Add methods to get the known/unknown bits from a flags value

WaterWhisperer · WaterWhisperer · commit 2041dc3ceb1e · 2026-02-12T13:15:57.000+08:00
diff --git a/src/traits.rs b/src/traits.rs
@@ -152,9 +152,19 @@ pub trait Flags: Sized + 'static {
         Self::from_bits_retain(truncated)
     }
 
+    /// Get the known bits from a flags value.
+    fn known_bits(&self) -> Self::Bits {
+        self.bits() & Self::all().bits()
+    }
+
+    /// Get the unknown bits from a flags value.
+    fn unknown_bits(&self) -> Self::Bits {
+        self.bits() & !Self::all().bits()
+    }
+
     /// This method will return `true` if any unknown bits are set.
     fn contains_unknown_bits(&self) -> bool {
-        Self::all().bits() & self.bits() != self.bits()
+        self.unknown_bits() != Self::Bits::EMPTY
     }
 
     /// Get the underlying bits value.
diff --git a/tests/compile-fail/bitflags_redefined.stderr b/tests/compile-fail/bitflags_redefined.stderr
@@ -1,19 +1,19 @@
 error[E0428]: the name `Flags1` is defined multiple times
-  --> tests/compile-fail/bitflags_redefined.rs:4:1
+  --> tests/compile-fail/bitflags_redefined.rs:10:1
    |
  4 | / bitflags! {
  5 | |     pub struct Flags1: u32 {
  6 | |         const A = 1;
  7 | |     }
  8 | | }
-   | |_^ `Flags1` redefined here
+   | |_- previous definition of the type `Flags1` here
  9 |
 10 | / bitflags! {
 11 | |     pub struct Flags1: u32 {
 12 | |         const A = 1;
 13 | |     }
 14 | | }
-   | |_- previous definition of the type `Flags1` here
+   | |_^ `Flags1` redefined here
    |
    = note: `Flags1` must be defined only once in the type namespace of this module
    = note: this error originates in the macro `$crate::__declare_public_bitflags` which comes from the expansion of the macro `bitflags` (in Nightly builds, run with -Z macro-backtrace for more info)
diff --git a/tests/compile-fail/unnamed_const.stderr b/tests/compile-fail/unnamed_const.stderr
@@ -3,22 +3,8 @@ error: expected identifier, found reserved identifier `_`
   |
 7 |         const A = Self::_.bits();
   |                         ^ expected identifier, found reserved identifier
-
-error[E0599]: no associated item named `_` found for struct `Unnamed` in the current scope
- --> tests/compile-fail/unnamed_const.rs:7:25
-  |
-3 | / bitflags! {
-4 | |     pub struct Unnamed: u8 {
-5 | |         const _ = 1;
-6 | |
-7 | |         const A = Self::_.bits();
-  | |                         ^ associated item not found in `Unnamed`
-8 | |     }
-9 | | }
-  | |_- associated item `_` not found for this struct
-  |
-help: there is an associated constant `A` with a similar name
   |
-7 -         const A = Self::_.bits();
-7 +         const A = Self::A.bits();
+ ::: src/lib.rs
   |
+  |                 const $Flag:tt = $value:expr;
+  |                                  ----------- while parsing argument for this `expr` macro fragment
