[css-properties-values-api] Fix syntax string parsing to not treat whitespace between components the same as pipes.

[emilio]

Fixes #893

[emilio]

r? @andruud

[andruud]

Oh, nice, thanks @emilio <3

I'm not actually an editor though, so I can't merge it.

--> @tabatkins

(It would be nice to have assign-review-to-people privileges, so I didn't have to ping people in a comment, like a commoner, djeez).

[emilio]

I don't seem to have merge access to this repo, so if you could do that @tabatkins it'd be awesome.

Thanks!

[andruud]

@emilio Just discovered that this allows a leading "|", e.g. "|foo" is a valid syntax.

[andruud]

Let's rethink step 5 as a whole. Drop the "repeatedly consume" thing and instead do:

Step 5:

• Consume a syntax component from stream. If failure was returned, return failure; otherwise, append the returned value to descriptor. [Note: Consume a syntax component consumes leading whitespace, which is relevant for repeats of this step].
• Consume as much whitespace as possible from stream.
• Consume the next input code point from stream:
  • EOF: Return descriptor. [Note: I don't think we still need the descriptor size check, since we'll now exit early if "Consume a syntax component" fails?]
  • U+007C VERTICAL LINE (|): Repeat this step.
  • Anything else: Return failure.

WDYT?

[emilio]

Err, yes indeed it does.

Or alternatively, also reconsume the current code-point even if it's |, if the output is empty. But yeah, that sounds cleaner.

[emilio]

Your algorithm also needs to skip trailing whitespace after parsing a component, otherwise you stop parsing foo | bar unless it's written foo|bar

[emilio]

Err, you did that already, should learn to read. Yeah, that looks good.