Add default output directory scalac in dotty project

[nicolasstucki]

The previous default output directory when executing scalac, run, scala3-bootstrapped/scalac and scala3-bootstrapped/run was the root directory of the project. This could easily pollute the project with .class/.tasty files. In some situations, these could be mistakenly loaded by some of the projects or scripts.

Now when we execute scalac with no -d option set, we output ./out/default-last-scalac-out.jar. We also make scala and run use that JAR by default in the classpath if no -classpath option is set.

[sjrd]

./out is not much better, since there are also subdirectories in there that could interfere with the classpath. We should use a directory that is only used for that purpose.

[nicolasstucki]

I only set the -d ./out/default-last-scalac-out.jar and do not touch the classpath. That should not conflict with the other folders in ./out.

[sjrd]

Ah, it's a .jar. That does address my comment.

Does the scala command also takes this into account to run the programs compiled by scalac?

[nicolasstucki]

Ah, it's a .jar. That does address my comment.

I thought so. I updated the PR description to make it clearer.

Does the scala command also takes this into account to run the programs compiled by scalac?

Currently not. Now we add the . to the classpath. Arguably adding ./out/default-last-scalac-out.jar to the classpath would be better.

[som-snytt]

That's an interesting idea. I have a PR for Scala 2 to use (or consider using) a small lib to conventionalize the location of output.

Maybe that would apply here because it doesn't matter how the tool is run, or perhaps in the project, the appropriate environment should be set, whatever that is.

The considerations (for the general case) are not only polluting home or current dir, but also putting files where they are exposed to others, such as /tmp. For example, scala runner should compile to a private jar.

scala/scala#10611