feat: basic extends support (#1)

Author: pi0

src/loader.ts

@@ -10,7 +10,7 @@ export interface LoadConfigOptions<T extends ConfigT=ConfigT> {
   name?: string
   cwd?: string
 
-  configFile?: false | string
+  configFile?: string
 
   rcFile?: false | string
   globalRc?: boolean
@@ -50,7 +50,7 @@ export async function loadConfig<T extends ConfigT=ConfigT> (opts: LoadConfigOpt
   }
 
   // Load config file
-  const { config, configPath } = await loadConfigFile(opts)
+  const { config, configPath } = await loadConfigFile(opts.cwd, opts.configFile)
   ctx.configPath = configPath
 
   // Load rc files
@@ -70,24 +70,54 @@ export async function loadConfig<T extends ConfigT=ConfigT> (opts: LoadConfigOpt
     opts.defaults
   ) as T
 
+  // Allow extending
+  await extendConfig(ctx.config, opts.configFile!, opts.cwd)
+  ctx.config = defu(
+    ctx.config,
+    ...ctx.config._extends.map(e => e.config)
+  ) as T
+
   // Return resolved context
   return ctx
 }
 
+async function extendConfig (config, configFile: string, cwd: string) {
+  console.log('Extending from', cwd)
+  config._extends = config._extends || []
+
+  const extendSources = (Array.isArray(config.extends) ? config.extends : [config.extends]).filter(Boolean)
+  for (const extendSource of extendSources) {
+    // TODO: Assuming extendSource is dir
+    const _cwd = resolve(cwd, extendSource)
+    const _config = await loadConfigFile(_cwd, configFile)
+    await extendConfig(_config.config, configFile, _cwd)
+    delete _config.config._extends
+    config._extends.push({
+      config: _config.config,
+      meta: {
+        cwd: _cwd,
+        configPath: _config.configPath
+      }
+    })
+  }
+
+  return config
+}
+
 const jiti = createJiti(null, { cache: false, interopDefault: true })
 
-async function loadConfigFile (opts: LoadConfigOptions) {
+async function loadConfigFile (cwd: string, configFile: string | false) {
   const res = {
     configPath: null,
     config: null
   }
 
-  if (!opts.configFile) {
+  if (!configFile) {
     return res
   }
 
   try {
-    res.configPath = jiti.resolve(resolve(opts.cwd, opts.configFile), { paths: [opts.cwd] })
+    res.configPath = jiti.resolve(resolve(cwd, configFile), { paths: [cwd] })
     res.config = jiti(res.configPath)
     if (typeof res.config === 'function') {
       res.config = await res.config()

test/fixture/base/foo.config.ts

@@ -0,0 +1,3 @@
+export default {
+  baseConfig: true
+}

test/fixture/foo.config.ts

@@ -1,4 +1,5 @@
 export default {
+  extends: './base',
   configFile: true,
   overriden: false
 }

test/index.test.ts

@@ -1,10 +1,13 @@
 import { fileURLToPath } from 'url'
+import { resolve } from 'pathe'
 import { expect, it, describe } from 'vitest'
 import { loadConfig } from '../src'
 
 describe('c12', () => {
   it('load fixture config', async () => {
     const fixtureDir = fileURLToPath(new URL('./fixture', import.meta.url))
+    const rFixture = (...segments: string[]) => resolve(fixtureDir, ...segments)
+
     const { config } = await loadConfig({
       cwd: fixtureDir,
       dotenv: true,
@@ -21,7 +24,17 @@ describe('c12', () => {
       configFile: true,
       rcFile: true,
       defaultConfig: true,
-      overriden: true
+      overriden: true,
+      baseConfig: true,
+      _extends: [
+        {
+          config: { baseConfig: true },
+          meta: {
+            configPath: rFixture('base/foo.config.ts'),
+            cwd: rFixture('base')
+          }
+        }
+      ]
     })
   })
 })