fix: remove trailing newline added by markdown-it

[KermanX]

Description

Scope: @shikijs/markdown-it

Shiki transpiles blank lines into <span class="line"></span>. And the source code received in markdownit.options.highlight has a trailing new line. This results in a blank line in the rendered HTML.

This PR fixes this by removing the last character of the source code.

Example input:

<!-- Blank -->
'''ts
'''

<!-- One blank line -->
'''ts

'''

<!-- Normal code -->
'''ts
123
'''

Output (simplified):

<!-- Blank -->
<pre><code>
  <span class="line"></span>
</code></pre>

<!-- One blank line -->
<pre><code>
  <span class="line"></span>
</code></pre>

<!-- Normal code -->
<pre><code>
  <span class="line">123</span>
</code></pre>

Linked Issues

fix slidevjs/slidev#1276

[netlify]

✅ Deploy Preview for shiki-next ready!

Name	Link
🔨 Latest commit	bb410c3
🔍 Latest deploy log	https://app.netlify.com/sites/shiki-next/deploys/65ca0bc23da1c000085497bb
😎 Deploy Preview	https://deploy-preview-585--shiki-next.netlify.app
📱 Preview on mobile	Toggle QR Code... Use your smartphone camera to open QR code link.

---

To edit notification comments on pull requests, go to your Netlify site configuration.

[netlify]

✅ Deploy Preview for shiki-matsu ready!

Name	Link
🔨 Latest commit	bb410c3
🔍 Latest deploy log	https://app.netlify.com/sites/shiki-matsu/deploys/65ca0bc2150d10000862973a
😎 Deploy Preview	https://deploy-preview-585--shiki-matsu.netlify.app
📱 Preview on mobile	Toggle QR Code... Use your smartphone camera to open QR code link.

---

To edit notification comments on pull requests, go to your Netlify site configuration.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (2f64ffd) 96.14% compared to head (d284098) 96.15%.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #585   +/-   ##
=======================================
  Coverage   96.14%   96.15%           
=======================================
  Files          70       70           
  Lines        5651     5664   +13     
  Branches      749      749           
=======================================
+ Hits         5433     5446   +13     
  Misses        212      212           
  Partials        6        6           

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[antfu]

Suggested change

	code.slice(0, -1),
	code.trimEnd(),

[KermanX]

I was wondering maybe there will be someone who intended to have a blank line or whitespaces at the end of the code?🤔

[antfu]

I found that VitePress is doing this mandatory: https://github.com/vuejs/vitepress/blob/c582a8d5fd82b84d412c7e6c84e74faeb23beac6/src/node/markdown/plugins/highlight.ts#L144

I wonder why markdown-it is doing this (if it always adds a tailing newline) - do you have a reference? .slice(0, -1) looks a bit magic and unreliable to me as it might strip out real code if the tailing newline is not a determined behavior.

[KermanX]

I think markdown-it always adds a tailing newline, bacause:

https://github.com/markdown-it/markdown-it/blob/master/lib/rules_block/fence.mjs#L89:

  token.content = state.getLines(startLine + 1, nextLine, len, true)
//                                                              ^ "keepLastLF"

and https://github.com/markdown-it/markdown-it/blob/master/lib/renderer.mjs#L43:

    highlighted = options.highlight(token.content, langName, langAttrs) || escapeHtml(token.content)

also https://github.com/markdown-it/markdown-it/blob/master/lib/rules_block/code.mjs#L26:

  token.content = state.getLines(startLine, last, 4 + state.blkIndent, false) + '\n'