Match ergonomics 2024: let `&` patterns eat `&mut`

7 files changed, 115 insertions, 69 deletions

diff --git a/tests/ui/match/ref_pat_eat_one_layer_2024/ref_pat_eat_one_layer_2024.rs b/tests/ui/match/ref_pat_eat_one_layer_2024/ref_pat_eat_one_layer_2024.rs
index f1ac3e340e9..62e4f82a3ff 100644
--- a/tests/ui/match/ref_pat_eat_one_layer_2024/ref_pat_eat_one_layer_2024.rs
+++ b/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;
diff --git a/tests/ui/match/ref_pat_eat_one_layer_2024/ref_pat_eat_one_layer_2024_fail.rs b/tests/ui/match/ref_pat_eat_one_layer_2024/ref_pat_eat_one_layer_2024_fail.rs
index ec091bb1746..61e61719458 100644
--- a/tests/ui/match/ref_pat_eat_one_layer_2024/ref_pat_eat_one_layer_2024_fail.rs
+++ b/tests/ui/match/ref_pat_eat_one_layer_2024/ref_pat_eat_one_layer_2024_fail.rs
@@ -14,16 +14,24 @@ 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(&Some(ref mut x)) = &mut Some(Some(0)) {
+        //~^ ERROR: cannot bind with `ref mut` behind an `&` pattern
+    }
+    if let &Some(Some(ref mut x)) = &mut Some(Some(0)) {
+        //~^ ERROR: cannot bind with `ref mut` behind an `&` pattern
+    }
+    if let Some(&mut Some(x)) = &Some(Some(0)) {
+        //~^ ERROR: mismatched types
+    }
 
     let &mut _= &&0;
     //~^ ERROR: mismatched types
diff --git a/tests/ui/match/ref_pat_eat_one_layer_2024/ref_pat_eat_one_layer_2024_fail.stderr b/tests/ui/match/ref_pat_eat_one_layer_2024/ref_pat_eat_one_layer_2024_fail.stderr
index be71ee606c7..2aa2e2851ce 100644
--- a/tests/ui/match/ref_pat_eat_one_layer_2024/ref_pat_eat_one_layer_2024_fail.stderr
+++ b/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}>>>`
@@ -65,7 +54,53 @@ 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[E0596]: cannot bind with `ref mut` behind an `&` pattern
+  --> $DIR/ref_pat_eat_one_layer_2024_fail.rs:26:31
+   |
+LL |     if let Some(&Some(ref mut x)) = &mut Some(Some(0)) {
+   |                               ^
+   |
+help: change this `&` pattern to an `&mut`
+  --> $DIR/ref_pat_eat_one_layer_2024_fail.rs:26:17
+   |
+LL |     if let Some(&Some(ref mut x)) = &mut Some(Some(0)) {
+   |                 ^
+
+error[E0596]: cannot bind with `ref mut` behind an `&` pattern
+  --> $DIR/ref_pat_eat_one_layer_2024_fail.rs:29:31
+   |
+LL |     if let &Some(Some(ref mut x)) = &mut Some(Some(0)) {
+   |                               ^
+   |
+help: change this `&` pattern to an `&mut`
+  --> $DIR/ref_pat_eat_one_layer_2024_fail.rs:29:12
+   |
+LL |     if let &Some(Some(ref mut x)) = &mut Some(Some(0)) {
+   |            ^
+
+error[E0308]: mismatched types
+  --> $DIR/ref_pat_eat_one_layer_2024_fail.rs:32:17
+   |
+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:36:9
    |
 LL |     let &mut _= &&0;
    |         ^^^^^^  --- this expression has type `&&{integer}`
@@ -76,7 +111,7 @@ LL |     let &mut _= &&0;
            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:39:9
    |
 LL |     let &mut _ = &&&&&&&&&&&&&&&&&&&&&&&&&&&&0;
    |         ^^^^^^   ----------------------------- this expression has type `&&&&&&&&&&&&&&&&&&&&&&&&&&&&{integer}`
@@ -86,6 +121,7 @@ LL |     let &mut _ = &&&&&&&&&&&&&&&&&&&&&&&&&&&&0;
    = note:           expected type `{integer}`
            found mutable reference `&mut _`
 
-error: aborting due to 8 previous errors
+error: aborting due to 11 previous errors
 
-For more information about this error, try `rustc --explain E0308`.
+Some errors have detailed explanations: E0308, E0596.
+For more information about an error, try `rustc --explain E0308`.
diff --git a/tests/ui/match/ref_pat_everywhere-mutability-mismatch.rs b/tests/ui/match/ref_pat_everywhere-fail.rs
index 9dd7a7893ec..d1b1c04730d 100644
--- a/tests/ui/match/ref_pat_everywhere-mutability-mismatch.rs
+++ b/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;
     }
diff --git a/tests/ui/match/ref_pat_everywhere-fail.stderr b/tests/ui/match/ref_pat_everywhere-fail.stderr
new file mode 100644
index 00000000000..25a01129f4a
--- /dev/null
+++ b/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`.
diff --git a/tests/ui/match/ref_pat_everywhere-mutability-mismatch.stderr b/tests/ui/match/ref_pat_everywhere-mutability-mismatch.stderr
deleted file mode 100644
index d512ea5f957..00000000000
--- a/tests/ui/match/ref_pat_everywhere-mutability-mismatch.stderr
+++ /dev/null
@@ -1,44 +0,0 @@
-error[E0308]: mismatched types
-  --> $DIR/ref_pat_everywhere-mutability-mismatch.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-mutability-mismatch.rs:8:12
-   |
-LL |     if let &Some(x) = &mut Some(0) {
-   |            ^^^^^^^^   ------------ this expression has type `&mut Option<{integer}>`
-   |            |
-   |            types differ in mutability
-   |
-   = note: expected mutable reference `&mut Option<{integer}>`
-                      found reference `&_`
-
-error[E0308]: mismatched types
-  --> $DIR/ref_pat_everywhere-mutability-mismatch.rs:12:17
-   |
-LL |     if let Some(&x) = &mut Some(0) {
-   |                 ^^    ------------ this expression has type `&mut Option<{integer}>`
-   |                 |
-   |                 expected integer, found `&_`
-   |
-   = note:   expected type `{integer}`
-           found reference `&_`
-help: consider removing `&` from the pattern
-   |
-LL |     if let Some(x) = &mut Some(0) {
-   |                 ~
-
-error: aborting due to 3 previous errors
-
-For more information about this error, try `rustc --explain E0308`.
diff --git a/tests/ui/match/ref_pat_everywhere.rs b/tests/ui/match/ref_pat_everywhere.rs
index b3daca48409..9a79c548475 100644
--- a/tests/ui/match/ref_pat_everywhere.rs
+++ b/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;
+    }
 }