django-shouty-templates 0.2.0
Applies a monkeypatch which forces Django's template language to error far more loudly about invalid assumptions
License: BSD License
Keywords: django templates DTL exception

django-shouty-templates
=======================

:author: Keryn Knight
:version: 0.2.0

Brief
-----

This app applies a monkeypatch which forces Django's template language to error
**very loudly** about variables which are *used* in a template but *don't exist* in the context.

Rationale
---------

Given a template like this::

    <html><head></head>
    <body>
    {% if chef.can_add_cakes %}
        <label class="alert alert-{{ chef.is_cake_chef|yesno:"success,danger,default" }}
    {% endif %}

everything works fine, until you refactor and any of the following happens:

- ``chef`` is no longer the name of the variable.
- ``can_add_cakes`` is refactored to be called ``can_add_pastries``
- ``is_cake_chef`` is renamed ``is_pastry_king``

If those happen, the template will either silently display nothing, or will
display the label incorrectly. This monkeypatch attempts to fix that.

Specifically:

- ``chef`` will raise an exception if the variable were called ``sous_chef``
- ``chef.can_add_cakes`` will raise an exception if ``can_add_cakes`` was no longer a valid attribute/property/method of ``chef``
- ``chef.is_cake_chef`` will raise an exception for the same reasons.

Thus you can refactor somewhat more freely, knowing that if the template renders
it's OK. It ain't compile time safety, but it's better than silently swallowing
errors because you forgot something!

The exception itself would look something like::

    Token 'chef' of 'chef.can_add_cakes' in template 'my/cool/template.html' does not resolve.
    Possibly you meant to use 'sous_chef'.
    Silence this occurance only by adding 'chef.can_add_cakes': ['my/cool/template.html'] to the settings.SHOUTY_VARIABLE_BLACKLIST dictionary.
    Silence this globally by adding 'chef.can_add_cakes': ['*'] to the settings.SHOUTY_VARIABLE_BLACKLIST dictionary.


Setup
-----

This package is available on `PyPI`_ and can be installed using pip or whatever like so::

    pip install django-shouty-templates==0.2.0

Then add ``shouty.Shout`` or ``shouty`` to your ``settings.INSTALLED_APPS``

Optional configuration
^^^^^^^^^^^^^^^^^^^^^^

A list of values which may be set in your project's settings module:

settings.SHOUTY_VARIABLES
+++++++++++++++++++++++++

May be ``True|False`` and determines if the exception is raised when trying to
use a variable which doesn't exist.

Defaults to ``True``.


settings.SHOUTY_URLS
++++++++++++++++++++

May be ``True|False`` and determines if an exception is raised when
doing ``{% url 'myurl' as my_var %}`` and ``myurl`` doesn't actually resolve to a view.

Defaults to ``True``.

settings.SHOUTY_VARIABLE_BLACKLIST
++++++++++++++++++++++++++++++++++

Useful for if you are trying to fix up an existing project, or ignore problems
in third-party templates.

Expects a ``dict`` of ``str`` keys and a sequence (eg: ``tuple`` or ``list``) of templates in which to ignore it::

    SHOUTY_VARIABLE_BLACKLIST = {
        "chef.can_add_cakes": ("*",),
        "my_sometimes_set_variable": ["admin/custom_view.html", "admin/custom_view_detail.html"],
        "random_in_memory_template": ["<unknown source>"],
        "*": ["admin/login.html", "<unknown source>"],
    }

Of special note is the use of ``*``, which has a more magical meaning.

- Using ``"key": ["*"]`` would silence errors about the variable named ``key`` in **all templates**
- Using ``"*": ["path/to/template.html"]`` would silence **all** variable errors in **that specific template** only (see `GitHub issue 6`_)

And also the far less frequently useful ``<unknown source>`` or ``django.template.base.UNKNOWN_SOURCE`` which is essentially usually for ``Template`` instances
not loaded from a *file on disk*

settings.SHOUTY_URL_BLACKLIST
+++++++++++++++++++++++++++++

A ``tuple`` of ``2-tuple`` to prevent certain URLs and their output variables f
rom shouting at you loudly. Useful for existing projects or third-party apps which are less strict.

By way of example, ``{% url "myurl" as my_var %}`` may be suppressed with::

    SHOUTY_URL_BLACKLIST = (
        ('myurl', 'my_var'),
    )

which would still let ``{% url "myurl" as "my_other_var" %}`` raise an exception.

Default configuration
^^^^^^^^^^^^^^^^^^^^^

There's a hard-coded blacklist of variables and URLs to make sure the Django admin (+ admindocs),
django-debug-toolbar, django-pipeline, django-admin-honeypot, djangorestframework, etc all work.

if/elif/else testing
--------------------

When an ``{% if x %}`` statement is seen in the template, all conditions are checked
to ensure the context will always resolve correctly. Additionally, if you use ``{% if %}``
and ``{% elif %}`` together and **don't** have an ``{% else %}`` it'll raise an error
to remind you to handle that case, even if handling it is just to output nothing.

Tests
-----

Just run ``python3 -m shouty`` and hope for the best. I usually do.

The license
-----------

It's `FreeBSD`_. There's should be a ``LICENSE`` file in the root of the repository, and in any archives.

.. _FreeBSD: http://en.wikipedia.org/wiki/BSD_licenses#2-clause_license_.28.22Simplified_BSD_License.22_or_.22FreeBSD_License.22.29
.. _PyPI: https://pypi.org/
.. _GitHub issue 6: https://github.com/kezabelle/django-shouty-templates/issues/6


----

Copyright (c) 2019, Keryn Knight
All rights reserved.

Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:

1. Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.

2. Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.


----

Change history for django-shouty-templates
------------------------------------------

0.2.0
^^^^^^
* Bugfix: Updates to ostensibly support Django 4.0+
* Feature: Error loudly when an ``{% if ... %}...{% elif %}`` statement is present without an ``{% else %}``
* Feature: Allow for silencing **all** missing variables within a single given template (or set of templates)
* Bugfix: Attempt to fix parsing of where a missing variable occurs within things like ``{% blocktrans with filter_title=title %}``
* Bugfix: when the ``render_context`` doesn't have a template *or* it's ``None`` it's now properly skipped.

0.1.6
^^^^^^
* Feature: Ignore variables which prevented much of REST Framework's browsable API from working.
* Feature: Ignore variables which would cause the ``django-admin-honeypot`` package's fake login screen to error.
* Feature: Ignore variables which might cause ``django-pipeline`` rendering of ``<link>`` and ``<script>`` to error.
* Bugfix: Improve per-template silencing via ``SHOUTY_VARIABLE_BLACKLIST``
* Bugfix: Attempt to have fewer false positives when highlighting the location in the template of the exception.

0.1.5
^^^^^^
* Feature: system check to validate any ``SHOUTY_VARIABLE_BLACKLIST`` in your settings.
* Feature: Attempt to highlight the exception location in any subtemplate, better than Django currently does.
* Feature: Update exception message with any potential typo candidates.
* Feature: Silencing missing variables on a per-template basis.
* Feature: Deep inspection of ``{% if ... %} {% elif ... %}`` nodes for any which are variables which don't exist.
* Bugfix: Patch methods hidden from the debug error page should now be consistently hidden always, rather than dependant on hitting the expected branch.
* Bugfix: Unit tests now exist to demonstrate how it should behave, at least on Django 2.2~

0.1.4
^^^^^^
* Feature: the patch methods themselves (``new_resolve_lookup`` and ``new_url_render``) are skipped during rendering the debug error page. The exception message and functionality remain the same.
* Feature: exception messages now attempt to clarify what template name (loader relative) was rendering when the missing variable was encountered.
* Chore: Updated the ``mypy`` type signatures for some of the variables and methods to indicate the only values I'm expecting to accept.

0.1.3
^^^^^^
* Feature: Silenced errors when using ``debug`` or ``sql_queries`` in a template, as they're conditionally set by ``django.template.context_processors.debug``

0.1.2
^^^^^^
* Feature: Added 11 new tokens to the default blacklist, covering more of the default Django admin and the default exception reporter.
* Bugfix: Changed the syntax of the ``AppConfig.ready`` method to be py2 type annotation compatible.

0.1.1
^^^^^^
* Initial release