remove experimental option in favor of a stage option

src/babel/transformation/file/option-parsers.js

@@ -11,6 +11,10 @@ export function transformerList(key, val) {
   return transform._ensureTransformerNames(key, val);
 }
 
+export function number(key, val) {
+  return +val;
+}
+
 export function boolean(key, val) {
   return !!val;
 }

src/babel/transformation/file/options.json

@@ -42,11 +42,11 @@
     "hidden": true
   },
 
-  "experimental": {
-    "description": "Enable all ES7+ transformers",
+  "stage": {
+    "description": "",
     "shorthand": "e",
-    "type": "boolean",
-    "default": false
+    "type": "number",
+    "default": 2
   },
 
   "blacklist": {

src/babel/transformation/transformer-pass.js

@@ -32,8 +32,9 @@ export default class TransformerPass {
     var whitelist = opts.whitelist;
     if (whitelist) return includes(whitelist, key);
 
-    // experimental
-    if (transformer.metadata.experimental && opts.experimental) return true;
+    // stage
+    var stage = transformer.metadata.stage;
+    if (stage != null && stage >= opts.stage) return true;
 
     // optional
     if (transformer.metadata.optional && !includes(opts.optional, key)) return false;

src/babel/transformation/transformer.js

@@ -30,6 +30,10 @@ export default class Transformer {
     this.post              = take("post");
     this.pre               = take("pre");
 
+    if (this.metadata.stage != null) {
+      this.metadata.optional = true;
+    }
+
     this.handlers = this.normalize(transformer);
     this.opts     ||= {};
     this.key      = transformerKey;

src/babel/transformation/transformers/es7/async-functions.js

@@ -1,6 +1,5 @@
 export var metadata = {
-  experimental: true,
-  optional: true
+  stage: 1
 };
 
 export function check() {

src/babel/transformation/transformers/es7/class-properties.js

@@ -1,6 +1,5 @@
 export var metadata = {
-  experimental: true,
-  optional: true
+  stage: 0
 };
 
 export function check() {

src/babel/transformation/transformers/es7/comprehensions.js

@@ -4,8 +4,7 @@ import * as util from  "../../../util";
 import * as t from "../../../types";
 
 export var metadata = {
-  experimental: true,
-  optional: true
+  stage: 0
 };
 
 export function ComprehensionExpression(node, parent, scope, file) {

src/babel/transformation/transformers/es7/decorators.js

@@ -1,4 +1,5 @@
 export var metadata = {
   experimental: true,
-  optional: true
+  optional: true,
+  stage: 1
 };

src/babel/transformation/transformers/es7/do-expressions.js

@@ -2,7 +2,8 @@ import * as t from "../../../types";
 
 export var metadata = {
   experimental: true,
-  optional: true
+  optional: true,
+  stage: 0
 };
 
 export var check = t.isDoExpression;

src/babel/transformation/transformers/es7/exponentiation-operator.js

@@ -3,6 +3,10 @@
 import build from "../../helpers/build-binary-assignment-operator-transformer";
 import * as t from "../../../types";
 
+export var metadata = {
+  stage: 2
+};
+
 var MATH_POW = t.memberExpression(t.identifier("Math"), t.identifier("pow"));
 
 build(exports, {

src/babel/transformation/transformers/es7/export-extensions.js

@@ -2,6 +2,10 @@
 
 import * as t from "../../../types";
 
+export var metadata = {
+  stage: 0
+};
+
 export function check(node) {
   return t.isExportDefaultSpecifier(node) || t.isExportNamespaceSpecifier(node);
 }

src/babel/transformation/transformers/es7/object-rest-spread.js

@@ -3,8 +3,7 @@
 import * as t from "../../../types";
 
 export var metadata = {
-  experimental: true,
-  optional: true
+  stage: 1
 };
 
 export function manipulateOptions(opts) {