Ruby Gem install Json fails on Mavericks and Xcode 5.1 - unknown argument: '-multiply_definedsuppress'

Question

I was trying run gem install json and got the following error

Gem::Ext::BuildError: ERROR: Failed to build gem native extension.      /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/bin/ruby extconf.rb  creating Makefile  make "DESTDIR=" clean  make "DESTDIR=" compiling generator.c linking shared-object json/ext/generator.bundle clang: error: unknown argument: '-multiply_definedsuppress' [-Wunused-command-line-argument-hard-error-in-future] clang: note: this will be a hard error (cannot be downgraded to a warning) in the future make: *** [generator.bundle] Error 1  make failed, exit code 2  Gem files will remain installed in /opt/boxen/repo/.bundle/ruby/2.0.0/gems/json-1.8.0 for inspection. Results logged to /opt/boxen/repo/.bundle/ruby/2.0.0/extensions/universal-darwin-13/2.0.0/json-1.8.0/gem_make.out 

I'm using:

Os X: 10.9.2
Xcode: 5.1 Build version 5B130a
Command Line Tools (CLT): 5.1.0.0.1.1393561416
Ruby: ruby 2.0.0p247 (2013-06-27 revision 41674) [universal.x86_64-darwin13]
Ruby Gem: 2.2.2
GCC: 4.2.1 Apple LLVM version 5.1 (clang-503.0.38) (based on LLVM 3.4svn)

Answer 1

I am encountering the exact same problem after updating Xcode to 5.1 and news from Apple aren't good. From Xcode 5.1 Release Notes:

• The Apple LLVM compiler in Xcode 5.1 treats unrecognized command-line options as errors. This issue has been seen when building both Python native extensions and Ruby Gems, where some invalid compiler options are currently specified.

Projects using invalid compiler options will need to be changed to remove those options. To help ease that transition, the compiler will temporarily accept an option to downgrade the error to a warning:

-Wno-error=unused-command-line-argument-hard-error-in-future

To workaround this issue, set the ARCHFLAGS environment variable to downgrade the error to a warning.

ARCHFLAGS=-Wno-error=unused-command-line-argument-hard-error-in-future gem install GemName

It seems that all gems violating the compiler options must be updated to use valid options. It is explicitly stated that: This option [downgrading error to warning] will not be supported in the future.

The clang note we are seeing (this will be a hard error (cannot be downgraded to a warning) in the future) corresponds to the change announced in the release notes.

---

To answer your question specifically, use the following to install the json gem:

ARCHFLAGS=-Wno-error=unused-command-line-argument-hard-error-in-future gem install json

Note, however, that this is only a temporary fix.

Answer 2

One-liner to fix that

curl https://gist.githubusercontent.com/Paulche/9713531/raw/1e57fbb440d36ca5607d1739cc6151f373b234b6/gistfile1.txt | sudo patch /System/Library/Frameworks/Ruby.framework/Versions/2.0/usr/lib/ruby/2.0.0/universal-darwin13/rbconfig.rb