Detect tuple variants used as struct pattern and suggest correct pattern

src/librustc_resolve/late/diagnostics.rs

@@ -701,7 +701,16 @@ impl<'a> LateResolutionVisitor<'a, '_, '_> {
                 if let Some(span) = self.def_span(def_id) {
                     err.span_label(span, &format!("`{}` defined here", path_str));
                 }
-                err.span_label(span, format!("did you mean `{}( /* fields */ )`?", path_str));
+                let fields =
+                    self.r.field_names.get(&def_id).map_or("/* fields */".to_string(), |fields| {
+                        vec!["_"; fields.len()].join(", ")
+                    });
+                err.span_suggestion(
+                    span,
+                    "use the tuple variant pattern syntax instead",
+                    format!("{}({})", path_str, fields),
+                    Applicability::HasPlaceholders,
+                );
             }
             (Res::SelfTy(..), _) if ns == ValueNS => {
                 err.span_label(span, fallback_label);

src/test/ui/empty/empty-struct-tuple-pat.stderr

@@ -23,23 +23,29 @@ LL |     Empty4()
    |     -------- `E::Empty4` defined here
 ...
 LL |         E::Empty4 => ()
-   |         ^^^^^^^^^ did you mean `E::Empty4( /* fields */ )`?
+   |         ^^^^^^^^^ help: use the tuple variant pattern syntax instead: `E::Empty4()`
 
 error[E0532]: expected unit struct, unit variant or constant, found tuple variant `XE::XEmpty5`
   --> $DIR/empty-struct-tuple-pat.rs:33:9
    |
 LL |         XE::XEmpty5 => (),
-   |         ^^^^-------
-   |         |   |
-   |         |   help: a unit variant with a similar name exists: `XEmpty4`
-   |         did you mean `XE::XEmpty5( /* fields */ )`?
+   |         ^^^^^^^^^^^
    | 
   ::: $DIR/auxiliary/empty-struct.rs:7:5
    |
 LL |     XEmpty4,
    |     ------- similarly named unit variant `XEmpty4` defined here
 LL |     XEmpty5(),
    |     --------- `XE::XEmpty5` defined here
+   |
+help: use the tuple variant pattern syntax instead
+   |
+LL |         XE::XEmpty5(/* fields */) => (),
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^
+help: a unit variant with a similar name exists
+   |
+LL |         XE::XEmpty4 => (),
+   |             ^^^^^^^
 
 error: aborting due to 4 previous errors
 

src/test/ui/issues/issue-32004.stderr

@@ -7,10 +7,16 @@ LL |     Baz
    |     --- similarly named unit variant `Baz` defined here
 ...
 LL |         Foo::Bar => {}
-   |         ^^^^^---
-   |         |    |
-   |         |    help: a unit variant with a similar name exists: `Baz`
-   |         did you mean `Foo::Bar( /* fields */ )`?
+   |         ^^^^^^^^
+   |
+help: use the tuple variant pattern syntax instead
+   |
+LL |         Foo::Bar(_) => {}
+   |         ^^^^^^^^^^^
+help: a unit variant with a similar name exists
+   |
+LL |         Foo::Baz => {}
+   |              ^^^
 
 error[E0532]: expected tuple struct or tuple variant, found unit struct `S`
   --> $DIR/issue-32004.rs:16:9

src/test/ui/issues/issue-63983.stderr

@@ -5,7 +5,7 @@ LL |     Tuple(i32),
    |     ---------- `MyEnum::Tuple` defined here
 ...
 LL |         MyEnum::Tuple => "",
-   |         ^^^^^^^^^^^^^ did you mean `MyEnum::Tuple( /* fields */ )`?
+   |         ^^^^^^^^^^^^^ help: use the tuple variant pattern syntax instead: `MyEnum::Tuple(_)`
 
 error[E0532]: expected unit struct, unit variant or constant, found struct variant `MyEnum::Struct`
   --> $DIR/issue-63983.rs:10:9

src/test/ui/parser/recover-from-bad-variant.rs

@@ -9,6 +9,7 @@ fn main() {
     match x {
         Enum::Foo(a, b) => {}
         //~^ ERROR expected tuple struct or tuple variant, found struct variant `Enum::Foo`
-        Enum::Bar(a, b) => {}
+        Enum::Bar { a, b } => {}
+        //~^ ERROR tuple variant `Enum::Bar` written as struct variant
     }
 }

src/test/ui/parser/recover-from-bad-variant.stderr

@@ -18,6 +18,13 @@ LL |     Foo { a: usize, b: usize },
 LL |         Enum::Foo(a, b) => {}
    |         ^^^^^^^^^^^^^^^ help: use struct pattern syntax instead: `Enum::Foo { a, b }`
 
-error: aborting due to 2 previous errors
+error[E0769]: tuple variant `Enum::Bar` written as struct variant
+  --> $DIR/recover-from-bad-variant.rs:12:9
+   |
+LL |         Enum::Bar { a, b } => {}
+   |         ^^^^^^^^^^^^^^^^^^ help: use the tuple variant pattern syntax instead: `Enum::Bar(a, b)`
+
+error: aborting due to 3 previous errors
 
-For more information about this error, try `rustc --explain E0532`.
+Some errors have detailed explanations: E0532, E0769.
+For more information about an error, try `rustc --explain E0532`.