fix(custom-element): ensure correct order of nested component styles

packages/runtime-dom/__tests__/customElement.spec.ts

@@ -791,6 +791,39 @@ describe('defineCustomElement', () => {
       assertStyles(el, [`div { color: blue; }`, `div { color: red; }`])
     })
 
+    test('child components styles should before parent styles', async () => {
+      const Baz = () => h(Bar)
+      const Bar = defineComponent({
+        styles: [`div { color: green; }`],
+        render() {
+          return 'bar'
+        },
+      })
+      const WarpperBar = defineComponent({
+        styles: [`div { color: blue; }`],
+        render() {
+          return h(Baz)
+        },
+      })
+      const WBaz = () => h(WarpperBar)
+      const Foo = defineCustomElement({
+        styles: [`div { color: red; }`],
+        render() {
+          return [h(Baz), h(WBaz)]
+        },
+      })
+      customElements.define('my-el-with-wrapper-child-styles', Foo)
+      container.innerHTML = `<my-el-with-wrapper-child-styles></my-el-with-wrapper-child-styles>`
+      const el = container.childNodes[0] as VueElement
+
+      // inject order should be child -> parent
+      assertStyles(el, [
+        `div { color: green; }`,
+        `div { color: blue; }`,
+        `div { color: red; }`,
+      ])
+    })
+
     test('with nonce', () => {
       const Foo = defineCustomElement(
         {

packages/runtime-dom/src/apiCustomElement.ts

@@ -229,7 +229,7 @@ export class VueElement
   private _connected = false
   private _resolved = false
   private _numberProps: Record<string, true> | null = null
-  private _styleChildren = new WeakSet()
+  private _styleChildren = new WeakMap<ConcreteComponent, HTMLStyleElement[]>()
   private _pendingResolve: Promise<void> | undefined
   private _parent: VueElement | undefined
   /**
@@ -581,18 +581,28 @@ export class VueElement
     owner?: ConcreteComponent,
   ) {
     if (!styles) return
+    const styleList: HTMLStyleElement[] = []
     if (owner) {
-      if (owner === this._def || this._styleChildren.has(owner)) {
+      if (owner === this._def) {
         return
       }
-      this._styleChildren.add(owner)
+      const styleChild = this._styleChildren.get(owner)
+      if (styleChild) {
+        this.shadowRoot!.prepend(...styleChild)
+        return
+      }
+      this._styleChildren.set(owner, styleList)
     }
+
     const nonce = this._nonce
     for (let i = styles.length - 1; i >= 0; i--) {
       const s = document.createElement('style')
       if (nonce) s.setAttribute('nonce', nonce)
       s.textContent = styles[i]
       this.shadowRoot!.prepend(s)
+      if (owner) {
+        styleList.unshift(s)
+      }
       // record for HMR
       if (__DEV__) {
         if (owner) {