Recover from C++ style enum struct

compiler/rustc_parse/src/parser/item.rs

@@ -1216,6 +1216,25 @@ impl<'a> Parser<'a> {
 
     /// Parses an enum declaration.
     fn parse_item_enum(&mut self) -> PResult<'a, ItemInfo> {
+        if self.token.is_keyword(kw::Struct) {
+            let mut err = self.struct_span_err(
+                self.prev_token.span.to(self.token.span),
+                "`enum` and `struct` are mutually exclusive",
+            );
+            err.span_suggestion(
+                self.prev_token.span.to(self.token.span),
+                "replace `enum struct` with",
+                "enum",
+                Applicability::MachineApplicable,
+            );
+            if self.look_ahead(1, |t| t.is_ident()) {
+                self.bump();
+                err.emit();
+            } else {
+                return Err(err);
+            }
+        }
+
         let id = self.parse_ident()?;
         let mut generics = self.parse_generics()?;
         generics.where_clause = self.parse_where_clause()?;

src/test/ui/parser/issue-99625-enum-struct-mutually-exclusive.fixed

@@ -0,0 +1,13 @@
+// run-rustfix
+
+pub enum Range {
+    //~^ ERROR `enum` and `struct` are mutually exclusive
+    Valid {
+        begin: u32,
+        len: u32,
+    },
+    Out,
+}
+
+fn main() {
+}

src/test/ui/parser/issue-99625-enum-struct-mutually-exclusive.rs

@@ -0,0 +1,13 @@
+// run-rustfix
+
+pub enum struct Range {
+    //~^ ERROR `enum` and `struct` are mutually exclusive
+    Valid {
+        begin: u32,
+        len: u32,
+    },
+    Out,
+}
+
+fn main() {
+}

src/test/ui/parser/issue-99625-enum-struct-mutually-exclusive.stderr

@@ -0,0 +1,8 @@
+error: `enum` and `struct` are mutually exclusive
+  --> $DIR/issue-99625-enum-struct-mutually-exclusive.rs:3:5
+   |
+LL | pub enum struct Range {
+   |     ^^^^^^^^^^^ help: replace `enum struct` with: `enum`
+
+error: aborting due to previous error
+