Add fragment plugin and parse fragmented list

CHANGELOG.md

@@ -2,6 +2,10 @@
 
 ## [Unreleased]
 
+### Added
+
+- Parse lists in `*` and `1)` marker as fragmented list ([#145](https://github.com/marp-team/marpit/issues/145), [#148](https://github.com/marp-team/marpit/pull/148))
+
 ### Changed
 
 - Upgrade dependent packages to the latest version ([#143](https://github.com/marp-team/marpit/pull/143))

src/markdown/fragment.js

@@ -0,0 +1,52 @@
+/** @module */
+import marpitPlugin from './marpit_plugin'
+
+const fragmentedListMarkups = ['*', ')']
+
+/**
+ * Marpit fragment plugin.
+ *
+ * @alias module:markdown/fragment
+ * @param {MarkdownIt} md markdown-it instance.
+ */
+function fragment(md) {
+  // Fragmented list
+  md.core.ruler.after('marpit_directives_parse', 'marpit_fragment', state => {
+    if (state.inlineMode) return
+
+    for (const token of state.tokens) {
+      if (
+        token.type === 'list_item_open' &&
+        fragmentedListMarkups.includes(token.markup)
+      ) {
+        token.meta = token.meta || {}
+        token.meta.marpitFragment = true
+      }
+    }
+  })
+
+  // Add data-marpit-fragment(s) attributes to token
+  md.core.ruler.after('marpit_fragment', 'marpit_apply_fragment', state => {
+    if (state.inlineMode) return
+
+    const fragments = { slide: undefined, count: 0 }
+
+    for (const token of state.tokens) {
+      if (token.meta && token.meta.marpitSlideElement === 1) {
+        fragments.slide = token
+        fragments.count = 0
+      } else if (token.meta && token.meta.marpitSlideElement === -1) {
+        if (fragments.slide && fragments.count > 0) {
+          fragments.slide.attrSet('data-marpit-fragments', fragments.count)
+        }
+      } else if (token.meta && token.meta.marpitFragment) {
+        fragments.count += 1
+
+        token.meta.marpitFragment = fragments.count
+        token.attrSet('data-marpit-fragment', fragments.count)
+      }
+    }
+  })
+}
+
+export default marpitPlugin(fragment)

src/marpit.js

@@ -7,6 +7,7 @@ import marpitBackgroundImage from './markdown/background_image'
 import marpitCollect from './markdown/collect'
 import marpitComment from './markdown/comment'
 import marpitContainerPlugin from './markdown/container'
+import marpitFragment from './markdown/fragment'
 import marpitHeaderAndFooter from './markdown/header_and_footer'
 import marpitHeadingDivider from './markdown/heading_divider'
 import marpitInlineSVG from './markdown/inline_svg'
@@ -179,8 +180,9 @@ class Marpit {
       .use(marpitSweep)
       .use(marpitInlineSVG)
       .use(marpitStyleAssign)
-      .use(marpitCollect)
       .use(marpitBackgroundImage)
+      .use(marpitFragment)
+      .use(marpitCollect)
   }
 
   /**

test/markdown/fragment.js

@@ -0,0 +1,84 @@
+import cheerio from 'cheerio'
+import MarkdownIt from 'markdown-it'
+import fragment from '../../src/markdown/fragment'
+import slide from '../../src/markdown/slide'
+
+describe('Marpit fragment plugin', () => {
+  const md = () => {
+    const instance = new MarkdownIt('commonmark')
+    instance.marpit = {}
+
+    return instance
+      .use(slide)
+      .use(m => m.core.ruler.push('marpit_directives_parse', () => {}))
+      .use(fragment)
+  }
+
+  describe('Fragmented unordered list', () => {
+    context('when using "*" markup', () => {
+      const markdown = '* A\n* B\n* C'
+      const $ = cheerio.load(md().render(markdown))
+
+      it('adds data-marpit-fragment attribute to <li> with index', () => {
+        const li = $('ul > li[data-marpit-fragment]')
+        expect(li).toHaveLength(3)
+
+        const indexes = li.map((_, el) => $(el).data('marpit-fragment')).get()
+        expect(indexes).toStrictEqual([1, 2, 3])
+      })
+
+      it('adds data-marpit-fragments attribute to <section> with count of fragments', () => {
+        const section = $('section[data-marpit-fragments]')
+
+        expect(section).toHaveLength(1)
+        expect(section.data('marpit-fragments')).toBe(3)
+      })
+    })
+
+    for (const char of ['-', '+']) {
+      context(`when using "${char}" markup`, () => {
+        const markdown = `${char} A\n${char} B\n${char} C`
+        const $ = cheerio.load(md().render(markdown))
+
+        it('does not add data-marpit-fragment attribute', () =>
+          expect($('[data-marpit-fragment]')).toHaveLength(0))
+
+        it('does not add data-marpit-fragments attribute', () =>
+          expect($('[data-marpit-fragments]')).toHaveLength(0))
+      })
+    }
+  })
+
+  describe('Fragmented ordered list', () => {
+    context('when using "1)" markup', () => {
+      const markdown = '1) A\n1) B\n1) C'
+      const $ = cheerio.load(md().render(markdown))
+
+      it('adds data-marpit-fragment attribute to <li> with index', () => {
+        const li = $('ol > li[data-marpit-fragment]')
+        expect(li).toHaveLength(3)
+
+        const indexes = li.map((_, el) => $(el).data('marpit-fragment')).get()
+        expect(indexes).toStrictEqual([1, 2, 3])
+      })
+
+      it('adds data-marpit-fragments attribute to <section> with count of fragments', () => {
+        const section = $('section[data-marpit-fragments]')
+
+        expect(section).toHaveLength(1)
+        expect(section.data('marpit-fragments')).toBe(3)
+      })
+    })
+
+    context(`when using "1." markup`, () => {
+      const markdown = `1. A\n1. B\n1. C`
+      const $ = cheerio.load(md().render(markdown))
+
+      it('does not add data-marpit-fragment attribute', () =>
+        expect($('[data-marpit-fragment]')).toHaveLength(0))
+
+      it('does not add data-marpit-fragments attribute', () =>
+        expect($('[data-marpit-fragments]')).toHaveLength(0))
+    })
+  })
+})