Add name_source_location() and value_source_location() to Attribute

[gmalette]

Exposes document-absolute byte ranges for attribute names and values via the existing SourceLocation type.

We need this to perform byte-level splice rewrites on attribute values without re-parsing the start tag... I know we're holding it wrong but this is the fastest and most correct way to achieve our goals :)

[kornelski]

Thanks for the PR.

The change isn't too bad, but it makes me wonder why aren't you using the rewriter to do rewriting?

[gmalette]

but it makes me wonder why aren't you using the rewriter to do rewriting?

Yes this is a very good question and I should've led with that.

The reason is: we rewrite html bodies not written by us. We used to do this with regexps and it was very imprecise and so often we targeted nodes that were unrelated to the reason for the rewrite. For example, if your body contained type="importmap", we injected the polyfill script before the very first <script>, even if it was unrelated.

Changing the payload we output is like turning a cargo ship around, and while we want to move to full rewriter, right now we use it also as a scanner for those cases. We register node positions and perform the string manipulation when it's all computed.

It's not great and I know it's not how you want us to use it, but it's also 2-7x faster and approximately infinity times more precise.

[gmalette]

@kornelski would you cut a new release please? 🙏