Remove surplus newlines (fixes #59)

lib/xml_builder.ex

@@ -257,8 +257,7 @@ defmodule XmlBuilder do
     do: format({nil, nil, string}, level, options)
 
   defp format(list, level, options) when is_list(list) do
-    formatter = formatter(options)
-    map_intersperse(list, formatter.line_break(), &format(&1, level, options))
+    format_children(list, level, options)
   end
 
   defp format({nil, nil, name}, level, options) when is_bitstring(name),
@@ -339,6 +338,25 @@ defmodule XmlBuilder do
     ]
   end
 
+  defp format_children(list, level, options) when is_list(list) do
+    line_break = formatter(options).line_break()
+
+    {result, _} =
+      Enum.flat_map_reduce(list, 0, fn
+        element, count when is_blank_list(element) ->
+          {[], count}
+
+        element, count ->
+          if line_break == "" or count == 0 do
+            {[format(element, level, options)], count + 1}
+          else
+            {[line_break, format(element, level, options)], count + 1}
+          end
+      end)
+
+    result
+  end
+
   defp elements_with_prolog([first | rest]) when length(rest) > 0,
     do: [first_element(first) | element(rest)]
 
@@ -360,7 +378,7 @@ defmodule XmlBuilder do
 
   defp format_content(children, level, options) when is_list(children) do
     format_char = formatter(options).line_break()
-    [format_char, map_intersperse(children, format_char, &format(&1, level, options))]
+    [format_char, format_children(children, level, options)]
   end
 
   defp format_content(content, _level, _options),

test/xml_builder_test.exs

@@ -320,6 +320,12 @@ defmodule XmlBuilderTest do
     assert warning =~ "doc/1 is deprecated. Use document/1 with generate/1 instead."
   end
 
+  test "removal of empty child elements" do
+    assert {:person, nil, [nil, {:first, nil, "Josh"}, [], {:last, nil, "Nussbaum"}]}
+           |> XmlBuilder.generate() ==
+             ~s|<person>\n  <first>Josh</first>\n  <last>Nussbaum</last>\n</person>|
+  end
+
   def element(name, arg),
     do: XmlBuilder.element(name, arg) |> XmlBuilder.generate()