Disallow exports between decorator & class body

For stage 2 decorators

src/parser/statement.js

@@ -157,6 +157,10 @@ export default class StatementParser extends ExpressionParser {
   }
 
   parseDecorators(allowExport?: boolean): void {
+    if (this.hasPlugin("decorators-stage-2")) {
+      allowExport = false;
+    }
+
     while (this.match(tt.at)) {
       const decorator = this.parseDecorator();
       this.state.decorators.push(decorator);

test/fixtures/experimental/decorators-stage-2/export-decorators-on-class/options.json

@@ -1,3 +1,4 @@
 {
-  "sourceType": "module"
+  "sourceType": "module",
+  "throws": "Leading decorators must be attached to a class declaration (2:0)"
 }