typing-copilot 0.2.0

Helper for starting to type-hint large codebases with mypy.

typing-copilot

Helper for starting to type-hint large codebases with mypy. When installed, available as the command tc.

Example output generated when generating a mypy.ini file for the GraphQL compiler project (PR link):

$ tc init
typing_copilot v0.2.0

Running mypy once with laxest settings to establish a baseline. Please wait...

Collecting mypy errors from strictest check configuration. Please wait...

Strict run completed and uncovered 2955 mypy errors. Building the strictest mypy config
such that all configured mypy checks still pass...

> Mypy was unable to find type hints for some 3rd party modules, configuring mypy to
ignore them.
    More info: https://mypy.readthedocs.io/en/stable/running_mypy.html#missing-imports
    Affected modules: ['arrow', 'cached_property', 'funcy', 'neo4j', 'parameterized',
        'pyorient', 'pytest', 'redisgraph', 'setuptools', 'snapshottest', 'sqlalchemy']

> Constructed 126 mypy error suppression rules across 65 modules.

Config generated (306 lines). Validating the new setup before updating your mypy.ini
file. Please wait...

Validation complete. Your mypy.ini file has been updated. Happy type-safe coding!

Motivation

Starting to use mypy in a large codebase can feel like a chicken-and-egg problem:

• You are unable to turn on meaningful mypy enforcement since a large portion of the codebase is not compliant.
• It is difficult to get the codebase compliant without mypy enforcement: since proper typing is not enforced, even brand-new code is frequently not fully compliant, and it feels like you are making one step forward and two steps back.

mypy allows specifying different levels of rule enforcement on a per-module basis. However, writing a good per-module mypy configuration is an extremely time-consuming process: mypy must be executed (in a strict configuration) against that module, the resulting errors must be triaged, and an appropriate set of rules for the modules must be produced. Applying this process on a large codebase can easily take hours or days of work.

typing-copilot aims to make this process extremely quick and simple. After installing this package in your project's development environment, running tc init will autogenerate a mypy.ini file with the strictest set of mypy rules that your code currently passes. In future runs, mypy will automatically use the new mypy.ini file, thereby ensuring that no future code edits violate any typing rules that the current codebase satisfies.

You can then also use the mypy.ini file to see which checks had to be disabled for which of your project's modules, and use that information to guide your future typing efforts. You can also periodically re-run tc init --overwrite to regenerate a mypy.ini file, in case your project's typing state has improved and stricter rules may now be adopted.

In the future, we hope to add additional functionality to typing-copilot:

• a command that highlights opportunities where a small amount of work can allow a new rule to be enabled for a new module, allowing you to maximize your project's typing enforcement;
• support for additional mypy rules.

Usage

Navigate to the root directory (and virtualenv, if using one) of the project on which you'd like to use typing-copilot. Then,

pip install typing-copilot

tc init

If you are already using mypy for your project and already have a mypy.ini file that you would like to overwrite, simply add the --overwrite option:

tc init --overwrite

typing-copilot will first run mypy using a minimal set of mypy checks which are always enabled and cannot be turned off. You'll need to fix any errors mypy finds using these checks before moving to the next step.

Once the minimal mypy checks pass, tc init will automatically re-run mypy with the strictest supported set of checks, and collect the reported errors. After analyzing the errors, it will generate the strictest set of checks that will not cause errors, validate them by running mypy against your project one more time, and then create a new mypy.ini file with this new "strictest valid" configuration.

Reporting issues

This is a project I built in my spare time, please be gentle :)

GitHub issues are the preferred avenue for reporting issues with typing-copilot. Please do not email me or any other contributors with questions or issue reports, unless you have our explicit consent to do so.

To ensure the best odds that we can diagnose and fix any problems together, please make sure to include in your issue report the log produced using the --verbose option, together with links to the source code being analyzed by mypy and typing-copilot.

As always, pull requests highly encouraged and gratefully accepted.