Tap migrations should allow to migrate from formula to cask in the same tap

[SMillerDev]

Verification

• This issue's title and/or description do not reference a single formula e.g. brew install wget. If they do, open an issue at https://github.com/Homebrew/homebrew-core/issues/new/choose instead.

Provide a detailed description of the proposed feature

The current tap_migrations.json file allows people to define migrations in or outside a tap. But a scenario where the maintainer starts to distribute prebuild binaries rather than building in a formula is not covered. Therefore it would be useful if tap_migrations.json would also check if the migration is from a formula to a cask and act accordingly.

What is the motivation for the feature?

GoReleaser is now distributing precompiled binaries for brew as casks rather than formulae. But this leaves a lot of users with a formula and a cask with the same name in the same tap, and no way to automatically switch the users.

See: https://github.com/orgs/goreleaser/discussions/5563#discussioncomment-14180870

How will the feature be relevant to at least 90% of Homebrew users?

A lot of smaller Go projects use Goreleaser and distribute their software to brew that way. Making the migration to casks (that better fit the Homebrew model) easier should be better for all Homebrew users.

What alternatives to the feature have been considered?

Just hoping users notice the disabling of the formulae and manually switch to casks.

[MikeMcQuaid]

Therefore it would be useful if tap_migrations.json would also check if the migration is from a formula to a cask and act accordingly.

This is already possible: https://github.com/Homebrew/homebrew-core/blob/b83323dad1849149ebc425b22d95322b66e23360/tap_migrations.json#L31-L32

The actual migration itself happens as part of brew update so that's the code that needs to change here.

[SMillerDev]

Yeah, I guess the important part is here:

But this leaves a lot of users with a formula and a cask with the same name in the same tap

I'm planning to have a look to see if I can find it in brew upgrade.

[gibfahn]

This is already possible: Homebrew/homebrew-core@b83323d/tap_migrations.json#L31-L32

As I understand it that only works because homebrew-core and homebrew-cask are different taps, so homebrew/core/foo and homebrew/cask/foo are different things, for any third-party tap you normally have them both together, so I don't believe this works, at least from my testing.

[gibfahn]

For what it's worth this would be really useful, I have mostly seen the following cases in the past few weeks as people update to the new goreleaser version:

1. Formula deleted, cask added with the same name
   Would be nice to prompt the user to uninstall the formula and install the cask. I guess brew uninstall myorg/tap/foo && brew install myorg/tap/foo would work?
2. Formula kept but disabled, cask added with the same name
   Would be nice to say "formula disabled, but there's a cask with the same name you probably want to use"
3. Both kept, tap author just runs goreleaser in CI and didn't realise there was a Formula to Cask change so you just have an outdated Formula
   Maybe something like "HINT: there are no updates for the installed formula myorg/tap/foo, but the cask myorg/tap/foo has newer updates, consider brew uninstall myorg/tap/foo && brew install myorg/tap/foo"

[caarlos0]

Hey, I'm the maintainer of GoReleaser.

FWIW, I believe what most users are ask is "what should I do so my users can just run brew upgrade and it just work?".

So, the tap_migrations.json would be awesome, IMHO, if it could handle it within the tap.

Right now, the advice I'm giving is to manually add a disable to the formula https://github.com/goreleaser/homebrew-tap/blob/master/Formula/goreleaser.rb#L11

[MikeMcQuaid]

I'm planning to have a look to see if I can find it in brew upgrade.

@SMillerDev brew update.

Here's the relevant logic that'd need extended to handle all taps:

brew/Library/Homebrew/cmd/update-report.rb

Lines 664 to 688 in df73746

	new_tap = Tap.fetch(new_tap_name)
	# For formulae migrated to cask: Auto-install cask or provide install instructions.
	if new_tap_name.start_with?("homebrew/cask")
	if new_tap.installed? && (HOMEBREW_PREFIX/"Caskroom").directory?
	ohai "#{name} has been moved to Homebrew Cask."
	ohai "brew unlink #{name}"
	system HOMEBREW_BREW_FILE, "unlink", name
	ohai "brew cleanup"
	system HOMEBREW_BREW_FILE, "cleanup"
	ohai "brew install --cask #{new_name}"
	system HOMEBREW_BREW_FILE, "install", "--cask", new_name
	ohai <<~EOS
	#{name} has been moved to Homebrew Cask.
	The existing keg has been unlinked.
	Please uninstall the formula when convenient by running:
	brew uninstall --force #{name}
	EOS
	else
	ohai "#{name} has been moved to Homebrew Cask.", <<~EOS
	To uninstall the formula and install the cask, run:
	brew uninstall --force #{name}
	brew tap #{new_tap_name}
	brew install --cask #{new_name}
	EOS
	end

FWIW, I believe what most users are ask is "what should I do so my users can just run brew upgrade and it just work?".

@caarlos0 Thanks! Yes, I think this is the right way about thinking about this problem and what should be solved in this issue 👍🏻