feat(core): scoped templates in SlotMixin

.changeset/hip-fishes-flash.md

@@ -0,0 +1,5 @@
+---
+'@lion/core': patch
+---
+
+Support scoped templates in SlotMixin

packages/core/src/SlotMixin.js

@@ -1,18 +1,20 @@
 /* eslint-disable class-methods-use-this */
 import { dedupeMixin } from '@open-wc/dedupe-mixin';
+import { render } from 'lit';
+import { isTemplateResult } from 'lit/directive-helpers.js';
 
 /**
  * @typedef {import('../types/SlotMixinTypes').SlotMixin} SlotMixin
  * @typedef {import('../types/SlotMixinTypes').SlotsMap} SlotsMap
+ * @typedef {import('../index').LitElement} LitElement
  */
 
 /**
  * @type {SlotMixin}
- * @param {import('@open-wc/dedupe-mixin').Constructor<HTMLElement>} superclass
+ * @param {import('@open-wc/dedupe-mixin').Constructor<LitElement>} superclass
  */
 const SlotMixinImplementation = superclass =>
-  // eslint-disable-next-line no-unused-vars, no-shadow
-  class extends superclass {
+  class SlotMixin extends superclass {
     /**
      * @return {SlotsMap}
      */
@@ -27,29 +29,47 @@ const SlotMixinImplementation = superclass =>
     }
 
     connectedCallback() {
-      // @ts-ignore checking this in case we pass LitElement, found no good way to type this...
-      if (super.connectedCallback) {
-        // @ts-ignore checking this in case we pass LitElement, found no good way to type this...
       super.connectedCallback();
-      }
       this._connectSlotMixin();
     }
 
+    /**
+     * @private
+     * @param {import('@lion/core').TemplateResult} template
+     */
+    __renderAsNodes(template) {
+      const tempRenderTarget = document.createElement('div');
+      render(template, tempRenderTarget, this.renderOptions);
+      return Array.from(tempRenderTarget.childNodes);
+    }
+
     /**
      * @protected
      */
     _connectSlotMixin() {
       if (!this.__isConnectedSlotMixin) {
         Object.keys(this.slots).forEach(slotName => {
-          if (!this.querySelector(`[slot=${slotName}]`)) {
-            const slotFactory = this.slots[slotName];
-            const slotContent = slotFactory();
-            // ignore non-elements to enable conditional slots
-            if (slotContent instanceof Element) {
-              slotContent.setAttribute('slot', slotName);
-              this.appendChild(slotContent);
-              this.__privateSlots.add(slotName);
+          if (!Array.from(this.children).find(el => el.slot === slotName)) {
+            const slotContent = this.slots[slotName]();
+            /** @type {Node[]} */
+            let nodes = [];
+
+            if (isTemplateResult(slotContent)) {
+              nodes = this.__renderAsNodes(slotContent);
+            } else if (!Array.isArray(slotContent)) {
+              nodes = [/** @type {Node} */ (slotContent)];
             }
+
+            nodes.forEach(node => {
+              if (!(node instanceof Node)) {
+                return;
+              }
+              if (node instanceof Element) {
+                node.setAttribute('slot', slotName);
+              }
+              this.appendChild(node);
+              this.__privateSlots.add(slotName);
+            });
           }
         });
         this.__isConnectedSlotMixin = true;

packages/core/test/SlotMixin.test.js

@@ -1,10 +1,12 @@
+import sinon from 'sinon';
 import { defineCE, expect, fixture } from '@open-wc/testing';
 import { SlotMixin } from '../src/SlotMixin.js';
+import { LitElement, ScopedElementsMixin, html } from '../index.js';
 
 describe('SlotMixin', () => {
   it('inserts provided element into lightdom and sets slot', async () => {
     const tag = defineCE(
-      class extends SlotMixin(HTMLElement) {
+      class extends SlotMixin(LitElement) {
         get slots() {
           return {
             ...super.slots,
@@ -19,7 +21,7 @@ describe('SlotMixin', () => {
 
   it('does not override user provided slots', async () => {
     const tag = defineCE(
-      class extends SlotMixin(HTMLElement) {
+      class extends SlotMixin(LitElement) {
         get slots() {
           return {
             ...super.slots,
@@ -33,9 +35,28 @@ describe('SlotMixin', () => {
     expect(/** @type HTMLParagraphElement */ (el.children[0]).innerText).to.equal('user-content');
   });
 
+  it('does add when user provided slots are not direct children', async () => {
+    const tag = defineCE(
+      class extends SlotMixin(LitElement) {
+        get slots() {
+          return {
+            ...super.slots,
+            content: () => document.createElement('div'),
+          };
+        }
+      },
+    );
+    const el = await fixture(`<${tag}><p><span slot="content">user-content</span></p></${tag}>`);
+    const slot = /** @type HTMLDivElement */ (
+      Array.from(el.children).find(elm => elm.slot === 'content')
+    );
+    expect(slot.tagName).to.equal('DIV');
+    expect(slot.innerText).to.equal('');
+  });
+
   it('supports complex dom trees as element', async () => {
     const tag = defineCE(
-      class extends SlotMixin(HTMLElement) {
+      class extends SlotMixin(LitElement) {
         constructor() {
           super();
           this.foo = 'bar';
@@ -67,7 +88,7 @@ describe('SlotMixin', () => {
   it('supports conditional slots', async () => {
     let renderSlot = true;
     const tag = defineCE(
-      class extends SlotMixin(HTMLElement) {
+      class extends SlotMixin(LitElement) {
         get slots() {
           return {
             ...super.slots,
@@ -92,7 +113,7 @@ describe('SlotMixin', () => {
 
   it("allows to check which slots have been created via this._isPrivateSlot('slotname')", async () => {
     let renderSlot = true;
-    class SlotPrivateText extends SlotMixin(HTMLElement) {
+    class SlotPrivateText extends SlotMixin(LitElement) {
       get slots() {
         return {
           ...super.slots,
@@ -116,4 +137,71 @@ describe('SlotMixin', () => {
     const elNoSlot = /** @type {SlotPrivateText} */ (await fixture(`<${tag}><${tag}>`));
     expect(elNoSlot.didCreateConditionalSlot()).to.be.false;
   });
+
+  it('supports templates', async () => {
+    const tag = defineCE(
+      class extends SlotMixin(LitElement) {
+        get slots() {
+          return {
+            ...super.slots,
+            template: () => html`<span>text</span>`,
+          };
+        }
+
+        render() {
+          return html`<slot name="template"></slot>`;
+        }
+      },
+    );
+    const el = await fixture(`<${tag}><${tag}>`);
+    const slot = /** @type HTMLSpanElement */ (
+      Array.from(el.children).find(elm => elm.slot === 'template')
+    );
+    expect(slot.slot).to.equal('template');
+    expect(slot.tagName).to.equal('SPAN');
+  });
+
+  it('supports scoped elements', async () => {
+    const scopedSpy = sinon.spy();
+    class ScopedEl extends LitElement {
+      connectedCallback() {
+        super.connectedCallback();
+        scopedSpy();
+      }
+    }
+
+    const tag = defineCE(
+      class extends ScopedElementsMixin(SlotMixin(LitElement)) {
+        static get scopedElements() {
+          return {
+            // @ts-expect-error
+            ...super.scopedElements,
+            'scoped-el': ScopedEl,
+          };
+        }
+
+        get slots() {
+          return {
+            ...super.slots,
+            template: () => html`<scoped-el></scoped-el>`,
+          };
+        }
+
+        connectedCallback() {
+          super.connectedCallback();
+
+          // Not rendered to shadowRoot, notScopedSpy should not be called
+          const notScoped = document.createElement('not-scoped');
+          this.appendChild(notScoped);
+        }
+
+        render() {
+          return html`<slot name="template"></slot>`;
+        }
+      },
+    );
+
+    await fixture(`<${tag}><${tag}>`);
+    expect(scopedSpy).to.have.been.called;
+  });
 });

packages/core/types/SlotMixinTypes.d.ts

@@ -1,6 +1,7 @@
 import { Constructor } from '@open-wc/dedupe-mixin';
+import { TemplateResult, LitElement } from '../index.js';
 
-declare function slotFunction(): HTMLElement | undefined;
+declare function slotFunction(): HTMLElement | Node[] | TemplateResult | undefined;
 
 export type SlotsMap = {
   [key: string]: typeof slotFunction;
@@ -48,11 +49,11 @@ export declare class SlotHost {
  *   };
  * }
  */
-export declare function SlotMixinImplementation<T extends Constructor<HTMLElement>>(
+export declare function SlotMixinImplementation<T extends Constructor<LitElement>>(
   superclass: T,
 ): T &
   Constructor<SlotHost> &
   Pick<typeof SlotHost, keyof typeof SlotHost> &
-  Pick<typeof HTMLElement, keyof typeof HTMLElement>;
+  Pick<typeof LitElement, keyof typeof LitElement>;
 
 export type SlotMixin = typeof SlotMixinImplementation;