pandoc: add caveats about pandoc formula in homebrew

[xu-cheng]

No description provided.

[tapeinosyne]

I think that this specific caveat is unnecessary, as the conflict between multiple binaries is basic and commonly understood; warnings on the matter are usually left unstated in software distribution.

Nonetheless, if we decide to merge, we should remember that the same rationale would apply to many other casks.

[rolandwalker]

This change would seem to be modeled on the caveats in macvim.rb.

We apparently don't have a specific policy on the these caveats, and @ndr-qef is right, they are not uniform.

The ideal solution would be a conflicts_with :formula addition to the DSL, yes?

In the meantime, I think @xu-cheng is trying to help a first-time user. I would merge this, with the idea that it could be deleted in the future, when conflicts_with :formula is implemented.

[tapeinosyne]

The underlying issue is larger: all package managers that can install globally are a potential source of conflict. @xu-cheng's contribution is a particularly good example, as Pandoc can be installed with Homebrew, Homebrew Cask, and Cabal.

However, I recognize that it might be desirable to tackle Homebrew specifically. If we decide to do it, I agree that we should merge this —and amend the docs, possibly— while we extend the DSL.

[rolandwalker]

I agree about other package managers; we should only worry about Homebrew.

And I point out a limitation of caveats/conflicts_with :formula : we check for conflict with Homebrew Formulae, but it goes only one way. Homebrew does not and will not check for conflicts with Casks.

[rolandwalker]

Merging this and filing some other issues as discussed.

Thanks @xu-cheng !