Revisit allowing casks as dependencies for formulas (at least for taps)?

[lgarron]

Output of brew config

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Output of brew doctor

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Description of issue

I'm finding more and more that I'm unable to write formulas that would properly install on a new system, because they depend on binaries that get installed with casks. For example, just in the last 2 days I've worked with formulas that depend on the following:

• openscad (installs openscad binary linked from /Applications/OpenSCAD.app/Contents/MacOS/OpenSCAD)
• arq (installs arqc binary linked from /Applications/Arq.app/Contents/Resources/arqc)
• usr-sse2-rdm (/Applications/RDM.app/Contents/MacOS/RDM can be invoked as a commandline binary)

There are also other commonly used binaries installed through casks, such as the code binary installed by visual-studio-code.

In some other cases this is resolved by including both a formula in homebrew-core as well an identically named cask in homebrew-cask, such as handbrake. However, I get the feeling Homebrew wouldn't want to expand this to casks like the ones I mentioned above. Having separate formulas:

• Is more maintenance work, and there will be a functionality gap unless every cask for an app with a binary also has a corresponding formula for the binary.
• Could introduce a bunch more identically named formulas and casks in the default Homebrew installation, which could cause more problems and confusion than necessary.
• Introduces the possibility that the binary and the app version could get out of sync and therefore install versions with incompatible functionality.
• Might run into issues installing the binaries without also installing the full apps.

As someone who wants to make sure their computer configuration properly expresses dependencies, I would find it really useful if a formula can also depend on a cask, at least in the taps I maintain.

There are some existing discussions about aspects of this, such as https://github.com/orgs/Homebrew/discussions/3163 discussing Docker. @SMillerDev's reply to one of the comments implies that depends_on cask: "…" should work for a formula in a tap, but I ever got this to work — it just produces an Unsupported special dependency :cask error. So it seems this isn't really robustly supported by the current Homebrew code, and therefore I'm asking here!

Relevant casks

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[p-linnane]

I am personally not opposed to allowing 3rd party taps to depend on casks. It would very much be an unsupported use case though. Software in Homebrew/core is required to be open-source using an OSI approved license and build from source on our CI, which is why we do not allow cask dependencies. Note that we have things like code-cli which is the VC Code cli component since it fulfills all the requirements for inclusion in Homebrew/core.