[rubygems/rubygems] Simplify logic for Gem::PathSupport#home, and make GEM_HOME always overide it.

https://github.com/rubygems/rubygems/commit/64273fd7e3

lib/rubygems/path_support.rb

@@ -24,19 +24,24 @@ class Gem::PathSupport
   # hashtable, or defaults to ENV, the system environment.
   #
   def initialize(env)
-    @home = default_home_dir(env)
+    # Current implementation of @home, which is exposed as `Gem.paths.home`:
+    # 1. If `env["GEM_HOME"]` is defined in the environment: `env["GEM_HOME"]`.
+    # 2. If `Gem.default_dir` is writable OR it does not exist and it's parent
+    #    directory is writable: `Gem.default_dir`.
+    # 3. Otherwise: `Gem.user_dir`.
 
-    # If @home (aka Gem.paths.home) exists, but we can't write to it,
+    if env.key?("GEM_HOME")
-    # fall back to Gem.user_dir (the directory used for user installs).
+      @home = normalize_home_dir(env["GEM_HOME"])
-    if File.exist?(@home) && !File.writable?(@home)
+    elsif File.writable?(Gem.default_dir) || \
-      warn "The default GEM_HOME (#{@home}) is not" \
+          (!File.exist?(Gem.default_dir) && File.writable?(File.expand_path("..", Gem.default_dir)))
-            " writable, so rubygems is falling back to installing" \
-            " under your home folder. To get rid of this warning" \
-            " permanently either fix your GEM_HOME folder permissions" \
-            " or add the following to your ~/.gemrc file:\n" \
-            "    gem: --install-dir #{Gem.user_dir}"
 
-      @home = Gem.user_dir
+      @home = normalize_home_dir(Gem.default_dir)
+    else
+      # If `GEM_HOME` is not set AND we can't use `Gem.default_dir`,
+      # default to a user installation and print a message about this.
+      puts "Defaulting to user installation because default GEM_HOME (#{Gem.default_dir}) is not writable."
+
+      @home = normalize_home_dir(Gem.user_dir)
     end
 
     @path = split_gem_path env["GEM_PATH"], @home
@@ -52,9 +57,7 @@ class Gem::PathSupport
   # The default home directory.
   # This function was broken out to accommodate tests in `bundler/spec/commands/doctor_spec.rb`.
 
-  def default_home_dir(env)
+  def normalize_home_dir(home)
-    home = env["GEM_HOME"] || Gem.default_dir
-
     if File::ALT_SEPARATOR
       home = home.gsub(File::ALT_SEPARATOR, File::SEPARATOR)
     end

spec/bundler/commands/doctor_spec.rb

@@ -40,8 +40,9 @@ RSpec.describe "bundle doctor" do
       allow(File).to receive(:readable?).with(unwritable_file) { true }
 
       # The following 2 lines are for `Gem::PathSupport#initialize`.
-      allow(File).to receive(:exist?).with(Gem.paths.send(:default_home_dir))
+      allow(File).to receive(:exist?).with(Gem.default_dir)
-      allow(File).to receive(:writable?).with(Gem.paths.send(:default_home_dir))
+      allow(File).to receive(:writable?).with(Gem.default_dir)
+      allow(File).to receive(:writable?).with(File.expand_path("..", Gem.default_dir))
     end
 
     it "exits with no message if the installed gem has no C extensions" do

test/rubygems/test_gem_install_update_options.rb

@@ -165,6 +165,9 @@ class TestGemInstallUpdateOptions < Gem::InstallerTestCase
       return
     end
 
+    orig_gem_home = ENV["GEM_HOME"]
+    ENV.delete("GEM_HOME")
+
     @spec = quick_gem "a" do |spec|
       util_make_exec spec
     end
@@ -179,11 +182,12 @@ class TestGemInstallUpdateOptions < Gem::InstallerTestCase
     FileUtils.chmod 0o755, @userhome
     FileUtils.chmod 0o000, @gemhome
 
-    Gem.use_paths @gemhome, @userhome
+    Gem.use_paths nil, @userhome
 
     assert_equal Gem.paths.home, Gem.user_dir
   ensure
     FileUtils.chmod 0o755, @gemhome
+    ENV["GEM_HOME"] = orig_gem_home if orig_gem_home
   end
 
   def test_vendor