Throw error when exporting non-declaration

fixes babel#238

src/parser/statement.js

@@ -848,7 +848,7 @@ pp.parseExport = function (node) {
     if (needsSemi) this.semicolon();
     this.checkExport(node, true, true);
     return this.finishNode(node, "ExportDefaultDeclaration");
-  } else if (this.state.type.keyword || this.shouldParseExportDeclaration()) {
+  } else if (this.shouldParseExportDeclaration()) {
     node.specifiers = [];
     node.source = null;
     node.declaration = this.parseExportDeclaration(node);
@@ -861,8 +861,22 @@ pp.parseExport = function (node) {
   return this.finishNode(node, "ExportNamedDeclaration");
 };
 
+pp.shouldParseExportDeclaration = function () {
+  return this.state.type.keyword || this.isContextual("async");
+};
+
+pp.isDeclaration = function (node): boolean {
+  return node.type === "VariableDeclaration"
+    || node.type === "FunctionDeclaration"
+    || node.type === "ClassDeclaration";
+};
+
 pp.parseExportDeclaration = function () {
-  return this.parseStatement(true);
+  const statement = this.parseStatement(true);
+  if (!this.isDeclaration(statement)) {
+    this.unexpected(statement.start);
+  }
+  return statement;
 };
 
 pp.isExportDefaultSpecifier = function () {
@@ -901,10 +915,6 @@ pp.parseExportFrom = function (node, expect?) {
   this.semicolon();
 };
 
-pp.shouldParseExportDeclaration = function () {
-  return this.isContextual("async");
-};
-
 pp.checkExport = function (node, checkNames, isDefault) {
   if (checkNames) {
     // Check for duplicate exports