Use a HTML-comment to escape code

[zeitgeist87]

If an element does not contain any code, but a single HTML-comment, then the comment is used as code.

<code class="language-markup"><!-- <p>Example</p> --><code>

It works very well, but I feel silly for even proposing this. It seems semantically wrong to abuse a comment like this. I created this to contribute to the discussion around #887.

[LeaVerou]

No matter what we do for this, it will be a hack. Which is ok, as long as we keep it out of the core and in the unescaped markup plugin. Wanna move the commit to that? :)

[LeaVerou]

Just please amend the documentation to mention this, and make sure to only apply it for block code (it's much more likely that inline code will actually contain a single comment, for block code I think it's kinda rare).
Nice hack!

[zeitgeist87]

I've updated the PR. Unfortunately some small changes to prism-core.js are still necessary. I had to move the check for empty code below the before-highlight hook.

[LeaVerou]

I’m a bit worried that this could be a breaking change for third party plugins. Perhaps we should add a new hook before the check?

[zeitgeist87]

I’m a bit worried that this could be a breaking change for third party plugins.

I think the chances of that happening are quite low, because env.code contains an empty string at that point and not something unexpected like undefined or null. Any plugin should be able to handle that. It seems to me, the if-statement is mainly a performance improvement that allows Prism to return early if there is nothing to highlight. In my opinion there is no reason to add another hook.

[zeitgeist87]

On the other hand, a new hook would guarantee, that the unescape-markup plugin runs before any other plugin that needs to change env.code.

[zeitgeist87]

@LeaVerou I've resolved the merge conflicts for this PR. Do you think it is ready to be merged?

[LeaVerou]

Sure, ok! Thanks!