Always suggest as MachineApplicable in recover_intersection_pat

compiler/rustc_parse/src/parser/pat.rs

@@ -491,17 +491,6 @@ impl<'a> Parser<'a> {
 
         if let PatKind::Ident(_, _, sub @ None) = &mut rhs.kind {
             // The user inverted the order, so help them fix that.
-            let mut applicability = Applicability::MachineApplicable;
-            // FIXME(bindings_after_at): Remove this code when stabilizing the feature.
-            lhs.walk(&mut |p| match p.kind {
-                // `check_match` is unhappy if the subpattern has a binding anywhere.
-                PatKind::Ident(..) => {
-                    applicability = Applicability::MaybeIncorrect;
-                    false // Short-circuit.
-                }
-                _ => true,
-            });
-
             let lhs_span = lhs.span;
             // Move the LHS into the RHS as a subpattern.
             // The RHS is now the full pattern.
@@ -510,7 +499,12 @@ impl<'a> Parser<'a> {
             self.struct_span_err(sp, "pattern on wrong side of `@`")
                 .span_label(lhs_span, "pattern on the left, should be on the right")
                 .span_label(rhs.span, "binding on the right, should be on the left")
-                .span_suggestion(sp, "switch the order", pprust::pat_to_string(&rhs), applicability)
+                .span_suggestion(
+                    sp,
+                    "switch the order",
+                    pprust::pat_to_string(&rhs),
+                    Applicability::MachineApplicable,
+                )
                 .emit();
         } else {
             // The special case above doesn't apply so we may have e.g. `A(x) @ B(y)`.

src/test/ui/parser/intersection-patterns-1.fixed

@@ -0,0 +1,35 @@
+// This tests the parser recovery in `recover_intersection_pat`
+// and serves as a regression test for the diagnostics issue #65400.
+//
+// The general idea is that for `$pat_lhs @ $pat_rhs` where
+// `$pat_lhs` is not generated by `ref? mut? $ident` we want
+// to suggest either switching the order or note that intersection
+// patterns are not allowed.
+
+// run-rustfix
+
+#![allow(unused_variables)]
+
+fn main() {
+    let s: Option<u8> = None;
+
+    match s {
+        y @ Some(x) => {}
+        //~^ ERROR pattern on wrong side of `@`
+        //~| pattern on the left, should be on the right
+        //~| binding on the right, should be on the left
+        //~| HELP switch the order
+        //~| SUGGESTION y @ Some(x)
+        _ => {}
+    }
+
+    match 2 {
+        e @ 1..=5 => {}
+        //~^ ERROR pattern on wrong side of `@`
+        //~| pattern on the left, should be on the right
+        //~| binding on the right, should be on the left
+        //~| HELP switch the order
+        //~| SUGGESTION e @ 1..=5
+        _ => {}
+    }
+}

src/test/ui/parser/intersection-patterns.rs → src/test/ui/parser/intersection-patterns-1.rs

@@ -6,6 +6,10 @@
 // to suggest either switching the order or note that intersection
 // patterns are not allowed.
 
+// run-rustfix
+
+#![allow(unused_variables)]
+
 fn main() {
     let s: Option<u8> = None;
 
@@ -19,15 +23,6 @@ fn main() {
         _ => {}
     }
 
-    match s {
-        Some(x) @ Some(y) => {}
-        //~^ ERROR left-hand side of `@` must be a binding
-        //~| interpreted as a pattern, not a binding
-        //~| also a pattern
-        //~| NOTE bindings are `x`, `mut x`, `ref x`, and `ref mut x`
-        _ => {}
-    }
-
     match 2 {
         1 ..= 5 @ e => {}
         //~^ ERROR pattern on wrong side of `@`

src/test/ui/parser/intersection-patterns.stderr → src/test/ui/parser/intersection-patterns-1.stderr

@@ -1,5 +1,5 @@
 error: pattern on wrong side of `@`
-  --> $DIR/intersection-patterns.rs:13:9
+  --> $DIR/intersection-patterns-1.rs:17:9
    |
 LL |         Some(x) @ y => {}
    |         -------^^^-
@@ -8,19 +8,8 @@ LL |         Some(x) @ y => {}
    |         pattern on the left, should be on the right
    |         help: switch the order: `y @ Some(x)`
 
-error: left-hand side of `@` must be a binding
-  --> $DIR/intersection-patterns.rs:23:9
-   |
-LL |         Some(x) @ Some(y) => {}
-   |         -------^^^-------
-   |         |         |
-   |         |         also a pattern
-   |         interpreted as a pattern, not a binding
-   |
-   = note: bindings are `x`, `mut x`, `ref x`, and `ref mut x`
-
 error: pattern on wrong side of `@`
-  --> $DIR/intersection-patterns.rs:32:9
+  --> $DIR/intersection-patterns-1.rs:27:9
    |
 LL |         1 ..= 5 @ e => {}
    |         -------^^^-
@@ -29,5 +18,5 @@ LL |         1 ..= 5 @ e => {}
    |         pattern on the left, should be on the right
    |         help: switch the order: `e @ 1..=5`
 
-error: aborting due to 3 previous errors
+error: aborting due to 2 previous errors
 

src/test/ui/parser/intersection-patterns-2.rs

@@ -0,0 +1,20 @@
+// This tests the parser recovery in `recover_intersection_pat`
+// and serves as a regression test for the diagnostics issue #65400.
+//
+// The general idea is that for `$pat_lhs @ $pat_rhs` where
+// `$pat_lhs` is not generated by `ref? mut? $ident` we want
+// to suggest either switching the order or note that intersection
+// patterns are not allowed.
+
+fn main() {
+    let s: Option<u8> = None;
+
+    match s {
+        Some(x) @ Some(y) => {}
+        //~^ ERROR left-hand side of `@` must be a binding
+        //~| interpreted as a pattern, not a binding
+        //~| also a pattern
+        //~| NOTE bindings are `x`, `mut x`, `ref x`, and `ref mut x`
+        _ => {}
+    }
+}

src/test/ui/parser/intersection-patterns-2.stderr

@@ -0,0 +1,13 @@
+error: left-hand side of `@` must be a binding
+  --> $DIR/intersection-patterns-2.rs:13:9
+   |
+LL |         Some(x) @ Some(y) => {}
+   |         -------^^^-------
+   |         |         |
+   |         |         also a pattern
+   |         interpreted as a pattern, not a binding
+   |
+   = note: bindings are `x`, `mut x`, `ref x`, and `ref mut x`
+
+error: aborting due to previous error
+