Allow OffensesFormatter to use DangerPlugin

[Catsuko]

This PR reworks the OffensesFormatter#format_offenses method to accept a Danger::Plugin instance rather than repo url.

Why

In the default formatter, linking to offending constants assumes a main branch does not work in repos that do not use a main branch. Linking to the "main" branch also does not work well in situations where the constant does not exist or has been moved\changed in the PR.

Danger provides has a rich set of formatting tools which I think are useful here and for custom formatters in general: https://danger.systems/reference. This includes the github#html_link method which is made for this kind of linking.

Problems

• #html_link provides an anchor tag which does not work well with the existing markdown formatting
• breaking change for existing OffensesFormatter classes that people are using

I'm interested to know what people think about this 🙏

[ashleywillard]

Thanks for making this PR! I think this is a great idea because as you pointed out, not every project is going to have a branch called main.

To make things more backwards compatible here and minimize changes, we could continue to pass in a repo_link but extend it to include the branch (#{github.pr_json[:base][:repo][:html_url]}/blob/#{github.head_commit} instead of github.pr_json[:base][:repo][:html_url]). This would require less refactoring so old uses of the previous type signature wouldn't result in exceptions.

[Catsuko]

To make things more backwards compatible here and minimize changes, we could continue to pass in a repo_link but extend it to include the branch (#{github.pr_json[:base][:repo][:html_url]}/blob/#{github.head_commit} instead of github.pr_json[:base][:repo][:html_url]). This would require less refactoring so old uses of the previous type signature wouldn't result in exceptions.

I like the idea of making it more backwards compatible but i think including the branch would be a breaking change for any formatter that doesn't expect repo_link to include the branch. For example, take the existing default implementation:

[<ins>`#{constant_name}`</ins>](#{repo_link}/blob/main/#{constant_location})

Do you think that would be a problem?

[martinemde]

@Catsuko, would #54 work for your use case or do you need the features provided by the full plugin interface?

[Catsuko]

@martinemde
That would work for me 🙌

I think the plugin interface is pretty nice but all i really want to do is replace main with the head commit of the PR.

[martinemde]

Yeah, I think we could reassess if there were more needs for the full plugin interface.

[Catsuko]

@martinemde
In that case, i'll close my PR and await your changes. Thanks for the help!