From 82aee1a9467c0f1bd33eb0247c5a0a8b8b9a5049 Mon Sep 17 00:00:00 2001
From: Jean Boussier <jean.boussier@gmail.com>
Date: Fri, 19 Jul 2024 15:12:04 +0200
Subject: [PATCH] bundled_gems.rb: Add a fast path

[Bug #20641] `Gem::BUNDLED_GEMS.warning?` adds a lot of extra
work on top of `require`. When the call end up atually loading code
the overhead is somewhat marginal.

However it's not uncommon for code to go some late `require` in some
paths, so it's expected that calling `require` with something already
required is somewhat fast, and `bundled_gems.rb` breaks this assumption.

To avoid this, we can have a fast path that in most case allow to
short-circuit all the heavy computations. If we extract the feature
basename and it doesn't match any of the bundled gems we care about
we can return very early.

With this change `require 'date'` is now only 1.33x slower on Ruby
3.3.3, than it was on Ruby 3.2.2, whereas before this change it
was at least 100x slower.
---
 lib/bundled_gems.rb       |  9 +++++++++
 test/test_bundled_gems.rb | 35 +++++++++++++++++++++++++++++++++++
 2 files changed, 44 insertions(+)
 create mode 100644 test/test_bundled_gems.rb

diff --git a/lib/bundled_gems.rb b/lib/bundled_gems.rb
index 932949576b..a42b12ac23 100644
--- a/lib/bundled_gems.rb
+++ b/lib/bundled_gems.rb
@@ -34,6 +34,8 @@ module Gem::BUNDLED_GEMS
     "logger" => "3.5.0",
   }.freeze
 
+  SINCE_FAST_PATH = SINCE.transform_keys { |g| g.sub(/\A.*\-/, "") }.freeze
+
   EXACT = {
     "kconv" => "nkf",
   }.freeze
@@ -92,6 +94,13 @@ module Gem::BUNDLED_GEMS
   def self.warning?(name, specs: nil)
     # name can be a feature name or a file path with String or Pathname
     feature = File.path(name)
+
+    if feature.include?("/")
+      return unless SINCE_FAST_PATH[File.basename(feature, ".*")]
+    else
+      return unless SINCE_FAST_PATH[feature]
+    end
+
     # bootsnap expands `require "csv"` to `require "#{LIBDIR}/csv.rb"`,
     # and `require "syslog"` to `require "#{ARCHDIR}/syslog.so"`.
     name = feature.delete_prefix(ARCHDIR)
diff --git a/test/test_bundled_gems.rb b/test/test_bundled_gems.rb
new file mode 100644
index 0000000000..36f7324336
--- /dev/null
+++ b/test/test_bundled_gems.rb
@@ -0,0 +1,35 @@
+require_relative "rubygems/helper"
+require "rubygems"
+require "bundled_gems"
+
+class TestBundlerGem < Gem::TestCase
+  def setup
+    Gem::BUNDLED_GEMS::WARNED.clear
+  end
+
+  def teardown
+    Gem::BUNDLED_GEMS::WARNED.clear
+  end
+
+  def test_warning
+    assert Gem::BUNDLED_GEMS.warning?("rss", specs: {})
+    assert_nil Gem::BUNDLED_GEMS.warning?("rss", specs: {})
+  end
+
+  def test_no_warning_warning
+    assert_nil Gem::BUNDLED_GEMS.warning?("some_gem", specs: {})
+    assert_nil Gem::BUNDLED_GEMS.warning?("/path/to/some_gem.rb", specs: {})
+  end
+
+  def test_warning_libdir
+    path = File.join(::RbConfig::CONFIG.fetch("rubylibdir"), "rss.rb")
+    assert Gem::BUNDLED_GEMS.warning?(path, specs: {})
+    assert_nil Gem::BUNDLED_GEMS.warning?(path, specs: {})
+  end
+
+  def test_warning_archdir
+    path = File.join(::RbConfig::CONFIG.fetch("rubyarchdir"), "syslog.so")
+    assert Gem::BUNDLED_GEMS.warning?(path, specs: {})
+    assert_nil Gem::BUNDLED_GEMS.warning?(path, specs: {})
+  end
+end