Allow user to override ~/.bundle with environment variables

lib/bundler.rb

@@ -193,8 +193,26 @@ def tmp_home_path(login, warning)
       raise e.exception("#{warning}\nBundler also failed to create a temporary home directory at `#{path}':\n#{e}")
     end
 
-    def user_bundle_path
-      Pathname.new(user_home).join(".bundle")
+    def user_bundle_path(dir = "home")
+      env_var, fallback = case dir
+                          when "home"
+                            ["BUNDLE_USER_HOME", Pathname.new(user_home).join(".bundle")]
+                          when "cache"
+                            ["BUNDLE_USER_CACHE", user_bundle_path.join("cache")]
+                          when "config"
+                            ["BUNDLE_USER_CONFIG", user_bundle_path.join("config")]
+                          when "plugin"
+                            ["BUNDLE_USER_PLUGIN", user_bundle_path.join("plugin")]
+                          else
+                            raise BundlerError, "Unknown user path requested: #{dir}"
+      end
+      # `fallback` will already be a Pathname, but Pathname.new() is
+      # idempotent so it's OK
+      Pathname.new(ENV.fetch(env_var, fallback))
+    end
+
+    def user_cache
+      user_bundle_path("cache")
     end
 
     def home
@@ -209,10 +227,6 @@ def specs_path
       bundle_path.join("specifications")
     end
 
-    def user_cache
-      user_bundle_path.join("cache")
-    end
-
     def root
       @root ||= begin
                   SharedHelpers.root

lib/bundler/plugin.rb

@@ -80,8 +80,8 @@ def index
 
     # The directory root for all plugin related data
     #
-    # Points to root in app_config_path if ran in an app else points to the one
-    # in user_bundle_path
+    # If run in an app, points to local root, in app_config_path
+    # Otherwise, points to global root, in Bundler.user_bundle_path("plugin")
     def root
       @root ||= if SharedHelpers.in_bundle?
         local_root
@@ -96,7 +96,7 @@ def local_root
 
     # The global directory root for all plugin related data
     def global_root
-      Bundler.user_bundle_path.join("plugin")
+      Bundler.user_bundle_path("plugin")
     end
 
     # The cache directory for plugin stuffs

lib/bundler/settings.rb

@@ -392,7 +392,7 @@ def global_config_file
         Pathname.new(ENV["BUNDLE_CONFIG"])
       else
         begin
-          Bundler.user_bundle_path.join("config")
+          Bundler.user_bundle_path("config")
         rescue PermissionError, GenericSystemCallError
           nil
         end

spec/bundler/bundler_spec.rb

@@ -227,4 +227,62 @@
       expect(Bundler.tmp_home_path("USER", "")).to eq(Pathname("/TMP/bundler/home/USER"))
     end
   end
+
+  context "user cache dir" do
+    let(:home_path)                  { Pathname.new(ENV["HOME"]) }
+
+    let(:xdg_data_home)              { home_path.join(".local") }
+    let(:xdg_cache_home)             { home_path.join(".cache") }
+    let(:xdg_config_home)            { home_path.join(".config") }
+
+    let(:bundle_user_home_default)   { home_path.join(".bundle") }
+    let(:bundle_user_home_custom)    { xdg_data_home.join("bundle") }
+
+    let(:bundle_user_cache_default)  { bundle_user_home_default.join("cache") }
+    let(:bundle_user_cache_custom)   { xdg_cache_home.join("bundle") }
+
+    let(:bundle_user_config_default) { bundle_user_home_default.join("config") }
+    let(:bundle_user_config_custom)  { xdg_config_home.join("bundle") }
+
+    let(:bundle_user_plugin_default) { bundle_user_home_default.join("plugin") }
+    let(:bundle_user_plugin_custom)  { xdg_data_home.join("bundle").join("plugin") }
+
+    describe "#user_bundle_path" do
+      before do
+        allow(Bundler.rubygems).to receive(:user_home).and_return(home_path)
+      end
+
+      it "should use the default home path" do
+        expect(Bundler.user_bundle_path).to           eq(bundle_user_home_default)
+        expect(Bundler.user_bundle_path("home")).to   eq(bundle_user_home_default)
+        expect(Bundler.user_bundle_path("cache")).to  eq(bundle_user_cache_default)
+        expect(Bundler.user_cache).to                 eq(bundle_user_cache_default)
+        expect(Bundler.user_bundle_path("config")).to eq(bundle_user_config_default)
+        expect(Bundler.user_bundle_path("plugin")).to eq(bundle_user_plugin_default)
+      end
+
+      it "should use custom home path as root for other paths" do
+        ENV["BUNDLE_USER_HOME"] = bundle_user_home_custom.to_s
+        expect(Bundler.user_bundle_path).to           eq(bundle_user_home_custom)
+        expect(Bundler.user_bundle_path("home")).to   eq(bundle_user_home_custom)
+        expect(Bundler.user_bundle_path("cache")).to  eq(bundle_user_home_custom.join("cache"))
+        expect(Bundler.user_cache).to                 eq(bundle_user_home_custom.join("cache"))
+        expect(Bundler.user_bundle_path("config")).to eq(bundle_user_home_custom.join("config"))
+        expect(Bundler.user_bundle_path("plugin")).to eq(bundle_user_home_custom.join("plugin"))
+      end
+
+      it "should use all custom paths, except home" do
+        ENV.delete("BUNDLE_USER_HOME")
+        ENV["BUNDLE_USER_CACHE"]  = bundle_user_cache_custom.to_s
+        ENV["BUNDLE_USER_CONFIG"] = bundle_user_config_custom.to_s
+        ENV["BUNDLE_USER_PLUGIN"] = bundle_user_plugin_custom.to_s
+        expect(Bundler.user_bundle_path).to           eq(bundle_user_home_default)
+        expect(Bundler.user_bundle_path("home")).to   eq(bundle_user_home_default)
+        expect(Bundler.user_bundle_path("cache")).to  eq(bundle_user_cache_custom)
+        expect(Bundler.user_cache).to                 eq(bundle_user_cache_custom)
+        expect(Bundler.user_bundle_path("config")).to eq(bundle_user_config_custom)
+        expect(Bundler.user_bundle_path("plugin")).to eq(bundle_user_plugin_custom)
+      end
+    end
+  end
 end