Expose "the" RawBitFlags trait in the public API

Resolves #23.

This is necessary to make blanket implementations possible. We export
a proxy trait, and keep the real thing in the _internal module.
This "prevents" users from relying on the trait items (either by
implementing the trait manually or calling its methods), while still
being able to name the trait in generic bounds.

Author: meithecatte

enumflags/src/fallible.rs

@@ -1,7 +1,7 @@
 use core::convert::TryFrom;
 use core::fmt;
 use super::BitFlags;
-use super::_internal::RawBitFlags;
+use super::RawBitFlags;
 
 // Coherence doesn't let us use a generic type here. Work around by implementing
 // for each integer type manually.

enumflags/src/formatting.rs

@@ -1,5 +1,5 @@
 use core::fmt::{self, Debug, Binary};
-use crate::{BitFlags, _internal::RawBitFlags};
+use crate::{BitFlags, RawBitFlags};
 
 impl<T> fmt::Debug for BitFlags<T>
 where

enumflags/src/lib.rs

@@ -99,6 +99,10 @@ extern crate enumflags2_derive;
 #[doc(hidden)]
 pub use enumflags2_derive::BitFlags_internal as BitFlags;
 
+/// A trait automatically implemented by `derive(BitFlags)` to make the enum
+/// a valid type parameter for `BitFlags<T>`.
+pub trait RawBitFlags: Copy + Clone + 'static + _internal::RawBitFlags {}
+
 /// While the module is public, this is only the case because it needs to be
 /// accessed by the derive macro. Do not use this directly. Stability guarantees
 /// don't apply.
@@ -163,8 +167,6 @@ mod formatting;
 mod fallible;
 pub use fallible::FromBitsError;
 
-use _internal::RawBitFlags;
-
 /// Represents a set of flags of some type `T`.
 /// The type must have the `#[derive(BitFlags)]` attribute applied.
 #[derive(Copy, Clone, Eq, Hash)]
@@ -391,7 +393,7 @@ mod impl_serde {
     extern crate serde;
     use self::serde::{Serialize, Deserialize};
     use self::serde::de::{Error, Unexpected};
-    use super::{BitFlags, _internal::RawBitFlags};
+    use super::{BitFlags, RawBitFlags};
 
     impl<'a, T> Deserialize<'a> for BitFlags<T>
     where

enumflags_derive/src/lib.rs

@@ -241,5 +241,7 @@ fn gen_enumflags(ident: &Ident, item: &DeriveInput, data: &DataEnum)
                     concat!("BitFlags<", stringify!(#ident), ">")
                 }
             }
+
+            impl ::enumflags2::RawBitFlags for #ident {}
     })
 }

test_suite/tests/requires_std.rs

@@ -85,7 +85,7 @@ fn format() {
 
 #[test]
 fn debug_generic() {
-    use enumflags2::{BitFlags, _internal::RawBitFlags};
+    use enumflags2::{BitFlags, RawBitFlags};
 
     #[derive(Debug)]
     struct Debug<T: RawBitFlags>(BitFlags<T>);