rust: types: Add declare_flags_type()

Add a helper macro that can be used to declare bitfield style types.

Signed-off-by: Asahi Lina <lina@asahilina.net>

Author: hoshinolina

rust/kernel/types.rs

@@ -635,3 +635,86 @@ pub struct False;
 
 // SAFETY: This is one of the only two implementations of `Bool`.
 unsafe impl Bool for False {}
+
+/// Helper macro to declare a bitfield style type. The type will automatically
+/// gain boolean operator implementations, as well as the `as_raw()` and `contains()`
+/// methods, Debug, Copy, Clone, and PartialEq implementations.
+///
+/// Optionally, a default value can be specified with `= value` syntax, which
+/// will add a Default trait implementation.
+///
+/// # Examples
+///
+/// ```
+/// declare_flags_type! {
+///     /// Flags to be used for foo.
+///     pub struct FooFlags(u32);
+/// }
+///
+/// declare_flags_type! {
+///     /// Flags to be used for bar.
+///     pub struct BarFlags(u32) = 0;
+/// }
+/// ```
+macro_rules! declare_flags_type (
+    (
+        $(#[$outer:meta])*
+        $v:vis struct $t:ident ( $base:ty );
+        $($rest:tt)*
+    ) => {
+        $(#[$outer])*
+        #[derive(Debug, Clone, Copy, PartialEq)]
+        $v struct $t($base);
+
+        impl $t {
+            /// Get the raw representation of this flag.
+            pub(crate) fn as_raw(self) -> $base {
+                self.0
+            }
+
+            /// Check whether `flags` is contained in `self`.
+            pub fn contains(self, flags: Self) -> bool {
+                (self & flags) == flags
+            }
+        }
+
+        impl core::ops::BitOr for $t {
+            type Output = Self;
+            fn bitor(self, rhs: Self) -> Self::Output {
+                Self(self.0 | rhs.0)
+            }
+        }
+
+        impl core::ops::BitAnd for $t {
+            type Output = Self;
+            fn bitand(self, rhs: Self) -> Self::Output {
+                Self(self.0 & rhs.0)
+            }
+        }
+
+        impl core::ops::Not for $t {
+            type Output = Self;
+            fn not(self) -> Self::Output {
+                Self(!self.0)
+            }
+        }
+    };
+    (
+        $(#[$outer:meta])*
+        $v:vis struct $t:ident ( $base:ty ) = $default:expr;
+        $($rest:tt)*
+    ) => {
+        declare_flags_type! {
+            $(#[$outer])*
+            $v struct $t ($base);
+            $($rest)*
+        }
+        impl Default for $t {
+            fn default() -> Self {
+                Self($default)
+            }
+        }
+    };
+);
+
+pub(crate) use declare_flags_type;