help: show help text for tapped external command

[Rylan12]

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Fixes #8641

Previously, running e.g. brew help bundle when homebrew-bundle was not tapped would tap homebrew-bundle and then run brew bundle showing Error: No Brewfile found instead of the expected help text.

I also added a message that lets the user know how to remove a tap that was automatically added. This was briefly discussed in #8641 but no conclusion was made so if this isn't wanted it can be easily removed.

Before:

$ brew help bundle
==> Tapping homebrew/bundle
Cloning into '/usr/local/Homebrew/Library/Taps/homebrew/homebrew-bundle'...
remote: Enumerating objects: 14, done.
remote: Counting objects: 100% (14/14), done.
remote: Compressing objects: 100% (14/14), done.
remote: Total 5159 (delta 4), reused 1 (delta 0), pack-reused 5145
Receiving objects: 100% (5159/5159), 1.15 MiB | 795.00 KiB/s, done.
Resolving deltas: 100% (3019/3019), done.
Tapped 1 command (104 files, 1.5MB).
Error: No Brewfile found

After:

$ brew help bundle
==> Tapping homebrew/bundle
Cloning into '/usr/local/Homebrew/Library/Taps/homebrew/homebrew-bundle'...
remote: Enumerating objects: 14, done.
remote: Counting objects: 100% (14/14), done.
remote: Compressing objects: 100% (14/14), done.
remote: Total 5159 (delta 4), reused 1 (delta 0), pack-reused 5145
Receiving objects: 100% (5159/5159), 1.15 MiB | 5.13 MiB/s, done.
Resolving deltas: 100% (3019/3019), done.
Tapped 1 command (104 files, 1.5MB).
Usage: brew bundle [subcommand]

Bundler for non-Ruby dependencies from Homebrew, Homebrew Cask, Mac App Store
and Whalebrew.
...

[maxim-belkin]

I know this is not within the scope of this PR, but... it seems strange that brew help taps things instead of reporting back to the user that there is nothing to display unless they tap X.

[Rylan12]

@maxim-belkin take a look at #8641 for some discussion (feel free to chime in as well). That was proposed but it was decided that the best option was to add a message letting the user know what happened after the fact.

(That issue's been repurposed a little but the initial conversation is about your concern)

[MikeMcQuaid]

The output indicates it was tapped so don't think this is necessary.

[Rylan12]

Fair, but it does sound like there is some confusion based on the linked issue. However, it's only one person (that I've seen) so I'm willing to remove it. If it comes up more in the future I'd ask that we take another look.

[MikeMcQuaid]

I know this is not within the scope of this PR, but... it seems strange that brew help taps things instead of reporting back to the user that there is nothing to display unless they tap X.

These are "official external commands" so this behaviour is intentional. Perhaps they should/could be migrated to Homebrew/brew instead but until then allowing brew bundle or brew services to work without extra intervention is desirable.

[MikeMcQuaid]

Very nice and simple 👏🏻 . Thanks for the fix, @Rylan12!