Cannot find png.h with custom Homebrew root because Boxen

I have a non-standard, but not-uncommon Homebrew config which causes this module to fail to build on OS X. Specifically, Homebrew is installed by Boxen under /opt/boxen instead of /usr/local:

$ brew --env
HOMEBREW_CC: clang
HOMEBREW_CXX: clang++
MAKEFLAGS: -j4
CMAKE_PREFIX_PATH: /opt/boxen/homebrew
CMAKE_INCLUDE_PATH: /usr/include/libxml2:/System/Library/Frameworks/OpenGL.framework/Versions/Current/Headers
CMAKE_LIBRARY_PATH: /System/Library/Frameworks/OpenGL.framework/Versions/Current/Libraries
PKG_CONFIG_LIBDIR: /usr/lib/pkgconfig:/opt/boxen/homebrew/Library/ENV/pkgconfig/10.10
ACLOCAL_PATH: /opt/boxen/homebrew/share/aclocal
PATH: /opt/boxen/homebrew/Library/ENV/4.3:/usr/bin:/bin:/usr/sbin:/sbin

I confess to being fairly ignorant how node extensions are built with gyp, but I would expect to see something like -I/opt/boxen/homebrew/include here:

$ npm install --loglevel verbose png
gyp verb `which` succeeded for `make` /usr/bin/make
gyp info spawn make
gyp info spawn args [ 'V=1', 'BUILDTYPE=Release', '-C', 'build' ]
  c++ '-D_DARWIN_USE_64_BIT_INODE=1' '-D_LARGEFILE_SOURCE' '-D_FILE_OFFSET_BITS=64' '-DBUILDING_NODE_EXTENSION' -I/Users/toolbear/.node-gyp/0.10.31/src -I/Users/toolbear/.node-gyp/0.10.31/deps/uv/include -I/Users/toolbear/.node-gyp/0.10.31/deps/v8/include  -Os -gdwarf-2 -mmacosx-version-min=10.5 -arch x86_64 -Wall -Wendif-labels -W -Wno-unused-parameter -fno-rtti -fno-threadsafe-statics -fno-strict-aliasing -MMD -MF ./Release/.deps/Release/obj.target/png/src/common.o.d.raw  -c -o Release/obj.target/png/src/common.o ../src/common.cpp
  c++ '-D_DARWIN_USE_64_BIT_INODE=1' '-D_LARGEFILE_SOURCE' '-D_FILE_OFFSET_BITS=64' '-DBUILDING_NODE_EXTENSION' -I/Users/toolbear/.node-gyp/0.10.31/src -I/Users/toolbear/.node-gyp/0.10.31/deps/uv/include -I/Users/toolbear/.node-gyp/0.10.31/deps/v8/include  -Os -gdwarf-2 -mmacosx-version-min=10.5 -arch x86_64 -Wall -Wendif-labels -W -Wno-unused-parameter -fno-rtti -fno-threadsafe-statics -fno-strict-aliasing -MMD -MF ./Release/.deps/Release/obj.target/png/src/png_encoder.o.d.raw  -c -o Release/obj.target/png/src/png_encoder.o ../src/png_encoder.cpp
In file included from ../src/png_encoder.cpp:3:

I can work around this issue with:

$ cd /usr/local
$ sudo ln -s /opt/boxen/homebrew/include include

And then everything builds.

With some pointers on what I should change, I'm happy to submit a pull request that incorporates brew --env values into the build config. The failure is trivial for me to reproduce and currently not blocking as png is an optional dependency ATM.

[LinusU]

What does pkg-config libpng output for you? Maybe you need to set your PKG_CONFIG_PATH to something under /opt/boxen...