Block support: Add anchor support for dynamic blocks

[t-hamano]

Closes #51402

What?

This PR adds anchor support to almost all dynamic blocks.

Why?

Efforts to add anchor support to dynamic blocks were made in the past in #44771. However, that work also affected static blocks, potentially breaking them, so it was eventually reverted.

To add consistent anchor support regardless of whether the block is dynamic or static, the anchor is now always kept in comment delimiters (See #70993). This means we can now add anchor support to dynamic blocks.

How?

• Add anchor support to almost all dynamic blocks.
• Add server-side rendering of anchor support.
• Add unit tests.

As a result, these are the blocks that do not support anchors. The reason I didn't enable it is either:

• It's a static block, so it's outside the scope of this PR.
• It's an experimental block.
• Deprecated block.
• The anchor doesn't work on this block.

Name	Title
core/navigation-overlay-close	Navigation Overlay Close
core/tabs	Tabs
core/accordion-panel	Accordion Panel
core/accordion-item	Accordion Item
core/pattern	Pattern Placeholder
core/template-part	Template Part
core/missing	Unsupported
core/freeform	Classic
core/block	Pattern
core/html	Custom HTML
core/shortcode	Shortcode
core/text-columns	Text Columns (deprecated)
core/post-comment	Comment (deprecated)
core/form-submission-notification	Form Submission Notification
core/form-submit-button	Form Submit Button
core/comment-author-avatar	Comment Author Avatar (deprecated)

Testing Instructions

• Insert any of the dynamic blocks.
• Open the Advanced panel and apply an anchor string.
• Save the post and open the post.
• Confirm that the block has an id attribute.

[github-actions]

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Co-authored-by: t-hamano <[email protected]>
Co-authored-by: SirLouen <[email protected]>
Co-authored-by: aaronrobertshaw <[email protected]>
Co-authored-by: Mamaduka <[email protected]>
Co-authored-by: stefanfisk <[email protected]>

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[Mamaduka]

The anchor doesn't work on this block.

Is this due to the nature of the block (Classic, HTML, blocks without a wrapper) or some other limitation with the feature?

[github-actions]

Flaky tests detected in 17a3b1d.
Some tests passed with failed attempts. The failures may not be related to this commit but are still reported for visibility. See the documentation for more information.

🔍 Workflow run URL: https://github.com/WordPress/gutenberg/actions/runs/20487968254
📝 Reported issues:

• [Flaky Test] Block settings - link DISABLED, lightbox ENABLED - should show UI while block override is active, but hide UI if override is removed #65157 in /test/e2e/specs/editor/blocks/image.spec.js
• [Flaky Test] should open and edit templates correctly when active_templates experiment is enabled #73752 in /test/e2e/specs/site-editor/template-id-format.spec.js

[SirLouen]

@t-hamano I've tested it, and it's looking good. ✅

But there are two proposed changes to the unit tests:

1. The file should end in -test.php so in this case anchor-test.php
2. Can you add this test to the data provider?

'anchor with zero string is applied' => array(
	'support'  => true,
	'value'    => '0',
	'expected' => array( 'id' => '0' ),
),

And test it?

[aaronrobertshaw]

This is testing well for me 👍

Other than the suggested rename of the test file and the additional test cases, I think this is pretty close. While updating the test cases I think we could cover some more edge cases there.

Some possible test cases

public function data_anchor_block_support() {
    return array(
        'anchor id attribute is applied' => array(
            'support'  => true,
            'value'    => 'my-anchor',
            'expected' => array( 'id' => 'my-anchor' ),
        ),
        'anchor id attribute is not applied if block does not support it' => array(
            'support'  => false,
            'value'    => 'my-anchor',
            'expected' => array(),
        ),
        'empty anchor value returns empty array' => array(
            'support'  => true,
            'value'    => '',
            'expected' => array(),
        ),
        'null anchor value returns empty array' => array(
            'support'  => true,
            'value'    => null,
            'expected' => array(),
        ),
        'whitespace-only anchor value is applied' => array(
            'support'  => true,
            'value'    => '   ',
            'expected' => array( 'id' => '   ' ),
        ),
        'anchor with hyphen and numbers' => array(
            'support'  => true,
            'value'    => 'section-123',
            'expected' => array( 'id' => 'section-123' ),
        ),
        'anchor with underscore' => array(
            'support'  => true,
            'value'    => 'my_anchor_id',
            'expected' => array( 'id' => 'my_anchor_id' ),
        ),
        'anchor with colon (valid in HTML5)' => array(
            'support'  => true,
            'value'    => 'my:anchor',
            'expected' => array( 'id' => 'my:anchor' ),
        ),
        'anchor with period (valid in HTML5)' => array(
            'support'  => true,
            'value'    => 'my.anchor',
            'expected' => array( 'id' => 'my.anchor' ),
        ),
        'numeric anchor value' => array(
            'support'  => true,
            'value'    => '123',
            'expected' => array( 'id' => '123' ),
        ),
        'zero value is treated as empty' => array(
            'support'  => true,
            'value'    => 0,
            'expected' => array(),
        ),
        'false value is treated as empty' => array(
            'support'  => true,
            'value'    => false,
            'expected' => array(),
        ),
    );
}

I primarily tested with the Calendar, Latest Comments, Search, and Navigation blocks but did randomly try several more. Each worked as per the test instructions.

Screen.Recording.2025-12-23.at.5.33.23.pm.mp4

[t-hamano]

Thanks everyone for the reviews!

Is this due to the nature of the block (Classic, HTML, blocks without a wrapper) or some other limitation with the feature?

These blocks don't seem to work because they don't have a block wrapper in the first place.

On the other hand, I thought we could add anchor support to the Template Part block, but it didn't work properly. Perhaps there's a problem with the server-side rendering code. I'll investigate this in a follow-up.

But there are two proposed changes to the unit tests:
While updating the test cases I think we could cover some more edge cases there.

Updated the test cases 👍

[t-hamano]

While this test result is correct, it doesn't actually produce the expected results. That is, when you set an ID value of zero, it doesn't actually render.

This is likely an issue with get_block_wrapper_attributes() function, which causes falsy values ​​to be skipped.

https://github.com/WordPress/wordpress-develop/blob/814279bbce8c938e437d3c7a12976419ca8a0c8a/src/wp-includes/class-wp-block-supports.php#L187

This issue should also occur with className support and ariaLabel support.

I'll submit a follow-up core ticket regarding this.

[Mamaduka]

Right, empty() will return true for '0' and 0.

[Mamaduka]

This is test well for me ✅

Request changes have already been addressed.