Bitfield enums use #[repr(transparent)] on Rust 1.28+

Fixes rust-lang#1474.

src/codegen/mod.rs

@@ -2573,7 +2573,11 @@ impl CodeGenerator for Enum {
         if variation.is_rust() {
             attrs.push(attributes::repr(repr_name));
         } else if variation.is_bitfield() {
-            attrs.push(attributes::repr("C"));
+            if ctx.options().rust_features.repr_transparent {
+                attrs.push(attributes::repr("transparent"));
+            } else {
+                attrs.push(attributes::repr("C"));
+            }
         }
 
         if let Some(comment) = item.comment(ctx) {

src/features.rs

@@ -100,6 +100,8 @@ macro_rules! rust_target_base {
             => Stable_1_26 => 1.26;
             /// Rust stable 1.27
             => Stable_1_27 => 1.27;
+            /// Rust stable 1.28
+            => Stable_1_28 => 1.28;
             /// Nightly rust
             => Nightly => nightly;
         );
@@ -184,6 +186,10 @@ rust_feature_def!(
         /// `must_use` attribute on functions ([PR](https://github.com/rust-lang/rust/pull/48925))
         => must_use_function;
     }
+    Stable_1_28 {
+        /// repr(transparent) ([PR](https://github.com/rust-lang/rust/pull/51562))
+        => repr_transparent;
+    }
     Nightly {
         /// `thiscall` calling convention ([Tracking issue](https://github.com/rust-lang/rust/issues/42202))
         => thiscall_abi;

tests/expectations/tests/bitfield-enum-basic.rs

@@ -1,6 +1,11 @@
 /* automatically generated by rust-bindgen */
 
-#![allow(dead_code, non_snake_case, non_camel_case_types, non_upper_case_globals)]
+#![allow(
+    dead_code,
+    non_snake_case,
+    non_camel_case_types,
+    non_upper_case_globals
+)]
 
 impl Foo {
     pub const Bar: Foo = Foo(2);

tests/expectations/tests/bitfield-enum-repr-c.rs

@@ -0,0 +1,50 @@
+/* automatically generated by rust-bindgen */
+
+#![allow(
+    dead_code,
+    non_snake_case,
+    non_camel_case_types,
+    non_upper_case_globals
+)]
+
+impl Foo {
+    pub const Bar: Foo = Foo(2);
+}
+impl Foo {
+    pub const Baz: Foo = Foo(4);
+}
+impl Foo {
+    pub const Duplicated: Foo = Foo(4);
+}
+impl Foo {
+    pub const Negative: Foo = Foo(-3);
+}
+impl ::std::ops::BitOr<Foo> for Foo {
+    type Output = Self;
+    #[inline]
+    fn bitor(self, other: Self) -> Self {
+        Foo(self.0 | other.0)
+    }
+}
+impl ::std::ops::BitOrAssign for Foo {
+    #[inline]
+    fn bitor_assign(&mut self, rhs: Foo) {
+        self.0 |= rhs.0;
+    }
+}
+impl ::std::ops::BitAnd<Foo> for Foo {
+    type Output = Self;
+    #[inline]
+    fn bitand(self, other: Self) -> Self {
+        Foo(self.0 & other.0)
+    }
+}
+impl ::std::ops::BitAndAssign for Foo {
+    #[inline]
+    fn bitand_assign(&mut self, rhs: Foo) {
+        self.0 &= rhs.0;
+    }
+}
+#[repr(C)]
+#[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
+pub struct Foo(pub i32);

tests/expectations/tests/bitfield-enum-repr-transparent.rs

@@ -0,0 +1,50 @@
+/* automatically generated by rust-bindgen */
+
+#![allow(
+    dead_code,
+    non_snake_case,
+    non_camel_case_types,
+    non_upper_case_globals
+)]
+
+impl Foo {
+    pub const Bar: Foo = Foo(2);
+}
+impl Foo {
+    pub const Baz: Foo = Foo(4);
+}
+impl Foo {
+    pub const Duplicated: Foo = Foo(4);
+}
+impl Foo {
+    pub const Negative: Foo = Foo(-3);
+}
+impl ::std::ops::BitOr<Foo> for Foo {
+    type Output = Self;
+    #[inline]
+    fn bitor(self, other: Self) -> Self {
+        Foo(self.0 | other.0)
+    }
+}
+impl ::std::ops::BitOrAssign for Foo {
+    #[inline]
+    fn bitor_assign(&mut self, rhs: Foo) {
+        self.0 |= rhs.0;
+    }
+}
+impl ::std::ops::BitAnd<Foo> for Foo {
+    type Output = Self;
+    #[inline]
+    fn bitand(self, other: Self) -> Self {
+        Foo(self.0 & other.0)
+    }
+}
+impl ::std::ops::BitAndAssign for Foo {
+    #[inline]
+    fn bitand_assign(&mut self, rhs: Foo) {
+        self.0 &= rhs.0;
+    }
+}
+#[repr(transparent)]
+#[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
+pub struct Foo(pub i32);

tests/headers/bitfield-enum-repr-c.hpp

@@ -0,0 +1,8 @@
+// bindgen-flags: --bitfield-enum "Foo" --rust-target 1.27  -- -std=c++11
+
+enum Foo {
+  Bar = 1 << 1,
+  Baz = 1 << 2,
+  Duplicated = 1 << 2,
+  Negative = -3,
+};

tests/headers/bitfield-enum-repr-transparent.hpp

@@ -0,0 +1,8 @@
+// bindgen-flags: --bitfield-enum "Foo" --rust-target 1.28  -- -std=c++11
+
+enum Foo {
+  Bar = 1 << 1,
+  Baz = 1 << 2,
+  Duplicated = 1 << 2,
+  Negative = -3,
+};