Match ergonomics 2024: let & patterns eat &mut

tests/ui/match/ref_pat_eat_one_layer_2024/ref_pat_eat_one_layer_2024.rs

@@ -53,6 +53,12 @@ pub fn main() {
     if let Some(&Some(Some(&x))) = &Some(Some(&mut Some(0))) {
         let _: u32 = x;
     }
+    if let Some(&Some(&x)) = Some(&Some(&mut 0)) {
+        let _: u32 = x;
+    }
+    if let Some(&Some(x)) = &mut Some(Some(0)) {
+        let _: u32 = x;
+    }
 
     let &mut x = &&mut 0;
     let _: &u32 = x;

tests/ui/match/ref_pat_eat_one_layer_2024/ref_pat_eat_one_layer_2024_fail.rs

@@ -14,18 +14,20 @@ pub fn main() {
         let _: &mut u32 = x;
         //~^ ERROR: mismatched types
     }
-    if let Some(&Some(&_)) = Some(&Some(&mut 0)) {
-        //~^ ERROR: mismatched types
-    }
     if let Some(&Some(&mut _)) = &mut Some(&Some(0)) {
         //~^ ERROR: mismatched types
     }
     if let Some(&Some(Some((&mut _)))) = &Some(Some(&mut Some(0))) {
         //~^ ERROR: mismatched types
     }
+    if let Some(&mut Some(x)) = &Some(Some(0)) {
+        //~^ ERROR: mismatched types
+    }
+    if let Some(&mut Some(x)) = &Some(Some(0)) {
+        //~^ ERROR: mismatched types
+    }
 
-
-    let &mut _= &&0;
+    let &mut _ = &&0;
     //~^ ERROR: mismatched types
 
     let &mut _ = &&&&&&&&&&&&&&&&&&&&&&&&&&&&0;

tests/ui/match/ref_pat_eat_one_layer_2024/ref_pat_eat_one_layer_2024_fail.stderr

@@ -34,17 +34,6 @@ LL |         let _: &mut u32 = x;
 error[E0308]: mismatched types
   --> $DIR/ref_pat_eat_one_layer_2024_fail.rs:17:23
    |
-LL |     if let Some(&Some(&_)) = Some(&Some(&mut 0)) {
-   |                       ^^     ------------------- this expression has type `Option<&Option<&mut {integer}>>`
-   |                       |
-   |                       types differ in mutability
-   |
-   = note: expected mutable reference `&mut {integer}`
-                      found reference `&_`
-
-error[E0308]: mismatched types
-  --> $DIR/ref_pat_eat_one_layer_2024_fail.rs:20:23
-   |
 LL |     if let Some(&Some(&mut _)) = &mut Some(&Some(0)) {
    |                       ^^^^^^     ------------------- this expression has type `&mut Option<&Option<{integer}>>`
    |                       |
@@ -54,7 +43,7 @@ LL |     if let Some(&Some(&mut _)) = &mut Some(&Some(0)) {
            found mutable reference `&mut _`
 
 error[E0308]: mismatched types
-  --> $DIR/ref_pat_eat_one_layer_2024_fail.rs:23:29
+  --> $DIR/ref_pat_eat_one_layer_2024_fail.rs:20:29
    |
 LL |     if let Some(&Some(Some((&mut _)))) = &Some(Some(&mut Some(0))) {
    |                             ^^^^^^       ------------------------- this expression has type `&Option<Option<&mut Option<{integer}>>>`
@@ -65,18 +54,40 @@ LL |     if let Some(&Some(Some((&mut _)))) = &Some(Some(&mut Some(0))) {
            found mutable reference `&mut _`
 
 error[E0308]: mismatched types
-  --> $DIR/ref_pat_eat_one_layer_2024_fail.rs:28:9
+  --> $DIR/ref_pat_eat_one_layer_2024_fail.rs:23:17
+   |
+LL |     if let Some(&mut Some(x)) = &Some(Some(0)) {
+   |                 ^^^^^^^^^^^^    -------------- this expression has type `&Option<Option<{integer}>>`
+   |                 |
+   |                 expected `Option<{integer}>`, found `&mut _`
+   |
+   = note:           expected enum `Option<{integer}>`
+           found mutable reference `&mut _`
+
+error[E0308]: mismatched types
+  --> $DIR/ref_pat_eat_one_layer_2024_fail.rs:26:17
+   |
+LL |     if let Some(&mut Some(x)) = &Some(Some(0)) {
+   |                 ^^^^^^^^^^^^    -------------- this expression has type `&Option<Option<{integer}>>`
+   |                 |
+   |                 expected `Option<{integer}>`, found `&mut _`
+   |
+   = note:           expected enum `Option<{integer}>`
+           found mutable reference `&mut _`
+
+error[E0308]: mismatched types
+  --> $DIR/ref_pat_eat_one_layer_2024_fail.rs:30:9
    |
-LL |     let &mut _= &&0;
-   |         ^^^^^^  --- this expression has type `&&{integer}`
+LL |     let &mut _ = &&0;
+   |         ^^^^^^   --- this expression has type `&&{integer}`
    |         |
    |         expected integer, found `&mut _`
    |
    = note:           expected type `{integer}`
            found mutable reference `&mut _`
 
 error[E0308]: mismatched types
-  --> $DIR/ref_pat_eat_one_layer_2024_fail.rs:31:9
+  --> $DIR/ref_pat_eat_one_layer_2024_fail.rs:33:9
    |
 LL |     let &mut _ = &&&&&&&&&&&&&&&&&&&&&&&&&&&&0;
    |         ^^^^^^   ----------------------------- this expression has type `&&&&&&&&&&&&&&&&&&&&&&&&&&&&{integer}`
@@ -86,6 +97,6 @@ LL |     let &mut _ = &&&&&&&&&&&&&&&&&&&&&&&&&&&&0;
    = note:           expected type `{integer}`
            found mutable reference `&mut _`
 
-error: aborting due to 8 previous errors
+error: aborting due to 9 previous errors
 
 For more information about this error, try `rustc --explain E0308`.

tests/ui/match/ref_pat_eat_one_layer_2024/ref_pat_eat_one_layer_2024_fail2.rs

@@ -8,4 +8,7 @@ pub fn main() {
         //~^ ERROR: cannot move out of a shared reference [E0507]
         let _: &u32 = x;
     }
+
+    let &ref mut x = &0;
+    //~^ cannot borrow data in a `&` reference as mutable [E0596]
 }

tests/ui/match/ref_pat_eat_one_layer_2024/ref_pat_eat_one_layer_2024_fail2.stderr

@@ -12,6 +12,13 @@ help: consider borrowing the pattern binding
 LL |     if let Some(&Some(ref x)) = Some(&Some(&mut 0)) {
    |                       +++
 
-error: aborting due to 1 previous error
+error[E0596]: cannot borrow data in a `&` reference as mutable
+  --> $DIR/ref_pat_eat_one_layer_2024_fail2.rs:12:10
+   |
+LL |     let &ref mut x = &0;
+   |          ^^^^^^^^^ cannot borrow as mutable
+
+error: aborting due to 2 previous errors
 
-For more information about this error, try `rustc --explain E0507`.
+Some errors have detailed explanations: E0507, E0596.
+For more information about an error, try `rustc --explain E0507`.

tests/ui/match/ref_pat_eat_one_layer_2024/ref_pat_eat_one_layer_2024_ref_mut_inside_and.fixed

@@ -0,0 +1,30 @@
+//@ edition: 2024
+//@ compile-flags: -Zunstable-options
+//@ run-rustfix
+#![allow(incomplete_features)]
+#![feature(ref_pat_eat_one_layer_2024)]
+
+pub fn main() {
+    if let Some(&mut Some(ref mut x)) = &mut Some(Some(0)) {
+        //~^ ERROR: cannot borrow as mutable inside an `&` pattern
+        let _: &mut u8 = x;
+    }
+
+    if let &mut Some(Some(ref mut x)) = &mut Some(Some(0)) {
+        //~^ ERROR: cannot borrow as mutable inside an `&` pattern
+        let _: &mut u8 = x;
+    }
+
+    macro_rules! pat {
+        ($var:ident) => { ref mut $var };
+    }
+    let &mut pat!(x) = &mut 0;
+    //~^ ERROR: cannot borrow as mutable inside an `&` pattern
+    let _: &mut u8 = x;
+
+    let &mut (ref mut a, ref mut b) = &mut (true, false);
+    //~^ ERROR: cannot borrow as mutable inside an `&` pattern
+    //~| ERROR: cannot borrow as mutable inside an `&` pattern
+    let _: &mut bool = a;
+    let _: &mut bool = b;
+}

tests/ui/match/ref_pat_eat_one_layer_2024/ref_pat_eat_one_layer_2024_ref_mut_inside_and.rs

@@ -0,0 +1,30 @@
+//@ edition: 2024
+//@ compile-flags: -Zunstable-options
+//@ run-rustfix
+#![allow(incomplete_features)]
+#![feature(ref_pat_eat_one_layer_2024)]
+
+pub fn main() {
+    if let Some(&Some(ref mut x)) = &mut Some(Some(0)) {
+        //~^ ERROR: cannot borrow as mutable inside an `&` pattern
+        let _: &mut u8 = x;
+    }
+
+    if let &Some(Some(ref mut x)) = &mut Some(Some(0)) {
+        //~^ ERROR: cannot borrow as mutable inside an `&` pattern
+        let _: &mut u8 = x;
+    }
+
+    macro_rules! pat {
+        ($var:ident) => { ref mut $var };
+    }
+    let &pat!(x) = &mut 0;
+    //~^ ERROR: cannot borrow as mutable inside an `&` pattern
+    let _: &mut u8 = x;
+
+    let &(ref mut a, ref mut b) = &mut (true, false);
+    //~^ ERROR: cannot borrow as mutable inside an `&` pattern
+    //~| ERROR: cannot borrow as mutable inside an `&` pattern
+    let _: &mut bool = a;
+    let _: &mut bool = b;
+}

tests/ui/match/ref_pat_eat_one_layer_2024/ref_pat_eat_one_layer_2024_ref_mut_inside_and.stderr

@@ -0,0 +1,43 @@
+error[E0596]: cannot borrow as mutable inside an `&` pattern
+  --> $DIR/ref_pat_eat_one_layer_2024_ref_mut_inside_and.rs:8:31
+   |
+LL |     if let Some(&Some(ref mut x)) = &mut Some(Some(0)) {
+   |                 -             ^
+   |                 |
+   |                 help: replace this `&` with `&mut`: `&mut`
+
+error[E0596]: cannot borrow as mutable inside an `&` pattern
+  --> $DIR/ref_pat_eat_one_layer_2024_ref_mut_inside_and.rs:13:31
+   |
+LL |     if let &Some(Some(ref mut x)) = &mut Some(Some(0)) {
+   |            -                  ^
+   |            |
+   |            help: replace this `&` with `&mut`: `&mut`
+
+error[E0596]: cannot borrow as mutable inside an `&` pattern
+  --> $DIR/ref_pat_eat_one_layer_2024_ref_mut_inside_and.rs:21:15
+   |
+LL |     let &pat!(x) = &mut 0;
+   |         -     ^
+   |         |
+   |         help: replace this `&` with `&mut`: `&mut`
+
+error[E0596]: cannot borrow as mutable inside an `&` pattern
+  --> $DIR/ref_pat_eat_one_layer_2024_ref_mut_inside_and.rs:25:19
+   |
+LL |     let &(ref mut a, ref mut b) = &mut (true, false);
+   |         -         ^
+   |         |
+   |         help: replace this `&` with `&mut`: `&mut`
+
+error[E0596]: cannot borrow as mutable inside an `&` pattern
+  --> $DIR/ref_pat_eat_one_layer_2024_ref_mut_inside_and.rs:25:30
+   |
+LL |     let &(ref mut a, ref mut b) = &mut (true, false);
+   |         -                    ^
+   |         |
+   |         help: replace this `&` with `&mut`: `&mut`
+
+error: aborting due to 5 previous errors
+
+For more information about this error, try `rustc --explain E0596`.

tests/ui/match/ref_pat_everywhere-mutability-mismatch.rs → tests/ui/match/ref_pat_everywhere-fail.rs

@@ -5,11 +5,7 @@ pub fn main() {
         //~^ ERROR: mismatched types [E0308]
         let _: u32 = x;
     }
-    if let &Some(x) = &mut Some(0) {
-        //~^ ERROR: mismatched types [E0308]
-        let _: u32 = x;
-    }
-    if let Some(&x) = &mut Some(0) {
+    if let Some(&mut x) = Some(&0) {
         //~^ ERROR: mismatched types [E0308]
         let _: u32 = x;
     }

tests/ui/match/ref_pat_everywhere-fail.stderr

@@ -0,0 +1,38 @@
+error[E0308]: mismatched types
+  --> $DIR/ref_pat_everywhere-fail.rs:4:17
+   |
+LL |     if let Some(&x) = Some(0) {
+   |                 ^^    ------- this expression has type `Option<{integer}>`
+   |                 |
+   |                 expected integer, found `&_`
+   |
+   = note:   expected type `{integer}`
+           found reference `&_`
+help: consider removing `&` from the pattern
+   |
+LL |     if let Some(x) = Some(0) {
+   |                 ~
+
+error[E0308]: mismatched types
+  --> $DIR/ref_pat_everywhere-fail.rs:8:17
+   |
+LL |     if let Some(&mut x) = Some(&0) {
+   |                 ^^^^^^    -------- this expression has type `Option<&{integer}>`
+   |                 |
+   |                 types differ in mutability
+   |
+   = note:      expected reference `&{integer}`
+           found mutable reference `&mut _`
+note: to declare a mutable binding use: `mut x`
+  --> $DIR/ref_pat_everywhere-fail.rs:8:17
+   |
+LL |     if let Some(&mut x) = Some(&0) {
+   |                 ^^^^^^
+help: consider removing `&mut` from the pattern
+   |
+LL |     if let Some(x) = Some(&0) {
+   |                 ~
+
+error: aborting due to 2 previous errors
+
+For more information about this error, try `rustc --explain E0308`.

tests/ui/match/ref_pat_everywhere.rs

@@ -15,4 +15,10 @@ pub fn main() {
     if let Some(Some(&x)) = &Some(&mut Some(0)) {
         let _: u32 = x;
     }
+    if let &Some(x) = &mut Some(0) {
+        let _: u32 = x;
+    }
+    if let Some(&x) = &mut Some(0) {
+        let _: u32 = x;
+    }
 }