homebrew: default `brewPrefix` should point to the default value of `$(brew --prefix)` not `$(brew --prefix)/bin`

[montchr]

The brewPrefix value defaults to /opt/homebrew/bin or /usr/local/bin, which is a bit misleading considering that the "prefix" should refer to the next level up (/opt/homebrew or /usr/local), which also happens to align with the output of brew --prefix.

This confusing terminology has bitten me a couple times when setting environment.systemPath = ["${config.homebrew.brewPrefix}/bin"], which results in the unexpected (and potentially shell-breaking) value of /opt/homebrew/bin/bin added to $PATH. Also, side note: shouldn't that value be added to $PATH automatically if config.homebrew.enable == true (or at least make that an option)?

From brew(1):

--prefix [--unbrewed] [--installed] [formula …]

Display Homebrew’s install path. Default:

• macOS Intel: /usr/local
• macOS ARM: /opt/homebrew
• Linux: /home/linuxbrew/.linuxbrew

And from GNU Autoconf documentation:

By default, configure sets the prefix for files it installs to /usr/local.

Also see:

• 4.9. /usr/local : Local hierarchy – Filesystem Hierarchy Standard

[montchr]

Also, for reference, here's the output of brew shellenv on my aarch64-darwin system:

❯ brew shellenv
export HOMEBREW_PREFIX="/opt/homebrew";
export HOMEBREW_CELLAR="/opt/homebrew/Cellar";
export HOMEBREW_REPOSITORY="/opt/homebrew";
export PATH="/opt/homebrew/bin:/opt/homebrew/sbin${PATH+:$PATH}";
export MANPATH="/opt/homebrew/share/man${MANPATH+:$MANPATH}:";
export INFOPATH="/opt/homebrew/share/info:${INFOPATH:-}";

[Enzime]

@malob any thoughts on this issue? I'm not too familiar as I don't personally use brew

[emilazy]

I think this would be reasonable but it would be a breaking change that we'd have to handle or warn about somehow. (Error out when the prefix ends with /bin?)

[montchr]

I just realized the "fix" I committed in my personal config (visible in history above) results in a $MANPATH that does not include anything managed by Nix.

I hadn't noticed until I couldn't find an rsync option that I know exists but was not found in its manpage. While rsync --version says 3.2.7, turns out that the manpage I get from man rsync is for rsync@2.6.9 (the version included in macOS).

[aidan-gibson]

@montchr This issue goes beyond nix-darwin (I haven't yet installed nix-darwin), but I brought this up in the nix installer here https://github.com/DeterminateSystems/nix-installer/issues/715 (not sure if that was the right place).