Add a helper function for rendering page breadcrumbs as HTML

[d-ronnqvist]

Bug/issue #, if applicable: rdar://163326857

Summary

This is another slice of #1366

It adds a helper function to the DocCHTML/MarkdownRenderer to render page breadcrumbs as HTML

Dependencies

None.

Testing

Nothing in particular for this PR. It only adds an internal helper function. See #1366 for how it eventually does get used.

Checklist

Make sure you check off the following items. If they cannot be completed, provide a reason.

• Added tests
• Ran the ./bin/test script and it succeeded
• Updated documentation if necessary

[d-ronnqvist]

@swift-ci please test

[d-ronnqvist]

@swift-ci please test

[heckj]

minor wording suggestion, LGTM

[mayaepps]

Looks good to me! Just one question about the behavior for language-specific names.

[mayaepps]

Why do we want this behavior if there is only one language-specific name? If there is a language-specific name, even if there is only one, wouldn't we want to go through the logic in the else block that applies a "class" attribute (which I assume is used for formatting)?

[d-ronnqvist]

That's a good question that I don't know if I've written down the answer to anywhere.

The idea is that the language specific elements would have classes like "swift-only" or "occ-only" that can be shown or hidden through very small CSS changes. For example, consider this HTML that represents a link to a method with different names in Swift and Objective-C:

<a href=../somemethod(with:and:)/index.html>
  <code class="swift-only">someMethod(with:and:)</code>
  <code class="occ-only">someMethodWithFirst:AndSecond:</code>
</a>

If we add this CSS to the page:

.swift-only {}
.occ-only {
    display: none;
}

the rendered page will only display the Swift title for that link. If we flip the CSS, then the rendered page will only display the Objective-C title for that link.

If the symbol has the same title on both languages, or is only available in a single language,then it's unnecessary to have 2 <code> elements, and the HTML can be simplified to just:

<a href=../somemethod(with:and:)/index.html>
  <code>someMethod(with:and:)</code>
</a>

[d-ronnqvist]

@swift-ci please test