Migrating from bazelruby/rules_ruby for gems with native extensions

[JasonLunn]

Follow up to #180

How do gem authors use bazel-contrib/rules_ruby to reference parts of the Ruby environment needed to construct native extensions?

For example, if building a native extension in C for MRI, under bazelruby/rules_ruby I might include "@rules_ruby//ruby/runtime:headers" in the deps of the cc_library to expose ruby.h. Similarly, for an native extension targeting JRuby, I might include "@rules_ruby//ruby/runtime:jars" in the deps of the java_library.

[p0deje]

I haven't seen an example of gems building native extensions yet, so you might be the first to encounter this. It's worth asking in the #ruby channel on Bazel Slack though.

If you have an example you could share, I can help figure out what needs to be changed in the ruleset to support your case.

[JasonLunn]

This is a good example of a Ruby C extension that needs to leverage definitions from ruby.h, and this is for the JRuby version of the same gem that needs jruby.jar.

[p0deje]

I will take a look at it, but please share if you have a simpler example I can experiment with (protobuf is quite large). It might be something w/o the Bazel bits, I just need to make sure I understand how to build platform-specific versions.

[JasonLunn]

bundle gem foo --ext=c will generate a trivial gem in the folder foo with a native extension implemented in C nested inside the ext subdirectory.

[p0deje]

@JasonLunn I've started experiment with native extensions in https://github.com/bazel-contrib/rules_ruby/tree/ext and so far I had no issues compiling the gem using rake compile or packaging it in a gem and then use gem install to install it. Can you give me an example of a command I can run to reproduce the issue with missing headers when compiling extensions?