Add "Enable HTML" option to allow HTML in Marp slide preview

package.json

@@ -40,6 +40,17 @@
   },
   "activationEvents": [],
   "contributes": {
+    "configuration": {
+      "type": "object",
+      "title": "Marp for VS Code",
+      "properties": {
+        "markdown.marp.enableHtml": {
+          "type": "boolean",
+          "default": false,
+          "description": "Enables all HTML elements in Marp Markdown."
+        }
+      }
+    },
     "markdown.markdownItPlugins": true,
     "markdown.previewScripts": [
       "./lib/preview.js"

src/__mocks__/vscode.ts

@@ -0,0 +1,3 @@
+export const workspace = {
+  getConfiguration: jest.fn(() => new Map()),
+}

src/extension.test.ts

@@ -3,8 +3,23 @@ import markdownItKatex from '@neilsustc/markdown-it-katex'
 import { Marp } from '@marp-team/marp-core'
 import markdownIt from 'markdown-it'
 import markdownItEmoji from 'markdown-it-emoji'
+import { workspace } from 'vscode'
 import { activate, extendMarkdownIt } from './extension'
 
+jest.mock('vscode')
+
+const mockWorkspaceConfig = (conf: { [key: string]: any } = {}) =>
+  jest.spyOn<any, any>(workspace, 'getConfiguration').mockImplementation(
+    () =>
+      new Map<string, any>(
+        Object.entries({
+          'markdown.marp.enableHtml': false,
+          ...conf,
+        })
+      )
+  )
+
+beforeEach(() => mockWorkspaceConfig())
 afterEach(() => jest.restoreAllMocks())
 
 describe('#activate', () => {
@@ -108,4 +123,31 @@ describe('#extendMarkdownIt', () => {
       expect(html).toContain('<code class="language-unknownlang">')
     })
   })
+
+  describe('Workspace config', () => {
+    const md = extendMarkdownIt(new markdownIt())
+
+    describe('markdown.marp.enableHtml', () => {
+      it('does not render HTML elements when disabled', () => {
+        mockWorkspaceConfig({ 'markdown.marp.enableHtml': false })
+
+        const html = md.render(marpMd('<b>Hi</b>'))
+        expect(html).not.toContain('<b>Hi</b>')
+      })
+
+      it("allows Marp Core's whitelisted HTML elements when disabled", () => {
+        mockWorkspaceConfig({ 'markdown.marp.enableHtml': false })
+
+        const html = md.render(marpMd('line<br>break'))
+        expect(html).toContain('line<br>break')
+      })
+
+      it('renders HTML elements when enabled', () => {
+        mockWorkspaceConfig({ 'markdown.marp.enableHtml': true })
+
+        const html = md.render(marpMd('<b>Hi</b>'))
+        expect(html).toContain('<b>Hi</b>')
+      })
+    })
+  })
 })

src/extension.ts

@@ -1,4 +1,5 @@
 import { Marp } from '@marp-team/marp-core'
+import { workspace } from 'vscode'
 
 const frontMatterRegex = /^---\s*([^]*)?(?:-{3}|\.{3})\s*/
 const marpDirectiveRegex = /^marp\s*:\s*true\s*$/m
@@ -11,8 +12,12 @@ export function extendMarkdownIt(md: any) {
 
   md.use(marp.markdownItPlugins)
     .use(instance => {
+      let originalOptions
+
       // Detect `marp: true` front-matter option
       instance.core.ruler.before('normalize', 'marp_vscode_toggle', state => {
+        originalOptions = instance.options
+
         if (state.inlineMode) return
 
         const fmMatch = frontMatterRegex.exec(state.src)
@@ -23,15 +28,29 @@ export function extendMarkdownIt(md: any) {
         instance[marpVscodeEnabled] = enabled
         state.marpit(enabled)
 
-        // Avoid collision to the other math plugins (markdown-it-katex)
         if (enabled) {
+          // Avoid collision to the other math plugins (markdown-it-katex)
           md.block.ruler.disable('math_block', true)
           md.inline.ruler.disable('math_inline', true)
+
+          // Override HTML option
+          instance.set({
+            html: workspace
+              .getConfiguration()
+              .get<boolean>('markdown.marp.enableHtml')
+              ? true
+              : marp.options.html,
+          })
         } else {
           md.block.ruler.enable('math_block', true)
           md.inline.ruler.enable('math_inline', true)
         }
       })
+
+      instance.core.ruler.push('marp_vscode_restore_options', state => {
+        if (state.inlineMode) return
+        instance.set(originalOptions)
+      })
     })
     .use(instance => {
       let originalEmojiRule