[native_assets_builder] Purge old directories

[dcharkes]

The native assets builder creates directories in the form of .dart_tool/native_assets_builder/<some-hash-of-the-config>. These directories should be purged at some point:

native/pkgs/native_assets_builder/lib/src/build_runner/build_runner.dart

Line 255 in 4c5fca9

// TODO(https://dartbug.com/50565): Purge old or unused folders.

Possible purging strategy:

• touch the config.json (or a last_read.json) every time it's read. And with a 1% chance delete everything that hasn't been read in a week.

[dcharkes]

@jonasfj @sigurdm Does pub delete unused packages versions? Or do they just stay around forever (until a dart pub cache clean)?

[sigurdm]

Currently they stay in the cache forever.

We have a cool idea for how we could "garbage collect" the cache, but no immediate plans for realizing it.

[dcharkes]

Version-specific cache directories are checked periodically (at most, every 24 hours) to determine whether they are still in use. They are deleted if they haven’t been used for 7 days.
https://docs.gradle.org/current/userguide/directory_layout.html#dir:project_root

Thanks @reidbaker!

We might follow a similar strategy of 24h and 7d. 👍