tests/ui/let-else/let-else-deref-coercion.rs

   1 // Taken from https://github.com/rust-lang/rust/blob/6cc0a764e082d9c0abcf37a768d5889247ba13e2/compiler/rustc_typeck/src/check/_match.rs#L445-L462
   2 //
   3 // We attempt to `let Bar::Present(_) = foo else { ... }` where foo is meant to Deref/DerefMut to
   4 // Bar. This fails, you must add a type annotation like `let _: &mut Bar = _ else { ... }`
   5
   6
   7 use std::ops::{Deref, DerefMut};
   8
   9 struct Foo(Bar);
  10
  11 enum Bar {
  12     Present(u32),
  13     Absent,
  14 }
  15 impl Deref for Foo {
  16     type Target = Bar;
  17     fn deref(&self) -> &Bar {
  18         &self.0
  19     }
  20 }
  21 impl DerefMut for Foo {
  22     fn deref_mut(&mut self) -> &mut Bar {
  23         &mut self.0
  24     }
  25 }
  26 impl Bar {
  27     fn bar(&self) -> Option<u32> {
  28         let Bar::Present(z): &Bar = self else {
  29             return None;
  30         };
  31         return Some(*z);
  32     }
  33 }
  34 impl Foo {
  35     // Try without the type annotation
  36     fn set_bar_unannotated(&mut self, value: u32) {
  37         let Bar::Present(z) = self else { //~ ERROR mismatched types
  38             return;
  39         };
  40         *z = value;
  41     }
  42 }
  43
  44 fn main() {
  45     let mut foo = Foo(Bar::Present(1));
  46     foo.set_bar_unannotated(54);
  47     assert_eq!(foo.bar(), Some(54));
  48     irrefutable::inner();
  49 }
  50
  51 // The original, to show it fails for irrefutable let decls
  52 mod irrefutable {
  53     use std::ops::{Deref, DerefMut};
  54     struct Foo(Bar);
  55     struct Bar(u32);
  56     impl Deref for Foo {
  57         type Target = Bar;
  58         fn deref(&self) -> &Bar {
  59             &self.0
  60         }
  61     }
  62     impl DerefMut for Foo {
  63         fn deref_mut(&mut self) -> &mut Bar {
  64             &mut self.0
  65         }
  66     }
  67     fn foo(x: &mut Foo) {
  68         let Bar(z) = x; //~ ERROR mismatched types
  69         *z = 54;
  70         assert_eq!((x.0).0, 54);
  71     }
  72     pub fn inner() {
  73         foo(&mut Foo(Bar(1)));
  74     }
  75 }