ffi_backend: convert numeric function args to pointers (#162)

This allows for passing integers as pointer arguments to functions when
using the FFI backend. This is a workaround until we can get JRuby's FFI
implementation to allow for it directly (see also
jruby/jruby#8423)

---------

Co-authored-by: Benoit Daloze <eregontp@gmail.com>

lib/fiddle/ffi_backend.rb

@@ -159,15 +159,16 @@ def call(*args, &block)
           args[i] = Fiddle::FFIBackend.to_ffi_type(args[i])
         end
       else
-        args.map! do |arg|
-          if arg.respond_to?(:to_ptr)
-            begin
-              arg = arg.to_ptr
-            end until arg.is_a?(FFI::Pointer) || !arg.respond_to?(:to_ptr)
-            arg
-          else
-            arg
-          end
+        @args.each_with_index do |arg_type, i|
+          next unless arg_type == Types::VOIDP
+
+          src = args[i]
+          next if src.nil?
+          next if src.is_a?(String)
+          next if src.is_a?(FFI::AbstractMemory)
+          next if src.is_a?(FFI::Struct)
+
+          args[i] = Pointer[src]
         end
       end
       result = @function.call(*args, &block)
@@ -316,6 +317,8 @@ def initialize(addr, size = nil, free = nil)
               end
             elsif addr.is_a?(IO)
               raise NotImplementedError, "IO ptr isn't supported"
+            else
+              FFI::Pointer.new(Integer(addr))
             end
 
       @size = size ? size : ptr.size

test/fiddle/test_function.rb

@@ -98,6 +98,15 @@ def test_call
       assert_in_delta 1.0, func.call(90 * Math::PI / 180), 0.0001
     end
 
+    def test_integer_pointer_conversion
+      func = Function.new(@libc['memcpy'], [TYPE_VOIDP, TYPE_VOIDP, TYPE_SIZE_T], TYPE_VOIDP)
+      str = 'hello'
+      Pointer.malloc(str.bytesize, Fiddle::RUBY_FREE) do |dst|
+        func.call(dst.to_i, str, dst.size)
+        assert_equal(str, dst.to_str)
+      end
+    end
+
     def test_argument_count
       closure_class = Class.new(Closure) do
         def call one

test/fiddle/test_pointer.rb

@@ -157,11 +157,17 @@ def test_to_ptr_with_ptr
       end
     end
 
-    def test_to_ptr_with_num
+    def test_to_ptr_with_int
       ptr = Pointer.new 0
       assert_equal ptr, Pointer[0]
     end
 
+    MimicInteger = Struct.new(:to_int)
+    def test_to_ptr_with_to_int
+      ptr = Pointer.new 0
+      assert_equal ptr, Pointer[MimicInteger.new(0)]
+    end
+
     def test_equals
       ptr   = Pointer.new 0
       ptr2  = Pointer.new 0