[rubygems/rubygems] Fix issue when cleaning up plugin stubs

When `gem uninstall <gem> --install-dir <dir>` is run, if the version
removed had a plugin, and that same version happened to also be
installed globally, then the plugin stub would fail to be removed.

https://github.com/rubygems/rubygems/commit/4e2fa0be77

lib/rubygems/specification.rb

@@ -906,9 +906,7 @@ class Gem::Specification < Gem::BasicSpecification
   # Return the directories that Specification uses to find specs.
 
   def self.dirs
-    @@dirs ||= Gem.path.collect do |dir|
-      File.join dir, "specifications"
-    end
+    @@dirs ||= Gem::SpecificationRecord.dirs_from(Gem.path)
   end
 
   ##
@@ -918,7 +916,7 @@ class Gem::Specification < Gem::BasicSpecification
   def self.dirs=(dirs)
     reset
 
-    @@dirs = Array(dirs).map {|dir| File.join dir, "specifications" }
+    @@dirs = Gem::SpecificationRecord.dirs_from(Array(dirs))
   end
 
   extend Enumerable

lib/rubygems/specification_record.rb

@@ -2,6 +2,16 @@
 
 module Gem
   class SpecificationRecord
+    def self.dirs_from(paths)
+      paths.map do |path|
+        File.join(path, "specifications")
+      end
+    end
+
+    def self.from_path(path)
+      new(dirs_from([path]))
+    end
+
     def initialize(dirs)
       @all = nil
       @stubs = nil

lib/rubygems/uninstaller.rb

@@ -49,7 +49,8 @@ class Gem::Uninstaller
     # TODO: document the valid options
     @gem                = gem
     @version            = options[:version] || Gem::Requirement.default
-    @gem_home           = File.realpath(options[:install_dir] || Gem.dir)
+    @install_dir        = options[:install_dir]
+    @gem_home           = File.realpath(@install_dir || Gem.dir)
     @force_executables  = options[:executables]
     @force_all          = options[:all]
     @force_ignore       = options[:ignore]
@@ -69,7 +70,7 @@ class Gem::Uninstaller
 
     # only add user directory if install_dir is not set
     @user_install = false
-    @user_install = options[:user_install] unless options[:install_dir]
+    @user_install = options[:user_install] unless @install_dir
 
     # Optimization: populated during #uninstall
     @default_specs_matching_uninstall_params = []
@@ -290,7 +291,8 @@ class Gem::Uninstaller
   # Regenerates plugin wrappers after removal.
 
   def regenerate_plugins
-    latest = Gem::Specification.latest_spec_for(@spec.name)
+    specification_record = @install_dir ? Gem::SpecificationRecord.from_path(@install_dir) : Gem::Specification.specification_record
+    latest = specification_record.latest_spec_for(@spec.name)
     return if latest.nil?
 
     regenerate_plugins_for(latest, plugin_dir_for(@spec))

test/rubygems/test_gem_uninstaller.rb

@@ -213,6 +213,37 @@ class TestGemUninstaller < Gem::InstallerTestCase
     Gem::Uninstaller.new(@spec.name, executables: true, install_dir: install_dir).uninstall
 
     assert File.exist?(plugin_path), "plugin unintentionally removed"
+    refute File.exist?(install_dir_plugin_path), "plugin not removed"
+  end
+
+  def test_uninstall_with_install_dir_regenerates_plugins
+    write_file File.join(@tempdir, "lib", "rubygems_plugin.rb") do |io|
+      io.write "# do nothing"
+    end
+
+    @spec.files += %w[lib/rubygems_plugin.rb]
+
+    install_dir = "#{@gemhome}2"
+
+    package = Gem::Package.build(@spec)
+
+    spec_v9 = @spec.dup
+    spec_v9.version = "9"
+    package_v9 = Gem::Package.build(spec_v9)
+
+    Gem::Installer.at(package, force: true, install_dir: install_dir).install
+    Gem::Installer.at(package_v9, force: true, install_dir: install_dir).install
+
+    install_dir_plugin_path = File.join install_dir, "plugins/a_plugin.rb"
+    assert File.exist?(install_dir_plugin_path), "plugin not written"
+
+    Gem::Specification.dirs = [install_dir]
+    Gem::Uninstaller.new(@spec.name, version: "9", executables: true, install_dir: install_dir).uninstall
+    assert File.exist?(install_dir_plugin_path), "plugin unintentionally removed"
+
+    Gem::Specification.dirs = [install_dir]
+    Gem::Uninstaller.new(@spec.name, executables: true, install_dir: install_dir).uninstall
+    refute File.exist?(install_dir_plugin_path), "plugin not removed"
   end
 
   def test_remove_plugins_user_installed