Include files are not linked at /usr/local/include or /usr/include

[watjurk]

Mac: M1 Apple Silicon, BigSur: 11.2.1
Brew: Homebrew 3.0.1-116-g3ff5795

I don't know if this is intended or not but /usr/local/include and /usr/include does not exist on my system. Brew don't care and the only include path with brew installed formulas is at /opt/homebrew/include.

Is there any way to get brew to "link" includes at /usr/local/include or /usr/include ?

Thanks !

[Bo98]

This is intentional for Apple Silicon.

Is there any way to get brew to "link" includes at /usr/local/include or /usr/include ?

brew does not support doing this. What issue are you having that makes you feel like you need this?

[Syzygies]

I'll describe an issue that brought me to this discussion. I do not need help with a particular issue; one can find workarounds each time. I would like to understand a "once and for all" solution.

I maintain a programming language zoo, and many of these builds take place outside Homebrew, but can take advantage of libraries provided most easily by Homebrew. I am at the moment setting up three Macs at once, in both flavors, and working around the M1 differences.

With some tweaking, one can base a native M1 build of Idris2 on Racket's native M1 build of Chez Scheme. The Idris2 build requires gmp. The build uses /usr/bin/cc which knows about /usr/local/include but not /opt/homebrew/include. One needs to set the CPATH environment variable on an M1 Mac, but not on an Intel Mac.

I have a reasonable expectation that external builds should be able to find Homebrew-installed libraries on either M1 or Intel Macs, without per-build intervention. eval $(${HOMEBREW_PREFIX}/bin/brew shellenv) does not suffice. What am I missing?

(An aside, definitely not worth its own thread, but why does brew shellenv put a trailing colon on MANPATH but not PATH or INFOPATH? I spent twenty minutes thinking I was being clumsy; I find there's a very thin line between understanding my code and falling off the cliff, so I chase everything like this. Is there a reason for this lack of parallelism in the code, or should I provide a pull request to remove that character?)

[carlocab]

I have a reasonable expectation that external builds should be able to find Homebrew-installed libraries on either M1 or Intel Macs, without per-build intervention. eval $(${HOMEBREW_PREFIX}/bin/brew shellenv) does not suffice. What am I missing?

I guess the difficulty is that build systems often defy reasonable expectations. Not because build system developers like being difficult (although there are many times where it seems like they do): the issue is that different users often have mutually exclusive expectations, all of which could be deemed reasonable depending on the context.

If you don't want to use processor-dependent build directives, you can always unconditionally add $(brew --prefix)/include to your CPATH (or the appropriate equivalent to CFLAGS/CXXFLAGS/CPPFLAGS) and -L$(brew --prefix)/lib to your LDFLAGS (or whatever is the equivalent of these for the build system you use). These will resolve to the correct values as long as you're using Homebrew-provided libraries.

why does brew shellenv put a trailing colon on MANPATH but not PATH or INFOPATH?

Because the semantics of MANPATH are different than that of PATH (and perhaps INFOPATH, but I haven't checked this). A trailing : in MANPATH means "append the default MANPATH specified by the system configuration files. A trailing : in PATH means append the current working directory to PATH, which isn't always a good idea.

[andrews05]

I ran into this issue when trying to build an existing program that relied on libpng. In addition to importing <png.h>, the make file used -lpng to link to the library. Under Intel, I just did brew install libpng and then it all just worked when I ran make.
Under M1, I ended up adding the following lines to my profile in order to get it to work:

export CPATH="$HOMEBREW_PREFIX/include:$CPATH"
export LIBRARY_PATH="$HOMEBREW_PREFIX/lib:$LIBRARY_PATH"

Is there a reason the homebrew shellenv doesn't/shouldn't set these itself? I wouldn't expect it to set CFLAGS or similar, but these paths certainly seem reasonable.

[lucarsso]

Same question. Homebrew install libpng current is installed into /opt/homebrew/Cellar/libpng/1.6.44. I have to specify specific link for each library I installed through homebrew. Is there a more convenient way to do this?

[gromgit]

I have to specify specific link for each library I installed through homebrew.

That's only true for keg-only formulae, which aren't automatically linked into the main Homebrew directories. The caveats for those formulae tell you quite clearly [a] that they're keg-only, and [b] the paths you need to configure for use (and they NEVER include the version numbers you mentioned above).

But for the vast majority of library formulae (and this includes libpng), you simply need to add /opt/homebrew/include to your build include path, and /opt/homebrew/lib to your build library path. That's about as convenient as it gets, and to answer @andrews05's question about why Homebrew doesn't automagically configure the appropriate environment variables:

1. different build systems may use different variables for this purpose
2. removing automatically-added directories from your build configuration (when you really don't want them there) is often MUCH LESS convenient than simply adding them when needed

[pinheadmz]

I am working with this issue as well after upgrading and migrating. I work on a few nodejs projects that use node-gyp to build native addons to nodejs. It's super inconvenient to add compiler flags to each of those dependencies' binding.gyp files. If I could add something like export CFLAGS -L$(brew --prefix)/lib to my ~/.bash_profile script I would be ok with that, but I dont think that will work

[carlocab]

Why won't it work?