gradle: add module

[britter]

Description

Introduces a new program called gradle for managing files stored in the
home directory by the Gradle Build Tool. Gradle
uses the $HOME/.gradle folder for all it's configuration.

Features of the new program module are:

• Automatically setting programs.java.enable = true to make a Java
  installation available for running Gradle.
• Specifying an alternate Gradle home directory
• Setting of abitrary values for gradle.properties stored inside the
  Gradle home directory.
• Defining init scripts either by pointing to a directory that will be
  linked to init.d inside the Gradle home directory or by specifying
  a list of init script definitions.

Checklist

• Change is backwards compatible.

• Code formatted with ./format.

• Code tested through nix-shell --pure tests -A run.all or nix develop --ignore-environment .#all using Flakes.

• Test cases updated/added. See example.

• Commit messages are formatted like

  {component}: {description}
  
  {long description}
  

  See CONTRIBUTING for more information and recent commit messages for examples.

• If this PR adds a new module

  • Added myself as module maintainer. See example.

Maintainer CC

[britter]

This is my first contribution to the nix eco system. I'm still learning nix. Hope this makes sense!

[liff]

Would it be possible to add another setting for customizing the dot directory? The environment variable GRADLE_USER_HOME can be used to change ~/.gradle to something else. Something like programs.gradle.home perhaps, that sets home.sessionVariables.GRADLE_USER_HOME accordingly?

[britter]

@liff I'll have a look into both your suggestions. Thank you for the feedback!

[britter]

@liff This is still WIP but I addressed your comments. PTAL.

I'm still not happy with the way init scripts are handled. I think it would be better if the user could either define them inline or reference a file that is copied to the store. But I don't know how to define the type for the option. Can you give me some pointers?

[liff]

The value of programs.gradle.home should be used for the location of the generated files.

[britter]

@liff this is now ready for the final review / merge. Thank you for your support. I learned a lot along the way. ❤️

[britter]

@liff anything missing in order to get this merged?

[liff]

Looks good to me, but I lack the power to merge 😔

[britter]

@liff do you know by any chance who to ping to get this merged?

[liff]

I guess it would be @rycee by default? Or you could ask on the IRC channel.

It occurred to me that since this is a new module, perhaps it’s worthy of a news entry. New modules usually seem to get one.

[rycee]

Thanks for the contribution! I've added a bunch of mostly stylistic comments. The most important is to reduce the test closure to avoid GBs of downloads whenever the tests run 🙂

[britter]

@rycee I think I addressed all your comments. Previously the code aggregated all init scripts in a store directory using symlinkJoin. I was unable to get that working with the new structure of the initScript submodule where the source is set from the text. So the current version links individual files from the store inside .gradle/init.d. Unfortunately I didn't find a more elegant solution than home.file = mkMerge ... which feels more complex than it should.

I also added a news entry.

[rycee]

Thanks! Merged to master now 🙂