Bug: qlty install fails to install rubocop when Gemfile contains a 'gemspec'

[olbrich]

What happened?

I've been updating a gem to add qlty support. After adding

[[plugin]]
name = "rubocop"
package_file = "Gemfile.qlty"
config_files = [".rubocop.yml", ".rubocop_todo.yml"]

to my qlty.toml file and running qlty install I get this error output..

❯ qlty install
  67% [========================================================================================>                                           ]  00:00:00
 ∟ rubocop@bundled bundle install (Gemfile.qlty) ⢀                                                                                                    (eval at -e:1):26:in `expand_path': no implicit conversion of nil into String (TypeError)
	from (eval at -e:1):26:in `block in <main>'
	from /Users/username/.qlty/cache/tools/ruby/3.3.7-6c2a2652355e/lib/ruby/3.3.0/rubygems/specification.rb:2009:in `initialize'
	from (eval at -e:1):7:in `new'
	from (eval at -e:1):7:in `<main>'
	from -e:1:in `eval'

   ERROR

 > Failed to install rubocop@bundled
 >
 > Caused by:
 >     0: Error installing rubocop@bundled.
 >
 >     1: command ["ruby", "-rrubygems", "-e", "s=eval(STDIN.read);s.dependencies.select!{|d|/^rubocop$|/i=~d.name};puts s.to_ruby"] exited with code 1

Where Gemfile.qlty looks like

gem "rubocop"
gem "rubocop-rake"
gem "rubocop-rspec"

gemspec

Removing the gemspec allows it to work as expected.
Adding a package_filters entry does not help.

What did you expect to happen?

qlty install should run without errors

Can you reproduce the problem?

Yes, consistently

CLI Version

qlty 0.600.0 macos-arm64 (da1f210 2025-12-23)

Relevant log output

[marschattha]

Hi,

1. Can you share why you need to place the gemspec in your Gemfile.qlty which looks like a custom Gemfile for qlty and you can just place all your dependencies in there?
2. Can you share the contents of your gemspec file?