From e8237910e89218d86225233493a74e75664da2a6 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Alu=C3=ADsio=20Augusto=20Silva=20Gon=C3=A7alves?=
 <aluisio@aasg.name>
Date: Wed, 14 Jan 2015 01:39:37 -0200
Subject: [PATCH] Add a transformer to import the runtime from a file

The `externalRuntime` optional transformer can be used in conjunction
with the `runtime` option to import and use the runtime from a module
instead of polluting the global environment.
---
 lib/6to5/transformation/modules/amd.js               |  2 +-
 lib/6to5/transformation/modules/common.js            | 12 +++++-------
 lib/6to5/transformation/transform.js                 |  1 +
 .../transformers/optional-external-runtime.js        | 11 +++++++++++
 4 files changed, 18 insertions(+), 8 deletions(-)
 create mode 100644 lib/6to5/transformation/transformers/optional-external-runtime.js

diff --git a/lib/6to5/transformation/modules/amd.js b/lib/6to5/transformation/modules/amd.js
index 3940c9d18d..d97ba66118 100644
--- a/lib/6to5/transformation/modules/amd.js
+++ b/lib/6to5/transformation/modules/amd.js
@@ -87,7 +87,7 @@ AMDFormatter.prototype.importSpecifier = function (specifier, node, nodes) {
   var key = t.getSpecifierName(specifier);
   var ref = this._push(node);
 
-  if (t.isImportBatchSpecifier(specifier)) {
+  if (t.isImportBatchSpecifier(specifier) || node._noInteropRequire) {
     // import * as bar from "foo";
   } else if (t.isSpecifierDefault(specifier) && !this.noInteropRequire) {
     // import foo from "foo";
diff --git a/lib/6to5/transformation/modules/common.js b/lib/6to5/transformation/modules/common.js
index 8e6044f2e9..c44f34078f 100644
--- a/lib/6to5/transformation/modules/common.js
+++ b/lib/6to5/transformation/modules/common.js
@@ -26,13 +26,11 @@ CommonJSFormatter.prototype.importSpecifier = function (specifier, node, nodes)
 
   // import foo from "foo";
   if (t.isSpecifierDefault(specifier)) {
-    nodes.push(t.variableDeclaration("var", [
-      t.variableDeclarator(variableName,
-        t.callExpression(this.file.addHelper("interop-require"), [util.template("require", {
-          MODULE_NAME: node.source
-        })])
-      )
-    ]));
+    var ref = util.template("require", {MODULE_NAME: node.source});
+    if (!node._noInteropRequire) {
+      ref = t.callExpression(this.file.addHelper("interop-require"), [ref]);
+    }
+    nodes.push(t.variableDeclaration("var", [t.variableDeclarator(variableName, ref)]));
   } else {
     if (specifier.type === "ImportBatchSpecifier") {
       // import * as bar from "foo";
diff --git a/lib/6to5/transformation/transform.js b/lib/6to5/transformation/transform.js
index 2a5cbb26a2..a1c7a104ac 100644
--- a/lib/6to5/transformation/transform.js
+++ b/lib/6to5/transformation/transform.js
@@ -95,6 +95,7 @@ _.each({
   _moduleFormatter:          require("./transformers/_module-formatter"),
 
   typeofSymbol:              require("./transformers/optional-typeof-symbol"),
+  externalRuntime:           require("./transformers/optional-external-runtime"),
   coreAliasing:              require("./transformers/optional-core-aliasing"),
   undefinedToVoid:           require("./transformers/optional-undefined-to-void"),
 
diff --git a/lib/6to5/transformation/transformers/optional-external-runtime.js b/lib/6to5/transformation/transformers/optional-external-runtime.js
new file mode 100644
index 0000000000..a2f52667cf
--- /dev/null
+++ b/lib/6to5/transformation/transformers/optional-external-runtime.js
@@ -0,0 +1,11 @@
+exports.optional = true;
+
+// In theory, it would be more appropriate to do this in `manipulateOptions`,
+// but we need an identifier for the import and we can't get that before the
+// AST is built.
+exports.ast = {
+  enter: function (ast, file) {
+    file.opts.runtime = file.addImport(file.opts.runtime, "to5Runtime").name;
+    file.dynamicImports[file.dynamicImports.length - 1]._noInteropRequire = true;
+  }
+};