From 25d2f59018d395c4bb65ef1b28fcf6a8b83bbd14 Mon Sep 17 00:00:00 2001
From: Logan Smyth <loganfsmyth@gmail.com>
Date: Thu, 16 Aug 2018 17:35:23 -0700
Subject: [PATCH] Ensure that presets properly flatten their options.

---
 packages/babel-core/src/config/config-chain.js | 16 +++++++++++++++-
 1 file changed, 15 insertions(+), 1 deletion(-)

diff --git a/packages/babel-core/src/config/config-chain.js b/packages/babel-core/src/config/config-chain.js
index e81ca81f74..ee48361708 100644
--- a/packages/babel-core/src/config/config-chain.js
+++ b/packages/babel-core/src/config/config-chain.js
@@ -55,7 +55,21 @@ export type ConfigContext = {
 /**
  * Build a config chain for a given preset.
  */
-export const buildPresetChain: (
+export function buildPresetChain(
+  arg: PresetInstance,
+  context: *,
+): ConfigChain | null {
+  const chain = buildPresetChainWalker(arg, context);
+  if (!chain) return null;
+
+  return {
+    plugins: dedupDescriptors(chain.plugins),
+    presets: dedupDescriptors(chain.presets),
+    options: chain.options,
+  };
+}
+
+export const buildPresetChainWalker: (
   arg: PresetInstance,
   context: *,
 ) => * = makeChainWalker({