Backport non gnu libc linux support from RubyGems

bundler/lib/bundler/rubygems_ext.rb

@@ -237,6 +237,32 @@ class Platform
     MINGW = Gem::Platform.new("x86-mingw32")
     X64_MINGW = [Gem::Platform.new("x64-mingw32"),
                  Gem::Platform.new("x64-mingw-ucrt")].freeze
+
+    if Gem::Platform.new("x86_64-linux-musl") === Gem::Platform.new("x86_64-linux")
+      remove_method :===
+
+      def ===(other)
+        return nil unless Gem::Platform === other
+
+        # universal-mingw32 matches x64-mingw-ucrt
+        return true if (@cpu == "universal" || other.cpu == "universal") &&
+                       @os.start_with?("mingw") && other.os.start_with?("mingw")
+
+        # cpu
+        ([nil,"universal"].include?(@cpu) || [nil, "universal"].include?(other.cpu) || @cpu == other.cpu ||
+        (@cpu == "arm" && other.cpu.start_with?("arm"))) &&
+
+          # os
+          @os == other.os &&
+
+          # version
+          (
+            (@os != "linux" && (@version.nil? || other.version.nil?)) ||
+            (@os == "linux" && ((@version.nil? && ["gnu", "musl"].include?(other.version)) || (@version == "gnu" && other.version.nil?))) ||
+            @version == other.version
+          )
+      end
+    end
   end
 
   Platform.singleton_class.module_eval do

bundler/spec/resolver/platform_spec.rb

@@ -82,6 +82,79 @@
     should_resolve_as %w[foo-1.0.0-x64-mingw32]
   end
 
+  describe "on a linux platform", :rubygems => ">= 3.1.0.pre.1" do
+    # Ruby's platform is *-linux => platform's libc is glibc, so not musl
+    # Ruby's platform is *-linux-musl => platform's libc is musl, so not glibc
+    # Gem's platform is *-linux => gem is glibc + maybe musl compatible
+    # Gem's platform is *-linux-musl => gem is musl compatible but not glibc
+
+    it "favors the platform version-specific gem on a version-specifying linux platform" do
+      @index = build_index do
+        gem "foo", "1.0.0"
+        gem "foo", "1.0.0", "x86_64-linux"
+        gem "foo", "1.0.0", "x86_64-linux-musl"
+      end
+      dep "foo"
+      platforms "x86_64-linux-musl"
+
+      should_resolve_as %w[foo-1.0.0-x86_64-linux-musl]
+    end
+
+    it "favors the version-less gem over the version-specific gem on a gnu linux platform" do
+      @index = build_index do
+        gem "foo", "1.0.0"
+        gem "foo", "1.0.0", "x86_64-linux"
+        gem "foo", "1.0.0", "x86_64-linux-musl"
+      end
+      dep "foo"
+      platforms "x86_64-linux"
+
+      should_resolve_as %w[foo-1.0.0-x86_64-linux]
+    end
+
+    it "ignores the platform version-specific gem on a gnu linux platform" do
+      @index = build_index do
+        gem "foo", "1.0.0", "x86_64-linux-musl"
+      end
+      dep "foo"
+      platforms "x86_64-linux"
+
+      should_not_resolve
+    end
+
+    it "falls back to the platform version-less gem on a linux platform with a version" do
+      @index = build_index do
+        gem "foo", "1.0.0"
+        gem "foo", "1.0.0", "x86_64-linux"
+      end
+      dep "foo"
+      platforms "x86_64-linux-musl"
+
+      should_resolve_as %w[foo-1.0.0-x86_64-linux]
+    end
+
+    it "falls back to the ruby platform gem on a gnu linux platform when only a version-specifying gem is available" do
+      @index = build_index do
+        gem "foo", "1.0.0"
+        gem "foo", "1.0.0", "x86_64-linux-musl"
+      end
+      dep "foo"
+      platforms "x86_64-linux"
+
+      should_resolve_as %w[foo-1.0.0]
+    end
+
+    it "falls back to the platform version-less gem on a version-specifying linux platform and no ruby platform gem is available" do
+      @index = build_index do
+        gem "foo", "1.0.0", "x86_64-linux"
+      end
+      dep "foo"
+      platforms "x86_64-linux-musl"
+
+      should_resolve_as %w[foo-1.0.0-x86_64-linux]
+    end
+  end
+
   it "takes the latest ruby gem if the platform specific gem doesn't match the required_ruby_version" do
     @index = build_index do
       gem "foo", "1.0.0"

bundler/spec/support/indexes.rb

@@ -33,6 +33,10 @@ def resolve(args = [])
       Bundler::Resolver.resolve(deps, source_requirements, *args)
     end
 
+    def should_not_resolve
+      expect { resolve }.to raise_error(Bundler::GemNotFound)
+    end
+
     def should_resolve_as(specs)
       got = resolve
       got = got.map(&:full_name).sort