Yosemiteでgem install --user-install rabbitするにはPKG_CONFIG_PATH=/usr/local/opt/libffi/lib/pkgconfigを指定する

gistfile1.txt

Fetching: gobject-introspection-3.0.7.gem (100%)
Building native extensions.  This could take a while...
ERROR:  Error installing rabbit:
  ERROR: Failed to build gem native extension.

    /usr/local/opt/ruby/bin/ruby -r ./siteconf20151121-1191-56d1zb.rb extconf.rb
checking for --enable-debug-build option... no
checking for -Wall option to compiler... yes
checking for -Waggregate-return option to compiler... yes
checking for -Wcast-align option to compiler... yes
checking for -Wextra option to compiler... yes
checking for -Wformat=2 option to compiler... yes
checking for -Winit-self option to compiler... yes
checking for -Wlarger-than-65500 option to compiler... yes
checking for -Wmissing-declarations option to compiler... yes
checking for -Wmissing-format-attribute option to compiler... yes
checking for -Wmissing-include-dirs option to compiler... yes
checking for -Wmissing-noreturn option to compiler... yes
checking for -Wmissing-prototypes option to compiler... yes
checking for -Wnested-externs option to compiler... yes
checking for -Wold-style-definition option to compiler... yes
checking for -Wpacked option to compiler... yes
checking for -Wp,-D_FORTIFY_SOURCE=2 option to compiler... yes
checking for -Wpointer-arith option to compiler... yes
checking for -Wswitch-default option to compiler... yes
checking for -Wswitch-enum option to compiler... yes
checking for -Wundef option to compiler... yes
checking for -Wout-of-line-declaration option to compiler... yes
checking for -Wunsafe-loop-optimizations option to compiler... no
checking for -Wwrite-strings option to compiler... yes
checking for rb_define_alloc_func() in ruby.h... yes
checking for rb_block_proc() in ruby.h... yes
checking for new allocation framework... yes
checking for attribute assignment... no
checking for Windows... no
checking for gobject-introspection-1.0... yes
*** extconf.rb failed ***
Could not create Makefile due to some reason, probably lack of necessary
libraries and/or headers.  Check the mkmf.log file for more details.  You may
need configuration options.

Provided configuration options:
  --with-opt-dir
  --with-opt-include
  --without-opt-include=${opt-dir}/include
  --with-opt-lib
  --without-opt-lib=${opt-dir}/lib
  --with-make-prog
  --without-make-prog
  --srcdir=.
  --curdir
  --ruby=/usr/local/Cellar/ruby/2.2.2/bin/$(RUBY_BASE_NAME)
  --enable-debug-build
  --disable-debug-build
  --with-pkg-config
  --without-pkg-config
  --with-override-variables
  --without-override-variables
/Users/zunda/.gem/ruby/2.2.0/gems/pkg-config-1.1.6/lib/pkg-config.rb:265:in `parse_pc': .pc for libffi doesn't exist. (RuntimeError)
  from /Users/zunda/.gem/ruby/2.2.0/gems/pkg-config-1.1.6/lib/pkg-config.rb:185:in `declaration'
  from /Users/zunda/.gem/ruby/2.2.0/gems/pkg-config-1.1.6/lib/pkg-config.rb:199:in `collect_cflags'
  from /Users/zunda/.gem/ruby/2.2.0/gems/pkg-config-1.1.6/lib/pkg-config.rb:138:in `cflags'
  from /Users/zunda/.gem/ruby/2.2.0/gems/pkg-config-1.1.6/lib/pkg-config.rb:201:in `block in collect_cflags'
  from /Users/zunda/.gem/ruby/2.2.0/gems/pkg-config-1.1.6/lib/pkg-config.rb:200:in `collect'
  from /Users/zunda/.gem/ruby/2.2.0/gems/pkg-config-1.1.6/lib/pkg-config.rb:200:in `collect_cflags'
  from /Users/zunda/.gem/ruby/2.2.0/gems/pkg-config-1.1.6/lib/pkg-config.rb:138:in `cflags'
  from /Users/zunda/.gem/ruby/2.2.0/gems/pkg-config-1.1.6/lib/pkg-config.rb:391:in `cflags'
  from /Users/zunda/.gem/ruby/2.2.0/gems/pkg-config-1.1.6/lib/pkg-config.rb:442:in `have_package'
  from /Users/zunda/.gem/ruby/2.2.0/gems/glib2-3.0.7/lib/mkmf-gnome2.rb:618:in `required_pkg_config_package'
  from extconf.rb:59:in `<main>'

extconf failed, exit code 1

Gem files will remain installed in /Users/zunda/.gem/ruby/2.2.0/gems/gobject-introspection-3.0.7 for inspection.
Results logged to /Users/zunda/.gem/ruby/2.2.0/extensions/x86_64-darwin-14/2.2.0/gobject-introspection-3.0.7/gem_make.out

gistfile2.txt

$ brew install libffi
Warning: libffi-3.0.13 already installed
$ brew test libffi
Testing libffi
==> /usr/bin/clang -o closure closure.c -L/usr/local/Cellar/libffi/3.0.13/lib -l
==> ./closure
$ brew upgrade libffi
Error: libffi 3.0.13 already installed

gistfile3.txt

$ PKG_CONFIG_PATH=/usr/local/opt/libffi/lib/pkgconfig gem install rabbit
Building native extensions.  This could take a while...
Successfully installed gobject-introspection-3.0.7
Fetching: gio2-3.0.7.gem (100%)
Building native extensions.  This could take a while...
Successfully installed gio2-3.0.7
Fetching: rabbit-2.1.8.gem (100%)
Successfully installed rabbit-2.1.8
Parsing documentation for gobject-introspection-3.0.7
Installing ri documentation for gobject-introspection-3.0.7
Parsing documentation for gio2-3.0.7
Installing ri documentation for gio2-3.0.7
Parsing documentation for rabbit-2.1.8
Installing ri documentation for rabbit-2.1.8
Done installing documentation for gobject-introspection, gio2, rabbit after 9 seconds
3 gems installed

ahhh yessss!