fix: anchor links in MDX files when prettyUrls is false

[GUI]

Description 📖

This attempts to fix a bug that appears to be present when prettyUrls: false which prevents MDX pages from linking to anchor tags on the page. Here is a reproduction of the issue: https://github.com/GUI/iles-debug-app/compare/anchor-links-pretty-urls

Background 📜

If the app is configured with prettyUrls: false, then anchor links in MDX files may not behave as expected. For example, a link like:

[foo](#bar)

Will be generated in the output as:

<a href="#bar.html">foo</a>

Instead of remaining href="#bar", like expected (since the anchor of '#bar.html` probably won't exist on the page).

Similarly, a link to /foo#bar will get translated to /foo#bar.html instead of what I think would be intended by how other URLs get rewritten (in which case, I think /foo.html#bar would be expected).

The Fix 🔨

This fixes the issue by skipping the MDX URL rewriting when anchor tags on the current page (no path is present) are encountered. For anchor links on other pages, the anchor is split from the path, and then the existing path rules are used, adding the anchor back in afterwards.

Using a URL parsing library, instead of simply splitting the string by # may be more robust, but Node.js's URL class doesn't handle relative links or fragment-only links, so it won't work for this use-case. But I think this simple splitting approach will hopefully meet the needs here.

But also welcome to any other suggestions for ways to fix this. Thanks!

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[ElMassimo]

Hi Nick, thanks for the fix! 😃

I've added a unit test for toExplicitHtmlPath to prevent regressions and ensure all cases are covered.

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There's one case which wasn't working that still doesn't work after the fix:

expectExplicitPath('/about/nested.html').toEqual('/about/nested.html')

I'll make additional changes to cover this one before releasing a new version.

[ElMassimo]

Released in @islands/mdx 0.7.5.

[GUI]

Perfect, thanks again so much for the speedy fixes, this appears to be working great now. And thanks for the more complete and tidier fix and the test coverage (I hadn't found the test suite yet, but now I see in your commits).