Move gem group setting to separate, cacheable file

.gitignore

@@ -26,6 +26,7 @@
 # Ignore Bundler files
 **/.bundle/bin
 **/.bundle/cache
+**/vendor/bundle/ruby/.homebrew_gemgroups
 **/vendor/bundle/ruby/*/bundler.lock
 **/vendor/bundle/ruby/*/bin
 **/vendor/bundle/ruby/*/build_info/

Library/Homebrew/dev-cmd/install-bundler-gems.rb

@@ -13,7 +13,8 @@ def install_bundler_gems_args
         Install Homebrew's Bundler gems.
       EOS
       comma_array "--groups",
-                  description: "Installs the specified comma-separated list of gem groups (default: last used)."
+                  description: "Installs the specified comma-separated list of gem groups (default: last used). " \
+                               "Prepend with `+` to install these groups in addition to what is already installed."
 
       named_args :none
     end
@@ -23,12 +24,14 @@ def install_bundler_gems
     args = install_bundler_gems_args.parse
 
     groups = args.groups
+    append_groups = groups&.first&.delete_prefix!("+")
+    all_groups = groups&.delete("all")
 
-    # Clear previous settings. We want to fully replace - not append.
-    Homebrew::Settings.delete(:gemgroups) if groups
+    # Clear previous settings. We want to fully replace - not append, unless `+` is prepended
+    Homebrew.forget_user_gem_groups! if groups && !all_groups && !append_groups
 
     groups ||= []
-    groups |= Homebrew.valid_gem_groups if groups.delete("all")
+    groups |= Homebrew.valid_gem_groups if all_groups
 
     Homebrew.install_bundler_gems!(groups: groups)
   end

Library/Homebrew/utils/gems.rb

@@ -12,6 +12,9 @@ module Homebrew
   # After updating this, run `brew vendor-gems --update=--bundler`.
   HOMEBREW_BUNDLER_VERSION = "2.4.18"
 
+  GEMGROUPS_FILE = "#{HOMEBREW_LIBRARY_PATH}/vendor/bundle/ruby/.homebrew_gemgroups"
+  private_constant :GEMGROUPS_FILE
+
   module_function
 
   # @api private
@@ -151,6 +154,33 @@ def install_bundler!
     ENV["BUNDLER_VERSION"] = old_bundler_version
   end
 
+  def user_gem_groups
+    @user_gem_groups ||= if File.exist?(GEMGROUPS_FILE)
+      File.readlines(GEMGROUPS_FILE, chomp: true)
+    else
+      # Backwards compatibility
+      require "settings"
+      groups = Homebrew::Settings.read(:gemgroups)&.split(";") || []
+      write_user_gem_groups(groups)
+      Homebrew::Settings.delete(:gemgroups)
+      groups
+    end
+  end
+
+  def write_user_gem_groups(groups)
+    File.write(GEMGROUPS_FILE, groups.join("\n"))
+  end
+
+  def forget_user_gem_groups!
+    if File.exist?(GEMGROUPS_FILE)
+      File.truncate(GEMGROUPS_FILE, 0)
+    else
+      # Backwards compatibility
+      require "settings"
+      Homebrew::Settings.delete(:gemgroups)
+    end
+  end
+
   def install_bundler_gems!(only_warn_on_failure: false, setup_path: true, groups: [])
     old_path = ENV.fetch("PATH", nil)
     old_gem_path = ENV.fetch("GEM_PATH", nil)
@@ -174,7 +204,7 @@ def install_bundler_gems!(only_warn_on_failure: false, setup_path: true, groups:
     require "settings"
 
     # Combine the passed groups with the ones stored in settings
-    groups |= (Homebrew::Settings.read(:gemgroups)&.split(";") || [])
+    groups |= (user_gem_groups & valid_gem_groups)
     groups.sort!
 
     ENV["BUNDLE_GEMFILE"] = gemfile
@@ -223,7 +253,7 @@ def install_bundler_gems!(only_warn_on_failure: false, setup_path: true, groups:
       end
 
       if bundle_installed
-        Homebrew::Settings.write(:gemgroups, groups.join(";"))
+        write_user_gem_groups(groups)
         @bundle_installed_groups = groups
       end
     end

completions/fish/brew.fish

@@ -921,7 +921,7 @@ __fish_brew_complete_arg 'install; and not __fish_seen_argument -l formula -l fo
 
 __fish_brew_complete_cmd 'install-bundler-gems' 'Install Homebrew\'s Bundler gems'
 __fish_brew_complete_arg 'install-bundler-gems' -l debug -d 'Display any debugging information'
-__fish_brew_complete_arg 'install-bundler-gems' -l groups -d 'Installs the specified comma-separated list of gem groups (default: last used)'
+__fish_brew_complete_arg 'install-bundler-gems' -l groups -d 'Installs the specified comma-separated list of gem groups (default: last used). Prepend with `+` to install these groups in addition to what is already installed'
 __fish_brew_complete_arg 'install-bundler-gems' -l help -d 'Show this message'
 __fish_brew_complete_arg 'install-bundler-gems' -l quiet -d 'Make some output more quiet'
 __fish_brew_complete_arg 'install-bundler-gems' -l verbose -d 'Make some output more verbose'

completions/zsh/_brew

@@ -1141,7 +1141,7 @@ _brew_install() {
 _brew_install_bundler_gems() {
   _arguments \
     '--debug[Display any debugging information]' \
-    '--groups[Installs the specified comma-separated list of gem groups (default: last used)]' \
+    '--groups[Installs the specified comma-separated list of gem groups (default: last used). Prepend with `+` to install these groups in addition to what is already installed]' \
     '--help[Show this message]' \
     '--quiet[Make some output more quiet]' \
     '--verbose[Make some output more verbose]'

docs/Manpage.md

@@ -1307,7 +1307,7 @@ Generate Homebrew's manpages and shell completions.
 Install Homebrew's Bundler gems.
 
 * `--groups`:
-  Installs the specified comma-separated list of gem groups (default: last used).
+  Installs the specified comma-separated list of gem groups (default: last used). Prepend with `+` to install these groups in addition to what is already installed.
 
 ### `irb` [`--examples`] [`--pry`]
 

manpages/brew.1

@@ -1879,7 +1879,7 @@ Install Homebrew\'s Bundler gems\.
 .
 .TP
 \fB\-\-groups\fR
-Installs the specified comma\-separated list of gem groups (default: last used)\.
+Installs the specified comma\-separated list of gem groups (default: last used)\. Prepend with \fB+\fR to install these groups in addition to what is already installed\.
 .
 .SS "\fBirb\fR [\fB\-\-examples\fR] [\fB\-\-pry\fR]"
 Enter the interactive Homebrew Ruby shell\.