🐛 Fix poor merge behavior of Config + overrides (#1519)

packages/core/src/service/Config.ts

@@ -1,6 +1,6 @@
 import rfdc from 'rfdc'
 import type { ExternalEventEmitter } from '../common/index.js'
-import { Arrayable, bufferToString, TypePredicates } from '../common/index.js'
+import { Arrayable, bufferToString, merge, TypePredicates } from '../common/index.js'
 import { ErrorSeverity } from '../source/index.js'
 import { FileCategories, RegistryCategories } from '../symbol/index.js'
 import type { Project } from './Project.js'
@@ -504,13 +504,6 @@ export class ConfigService implements ExternalEventEmitter {
 	}
 
 	public static merge(base: Config, ...overrides: any[]): Config {
-		// FIXME
-		const ans = rfdc()(base)
-		for (const override of overrides) {
-			for (const key of ['env', 'format', 'lint', 'snippet'] as const) {
-				ans[key] = { ...ans[key], ...override[key] } as any
-			}
-		}
-		return ans
+		return overrides.reduce(merge, rfdc()(base))
 	}
 }

packages/core/test/service/Config.spec.ts

@@ -0,0 +1,56 @@
+import assert from 'assert'
+import { describe, it } from 'mocha'
+import snapshot from 'snap-shot-it'
+import type { Config } from '../../lib/index.js'
+import { ConfigService } from '../../lib/index.js'
+
+describe('ConfigService', () => {
+	describe('merge()', () => {
+		const base = {
+			env: {
+				dataSource: 'GitHub',
+				dependencies: [
+					'@vanilla-mcdoc',
+				],
+				feature: {
+					a: true,
+					b: false,
+				},
+			},
+		} as unknown as Config
+
+		it('Should create a clone of the base object', async () => {
+			const merged = ConfigService.merge(base)
+			merged.env.dataSource = 'new string'
+			assert.notEqual(base.env.dataSource, merged.env.dataSource)
+		})
+
+		it('Should merge empty overrides correctly', async () => {
+			snapshot(ConfigService.merge(base))
+			snapshot(ConfigService.merge(base, {}))
+			snapshot(ConfigService.merge(base, {}, {}))
+		})
+
+		it('Should merge top-level overrides correctly', async () => {
+			snapshot(ConfigService.merge(base, { test: true }))
+		})
+
+		it('Should merge nested overrides correctly', async () => {
+			snapshot(ConfigService.merge(base, { env: { dataSource: 'TEST' } }))
+			snapshot(ConfigService.merge(base, { env: { feature: {} } }))
+			snapshot(ConfigService.merge(base, { env: { feature: { b: true } } }))
+			snapshot(ConfigService.merge(base, { env: { feature: { b: true, c: 9 } } }))
+			snapshot(ConfigService.merge(base, { env: { dependencies: [] } }))
+		})
+
+		it('Should merge multiple overrides correctly', async () => {
+			snapshot(
+				ConfigService.merge(
+					base,
+					{ env: { dataSource: 'TEST', foo: 'bar' } },
+					{ env: { foo: 'qux', erm: 3 } },
+				),
+			)
+		})
+	})
+})