Discussion: longterm Homebrew prefix on Apple Silicon Macs

[mistydemeo]

Feature suggestion

We need to determine which prefix we'll use as the default prefix for Apple Silicon-based Macs on a permanent basis.

A detailed description of the proposed feature

In #9117, we switched to a new prefix of /opt/homebrew for installations on Apple Silicon. This was written and shipped with heroic speed to help prevent strange issues with bleeding edge users on the first consumer Apple Silicon Macs. I'd like to make sure we have a conversation about our longterm plans here before we commit to something. This is an aspect with potential consequences for users, so it's important we've fully weighed the pros and cons before we come to a final decision.

Today, Homebrew's prefix is /usr/local, with the repository in /usr/local/Homebrew. In the initial phase of Apple Silicon migration, in order to avoid using the same prefix for both Intel and ARM binaries, we have two prefixes instead: /usr/local for Intel, and /opt/homebrew for Apple Silicon. Eventually, the need for /usr/local as a Rosetta installation of Homebrew will go away and Apple Silicon users will have only one installation.

Way back in the mists of history, /usr/local was chosen for a few reasons:

1. /usr/local/bin is in the default PATH, so most things a user will use will end up seeing Homebrew-installed tools without configuration.
2. Buildsystems look in /usr/local/include, /usr/local/lib and /usr/local/lib/pkgconfig by default, so non-Homebrew software will find Homebrew-installed libraries without configuration.

These reasons were all in contrast to MacPorts, which installed its software in /opt/local. /usr/local was chosen in response to the issues users were experiencing at the time. We have also received some feedback from users who would prefer a different default prefix, namely:

1. Some non-Homebrew tools also install libraries and binaries in /usr/local, for the same reason Homebrew does, and so there are sometimes conflicts between them.
2. Some users don't want Homebrew-installed software to be found by default / without configuration, making an alternate prefix preferable.

Consequently, the question here is: once Apple Silicon Homebrew becomes the primary installation on Apple Silicon Macs, which should be prefix be?

• /usr/local
• /opt/homebrew
• Something else

We have a bit of time before we start creating our first bottles, so let's make sure we've discussed this in detail before then.

The motivation for the feature

Ensuring the best user experience.

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

Eventually, close to 100% of Homebrew users will be using Apple Silicon.

What alternatives to the feature have been considered

See the discussion above.

[sjackman]

My preference is /opt/homebrew for Homebrew on Apple Silicon. (I'm not on the TSC.)
Thanks for starting this discussion, Misty!

[reitermarkus]

Some non-Homebrew tools also install libraries and binaries in /usr/local, for the same reason Homebrew does, and so there are sometimes conflicts between them.

I'd say /opt/homebrew (or really anything other than /usr/local) is preferable in this case.

/usr/local/bin is in the default PATH

I think we can still accomplish this by adding /etc/paths.d/homebrew.

[claui]

My preference is /opt/homebrew (I’m not a TSC member).

Early feedback from people outside of Homebrew has been largely positive. I’m looking forward to getting one of the most often-cited pain points solved.

[claui]

Sorry fat fingers

[claui]

I think we can still accomplish this by adding /etc/paths.d/homebrew.

Any chance how to get launchd to pick this up, too, so GUI apps can inherit it?

That would keep brewed commands (and scripts that use them) working when launched from Xcode or a text editor.

[iMichka]

Eventually, the need for /usr/local as a Rosetta installation of Homebrew will go away and Apple Silicon users will have only one installation.

I am unsure about this. Some software might never compile under ARM. So we will always need 2 prefixes, one for ARM, one for Rosetta.

[cmarquardt]

I am unsure about this. Some software might never compile under ARM. So we will always need 2 prefixes, one for ARM, one for Rosetta.

You could use a subdirectory under /opt/homebrewindicating the architecture to separate the installation trees, e.g. something like

/opt/homebrew/x86_64
/opt/homebrew/arm_apple       # ...or whatever the standard name for the apple silicon is

I've bee using homebrew with a different prefix for many years now (/opt/homebrew, accidentally), and setting up the PATH via /etc/paths or a dedicated file in /etc/paths.d/ works fine. TeXLive uses the same mechanism, for example, XQuartz as well (I believe).

[mistydemeo]

My preference is /opt/homebrew for Homebrew on Apple Silicon. (I'm not on the TSC.)

Can you tell me more, from a Linuxbrew perspective, how well this works for users? Do users get confused by libraries and headers not being found by compilers by default?

I am unsure about this. Some software might never compile under ARM. So we will always need 2 prefixes, one for ARM, one for Rosetta.

Rosetta isn't staying around forever. If it's like PowerPC support, we'll only have support for running Intel binaries on ARM for another few years.

[MikeMcQuaid]

Consequently, the question here is: once Apple Silicon Homebrew becomes the primary installation on Apple Silicon Macs, which should be prefix be?

/opt/homebrew.

Reasoning: we've talked a bunch in the past about whether we should move the default prefix away from /usr/local because:

• people endlessly complain about it
• more and more software now dumps crap in there
• superenv has (for a pretty long time now) meant that far less stuff breaks outside of /usr/local
• CMake and friends have a habit of opportunistically linking into /usr/local

The main reason I can see against is that e.g. RubyGems won't automatically find things in /usr/local but, in my experience, this has been becoming more and more of a thing since we use keg-only and versioned formulae more liberally.

You could use a subdirectory under /opt/homebrewindicating the architecture to separate the installation trees, e.g. something like

@cmarquardt Thanks! That's something we considered but it feels inelegant to me given the existing locations. I've locked this thread not because of your (insightful) comment but just generally to keep this discussion limited to Homebrew maintainers.

I am unsure about this. Some software might never compile under ARM. So we will always need 2 prefixes, one for ARM, one for Rosetta.

Agreed @iMichka.

/usr/local/bin is in the default PATH

I think we can still accomplish this by adding /etc/paths.d/homebrew.

In my experience it's less of an issue with PATH and more of an issue with "default compiler lookup paths" for things like RubyGems that don't want to configure this.