Rollup merge of #73634 - nbdd0121:typeck, r=nikomatsakis
Add UI test for issue 73592 It happens that #72280 accidentally fixed a bug which is later discovered in #73592. This PR adds a UI test to prevent future regression. Closes #73592
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src/test/ui/typeck/issue-73592-borrow_mut-through-deref.rs
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src/test/ui/typeck/issue-73592-borrow_mut-through-deref.rs
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// check-pass
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//
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// rust-lang/rust#73592: borrow_mut through Deref should work.
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//
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// Before #72280, when we see something like `&mut *rcvr.method()`, we
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// incorrectly requires `rcvr` to be type-checked as a mut place. While this
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// requirement is usually correct for smart pointers, it is overly restrictive
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// for types like `Mutex` or `RefCell` which can produce a guard that
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// implements `DerefMut` from `&self`.
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//
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// Making it more confusing, because we use Deref as the fallback when DerefMut
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// is implemented, we won't see an issue when the smart pointer does not
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// implement `DerefMut`. It only causes an issue when `rcvr` is obtained via a
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// type that implements both `Deref` or `DerefMut`.
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//
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// This bug is only discovered in #73592 after it is already fixed as a side-effect
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// of a refactoring made in #72280.
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#![warn(unused_mut)]
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use std::pin::Pin;
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use std::cell::RefCell;
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struct S(RefCell<()>);
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fn test_pin(s: Pin<&S>) {
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// This works before #72280.
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let _ = &mut *s.0.borrow_mut();
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}
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fn test_pin_mut(s: Pin<&mut S>) {
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// This should compile but didn't before #72280.
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let _ = &mut *s.0.borrow_mut();
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}
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fn test_vec(s: &Vec<RefCell<()>>) {
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// This should compile but didn't before #72280.
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let _ = &mut *s[0].borrow_mut();
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}
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fn test_mut_pin(mut s: Pin<&S>) {
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//~^ WARN variable does not need to be mutable
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let _ = &mut *s.0.borrow_mut();
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}
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fn test_mut_pin_mut(mut s: Pin<&mut S>) {
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//~^ WARN variable does not need to be mutable
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let _ = &mut *s.0.borrow_mut();
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}
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fn main() {
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let mut s = S(RefCell::new(()));
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test_pin(Pin::new(&s));
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test_pin_mut(Pin::new(&mut s));
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test_mut_pin(Pin::new(&s));
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test_mut_pin_mut(Pin::new(&mut s));
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test_vec(&vec![s.0]);
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}
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warning: variable does not need to be mutable
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--> $DIR/issue-73592-borrow_mut-through-deref.rs:41:17
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LL | fn test_mut_pin(mut s: Pin<&S>) {
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| ----^
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| |
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| help: remove this `mut`
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note: the lint level is defined here
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--> $DIR/issue-73592-borrow_mut-through-deref.rs:19:9
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LL | #![warn(unused_mut)]
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| ^^^^^^^^^^
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warning: variable does not need to be mutable
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--> $DIR/issue-73592-borrow_mut-through-deref.rs:46:21
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LL | fn test_mut_pin_mut(mut s: Pin<&mut S>) {
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| ----^
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| |
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| help: remove this `mut`
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warning: 2 warnings emitted
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