Treat NSTextInputClient ranges as UTF-16

crates/text/src/offset_utf16.rs

@@ -0,0 +1,50 @@
+use std::ops::{Add, AddAssign, Sub};
+
+#[derive(Copy, Clone, Debug, Default, Eq, PartialEq, Ord, PartialOrd)]
+pub struct OffsetUtf16(pub usize);
+
+impl<'a> Add<&'a Self> for OffsetUtf16 {
+    type Output = Self;
+
+    fn add(self, other: &'a Self) -> Self::Output {
+        Self(self.0 + other.0)
+    }
+}
+
+impl Add for OffsetUtf16 {
+    type Output = Self;
+
+    fn add(self, other: Self) -> Self::Output {
+        Self(self.0 + other.0)
+    }
+}
+
+impl<'a> Sub<&'a Self> for OffsetUtf16 {
+    type Output = Self;
+
+    fn sub(self, other: &'a Self) -> Self::Output {
+        debug_assert!(*other <= self);
+        Self(self.0 - other.0)
+    }
+}
+
+impl Sub for OffsetUtf16 {
+    type Output = OffsetUtf16;
+
+    fn sub(self, other: Self) -> Self::Output {
+        debug_assert!(other <= self);
+        Self(self.0 - other.0)
+    }
+}
+
+impl<'a> AddAssign<&'a Self> for OffsetUtf16 {
+    fn add_assign(&mut self, other: &'a Self) {
+        self.0 += other.0;
+    }
+}
+
+impl AddAssign<Self> for OffsetUtf16 {
+    fn add_assign(&mut self, other: Self) {
+        self.0 += other.0;
+    }
+}