If you have a C file like:

// enum.c
enum Foo {
    FOO_0,
    FOO_1,
    FOO_2,
};

which you convert to a .di file, it will contain (macro enums removed for brevity):

extern (C)
{
	enum Foo
	{
		FOO_0,
		FOO_1,
		FOO_2,
	}
}

Which is an incorrect translation. The imported C file will allow you to access the members of Foo without name spacing, like `FOO_0`, while the .di file will require you to write `Foo.FOO_0`. The enum members should be aliased into the module scope so that both imports function the same way. That is important as you might generate a .di file so your editor auto-complete works, but you want to compile with the actual .c file in case the code you are compiling against changes.