Rollup merge of #73534 - estebank:borrowck-suggestions, r=matthewjasper

Provide suggestions for some moved value errors

When encountering an used moved value where the previous move happened
in a `match` or `if let` pattern, suggest using `ref`. Fix #63988.

When encountering a `&mut` value that is used in multiple iterations of
a loop, suggest reborrowing it with `&mut *`. Fix #62112.

src/test/ui/borrowck/issue-41962.stderr

@@ -5,6 +5,10 @@ LL |         if let Some(thing) = maybe {
    |                     ^^^^^ value moved here, in previous iteration of loop
    |
    = note: move occurs because value has type `std::vec::Vec<bool>`, which does not implement the `Copy` trait
+help: borrow this field in the pattern to avoid moving `maybe.0`
+   |
+LL |         if let Some(ref thing) = maybe {
+   |                     ^^^
 
 error: aborting due to previous error
 

src/test/ui/borrowck/move-in-pattern-mut.rs

@@ -0,0 +1,23 @@
+// Issue #63988
+#[derive(Debug)]
+struct S;
+fn foo(_: Option<S>) {}
+
+enum E {
+    V {
+        s: S,
+    }
+}
+fn bar(_: E) {}
+
+fn main() {
+    let s = Some(S);
+    if let Some(mut x) = s {
+        x = S;
+    }
+    foo(s); //~ ERROR use of moved value: `s`
+    let mut e = E::V { s: S };
+    let E::V { s: mut x } = e;
+    x = S;
+    bar(e); //~ ERROR use of moved value: `e`
+}

src/test/ui/borrowck/move-in-pattern-mut.stderr

@@ -0,0 +1,33 @@
+error[E0382]: use of moved value: `s`
+  --> $DIR/move-in-pattern-mut.rs:18:9
+   |
+LL |     if let Some(mut x) = s {
+   |                 ----- value moved here
+...
+LL |     foo(s);
+   |         ^ value used here after partial move
+   |
+   = note: move occurs because value has type `S`, which does not implement the `Copy` trait
+help: borrow this field in the pattern to avoid moving `s.0`
+   |
+LL |     if let Some(ref mut x) = s {
+   |                 ^^^
+
+error[E0382]: use of moved value: `e`
+  --> $DIR/move-in-pattern-mut.rs:22:9
+   |
+LL |     let E::V { s: mut x } = e;
+   |                   ----- value moved here
+LL |     x = S;
+LL |     bar(e);
+   |         ^ value used here after partial move
+   |
+   = note: move occurs because value has type `S`, which does not implement the `Copy` trait
+help: borrow this field in the pattern to avoid moving `e.s`
+   |
+LL |     let E::V { s: ref mut x } = e;
+   |                   ^^^
+
+error: aborting due to 2 previous errors
+
+For more information about this error, try `rustc --explain E0382`.

src/test/ui/borrowck/move-in-pattern.fixed

@@ -0,0 +1,24 @@
+// run-rustfix
+// Issue #63988
+#[derive(Debug)]
+struct S;
+fn foo(_: Option<S>) {}
+
+enum E {
+    V {
+        s: S,
+    }
+}
+fn bar(_: E) {}
+
+fn main() {
+    let s = Some(S);
+    if let Some(ref x) = s {
+        let _ = x;
+    }
+    foo(s); //~ ERROR use of moved value: `s`
+    let e = E::V { s: S };
+    let E::V { s: ref x } = e;
+    let _ = x;
+    bar(e); //~ ERROR use of moved value: `e`
+}

src/test/ui/borrowck/move-in-pattern.rs

@@ -0,0 +1,24 @@
+// run-rustfix
+// Issue #63988
+#[derive(Debug)]
+struct S;
+fn foo(_: Option<S>) {}
+
+enum E {
+    V {
+        s: S,
+    }
+}
+fn bar(_: E) {}
+
+fn main() {
+    let s = Some(S);
+    if let Some(x) = s {
+        let _ = x;
+    }
+    foo(s); //~ ERROR use of moved value: `s`
+    let e = E::V { s: S };
+    let E::V { s: x } = e;
+    let _ = x;
+    bar(e); //~ ERROR use of moved value: `e`
+}

src/test/ui/borrowck/move-in-pattern.stderr

@@ -0,0 +1,33 @@
+error[E0382]: use of moved value: `s`
+  --> $DIR/move-in-pattern.rs:19:9
+   |
+LL |     if let Some(x) = s {
+   |                 - value moved here
+...
+LL |     foo(s);
+   |         ^ value used here after partial move
+   |
+   = note: move occurs because value has type `S`, which does not implement the `Copy` trait
+help: borrow this field in the pattern to avoid moving `s.0`
+   |
+LL |     if let Some(ref x) = s {
+   |                 ^^^
+
+error[E0382]: use of moved value: `e`
+  --> $DIR/move-in-pattern.rs:23:9
+   |
+LL |     let E::V { s: x } = e;
+   |                   - value moved here
+LL |     let _ = x;
+LL |     bar(e);
+   |         ^ value used here after partial move
+   |
+   = note: move occurs because value has type `S`, which does not implement the `Copy` trait
+help: borrow this field in the pattern to avoid moving `e.s`
+   |
+LL |     let E::V { s: ref x } = e;
+   |                   ^^^
+
+error: aborting due to 2 previous errors
+
+For more information about this error, try `rustc --explain E0382`.

src/test/ui/borrowck/mut-borrow-in-loop-2.fixed

@@ -0,0 +1,35 @@
+// run-rustfix
+#![allow(dead_code)]
+
+struct Events<R>(R);
+
+struct Other;
+
+pub trait Trait<T> {
+    fn handle(value: T) -> Self;
+}
+
+// Blanket impl. (If you comment this out, compiler figures out that it
+// is passing an `&mut` to a method that must be expecting an `&mut`,
+// and injects an auto-reborrow.)
+impl<T, U> Trait<U> for T where T: From<U> {
+    fn handle(_: U) -> Self { unimplemented!() }
+}
+
+impl<'a, R> Trait<&'a mut Events<R>> for Other {
+    fn handle(_: &'a mut Events<R>) -> Self { unimplemented!() }
+}
+
+fn this_compiles<'a, R>(value: &'a mut Events<R>) {
+    for _ in 0..3 {
+        Other::handle(&mut *value);
+    }
+}
+
+fn this_does_not<'a, R>(value: &'a mut Events<R>) {
+    for _ in 0..3 {
+        Other::handle(&mut *value); //~ ERROR use of moved value: `value`
+    }
+}
+
+fn main() {}

src/test/ui/borrowck/mut-borrow-in-loop-2.rs

@@ -0,0 +1,35 @@
+// run-rustfix
+#![allow(dead_code)]
+
+struct Events<R>(R);
+
+struct Other;
+
+pub trait Trait<T> {
+    fn handle(value: T) -> Self;
+}
+
+// Blanket impl. (If you comment this out, compiler figures out that it
+// is passing an `&mut` to a method that must be expecting an `&mut`,
+// and injects an auto-reborrow.)
+impl<T, U> Trait<U> for T where T: From<U> {
+    fn handle(_: U) -> Self { unimplemented!() }
+}
+
+impl<'a, R> Trait<&'a mut Events<R>> for Other {
+    fn handle(_: &'a mut Events<R>) -> Self { unimplemented!() }
+}
+
+fn this_compiles<'a, R>(value: &'a mut Events<R>) {
+    for _ in 0..3 {
+        Other::handle(&mut *value);
+    }
+}
+
+fn this_does_not<'a, R>(value: &'a mut Events<R>) {
+    for _ in 0..3 {
+        Other::handle(value); //~ ERROR use of moved value: `value`
+    }
+}
+
+fn main() {}

src/test/ui/borrowck/mut-borrow-in-loop-2.stderr

@@ -0,0 +1,17 @@
+error[E0382]: use of moved value: `value`
+  --> $DIR/mut-borrow-in-loop-2.rs:31:23
+   |
+LL | fn this_does_not<'a, R>(value: &'a mut Events<R>) {
+   |                         ----- move occurs because `value` has type `&mut Events<R>`, which does not implement the `Copy` trait
+LL |     for _ in 0..3 {
+LL |         Other::handle(value);
+   |                       ^^^^^ value moved here, in previous iteration of loop
+   |
+help: consider creating a fresh reborrow of `value` here
+   |
+LL |         Other::handle(&mut *value);
+   |                       ^^^^^^
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0382`.

src/test/ui/moves/moves-based-on-type-cyclic-types-issue-4821.stderr

@@ -8,6 +8,10 @@ LL |     consume(node) + r
    |             ^^^^ value used here after partial move
    |
    = note: move occurs because value has type `std::boxed::Box<List>`, which does not implement the `Copy` trait
+help: borrow this field in the pattern to avoid moving `node.next.0`
+   |
+LL |         Some(ref right) => consume(right),
+   |              ^^^
 
 error: aborting due to previous error
 

src/test/ui/nll/issue-53807.stderr

@@ -5,6 +5,10 @@ LL |         if let Some(thing) = maybe {
    |                     ^^^^^ value moved here, in previous iteration of loop
    |
    = note: move occurs because value has type `std::vec::Vec<bool>`, which does not implement the `Copy` trait
+help: borrow this field in the pattern to avoid moving `maybe.0`
+   |
+LL |         if let Some(ref thing) = maybe {
+   |                     ^^^
 
 error: aborting due to previous error
 

src/test/ui/pattern/bindings-after-at/bind-by-move-neither-can-live-while-the-other-survives-1.stderr

@@ -46,6 +46,10 @@ LL |         Some(_z @ ref _y) => {}
    |              value moved here
    |
    = note: move occurs because value has type `X`, which does not implement the `Copy` trait
+help: borrow this field in the pattern to avoid moving `x.0`
+   |
+LL |         Some(ref _z @ ref _y) => {}
+   |              ^^^
 
 error[E0382]: borrow of moved value
   --> $DIR/bind-by-move-neither-can-live-while-the-other-survives-1.rs:35:19
@@ -57,6 +61,10 @@ LL |         Some(_z @ ref mut _y) => {}
    |              value moved here
    |
    = note: move occurs because value has type `X`, which does not implement the `Copy` trait
+help: borrow this field in the pattern to avoid moving `x.0`
+   |
+LL |         Some(ref _z @ ref mut _y) => {}
+   |              ^^^
 
 error: aborting due to 6 previous errors
 

src/test/ui/pattern/bindings-after-at/borrowck-pat-by-move-and-ref-inverse.stderr

@@ -357,6 +357,10 @@ LL |         a @ Some((mut b @ ref mut c, d @ ref e)) => {}
    |                   value moved here
    |
    = note: move occurs because value has type `main::U`, which does not implement the `Copy` trait
+help: borrow this field in the pattern to avoid moving the value
+   |
+LL |         a @ Some((ref mut b @ ref mut c, d @ ref e)) => {}
+   |                   ^^^
 
 error[E0382]: use of moved value
   --> $DIR/borrowck-pat-by-move-and-ref-inverse.rs:61:38
@@ -379,6 +383,10 @@ LL |         a @ Some((mut b @ ref mut c, d @ ref e)) => {}
    |                                      value moved here
    |
    = note: move occurs because value has type `main::U`, which does not implement the `Copy` trait
+help: borrow this field in the pattern to avoid moving the value
+   |
+LL |         a @ Some((mut b @ ref mut c, ref d @ ref e)) => {}
+   |                                      ^^^
 
 error[E0382]: borrow of moved value
   --> $DIR/borrowck-pat-by-move-and-ref-inverse.rs:71:30
@@ -412,6 +420,10 @@ LL |         a @ Some((mut b @ ref mut c, d @ ref e)) => {}
    |                   value moved here
    |
    = note: move occurs because value has type `main::U`, which does not implement the `Copy` trait
+help: borrow this field in the pattern to avoid moving the value
+   |
+LL |         a @ Some((ref mut b @ ref mut c, d @ ref e)) => {}
+   |                   ^^^
 
 error[E0382]: use of moved value
   --> $DIR/borrowck-pat-by-move-and-ref-inverse.rs:83:38
@@ -434,6 +446,10 @@ LL |         a @ Some((mut b @ ref mut c, d @ ref e)) => {}
    |                                      value moved here
    |
    = note: move occurs because value has type `main::U`, which does not implement the `Copy` trait
+help: borrow this field in the pattern to avoid moving the value
+   |
+LL |         a @ Some((mut b @ ref mut c, ref d @ ref e)) => {}
+   |                                      ^^^
 
 error[E0382]: borrow of moved value
   --> $DIR/borrowck-pat-by-move-and-ref-inverse.rs:93:30

src/test/ui/ref-suggestion.stderr

@@ -28,6 +28,10 @@ LL |     x;
    |     ^ value used here after partial move
    |
    = note: move occurs because value has type `std::vec::Vec<i32>`, which does not implement the `Copy` trait
+help: borrow this field in the pattern to avoid moving `x.0.0`
+   |
+LL |         (Some(ref y), ()) => {},
+   |               ^^^
 
 error: aborting due to 3 previous errors