Support nativeTarget to build Scala Native static/shared libraries

[keynmol]

Scala Native CLI supports building dynamic and shared libraries using --build-target argument.

So far it hasn't been supported. This PR adds the support, by

• Adding nativeTarget directive and native-target CLI option
• Splitting PackageType.Native into 3 different types
• Modifying the logic to not throw when main class is not found if we are building a library
• IMPORTANT: use -Wl,install_name argument to rename the library inside its own metadata, otherwise it points to .scala-build/project_asdkljadljk190/main - instead of test.dylib that we want

[lwronski]

It looks promising to me, and I would be happy to merge it. Unfortunately, there is one new test that is failing. You can find more details here.

To fix the checks and reference-doc jobs, run the following commands before pushing your changes:

./mill -i __.fix
./mill -i generate-reference-doc.run

[keynmol]

@lwronski, thanks, that's exactly the commands I was looking for :)

If you are happy with the overall approach I will start fixing and cleaning up the PR

[lwronski]

@lwronski, thanks, that's exactly the commands I was looking for :)

If you are happy with the overall approach I will start fixing and cleaning up the PR

Yes, I'm satisfied with the overall approach, so I will wait for the final results.

[Gedochao]

@keynmol what is the current status on this? can we unblock you somehow?

[keynmol]

Hey @Gedochao! I didn't forget about this PR, just was short on time.

I resolved the conflicts (but incorrectly it seems, I will address those failures).

Now that I re-ran the tests on Linux, I remember the main problem - this PR relies on passing -install_name linker flag, to make sure that the dynamic library loading entries refer to the correct (relative) location of the built dynamic library, instead of the location where it's actually built (.scala-build/.../).

Problem is - on Linux this flag doesn't seem to work

Just as I was writing those last two paragraphs I found the linux equivalent option 🤦

I'll pick this up again and hopefully will address remaining test failures.

[MaciejG604]

LGTM

[keynmol]

🎉

Thanks @Gedochao and @MaciejG604