feat: add vite-layers

vite-layers/test/config.test.ts

@@ -0,0 +1,54 @@
+import { fileURLToPath } from 'node:url'
+import { dirname, resolve } from 'node:path'
+import { describe, expect, it } from 'vitest'
+import { resolveLayerStack } from '../src/config'
+
+const here = dirname(fileURLToPath(import.meta.url))
+const fixture = (p: string) => resolve(here, 'fixtures', p)
+const toPosix = (p: string) => p.replace(/\\/g, '/')
+const names = (s: { layers: { name: string }[] }) => s.layers.map(l => l.name)
+
+describe('resolveLayerStack', () => {
+  it('orders the stack project-first (layers[0] = project), then extends depth-first', async () => {
+    const stack = await resolveLayerStack(fixture('stack/app'))
+    expect(names(stack)).toEqual(['app', 'base', 'core'])
+    expect(stack.layers[0].name).toBe('app')
+  })
+
+  it('merges configs with project winning on key collision (defu first-wins)', async () => {
+    const { merged } = await resolveLayerStack(fixture('stack/app'))
+    const features = merged.features as Record<string, unknown>
+    expect(features.shared).toBe('app') // app overrides base overrides core
+    expect(features).toMatchObject({ app: true, base: true, core: true })
+  })
+
+  it('resolves srcDir per layer (default "src")', async () => {
+    const stack = await resolveLayerStack(fixture('stack/app'))
+    expect(stack.layers[0].srcDir).toBe(toPosix(resolve(fixture('stack/app'), 'src')))
+  })
+
+  it('dedupes a diamond by rootDir (shared base appears once, first-wins position)', async () => {
+    const stack = await resolveLayerStack(fixture('diamond/app'))
+    expect(names(stack)).toEqual(['app', 'b', 'd', 'c'])
+    expect(names(stack).filter(n => n === 'd')).toHaveLength(1)
+  })
+
+  it('survives a cycle (A→B→A) without stack overflow [improvement over raw c12]', async () => {
+    const stack = await resolveLayerStack(fixture('cycle/x'))
+    expect(names(stack)).toEqual(['x', 'y'])
+  })
+
+  it('auto-scans layers/* with descending priority (Z > A / higher numeric prefix)', async () => {
+    const stack = await resolveLayerStack(fixture('autoscan'))
+    // project first, then 2.z-layer before 1.a-layer (descending sort)
+    expect(names(stack)).toEqual(['root', '2.z-layer', '1.a-layer'])
+  })
+
+  it('applies per-layer $production/$development overrides by Vite mode', async () => {
+    const dev = await resolveLayerStack(fixture('env/app'), { mode: 'development' })
+    const prod = await resolveLayerStack(fixture('env/app'), { mode: 'production' })
+    expect((dev.merged.features as Record<string, unknown>).flag).toBe('dev') // no $development block
+    expect((prod.merged.features as Record<string, unknown>).flag).toBe('prod') // $production wins
+    expect((prod.merged.features as Record<string, unknown>).shared).toBe(true) // base flags preserved
+  })
+})