fixes C file translation

lib/zig/_c.ex

@@ -25,55 +25,60 @@ defmodule Zig.C do
 
   @type src_opts :: term
 
-  def new(opts, module_file) do
+  def new(opts, module_opts) do
+    module_dir = cond do
+      dir = module_opts[:dir] -> dir
+      file = module_opts[:file] -> Path.dirname(file)
+    end
+
     struct!(__MODULE__,
-      include_dirs: normalize_filelist(opts, :include_dirs, module_file),
-      link_lib: normalize_filelist(opts, :link_lib, module_file),
+      include_dirs: normalize_filelist(opts, :include_dirs, module_dir),
+      link_lib: normalize_filelist(opts, :link_lib, module_dir),
       link_libcpp: Keyword.get(opts, :link_libcpp, false),
-      src: normalized_srclist(opts, module_file)
+      src: normalized_srclist(opts, module_dir)
     )
   end
 
-  defp normalize_filelist(opts, key, module_file) do
+  defp normalize_filelist(opts, key, module_dir) do
     opts
     |> Keyword.get(key)
     |> List.wrap()
-    |> Enum.map(&solve_relative(&1, module_file))
+    |> Enum.map(&solve_relative(&1, module_dir))
   end
 
-  defp normalized_srclist(opts, module_file) do
+  defp normalized_srclist(opts, module_dir) do
     opts
     |> Keyword.get(:src)
     |> List.wrap()
-    |> Enum.flat_map(&normalize_src(&1, module_file))
+    |> Enum.flat_map(&normalize_src(&1, module_dir))
   end
 
   defp solve_relative({:system, _} = system, _), do: system
 
-  defp solve_relative(file, module_file) do
-    Path.expand(file, module_file)
+  defp solve_relative(file, module_dir) do
+    Path.expand(file, module_dir)
   end
 
-  defp normalize_src(file, module_file) when is_binary(file) do
-    maybe_with_wildcard(file, module_file, [])
+  defp normalize_src(file, module_dir) when is_binary(file) do
+    maybe_with_wildcard(file, module_dir, [])
   end
 
-  defp normalize_src({file, opts}, module_file) do
-    maybe_with_wildcard(file, module_file, opts)
+  defp normalize_src({file, opts}, module_dir) do
+    maybe_with_wildcard(file, module_dir, opts)
   end
 
-  defp maybe_with_wildcard(file, module_file, opts) do
+  defp maybe_with_wildcard(file, module_dir, opts) do
     if String.ends_with?(file, "/*") do
       file
-      |> solve_relative(module_file)
       |> Path.dirname()
+      |> solve_relative(module_dir)
       |> then(fn wildcard_dir ->
         wildcard_dir
         |> File.ls!()
         |> Enum.map(&{Path.join(wildcard_dir, &1), opts})
       end)
     else
-      [{solve_relative(file, module_file), opts}]
+      [{solve_relative(file, module_dir), opts}]
     end
   end
 end

lib/zig/_module.ex

@@ -124,7 +124,7 @@ defmodule Zig.Module do
   defp normalize_options(opts) do
     opts
     |> obtain_version
-    |> Keyword.update(:c, %C{}, &C.new(&1, Keyword.fetch!(opts, :file)))
+    |> Keyword.update(:c, %C{}, &C.new(&1, opts))
     |> Keyword.update(:callbacks, [], &normalize_callbacks(&1, opts))
   end