Allow installation on non-supported systems

Closes #6

Rakefile

@@ -1,13 +1,15 @@
 #!/usr/bin/env rake
 require 'bundler/gem_tasks'
 require 'rake/extensiontask'
-
-# Compile the extension
-Rake::ExtensionTask.new('wdm')
-
 require 'rspec/core/rake_task'
+
 RSpec::Core::RakeTask.new(:spec)
 
+# Compile the extension
+Rake::ExtensionTask.new('wdm_ext') do |ext|
+  ext.ext_dir = 'ext/wdm'
+end
+
 desc "Open an irb session preloaded with WDM"
 task :console do
   sh "irb -rubygems -I lib -r wdm"

ext/wdm/extconf.rb

@@ -1,9 +1,27 @@
 require 'mkmf'
+require 'rbconfig'
 
-if have_library("kernel32") and
+def generate_makefile
+  create_makefile("wdm_ext")
+end
+
+def generate_dummy_makefile
+  File.open("Makefile", "w") do |f|
+    f.puts dummy_makefile('wdm_ext').join
+  end
+end
+
+def windows?
+  RbConfig::CONFIG['host_os'] =~ /mswin|mingw|cygwin/
+end
+
+if windows? and
+   have_library("kernel32") and
    have_header("windows.h") and
    have_header("ruby.h")    and
    have_const('HAVE_RUBY_ENCODING_H')
 then
-    create_makefile("wdm")
+   generate_makefile()
+else
+  generate_dummy_makefile() 
 end

ext/wdm/wdm.c

@@ -32,7 +32,7 @@ rb_encoding *wdm_rb_enc_utf8;
 // ----------------------------------------------------------
 
 void
-Init_wdm()
+Init_wdm_ext()
 {
     WDM_DEBUG("Registering WDM with Ruby!");
 

ext/wdm/wdm.h

@@ -57,6 +57,12 @@ extern VALUE eWDM_Error;
 
 extern rb_encoding *wdm_rb_enc_utf8;
 
+// ---------------------------------------------------------
+// Prototypes
+// ---------------------------------------------------------
+
+void Init_wdm_ext();
+
 // ---------------------------------------------------------
 
 #ifdef __cplusplus

lib/wdm.rb

@@ -0,0 +1,10 @@
+begin
+  require 'wdm_ext'
+rescue LoadError
+  raise LoadError.new(<<-EOS)
+    Can't load WDM!
+    
+    WDM is not supported on your system. For a cross-platform alternative,
+    we recommend using Listen: http://github.com/guard/listen
+  EOS
+end

wdm.gemspec

@@ -7,7 +7,7 @@ Gem::Specification.new do |gem|
   gem.summary       = %q{Windows Directory Monitor (WDM) is a threaded directories monitor for Windows.}
   gem.homepage      = "https://github.com/Maher4Ever/wdm"
 
-  gem.files         = `git ls-files -- ext/*`.split($\) + %w[LICENSE README.md]
+  gem.files         = `git ls-files -- ext/* lib/*`.split($\) + %w[LICENSE README.md]
   gem.extensions    = ['ext/wdm/extconf.rb']
   gem.executables   = gem.files.grep(%r{^bin/}).map{ |f| File.basename(f) }
   gem.test_files    = gem.files.grep(%r{^(test|spec|features)/})