To make {,de}serialization of ImageBitmap work we also had to add
support for creating an ImageBitmap from a HTMLCanvasElement in
WindowOrWorkerGlobalScopeMixin::create_image_bitmap_impl().
similar-origin window agents have the [[CanBlock]] flag set to false.
Achieve this by hooking up JS's concept with an agent to HTML::Agent.
For now, this is only hooked up to the similar-origin window agent
case but should be extended to the other agent types in the future.
There are two changes happening here: a correctness fix, and an
optimization. In theory they are unrelated, but the optimization
actually paves the way for the correctness fix.
Before this commit, the HTML tokenizer would attempt to look for named
character references by checking from after the `&` until the end of
m_decoded_input, which meant that it was unable to recognize things like
named character references that are inserted via `document.write` one
byte at a time. For example, if `∉` was written one-byte-at-a-time
with `document.write`, then the tokenizer would only check against `n`
since that's all that would exist at the time of the check and therefore
erroneously conclude that it was an invalid named character reference.
This commit modifies the approach taken for named character reference
matching by using a trie-like structure (specifically, a deterministic
acyclic finite state automaton or DAFSA), which allows for efficiently
matching one-character-at-a-time and therefore it is able to pick up
matching where it left off after each code point is consumed.
Note: Because it's possible for a partial match to not actually develop
into a full match (e.g. `¬indo` which could lead to `⋵̸`),
some backtracking is performed after-the-fact in order to only consume
the code points within the longest match found (e.g. `¬indo` would
backtrack back to `¬`).
With this new approach, `document.write` being called one-byte-at-a-time
is handled correctly, which allows for passing more WPT tests, with the
most directly relevant tests being
`/html/syntax/parsing/html5lib_entities01.html`
and
`/html/syntax/parsing/html5lib_entities02.html`
when run with `?run_type=write_single`. Additionally, the implementation
now better conforms to the language of the spec (and resolves a FIXME)
because exactly the matched characters are consumed and nothing more, so
SWITCH_TO is able to be used as the spec says instead of RECONSUME_IN.
The new approach is also an optimization:
- Instead of a linear search using `starts_with`, the usage of a DAFSA
means that it is always aware of which characters can lead to a match
at any given point, and will bail out whenever a match is no longer
possible.
- The DAFSA is able to take advantage of the note in the section
`13.5 Named character references` that says "This list is static and
will not be expanded or changed in the future." and tailor its Node
struct accordingly to tightly pack each node's data into 32-bits.
Together with the inherent DAFSA property of redundant node
deduplication, the amount of data stored for named character reference
matching is minimized.
In my testing:
- A benchmark tokenizing an arbitrary set of HTML test files was about
1.23x faster (2070ms to 1682ms).
- A benchmark tokenizing a file with tens of thousands of named
character references mixed in with truncated named character
references and arbitrary ASCII characters/ampersands runs about 8x
faster (758ms to 93ms).
- The size of `liblagom-web.so` was reduced by 94.96KiB.
Some technical details:
A DAFSA (deterministic acyclic finite state automaton) is essentially a
trie flattened into an array, but it also uses techniques to minimize
redundant nodes. This provides fast lookups while minimizing the
required data size, but normally does not allow for associating data
related to each word. However, by adding a count of the number of
possible words from each node, it becomes possible to also use it to
achieve minimal perfect hashing for the set of words (which allows going
from word -> unique index as well as unique index -> word). This allows
us to store a second array of data so that the DAFSA can be used as a
lookup for e.g. the associated code points.
For the Swift implementation, the new NamedCharacterReferenceMatcher
was used to satisfy the previous API and the tokenizer was left alone
otherwise. In the future, the Swift implementation should be updated to
use the same implementation for its NamedCharacterReference state as
the updated C++ implementation.
There's a quirk in HTML where the parser should ignore any line feed
character immediately following a `pre` or `textarea` start tag.
This was working fine when we could peek ahead in the input stream and
see the next token, but didn't work in character-at-a-time parsing with
document.write().
This commit adds the "can ignore next line feed character" as a parser
flag that is maintained across invocations, making it work in this
parsing mode as well.
20 new passes in WPT/html/syntax/parsing/ :^)
Instead of always inserting a new text node, we now continue appending
to an extisting text node if the parser's character insertion point is
a suitable text node.
This fixes an issue where multiple invocations of document.write() would
create unnecessary sequences of text nodes. Such sequences are now
merged automatically.
19 new passes in WPT/html/syntax/parsing/ :^)
Before this change, the explicit EOF inserted by document.close() would
instantly abort the parser. This meant that parsing algorithms that ran
as part of the parser unwinding on EOF would never actually run.
591 new passes in WPT/html/syntax/parsing/ :^)
This exposed a problem where the parser would try to insert a root
<html> element on EOF in a document where someone already inserted such
an element via direct DOM manipulation. The parser now gracefully
handles this scenario. It's covered by existing tests (which would
crash without this change.)
This fixes a crash in the included test that regressed in 0adf261,
and is hit by the following HTML:
```html
<body></body>
<script>
const frame = document.body.appendChild(document.createElement("iframe"));
frame.contentDocument.open();
const child = frame.contentDocument.createElement("html")
const html = frame.contentDocument.appendChild(child);
frame.contentDocument.close();
</script>
```
I am not 100% sure this is fully the correct fix and there are other
cases which would not work properly. But it's definitely an improvement
to make the confuisingly named 'insert_an_eof' function of the tokenizer
actually do something.
Instead of always reporting a colno and lineno of zero try and use the
values from the Error object that may be provided, falling back to the
source location of the invocation if not provided. We can definitely
improve the reporting even more, but this is a start!
Also update this function to latest spec while we're in the area.
The 'reason' was getting initialized to 'empty' state when not
provided through the constructor, which results in a crash when
accessed through throw_dom_exception_if_needed in the generated
IDL getter.
This allows us to disable test output, which performs expensive assert
tracking. This was making our imported tests run significantly slower
than tests run via `WPT.sh`.
Formatting the output ourselves also allows us to remove unnecessary
information from the test output.
This commit also rebaselines all existing imported WPT tests to follow
the new format.
In particular, input character lookahead now knows how to stop at the
insertion point marker if needed.
This makes it possible to do amazing things like having document.write()
insert doctypes one character at a time.
If we reach the insertion point at the same time as we switch to another
tokenizer state, we have to bail immediately without proceeding with the
next code point. Otherwise we'd fetch the next token, get an EOF marker,
and then proceed as if we're at the end of the input stream, even though
more data may be coming (with more calls to document.write()..)
