From df0fe8a802352befd8f3e3dd5bd6b7742da7eb45 Mon Sep 17 00:00:00 2001
From: Mike McQuaid <mike@mikemcquaid.com>
Date: Mon, 24 Mar 2025 17:34:35 +0000
Subject: [PATCH] Add `version_file:` DSL to `Brewfile`

This allows writing to e.g. `.ruby-version` files directly from the
`Brewfile`, making it easy to keep these versions in sync.
---
 Library/Homebrew/bundle.rb                    | 28 +++++++++++++++++++
 Library/Homebrew/bundle/brew_installer.rb     | 14 ++++++++++
 Library/Homebrew/bundle/commands/exec.rb      | 13 +--------
 .../test/bundle/commands/exec_spec.rb         |  1 +
 docs/Brew-Bundle-and-Brewfile.md              |  2 ++
 5 files changed, 46 insertions(+), 12 deletions(-)

diff --git a/Library/Homebrew/bundle.rb b/Library/Homebrew/bundle.rb
index d4ce509cac..726d70e9cf 100644
--- a/Library/Homebrew/bundle.rb
+++ b/Library/Homebrew/bundle.rb
@@ -82,6 +82,34 @@ module Homebrew
 
         return_value
       end
+
+      def formula_versions_from_env
+        @formula_versions_from_env ||= begin
+          formula_versions = {}
+
+          ENV.each do |key, value|
+            match = key.match(/^HOMEBREW_BUNDLE_EXEC_FORMULA_VERSION_(.+)$/)
+            next if match.blank?
+
+            formula_name = match[1]
+            next if formula_name.blank?
+
+            ENV.delete(key)
+            formula_versions[formula_name.downcase] = value
+          end
+
+          formula_versions
+        end
+      end
+
+      sig { void }
+      def reset!
+        @mas_installed = nil
+        @vscode_installed = nil
+        @whalebrew_installed = nil
+        @cask_installed = nil
+        @formula_versions_from_env = nil
+      end
     end
   end
 end
diff --git a/Library/Homebrew/bundle/brew_installer.rb b/Library/Homebrew/bundle/brew_installer.rb
index 5b0783f163..cf5112e53b 100644
--- a/Library/Homebrew/bundle/brew_installer.rb
+++ b/Library/Homebrew/bundle/brew_installer.rb
@@ -27,6 +27,7 @@ module Homebrew
         @start_service = options.fetch(:start_service, @restart_service)
         @link = options.fetch(:link, nil)
         @postinstall = options.fetch(:postinstall, nil)
+        @version_file = options.fetch(:version_file, nil)
         @changed = nil
       end
 
@@ -57,6 +58,19 @@ module Homebrew
 
           postinstall_result = postinstall_change_state!(verbose:)
           result &&= postinstall_result
+
+          if result && @version_file.present?
+            # Use the version from the environment if it hasn't changed.
+            version = if !changed? && (env_version = Bundle.formula_versions_from_env[@name])
+              env_version
+            else
+              Formula[@full_name].version.to_s
+            end
+            version_path = Pathname.new(@version_file)
+            version_path.write("#{version}\n")
+
+            puts "Wrote #{@name} version #{version} to #{@version_file}" if verbose
+          end
         end
 
         result
diff --git a/Library/Homebrew/bundle/commands/exec.rb b/Library/Homebrew/bundle/commands/exec.rb
index c0a55f7035..8fc9007bd9 100644
--- a/Library/Homebrew/bundle/commands/exec.rb
+++ b/Library/Homebrew/bundle/commands/exec.rb
@@ -108,18 +108,7 @@ module Homebrew
           end
 
           # Replace the formula versions from the environment variables
-          formula_versions = {}
-          ENV.each do |key, value|
-            match = key.match(/^HOMEBREW_BUNDLE_EXEC_FORMULA_VERSION_(.+)$/)
-            next if match.blank?
-
-            formula_name = match[1]
-            next if formula_name.blank?
-
-            ENV.delete(key)
-            formula_versions[formula_name.downcase] = value
-          end
-          formula_versions.each do |formula_name, formula_version|
+          Bundle.formula_versions_from_env.each do |formula_name, formula_version|
             ENV.each do |key, value|
               opt = %r{/opt/#{formula_name}([/:$])}
               next unless value.match(opt)
diff --git a/Library/Homebrew/test/bundle/commands/exec_spec.rb b/Library/Homebrew/test/bundle/commands/exec_spec.rb
index 1d127fc303..21c8b8fc48 100644
--- a/Library/Homebrew/test/bundle/commands/exec_spec.rb
+++ b/Library/Homebrew/test/bundle/commands/exec_spec.rb
@@ -29,6 +29,7 @@ RSpec.describe Homebrew::Bundle::Commands::Exec do
     context "with valid command setup" do
       before do
         allow(described_class).to receive(:exec).and_return(nil)
+        Homebrew::Bundle.reset!
       end
 
       it "does not raise an error" do
diff --git a/docs/Brew-Bundle-and-Brewfile.md b/docs/Brew-Bundle-and-Brewfile.md
index 11d2a59c81..0351ed3b7b 100644
--- a/docs/Brew-Bundle-and-Brewfile.md
+++ b/docs/Brew-Bundle-and-Brewfile.md
@@ -40,6 +40,8 @@ brew "mysql@5.6", restart_service: :changed, link: true, conflicts_with: ["mysql
 # 'brew install' and run a command if installer or upgraded.
 brew "postgresql@16",
      postinstall: "${HOMEBREW_PREFIX}/opt/postgresql@16/bin/postgres -D ${HOMEBREW_PREFIX}/var/postgresql@16"
+# 'brew install' and write the installed version to the '.ruby-version' file.
+brew "ruby", version_file: ".ruby-version"
 # install only on specified OS
 brew "gnupg" if OS.mac?
 brew "glibc" if OS.linux?