rstackjs · chenjiahan · Sep 26, 2026 · Sep 24, 2026 · Sep 26, 2026
diff --git a/packages/rstack/src/configLayers.ts b/packages/rstack/src/configLayers.ts
@@ -28,7 +28,7 @@ type ConfigArgs<K extends keyof Configs> = K extends 'app'
 
 /**
  * Resolve one tool from ordered, normalized config layers. Lint factories are
- * already wrapped by define.lint; merging belongs to the tool adapters.
+ * already wrapped by define.lint. This function does not merge the results.
  */
 export const resolveConfigLayers = async <K extends keyof Configs>(
   layers: readonly Configs[],
@@ -56,3 +56,10 @@ export const resolveConfigLayers = async <K extends keyof Configs>(
 
   return configs;
 };
+
+export const resolveRslintConfig = async (
+  layers: readonly Configs[],
+): Promise<RslintConfig | undefined> => {
+  const configs = await resolveConfigLayers(layers, 'lint');
+  return configs.length > 1 ? configs.flat() : configs[0];
+};
diff --git a/packages/rstack/src/rslintConfig.ts b/packages/rstack/src/rslintConfig.ts
@@ -3,24 +3,19 @@ import { join } from 'node:path';
 import { loadRstackConfig, type LoadedRstackConfig } from './config.ts';
 import type { RslintConfig } from '@rslint/core';
 import { color, logger } from 'rslog';
+import { resolveRslintConfig } from './configLayers.ts';
 
 // Expose the loaded config so `rs check` can pass it to fmt instead of loading
 // and executing the Rstack config a second time.
 export const loadedConfig: LoadedRstackConfig = await loadRstackConfig();
 const { configs } = loadedConfig;
-const lintDefinition = configs.lint;
+const lintConfig = await resolveRslintConfig([configs]);
 
-let lintConfig: RslintConfig;
-
-if (lintDefinition === undefined) {
+if (lintConfig === undefined) {
   logger.error(
     `No lint configuration found. Add ${color.cyan('define.lint(...)')} to your Rstack config file.`,
   );
   process.exit(1);
-} else if (typeof lintDefinition === 'function') {
-  lintConfig = await lintDefinition();
-} else {
-  lintConfig = lintDefinition;
 }
 
 const basePath = process.cwd();

diff --git a/packages/rstack/tests/config/lint-merge.test.ts b/packages/rstack/tests/config/lint-merge.test.ts
@@ -0,0 +1,26 @@
+import type { RslintConfig } from '@rslint/core';
+import { expect, test } from 'rstack/test';
+import { normalizeRstackConfig } from '../../src/config.ts';
+import { resolveRslintConfig } from '../../src/configLayers.ts';
+
+test('concatenates lint layers in order without merging entries', async () => {
+  const shared: RslintConfig = [
+    { ignores: ['dist/**'] },
+    [{ files: ['**/*.js'], rules: { 'no-debugger': 'error' } }],
+  ];
+  const project: RslintConfig = [{ rules: { 'no-debugger': 'off' } }];
+
+  const config = await resolveRslintConfig([
+    { lint: shared },
+    normalizeRstackConfig({ lint: () => Promise.resolve(project) }),
+  ]);
+
+  expect(config).toEqual([...shared, ...project]);
+});
+
+test('preserves a single lint config and distinguishes missing from empty', async () => {
+  const config: RslintConfig = [];
+
+  expect(await resolveRslintConfig([{}])).toBeUndefined();
+  expect(await resolveRslintConfig([{}, { lint: config }])).toBe(config);
+});