bugfix: Redownload artifacts if missing

[tgodzik]

Fixes #821

This might cause loading configuration a bit, but that should not be an issue compared to potential user trouble when the artifacts are missing.

The alternative is to only react to missing main scala jars, which would indicate that a cache was cleaned, but not if it was deleted only partly

[adpi2]

I am not sure about this. Cleaning the cache is not something we can or should do blindly. When we decide to do it anyway, for whatever reason, maybe it is reasonable that we have to re-import each project.

Also technically I have a few concerns:

• Resolving each artifact one after the other can be very slow: Coursier needs to do the conflict resolution of transitive dependencies again and again. Can we bypass the resolution and directly download the missing JAR? Or, should we do one resolution of all the missing libraries at once?
• We don't even know if Coursier is going to put the JAR in the right folder. Maybe the project does not use Coursier, or it has some custom cache configuration. Should we check the output files and copy them if necessary?

[tgodzik]

You're right about the points raised, I should fix that.

As for the validity of the approach I just felt it's not that big of an issue to add it, since currently users are quite confused about what is happening. And sometimes those artifacts are removed by the build tool like in case of gradle.

The alternative approach would be to have that check and add a better error message so that the users know they need to reimport.

What do you think?

[adpi2]

And sometimes those artifacts are removed by the build tool like in case of gradle.

Do you know why Gradle does such thing?

[tgodzik]

I think it was local cache inside the project, but not sure if that is a standard behaviour even

[adpi2]

I think it was local cache inside the project, but not sure if that is a standard behaviour even

Then I think it would be weird for Bloop to write files inside Gradle local cache.

Maybe it is safer for Bloop not to interact too much with project dependencies. So I would opt for a better error message.

Although I would not be mad if you disagree :)

[tgodzik]

I think it was local cache inside the project, but not sure if that is a standard behaviour even

Then I think it would be weird for Bloop to write files inside Gradle local cache.

Maybe it is safer for Bloop not to interact too much with project dependencies. So I would opt for a better error message.

Although I would not be mad if you disagree :)

Not super sure if I disagree 😅 Potentially we could only do it for things in coursier cache, but yeah it all kind of falls apart