doctor: disable python symlink message

[Rylan12]

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brew doctor will soon start to fail on ubuntu-latest actions runs once they migrate to Ubuntu 20.04. This has already happened to me in personal taps.

The issue is that Ubuntu 20.04 no longer comes with Python 2. Instead, the python executable points to Python 3.8.5.

I think there are three options:

1. Use ubuntu-18.04 instead of ubuntu-latest on all our runners. This isn't a good long-term solution
2. Conditionally allow this doctor failure on CI machines to allow them to continue running
3. Disable this check (everywhere or only on Linux) (suggested to me on Slack by @sjackman)

I don't know much about Homebrew on Linux, but I think that option 3 is the best option (mainly because @sjackman suggested it 😄). Ideally, now that Python 2 is no longer supported, we should expect to not deal with it in the future. Unfortunately, I'm not sure that's feasible on macOS (especially not yet).

[BrewTestBot]

Review period will end on 2020-12-31 at 16:28:40 UTC.

[BrewTestBot]

Review period will end on 2020-12-31 at 16:28:40 UTC.

[iMichka]

I think this needs to be implemented in extend/os/linux/diagnostic.rb instead. We separated the linux from the Mac implementation with 2 different files.

[Rylan12]

Makes sense. I'll just move the check to extend/os/mac/disagnostic.rb. That way no need forreturn if OS.linux?

Before I do, though, I'm going to change the ubuntu runner to ubuntu-20.04 to make it easier to verify that the change is effective in this PR.

[Rylan12]

CI (on ubuntu-20.04) is now failing with the following message:

In /home/linuxbrew/.linuxbrew/Homebrew/Library/Homebrew/utils/ruby.sh line 20:
    for ruby_exec in $(which -a ruby 2>/dev/null) $(PATH=$HOMEBREW_PATH which -a ruby 2>/dev/null)
                       ^---^ SC2230: which is non-standard. Use builtin 'command -v' instead.
                                                                        ^---^ SC2230: which is non-standard. Use builtin 'command -v' instead.

For more information:
  https://www.shellcheck.net/wiki/SC2230 -- which is non-standard. Use builti...
Error: which is non-standard. Use builtin 'command -v' instead.

According to https://www.shellcheck.net/wiki/SC2230, this is opt-in only and I don't believe we've opted in... Odd that this is only the case on Ubuntu 20.04.

[Rylan12]

Thinking out loud here, is this the right solution? Since the brew docker container uses 20.04 and doesn't include a python executable, should taps just use that brew docker container?

Interestingly, brew doctor didn't fail when running on ubuntu-20.04 before I removed the check (see, for example, this action run). It doesn't look to me like we're using the docker container for the tap-syntax job. That makes me think that the issue is just an issue with my configuration...

I'm not a Linux guy and I've almost never used docker so I'm a tad out of my comfort zone here. Let me know if I'm misunderstanding the situation.

[Rylan12]

Okay, this PR now removed the check altogether.

In the future, we'll likely have to deal with the ubuntu-20.04 issue. Maybe I'll open a new PR and take a look to see if I can solve it.

[MikeMcQuaid]

Maybe I'll open a new PR and take a look to see if I can solve it.

That'd be great, thanks ❤️. Happy to help if you get blocked.

[BrewTestBot]

Review period ended.