Add support for preserving comments in babel-template. (#3689)

* Add support for preserving comments in babel-template.

* Add an API section to babel-template.

packages/babel-template/README.md

@@ -32,3 +32,33 @@ console.log(generate(ast).code);
 ```js
 var myModule = require('my-module');
 ```
+
+## API
+
+### `template(code, [opts])`
+
+#### code
+
+Type: `string`
+
+#### options
+
+`babel-template` accepts all of the options from [babylon], and specifies
+some defaults of its own:
+
+* `allowReturnOutsideFunction` is set to `true` by default.
+* `allowSuperOutsideMethod` is set to `true` by default.
+
+##### preserveComments
+
+Type: `boolean`
+Default: `false`
+
+Set this to `true` to preserve any comments from the `code` parameter.
+
+#### Return value
+
+`babel-template` returns a `function` which is invoked with an optional object
+of replacements. See the usage section for an example.
+
+[babylon]: https://github.com/babel/babylon#options

packages/babel-template/src/index.js

@@ -24,16 +24,19 @@ export default function (code: string, opts?: Object): Function {
     }
   }
 
+  opts = assign({
+    allowReturnOutsideFunction: true,
+    allowSuperOutsideMethod: true,
+    preserveComments: false,
+  }, opts);
+
   let getAst = function () {
     let ast;
 
     try {
-      ast = babylon.parse(code, assign({
-        allowReturnOutsideFunction: true,
-        allowSuperOutsideMethod: true
-      }, opts));
+      ast = babylon.parse(code, opts);
 
-      ast = traverse.removeProperties(ast);
+      ast = traverse.removeProperties(ast, {preserveComments: opts.preserveComments});
 
       traverse.cheap(ast, function (node) {
         node[FROM_TEMPLATE] = true;

packages/babel-template/test/index.js

@@ -1,6 +1,9 @@
+var generator = require('../../babel-generator').default;
 var template  = require("../lib");
 var chai      = require("chai");
 
+var comments = "// Sum two numbers\nconst add = (a, b) => a + b;";
+
 suite("templating", function () {
   test("import statement will cause parser to throw by default", function () {
     chai.expect(function () {
@@ -13,4 +16,15 @@ suite("templating", function () {
       template("import foo from 'foo'", {sourceType: 'module'})({});
     }).not.to.throw();
   });
+
+  test("should strip comments by default", function () {
+    var code = "const add = (a, b) => a + b;"
+    var output = template(comments)();
+    chai.expect(generator(output).code).to.be.equal(code);
+  });
+
+  test("should preserve comments with a flag", function () {
+    var output = template(comments, {preserveComments: true})();
+    chai.expect(generator(output).code).to.be.equal(comments);
+  });
 });