Running dmypy as a systemd user service

从 dmypy start 和 dmypy daemon 入口点开始，然后跟踪 --status-file 和默认 .dmypy.json 位置的解析方式。将该行为与建议的 XDG_RUNTIME_DIR 或 /run/user/$UID/mypy 位置进行比较。当 systemd 用户服务可以在不使用 wrapper 的情况下运行 dmypy，同时现有的 status-file 行为仍然可用时，即视为完成。

Feature

Make dmypy look for either its status file or maybe even the socket in a well-known place.

As this well-known place I propose for Linux systems a directory /run/user/$UID/mypy (or the value of the environment variable XDG_RUNTIME_DIR). The name of status file would encode the path for which dmypy is running.

Pitch

mypy can be run as a daemon, which is currently manually started via dmypy start. It can already run in the foreground via dmypy daemon and I have started to use this to start the mypy daemon on login on my Linux system as a systemd user service as this moves the management of the lifecycle of the daemon to the service manager, that I already have running (as does the vast majority of Linux systems), so that I don't have to think about it anymore.

I do this via this service file in ~/.config/systemd/user/

# mypy@.service
[Unit]
Description=mypy daemon

[Service]
Type=simple
WorkingDirectory=%I
ExecStart=dmypy --status-file %t/mypy/%I.json daemon
RuntimeDirectory=mypy

which is instantiated via systemctl enable mypy@$(systemd-escape /path/to/my/project).service. The specifiers %I and %t expand to /path/to/my/project and the value of XDG_RUNTIME_DIR (by default /run/user/$UID). respectively. I then have a wrapper function for dmypy that sets --status-file to the appropriate value for my project directory (/run/user/$UID/mypy/$(systemd-escape $(git rev-parse --show-toplevel)).json to be specific).

I would like to streamline this setup, so that the wrapper is no longer necessary by having mypy look not only for .dmypy.json by default, but also check for the existence of the status file in the above described well-known location. This would allow e.g. for distributions packaging mypy to ship this or a similar service file to users and automatically restart the daemon on upgrades.

The feature itself is extensible. This directory could be used for the dmypy socket directly instead of giving it a random name in /tmp, but I have not yet looked into why this was designed as it is.

I guess a similar feature could be implemented for launchd on MacOS and on Windows, but I have no knowledge of these systems.