feat: add vite-layers

vite-layers/test/hooks.test.ts

@@ -0,0 +1,44 @@
+import { describe, expect, it } from 'vitest'
+import { createLayerHooks, registerLayerHooks } from '../src/hooks'
+import type { Layer, LayerStack } from '../src/types'
+
+const fakeStack = (): LayerStack => ({ merged: {}, layers: [] })
+
+describe('layer hooks', () => {
+  it('accumulates layer hooks base-first, then programmatic, and runs serially', async () => {
+    const hooks = createLayerHooks()
+    const order: string[] = []
+    // layers are high→low; registration is base-first (reversed), programmatic last.
+    const layers: Pick<Layer, 'config'>[] = [
+      { config: { hooks: { 'layers:resolved': () => void order.push('high') } } },
+      { config: { hooks: { 'layers:resolved': () => void order.push('low') } } },
+    ]
+    registerLayerHooks(hooks, layers, { 'layers:resolved': () => void order.push('prog') })
+    await hooks.callHook('layers:resolved', fakeStack())
+    expect(order).toEqual(['low', 'high', 'prog'])
+  })
+
+  it('handlers mutate the shared argument (mutation-style)', async () => {
+    const hooks = createLayerHooks()
+    const layers: Pick<Layer, 'config'>[] = [
+      { config: { hooks: { 'layers:resolved': s => void ((s.merged.features ??= {}).x = 1) } } },
+    ]
+    registerLayerHooks(hooks, layers)
+    const stack = fakeStack()
+    await hooks.callHook('layers:resolved', stack)
+    expect((stack.merged.features as Record<string, unknown>).x).toBe(1)
+  })
+
+  it('awaits async handlers serially', async () => {
+    const hooks = createLayerHooks()
+    const order: string[] = []
+    const layers: Pick<Layer, 'config'>[] = [
+      // high layer (registered last): async, must still complete before callHook resolves
+      { config: { hooks: { 'layers:resolved': async () => { await Promise.resolve(); order.push('high') } } } },
+      { config: { hooks: { 'layers:resolved': () => void order.push('low') } } },
+    ]
+    registerLayerHooks(hooks, layers)
+    await hooks.callHook('layers:resolved', fakeStack())
+    expect(order).toEqual(['low', 'high'])
+  })
+})