Add Coursier to Travis cache

[ashawley]

This should speed up the pull requests again.

[lrytz]

👍 - any .lock files or so that need to be deleted? i googled a bit and found this: https://github.com/softwaremill/sttp/blob/master/.travis.yml#L17

[SethTisue]

for anyone visiting this PR because I just tweeted about it, note that it's intentional that we keep the ~/.ivy2 entry, because the sbt launcher still uses it

[ashawley]

I've added the .lock file removal. It gave an opportunity to re-run the build with caching. It seemed to knock off 60 seconds from the build times.

[djspiewak]

I'm relatively certain that coursier doesn't actually lock anything. I don't think removing the lock files as here or in SoftwareMill's build hurts anything, but it also probably doesn't matter.

[eed3si9n]

Suggested change

	- $HOME/.coursier
	- $HOME/.cache/coursier

https://get-coursier.io/docs/cache says:

• on Linux, ~/.cache/coursier/v1. This also applies to Linux-based CI environments, and FreeBSD too.

...
The default location above was set up in coursier 1.0.0-RC12-1 (released on 2017/10/31). The default cache path of former versions was ~/.coursier/cache/v1, both on Linux and OS X.

In order not to re-download all artifacts again, the first version of coursier run on a system, either former or newer, sets the location for newer versions.

In other words, the location of the Coursier cache changes depending on if you've ever ran older coursier or not.

[SethTisue]

gah

[ashawley]

depending on if you've ever ran older coursier or not.

How does Coursier determine that?

Travis doesn't cache ~/.coursier or ~/.cache/coursier until the user says so.

[lrytz]

I guess coursier will use .coursier if it exists, and .cache/coursier otherwise. In the case of travis, both don't exist we didn't cache so far, so it's using the .cache/coursier. I checked that with my https://github.com/lrytz/travis-test repo.

[SethTisue]

@alexarchambault do we not need the lock-removal line?

[ashawley]

I had the same skepticism about the lock file, but I came across a reference to a cache lock file named .structure.lock in Coursier's source code, so one assumes it could exist.

[SethTisue]

but -name "*.lock" wouldn't catch .structure.lock (because of the initial dot)

[ashawley]

I thought that too, but it seems to work.

[SethTisue]

right you are

% mkdir foo
% cd foo
~/foo % touch .lock
~/foo % find . -name \*.lock
./.lock

[lrytz]

This should probably search in .cache/coursier too?

[alexarchambault]

I had the same skepticism about the lock file, but I came across a reference to a cache lock file named .structure.lock in Coursier's source code, so one assumes it could exist.

The existence of this file has no impact in itself. Only another process holding a FileLock on it is taken into account. So it doesn't matter if that file is kept in cache, or simply exists before running resolutions.

You can remove those, but it won't change anything down the line (it's not worth the noise IMO, which is why I don't add that line to any of my projects' .travis.yml).