1 files changed, 92 insertions, 0 deletions
diff --git a/third_party/rust/bitflags/src/tests/difference.rs b/third_party/rust/bitflags/src/tests/difference.rs
new file mode 100644
index 0000000000..6ce9c0bf19
--- /dev/null
+++ b/third_party/rust/bitflags/src/tests/difference.rs
@@ -0,0 +1,92 @@
+use super::*;
+
+use crate::Flags;
+
+#[test]
+fn cases() {
+    case(
+        TestFlags::A | TestFlags::B,
+        &[
+            (TestFlags::A, 1 << 1),
+            (TestFlags::B, 1),
+            (TestFlags::from_bits_retain(1 << 3), 1 | 1 << 1),
+        ],
+        TestFlags::difference,
+    );
+
+    case(
+        TestFlags::from_bits_retain(1 | 1 << 3),
+        &[
+            (TestFlags::A, 1 << 3),
+            (TestFlags::from_bits_retain(1 << 3), 1),
+        ],
+        TestFlags::difference,
+    );
+
+    case(
+        TestExternal::from_bits_retain(!0),
+        &[(TestExternal::A, 0b1111_1110)],
+        TestExternal::difference,
+    );
+
+    assert_eq!(
+        0b1111_1110,
+        (TestExternal::from_bits_retain(!0) & !TestExternal::A).bits()
+    );
+
+    assert_eq!(
+        0b1111_1110,
+        (TestFlags::from_bits_retain(!0).difference(TestFlags::A)).bits()
+    );
+
+    // The `!` operator unsets bits that don't correspond to known flags
+    assert_eq!(
+        1 << 1 | 1 << 2,
+        (TestFlags::from_bits_retain(!0) & !TestFlags::A).bits()
+    );
+}
+
+#[track_caller]
+fn case<T: Flags + std::fmt::Debug + std::ops::Sub<Output = T> + std::ops::SubAssign + Copy>(
+    value: T,
+    inputs: &[(T, T::Bits)],
+    mut inherent: impl FnMut(T, T) -> T,
+) where
+    T::Bits: std::fmt::Debug + PartialEq + Copy,
+{
+    for (input, expected) in inputs {
+        assert_eq!(
+            *expected,
+            inherent(value, *input).bits(),
+            "{:?}.difference({:?})",
+            value,
+            input
+        );
+        assert_eq!(
+            *expected,
+            Flags::difference(value, *input).bits(),
+            "Flags::difference({:?}, {:?})",
+            value,
+            input
+        );
+        assert_eq!(
+            *expected,
+            (value - *input).bits(),
+            "{:?} - {:?}",
+            value,
+            input
+        );
+        assert_eq!(
+            *expected,
+            {
+                let mut value = value;
+                value -= *input;
+                value
+            }
+            .bits(),
+            "{:?} -= {:?}",
+            value,
+            input,
+        );
+    }
+}