Automatically unlock dependants released in lockstep

[deivid-rodriguez]

What was the end-user or developer problem that led to this PR?

Sometimes users might run bundle update <transitive-dependency>, for example, because <transitive-dependency> has a security issue and they want to pick up a release with a fix. This will only work if there are no dependents holding the previous version. A very common case where it does not work is when dependants are released in lockstep with the gem being updated.

What is your fix for the problem, implemented in this PR?

Smartly detecting dependants holding updates and retrying resolution with those unlocked is a general improvement that could be worth adding to the resolver. However, exact dependencies is a very easy case that can be detected in advance without having to retry at all.

Once dependencies to be unlocked have been figured out, have one more pass to check whether any gems have exact dependencies on them, and unlock those too.

This PR allows things like bundle update actionview just work, by updating the whole "Rails family" at once. It also makes it easier for dependabot to create automated PRs to fix this kind of issue.

Fixes #5463.

Make sure the following tasks are checked

• Describe the problem / feature
• Write tests for features and bug fixes
• Write code to solve the problem
• Make sure you follow the current code style and write meaningful commit messages without tags

[vitaly-pushkar]

Any chance this gets merged at some point? Would love to have this feature

[deivid-rodriguez]

I think the better way to go is to make this work in general.

Special casing exact dependencies works for the most common cases, but it's not compulsory to keep releasing in lockstep once you've done that once, you should be free to relax those constraints if you need to and special casing exact dependencies would not play nice with that.

I do plan to revisit this.

Smartly detecting dependants holding updates and retrying resolution with those unlocked is a general improvement that could be worth adding to the resolver. However, exact dependencies is a very easy case that can be detected in advance without having to retry at all.

[deivid-rodriguez]

I'm working on a more general solution at #7558, so closing this!