Raise error with proper message

Add comments explaining each condition.

1 files changed, 17 insertions, 9 deletions

diff --git a/lib/rake/javaextensiontask.rb b/lib/rake/javaextensiontask.rb
index 916de53..592da3a 100644
--- a/lib/rake/javaextensiontask.rb
+++ b/lib/rake/javaextensiontask.rb
@@ -213,25 +213,33 @@ execute the Rake compilation task using the JRuby interpreter.
         end
       end
 
+      # jruby_cpath might not be present from Java-9 onwards as it removes
+      # sun.boot.class.path. Check if JRUBY_HOME is set as env variable and try
+      # to find jruby.jar under JRUBY_HOME
+      unless jruby_cpath
+        jruby_home = ENV['JRUBY_HOME']
+        if jruby_home
+          candidate = File.join(jruby_home, 'lib', 'jruby.jar')
+          jruby_cpath = candidate if File.exist? candidate
+        end
+      end
+
+      # JRUBY_HOME is not necessarily set in JRuby-9.x
+      # Find the libdir from RbConfig::CONFIG and find jruby.jar under the
+      # found lib path
       unless jruby_cpath
         libdir = RbConfig::CONFIG['libdir']
-        if libdir.start_with? "classpath:"
-          raise 'Cannot build with jruby-complete'
+        if libdir.start_with? "uri:classloader:"
+          raise 'Cannot build with jruby-complete from Java 9 onwards'
         end
         candidate = File.join(libdir, "jruby.jar")
         jruby_cpath = candidate if File.exist? candidate
       end
 
       unless jruby_cpath
-        jruby_home = ENV['JRUBY_HOME']
-        if jruby_home
-          candidate = File.join(jruby_home, 'lib', 'jruby.jar')
-          jruby_cpath = candidate if File.exist? candidate
-        end
+        raise "Could not find jruby.jar. Please set JRUBY_HOME or Use jruby in rvm"
       end
 
-      raise "jruby.jar path not found" unless jruby_cpath
-
       jruby_cpath += File::PATH_SEPARATOR + args.join(File::PATH_SEPARATOR) unless args.empty?
       jruby_cpath ? "-cp \"#{jruby_cpath}\"" : ""
     end