[Ruby] ERROR: cannot discover where libxml2 is located on your system. please make sure `pkg-config` is installed. の解決方法

Ruby on Rails 5 を bundle install でインストール中に libxml2 が無くて nokogiri がインストールできないというエラーが発生しました。

MacOS に nokogiri のインストールに必要なライブラリがインストールされてなかっただけなのですが、無事に解決できたのでその方法をご紹介します。

Ruby | ルビー

libxml2 が無くて nokogiri がインストールできないエラーメッセージ

Gem::Ext::BuildError: ERROR: Failed to build gem native extension.
 
    current directory: /Users/yourname/.rvm/gems/ruby-2.4.1@my-web/gems/nokogiri-1.8.0/ext/nokogiri
/Users/yourname/.rvm/rubies/ruby-2.4.1/bin/ruby -r ./siteconf20170812-11295-n8mq5e.rb extconf.rb
checking if the C compiler accepts ... 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 2.2.0
checking for iconv.h... yes
checking for gzdopen() in -lz... yes
checking for iconv using --with-opt-* flags... yes
************************************************************************
IMPORTANT NOTICE:
 
Building Nokogiri with a packaged version of libxml2-2.9.4
with the following patches applied:
	- 0001-Fix-comparison-with-root-node-in-xmlXPathCmpNodes.patch
	- 0002-Fix-XPointer-paths-beginning-with-range-to.patch
	- 0003-Disallow-namespace-nodes-in-XPointer-ranges.patch
 
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-darwin15.6.0/ports/libxml2/2.9.4... OK
Running git apply with
/Users/yourname/.rvm/gems/ruby-2.4.1@my-web/gems/nokogiri-1.8.0/patches/libxml2/0001-Fix-comparison-with-root-node-in-xmlXPathCmpNodes.patch... OK
Running git apply with
/Users/yourname/.rvm/gems/ruby-2.4.1@my-web/gems/nokogiri-1.8.0/patches/libxml2/0002-Fix-XPointer-paths-beginning-with-range-to.patch... OK
Running git apply with
/Users/yourname/.rvm/gems/ruby-2.4.1@my-web/gems/nokogiri-1.8.0/patches/libxml2/0003-Disallow-namespace-nodes-in-XPointer-ranges.patch... OK
Running 'configure' for libxml2 2.9.4... OK
Running 'compile' for libxml2 2.9.4... ERROR, review
'/Users/yourname/.rvm/gems/ruby-2.4.1@my-web/gems/nokogiri-1.8.0/ext/nokogiri/tmp/x86_64-apple-darwin15.6.0/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
	--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/yourname/.rvm/rubies/ruby-2.4.1/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/yourname/.rvm/gems/ruby-2.4.1@my-web/gems/mini_portile2-2.2.0/lib/mini_portile2/mini_portile.rb:400:in `block in execute': Failed to complete
compile task (RuntimeError)
	from /Users/yourname/.rvm/gems/ruby-2.4.1@my-web/gems/mini_portile2-2.2.0/lib/mini_portile2/mini_portile.rb:371:in `chdir'
	from /Users/yourname/.rvm/gems/ruby-2.4.1@my-web/gems/mini_portile2-2.2.0/lib/mini_portile2/mini_portile.rb:371:in `execute'
	from /Users/yourname/.rvm/gems/ruby-2.4.1@my-web/gems/mini_portile2-2.2.0/lib/mini_portile2/mini_portile.rb:114:in `compile'
	from /Users/yourname/.rvm/gems/ruby-2.4.1@my-web/gems/mini_portile2-2.2.0/lib/mini_portile2/mini_portile.rb:153:in `cook'
	from extconf.rb:365: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:364:in `block in process_recipe'
	from extconf.rb:262:in `tap'
	from extconf.rb:262:in `process_recipe'
	from extconf.rb:548:in `<main>'
 
To see why this extension failed to compile, please check the mkmf.log which can be found here:
 
  /Users/yourname/.rvm/gems/ruby-2.4.1@my-web/extensions/x86_64-darwin-15/2.4.0/nokogiri-1.8.0/mkmf.log
 
extconf failed, exit code 1
 
Gem files will remain installed in /Users/yourname/.rvm/gems/ruby-2.4.1@my-web/gems/nokogiri-1.8.0 for inspection.
Results logged to /Users/yourname/.rvm/gems/ruby-2.4.1@my-web/extensions/x86_64-darwin-15/2.4.0/nokogiri-1.8.0/gem_make.out
 
An error occurred while installing nokogiri (1.8.0), and Bundler cannot continue.
Make sure that `gem install nokogiri -v '1.8.0'` succeeds before bundling.
 
In Gemfile:
  rails was resolved to 5.1.3, which depends on
    actioncable was resolved to 5.1.3, which depends on
      actionpack was resolved to 5.1.3, which depends on
        actionview was resolved to 5.1.3, which depends on
          rails-dom-testing was resolved to 2.0.3, which depends on
            nokogiri
 
 
ERROR: cannot discover where libxml2 is located on your system. please make sure `pkg-config` is installed.

nokogiri は libxml2 libxslt libiconv が必要

MacOS に libxml2 libxslt libiconv という三種の神器がインストールされていないため、nokogiri のインストールに失敗してしまっていたようでした。

何も考えずに brew install しましょう。

brew install libxml2 libxslt libiconv

インストール後に brew link –force でインストールした lib* へのシンボリックリンクを作成しましょう。

brew link --force libxml2
brew link --force libxslt
brew link --force libiconv

最後に MacOS にインストールしたシステムライブラリを利用して build するような設定を有効にして、再度 bundle install すれば完了です。

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

Rails のインストールでこういう風にエラー対応をしないといけないの地味に面倒なので、開発環境の Docker 化の機運が高まりますね。

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