Fix numeric array save options being dropped in :memory and stream writes

lib/image.ex

@@ -917,6 +917,12 @@ defmodule Image do
     "[" <> Enum.map_join(options, ",", &loader_option/1) <> "]"
   end
 
+  # Numeric arrays (e.g. `background=0 128 0`) are space separated in a
+  # filename suffix string.
+  defp loader_option({key, [number | _rest] = value}) when is_number(number) do
+    "#{key}=" <> Enum.map_join(value, " ", &to_string/1)
+  end
+
   # Flag-valued options are passed to libvips as a list of flag atoms.
   # In a filename suffix string flags are written by name joined with `:`,
   # e.g. `keep=VIPS_FOREIGN_KEEP_EXIF:VIPS_FOREIGN_KEEP_XMP`.

test/image_write_background_test.exs

@@ -54,5 +54,25 @@ defmodule Image.Write.Background.Test do
 
       assert message =~ "Invalid background color :not_a_real_color"
     end
+
+    test "the background survives a :memory write", %{rgba: rgba} do
+      # Regression: the suffix option string joined numeric arrays with ":"
+      # (".jpg[background=0:128:0]"), which libvips silently drops. Arrays
+      # must be space separated.
+      {:ok, binary} = Image.write(rgba, :memory, suffix: ".jpg", background: :green)
+      pixel = Image.get_pixel!(Image.open!(binary), 4, 4)
+
+      assert close_to?(pixel, [0, 128, 0])
+    end
+
+    test "the background survives a stream write", %{rgba: rgba, tmp_dir: tmp_dir} do
+      path = Temp.path!(suffix: ".jpg", basedir: tmp_dir)
+      stream = File.stream!(path, 2048)
+
+      {:ok, _} = Image.write(rgba, stream, background: :green)
+      pixel = Image.get_pixel!(Image.open!(path), 4, 4)
+
+      assert close_to?(pixel, [0, 128, 0])
+    end
   end
 end