Mono requirement or pseudo-formula

[alexreg]

The formula mono and the casks mono-mdk and mono-mdk-for-visual-studio are of course mutually exclusive and provide essentially the same software, albeit at times slightly different versions. It would seem highly desirable to create some sort of requirement or pseudo-formula that is satisfied by any of the three being installed (so long as the version is compatible). As it is right now, some formulas cannot be installed because a given formula depends on a specific one of these three formulas/casks, though it really doesn't make a difference.

Thoughts on what to do about the above would be appreciated. If we can decide on a solution, I would be happy to create a PR.

[carlocab]

We have the same situation for the various JDK formulae/casks.

There was a time when Java dependencies were a Requirement that could be fulfilled by any Java installation, even if it was not installed via Homebrew.

This resulted in regular bug reports about things not working, because it meant that users were using configurations that were not tested in CI.

Adding flexibility for the Mono dependency is likely going to lead to a similar situation, so I don’t think that’s something we want to do, at least for formulae in Homebrew/core. (You’ll also notice that no dependencies are fulfilled by casks there, and that’s intentional.) You can do whatever you like in an external tap.

[alexreg]

@carlocab Thanks for the response. It largely makes sense. Do you however have a recommendation of what to do in the case a formula depends on mono but I have mono-mdk installed? I suppose I could use --ignore-dependencies, but then subsequent updates would fail.

[carlocab]

You could brew unlink mono. That should stick until it's next reinstalled or upgraded. (Arguably it should stick after that too, but brew doesn't know how to handle that.)

[alexreg]

Hmm, that seems less than ideal. Do you think we could make that option stick? Or have --ignore-dependencies stick? Or some new option?

[carlocab]

--ignore-dependencies is an unsupported developer flag, so we'd probably sooner remove it than expand it by making it stick.

Making brew unlink stick has been on my wish list for a while, but I haven't had the time to look into it. I'd be happy to review a PR that implements it.

[alexreg]

Sounds good. I'll have a look at that.

Also, I do think --ignore-dependencies is useful for testing formulas during creation, regardless.

[carlocab]

Yes, I don't think --ignore-dependencies is going away. I was just emphasising how unlikely it was that we'd support making it persist across reinstalls/upgrades.

[MikeMcQuaid]

IMO a better fix for this would be to avoid manual brew unlinking but instead have a DSL to define formulae and casks to have overlapping links and somehow decide which one gets linked.

[alexreg]

Is it not bad practice for formulas to assume their dependencies are linked?

[SMillerDev]

If it was your solution wouldn't work either. Since that depends on a cask taking the link location of a formula

[alexreg]

@SMillerDev Whom are you addressing?

[MikeMcQuaid]

Is it not bad practice for formulas to assume their dependencies are linked?

Quite possibly. We don't audit or test against it, though, so it's impossible to tell how many are assuming this.

[alexreg]

@MikeMcQuaid I see. Well, your point is certainly stronger in that case. I personally will be relatively happy as long as there is some sort of solution to this issue from a user perspective. Would your approach allow the user to choose which of a set of overlapping formulas gets linked, or would it be by some sort of priority list?