FEATURE: add html-block rich editor extension (#31181)

Continues the work done on
https://github.com/discourse/discourse/pull/30815.

Adds an `html_block` node and its parsing/serialization logic.

It's rendered as a code block with HTML syntax highlighting, and
serialized as-is to the Markdown output.

app/assets/javascripts/discourse/app/static/prosemirror/extensions/html-block.js

@@ -0,0 +1,35 @@
+/** @type {RichEditorExtension} */
+const extension = {
+  nodeSpec: {
+    html_block: {
+      attrs: { params: { default: "html" } },
+      group: "block",
+      content: "text*",
+      code: true,
+      defining: true,
+      marks: "",
+      isolating: true,
+      selectable: true,
+      draggable: true,
+      parseDOM: [{ tag: "pre.html-block", preserveWhitespace: "full" }],
+      toDOM() {
+        return ["pre", { class: "html-block" }, ["code", 0]];
+      },
+    },
+  },
+  parse: {
+    html_block: (state, token) => {
+      state.openNode(state.schema.nodes.html_block);
+      state.addText(token.content.trim());
+      state.closeNode();
+    },
+  },
+  serializeNode: {
+    html_block: (state, node) => {
+      state.renderContent(node);
+      state.write("\n\n");
+    },
+  },
+};
+
+export default extension;

app/assets/javascripts/discourse/app/static/prosemirror/extensions/register-default.js

@@ -3,6 +3,7 @@ import codeBlock from "./code-block";
 import emoji from "./emoji";
 import hashtag from "./hashtag";
 import heading from "./heading";
+import htmlBlock from "./html-block";
 import htmlInline from "./html-inline";
 import image from "./image";
 import link from "./link";
@@ -31,6 +32,7 @@ const defaultExtensions = [
   strikethrough,
   underline,
   htmlInline,
+  htmlBlock,
   table,
   markdownPaste,
 ];

app/assets/javascripts/discourse/tests/integration/components/prosemirror-editor/html-block-test.js

@@ -0,0 +1,38 @@
+import { module, test } from "qunit";
+import { setupRenderingTest } from "discourse/tests/helpers/component-test";
+import { testMarkdown } from "discourse/tests/helpers/rich-editor-helper";
+
+module(
+  "Integration | Component | prosemirror-editor - html block extension",
+  function (hooks) {
+    setupRenderingTest(hooks);
+
+    Object.entries({
+      "unclosed html block": [
+        "<div>Hello World\n\n",
+        '<pre class="html-block"><code>&lt;div&gt;Hello World</code></pre>',
+        "<div>Hello World\n\n",
+      ],
+      "html block with attributes": [
+        'Hey\n\n<div class="test">Hello World</div>\nYou',
+        '<p>Hey</p><pre class="html-block"><code>&lt;div class="test"&gt;Hello World&lt;/div&gt;\nYou</code></pre>',
+        'Hey\n\n<div class="test">Hello World</div>\nYou\n\n',
+      ],
+      "html block with multiple lines": [
+        "<div>\n  <p>Hello</p>\n  <p>World</p>\n</div>",
+        '<pre class="html-block"><code>&lt;div&gt;\n  &lt;p&gt;Hello&lt;/p&gt;\n  &lt;p&gt;World&lt;/p&gt;\n&lt;/div&gt;</code></pre>',
+        "<div>\n  <p>Hello</p>\n  <p>World</p>\n</div>\n\n",
+      ],
+      "html block multiple times": [
+        "<div>1</div>\n\nA\n\n<div>2</div>",
+        '<pre class="html-block"><code>&lt;div&gt;1&lt;/div&gt;</code></pre><p>A</p><pre class="html-block"><code>&lt;div&gt;2&lt;/div&gt;</code></pre>',
+        "<div>1</div>\n\nA\n\n<div>2</div>\n\n",
+      ],
+    }).forEach(([name, [markdown, html, expectedMarkdown]]) => {
+      test(name, async function (assert) {
+        this.siteSettings.rich_editor = true;
+        await testMarkdown(assert, markdown, html, expectedMarkdown);
+      });
+    });
+  }
+);