[ruby/nkf] Expose NKF::GEM_VERSION

https://github.com/ruby/nkf/commit/0d0fb3a162

ext/nkf/nkf.c

@@ -9,6 +9,7 @@
 
 #define RUBY_NKF_REVISION "$Revision$"
 #define RUBY_NKF_VERSION NKF_VERSION " (" NKF_RELEASE_DATE ")"
+#define NKF_GEM_VERSION "0.1.2"
 
 #include "ruby/ruby.h"
 #include "ruby/encoding.h"
@@ -500,4 +501,6 @@ Init_nkf(void)
     rb_define_const(mNKF, "NKF_VERSION", rb_str_new2(NKF_VERSION));
     /* Release date of nkf */
     rb_define_const(mNKF, "NKF_RELEASE_DATE", rb_str_new2(NKF_RELEASE_DATE));
+    /* Version of nkf library */
+    rb_define_const(mNKF, "GEM_VERSION", rb_str_new_cstr(NKF_GEM_VERSION));
 }

ext/nkf/nkf.gemspec

@@ -1,6 +1,16 @@
+source_version = ["", "ext/nkf/"].find do |dir|
+  begin
+    break File.open(File.join(__dir__, "#{dir}nkf.c")) {|f|
+      f.gets("\n#define NKF_GEM_VERSION ")
+      f.gets[/\s*"(.+)"/, 1]
+    }
+  rescue Errno::ENOENT
+  end
+end
+
 Gem::Specification.new do |spec|
   spec.name          = "nkf"
-  spec.version       = "0.1.2"
+  spec.version       = source_version
   spec.authors       = ["NARUSE Yui"]
   spec.email         = ["naruse@airemix.jp"]