Add MSYS2 platform support (#16)

This PR adds support for the MSYS2 environment on Windows, porting the
functionality from the deprecated native-package-installer gem.

Note that this isn't for Ruby installed by RubyInstaller. Ruby installed
by RubyInstaller must use `msys2_mingw_dependencies` gemspec metadata
instead of this.

Supported MSYS2 platforms:
- CLANG64
- CLANGARM64
- MINGW32
- MINGW64
- UCRT64

Author: otegami

.github/workflows/test.yml

@@ -92,3 +92,47 @@ jobs:
           cd test/fixture/dummy-cairo
           gem build *.gemspec
           gem install ./*.gem
+
+  windows-msys2:
+    name: Windows ${{ matrix.msystem }}
+    runs-on: ${{ matrix.runner }}
+    timeout-minutes: 10
+    strategy:
+      fail-fast: false
+      matrix:
+        include:
+          - msystem: CLANG64
+            package-prefix: mingw-w64-clang-x86_64
+            runner: windows-latest
+          - msystem: CLANGARM64
+            package-prefix: mingw-w64-clang-aarch64
+            runner: windows-11-arm
+          - msystem: MINGW32
+            package-prefix: mingw-w64-i686
+            runner: windows-latest
+          - msystem: MINGW64
+            package-prefix: mingw-w64-x86_64
+            runner: windows-latest
+          - msystem: UCRT64
+            package-prefix: mingw-w64-ucrt-x86_64
+            runner: windows-latest
+    steps:
+      - uses: actions/checkout@v6
+      - uses: msys2/setup-msys2@v2
+        with:
+          msystem: ${{ matrix.msystem }}
+          update: true
+          install: >-
+            base-devel
+            ${{ matrix.package-prefix }}-ruby
+            ${{ matrix.package-prefix }}-toolchain
+      - name: Install
+        shell: msys2 {0}
+        run: |
+          rake install
+      - name: Install dummy-cairo gem
+        shell: msys2 {0}
+        run: |
+          cd test/fixture/dummy-cairo
+          gem build *.gemspec
+          gem install ./*.gem

lib/rubygems-requirements-system/platform.rb

@@ -62,6 +62,10 @@ def detect(ui)
 require_relative "platform/alpine-linux"
 
 
+# Windows
+require_relative "platform/msys2"
+
+
 # Platform independent
 require_relative "platform/homebrew"
 require_relative "platform/conda"

lib/rubygems-requirements-system/platform/msys2.rb

@@ -0,0 +1,54 @@
+# Copyright (C) 2025  Ruby-GNOME Project Team
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Lesser General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU Lesser General Public License for more details.
+#
+# You should have received a copy of the GNU Lesser General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+require_relative "base"
+
+module RubyGemsRequirementsSystem
+  module Platform
+    class MSYS2 < Base
+      Platform.register(self)
+
+      class << self
+        def current_platform?
+          return false if Object.const_defined?(:RubyInstaller)
+          return false if package_prefix.nil?
+          ExecutableFinder.exist?("pacman")
+        end
+
+        def package_prefix
+          ENV["MINGW_PACKAGE_PREFIX"]
+        end
+      end
+
+      def target?(platform)
+        platform == "msys2"
+      end
+
+      private
+      def install_command_line(package)
+        [
+          "pacman",
+          "-S",
+          "--noconfirm",
+          "#{self.class.package_prefix}-#{package}"
+        ]
+      end
+
+      def need_super_user_priviledge?
+        false
+      end
+    end
+  end
+end

test/fixture/dummy-cairo/dummy-cairo.gemspec

@@ -52,6 +52,7 @@ Gem::Specification.new do |spec|
   spec.requirements << "system: cairo >= 1.2.0: gentoo_linux: x11-libs/cairo"
   spec.requirements << "system: cairo >= 1.2.0: homebrew: cairo"
   spec.requirements << "system: cairo >= 1.2.0: macports: cairo"
+  spec.requirements << "system: cairo >= 1.2.0: msys2: cairo"
   spec.requirements << "system: cairo >= 1.2.0: pld_linux: cairo-devel"
   spec.requirements << "system: cairo >= 1.2.0: suse: cairo-devel"
 end