[ruby-core:125031] [Ruby Bug#21954] NoMethodError instead of Gem::LoadError on gem activation problem in Ruby 4.0.2

17 Mar 2026

      Issue #21954 has been updated by hsbt (Hiroshi SHIBATA).

@jeremyevans0 Thank you for your report. I confirmed this.

This issue was introduced RubyGems [4.0.5](https://github.com/ruby/rubygems/releases/tag/v4.0.5).

I will fix this at https://github.com/ruby/rubygems/pull/9404 and release RubyGems 4.0.9 with this fix at next week.

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Bug #21954: NoMethodError instead of Gem::LoadError on gem activation problem in Ruby 4.0.2
https://bugs.ruby-lang.org/issues/21954#change-116728

* Author: jeremyevans0 (Jeremy Evans)
* Status: Assigned
* Assignee: hsbt (Hiroshi SHIBATA)
* ruby -v: ruby 4.0.2 (2026-03-17 revision d3da9fec82) +PRISM [x86_64-linux]
* Backport: 3.2: DONTNEED, 3.3: DONTNEED, 3.4: DONTNEED, 4.0: REQUIRED
----------------------------------------
I'm seeing a regression in Ruby 4.0.2 when there is a gem activation problem.

Install two versions of a gem, where one version has a file the other doesn't. One example here is rack:

```
$ gem install rack --version '< 3'
$ gem install rack
```

Force activation of the version that doesn't have the file, and then require the file and rescue `LoadError`:

```ruby
gem 'rack', '< 3'

begin
  require 'rack/headers'
rescue LoadError
end
```

In previous versions of Ruby, the `Gem::LoadError` would be correctly rescued, and you would get no output. In Ruby 4.0.2, you get a `NoMethodError` raised:

```
/usr/local/lib/ruby/4.0/rubygems.rb:196:in 'Gem.try_activate': undefined method 'name' for nil (NoMethodError)

      spec ||= Gem::Specification.find_by_name(spec.name)
                                                   ^^^^^
        from /home/jeremy/gem-activate-problem.rb:4:in 'Kernel#require'
        from /home/jeremy/gem-activate-problem.rb:4:in '<main>'
/usr/local/lib/ruby/4.0/rubygems/specification.rb:2170:in 'Gem::Specification#check_version_conflict': can't activate rack-3.2.4, already activated rack-2.2.21 (Gem::LoadError)
        from /usr/local/lib/ruby/4.0/rubygems/specification.rb:1379:in 'Gem::Specification#activate'
        from /usr/local/lib/ruby/4.0/rubygems.rb:193:in 'Gem.try_activate'
        from /home/jeremy/gem-activate-problem.rb:4:in 'Kernel#require'
        from /home/jeremy/gem-activate-problem.rb:4:in '<main>'
/home/jeremy/gem-activate-problem.rb:4:in 'Kernel#require': cannot load such file -- rack/headers (LoadError)
        from /home/jeremy/gem-activate-problem.rb:4:in '<main>'
```

Same behavior on both OpenBSD and Linux.

-- 
https://bugs.ruby-lang.org/