Gem installation error: You have to install development tools first

Question

I tried installing the gem 'sinatra-websocket', but when I ran gem install sinatra-websocket, I got this error...

ERROR: Failed to build gem native extension

... along with ...

C:/Ruby193/bin/ruby.exe extconf.rb
checking for main() in -lc... *** 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=C:/Ruby193/bin/ruby
    --with-thin_parser-dir
    --without-thin_parser-dir
    --with-thin_parser-include
    --without-thin_parser-include=${thin_parser-dir}/include
    --with-thin_parser-lib
    --without-thin_parser-lib=${thin_parser-dir}/lib
    --with-clib
    --without-clib
C:/Ruby193/lib/ruby/1.9.1/mkmf.rb:381:in `try_do': The compiler failed to generate an executable file. (RuntimeError)
You have to install development tools first.
    from C:/Ruby193/lib/ruby/1.9.1/mkmf.rb:461:in `try_link0'
    from C:/Ruby193/lib/ruby/1.9.1/mkmf.rb:476:in `try_link'
    from C:/Ruby193/lib/ruby/1.9.1/mkmf.rb:619:in `try_func'
    from C:/Ruby193/lib/ruby/1.9.1/mkmf.rb:845:in `block in have_library'
    from C:/Ruby193/lib/ruby/1.9.1/mkmf.rb:790:in `block in checking_for'
    from C:/Ruby193/lib/ruby/1.9.1/mkmf.rb:284:in `block (2 levels) in postpone'
    from C:/Ruby193/lib/ruby/1.9.1/mkmf.rb:254:in `open'
    from C:/Ruby193/lib/ruby/1.9.1/mkmf.rb:284:in `block in postpone'
    from C:/Ruby193/lib/ruby/1.9.1/mkmf.rb:254:in `open'
    from C:/Ruby193/lib/ruby/1.9.1/mkmf.rb:280:in `postpone'
    from C:/Ruby193/lib/ruby/1.9.1/mkmf.rb:789:in `checking_for'
    from C:/Ruby193/lib/ruby/1.9.1/mkmf.rb:840:in `have_library'
    from extconf.rb:4:in `<main>'

Here's what the mkmf file in C:\Ruby193\lib\ruby\gems\1.9.1\gems\thin-1.6.3\ext\thin_parser looks like:

"gcc -o conftest -IC:/Ruby193/include/ruby-1.9.1/i386-mingw32 -IC:/Ruby193/include/ruby-1.9.1/ruby/backward -IC:/Ruby193/include/ruby-1.9.1 -I. -DFD_SETSIZE=2048  -DFD_SETSIZE=2048  -O3 -fno-omit-frame-pointer -g -Wall -Wextra -Wno-unused-parameter -Wno-parentheses -Wno-long-long -Wno-missing-field-initializers -Wpointer-arith -Wwrite-strings -Wdeclaration-after-statement -Wimplicit-function-declaration conftest.c  -L. -LC:/Ruby193/lib -L.   -march=i486   -lmsvcrt-ruby191  -lshell32 -lws2_32 -limagehlp -lshlwapi  "
checked program was:
/* begin */
1: #include "ruby.h"
2: 
3: #include <winsock2.h>
4: #include <windows.h>
5: int main(int argc, char **argv)
6: {
7:   return 0;
8: }
/* end */

I'm using Windows 7.

Why am I getting the error? There's a line stating "could not create Makefile...", but is that relevant?

Answer 1

This worked for me:

sudo xcode-select -switch /