[Fix #8761] Read required_ruby_version from gemspec file if it exists

[HeroProtagonist]

Closes #8761

• Added GemspecFile class to search upwards for <project_base>.gemspec and read from required_ruby_version if present in the file
• Placed it in the Sources array right before Default
• Created specs over new class
• Update docs to clarify which files are looked at for ruby version
• Updated changelog

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Before submitting the PR make sure the following are checked:

• Wrote good commit messages.
• Commit message starts with [Fix #issue-number] (if the related issue exists).
• Feature branch is up-to-date with master (if not - rebase it).
• Squashed related commits together.
• Added tests.
• Added an entry to the Changelog if the new code introduces user-observable changes. See changelog entry format.
• The PR relates to only one subject with a clear title and description in grammatically correct, complete sentences.
• Run bundle exec rake default. It executes all tests and RuboCop for itself, and generates the documentation.

[pBorak]

@HeroProtagonist
Hey, great job, I was also doing some work related to this issue :)
One question though, have you taken under consideration that the ruby version format in Gemspec may be written in different ways?
s.required_ruby_version = '< 3.0.0' or even s.required_ruby_version =['>= 2.2.0', '< 2.3.0']

[HeroProtagonist]

@pBorak Right now mine is pretty simple, just checking for the numbers after required_ruby_version.

The other files where version are checked are here:
https://github.com/rubocop-hq/rubocop/blob/de5b74fece1166133cedd860c07c75d5a4426cbc/lib/rubocop/target_ruby.rb#L133

I guess the question to be answered is how they support those cases, where applicable, and then matching that behavior

[bbatsov]

I'm fine with the proposed change, but we should document the new behavior as otherwise it might confuse people.

I guess the question to be answered is how they support those cases, where applicable, and then matching that behavior

As for bounded version - I guess you can check for an array and extract a minimum version from there. If only a maximum version is present there's nothing for us to do.

[bbatsov]

You'll also need to rebase on top of master.

[HeroProtagonist]

@bbatsov updated and rebased 👍

[bbatsov]

Thanks!