xml5ever: Bubble parser blocking scripts to the caller instead of the TreeSink

[simonwuelker]

This is the same approach used by html5ever, which will hopefully allow unifying their API a bit as part of the effort for encoding support.

This is a breaking change. The TreeSink::complete_script method (among other things) is removed.

[simonwuelker]

The difference between the way html5ever and xml5ever block on script elements is best explained by looking at by the feed method for both parsers in servo:

The html parser pushes the input into the tokenizer and waits to see if any blocking scripts come back: https://github.com/servo/servo/blob/0d38d6239a4356928c2a7ec0a3cd53ecc32096b0/components/script/dom/servoparser/html.rs#L87-L94

The xml parser pushes the input into the tokenizer, waits until it stops and then checks whether the sink has received any blocking scripts: https://github.com/servo/servo/blob/0d38d6239a4356928c2a7ec0a3cd53ecc32096b0/components/script/dom/servoparser/xml.rs#L45-L51

[simonwuelker]

This is okay, because it is exactly what html5ever does too:

html5ever/html5ever/src/driver.rs

Lines 107 to 109 in 31a2c31

	self.input_buffer.push_back(t);
	// FIXME: Properly support </script> somehow.
	while let TokenizerResult::Script(_) = self.tokenizer.feed(&self.input_buffer) {}

[mrobinson]

Seems good to me, though perhaps someone more familiar with html5ever should review.

[jdm]

This is great! Thanks for digging into this.