env_config: add HOMEBREW_BUNDLE_USER_CACHE.

Used to configure `BUNDLE_USER_CACHE`.

Library/Homebrew/env_config.rb

@@ -91,6 +91,9 @@ module Homebrew
         description:  "Use this as the browser when opening project homepages.",
         default_text: "`$BROWSER` or the OS's default browser.",
       },
+      HOMEBREW_BUNDLE_USER_CACHE:                {
+        description: "If set, use this directory as the `bundle`(1) user cache.",
+      },
       HOMEBREW_CACHE:                            {
         description:  "Use this directory as the download cache.",
         default_text: "macOS: `$HOME/Library/Caches/Homebrew`, " \

Library/Homebrew/sorbet/rbi/dsl/homebrew/env_config.rbi

@@ -52,6 +52,9 @@ module Homebrew::EnvConfig
     sig { returns(T.nilable(::String)) }
     def browser; end
 
+    sig { returns(T.nilable(::String)) }
+    def bundle_user_cache; end
+
     sig { returns(String) }
     def cache; end
 

Library/Homebrew/utils/gems.rb

@@ -224,7 +224,6 @@ module Homebrew
     old_path = ENV.fetch("PATH", nil)
     old_gem_path = ENV.fetch("GEM_PATH", nil)
     old_gem_home = ENV.fetch("GEM_HOME", nil)
-    old_bundle_user_cache = ENV.fetch("BUNDLE_USER_CACHE", nil)
     old_bundle_gemfile = ENV.fetch("BUNDLE_GEMFILE", nil)
     old_bundle_with = ENV.fetch("BUNDLE_WITH", nil)
     old_bundle_frozen = ENV.fetch("BUNDLE_FROZEN", nil)
@@ -244,12 +243,9 @@ module Homebrew
     groups |= (user_gem_groups & valid_gem_groups)
     groups.sort!
 
-    homebrew_cache = if defined?(HOMEBREW_CACHE)
-      HOMEBREW_CACHE.to_s
-    else
-      ENV.fetch("HOMEBREW_CACHE")
+    if (homebrew_bundle_user_cache = ENV.fetch("HOMEBREW_BUNDLE_USER_CACHE", nil))
+      ENV["BUNDLE_USER_CACHE"] = homebrew_bundle_user_cache
     end
-    ENV["BUNDLE_USER_CACHE"] = "#{homebrew_cache}/bundler_cache"
     ENV["BUNDLE_GEMFILE"] = gemfile
     ENV["BUNDLE_WITH"] = groups.join(" ")
     ENV["BUNDLE_FROZEN"] = "true"
@@ -346,7 +342,6 @@ module Homebrew
       ENV["BUNDLE_GEMFILE"] = old_bundle_gemfile
       ENV["BUNDLE_WITH"] = old_bundle_with
       ENV["BUNDLE_FROZEN"] = old_bundle_frozen
-      ENV["BUNDLE_USER_CACHE"] = old_bundle_user_cache
     end
   end
 end

bin/brew

@@ -144,6 +144,7 @@ MANPAGE_VARS=(
   BAT_CONFIG_PATH
   BAT_THEME
   BROWSER
+  BUNDLE_USER_CACHE
   DISPLAY
   EDITOR
   NO_COLOR

docs/Manpage.md

@@ -3568,6 +3568,10 @@ command execution e.g. `$(cat file)`.
   
   *Default:* `$BROWSER` or the OS's default browser.
 
+`HOMEBREW_BUNDLE_USER_CACHE`
+
+: If set, use this directory as the `bundle`(1) user cache.
+
 `HOMEBREW_CACHE`
 
 : Use this directory as the download cache.

manpages/brew.1

@@ -2295,6 +2295,9 @@ Use this as the browser when opening project homepages\.
 \fIDefault:\fP \fB$BROWSER\fP or the OS\[u2019]s default browser\.
 .RE
 .TP
+\fBHOMEBREW_BUNDLE_USER_CACHE\fP
+If set, use this directory as the \fBbundle\fP(1) user cache\.
+.TP
 \fBHOMEBREW_CACHE\fP
 Use this directory as the download cache\.
 .RS