Add check for missing fields in enum variant pattern

compiler/rustc_resolve/src/late/diagnostics.rs

@@ -1130,7 +1130,7 @@ impl<'ast, 'ra: 'ast, 'tcx> LateResolutionVisitor<'_, 'ast, 'ra, 'tcx> {
         let None = following_seg else { return };
         for rib in self.ribs[ValueNS].iter().rev() {
             for (def_id, spans) in &rib.patterns_with_skipped_bindings {
-                if let DefKind::Struct = self.r.tcx.def_kind(*def_id)
+                if let DefKind::Struct | DefKind::Variant = self.r.tcx.def_kind(*def_id)
                     && let Some(fields) = self.r.field_idents(*def_id)
                 {
                     for field in fields {

tests/ui/pattern/struct-pattern-with-missing-fields-resolve-error.rs

@@ -3,6 +3,10 @@ struct Website {
     title: Option<String>,
 }
 
+enum Foo {
+    Bar { a: i32 },
+}
+
 fn main() {
     let website = Website {
         url: "http://www.example.com".into(),
@@ -18,4 +22,9 @@ fn main() {
         println!("[{}]({})", title, url); //~ ERROR cannot find value `title` in this scope
         //~^ NOTE not found in this scope
     }
+
+    let x = Foo::Bar { a: 1 };
+    if let Foo::Bar { .. } = x { //~ NOTE this pattern
+        println!("{a}"); //~ ERROR cannot find value `a` in this scope
+    }
 }

tests/ui/pattern/struct-pattern-with-missing-fields-resolve-error.stderr

@@ -1,5 +1,5 @@
 error: expected `,`
-  --> $DIR/struct-pattern-with-missing-fields-resolve-error.rs:12:31
+  --> $DIR/struct-pattern-with-missing-fields-resolve-error.rs:16:31
    |
 LL |     if let Website { url, Some(title) } = website {
    |            -------            ^
@@ -7,13 +7,21 @@ LL |     if let Website { url, Some(title) } = website {
    |            while parsing the fields for this pattern
 
 error[E0425]: cannot find value `title` in this scope
-  --> $DIR/struct-pattern-with-missing-fields-resolve-error.rs:18:30
+  --> $DIR/struct-pattern-with-missing-fields-resolve-error.rs:22:30
    |
 LL |     if let Website { url, .. } = website {
    |            ------------------- this pattern doesn't include `title`, which is available in `Website`
 LL |         println!("[{}]({})", title, url);
    |                              ^^^^^ not found in this scope
 
-error: aborting due to 2 previous errors
+error[E0425]: cannot find value `a` in this scope
+  --> $DIR/struct-pattern-with-missing-fields-resolve-error.rs:28:20
+   |
+LL |     if let Foo::Bar { .. } = x {
+   |            --------------- this pattern doesn't include `a`, which is available in `Bar`
+LL |         println!("{a}");
+   |                    ^ help: a local variable with a similar name exists: `x`
+
+error: aborting due to 3 previous errors
 
 For more information about this error, try `rustc --explain E0425`.