cherry-pick and fix merge conflicts in #2695 - closes #2695

packages/babel-core/src/transformation/file/options/config.js

@@ -84,6 +84,11 @@ module.exports = {
     type: "boolean"
   },
 
+  extends: {
+    type: "string",
+    hidden: true
+  },
+
   comments: {
     type: "boolean",
     default: true,

packages/babel-core/src/transformation/file/options/option-manager.js

@@ -128,8 +128,10 @@ export default class OptionManager {
     });
   }
 
-  addConfig(loc: string, key?: string, json = json5) {
-    if (this.resolvedConfigs.indexOf(loc) >= 0) return;
+  addConfig(loc: string, key?: string, json = json5): boolean {
+    if (this.resolvedConfigs.indexOf(loc) >= 0) {
+      return false;
+    }
 
     let content = fs.readFileSync(loc, "utf8");
     let opts;
@@ -144,6 +146,8 @@ export default class OptionManager {
 
     this.mergeOptions(opts, loc);
     this.resolvedConfigs.push(loc);
+
+    return !!opts;
   }
 
   /**
@@ -272,8 +276,7 @@ export default class OptionManager {
 
         let pkgLoc = path.join(loc, PACKAGE_FILENAME);
         if (exists(pkgLoc)) {
-          this.addConfig(pkgLoc, "babel", JSON);
-          foundConfig = true;
+          foundConfig = this.addConfig(pkgLoc, "babel", JSON);
         }
       }