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.

Library/Homebrew/cmd/nodenv-sync.rb

@@ -0,0 +1,83 @@
+# frozen_string_literal: true
+
+require "cli/parser"
+require "formula"
+
+module Homebrew
+  module_function
+
+  def nodenv_sync_args
+    Homebrew::CLI::Parser.new do
+      usage_banner <<~EOS
+        `nodenv-sync`
+
+        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
+
+  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)
+                   .sort_by(&method(:gem_like_version))
+                   .each(&method(:link_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
+
+  def gem_like_version(version_path)
+    Gem::Version.new(version_path.basename
+                                 .to_s
+                                 .tr("_", "."))
+  end
+
+  def gem_version_segments(version_path)
+    basename_without_revision = version_path.basename
+                                            .to_s
+                                            .gsub(/_\d+$/, "")
+    Gem::Version.new(basename_without_revision)
+                .canonical_segments
+  end
+
+  def link_version(version_path, version_name, versions_path)
+    link_path = versions_path / version_name
+
+    FileUtils.rm_f link_path
+    FileUtils.ln_sf version_path, link_path
+  end
+
+  def link_nodenv_versions(version_path)
+    @nodenv_versions.mkpath
+
+    major_version, minor_version, patch_version = gem_version_segments(version_path)
+    minor_version ||= 0
+    (0..minor_version).each do |minor|
+      patch_version ||= 0
+      (0..patch_version).each do |patch|
+        link_version(version_path, "#{major_version}.#{minor}.#{patch}", @nodenv_versions)
+      end
+    end
+  end
+end

Library/Homebrew/cmd/rbenv-sync.rb

@@ -0,0 +1,78 @@
+# frozen_string_literal: true
+
+require "cli/parser"
+require "formula"
+
+module Homebrew
+  module_function
+
+  def rbenv_sync_args
+    Homebrew::CLI::Parser.new do
+      usage_banner <<~EOS
+        `rbenv-sync`
+
+        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
+
+  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)
+                   .sort_by(&method(:gem_like_version))
+                   .each(&method(:link_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
+
+  def gem_like_version(version_path)
+    Gem::Version.new(version_path.basename
+                                 .to_s
+                                 .tr("_", "."))
+  end
+
+  def gem_version_segments(version_path)
+    basename_without_revision = version_path.basename
+                                            .to_s
+                                            .gsub(/_\d+$/, "")
+    Gem::Version.new(basename_without_revision)
+                .canonical_segments
+  end
+
+  def link_version(version_path, version_name, versions_path)
+    link_path = versions_path/version_name
+
+    FileUtils.rm_f link_path
+    FileUtils.ln_sf version_path, link_path
+  end
+
+  def link_rbenv_versions(version_path)
+    major_version, minor_version, patch_version = gem_version_segments(version_path)
+    patch_version ||= 0
+    (0..patch_version).each do |patch|
+      link_version(version_path, "#{major_version}.#{minor_version}.#{patch}", @rbenv_versions)
+    end
+  end
+end