Support dynamic import (#100)

* Add support for dynamic Import expressions. See https://tc39.github.io/proposal-dynamic-import/

* Added skipped failing tests for dynamic import. Tests depend on espree supporting dynamic import

* Update dynamic import test with literal parse tree instead of depending on espree having dynamic import support

* Align with estree/estree#198

Author: Munter

estraverse.js

@@ -108,6 +108,7 @@
         GeneratorExpression: 'GeneratorExpression',  // CAUTION: It's deferred to ES7.
         Identifier: 'Identifier',
         IfStatement: 'IfStatement',
+        ImportExpression: 'ImportExpression',
         ImportDeclaration: 'ImportDeclaration',
         ImportDefaultSpecifier: 'ImportDefaultSpecifier',
         ImportNamespaceSpecifier: 'ImportNamespaceSpecifier',
@@ -182,6 +183,7 @@
         GeneratorExpression: ['blocks', 'filter', 'body'],  // CAUTION: It's deferred to ES7.
         Identifier: [],
         IfStatement: ['test', 'consequent', 'alternate'],
+        ImportExpression: ['source'],
         ImportDeclaration: ['specifiers', 'source'],
         ImportDefaultSpecifier: ['local'],
         ImportNamespaceSpecifier: ['local'],

test/es6.js

@@ -320,6 +320,32 @@ describe('import', function() {
     });
 });
 
+describe('dynamic import', function() {
+    it('expression pattern #1', function() {
+        // TODO: espree currently doesn't support dynamic imports. Update when it does
+        // const tree = espree(`import('rabbit-house')`, {
+        //     ecmaFeatures: {
+        //         modules: true
+        //     }
+        // });
+
+        const tree = {
+            type: 'ImportExpression',
+            source: {
+                type: 'Literal',
+                value: 'rabbit-house'
+            }
+        };
+
+      checkDump(Dumper.dump(tree), `
+          enter - ImportExpression
+          enter - Literal
+          leave - Literal
+          leave - ImportExpression
+      `);
+    });
+});
+
 describe('pattern', function() {
     it('assignment pattern#1', function() {
         const tree = {