From: "hsbt (Hiroshi SHIBATA) via ruby-core" <ruby-core@...>
Date: 2025-03-13T04:22:02+00:00
Subject: [ruby-core:121313] [Ruby master Bug#21032] `Module#autoload?` is slow when `$LOAD_PATH` contains a relative path

Issue #21032 has been updated by hsbt (Hiroshi SHIBATA).

Backport changed from 3.1: WONTFIX, 3.2: REQUIRED, 3.3: DONE, 3.4: DONE to 3.1: WONTFIX, 3.2: DONE, 3.3: DONE, 3.4: DONE

ruby_3_2 commit:fd15d0f4cbddc8cf69013959e2a60734d0995d56 merged revision(s) commit:d4a1a2780c39bc648496ac92fc6e6ce2eb38ab47.

----------------------------------------
Bug #21032: `Module#autoload?` is slow when `$LOAD_PATH` contains a relative path
https://bugs.ruby-lang.org/issues/21032#change-112277

* Author: byroot (Jean Boussier)
* Status: Closed
* Backport: 3.1: WONTFIX, 3.2: DONE, 3.3: DONE, 3.4: DONE
----------------------------------------
Reproduction script:

```ruby
require 'benchmark'

$LOAD_PATH << 'relative-path'

autoload :FOO, '/tmp/foo.rb'

puts Benchmark.realtime {
  500_000.times do
    Object.autoload?(:FOO)
  end
}
```

The above takes 2.5 to 3 seconds on my machine, but just removing `$LOAD_PATH << 'relative-path'` make it complete in 50ms.
It's such a stark difference that I think it is a bug, and it cause Zeitwerk, a very popular gem, to be way slower than it should
when the load path contains relative paths.

I have a patch for it, that passes all tests, but I'd appreciate some eyes on it: https://github.com/ruby/ruby/pull/12562

cc @fxn 



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