Building native extensions.  This could take a while...
ERROR:  Error installing therubyracer:
    ERROR: Failed to build gem native extension.
    current directory: /Users/koichi/.rbenv/versions/2.3.4/lib/ruby/gems/2.3.0/gems/therubyracer-0.12.3/ext/v8
/Users/koichi/.rbenv/versions/2.3.4/bin/ruby -r ./siteconf20200120-28144-771md0.rb extconf.rb
checking for main() in -lpthread... yes
checking for main() in -lobjc... yes
checking for v8.h... no
*** 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/koichi/.rbenv/versions/2.3.4/bin/$(RUBY_BASE_NAME)
    --with-pthreadlib
    --without-pthreadlib
    --with-objclib
    --without-objclib
    --enable-debug
    --disable-debug
    --with-v8-dir
    --without-v8-dir
    --with-v8-include
    --without-v8-include=${v8-dir}/include
    --with-v8-lib
    --without-v8-lib=${v8-dir}/lib
/Users/koichi/.rbenv/versions/2.3.4/lib/ruby/gems/2.3.0/gems/libv8-3.16.14.19/ext/libv8/location.rb:50:in `configure': By using --with-system-v8, you have chosen to use the version  (Libv8::Location::System::NotFoundError)
of V8 found on your system and *not* the one that is bundled with 
the libv8 rubygem. 
However, your system version of v8 could not be located. 
Please make sure your system version of v8 that is compatible 
with 3.16.14.19 installed. You may need to use the 
--with-v8-dir option if it is installed in a non-standard location
    from /Users/koichi/.rbenv/versions/2.3.4/lib/ruby/gems/2.3.0/gems/libv8-3.16.14.19/lib/libv8.rb:7:in `configure_makefile'
    from extconf.rb:32:in `<main>'
To see why this extension failed to compile, please check the mkmf.log which can be found here:
  /Users/koichi/.rbenv/versions/2.3.4/lib/ruby/gems/2.3.0/extensions/x86_64-darwin-19/2.3.0-static/therubyracer-0.12.3/mkmf.log
extconf failed, exit code 1
Gem files will remain installed in /Users/koichi/.rbenv/versions/2.3.4/lib/ruby/gems/2.3.0/gems/therubyracer-0.12.3 for inspection.
Results logged to /Users/koichi/.rbenv/versions/2.3.4/lib/ruby/gems/2.3.0/extensions/x86_64-darwin-19/2.3.0-static/therubyracer-0.12.3/gem_make.out

brew install [email protected]

bundle config --local build.libv8 --with-system-v8
bundle config --local build.therubyracer --with-v8-dir=/usr/local/opt/[email protected]

bundle install

v8 engine に ”3.15系統” と ”最新の７系統” がある？

% brew info v8
v8: stable 7.9.317.31 (bottled)
Google's JavaScript engine
https://github.com/v8/v8/wiki
/usr/local/Cellar/v8/7.9.317.31 (38 files, 38.9MB) *
  Poured from bottle on 2020-01-22 at 11:43:33
From: https://github.com/Homebrew/homebrew-core/blob/master/Formula/v8.rb
==> Dependencies
Build: ninja ✘
==> Requirements
Build: xcode ✔
==> Analytics
install: 2,444 (30 days), 10,549 (90 days), 38,848 (365 days)
install-on-request: 2,138 (30 days), 8,718 (90 days), 28,839 (365 days)
build-error: 0 (30 days)