trove-pylint
------------

trove-pylint.py is a wrapper around pylint which allows for some
custom processing relevant to the trove source tree, and suitable to
run as a CI job for trove.

The purpose is to perform a lint check on the code and detect obvious
(lintable) errors and fix them.

How trove-pylint works
----------------------

trove-pylint is driven by a configuration file which is by default,
located in tools/trove-pylint.config. This file is a json dump of the
configuration. A default configuration file looks like this.

   {
      "include": ["*.py"],
      "folder": "trove",
      "options": ["--rcfile=./pylintrc", "-E"],
      "ignored_files": ['trove/tests'],
      "ignored_codes": [],
      "ignored_messages": [],
      "ignored_file_codes": [],
      "ignored_file_messages": [],
      "ignored_file_code_messages": [],
      "always_error_messages": [
         "Undefined variable '_'",
         "Undefined variable '_LE'",
         "Undefined variable '_LI'",
         "Undefined variable '_LW'",
         "Undefined variable '_LC'"
      ]
   }

include
-------

    Provide a list of match specs (passed to fnmatch.fnmatch). The
    default is only "*.py".

folder
------

    Provide the name of the top level folder to lint. This is a single
    value.

options
-------

    These are the pylint launch options. The default is to specify an
    rcfile and only errors. Specifying the rcfile is required, and the
    file is a dummy, to suppress an annoying warning.

ignored_files
-------------

    This is a list of paths that we wish to ignore. When a file is
    considered for linting, if the path name begins with any of these
    provided prefixes, the file will not be linted. We ignore the
    tests directory because it has a high instance of false positives.

ignored_codes, ignored_messages, ignored_file_codes,
ignored_file_messages, and ignored_file_code_messages
-----------------------------------------------------

    These settings identify specific failures that are to be
    ignored. Each is a list, some are lists of single elements, others
    are lists of lists.

    ignored_codes, and ignored_messages are lists of single elements
    that are to be ignored. You could specify either the code name, or
    the code numeric representation. You must specify the exact
    message.

    ignored_file_codes and ignored_file_messages are lists of lists
    where each element is a code and a message.

    ignored_file_code_messages is a list of lists where each element
    consists of a filename, an errorcode, a message, a line number and
    a function name.

always_error_messages
---------------------

    This is a list of messages which have a low chance of false
    positives, which are always flagged as errors.

Using trove-pylint
------------------

You can check your code for errors by simply running:

   tox -e pylint

or explicitly as:

   tox -e pylint check

The equivalent result can be obtained by running the command:

    tools/trove-pylint.py

or

    tools/trove-pylint.py check

Running the tool directly may require installing addition pip
modules on your machine (such as pylint), so using 'tox' is the
preferred method.


For example, here is the result from such a run.

    $ tox -e pylint check
    ERROR: trove/common/extensions.py 575: E1003 bad-super-call, \
    TroveExtensionMiddleware.__init__: Bad first argument \
    'ExtensionMiddleware' given to super()
    Check failed. 367 files processed, 1 had errors, 1 errors recorded.

I wish to ignore this error and keep going. To do this, I rebuild the
list of errors to ignore as follows.

    $ tox -e pylint rebuild
    Rebuild completed. 367 files processed, 177 exceptions recorded.

This caused the tool to add the following two things to the config file.

    [
      "trove/common/extensions.py",
      "E1003",
      "Bad first argument 'ExtensionMiddleware' given to super()",
      "TroveExtensionMiddleware.__init__"
    ],
    [
      "trove/common/extensions.py",
      "bad-super-call",
      "Bad first argument 'ExtensionMiddleware' given to super()",
      "TroveExtensionMiddleware.__init__"
    ],

With that done, I can recheck as shown below.

    $ tox -e pylint
    Check succeeded. 367 files processed

You can review the errors that are being currently ignored by reading
the file tools/trove-pylint.config.

If you want to fix some of these errors, identify the configuration(s)
that are causing those errors to be ignored, remove them and re-run the
check. Once you see that the errors are in fact being reported by the
tool, go ahead and fix the problem(s) and retest.

Known issues
------------

1. The tool appears to be very sensitive to the version(s) of pylint
and astroid. In testing, I've found that if the version of either of
these changes, you could either have a failure of the tool (exceptions
thrown, ...) or a different set of errors reported.

Refer to test-requirements.txt to see the versions currently being used.

If you run the tool on your machine and find that there are no errors,
but find that either the CI generates errors, or that the tool run
through tox generates errors, check what versions of astroid and
pylint are being run in each configuration.