const fn: union, intersect

Author: meithecatte

src/lib.rs

@@ -365,6 +365,36 @@ impl<T: BitFlag> From<T> for BitFlags<T> {
     }
 }
 
+for_each_uint! { ty =>
+    impl<T> BitFlags<T, $ty> {
+        /// Bitwise OR — return value contains flag if either argument does.
+        ///
+        /// Also available as `a | b`, but operator overloads are not usable
+        /// in `const fn`s at the moment.
+        #[must_use]
+        #[inline(always)]
+        pub const fn union(self, other: Self) -> Self {
+            BitFlags {
+                val: self.val | other.val,
+                marker: PhantomData,
+            }
+        }
+
+        /// Bitwise AND — return value contains flag if both arguments do.
+        ///
+        /// Also available as `a & b`, but operator overloads are not usable
+        /// in `const fn`s at the moment.
+        #[must_use]
+        #[inline(always)]
+        pub const fn intersection(self, other: Self) -> Self {
+            BitFlags {
+                val: self.val & other.val,
+                marker: PhantomData,
+            }
+        }
+    }
+}
+
 impl<T> BitFlags<T>
 where
     T: BitFlag,

test_suite/Cargo.toml

@@ -13,6 +13,7 @@ features = ["derive"]
 
 [dev-dependencies]
 trybuild = "1.0"
+glob = "0.3"
 
 [[test]]
 name = "ui-tests"

test_suite/ui/must_use_warning.rs

@@ -0,0 +1,17 @@
+use enumflags2::{bitflags, BitFlags};
+
+#[bitflags]
+#[repr(u8)]
+#[derive(Clone, Copy, Debug)]
+enum Flag {
+    Foo = 1 << 0,
+    Bar = 1 << 1,
+}
+
+fn main() {
+    let mut thing: BitFlags<Flag> = Flag::Foo.into();
+    let _ = thing;
+    // let's pretend the unused_mut warning doesn't trigger
+    thing = Flag::Bar.into();
+    thing.union(Flag::Foo.into());
+}

test_suite/ui/must_use_warning.stderr

@@ -0,0 +1,16 @@
+warning: unused import: `BitFlags`
+ --> $DIR/must_use_warning.rs:1:28
+  |
+1 | use enumflags2::{bitflags, BitFlags};
+  |                            ^^^^^^^^
+  |
+  = note: `#[warn(unused_imports)]` on by default
+
+error[E0599]: no method named `union` found for enum `Flag` in the current scope
+  --> $DIR/must_use_warning.rs:13:11
+   |
+6  | enum Flag {
+   | --------- method `union` not found for this
+...
+13 |     thing.union(Flag::Bar.into());
+   |           ^^^^^ method not found in `Flag`

test_suite/ui_tests.rs

@@ -1,5 +1,14 @@
+use glob::glob;
+use std::os::unix::ffi::OsStrExt;
+
 #[test]
 fn ui() {
     let t = trybuild::TestCases::new();
-    t.compile_fail("ui/*.rs");
+    for test in glob("ui/*.rs").unwrap() {
+        let path = test.unwrap();
+        match path.as_os_str().as_bytes() {
+            b"ui/must_use_warning.rs" => t.pass(path),
+            _ => t.compile_fail(path),
+        }
+    }
 }