[Ruby 3.0] replace slack-notifier gem with internal library

[ainame]

Checklist

• I've run bundle exec rspec from the root directory to see all new and existing tests pass
• I've followed the fastlane code style and run bundle exec rubocop -a to ensure the code style is valid
• I've read the Contribution Guidelines
• I've updated the documentation if necessary.

Motivation and Context

As per the plan #17931 for Ruby 3.0, I've been working on fixing Ruby 2.7's deprecation warnings which will crash on Ruby 3.0. There is an issue where one of the fastlane's dependencies slack-notifier, which is not maintained any more, keeps producing that warning. As I explained in #18512 I decided to go with having our own implementation to post messages to Slack in fastlane. That way we get full control of logic. It is not only about Ruby version support but also Slack's webhook transition.

Right now there are two translations ongoing

• Legacy incoming webhook https://api.slack.com/legacy/custom-integrations/messaging/webhooks vs The latest incoming webhook using Slack app https://api.slack.com/messaging/webhooks
• Legacy attachments in formatting https://api.slack.com/reference/messaging/attachments vs BlockKit https://api.slack.com/messaging/composing/layouts#sending-messages

To be fair, slack-notifier does support those but we don't know what changes will be coming from Slack in future.

Description

Prior to this PR, I've updated fastlane/spec/fastlane/actions_specs/slack_spec.rb so it's now independent from the gem. This PR added Fastlane::Notification::Slack class to own simple alternative of slack-notifier. (I suppose it might be interesting to support Microsoft teams or whatever other popular chat tools in fastlane as it's remote working era🙂 That's why it's got Fastlane::Notification namespace.)

After digging through the gem, I realised most of the extra features in slack-notifier was not used by fastlane. Only Slack::Notifier::Util::LinkFormatter was needed to be re-implemented.

Testing Steps

Get an incoming webook url from here
https://www.slack.com/apps/manage/custom-integrations

Add this snippet to fastlane/Fastfile in the repo

lane :slack_test do
  slack(
    slack_url: 'https://hooks.slack.com/services/xxxxxxxxxxx',
    pretext: 'pretext test <@xxxxxx> #general',
    username: 'ainame-bot',
    channel: '#general',
    message: 'test <@xxxxxx> #general  <a href="https://fastlane.tools">fastlane</a> [GitHub](https://github.com/fastlane)',
    link_names: true,
  )
end

Run bundle exec fastlane slack_test

Legacy incoming webhook	Slack App's incoming webhook

As you can see Slack app's incoming webhook can't overwrite username and icon. Instead, you need to customise them on its settings page.

[rogerluan]

🚀 Really good stuff!!

[rogerluan]

I almost forgot to mention that I like this namespace strategy a lot 😊

[joshdholtz]

@ainame This is ready for a rebase whenever you got time! I tried to do it on my own but it looked liked a large rebase than I felt comfortable doing as I didn’t want to mess up your PR 😉

[ainame]

FYI: We can rebase this branch without having to resolve conflicts like below🙂

$ git rebase --onto origin/master dc2cd566

dc2cd56 is the last commit in the previous branch. This way commits made for this PR will be applied to the master branch that has previous PR's changes squashed.

[ainame]

@joshdholtz Thanks! This PR is ready to review!

[joshdholtz]

FYI: We can rebase this branch without having to resolve conflicts like below🙂

$ git rebase --onto origin/master dc2cd566

dc2cd56 is the last commit in the previous branch. This way commits made for this PR will be applied to the master branch that has previous PR's changes squashed.

OMG... I had no idea about --onto 🤯 Thanks!

[crazymanish]

This looks great to me, thank you 👏

[google-cla]

All (the pull request submitter and all commit authors) CLAs are signed, but one or more commits were authored or co-authored by someone other than the pull request submitter.

We need to confirm that all authors are ok with their commits being contributed to this project. Please have them confirm that by leaving a comment that contains only @googlebot I consent. in this pull request.

Note to project maintainer: There may be cases where the author cannot leave a comment, or the comment is not properly detected as consent. In those cases, you can manually confirm consent of the commit author(s), and set the cla label to yes (if enabled on your project).

ℹ️ Googlers: Go here for more info.

[ainame]

@googlebot I consent.

[google-cla]

All (the pull request submitter and all commit authors) CLAs are signed, but one or more commits were authored or co-authored by someone other than the pull request submitter.

We need to confirm that all authors are ok with their commits being contributed to this project. Please have them confirm that by leaving a comment that contains only @googlebot I consent. in this pull request.

Note to project maintainer: There may be cases where the author cannot leave a comment, or the comment is not properly detected as consent. In those cases, you can manually confirm consent of the commit author(s), and set the cla label to yes (if enabled on your project).

ℹ️ Googlers: Go here for more info.

[joshdholtz]

This is beautiful 😍 Thanks again for all your work. This 3.0 dream is getting reeaaaalllll ❤️

[fastlane-bot]

Hey @ainame 👋

Thank you for your contribution to fastlane and congrats on getting this pull request merged 🎉
The code change now lives in the master branch, however it wasn't released to RubyGems yet.
We usually ship about once a week, and your PR will be included in the next one.

Please let us know if this change requires an immediate release by adding a comment here 👍
We'll notify you once we shipped a new release with your changes 🚀

[fastlane-bot]

Congratulations! 🎉 This was released as part of fastlane 2.182.0 🚀