@ruby//:headers assumes headers are in subdirectory of `dist`

[JasonLunn]

#197 exposes the location of Ruby headers/jars for use in rules that build native extensions, but it appears to make assumptions about the location of these files (e.g. that they are in a subdirectory named dist) that aren't universal.

When I install CRuby via RVM (inside a docker image):

ruby -e 'puts RbConfig::CONFIG["rubyhdrdir"]' outputs /usr/local/rvm/rubies/ruby-3.0.2/include/ruby-3.0.0

Similarly, for a user local installation of JRuby on my laptop, I find jruby.jar in ~/.rubies/jruby-9.4.5.0/lib/jruby.jar, which aligns with the output from ruby -e 'puts RbConfig::CONFIG["libdir"]'

In neither the CRuby or JRuby cases are the headers within a dist directory.

As a result, when I try to build the native extension examples on these system, I see 'ruby.h' file not found build errors.

[JasonLunn]

CC @p0deje

[p0deje]

@JasonLunn Do you use the system toolchain?

[JasonLunn]

Indeed; I've got:

rb_register_toolchains(
    version = "system",
)

[p0deje]

Any reason why you would want to use the system toolchain? it makes the builds non-hermetic / non-reproducible and is generally discouraged, so I'm hesitant to add workarounds for headers/jars specifically targeting the system toolchain.

[JasonLunn]

This is typically used from a docker image in our CI infrastructure.

[p0deje]

This should now be fixed in 0.17.3