Trouble installing Ruby with RVM on Cygwin

Question

I'm on Windows and I currently have Ruby v2.1.5 as that is what came with RailsInstaller. However, I need to downgrade to 2.1.1 for another project and I'm not sure how to.

I have installed rvm on Cygwin and I'm getting these problems when trying to execute rvm install 2.1.1

Searching for binary rubies, this might take some time.
No binary rubies available for: cygwin/unknown/x86_64/ruby-2.1.1.
Continuing with compilation. Please read 'rvm help mount' to get more 
information on binary rubies.

and

Checking requirements for cygwin.
Installing requirements for cygwin.
Updating system.
Installing required packages: mingw64-i686-gcc, mingw64-x86_64-gcc.
Requirements installation successful.
Installing Ruby from source to: /home/K/.rvm/rubies/ruby-2.1.1, this may take a while depending on your cpu(s)...
ruby-2.1.1 - #downloading ruby-2.1.1, this may take a while depending on your connection...
ruby-2.1.1 - #extracting ruby-2.1.1 to /home/K/.rvm/src/ruby-2.1.1....
ruby-2.1.1 - #applying patch /home/K/.rvm/patches/ruby/2.1.1/libyaml.patch.
ruby-2.1.1 - #applying patch /home/K/.rvm/patches/ruby/changeset_r45225.diff.
ruby-2.1.1 - #applying patch /home/K/.rvm/patches/ruby/changeset_r45240.diff.
ruby-2.1.1 - #configuring....................................................
ruby-2.1.1 - #post-configuration..
ruby-2.1.1 - #compiling....................................................
Error running '__rvm_make -j4',
showing last 15 lines of /home/K/.rvm/log/1433355357_ruby-2.1.1/make.log
make[2]: Leaving directory '/home/K/.rvm/src/ruby-2.1.1/ext/-test-/printf'
exts.mk:109: recipe for target 'ext/-test-/printf/all' failed
make[1]: *** [ext/-test-/printf/all] Error 2
make[1]: *** Waiting for unfinished jobs....
installing default rational libraries
installing default recursion libraries
make[2]: Leaving directory '/home/K/.rvm/src/ruby-2.1.1/ext/-test-/postponed_job'
linking shared-object -test-/rational.so
linking shared-object -test-/recursion.so
make[2]: Leaving directory '/home/K/.rvm/src/ruby-2.1.1/ext/-test-/recursion'
make[2]: Leaving directory '/home/K/.rvm/src/ruby-2.1.1/ext/-test-/rational'
make[1]: Leaving directory '/home/K/.rvm/src/ruby-2.1.1'
uncommon.mk:180: recipe for target 'build-ext' failed
make: *** [build-ext] Error 2
++ return 2
There has been an error while running make. Halting the installation.

Any help would be appreciated. Thanks

Answer 1

You need to patch ruby soure code so it would compile on cygwin. Thankfully rvm supports patches out of the box!

Create a file called cygwin.patch with the following content:

--- /ext/-test-/printf/printf.c 2014-06-29 10:17:20.000000000 -0700
+++ /ext/-test-/printf/printf.c 2015-07-08 16:58:15.882479100 -0700
@@ -1,3 +1,4 @@
+#define __STRICT_ANSI__ /* avoid conflicting utoa */
#include <ruby.h>
#include <ruby/encoding.h>

And now simply execute rvm with a --patch parameter like shown below:

rvm install 2.2-head --patch cygwin.patch