fix: list spread across multiple slide steps were not properly parsed

Author: dpecos

src/__tests__/list_incremental_bug.test.ts

@@ -0,0 +1,55 @@
+import { describe, it, expect } from 'vitest';
+import { Parser } from '../mdeck/parser.js';
+import { Slideshow } from '../mdeck/models/slideshow.js';
+import { convertMarkdown } from '../mdeck/converter.js';
+import type { Dom } from '../mdeck/dom.js';
+import EventEmitter from 'eventemitter3';
+
+function makeDom(): Dom {
+  return {
+    getHTMLElement: () => document.documentElement,
+    getBodyElement: () => document.body as HTMLBodyElement,
+    getElementById: () => null,
+    getLocationHash: () => '',
+    setLocationHash: () => {},
+    XMLHttpRequest: class {
+      open() {}
+      send() {}
+      onload?: () => void;
+      readyState = 0;
+      status = 0;
+      responseText = '';
+    } as unknown as typeof XMLHttpRequest,
+  } as unknown as Dom;
+}
+
+describe('incremental list items', () => {
+  const src = `# Agenda
+
+   - Testing Integrations
+--
+   - OpenAPI
+--
+   - Pact
+--
+   - Conclusions
+--
+   - Questions`;
+
+  it('parses into 5 slides', () => {
+    const parser = new Parser();
+    expect(parser.parse(src)).toHaveLength(5);
+  });
+
+  it('renders each incremental slide with the correct number of list items', () => {
+    const slideshow = new Slideshow(new EventEmitter(), makeDom(), {});
+    slideshow.loadFromString(src);
+    const slides = slideshow.getSlides();
+
+    slides.forEach((slide, i) => {
+      const html = convertMarkdown(slide.content);
+      const liCount = (html.match(/<li>/g) || []).length;
+      expect(liCount).toBe(i + 1);
+    });
+  });
+});

src/mdeck/models/slide.ts

@@ -78,7 +78,17 @@ function inheritContent(slide: Slide, template: Slide) {
   deepCopyContent(slide, template.content);
   const expanded = slide.expandVariables(true);
   if (expanded.content === undefined) {
-    slide.content = slide.content.concat(slide.properties.content as unknown as ContentItem[]);
+    const slideContent = slide.properties.content as unknown as ContentItem[];
+    // Ensure newline separator between inherited template content and new slide content,
+    // otherwise markdown fragments run together and break list items, headings, etc.
+    if (slideContent.length > 0 && slide.content.length > 0) {
+      const last = slide.content[slide.content.length - 1];
+      const first = slideContent[0];
+      if (typeof last === 'string' && typeof first === 'string') {
+        slideContent[0] = '\n' + first;
+      }
+    }
+    slide.content = slide.content.concat(slideContent);
   }
   delete slide.properties.content;
 }