Merge bundler to standard libraries.

rubygems 2.7.x depends bundler-1.15.x. This is preparation for
  rubygems and bundler migration.

  * lib/bundler.rb, lib/bundler/*: files of bundler-1.15.4
  * spec/bundler/*: rspec examples of bundler-1.15.4. I applied patches.
    * https://github.com/bundler/bundler/pull/6007
    * Exclude not working examples on ruby repository.
    * Fake ruby interpriter instead of installed ruby.
  * Makefile.in: Added test task named `test-bundler`. This task is only
    working macOS/linux yet. I'm going to support Windows environment later.
  * tool/sync_default_gems.rb: Added sync task for bundler.

  [Feature #12733][ruby-core:77172]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@59779 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

lib/bundler/gem_helpers.rb

@@ -0,0 +1,100 @@
+# frozen_string_literal: true
+module Bundler
+  module GemHelpers
+    GENERIC_CACHE = {} # rubocop:disable MutableConstant
+    GENERICS = [
+      [Gem::Platform.new("java"), Gem::Platform.new("java")],
+      [Gem::Platform.new("mswin32"), Gem::Platform.new("mswin32")],
+      [Gem::Platform.new("mswin64"), Gem::Platform.new("mswin64")],
+      [Gem::Platform.new("universal-mingw32"), Gem::Platform.new("universal-mingw32")],
+      [Gem::Platform.new("x64-mingw32"), Gem::Platform.new("x64-mingw32")],
+      [Gem::Platform.new("x86_64-mingw32"), Gem::Platform.new("x64-mingw32")],
+      [Gem::Platform.new("mingw32"), Gem::Platform.new("x86-mingw32")]
+    ].freeze
+
+    def generic(p)
+      return p if p == Gem::Platform::RUBY
+
+      GENERIC_CACHE[p] ||= begin
+        _, found = GENERICS.find do |match, _generic|
+          p.os == match.os && (!match.cpu || p.cpu == match.cpu)
+        end
+        found || Gem::Platform::RUBY
+      end
+    end
+    module_function :generic
+
+    def generic_local_platform
+      generic(Bundler.local_platform)
+    end
+    module_function :generic_local_platform
+
+    def platform_specificity_match(spec_platform, user_platform)
+      spec_platform = Gem::Platform.new(spec_platform)
+      return PlatformMatch::EXACT_MATCH if spec_platform == user_platform
+      return PlatformMatch::WORST_MATCH if spec_platform.nil? || spec_platform == Gem::Platform::RUBY || user_platform == Gem::Platform::RUBY
+
+      PlatformMatch.new(
+        PlatformMatch.os_match(spec_platform, user_platform),
+        PlatformMatch.cpu_match(spec_platform, user_platform),
+        PlatformMatch.platform_version_match(spec_platform, user_platform)
+      )
+    end
+    module_function :platform_specificity_match
+
+    def select_best_platform_match(specs, platform)
+      specs.select {|spec| spec.match_platform(platform) }.
+        min_by {|spec| platform_specificity_match(spec.platform, platform) }
+    end
+    module_function :select_best_platform_match
+
+    PlatformMatch = Struct.new(:os_match, :cpu_match, :platform_version_match)
+    class PlatformMatch
+      def <=>(other)
+        return nil unless other.is_a?(PlatformMatch)
+
+        m = os_match <=> other.os_match
+        return m unless m.zero?
+
+        m = cpu_match <=> other.cpu_match
+        return m unless m.zero?
+
+        m = platform_version_match <=> other.platform_version_match
+        m
+      end
+
+      EXACT_MATCH = new(-1, -1, -1).freeze
+      WORST_MATCH = new(1_000_000, 1_000_000, 1_000_000).freeze
+
+      def self.os_match(spec_platform, user_platform)
+        if spec_platform.os == user_platform.os
+          0
+        else
+          1
+        end
+      end
+
+      def self.cpu_match(spec_platform, user_platform)
+        if spec_platform.cpu == user_platform.cpu
+          0
+        elsif spec_platform.cpu == "arm" && user_platform.cpu.to_s.start_with?("arm")
+          0
+        elsif spec_platform.cpu.nil? || spec_platform.cpu == "universal"
+          1
+        else
+          2
+        end
+      end
+
+      def self.platform_version_match(spec_platform, user_platform)
+        if spec_platform.version == user_platform.version
+          0
+        elsif spec_platform.version.nil?
+          1
+        else
+          2
+        end
+      end
+    end
+  end
+end