Add support for RubyGems 3.3.21 or later (#209)

Since Rubygems 3.3.21, the Gem::Platform name always contains the
library version for gnu platforms. So where the rake-compiler config
entries previously were:

```yaml
---
rbconfig-x86_64-linux-gnu-2.7.0: "/usr/local/rake-compiler/ruby/x86_64-redhat-linux/ruby-2.7.0/lib/ruby/2.7.0/x86_64-linux-gnu/rbconfig.rb"
rbconfig-x86_64-linux-2.7.0: "/usr/local/rake-compiler/ruby/x86_64-redhat-linux/ruby-2.7.0/lib/ruby/2.7.0/x86_64-linux-gnu/rbconfig.rb"
```

with later versions of rubygems, it is only

```yaml
---
rbconfig-x86_64-linux-gnu-2.7.0: "/usr/local/rake-compiler/ruby/x86_64-redhat-linux/ruby-2.7.0/lib/ruby/2.7.0/x86_64-linux-gnu/rbconfig.rb"
```

This means that the current way of finding a matching runtime, by doing
a string comparison on the config keys, is no longer appropriate. This
is causing failing builds downstream in `rake-compiler-dock`.

This PR:

- extracts a new CompilerConfig class to encapsulate the logic
- uses `Gem::Platform#=~` to tell if the gem platform matches the
runtime platform

3 files changed, 45 insertions, 7 deletions

diff --git a/lib/rake/baseextensiontask.rb b/lib/rake/baseextensiontask.rb
index cf32147..063a555 100644
--- a/lib/rake/baseextensiontask.rb
+++ b/lib/rake/baseextensiontask.rb
@@ -5,6 +5,8 @@ require 'rbconfig'
 
 require 'pathname'
 
+require_relative "compiler_config"
+
 module Rake
   class BaseExtensionTask < TaskLib
 
diff --git a/lib/rake/compiler_config.rb b/lib/rake/compiler_config.rb
new file mode 100644
index 0000000..e9832dc
--- /dev/null
+++ b/lib/rake/compiler_config.rb
@@ -0,0 +1,38 @@
+module Rake
+  class CompilerConfig
+    def initialize(config_path)
+      require "yaml"
+      @config = YAML.load_file(config_path)
+    end
+
+    def find(ruby_version, gem_platform)
+      gem_platform = Gem::Platform.new(gem_platform)
+
+      @config.each do |config_name, config_location|
+        # There are two variations we might find in the rake-compiler config.yml
+        #
+        # 1. config_name: rbconfig-x86_64-linux-3.0.0
+        #    runtime_platform_name: x86_64-linux
+        #    runtime_version: 3.0.0
+        #
+        # 2. config_name: rbconfig-x86_64-linux-gnu-3.0.0
+        #    runtime_platform_name: x86_64-linux-gnu
+        #    runtime_version: 3.0.0
+        #
+        # With rubygems < 3.3.21, both variations will be present (two entries pointing at the same
+        # installation).
+        #
+        # With rubygems >= 3.3.21, only the second variation will be present.
+        runtime_platform_name = config_name.split("-")[1..-2].join("-")
+        runtime_version = config_name.split("-").last
+        runtime_platform = Gem::Platform.new(runtime_platform_name)
+
+        if (ruby_version == runtime_version) && (gem_platform =~ runtime_platform)
+          return config_location
+        end
+      end
+
+      nil
+    end
+  end
+end
diff --git a/lib/rake/extensiontask.rb b/lib/rake/extensiontask.rb
index 7c69741..0f48520 100644
--- a/lib/rake/extensiontask.rb
+++ b/lib/rake/extensiontask.rb
@@ -393,8 +393,11 @@ Java extension should be preferred.
         return
       end
 
-      require "yaml"
-      config_file = YAML.load_file(config_path)
+      rbconfig_file = Rake::CompilerConfig.new(config_path).find(ruby_ver, for_platform)
+      unless rbconfig_file
+        warn "no configuration section for specified version of Ruby (rbconfig-#{for_platform}-#{ruby_ver})"
+        return
+      end
 
       # tmp_path
       tmp_path = "#{@tmp_dir}/#{for_platform}/#{@name}/#{ruby_ver}"
@@ -405,11 +408,6 @@ Java extension should be preferred.
       # lib_binary_path
       lib_binary_path = "#{lib_path}/#{File.basename(binary(for_platform))}"
 
-      unless rbconfig_file = config_file["rbconfig-#{for_platform}-#{ruby_ver}"] then
-        warn "no configuration section for specified version of Ruby (rbconfig-#{for_platform}-#{ruby_ver})"
-        return
-      end
-
       # mkmf
       mkmf_file = File.expand_path(File.join(File.dirname(rbconfig_file), '..', 'mkmf.rb'))