Adding a New Linter to the Tree =============================== Linter Requirements ------------------- For a linter to be integrated into the mozilla-central tree, it needs to have: * Any required dependencies should be installed as part of ``./mach bootstrap`` * A ``./mach lint`` interface * Running ``./mach lint`` command must pass (note, linters can be disabled for individual directories) * Taskcluster/Treeherder integration * In tree documentation (under ``docs/code-quality/lint``) to give a basic summary, links and any other useful information * Unit tests (under ``tools/lint/test``) to make sure that the linter works as expected and we don't regress. The review group in Phabricator is ``#linter-reviewers``. Linter Basics ------------- A linter is a yaml file with a ``.yml`` extension. Depending on how the type of linter, there may be python code alongside the definition, pointed to by the 'payload' attribute. Here's a trivial example: no-eval.yml .. code-block:: yaml EvalLinter: description: Ensures the string eval doesn't show up. extensions: ['js'] type: string payload: eval Now ``no-eval.yml`` gets passed into :func:`LintRoller.read`. Linter Types ------------ There are four types of linters, though more may be added in the future. 1. string - fails if substring is found 2. regex - fails if regex matches 3. external - fails if a python function returns a non-empty result list 4. structured_log - fails if a mozlog logger emits any lint_error or lint_warning log messages As seen from the example above, string and regex linters are very easy to create, but they should be avoided if possible. It is much better to use a context aware linter for the language you are trying to lint. For example, use eslint to lint JavaScript files, use flake8 to lint python files, etc. Which brings us to the third and most interesting type of linter, external. External linters call an arbitrary python function which is responsible for not only running the linter, but ensuring the results are structured properly. For example, an external type could shell out to a 3rd party linter, collect the output and format it into a list of :class:`Issue` objects. The signature for this python function is ``lint(files, config, **kwargs)``, where ``files`` is a list of files to lint and ``config`` is the linter definition defined in the ``.yml`` file. Structured log linters are much like external linters, but suitable for cases where the linter code is using mozlog and emits ``lint_error`` or ``lint_warning`` logging messages when the lint fails. This is recommended for writing novel gecko-specific lints. In this case the signature for lint functions is ``lint(files, config, logger, **kwargs)``. Linter Definition ----------------- Each ``.yml`` file must have at least one linter defined in it. Here are the supported keys: * description - A brief description of the linter's purpose (required) * type - One of 'string', 'regex' or 'external' (required) * payload - The actual linting logic, depends on the type (required) * include - A list of file paths that will be considered (optional) * exclude - A list of file paths or glob patterns that must not be matched (optional) * extensions - A list of file extensions to be considered (optional) * setup - A function that sets up external dependencies (optional) * support-files - A list of glob patterns matching configuration files (optional) * find-dotfiles - If set to ``true``, run on dot files (.*) (optional) * ignore-case - If set to ``true`` and ``type`` is regex, ignore the case (optional) In addition to the above, some ``.yml`` files correspond to a single lint rule. For these, the following additional keys may be specified: * message - A string to print on infraction (optional) * hint - A string with a clue on how to fix the infraction (optional) * rule - An id string for the lint rule (optional) * level - The severity of the infraction, either 'error' or 'warning' (optional) For structured_log lints the following additional keys apply: * logger - A StructuredLog object to use for logging. If not supplied one will be created (optional) Example ------- Here is an example of an external linter that shells out to the python flake8 linter, let's call the file ``flake8_lint.py`` (`in-tree version `_): .. code-block:: python import json import os import subprocess from collections import defaultdict from mozlint import result try: from shutil import which except ImportError: from shutil_which import which FLAKE8_NOT_FOUND = """ Could not find flake8! Install flake8 and try again. """.strip() def lint(files, config, **lintargs): binary = os.environ.get('FLAKE8') if not binary: binary = which('flake8') if not binary: print(FLAKE8_NOT_FOUND) return 1 # Flake8 allows passing in a custom format string. We use # this to help mold the default flake8 format into what # mozlint's Issue object expects. cmdargs = [ binary, '--format', '{"path":"%(path)s","lineno":%(row)s,"column":%(col)s,"rule":"%(code)s","message":"%(text)s"}', ] + files proc = subprocess.Popen(cmdargs, stdout=subprocess.PIPE, env=os.environ) output = proc.communicate()[0] # all passed if not output: return [] results = [] for line in output.splitlines(): # res is a dict of the form specified by --format above res = json.loads(line) # parse level out of the id string if 'code' in res and res['code'].startswith('W'): res['level'] = 'warning' # result.from_linter is a convenience method that # creates a Issue using a LINTER definition # to populate some defaults. results.append(result.from_config(config, **res)) return results Now here is the linter definition that would call it: .. code-block:: yaml flake8: description: Python linter include: ['.'] extensions: ['py'] type: external payload: py.flake8:lint support-files: - '**/.flake8' Notice the payload has two parts, delimited by ':'. The first is the module path, which ``mozlint`` will attempt to import. The second is the object path within that module (e.g, the name of a function to call). It is up to consumers of ``mozlint`` to ensure the module is in ``sys.path``. Structured log linters use the same import mechanism. The ``support-files`` key is used to list configuration files or files related to the running of the linter itself. If using ``--outgoing`` or ``--workdir`` and one of these files was modified, the entire tree will be linted instead of just the modified files. Result definition ----------------- When generating the list of results, the following values are available. .. csv-table:: :header: "Name", "Description", "Optional" :widths: 20, 40, 10 "linter", "Name of the linter that flagged this error", "" "path", "Path to the file containing the error", "" "message", "Text describing the error", "" "lineno", "Line number that contains the error", "" "column", "Column containing the error", "" "level", "Severity of the error, either 'warning' or 'error' (default 'error')", "Yes" "hint", "Suggestion for fixing the error", "Yes" "source", "Source code context of the error", "Yes" "rule", "Name of the rule that was violated", "Yes" "lineoffset", "Denotes an error spans multiple lines, of the form (, )", "Yes" "diff", "A diff describing the changes that need to be made to the code", "Yes" Automated testing ----------------- Every new checker must have tests associated. They should be pretty easy to write as most of the work is managed by the Mozlint framework. The key declaration is the ``LINTER`` variable which must match the linker declaration. As an example, the `Flake8 test `_ looks like the following snippet: .. code-block:: python import mozunit LINTER = 'flake8' def test_lint_single_file(lint, paths): results = lint(paths('bad.py')) assert len(results) == 2 assert results[0].rule == 'F401' assert results[1].rule == 'E501' assert results[1].lineno == 5 if __name__ == '__main__': mozunit.main() As always with tests, please make sure that enough positive and negative cases are covered. To run the tests: .. code-block:: shell $ ./mach python-test --python 3 --subsuite mozlint More tests can be `found in-tree `_. Bootstrapping Dependencies -------------------------- Many linters, especially 3rd party ones, will require a set of dependencies. It could be as simple as installing a binary from a package manager, or as complicated as pulling a whole graph of tools, plugins and their dependencies. Either way, to reduce the burden on users, linters should strive to provide automated bootstrapping of all their dependencies. To help with this, ``mozlint`` allows linters to define a ``setup`` config, which has the same path object format as an external payload. For example (`in-tree version `_): .. code-block:: yaml flake8: description: Python linter include: ['.'] extensions: ['py'] type: external payload: py.flake8:lint setup: py.flake8:setup The setup function takes a single argument, the root of the repository being linted. In the case of ``flake8``, it might look like: .. code-block:: python import subprocess from distutils.spawn import find_executable def setup(root, **lintargs): # This is a simple example. Please look at the actual source for better examples. if not find_executable('flake8'): subprocess.call(['pip', 'install', 'flake8']) The setup function will be called implicitly before running the linter. This means it should return fast and not produce any output if there is no setup to be performed. The setup functions can also be called explicitly by running ``mach lint --setup``. This will only perform setup and not perform any linting. It is mainly useful for other tools like ``mach bootstrap`` to call into. Adding the linter to the CI --------------------------- First, the job will have to be declared in Taskcluster. This should be done in the `mozlint Taskcluster configuration `_. You will need to define a symbol, how it is executed and on what kind of change. For example, for flake8, the configuration is the following: .. code-block:: yaml py-flake8: description: flake8 run over the gecko codebase treeherder: symbol: py(f8) run: mach: lint -l flake8 -f treeherder -f json:/builds/worker/mozlint.json when: files-changed: - '**/*.py' - '**/.flake8' # moz.configure files are also Python files. - '**/*.configure' If the linter requires an external program, you will have to install it in the `setup script `_ and maybe install the necessary files in the `Docker configuration `_. .. note:: If the defect found by the linter is minor, make sure that it is run as `tier 2 `_. This prevents the tree from closing because of a tiny issue. For example, the typo detection is run as tier-2.