reverse binding order in matches to allow the subbinding of copyable fields in bindings after @

compiler/rustc_mir_build/src/build/matches/simplify.rs

@@ -131,7 +131,20 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
             }
 
             PatKind::Binding { name, mutability, mode, var, ty, ref subpattern, is_primary: _ } => {
-                candidate.bindings.push(Binding {
+                // issue #69971: the binding order should be right to left if there are more
+                // bindings after `@` to please the borrow checker
+                // Ex
+                // struct NonCopyStruct {
+                //     copy_field: u32,
+                // }
+                //
+                // fn foo1(x: NonCopyStruct) {
+                //     let y @ NonCopyStruct { copy_field: z } = x;
+                //     // the above should turn into
+                //     let z = x.copy_field;
+                //     let y = x;
+                // }
+                candidate.bindings.insert(0, Binding {
                     name,
                     mutability,
                     span: match_pair.pattern.span,

src/test/ui/borrowck/borrowck-move-error-with-note.stderr

@@ -1,4 +1,4 @@
-error[E0507]: cannot move out of `f.0` which is behind a shared reference
+error[E0507]: cannot move out of `f.1` which is behind a shared reference
   --> $DIR/borrowck-move-error-with-note.rs:11:11
    |
 LL |     match *f {

src/test/ui/borrowck/borrowck-slice-pattern-element-loan-slice.stderr

@@ -32,23 +32,23 @@ error[E0502]: cannot borrow `s[..]` as mutable because it is also borrowed as im
   --> $DIR/borrowck-slice-pattern-element-loan-slice.rs:25:23
    |
 LL |     if let [.., _, ref from_end4, ref from_end3, _, ref from_end1] = *s {
-   |                                   ------------- immutable borrow occurs here
+   |                    ------------- immutable borrow occurs here
 ...
 LL |         if let [_, _, ref mut from_begin2, ..] = *s {
    |                       ^^^^^^^^^^^^^^^^^^^ mutable borrow occurs here
 LL |             nop(&[from_begin2, from_end1, from_end3, from_end4]);
-   |                                           --------- immutable borrow later used here
+   |                                                      --------- immutable borrow later used here
 
 error[E0502]: cannot borrow `s[..]` as mutable because it is also borrowed as immutable
   --> $DIR/borrowck-slice-pattern-element-loan-slice.rs:28:26
    |
 LL |     if let [.., _, ref from_end4, ref from_end3, _, ref from_end1] = *s {
-   |                                   ------------- immutable borrow occurs here
+   |                    ------------- immutable borrow occurs here
 ...
 LL |         if let [_, _, _, ref mut from_begin3, ..] = *s {
    |                          ^^^^^^^^^^^^^^^^^^^ mutable borrow occurs here
 LL |             nop(&[from_begin3, from_end1, from_end3, from_end4]);
-   |                                           --------- immutable borrow later used here
+   |                                                      --------- immutable borrow later used here
 
 error[E0502]: cannot borrow `s[..]` as mutable because it is also borrowed as immutable
   --> $DIR/borrowck-slice-pattern-element-loan-slice.rs:33:21
@@ -75,12 +75,12 @@ error[E0502]: cannot borrow `s[..]` as mutable because it is also borrowed as im
   --> $DIR/borrowck-slice-pattern-element-loan-slice.rs:39:21
    |
 LL |     if let [ref from_begin0, ref from_begin1, _, ref from_begin3, _, ..] = *s {
-   |                              --------------- immutable borrow occurs here
+   |                                                  --------------- immutable borrow occurs here
 ...
 LL |         if let [.., ref mut from_end4, _, _, _] = *s {
    |                     ^^^^^^^^^^^^^^^^^ mutable borrow occurs here
 LL |             nop(&[from_begin0, from_begin1, from_begin3, from_end4]);
-   |                                ----------- immutable borrow later used here
+   |                                             ----------- immutable borrow later used here
 
 error[E0502]: cannot borrow `s[..]` as mutable because it is also borrowed as immutable
   --> $DIR/borrowck-slice-pattern-element-loan-slice.rs:47:20

src/test/ui/issues/issue-12567.stderr

@@ -8,7 +8,7 @@ LL |         (&[], &[hd, ..]) | (&[hd, ..], &[])
    |                 -- data moved here
 LL |             => println!("one empty"),
 LL |         (&[hd1, ..], &[hd2, ..])
-   |            --- ...and here
+   |                        --- ...and here
    |
    = note: move occurs because these variables have types that don't implement the `Copy` trait
 
@@ -22,7 +22,7 @@ LL |         (&[], &[hd, ..]) | (&[hd, ..], &[])
    |                 -- data moved here
 LL |             => println!("one empty"),
 LL |         (&[hd1, ..], &[hd2, ..])
-   |                        --- ...and here
+   |            --- ...and here
    |
    = note: move occurs because these variables have types that don't implement the `Copy` trait
 

src/test/ui/nll/move-errors.stderr

@@ -97,18 +97,6 @@ LL |         B::U(D(s)) => (),
    |                data moved here
    |                move occurs because `s` has type `String`, which does not implement the `Copy` trait
 
-error[E0509]: cannot move out of type `D`, which implements the `Drop` trait
-  --> $DIR/move-errors.rs:92:11
-   |
-LL |     match x {
-   |           ^ cannot move out of here
-...
-LL |         (D(s), &t) => (),
-   |            -
-   |            |
-   |            data moved here
-   |            move occurs because `s` has type `String`, which does not implement the `Copy` trait
-
 error[E0507]: cannot move out of `*x.1` which is behind a shared reference
   --> $DIR/move-errors.rs:92:11
    |
@@ -121,6 +109,18 @@ LL |         (D(s), &t) => (),
    |                 data moved here
    |                 move occurs because `t` has type `String`, which does not implement the `Copy` trait
 
+error[E0509]: cannot move out of type `D`, which implements the `Drop` trait
+  --> $DIR/move-errors.rs:92:11
+   |
+LL |     match x {
+   |           ^ cannot move out of here
+...
+LL |         (D(s), &t) => (),
+   |            -
+   |            |
+   |            data moved here
+   |            move occurs because `s` has type `String`, which does not implement the `Copy` trait
+
 error[E0509]: cannot move out of type `F`, which implements the `Drop` trait
   --> $DIR/move-errors.rs:102:11
    |

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

@@ -12,28 +12,28 @@ fn main() {
     let x = Some(X { x: () });
     match x {
         Some(ref _y @ _z) => {} //~ ERROR cannot move out of value because it is borrowed
+        //~| ERROR borrow of moved value
         None => panic!(),
     }
 
     let x = Some(X { x: () });
     match x {
         Some(_z @ ref _y) => {}
         //~^ ERROR borrow of moved value
-        //~| ERROR borrow of moved value
         None => panic!(),
     }
 
     let mut x = Some(X { x: () });
     match x {
         Some(ref mut _y @ _z) => {} //~ ERROR cannot move out of value because it is borrowed
+        //~| ERROR borrow of moved value
         None => panic!(),
     }
 
     let mut x = Some(X { x: () });
     match x {
         Some(_z @ ref mut _y) => {}
         //~^ ERROR borrow of moved value
-        //~| ERROR borrow of moved value
         None => panic!(),
     }
 }

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

@@ -8,7 +8,7 @@ LL |         Some(ref _y @ _z) => {}
    |              value borrowed, by `_y`, here
 
 error: borrow of moved value
-  --> $DIR/bind-by-move-neither-can-live-while-the-other-survives-1.rs:20:14
+  --> $DIR/bind-by-move-neither-can-live-while-the-other-survives-1.rs:21:14
    |
 LL |         Some(_z @ ref _y) => {}
    |              --^^^------
@@ -27,7 +27,7 @@ LL |         Some(ref mut _y @ _z) => {}
    |              value borrowed, by `_y`, here
 
 error: borrow of moved value
-  --> $DIR/bind-by-move-neither-can-live-while-the-other-survives-1.rs:34:14
+  --> $DIR/bind-by-move-neither-can-live-while-the-other-survives-1.rs:35:14
    |
 LL |         Some(_z @ ref mut _y) => {}
    |              --^^^----------
@@ -37,34 +37,34 @@ LL |         Some(_z @ ref mut _y) => {}
    |              move occurs because `_z` has type `X` which does not implement the `Copy` trait
 
 error[E0382]: borrow of moved value
-  --> $DIR/bind-by-move-neither-can-live-while-the-other-survives-1.rs:20:19
+  --> $DIR/bind-by-move-neither-can-live-while-the-other-survives-1.rs:14:14
    |
-LL |         Some(_z @ ref _y) => {}
-   |              -----^^^^^^
-   |              |    |
-   |              |    value borrowed here after move
-   |              value moved here
+LL |         Some(ref _y @ _z) => {}
+   |              ^^^^^^^^^--
+   |              |        |
+   |              |        value moved here
+   |              value borrowed here after move
    |
    = 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) => {}
-   |              ^^^
+LL |         Some(ref _y @ ref _z) => {}
+   |                       ^^^
 
 error[E0382]: borrow of moved value
-  --> $DIR/bind-by-move-neither-can-live-while-the-other-survives-1.rs:34:19
+  --> $DIR/bind-by-move-neither-can-live-while-the-other-survives-1.rs:28:14
    |
-LL |         Some(_z @ ref mut _y) => {}
-   |              -----^^^^^^^^^^
-   |              |    |
-   |              |    value borrowed here after move
-   |              value moved here
+LL |         Some(ref mut _y @ _z) => {}
+   |              ^^^^^^^^^^^^^--
+   |              |            |
+   |              |            value moved here
+   |              value borrowed here after move
    |
    = 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) => {}
-   |              ^^^
+LL |         Some(ref mut _y @ ref _z) => {}
+   |                           ^^^
 
 error: aborting due to 6 previous errors
 

src/test/ui/pattern/bindings-after-at/bind-by-move-no-subbindings-fun-param.rs

@@ -7,7 +7,7 @@ fn main() {}
 struct A(Box<u8>);
 
 fn f(a @ A(u): A) -> Box<u8> {
-    //~^ ERROR use of moved value
+    //~^ ERROR use of partially moved value
     drop(a);
     u
 }

src/test/ui/pattern/bindings-after-at/bind-by-move-no-subbindings-fun-param.stderr

@@ -1,12 +1,13 @@
-error[E0382]: use of moved value
-  --> $DIR/bind-by-move-no-subbindings-fun-param.rs:9:12
+error[E0382]: use of partially moved value
+  --> $DIR/bind-by-move-no-subbindings-fun-param.rs:9:6
    |
 LL | fn f(a @ A(u): A) -> Box<u8> {
-   |      ------^-
+   |      ^^^^^^-^
    |      |     |
-   |      |     value used here after move
-   |      value moved here
-   |      move occurs because value has type `A`, which does not implement the `Copy` trait
+   |      |     value partially moved here
+   |      value used here after partial move
+   |
+   = note: partial move occurs because value has type `Box<u8>`, which does not implement the `Copy` trait
 
 error: aborting due to previous error
 

src/test/ui/pattern/bindings-after-at/borrowck-move-and-move.rs

@@ -12,22 +12,22 @@ fn main() {
 
     let a @ b = U; //~ ERROR use of moved value
 
-    let a @ (b, c) = (U, U); //~ ERROR use of moved value
+    let a @ (b, c) = (U, U); //~ ERROR use of partially moved value
 
-    let a @ (b, c) = (u(), u()); //~ ERROR use of moved value
+    let a @ (b, c) = (u(), u()); //~ ERROR use of partially moved value
 
     match Ok(U) {
-        a @ Ok(b) | a @ Err(b) => {} //~ ERROR use of moved value
-                                     //~^ ERROR use of moved value
+        a @ Ok(b) | a @ Err(b) => {} //~ ERROR use of partially moved value
+                                     //~^ ERROR use of partially moved value
     }
 
     fn fun(a @ b: U) {} //~ ERROR use of moved value
 
     match [u(), u(), u(), u()] {
-        xs @ [a, .., b] => {} //~ ERROR use of moved value
+        xs @ [a, .., b] => {} //~ ERROR use of partially moved value
     }
 
     match [u(), u(), u(), u()] {
-        xs @ [_, ys @ .., _] => {} //~ ERROR use of moved value
+        xs @ [_, ys @ .., _] => {} //~ ERROR use of partially moved value
     }
 }