Add 84727

Issue: rust-lang/rust#84727

ices/84727.rs

@@ -0,0 +1,55 @@
+pub struct Color<T>(pub T);
+
+pub struct Cell<Fg, Bg = Fg> {
+    foreground: Color<Fg>,
+    background: Color<Bg>,
+}
+
+pub trait Over<Bottom, Output> {
+    fn over(self, bottom: Bottom) -> Output;
+}
+
+// Cell: Over<Color, Cell>
+impl<C, Fg, Bg, NewFg, NewBg> Over<Color<C>, Cell<NewFg, NewBg>> for Cell<Fg, Bg>
+where
+    Fg: Over<C, NewFg>,
+    Bg: Over<C, NewBg>,
+{
+    fn over(self, _: Color<C>) -> Cell<NewFg, NewBg> {
+        todo!();
+    }
+}
+
+// Cell: Over<Cell, Cell>
+impl<TopFg, TopBg, BottomFg, BottomBg, NewFg, NewBg>
+    Over<Cell<BottomFg, BottomBg>, Cell<NewFg, NewBg>> for Cell<TopFg, TopBg>
+where
+    Self: Over<Color<BottomBg>, Cell<NewFg, NewBg>>,
+{
+    fn over(self, bottom: Cell<BottomFg, BottomBg>) -> Cell<NewFg, NewBg> {
+        self.over(bottom.background);
+        todo!();
+    }
+}
+
+// Cell: Over<&mut Cell, ()>
+impl<'b, TopFg, TopBg, BottomFg, BottomBg> Over<&'b mut Cell<BottomFg, BottomBg>, ()>
+    for Cell<TopFg, TopBg>
+where
+    Cell<TopFg, TopBg>: Over<Cell<BottomFg, BottomBg>, Cell<BottomFg, BottomBg>>,
+{
+    fn over(self, _: &'b mut Cell<BottomFg, BottomBg>) {
+        todo!();
+    }
+}
+
+// &Cell: Over<&mut Cell, ()>
+impl<'t, 'b, TopFg, TopBg, BottomFg, BottomBg> Over<&'b mut Cell<BottomFg, BottomBg>, ()>
+    for &'t Cell<TopFg, TopBg>
+where
+    Cell<TopFg, TopBg>: Over<Cell<BottomFg, BottomBg>, Cell<BottomFg, BottomBg>>,
+{
+    fn over(self, _: &'b mut Cell<BottomFg, BottomBg>) {
+        todo!();
+    }
+}