Install Rails into os x

OS X に Rails をインストールしようとして失敗した話。
Homebrew を使って rbenv の Ruby 2.3.0 の設定まで完了しているのが前提。

- OS X 10.9.5
- Homebrew 0.9.9
- rbenv 1.0.0
- Ruby 2.3.0

```
~$ gem install rails
Fetching: i18n-0.7.0.gem (100%)
Successfully installed i18n-0.7.0
Fetching: thread_safe-0.3.5.gem (100%)
Successfully installed thread_safe-0.3.5
Fetching: tzinfo-1.2.2.gem (100%)
Successfully installed tzinfo-1.2.2
Fetching: concurrent-ruby-1.0.2.gem (100%)
Successfully installed concurrent-ruby-1.0.2
Fetching: activesupport-5.0.0.gem (100%)
Successfully installed activesupport-5.0.0
Fetching: rack-2.0.1.gem (100%)
Successfully installed rack-2.0.1
Fetching: rack-test-0.6.3.gem (100%)
Successfully installed rack-test-0.6.3
Fetching: mini_portile2-2.1.0.gem (100%)
Successfully installed mini_portile2-2.1.0
Fetching: pkg-config-1.1.7.gem (100%)
Successfully installed pkg-config-1.1.7
Fetching: nokogiri-1.6.8.gem (100%)
Building native extensions.  This could take a while...
ERROR:  Error installing rails:
	ERROR: Failed to build gem native extension.

    current directory: /Users/deathmetalland/.rbenv/versions/2.3.0/lib/ruby/gems/2.3.0/gems/nokogiri-1.6.8/ext/nokogiri
/Users/deathmetalland/.rbenv/versions/2.3.0/bin/ruby -r ./siteconf20160731-38067-s11v16.rb extconf.rb
Using pkg-config version 1.1.7
checking if the C compiler accepts -Wno-error=shorten-64-to-32... yes
checking if the C compiler accepts -Wno-error=unused-command-line-argument-hard-error-in-future... no
Building nokogiri using packaged libraries.
Using mini_portile version 2.1.0
checking for iconv.h... yes
checking for gzdopen() in -lz... yes
checking for iconv... yes
************************************************************************
IMPORTANT NOTICE:

Building Nokogiri with a packaged version of libxml2-2.9.4.

Team Nokogiri will keep on doing their best to provide security
updates in a timely manner, but if this is a concern for you and want
to use the system library instead; abort this installation process and
reinstall nokogiri as follows:

    gem install nokogiri -- --use-system-libraries
        [--with-xml2-config=/path/to/xml2-config]
        [--with-xslt-config=/path/to/xslt-config]

If you are using Bundler, tell it to use the option:

    bundle config build.nokogiri --use-system-libraries
    bundle install

Note, however, that nokogiri is not fully compatible with arbitrary
versions of libxml2 provided by OS/package vendors.
************************************************************************
Extracting libxml2-2.9.4.tar.gz into tmp/x86_64-apple-darwin13.4.0/ports/libxml2/2.9.4... OK
Running 'configure' for libxml2 2.9.4... OK
Running 'compile' for libxml2 2.9.4... ERROR, review '/Users/deathmetalland/.rbenv/versions/2.3.0/lib/ruby/gems/2.3.0/gems/nokogiri-1.6.8/ext/nokogiri/tmp/x86_64-apple-darwin13.4.0/ports/libxml2/2.9.4/compile.log' to see what happened. Last lines are:
========================================================================
    unsigned short* in = (unsigned short*) inb;
                         ^~~~~~~~~~~~~~~~~~~~~
encoding.c:815:27: warning: cast from 'unsigned char *' to 'unsigned short *' increases required alignment from 1 to 2 [-Wcast-align]
    unsigned short* out = (unsigned short*) outb;
                          ^~~~~~~~~~~~~~~~~~~~~~
4 warnings generated.
  CC       error.lo
  CC       parserInternals.lo
  CC       parser.lo
  CC       tree.lo
  CC       hash.lo
  CC       list.lo
  CC       xmlIO.lo
xmlIO.c:1450:52: error: use of undeclared identifier 'LZMA_OK'
    ret =  (__libxml2_xzclose((xzFile) context) == LZMA_OK ) ? 0 : -1;
                                                   ^
1 error generated.
make[2]: *** [xmlIO.lo] Error 1
make[1]: *** [all-recursive] Error 1
make: *** [all] Error 2
========================================================================
*** 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
	--without-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=/Users/deathmetalland/.rbenv/versions/2.3.0/bin/$(RUBY_BASE_NAME)
	--help
	--clean
	--use-system-libraries
	--enable-static
	--disable-static
	--with-zlib-dir
	--without-zlib-dir
	--with-zlib-include
	--without-zlib-include=${zlib-dir}/include
	--with-zlib-lib
	--without-zlib-lib=${zlib-dir}/lib
	--enable-cross-build
	--disable-cross-build
/Users/deathmetalland/.rbenv/versions/2.3.0/lib/ruby/gems/2.3.0/gems/mini_portile2-2.1.0/lib/mini_portile2/mini_portile.rb:366:in `block in execute': Failed to complete compile task (RuntimeError)
	from /Users/deathmetalland/.rbenv/versions/2.3.0/lib/ruby/gems/2.3.0/gems/mini_portile2-2.1.0/lib/mini_portile2/mini_portile.rb:337:in `chdir'
	from /Users/deathmetalland/.rbenv/versions/2.3.0/lib/ruby/gems/2.3.0/gems/mini_portile2-2.1.0/lib/mini_portile2/mini_portile.rb:337:in `execute'
	from /Users/deathmetalland/.rbenv/versions/2.3.0/lib/ruby/gems/2.3.0/gems/mini_portile2-2.1.0/lib/mini_portile2/mini_portile.rb:111:in `compile'
	from /Users/deathmetalland/.rbenv/versions/2.3.0/lib/ruby/gems/2.3.0/gems/mini_portile2-2.1.0/lib/mini_portile2/mini_portile.rb:150:in `cook'
	from extconf.rb:364:in `block (2 levels) in process_recipe'
	from extconf.rb:257:in `block in chdir_for_build'
	from extconf.rb:256:in `chdir'
	from extconf.rb:256:in `chdir_for_build'
	from extconf.rb:363:in `block in process_recipe'
	from extconf.rb:262:in `tap'
	from extconf.rb:262:in `process_recipe'
	from extconf.rb:555:in `<main>'

To see why this extension failed to compile, please check the mkmf.log which can be found here:

  /Users/deathmetalland/.rbenv/versions/2.3.0/lib/ruby/gems/2.3.0/extensions/x86_64-darwin-13/2.3.0-static/nokogiri-1.6.8/mkmf.log

extconf failed, exit code 1

Gem files will remain installed in /Users/deathmetalland/.rbenv/versions/2.3.0/lib/ruby/gems/2.3.0/gems/nokogiri-1.6.8 for inspection.
Results logged to /Users/deathmetalland/.rbenv/versions/2.3.0/lib/ruby/gems/2.3.0/extensions/x86_64-darwin-13/2.3.0-static/nokogiri-1.6.8/gem_make.out
```

nokogiri のインストール時に libxml2 が原因で失敗した。
Homebrew に libxml2 がなかったのでインストールし直す。
それだけだと nokogiri の再インストール時に見れていないのでリンクもつける。
これでインストールできた。

```
~$ brew install libxml2
~$ brew link --force libxml2
~$ gem install nokogiri -- --use-system-libraries
~$ gem install rails
```