ruff/crates/ty/docs/mypy_primer.md
2025-05-03 19:49:15 +02:00

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# Running `mypy_primer`
## Basics
`mypy_primer` can be run using `uvx --from "…" mypy_primer`. For example, to see the help message, run:
```sh
uvx --from "git+https://github.com/hauntsaninja/mypy_primer" mypy_primer -h
```
Alternatively, you can install the forked version of `mypy_primer` using:
```sh
uv tool install "git+https://github.com/hauntsaninja/mypy_primer"
```
and then run it using `uvx mypy_primer` or just `mypy_primer`, if your `PATH` is set up accordingly (see: [Tool executables]).
## Showing the diagnostics diff between two Git revisions
To show the diagnostics diff between two Git revisions (e.g. your feature branch and `main`), run:
```sh
mypy_primer \
--type-checker ty \
--old origin/main \
--new my/feature \
--debug \
--output concise \
--project-selector '/black$'
```
This will show the diagnostics diff for the `black` project between the `main` branch and your `my/feature` branch. To run the
diff for all projects we currently enable in CI, use `--project-selector "/($(paste -s -d'|' crates/ty_python_semantic/resources/primer/good.txt))\$"`.
You can also take a look at the [full list of ecosystem projects]. Note that some of them might still need a `ty_paths` configuration
option to work correctly.
## Avoiding recompilation
If you want to run `mypy_primer` repeatedly, e.g. for different projects, but for the same combination of `--old` and `--new`, you
can use set the `MYPY_PRIMER_NO_REBUILD` environment variable to avoid recompilation of ty:
```sh
MYPY_PRIMER_NO_REBUILD=1 mypy_primer …
```
## Running from a local copy of the repository
If you are working on a local branch, you can use `mypy_primer`'s `--repo` option to specify the path to your local copy of the `ruff` repository.
This allows `mypy_primer` to check out local branches:
```sh
mypy_primer --repo /path/to/ruff --old origin/main --new my/local-branch …
```
Note that you might need to clean up `/tmp/mypy_primer` in order for this to work correctly.
[full list of ecosystem projects]: https://github.com/hauntsaninja/mypy_primer/blob/master/mypy_primer/projects.py
[tool executables]: https://docs.astral.sh/uv/concepts/tools/#tool-executables