When encountering an HTML tag with duplicate copies of an attribute the tag processor ignores the duplicate values, according to the specification. However, when removing an attribute it must remove all copies of that attribute lest one of the duplicates becomes the primary and it appears as if no attributes were removed.
In this patch we're adding tests that will be used to ensure that all attribute copies are removed from a tag when one is request to be removed.
**Before**
{{{#!php
<?php
$p = new WP_HTML_Tag_Processor( '<br id=one id="two" id='three' id>' );
$p->next_tag();
$p->remove_attribute( 'id' );
$p->get_updated_html();
// <br id="two" id='three' id>
}}}
**After**
{{{#!php
<?php
$p = new WP_HTML_Tag_Processor( '<br id=one id="two" id='three' id>' );
$p->next_tag();
$p->remove_attribute( 'id' );
$p->get_updated_html();
// <br>
}}}
Previously we have been overlooking duplicate attributes since they don't have an impact on what parses into the DOM. However, as one unit test affirmed (asserting the presence of the bug in the tag processor) when removing an attribute where duplicates exist this meant we ended up changing the value of an attribute instead of removing it.
In this patch we're tracking the text spans of the parsed duplicate attributes so that ''if'' we attempt to remove them then we'll have the appropriate information necessary to do so. When an attribute isn't removed we'll simply forget about the tracked duplicates. This involves some overhead for normal operation ''when'' in fact there are duplicate attributes on a tag, but that overhead is minimal in the form of integer pairs of indices for each duplicated attribute.
Props dmsnell, zieladam.
Merges [56684] to the 6.3 branch.
Fixes#58119.
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