Relax `<select>` parser #10557

josepharhar · 2024-08-13T22:37:01Z

This patch makes the parser allow additional tags in <select> besides <option>, <optgroup>, and <hr>, mostly by removing the "in select" and "in select in table" parser modes.

In order to replicate the behavior where opening a <select> tag within another open <select> tag inserts a </select> close tag, a traversal through the stack of open elements was added which I borrowed from the <button> part of the parser.

This patch also changes the processing model to make <select> look through all its descendants in the DOM tree for <option> elements, rather than just children and optgroup children which conform to the content model. This is needed for compat reasons because there are websites which put other tags in between their <select> and <option>s which would break with this parser change unless we also update this processing model. More context here and here.

Fixes #10310

At least two implementers are interested (and none opposed):
Tests are written and can be reviewed and commented upon at:
- Update tests for relaxed <select> parser html5lib/html5lib-tests#178
- https://wpt.fyi/results/html/semantics/forms/the-select-element/customizable-select/select-parsing.tentative.html
Implementation bugs are filed:
- Chromium: Already implemented
- Gecko: …
- WebKit: …
MDN issue is filed: …
The top of this comment includes a clear commit message to use.

(See WHATWG Working Mode: Changes for more details.)

/form-elements.html ( diff )
/index.html ( diff )
/infrastructure.html ( diff )
/parsing.html ( diff )

annevk · 2024-08-14T11:39:54Z

Why does this also make a bunch of changes to the processing model of select elements? If that needs to be part of this change that should really be better motivated in the commit message.

josepharhar · 2024-08-16T00:08:20Z

Why does this also make a bunch of changes to the processing model of select elements? If that needs to be part of this change that should really be better motivated in the commit message.

The changes in the processing model do support the new proposed content model for select, but they also mitigate compat issues for websites which are already putting tags in between <select> and <option> in their HTML.

For example, without these changes to the processing model, the following <select> would not register as having any options at all:

<select>
  <div>
    <option>...</option>
    ...
  </div>
</select>

In my compat analysis, I found a lot of websites which are doing this, so in order to ship the parser changes separately from customizable select in chrome, I plan to ship the parser changes and these processing model changes together, because otherwise there would be too much breakage.

I'm happy to put them in a separate PR if you want, or keep them here and update the commit message (sorry for not putting it in there). Which would you prefer?

annevk · 2024-08-16T06:11:37Z

Thanks! Given that rationale I think it's good to couple the changes, but that should be in the commit message as well.

zcorpan · 2024-08-19T15:59:08Z

This doesn't define optional tags for </option> and </optgroup> correctly.

The definition for "have a particular element in select scope" may be needed for that, but should be changed to be similar to "have a particular element in button scope" (but for select).

In particular, allow these without a parse error:

<select>
<optgroup>
<option>
<optgroup>
</select>

The second <optgroup> should pop the option and optgroup

<select>
<option><p>
<option>
</select>

This should generate implied end tags and pop the option.

<select>
<optgroup>
<hr>
<option>
<hr>
</select>

The hrs should pop the optgroup and option in a select.

See how the parser deals with <ruby><rtc><rt>, I think that can be used as a model for select.

source

josepharhar · 2024-08-19T21:28:14Z

Thanks! Given that rationale I think it's good to couple the changes, but that should be in the commit message as well.

Done.

This doesn't define optional tags for </option> and </optgroup> correctly.

@zcorpan thanks for the feedback! I did some experimenting and added some logic to the start tags for option, optgroup, and hr. What do you think?

zcorpan · 2024-08-22T09:02:46Z

Need to check that a select element is in scope so that parsing of option/optgroup tags outside of select doesn't change. Example <option><p>1</option>2<option>3
Need to add select to the "in scope" list so that <div><select></div><option> doesn't close the select.
Should report parse errors when unexpected elements are popped. Compare with what the spec does for rt/rtc in ruby. Example <select><option><span>1</option>2<option>3

josepharhar · 2024-08-22T23:57:54Z

Need to check that a select element is in scope so that parsing of option/optgroup tags outside of select doesn't change. Example <option><p>1</option>2<option>3

I thought that this is covered by "While the stack of open elements has an option element in select scope". What exactly should I change?

Need to add select to the "in scope" list so that <div><select></div><option> doesn't close the select.

Done

Should report parse errors when unexpected elements are popped. Compare with what the spec does for rt/rtc in ruby. Example <select><option><span>1</option>2<option>3

I'm guessing this is from "If the current node is not now a rtc element or a ruby element, this is a parse error," right?

Should I add "If the current node is not now an option element, this is a parse error" after "While the stack of open elements has an option element in select scope, pop an element from the stack of open elements"?

zcorpan · 2024-08-23T11:58:59Z

The "in select scope" I think should be removed altogether since it assumes the stack will not have other elements when in a select, which is no longer the case. Use the normal "in scope" instead.

High-level of what I think should happen: when parsing option or optgroup start tag: check that select is in scope, check that option or optgroup is in scope, generate implied end tags (except for optgroup when handling <option>), check the current node or the stack of open elements again, report a parse error if appropriate, then pop elements off the stack until the option or optgroup has been popped, then insert the new element.

I can look into this more next week and suggest more specific changes.

josepharhar · 2024-08-28T00:26:31Z

High-level of what I think should happen: when parsing option or optgroup start tag: check that select is in scope, check that option or optgroup is in scope, generate implied end tags (except for optgroup when handling <option>), check the current node or the stack of open elements again, report a parse error if appropriate, then pop elements off the stack until the option or optgroup has been popped, then insert the new element.

Thanks! I gave this a try

josepharhar · 2024-09-04T20:34:56Z

@zcorpan how does the latest text look?

zcorpan

I think the option/optgroup cases are right after these changes.

source

josepharhar · 2024-09-10T22:34:51Z

This doesn't define optional tags for </option> and </optgroup> correctly.

I was talking to @mfreed7 about the changes we've made in the PR so far, and I feel like I couldn't provide a good explanation for why we are making the parser not support cases like these:

<hr> inside an <option>
nested <optgroup>s

Is it just compat reasons? Is there a good justification?

This patch makes the parser allow additional tags in <select> besides <option>, <optgroup>, and <hr>, mostly by removing the "in select" and "in select in table" parser modes. In order to replicate the behavior where opening a <select> tag within another open <select> tag inserts a </select> close tag, a traversal through the stack of open elements was added which I borrowed from the <button> part of the parser. This will need test changes to be implemented in html5lib. Fixes whatwg#10310

zcorpan · 2024-09-11T08:53:59Z

It would be a breaking change from what is conforming HTML today, and break compat for sites that omit </option> and </optgroup> tags. It's the same as why we can't allow certain elements in p.

hsivonen

I think we should retain existing behavior for hr both for imaginable Web compat and for the principle of avoiding breaking existing conforming HTML.

I'm marking this as Request changes for that reason, but I admit that I'm not confident from looking at the spec diff alone that I can understand all other implications of this spec change, so there may well be other issues.

josepharhar · 2024-09-20T22:32:52Z

Ok, I pushed a change to disallow hr in option. How does it look now?

josepharhar · 2024-10-02T18:23:10Z

@zcorpan @hsivonen are there any other changes you think should be made?

josepharhar · 2024-10-02T21:07:31Z

I just re-added some cases to option and optgroup parsing to continue supporting auto-closing tags outside of a select tag to support cases like this, which I found in a test case here:

const select = document.createElement('select');
select.innerHTML = '<option>one<option>two';

source

dbaron

Two small comments I just noticed:

source

zcorpan · 2024-10-07T19:49:01Z

source

+     <li><p><span>Generate implied end tags</span> except for <code>optgroup</code>
+     elements.</p></li>
+
+     <li><p>If the <span>stack of open elements</span> <span data-x="has an element in scope">has an
+     <code>option</code> element in scope</span>, then this is a <span>parse error</span>.</p></li>


"hr" should be changed to match what "optgroup" does (when select is in scope)

If the stack of open elements has a select element in scope , then:

Generate implied end tags .

If the stack of open elements has an option element in scope or has an optgroup element in scope , then this is a parse error .

...to more closely match the current spec. However, if there's a desire to change this for #9247 then the current text (which is like "option") is better. cc @annevk

Still need to remove "except for <code>optgroup</code> elements" here and check for optgroup in the parse error step.

zcorpan · 2024-10-10T10:54:08Z

source

@@ -129413,8 +129413,6 @@ document.body.appendChild(text);
    <ol>
     <li><p>If the <span>current node</span> is an <code>option</code> element, then pop the
     <span>current node</span> off the <span>stack of open elements</span>.</p></li>
-
-     <li><p><span>Reconstruct the active formatting elements</span>, if any.</p></li>


Why was this removed?

Whoops, I re-added it to the "otherwise" case.

Do you think we should also run this in the not-"otherwise" case when we are in a select tag?

If we parse this html:

<select><div><i></div><option>option

We will get this resulting innerHTML if we reconstruct in both cases:

<select><div><i></i></div><i><option>option</option></i></select><i>

Otherwise if we only reconstruct in the "otherwise" case, we get this:

<select><div><i></i></div><option><i>option</i></option></select><i>

Doing the same thing in both cases for consistency sounds somewhat appealing to me

Yeah always reconstructing sounds good.

source

zcorpan · 2024-10-10T10:56:54Z

source


-     <li><p><span>Reconstruct the active formatting elements</span>, if any.</p></li>


Why was this removed?

re-added, but leaving this open to make sure we match the same behavior for option and optgroup based on the outcome of the other thread

annevk · 2024-10-10T13:59:14Z

source

+    <p>For each <var>ancestor</var> of <var>insertedOption</var>'s <span
+    data-x="ancestor">ancestors</span>:</p>


I think you need to define ordering here and below.

I agree that would be good to clarify. I've seen "in tree order" appended to loops like this before, but I'm not sure that's appropriate here - I want to start at the parent of insertedOption, and then keep going up from there. I'm worried that saying "in tree order" could imply the opposite.

Should I say "starting from the parent of insertedOption"?

https://dom.spec.whatwg.org/#dom-element-closest says "in reverse tree order"

This PR updates the tree-construction dat files for the HTML change which will allow additional tags within <select>: whatwg/html#10557

josepharhar · 2024-10-11T23:06:23Z

I created an html5lib PR to update tests: html5lib/html5lib-tests#178

- whatwg/html#10557 - html5lib/html5lib-tests#178

Neither the proposal nor the test changes are merged yet. Also, the tests are still failing. html5lib/html5lib-tests#178 whatwg/html#10557

zcorpan · 2024-11-05T09:43:53Z

source

+    <p>If the <span>stack of open elements</span> <span data-x="has an element in scope">has a
+    <code>select</code> element in scope</span>, then:</p>
+
+    <ol>
+     <li><p><span>Parse error</span>.</p></li>
+
+     <li><p>Pop elements from the <span>stack of open elements</span> until a <code>select</code>
+     element has been popped from the stack.</p></li>
+    </ol>
+
    <p><span>Reconstruct the active formatting elements</span>, if any.</p>

    <p><span>Insert an HTML element</span> for the token.</p>

    <p>Set the <span>frameset-ok flag</span> to "not ok".</p>


This needs to be changed to not insert a new select element in <select><select>, only close the open one. That is, <select><select> should be parsed like <select></select> and not like <select></select><select>.

Put the three trailing paragraphs in an "Otherwise:" step.

Why? I did this for backwards compat since the old/current parser creates two select elements in this case.

josepharhar marked this pull request as ready for review August 13, 2024 22:39

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HTML parser changes for customizable <select> #10310

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dont allow hr in option

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This was referenced Oct 9, 2024

Relax <select> parser mozilla/standards-positions#1086

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Relax <select> parser WebKit/standards-positions#414

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josepharhar added 2 commits October 9, 2024 11:54

fix non-select case

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fix variable names

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re-add reconstruct active formatting elements

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josepharhar added a commit to josepharhar/html5lib-tests that referenced this pull request Oct 11, 2024

Update tests for relaxed <select> parser

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This PR updates the tree-construction dat files for the HTML change which will allow additional tags within <select>: whatwg/html#10557

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Update tests for relaxed <select> parser html5lib/html5lib-tests#178

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Implement the latest select parsing changes

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Implement the latest select parsing changes sparklemotion/nokogiri#3317

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Implement the latest select parsing changes

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Relax selector parsing

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Neither the proposal nor the test changes are merged yet. Also, the tests are still failing. html5lib/html5lib-tests#178 whatwg/html#10557

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Relax <select> parser (WHATWG proposal) servo/html5ever#560

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Relax `<select>` parser #10557

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		<li><p><span>Reconstruct the active formatting elements</span>, if any.</p></li>

		<p>For each <var>ancestor</var> of <var>insertedOption</var>'s <span
		data-x="ancestor">ancestors</span>:</p>

Relax <select> parser #10557

Are you sure you want to change the base?

Relax <select> parser #10557

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Relax `<select>` parser #10557

Relax `<select>` parser #10557

josepharhar commented Aug 13, 2024 •

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