How to effectively clean target folder for CI caching

I have a workspace repository with several crates in it (> 10). A clean build of all of them takes about 10 minutes on Travis, which is why I want to cache the target/ folder.

The problem is, the target folder gets quite big (~ 1.7GB) so it takes also about 3 minutes to upload the cache to S3 after the build.

The question is: How can I clean the target folder from any artifacts generated by my own code?

If I can achieve that, then the target folder would only have the artifacts of all the dependencies in it. As long as they don't change, Travis would not have to re-upload the cache. At the same time, rebuilding only the workspace crates takes only 30 seconds.

I have already tried several things:

• cargo clean -p for every workspace package
• Delete all files in target that mention a workspace crate's name

None of the above were enough in order to get the target folder into a state where NOTHING changes between two builds.

I couldn't really understand the layout of the target folder: The artifacts of dependencies seem to be mixed up with those of the workspace crates. Is there some documentation available on how the target folder is structured?

Start by investigating the target/ layout for a workspace with more than 10 crates and the behavior of cargo clean -p for workspace packages. Compare the resulting artifacts across repeated Travis builds and document which dependency and workspace artifacts remain, along with whether a stable cache-cleaning procedure exists.