From 5ceb4fcc65c44bd3e655d39fca175f2d91f60994 Mon Sep 17 00:00:00 2001
From: neverland <chenjiahan.jait@bytedance.com>
Date: Thu, 1 Oct 2026 09:45:54 +0800
Subject: [PATCH 1/2] refactor(config): shallowly merge format config layers

---
 packages/rstack/src/fmt/cli.ts           |  2 +-
 packages/rstack/src/fmt/config.ts        | 14 +++++---
 packages/rstack/tests/fmt/config.test.ts | 45 ++++++++++++++++++++++++
 3 files changed, 55 insertions(+), 6 deletions(-)

diff --git a/packages/rstack/src/fmt/cli.ts b/packages/rstack/src/fmt/cli.ts
index f4c96402..ec47edf2 100644
--- a/packages/rstack/src/fmt/cli.ts
+++ b/packages/rstack/src/fmt/cli.ts
@@ -253,7 +253,7 @@ const loadFmtConfig = async (
     loadedConfig ?? (await loadRstackConfig({ cwd }));
 
   return resolveFmtConfig({
-    definition: configs.fmt,
+    layers: [configs],
     configFilePath: filePath,
     cwd,
   });
diff --git a/packages/rstack/src/fmt/config.ts b/packages/rstack/src/fmt/config.ts
index 5e4c543d..54d735b7 100644
--- a/packages/rstack/src/fmt/config.ts
+++ b/packages/rstack/src/fmt/config.ts
@@ -1,15 +1,16 @@
 import { dirname } from 'node:path';
 import micromatch from 'micromatch';
+import type { Configs } from '../config.ts';
+import { resolveConfigLayers } from '../configLayers.ts';
 import { createRelativePathResolver } from './pathHelpers.ts';
 import type {
   FmtConfig,
-  FmtConfigDefinition,
   ResolvedFmtConfig,
   ResolvedFmtOptions,
 } from './types.ts';
 
 type ResolveFmtConfigOptions = {
-  definition: FmtConfigDefinition | undefined;
+  layers: readonly Configs[];
   configFilePath: string | null;
   cwd: string;
 };
@@ -150,14 +151,17 @@ const createOptionsResolver = (
   };
 };
 
-/** Resolves a formatter config definition and its project root. */
+/** Resolves formatter config layers and their project root. */
 const resolveFmtConfig = async ({
-  definition,
+  layers,
   configFilePath,
   cwd,
 }: ResolveFmtConfigOptions): Promise<ResolvedFmtConfig> => {
+  const configs = await resolveConfigLayers(layers, 'fmt');
   const config =
-    typeof definition === 'function' ? await definition() : definition;
+    configs.length > 1
+      ? (Object.assign({}, ...configs) as FmtConfig)
+      : configs[0];
   const rootPath = configFilePath ? dirname(configFilePath) : cwd;
 
   return normalizeFmtConfig(config, rootPath);
diff --git a/packages/rstack/tests/fmt/config.test.ts b/packages/rstack/tests/fmt/config.test.ts
index eb5a9b28..fa3bc5ba 100644
--- a/packages/rstack/tests/fmt/config.test.ts
+++ b/packages/rstack/tests/fmt/config.test.ts
@@ -3,10 +3,55 @@ import { expect, test } from 'rstack/test';
 import {
   createOptionsResolver,
   normalizeFmtConfig,
+  resolveFmtConfig,
 } from '../../src/fmt/config.ts';
 
 const rootPath = path.join(import.meta.dirname, 'project');
 
+test('shallowly merges fmt layers before normalizing options and overrides', async () => {
+  const config = await resolveFmtConfig({
+    layers: [
+      {
+        fmt: {
+          singleQuote: true,
+          semi: true,
+          plugins: ['shared-plugin'],
+          ignorePatterns: ['dist/**'],
+          overrides: [{ files: '*.ts', options: { tabWidth: 8 } }],
+          pluginOptions: { shared: true, project: false },
+        },
+      },
+      {
+        fmt: () =>
+          Promise.resolve({
+            semi: false,
+            plugins: ['project-plugin'],
+            ignorePatterns: ['generated/**'],
+            overrides: [{ files: '*.ts', options: { semi: true } }],
+            pluginOptions: { project: true },
+          }),
+      },
+    ],
+    configFilePath: path.join(rootPath, 'rstack.config.ts'),
+    cwd: path.dirname(rootPath),
+  });
+
+  expect(config.rootPath).toBe(rootPath);
+  expect(config.baseOptions).toEqual({
+    singleQuote: true,
+    semi: false,
+    plugins: ['project-plugin'],
+    pluginOptions: { project: true },
+  });
+  expect(config.ignorePatterns).toEqual(['generated/**']);
+  expect(
+    createOptionsResolver(config)(path.join(rootPath, 'index.ts')),
+  ).toEqual({
+    ...config.baseOptions,
+    semi: true,
+  });
+});
+
 test('reuses base options when no override matches', () => {
   const config = normalizeFmtConfig(
     {

From e38c6336b5b2ff3fe2c9428d03cae1f575d99c51 Mon Sep 17 00:00:00 2001
From: neverland <chenjiahan.jait@bytedance.com>
Date: Thu, 1 Oct 2026 17:04:51 +0800
Subject: [PATCH 2/2] test(config): assert the complete merged format config

---
 packages/rstack/tests/fmt/config.test.ts | 28 +++++++++++++-----------
 1 file changed, 15 insertions(+), 13 deletions(-)

diff --git a/packages/rstack/tests/fmt/config.test.ts b/packages/rstack/tests/fmt/config.test.ts
index fa3bc5ba..978f1350 100644
--- a/packages/rstack/tests/fmt/config.test.ts
+++ b/packages/rstack/tests/fmt/config.test.ts
@@ -36,19 +36,21 @@ test('shallowly merges fmt layers before normalizing options and overrides', asy
     cwd: path.dirname(rootPath),
   });
 
-  expect(config.rootPath).toBe(rootPath);
-  expect(config.baseOptions).toEqual({
-    singleQuote: true,
-    semi: false,
-    plugins: ['project-plugin'],
-    pluginOptions: { project: true },
-  });
-  expect(config.ignorePatterns).toEqual(['generated/**']);
-  expect(
-    createOptionsResolver(config)(path.join(rootPath, 'index.ts')),
-  ).toEqual({
-    ...config.baseOptions,
-    semi: true,
+  expect(config).toEqual({
+    rootPath,
+    baseOptions: {
+      singleQuote: true,
+      semi: false,
+      plugins: ['project-plugin'],
+      pluginOptions: { project: true },
+    },
+    ignorePatterns: ['generated/**'],
+    overrides: [
+      {
+        matches: expect.any(Function) as unknown,
+        options: { semi: true },
+      },
+    ],
   });
 });