feat: allow extending from multiple keys

resolves #24

Author: pi0

src/loader.ts

@@ -40,7 +40,7 @@ export interface LoadConfigOptions<T extends InputConfig=InputConfig> {
   resolve?: (id: string, opts: LoadConfigOptions) => null | ResolvedConfig | Promise<ResolvedConfig | null>
 
   extend?: false | {
-    extendKey?: string
+    extendKey?: string | string[]
   }
 }
 
@@ -128,12 +128,14 @@ export async function loadConfig<T extends InputConfig=InputConfig> (opts: LoadC
 
 async function extendConfig (config, opts: LoadConfigOptions) {
   config._layers = config._layers || []
-  if (!opts.extend) {
-    return
+  if (!opts.extend) { return }
+  let keys = opts.extend.extendKey
+  if (typeof keys === 'string') { keys = [keys] }
+  const extendSources = []
+  for (const key of keys) {
+    extendSources.push(...(Array.isArray(config[key]) ? config[key] : [config[key]]).filter(Boolean))
+    delete config[key]
   }
-  const key = opts.extend.extendKey
-  const extendSources = (Array.isArray(config[key]) ? config[key] : [config[key]]).filter(Boolean)
-  delete config[key]
   for (const extendSource of extendSources) {
     const _config = await resolveConfig(extendSource, opts)
     if (!_config.config) {

test/fixture/config.ts

@@ -1,6 +1,6 @@
 export default {
+  theme: './theme',
   extends: [
-    './theme',
     './config.dev',
     'c12-npm-test'
   ],

test/index.test.ts

@@ -11,6 +11,9 @@ describe('c12', () => {
     const { config, layers } = await loadConfig({
       cwd: r('./fixture'),
       dotenv: true,
+      extend: {
+        extendKey: ['theme', 'extends']
+      },
       resolve: (id) => {
         if (id === 'virtual') {
           return { config: { virtual: true } }
@@ -67,11 +70,11 @@ describe('c12', () => {
             },
             "configFile": true,
             "extends": [
-              "./theme",
               "./config.dev",
               "c12-npm-test",
             ],
             "overriden": false,
+            "theme": "./theme",
           },
           "configFile": "config",
           "cwd": "<path>/fixture",
@@ -82,11 +85,6 @@ describe('c12', () => {
           },
           "configFile": ".configrc",
         },
-        {
-          "config": {
-            "virtual": true,
-          },
-        },
         {
           "config": {
             "colors": {
@@ -111,6 +109,11 @@ describe('c12', () => {
           "configFile": "<path>/fixture/base/config.ts",
           "cwd": "<path>/fixture/base",
         },
+        {
+          "config": {
+            "virtual": true,
+          },
+        },
         {
           "config": {
             "devConfig": true,