6.0.0

I'm extremely stupid and didn't commit as I go. To anyone reading this
I'm extremely sorry. A lot of these changes are very broad and I plan on
releasing Babel 6.0.0 today live on stage at Ember Camp London so I'm
afraid I couldn't wait. If you're ever in London I'll buy you a beer
(or assorted beverage!) to make up for it, also I'll kiss your feet and
give you a back massage, maybe.

packages/babel-helper-builder-conditional-assignment-operator-visitor/README.md

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+# babel-helper-builder-conditional-assignment-operator-visitor
+
+## Usage
+
+TODO

packages/babel-helper-builder-conditional-assignment-operator-visitor/package.json

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+{
+  "name": "babel-helper-builder-conditional-assignment-operator-visitor",
+  "version": "1.0.0",
+  "description": "",
+  "repository": "babel/babel",
+  "license": "MIT",
+  "main": "lib/index.js",
+  "dependencies": {
+    "babel-helper-explode-assignable-expression": "^5.8.20",
+    "babel-runtime": "^5.8.20",
+    "babel-types": "^5.8.20"
+  }
+}

packages/babel-helper-builder-conditional-assignment-operator-visitor/src/index.js

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+/* @flow */
+
+import explode from "babel-helper-explode-assignable-expression";
+import * as t from "babel-types";
+
+export default function (
+  exports: Object,
+  opts: {
+    build: Function;
+    is: Function;
+  },
+) {
+  let buildAssignment = function (left, right) {
+    return t.assignmentExpression("=", left, right);
+  };
+
+  exports.ExpressionStatement = function (path, file) {
+    // hit the `AssignmentExpression` one below
+    if (path.isCompletionRecord()) return;
+
+    let expr = path.node.expression;
+    if (!opts.is(expr, file)) return;
+
+    let nodes = [];
+
+    let exploded = explode(expr.left, nodes, file, path.scope);
+
+    nodes.push(t.ifStatement(
+      opts.build(exploded.uid, file),
+      t.expressionStatement(buildAssignment(exploded.ref, expr.right))
+    ));
+
+    return nodes;
+  };
+
+  exports.AssignmentExpression = function (path, file) {
+    let node = path.node;
+    if (!opts.is(node, file)) return;
+
+    let nodes    = [];
+    let exploded = explode(node.left, nodes, file, path.scope);
+
+    nodes.push(t.logicalExpression(
+      "&&",
+      opts.build(exploded.uid, file),
+      buildAssignment(exploded.ref, node.right)
+    ));
+
+    // todo: duplicate expression node
+    nodes.push(exploded.ref);
+
+    return nodes;
+  };
+}