Correctly handle relative browserslistConfigFile paths (#13031)

* Correctly handle relative `browserslistConfigFile`

* Fix flow

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

@@ -19,6 +19,8 @@ import type {
   PluginItem,
 } from "./validation/options";
 
+import { resolveBrowserslistConfigFile } from "./resolve-targets";
+
 // Represents a config object and functions to lazily load the descriptors
 // for the plugins and presets so we don't load the plugins/presets unless
 // the options object actually ends up being applicable.
@@ -71,6 +73,19 @@ function* handlerOf<T>(value: T): Handler<T> {
   return value;
 }
 
+function optionsWithResolvedBrowserslistConfigFile(
+  options: ValidatedOptions,
+  dirname: string,
+): ValidatedOptions {
+  if (typeof options.browserslistConfigFile === "string") {
+    options.browserslistConfigFile = resolveBrowserslistConfigFile(
+      options.browserslistConfigFile,
+      dirname,
+    );
+  }
+  return options;
+}
+
 /**
  * Create a set of descriptors from a given options object, preserving
  * descriptor identity based on the identity of the plugin/preset arrays
@@ -83,7 +98,7 @@ export function createCachedDescriptors(
 ): OptionsAndDescriptors {
   const { plugins, presets, passPerPreset } = options;
   return {
-    options,
+    options: optionsWithResolvedBrowserslistConfigFile(options, dirname),
     plugins: plugins
       ? () => createCachedPluginDescriptors(plugins, dirname)(alias)
       : () => handlerOf([]),
@@ -112,7 +127,7 @@ export function createUncachedDescriptors(
   let presets;
 
   return {
-    options,
+    options: optionsWithResolvedBrowserslistConfigFile(options, dirname),
     *plugins() {
       if (!plugins) {
         plugins = yield* createPluginDescriptors(

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

@@ -126,7 +126,7 @@ export default function* loadPrivatePartialConfig(
 
   const options: NormalizedOptions = {
     ...merged,
-    targets: resolveTargets(merged, absoluteRootDir, absoluteRootDir),
+    targets: resolveTargets(merged, absoluteRootDir),
 
     // Tack the passes onto the object itself so that, if this object is
     // passed back to Babel a second time, it will be in the right structure

packages/babel-core/src/config/resolve-targets-browser.js

@@ -3,12 +3,19 @@
 import type { ValidatedOptions } from "./validation/options";
 import getTargets, { type Targets } from "@babel/helper-compilation-targets";
 
+export function resolveBrowserslistConfigFile(
+  // eslint-disable-next-line no-unused-vars
+  browserslistConfigFile: string,
+  // eslint-disable-next-line no-unused-vars
+  configFilePath: string,
+): string | void {
+  return undefined;
+}
+
 export function resolveTargets(
   options: ValidatedOptions,
   // eslint-disable-next-line no-unused-vars
   root: string,
-  // eslint-disable-next-line no-unused-vars
-  configFilePath: string | void,
 ): Targets {
   let { targets } = options;
   if (typeof targets === "string" || Array.isArray(targets)) {

packages/babel-core/src/config/resolve-targets.js

@@ -11,10 +11,16 @@ import type { ValidatedOptions } from "./validation/options";
 import path from "path";
 import getTargets, { type Targets } from "@babel/helper-compilation-targets";
 
+export function resolveBrowserslistConfigFile(
+  browserslistConfigFile: string,
+  configFileDir: string,
+): string | void {
+  return path.resolve(configFileDir, browserslistConfigFile);
+}
+
 export function resolveTargets(
   options: ValidatedOptions,
   root: string,
-  configFilePath: string = root,
 ): Targets {
   let { targets } = options;
   if (typeof targets === "string" || Array.isArray(targets)) {
@@ -25,13 +31,17 @@ export function resolveTargets(
     targets = { ...targets, esmodules: "intersect" };
   }
 
+  const { browserslistConfigFile } = options;
   let configFile;
-  if (typeof options.browserslistConfigFile === "string") {
+  let ignoreBrowserslistConfig = false;
-    configFile = path.resolve(configFilePath, options.browserslistConfigFile);
+  if (typeof browserslistConfigFile === "string") {
+    configFile = browserslistConfigFile;
+  } else {
+    ignoreBrowserslistConfig = browserslistConfigFile === false;
   }
 
   return getTargets((targets: any), {
-    ignoreBrowserslistConfig: options.browserslistConfigFile === false,
+    ignoreBrowserslistConfig,
     configFile,
     configPath: root,
     browserslistEnv: options.browserslistEnv,

packages/babel-core/test/targets.js

@@ -100,19 +100,6 @@ describe("browserslist", () => {
     ).toEqual({ chrome: "80.0.0" });
   });
 
-  // TODO: browserslistConfig is currently resolved starting from the root
-  // rather than from the config file.
-  // eslint-disable-next-line jest/no-disabled-tests
-  it.skip("loads nested .browserslistrc files if explicitly specified", () => {
-    expect(
-      loadOptions({
-        cwd: join(cwd, "fixtures", "targets"),
-        filename: "./node_modules/dep/test.js",
-        babelrcRoots: ["./node_modules/dep/"],
-      }).targets,
-    ).toEqual({ edge: "14.0.0" });
-  });
-
   describe("browserslistConfigFile", () => {
     it("can disable config loading", () => {
       expect(
@@ -132,16 +119,26 @@ describe("browserslist", () => {
       ).toEqual({ firefox: "74.0.0" });
     });
 
-    it("is relative to the project root", () => {
+    it("is relative to the cwd even if specifying 'root'", () => {
       expect(
         loadOptions({
           cwd: join(cwd, "fixtures", "targets"),
           root: "..",
           filename: "./nested/test.js",
-          browserslistConfigFile: "./targets/.browserslistrc-firefox",
+          browserslistConfigFile: "./.browserslistrc-firefox",
         }).targets,
       ).toEqual({ firefox: "74.0.0" });
     });
+
+    it("is relative to the config files that defines it", () => {
+      expect(
+        loadOptions({
+          cwd: join(cwd, "fixtures", "targets"),
+          filename: "./node_modules/dep/test.js",
+          babelrcRoots: ["./node_modules/dep/"],
+        }).targets,
+      ).toEqual({ edge: "14.0.0" });
+    });
   });
 
   describe("browserslistEnv", () => {