the value: getattr(__obj, "contextfunction", 0) is True rather than just getattr(__obj, "contextfunction", 0).

[Jun Omae]

Proposed changes in [332bf1f51/jomae.git].

[Ryan J Ollos]

Looks good. Nice solution!

[Jun Omae]

Thanks for the review! Committed in [17238] and merged in [17239].

[Ryan J Ollos]

I posted a related question in ​Jinja2 issue #1139.

[Ryan J Ollos]

Replying to Ryan J Ollos:

I posted a related question in ​Jinja2 issue #1139.

They may address the issue in ​Jinja2 issue #1145, targeted to Jinja2 2.11.2. We can probably remove the Href attributes (contextfunction, …) if we ever drop support for Jinja < 2.11.2.

[Jun Omae]

Another work around without contextfunction attribute: we could simply ignore Jinja2 context instance because the arguments of Href.__call__() are typically instances of basestring, dict, list and tuple.

trac/web/href.py

@@ -16 +16 @@
 # Author: Jonas Borgström <jonas@edgewall.com>
 #         Christopher Lenz <cmlenz@gmx.de>
 
+from jinja2.runtime import Context as Jinja2Context
 import re
 
 from trac.util.text import unicode_quote, unicode_urlencode
@@ -140 +141 @@
     '/milestone/<look,here%3E?param=%3Chere,too>'
     """
 
-    # Avoid passing Jinja2 context to __call__ (#13244)
-    contextfunction = 0
-    evalcontextfunction = 0
-    environmentfunction = 0
-
     def __init__(self, base, path_safe="/!~*'()", query_safe="!~*'()"):
         self.base = base.rstrip('/')
         self.path_safe = path_safe
@@ -165 +161 @@
             elif value is not None:
                 params.append((name, value))
 
+        # Skip Jinja2 context (#13244)
+        if args and isinstance(args[0], Jinja2Context):
+            args = args[1:]
         if args:
             lastp = args[-1]
             if isinstance(lastp, dict):

[Ryan J Ollos]

The comment:9 patch seems like a better solution because it doesn't prevent a path like /contextfunction.

One minor tweak is that the third-party import should be placed after the stdlib import:

import re

from jinja2.runtime import Context as Jinja2Context

from trac.util.text import unicode_quote, unicode_urlencode

[Jun Omae]

Thanks. Committed with your suggestion in [17246] and merged in [17247].

[Ryan J Ollos]

I was thinking we should add a comment in the code below the Skip Jinja2 context (#13244) comment: Only needed for Jinja 2.11.0 and 2.11.1.

The workaround shouldn't be needed after ​99333246.

[Ryan J Ollos]

Added additional comment in r17260, r17261.

[Ryan J Ollos]

Moving change notes to Internal Changes since Jinja2 2.11 compatibility is announced in #13242.