Only allow declares inside declare module (#73)

* Only allow declares inside declare module

* Better error message

src/parser/util.js

@@ -45,8 +45,8 @@ pp.eatContextual = function (name) {
 
 // Asserts that following token is given contextual keyword.
 
-pp.expectContextual = function (name) {
-  if (!this.eatContextual(name)) this.unexpected();
+pp.expectContextual = function (name, message) {
+  if (!this.eatContextual(name)) this.unexpected(null, message);
 };
 
 // Test whether a semicolon can be inserted at the current position.
@@ -79,6 +79,6 @@ pp.expect = function (type) {
 
 // Raise an unexpected token error.
 
-pp.unexpected = function (pos) {
-  this.raise(pos != null ? pos : this.state.start, "Unexpected token");
+pp.unexpected = function (pos, message = "Unexpected token") {
+  this.raise(pos != null ? pos : this.state.start, message);
 };

src/plugins/flow.js

@@ -102,8 +102,7 @@ pp.flowParseDeclareModule = function (node) {
   while (!this.match(tt.braceR)) {
     let node2 = this.startNode();
 
-    // todo: declare check
-    this.next();
+    this.expectContextual("declare", "Unexpected token. Only declares are allowed inside declare module");
 
     body.push(this.flowParseDeclare(node2));
   }

test/fixtures/flow/declare-module/8/actual.js

@@ -0,0 +1,3 @@
+declare module A {
+  declar var a:number
+}

test/fixtures/flow/declare-module/8/options.json

@@ -0,0 +1,3 @@
+{
+  "throws": "Unexpected token. Only declares are allowed inside declare module (2:2)"
+}