Centralize the plugin/configuration API object.

packages/babel-core/src/config/caching.js

@@ -1,6 +1,6 @@
 // @flow
 
-type SimpleCacheConfigurator = SimpleCacheConfiguratorFn &
+export type SimpleCacheConfigurator = SimpleCacheConfiguratorFn &
   SimpleCacheConfiguratorObj;
 
 type SimpleCacheConfiguratorFn = {

packages/babel-core/src/config/files/configuration.js

@@ -6,6 +6,7 @@ import fs from "fs";
 import json5 from "json5";
 import resolve from "resolve";
 import { makeStrongCache, type CacheConfigurator } from "../caching";
+import makeAPI from "../helpers/config-api";
 
 const debug = buildDebug("babel:config:loading:files:configuration");
 
@@ -150,12 +151,7 @@ const readConfigJS = makeStrongCache(
     }
 
     if (typeof options === "function") {
-      options = options({
-        cache: cache.simple(),
-        // Expose ".env()" so people can easily get the same env that we expose using the "env" key.
-        env: () => cache.using(data => data.envName),
-        async: () => false,
-      });
+      options = options(makeAPI(cache));
 
       if (!cache.configured()) throwConfigError();
     }

packages/babel-core/src/config/helpers/config-api.js

@@ -0,0 +1,19 @@
+// @flow
+import type { CacheConfigurator, SimpleCacheConfigurator } from "../caching";
+
+export type PluginAPI = {
+  cache: SimpleCacheConfigurator,
+  env: () => string,
+  async: () => boolean,
+};
+
+export default function makeAPI(
+  cache: CacheConfigurator<{ envName: string }>,
+): PluginAPI {
+  return {
+    cache: cache.simple(),
+    // Expose ".env()" so people can easily get the same env that we expose using the "env" key.
+    env: () => cache.using(data => data.envName),
+    async: () => false,
+  };
+}

packages/babel-core/src/config/index.js

@@ -16,6 +16,7 @@ import { makeWeakCache, type CacheConfigurator } from "./caching";
 import { getEnv } from "./helpers/environment";
 import { validate, type ValidatedOptions } from "./validation/options";
 import { validatePluginObject } from "./validation/plugins";
+import makeAPI from "./helpers/config-api";
 
 type LoadedDescriptor = {
   value: {},
@@ -202,11 +203,7 @@ const loadDescriptor = makeWeakCache(
 
     let item = value;
     if (typeof value === "function") {
-      const api = Object.assign(Object.create(context), {
-        cache: cache.simple(),
-        env: () => cache.using(data => data.envName),
-        async: () => false,
-      });
+      const api = Object.assign(Object.create(context), makeAPI(cache));
 
       try {
         item = value(api, options, dirname);