test-bot: inline portable-ruby validation into portable_formula!

After `brew bottle portable-ruby` succeeds, stage the just-built bottle
into `HOMEBREW_CACHE`, swap in the vendored portable-ruby, and run the
Homebrew/brew PR CI surface against it so issues are caught in the
homebrew-core PR rather than the follow-up brew bump PR.

Shared bundler-syncing logic lives in a small `Utils::PortableRuby`
helper for reuse with the new `bump-portable-ruby` workflow.

Author: p-linnane

Library/Homebrew/test_bot.rb

@@ -15,6 +15,7 @@
 require "tap"
 require "utils"
 require "utils/bottles"
+require "utils/portable_ruby"
 
 module Homebrew
   module TestBot

Library/Homebrew/test_bot/formulae.rb

@@ -69,7 +69,7 @@ def run!(args:)
         sorted_formulae.each do |f|
           verify_local_bottles
           if testing_portable_ruby?
-            portable_formula!(f)
+            portable_formula!(f, args:)
           else
             formula!(f, args:)
           end
@@ -754,8 +754,8 @@ def formula!(formula_name, args:)
         end
       end
 
-      sig { params(formula_name: String).void }
-      def portable_formula!(formula_name)
+      sig { params(formula_name: String, args: Homebrew::Cmd::TestBotCmd::Args).void }
+      def portable_formula!(formula_name, args:)
         test_header(:Formulae, method: "portable_formula!(#{formula_name})")
 
         install_ca_certificates_if_needed
@@ -788,6 +788,66 @@ def portable_formula!(formula_name)
         test "brew", "test", formula_name
         test "brew", "linkage", formula_name
         test "brew", "bottle", "--skip-relocation", "--json", "--no-rebuild", formula_name
+
+        # We only do full testing on `portable-ruby` itself.
+        return if formula_name != "portable-ruby"
+        return if args.dry_run?
+
+        bottle_file = bottle_glob(formula_name).first
+        if bottle_file.nil?
+          failed formula_name, "no bottle file found for portable-ruby validation"
+          return
+        end
+
+        filename = bottle_file.basename.to_s
+        _, tag_string, = Utils::Bottles.extname_tag_rebuild(filename)
+        if tag_string.blank?
+          failed formula_name, "could not parse bottle filename #{filename}"
+          return
+        end
+
+        pkg_version = filename.delete_prefix("portable-ruby--")
+                              .sub(/\.#{Regexp.escape(tag_string)}\.bottle.*\.tar\.gz\z/, "")
+        if pkg_version.empty?
+          failed formula_name, "could not parse portable-ruby version from #{filename}"
+          return
+        end
+
+        tag_symbol = tag_string.to_sym
+        bottle_tag = Utils::Bottles::Tag.from_symbol(tag_symbol)
+        sha256 = bottle_file.sha256
+        version = pkg_version.split("_").first.to_s
+
+        vendor_dir = HOMEBREW_LIBRARY_PATH/"vendor"
+        (vendor_dir/"portable-ruby-version").atomic_write("#{pkg_version}\n")
+        (HOMEBREW_LIBRARY_PATH/".ruby-version").atomic_write("#{version}\n")
+        os = bottle_tag.linux? ? "linux" : "darwin"
+        platform_file = vendor_dir/"portable-ruby-#{bottle_tag.standardized_arch}-#{os}"
+        platform_file.atomic_write("ruby_TAG=#{tag_symbol}\nruby_SHA=#{sha256}\n")
+
+        # Seed `HOMEBREW_CACHE` so `brew vendor-install ruby` finds the just-built
+        # bottle locally instead of trying to download it.
+        HOMEBREW_CACHE.mkpath
+        FileUtils.cp(bottle_file, HOMEBREW_CACHE/"portable-ruby-#{pkg_version}.#{tag_symbol}.bottle.tar.gz")
+
+        test "brew", "vendor-install", "ruby"
+
+        bundler_version = Utils::PortableRuby.sync_bundler_version!(pkg_version)
+        test "brew", "vendor-gems", "--no-commit", "--update=--ruby,--bundler=#{bundler_version}"
+        test "brew", "typecheck", "--update"
+
+        # Run the checks that gate a Homebrew/brew pull request.
+        test "brew", "style"
+        test "brew", "typecheck"
+        test "brew", "install-bundler-gems", "--groups=all"
+        test "brew", "vendor-gems", "--non-bundler-gems", "--no-commit"
+        test "brew", "tests", "--online", "--coverage"
+        test "brew", "tests", "--generic", "--coverage"
+        test "brew", "update-test"
+        test "brew", "update-test", "--to-tag"
+        test "brew", "update-test", "--commit=HEAD"
+        test "brew", "test-bot", "--only-formulae", "--only-json-tab", "--test-default-formula",
+             env: { "GITHUB_ACTIONS" => nil }
       end
 
       sig { params(formula_name: String).void }

Library/Homebrew/utils/portable_ruby.rb

@@ -0,0 +1,29 @@
+# typed: strict
+# frozen_string_literal: true
+
+require "utils/output"
+
+module Utils
+  # Helper functions for the vendored portable-ruby.
+  module PortableRuby
+    extend Utils::Output::Mixin
+
+    # Syncs `HOMEBREW_BUNDLER_VERSION` in `utils/ruby.sh` with the bundler shipped
+    # by the portable-ruby unpacked at `pkg_version`.
+    sig { params(pkg_version: String).returns(String) }
+    def self.sync_bundler_version!(pkg_version)
+      unpacked = HOMEBREW_LIBRARY_PATH/"vendor/portable-ruby/#{pkg_version}"
+      bundler_dir = Pathname.glob(unpacked/"lib/ruby/gems/*/gems/bundler-*").first
+      odie "Cannot find vendored bundler for portable-ruby #{pkg_version}." if bundler_dir.nil?
+
+      bundler_version = bundler_dir.basename.to_s.delete_prefix("bundler-")
+
+      ruby_sh = HOMEBREW_LIBRARY_PATH/"utils/ruby.sh"
+      original = ruby_sh.read
+      updated = original.sub(/(?<=^export HOMEBREW_BUNDLER_VERSION=")[^"]+/, bundler_version)
+      ruby_sh.atomic_write(updated) if original != updated
+
+      bundler_version
+    end
+  end
+end