我将macos升级到Mojave并重新安装了xcode，xcode CLT，ruby等 . 然后我尝试了：
gem install nokogiri
我收到以下错误（安装其他宝石给出了类似的错误）：
ERROR: Failed to build gem native extension.
current directory: /usr/local/lib/ruby/gems/2.5.0/gems/nokogiri-1.8.5/ext/nokogiri
/usr/local/opt/ruby/bin/ruby -r ./siteconf20181209-20884-etfc5r.rb extconf.rb
checking if the C compiler accepts ... *** 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.
我检查了 mkmf.log ，其中包含以下内容：
"clang -o conftest -I/usr/local/Cellar/ruby/2.5.3_1/include/ruby-2.5.0/x86_64-darwin18 -I/usr/local/Cellar/ruby/2.5.3_1/include/ruby-2.5.0/ruby/backward -I/usr/local/Cellar/ruby/2.5.3_1/include/ruby-2.5.0 -I. -I/usr/local/opt/libyaml/include -I/usr/local/opt/openssl/include -I/usr/local/opt/readline/include -D_XOPEN_SOURCE -D_DARWIN_C_SOURCE -D_DARWIN_UNLIMITED_SELECT -D_REENTRANT -O3 -ggdb3 -Wall -Wextra -Wno-unused-parameter -Wno-parentheses -Wno-long-long -Wno-missing-field-initializers -Wno-tautological-compare -Wno-parentheses-equality -Wno-constant-logical-operand -Wno-self-assign -Wunused-variable -Wimplicit-int -Wpointer-arith -Wwrite-strings -Wdeclaration-after-statement -Wshorten-64-to-32 -Wimplicit-function-declaration -Wdivision-by-zero -Wdeprecated-declarations -Wextra-tokens -fno-common -pipe conftest.c -L. -L/usr/local/Cellar/ruby/2.5.3_1/lib -L/usr/local/opt/libyaml/lib -L/usr/local/opt/openssl/lib -L/usr/local/opt/readline/lib -L. -fstack-protector -L/usr/local/lib -L/usr/local/opt/libyaml/lib -L/usr/local/opt/openssl/lib -L/usr/local/opt/readline/lib -lruby.2.5.3 -lpthread -ldl -lobjc "
In file included from conftest.c:1:
In file included from /usr/local/Cellar/ruby/2.5.3_1/include/ruby-2.5.0/ruby.h:33:
In file included from /usr/local/Cellar/ruby/2.5.3_1/include/ruby-2.5.0/ruby/ruby.h:29:
这段文字就这样了一段时间 . 我也 cd 到nokogiri文件夹并直接运行 extconf.rb ，并收到以下错误：
checking if the C compiler accepts ... *** 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
...（为简洁而跳过类似的内容并继续在下面）
usr/local/Cellar/ruby/2.5.3_1/lib/ruby/2.5.0/mkmf.rb:456:in 'try_do': The compiler failed to generate an executable file. (RuntimeError)
You have to install development tools first.
我试着安装xcode . 我还安装了 Headers 并确认了许可证 . 我起初认为它与GCC有关，但mkmf文件显示问题出在 Clang 上 .
希望有人能提供帮助 .