[rubygems/rubygems] Fix contradictory message about deletion of default gem

[Fixes #4733]

https://github.com/rubygems/rubygems/commit/fce7f3eb7d

lib/rubygems/uninstaller.rb

@@ -70,6 +70,9 @@ 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]
+
+    # Optimization: populated during #uninstall
+    @default_specs_matching_uninstall_params = []
   end
 
   ##
@@ -98,10 +101,8 @@ class Gem::Uninstaller
     default_specs, list = list.partition do |spec|
       spec.default_gem?
     end
-
-    default_specs.each do |default_spec|
-      say "Gem #{default_spec.full_name} cannot be uninstalled because it is a default gem"
-    end
+    warn_cannot_uninstall_default_gems(default_specs - list)
+    @default_specs_matching_uninstall_params = default_specs
 
     list, other_repo_specs = list.partition do |spec|
       @gem_home == spec.base_dir or
@@ -273,7 +274,7 @@ class Gem::Uninstaller
     end
 
     safe_delete { FileUtils.rm_r gemspec }
-    say "Successfully uninstalled #{spec.full_name}"
+    announce_deletion_of(spec)
 
     Gem::Specification.reset
   end
@@ -376,4 +377,34 @@ class Gem::Uninstaller
 
     raise e
   end
+
+  private
+
+  def announce_deletion_of(spec)
+    name = spec.full_name
+    say "Successfully uninstalled #{name}"
+    if default_spec_matches?(spec)
+      say(
+        "There was both a regular copy and a default copy of #{name}. The " \
+          "regular copy was successfully uninstalled, but the default copy " \
+          "was left around because default gems can't be removed."
+      )
+    end
+  end
+
+  # @return true if the specs of any default gems are `==` to the given `spec`.
+  def default_spec_matches?(spec)
+    !default_specs_that_match(spec).empty?
+  end
+
+  # @return [Array] specs of default gems that are `==` to the given `spec`.
+  def default_specs_that_match(spec)
+    @default_specs_matching_uninstall_params.select {|default_spec| spec == default_spec }
+  end
+
+  def warn_cannot_uninstall_default_gems(specs)
+    specs.each do |spec|
+      say "Gem #{spec.full_name} cannot be uninstalled because it is a default gem"
+    end
+  end
 end

test/rubygems/test_gem_uninstaller.rb

@@ -295,8 +295,15 @@ class TestGemUninstaller < Gem::InstallerTestCase
 
     uninstaller = Gem::Uninstaller.new spec.name, :executables => true
 
+    ui = Gem::MockGemUi.new "1\ny\n"
+    use_ui ui do
       uninstaller.uninstall
-
+    end
+    expected = "Successfully uninstalled default-2\n" \
+      "There was both a regular copy and a default copy of default-2. The " \
+      "regular copy was successfully uninstalled, but the default copy " \
+      "was left around because default gems can't be removed.\n"
+    assert_equal expected, ui.output
     assert_path_not_exist spec.gem_dir
   end