Stub out extension build on JRuby

Gemfile

@@ -3,7 +3,7 @@ source 'https://rubygems.org'
 gemspec
 
 gem "benchmark_driver"
-gem "fiddle"
+gem "fiddle", platform: :ruby
 gem "rake", ">= 12.3.3"
 gem "rake-compiler", ">= 0.9"
 gem "minitest", "< 5.0.0"

Rakefile

@@ -6,7 +6,12 @@ require "rake/extensiontask"
 require "rake/testtask"
 
 spec = eval(File.read('bigdecimal.gemspec'))
-Rake::ExtensionTask.new('bigdecimal', spec)
+if RUBY_ENGINE == 'jruby'
+  # JRuby's extension is included with JRuby currently
+  task :compile do; end
+else
+  Rake::ExtensionTask.new('bigdecimal', spec)
+end
 
 Rake::TestTask.new do |t|
   t.libs << 'test/lib'

bigdecimal.gemspec

@@ -12,17 +12,8 @@ Gem::Specification.new do |s|
   s.licenses       = ["Ruby", "bsd-2-clause"]
 
   s.require_paths = %w[lib]
-  s.extensions    = %w[ext/bigdecimal/extconf.rb]
   s.files         = %w[
     bigdecimal.gemspec
-    ext/bigdecimal/bigdecimal.c
-    ext/bigdecimal/bigdecimal.h
-    ext/bigdecimal/bits.h
-    ext/bigdecimal/feature.h
-    ext/bigdecimal/missing.c
-    ext/bigdecimal/missing.h
-    ext/bigdecimal/missing/dtoa.c
-    ext/bigdecimal/static_assert.h
     lib/bigdecimal.rb
     lib/bigdecimal/jacobian.rb
     lib/bigdecimal/ludcmp.rb
@@ -33,6 +24,21 @@ Gem::Specification.new do |s|
     sample/nlsolve.rb
     sample/pi.rb
   ]
+  if Gem::Platform === s.platform and s.platform =~ 'java' or RUBY_ENGINE == 'jruby'
+    s.platform      = 'java'
+  else
+    s.extensions    = %w[ext/bigdecimal/extconf.rb]
+    s.files += %w[
+      ext/bigdecimal/bigdecimal.c
+      ext/bigdecimal/bigdecimal.h
+      ext/bigdecimal/bits.h
+      ext/bigdecimal/feature.h
+      ext/bigdecimal/missing.c
+      ext/bigdecimal/missing.h
+      ext/bigdecimal/missing/dtoa.c
+      ext/bigdecimal/static_assert.h
+    ]
+  end
 
   s.required_ruby_version = Gem::Requirement.new(">= 2.5.0")
 end

lib/bigdecimal.rb

@@ -1 +1,5 @@
-require 'bigdecimal.so'
+if RUBY_ENGINE == 'jruby'
+  JRuby::Util.load_ext("org.jruby.ext.bigdecimal.BigDecimalLibrary")
+else
+  require 'bigdecimal.so'
+end