Molinillo 0.6.0 breaks ruby solver

[ChiefAlexander]

The update to Molinillo 0.6.0 appears to have broken the ruby solver.

https://github.com/CocoaPods/Molinillo/blob/master/CHANGELOG.md#breaking

Locking down Molinillo to 0.5.7 allows berks to resolve successfully.

Example error with Molinillo 0.6.0:

/Users/ah042823/.rbenv/versions/2.3.1/lib/ruby/gems/2.3.0/gems/solve-3.1.0/lib/solve/ruby_solver.rb:80:in `block in resolve': undefined method `name' for nil:NilClass (NoMethodError)
	from /Users/ah042823/.rbenv/versions/2.3.1/lib/ruby/gems/2.3.0/gems/solve-3.1.0/lib/solve/ruby_solver.rb:79:in `each'
	from /Users/ah042823/.rbenv/versions/2.3.1/lib/ruby/gems/2.3.0/gems/solve-3.1.0/lib/solve/ruby_solver.rb:79:in `inject'
	from /Users/ah042823/.rbenv/versions/2.3.1/lib/ruby/gems/2.3.0/gems/solve-3.1.0/lib/solve/ruby_solver.rb:79:in `resolve'
	from /Users/ah042823/.rbenv/versions/2.3.1/lib/ruby/gems/2.3.0/gems/solve-3.1.0/lib/solve.rb:64:in `it!'
	from /Users/ah042823/.rbenv/versions/2.3.1/lib/ruby/gems/2.3.0/gems/berkshelf-6.2.1/lib/berkshelf/resolver.rb:78:in `resolve'
	from /Users/ah042823/.rbenv/versions/2.3.1/lib/ruby/gems/2.3.0/gems/berkshelf-6.2.1/lib/berkshelf/installer.rb:181:in `install_from_universe'
	from /Users/ah042823/.rbenv/versions/2.3.1/lib/ruby/gems/2.3.0/gems/berkshelf-6.2.1/lib/berkshelf/installer.rb:43:in `run'
	from /Users/ah042823/.rbenv/versions/2.3.1/lib/ruby/gems/2.3.0/gems/berkshelf-6.2.1/lib/berkshelf/berksfile.rb:426:in `install'
	from /Users/ah042823/.rbenv/versions/2.3.1/lib/ruby/gems/2.3.0/gems/berkshelf-6.2.1/lib/berkshelf/cli.rb:140:in `install'
	from /Users/ah042823/.rbenv/versions/2.3.1/lib/ruby/gems/2.3.0/gems/thor-0.19.1/lib/thor/command.rb:27:in `run'
	from /Users/ah042823/.rbenv/versions/2.3.1/lib/ruby/gems/2.3.0/gems/thor-0.19.1/lib/thor/invocation.rb:126:in `invoke_command'
	from /Users/ah042823/.rbenv/versions/2.3.1/lib/ruby/gems/2.3.0/gems/thor-0.19.1/lib/thor.rb:359:in `dispatch'
	from /Users/ah042823/.rbenv/versions/2.3.1/lib/ruby/gems/2.3.0/gems/berkshelf-6.2.1/lib/berkshelf/cli.rb:49:in `dispatch'
	from /Users/ah042823/.rbenv/versions/2.3.1/lib/ruby/gems/2.3.0/gems/thor-0.19.1/lib/thor/base.rb:440:in `start'
	from /Users/ah042823/.rbenv/versions/2.3.1/lib/ruby/gems/2.3.0/gems/berkshelf-6.2.1/lib/berkshelf/cli.rb:25:in `execute!'
	from /Users/ah042823/.rbenv/versions/2.3.1/lib/ruby/gems/2.3.0/gems/berkshelf-6.2.1/bin/berks:5:in `<top (required)>'
	from /Users/ah042823/.rbenv/versions/2.3.1/bin/berks:23:in `load'
	from /Users/ah042823/.rbenv/versions/2.3.1/bin/berks:23:in `<main>'

[hartmantis]

Pulling solve from master seems to get around this and work normally because of #66. Although, that PR mentions the 0.6.0 release was supposed to fix this error, not make it occur more often...

[ofir-petrushka]

(might help people find this when searching for the issue)
Discovered with berks install / berks update crashing with an error like:

/usr/local/var/rbenv/versions/2.4.1/lib/ruby/gems/2.4.0/gems/solve-3.1.0/lib/solve/ruby_solver.rb:80:in block in resolve': undefined method name' for nil:NilClass (NoMethodError)

[thommay]

I've pushed solve 3.1.1 that should resolve this.

[taharah]

@thommay the update pushed does not fix the issue it only masks it. Now instead of failing resolution will complete, but only a subset of all dependencies in the chain will be resolved.

[kamaradclimber]

Indeed the only known workaround for now is to constrain molinillo gem to < 6.0

[hartmantis]

I won't pretend to know much of anything about depsolving, but this is the commit that started solve getting a bunch of nil artifacts: CocoaPods/Molinillo#75

[thommay]

thanks; I'm working my through figuring out why we're seeing these nulls.

[thommay]

Released solve 4.0.0 that resolves this.