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

Library/Homebrew/bundle/brewfile.rb

@@ -24,7 +24,21 @@ 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")
+            # Determine if we're in XDG mode by checking if user_config_home is XDG-based
+            # In bin/brew: XDG_CONFIG_HOME set -> HOMEBREW_USER_CONFIG_HOME="${XDG_CONFIG_HOME}/homebrew"
+            # XDG_CONFIG_HOME not set -> HOMEBREW_USER_CONFIG_HOME="${HOME}/.homebrew"
+            using_xdg = user_config_home&.end_with?("/homebrew")
+
+            if using_xdg && user_config_home
+              # XDG mode: check both XDG and legacy locations, preferring existing files
+              xdg_brewfile = "#{user_config_home}/Brewfile"
+              if File.exist?(xdg_brewfile)
+                xdg_brewfile
+              else
+                legacy_brewfile = Bundle.exchange_uid_if_needed! { "#{Dir.home}/.Brewfile" }
+                File.exist?(legacy_brewfile) ? legacy_brewfile : xdg_brewfile
+              end
+            elsif user_config_home && File.exist?("#{user_config_home}/Brewfile")
               "#{user_config_home}/Brewfile"
             else
               Bundle.exchange_uid_if_needed! do

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

@@ -26,8 +26,12 @@
 
       allow(ENV).to receive(:fetch).with("HOMEBREW_USER_CONFIG_HOME", any_args)
                                    .and_return(env_user_config_home_value)
+      allow(ENV).to receive(:[]).with("XDG_CONFIG_HOME").and_return(nil)
       allow(File).to receive(:exist?).with("/Users/username/.homebrew/Brewfile")
                                      .and_return(config_dir_brewfile_exist)
+      # Allow any other File.exist? calls and Dir.home calls for flexibility
+      allow(File).to receive(:exist?).and_return(false)
+      allow(Dir).to receive(:home).and_return("/Users/username")
     end
 
     context "when `file` is specified with a relative path" do
@@ -171,6 +175,33 @@
           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 }
+
+        context "when XDG_CONFIG_HOME is set" do
+          before do
+            allow(ENV).to receive(:[]).with("XDG_CONFIG_HOME").and_return("/custom/xdg")
+            # 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
+
+        context "when XDG_CONFIG_HOME is not set" do
+          before do
+            allow(ENV).to receive(:[]).with("XDG_CONFIG_HOME").and_return(nil)
+          end
+
+          it "returns the legacy path" do
+            expect(path).to eq(Pathname.new("#{Dir.home}/.Brewfile"))
+          end
+        end
+      end
     end
 
     context "when HOMEBREW_BUNDLE_FILE has a value" do