Disallow in object literals, params, class props

And add tests to reflect the same

src/parser/expression.js

@@ -847,8 +847,16 @@ export default class ExpressionParser extends LValParser {
         if (this.eat(tt.braceR)) break;
       }
 
-      while (this.match(tt.at)) {
-        decorators.push(this.parseDecorator());
+      if (this.match(tt.at)) {
+        if (this.hasPlugin("decorators-stage-2")) {
+          this.raise(this.state.start, "decorators-stage-2 disallows object literal property decorators");
+        } else {
+          // we needn't check if decorators (stage 0) plugin is enabled since it's checked by
+          // the call to this.parseDecorator
+          while (this.match(tt.at)) {
+            decorators.push(this.parseDecorator());
+          }
+        }
       }
 
       let prop = this.startNode(), isGenerator = false, isAsync = false, startPos, startLoc;

src/parser/lval.js

@@ -187,6 +187,9 @@ export default class LValParser extends NodeUtils {
         break;
       } else {
         const decorators = [];
+        if (this.match(tt.at) && this.hasPlugin("decorators-stage-2")) {
+          this.raise(this.state.start, "Stage 2 decorators cannot be used to decorate parameters");
+        }
         while (this.match(tt.at)) {
           decorators.push(this.parseDecorator());
         }

src/parser/statement.js

@@ -709,6 +709,10 @@ export default class StatementParser extends ExpressionParser {
       }
 
       this.parseClassMember(classBody, member, state);
+
+      if (this.hasPlugin("decorators-stage-2") && member.kind != "method" && member.decorators && member.decorators.length > 0) {
+        this.raise(member.start, "Stage 2 decorators may only be used with a class or a class method");
+      }
     }
 
     if (decorators.length) {
@@ -776,6 +780,7 @@ export default class StatementParser extends ExpressionParser {
     if (!methodOrProp.computed && methodOrProp.static && (methodOrProp.key.name === "prototype" || methodOrProp.key.value === "prototype")) {
       this.raise(methodOrProp.key.start, "Classes may not have static property named prototype");
     }
+
     if (this.isClassMethod()) {
       // a normal method
       if (this.isNonstaticConstructor(method)) {