Fix brew bundle dump --global to respect XDG_CONFIG_HOME for initial Brewfile creation with backwards compatibility

Library/Homebrew/bundle/brewfile.rb

@@ -24,8 +24,16 @@ def self.path(dash_writes_to_stdout: false, global: false, file: nil)
           else
             raise "'HOMEBREW_BUNDLE_FILE' cannot be specified with '--global'" if env_bundle_file.present?
 
-            if user_config_home && File.exist?("#{user_config_home}/Brewfile")
-              "#{user_config_home}/Brewfile"
+            if user_config_home
+              xdg_path = "#{user_config_home}/Brewfile"
+              legacy_path = Bundle.exchange_uid_if_needed! { "#{Dir.home}/.Brewfile" }
+
+              # Prefer existing file to maintain backwards compatibility
+              if File.exist?(xdg_path) || !File.exist?(legacy_path)
+                xdg_path
+              else
+                legacy_path
+              end
             else
               Bundle.exchange_uid_if_needed! do
                 "#{Dir.home}/.Brewfile"

Library/Homebrew/bundle/dumper.rb

@@ -81,6 +81,7 @@ def self.brewfile_path(global: false, file: nil)
       sig { params(file: Pathname, content: String).void }
       def self.write_file(file, content)
         Bundle.exchange_uid_if_needed! do
+          file.parent.mkpath
           file.open("w") { |io| io.write content }
         end
       end

Library/Homebrew/test/bundle/brewfile_spec.rb

@@ -171,6 +171,20 @@
           expect(path).to eq(expected_pathname)
         end
       end
+
+      context "when HOMEBREW_USER_CONFIG_HOME is set but neither Brewfile exists" do
+        let(:config_dir_brewfile_exist) { false }
+
+        before do
+          # Mock that both XDG and legacy Brewfiles don't exist
+          allow(File).to receive(:exist?).with("/Users/username/.homebrew/Brewfile").and_return(false)
+          allow(File).to receive(:exist?).with("#{Dir.home}/.Brewfile").and_return(false)
+        end
+
+        it "returns the XDG path for initial Brewfile creation" do
+          expect(path).to eq(Pathname.new("#{env_user_config_home_value}/Brewfile"))
+        end
+      end
     end
 
     context "when HOMEBREW_BUNDLE_FILE has a value" do