cmd/{rb,nod}env-sync: add new commands.

Add these commands to ease use of Homebrew's bottles with `rbenv` and
`nodenv`.

I've had a lot of people request this over the years and it's worked
well for me for a long time.

I could see people extending these to support other languages or version
managers so perhaps we want a more generic name.

Co-authored-by: Rylan Polster <rslpolster@gmail.com>

Library/Homebrew/cmd/nodenv-sync.rb

@@ -0,0 +1,68 @@
+# typed: true
+# frozen_string_literal: true
+
+require "cli/parser"
+require "formula"
+
+module Homebrew
+  module_function
+
+  sig { returns(CLI::Parser) }
+  def nodenv_sync_args
+    Homebrew::CLI::Parser.new do
+      description <<~EOS
+        Create symlinks for Homebrew's installed NodeJS versions in ~/.nodenv/versions.
+
+        Note that older version symlinks will also be created so e.g. NodeJS 19.1.0 will
+        also be symlinked to 19.0.0.
+      EOS
+
+      named_args :none
+    end
+  end
+
+  sig { void }
+  def nodenv_sync
+    dot_nodenv = Pathname(Dir.home)/".nodenv"
+
+    # Don't run multiple times at once.
+    nodenv_sync_running = dot_nodenv/".nodenv_sync_running"
+    return if nodenv_sync_running.exist?
+
+    nodenv_versions = dot_nodenv/"versions"
+    nodenv_versions.mkpath
+    FileUtils.touch nodenv_sync_running
+
+    nodenv_sync_args.parse
+
+    HOMEBREW_CELLAR.glob("node{,@*}")
+                   .flat_map(&:children)
+                   .each { |path| link_nodenv_versions(path, nodenv_versions) }
+
+    nodenv_versions.children
+                   .select(&:symlink?)
+                   .reject(&:exist?)
+                   .each { |path| FileUtils.rm_f path }
+  ensure
+    nodenv_sync_running.unlink if nodenv_sync_running.exist?
+  end
+
+  sig { params(path: Pathname, nodenv_versions: Pathname).void }
+  def link_nodenv_versions(path, nodenv_versions)
+    nodenv_versions.mkpath
+
+    version = Keg.new(path).version
+    major_version = version.major.to_i
+    minor_version = version.minor.to_i || 0
+    patch_version = version.patch.to_i || 0
+
+    (0..minor_version).each do |minor|
+      (0..patch_version).each do |patch|
+        link_path = nodenv_versions/"#{major_version}.#{minor}.#{patch}"
+
+        FileUtils.rm_f link_path
+        FileUtils.ln_sf path, link_path
+      end
+    end
+  end
+end

Library/Homebrew/cmd/rbenv-sync.rb

@@ -0,0 +1,66 @@
+# typed: true
+# frozen_string_literal: true
+
+require "cli/parser"
+require "formula"
+
+module Homebrew
+  module_function
+
+  sig { returns(CLI::Parser) }
+  def rbenv_sync_args
+    Homebrew::CLI::Parser.new do
+      description <<~EOS
+        Create symlinks for Homebrew's installed Ruby versions in ~/.rbenv/versions.
+
+        Note that older version symlinks will also be created so e.g. Ruby 3.2.1 will
+        also be symlinked to 3.2.0.
+      EOS
+
+      named_args :none
+    end
+  end
+
+  sig { void }
+  def rbenv_sync
+    dot_rbenv = Pathname(Dir.home)/".rbenv"
+
+    # Don't run multiple times at once.
+    rbenv_sync_running = dot_rbenv/".rbenv_sync_running"
+    return if rbenv_sync_running.exist?
+
+    rbenv_versions = dot_rbenv/"versions"
+    rbenv_versions.mkpath
+    FileUtils.touch rbenv_sync_running
+
+    rbenv_sync_args.parse
+
+    HOMEBREW_CELLAR.glob("ruby{,@*}")
+                   .flat_map(&:children)
+                   .each { |path| link_rbenv_versions(path, rbenv_versions) }
+
+    rbenv_versions.children
+                  .select(&:symlink?)
+                  .reject(&:exist?)
+                  .each { |path| FileUtils.rm_f path }
+  ensure
+    rbenv_sync_running.unlink if rbenv_sync_running.exist?
+  end
+
+  sig { params(path: Pathname, rbenv_versions: Pathname).void }
+  def link_rbenv_versions(path, rbenv_versions)
+    rbenv_versions.mkpath
+
+    version = Keg.new(path).version
+    major_version = version.major.to_i
+    minor_version = version.minor.to_i
+    patch_version = version.patch.to_i || 0
+
+    (0..patch_version).each do |patch|
+      link_path = rbenv_versions/"#{major_version}.#{minor_version}.#{patch}"
+
+      FileUtils.rm_f link_path
+      FileUtils.ln_sf path, link_path
+    end
+  end
+end