Super-ugly workaround:

gem_spec = Gem::Specification.load("sassc.gemspec")

# HACK: Prevent rake-compiler from overriding required_ruby_version,
# because the shared library here is Ruby-agnostic.
# See https://github.com/rake-compiler/rake-compiler/issues/153
module FixRequiredRubyVersion
  def required_ruby_version=(*); end
end
Gem::Specification.prepend(FixRequiredRubyVersion)

Rake::ExtensionTask.new('libsass', gem_spec) do |ext|
  ...
end

sass/sassc-ruby@f1c7677

sass/sassc-ruby@f1c7677#diff-52c976fc38ed2b4e3b1192f8a8e24cffL25 is expected code for this case.

The cross_compiling block exists for customizing corss-compiled gemspec:

Doesn't work when I override in the block. Perhaps it is invoked earlier?

How to reproduce your problem?

@kou Looks like it may be possible to override it in the block (not sure why it seemed to not work for me).

Still, I'd like to add a setting for this instead, as there is another thing to check when the gem doesn't use libruby: there should only be one RUBY_CC_VERSION.

spec.required_ruby_version can be overwritten by the registered ext.cross_compiling block. But there is an issue that this callback isn't called in any case, unless ext.no_native=true is set. This has been discussed in
#171 .

Next rake-compiler-dock version will set no_native=true per default, so that the callback can be used for cases like this.

The required_ruby_version can be set per cross compile block like so:

Rake::ExtensionTask.new('my_extension', gem_spec) do |ext|
  ext.cross_compiling do |spec|
    spec.required_ruby_version = [">= 2.5", "< 3.2.dev"]
  end
end

The issue with not calling the cross_compiling block is solved in #171 . So can this issue be closed now?

I agree that we can probably close it, given that the workaround exists.