Deprecate FUSE formulae.

[jonchang]

• Have you followed the guidelines for contributing?
• Have you checked that there aren't other open pull requests for the same formula update/change?
• Have you built your formula locally with brew install --build-from-source <formula>, where <formula> is the name of the formula you're submitting?
• Is your test running fine brew test <formula>, where <formula> is the name of the formula you're submitting?
• Does your build pass brew audit --strict <formula> (after doing brew install <formula>)?

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Homebrew historically has supported building against dependencies that were not installed by other formulae. However, as our documentation outlines, we've moved away from this practice as it has become increasingly more challenging to support and maintain formulae that use Requirements, as these require special intervention by a small set of (very busy) maintainers and cannot be easily tested on our continuous integration infrastructure.

Together with Java 1.8 (#63290) and XQuartz (#64166), FUSE is one of the last Cask-based Requirements that we have in Homebrew-core. Thanks to the efforts of many maintainers and contributors, Java 1.8 and XQuartz now have formula replacements in Homebrew-core. However, FUSE for macOS cannot be replaced by a formula as it no longer has public source releases and does not have a license that is compatible with Homebrew:

The license has changed. Starting with the 4.0.0 release, redistributions bundled with commercial software are not allowed without specific prior written permission. This includes the automated download or installation in the context of commercial software.

In addition, versions of FUSE for macOS prior to the licensing change in 3.10 will soon no longer work on our supported versions of macOS.

While you can still brew install these formulae today, Homebrew maintainers will no longer be updating or supporting FUSE formulae, and our continuous integration will not test them going forwards. These formulae will eventually be removed in the indeterminate future.

If you are a consumer of these formulae, please consider maintaining your own tap to house the formulae you need. Homebrew will not provide an automatic migration to a third-party tap for users with these formulae currently installed, but you are welcome to add your tap to our documentation by opening a pull request against Homebrew/brew.

cc @Homebrew/core

[iMichka]

We might keep them as linux-only formulae, as these build against the open source libfuse linux library. But I am not sure I want to go down that road.

I also have the feeling that there is less and less need for fuse nowadays, but I might be wrong.

[SMillerDev]

I think we can re-enable them if they prove needed on linux. But for now, LGTM

[MikeMcQuaid]

Makes sense, thanks @jonchang!