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get_adjacent_post: adjacent post query plugin compatibility #10620

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get_adjacent_post: adjacent post query plugin compatibility #10620

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Add deterministic fallback for adjacent post queries only when the qu…
ramonjd Dec 12, 2025
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ramonjd Dec 12, 2025
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ramonjd Dec 12, 2025
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Update var name and PHP docs
ramonjd Dec 19, 2025
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23 changes: 19 additions & 4 deletions src/wp-includes/link-template.php
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Original file line number Diff line number Diff line change
Expand Up @@ -1814,6 +1814,8 @@ function get_next_post( $in_same_term = false, $excluded_terms = '', $taxonomy =
* Can either be next or previous post.
*
* @since 2.5.0
* @since 6.9.0 Introduce deterministic fallback based in IDs to account for date collisions.
* @since 6.9.1 Remove deterministic fallback for sites modifying the WHERE clause via a filter. See #64390.
*
* @global wpdb $wpdb WordPress database abstraction object.
*
Expand Down Expand Up @@ -1965,7 +1967,8 @@ function get_adjacent_post( $in_same_term = false, $excluded_terms = '', $previo
$join = apply_filters( "get_{$adjacent}_post_join", $join, $in_same_term, $excluded_terms, $taxonomy, $post );

// Prepare the where clause for the adjacent post query.
$where_prepared = $wpdb->prepare( "WHERE (p.post_date $comparison_operator %s OR (p.post_date = %s AND p.ID $comparison_operator %d)) AND p.post_type = %s $where", $current_post_date, $current_post_date, $post->ID, $post->post_type ); // phpcs:ignore WordPress.DB.PreparedSQL.InterpolatedNotPrepared -- $comparison_operator is a string literal, either '<' or '>'.
$where_prepared = $wpdb->prepare( "WHERE p.post_date $comparison_operator %s AND p.post_type = %s $where", $current_post_date, $post->post_type ); // phpcs:ignore WordPress.DB.PreparedSQL.InterpolatedNotPrepared -- $comparison_operator is a string literal, either '<' or '>'.
$deterministic_where_prepared = $wpdb->prepare( "WHERE (p.post_date $comparison_operator %s OR (p.post_date = %s AND p.ID $comparison_operator %d)) AND p.post_type = %s $where", $current_post_date, $current_post_date, $post->ID, $post->post_type ); // phpcs:ignore WordPress.DB.PreparedSQL.InterpolatedNotPrepared -- $comparison_operator is a string literal, either '<' or '>'.

/**
* Filters the WHERE clause in the SQL for an adjacent post query.
Expand All @@ -1980,16 +1983,22 @@ function get_adjacent_post( $in_same_term = false, $excluded_terms = '', $previo
*
* @since 2.5.0
* @since 4.4.0 Added the `$taxonomy` and `$post` parameters.
* @since 6.9.0 Adds ID-based fallback for posts with identical dates in adjacent post queries.
*
* @param string $where The `WHERE` clause in the SQL.
* @param string $where_prepared The `WHERE` clause in the SQL.
* @param bool $in_same_term Whether post should be in the same taxonomy term.
* @param int[]|string $excluded_terms Array of excluded term IDs. Empty string if none were provided.
* @param string $taxonomy Taxonomy. Used to identify the term used when `$in_same_term` is true.
* @param WP_Post $post WP_Post object.
*/
$where = apply_filters( "get_{$adjacent}_post_where", $where_prepared, $in_same_term, $excluded_terms, $taxonomy, $post );

// Only force deterministic fallback if the where clause has not been modified by a filter.
if ( $where === $where_prepared ) {
$where = $deterministic_where_prepared;
}

$sort_prepared = "ORDER BY p.post_date $order LIMIT 1";

/**
* Filters the ORDER BY clause in the SQL for an adjacent post query.
*
Expand All @@ -2005,12 +2014,18 @@ function get_adjacent_post( $in_same_term = false, $excluded_terms = '', $previo
* @since 4.4.0 Added the `$post` parameter.
* @since 4.9.0 Added the `$order` parameter.
* @since 6.9.0 Adds ID sort to ensure deterministic ordering for posts with identical dates.
* @since 6.9.1 Remove deterministic fallback for sites modifying the SORT clause via a filter. See #64390.
*
* @param string $order_by The `ORDER BY` clause in the SQL.
* @param WP_Post $post WP_Post object.
* @param string $order Sort order. 'DESC' for previous post, 'ASC' for next.
*/
$sort = apply_filters( "get_{$adjacent}_post_sort", "ORDER BY p.post_date $order, p.ID $order LIMIT 1", $post, $order );
$sort = apply_filters( "get_{$adjacent}_post_sort", $sort_prepared, $post, $order );

// Only force deterministic sort if the sort clause has not been modified by a filter.
if ( $sort === $sort_prepared ) {
$sort = "ORDER BY p.post_date $order, p.ID $order LIMIT 1";
}

$query = "SELECT p.ID FROM $wpdb->posts AS p $join $where $sort";
$key = md5( $query );
Expand Down
219 changes: 219 additions & 0 deletions tests/phpunit/tests/link/getAdjacentPost.php
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Original file line number Diff line number Diff line change
Expand Up @@ -622,6 +622,225 @@ public function test_get_adjacent_post_with_identical_dates() {
$this->assertEquals( $post_ids[3], $next->ID );
}

/**
* Test that deterministic ID fallback is applied when WHERE filter doesn't modify the clause.
*
* @ticket 64390
*/
public function test_get_adjacent_post_identical_dates_applies_deterministic_where_when_filter_unmodified() {
$identical_date = '2024-01-01 12:00:00';

// Create posts with identical dates but different IDs.
$post_ids = array();
for ( $i = 1; $i <= 5; $i++ ) {
$post_ids[] = self::factory()->post->create(
array(
'post_title' => "Post $i",
'post_date' => $identical_date,
)
);
}

// Add a filter that doesn't modify the WHERE clause (returns unchanged).
add_filter(
'get_next_post_where',
static function ( $where ) {
// Return unchanged - deterministic fallback should be applied.
return $where;
}
);

// Test navigation from the middle post (ID: 3rd post).
$current_post_id = $post_ids[2]; // 3rd post
$this->go_to( get_permalink( $current_post_id ) );

// Next post should be the 4th post (higher ID, same date) - deterministic.
$next = get_adjacent_post( false, '', false );
$this->assertInstanceOf( 'WP_Post', $next );
$this->assertSame( $post_ids[3], $next->ID, 'Next post should be the 4th post (higher ID, same date).' );
}

/**
* Test that deterministic ID fallback is NOT applied when WHERE filter modifies the clause.
*
* @ticket 64390
*/
public function test_get_adjacent_post_identical_dates_respects_modified_where_filter() {
$identical_date = '2024-01-01 12:00:00';

// Create posts with identical dates but different IDs.
$post_ids = array();
for ( $i = 1; $i <= 5; $i++ ) {
$post_ids[] = self::factory()->post->create(
array(
'post_title' => "Post $i",
'post_date' => $identical_date,
)
);
}

// Capture what the filter receives and what it returns.
$filter_received = '';
$filter_returned = '';
add_filter(
'get_next_post_where',
static function ( $where ) use ( &$filter_received, &$filter_returned ) {
$filter_received = $where;
/*
* Modify the WHERE clause - deterministic fallback should NOT be applied.
* Add a harmless condition that won't affect results but proves the filter was applied.
* This is to ensure that the deterministic fallback is not applied on top of the filter's modification.
*/
$filter_returned = $where . ' AND 1=1';
return $filter_returned;
}
);

// Test navigation from the middle post (ID: 3rd post).
$current_post_id = $post_ids[2]; // 3rd post
$this->go_to( get_permalink( $current_post_id ) );

// Call get_adjacent_post to trigger the filter.
get_adjacent_post( false, '', false );

// Verify the filter received the non-deterministic WHERE clause (without ID fallback).
$this->assertNotEmpty( $filter_received, 'Filter should have been called.' );
$this->assertStringNotContainsString( 'AND p.ID', $filter_received, 'Filter should receive WHERE clause without deterministic ID fallback.' );
// Verify the filter's modification is preserved (proves deterministic logic wasn't applied on top).
$this->assertStringContainsString( 'AND 1=1', $filter_returned, 'Filter modification should be preserved.' );
}

/**
* Test that deterministic ID sort is applied when SORT filter doesn't modify the clause.
*
* @ticket 64390
*/
public function test_get_adjacent_post_identical_dates_applies_deterministic_sort_when_filter_unmodified() {
$identical_date = '2024-01-01 12:00:00';

// Create posts with identical dates but different IDs.
$post_ids = array();
for ( $i = 1; $i <= 5; $i++ ) {
$post_ids[] = self::factory()->post->create(
array(
'post_title' => "Post $i",
'post_date' => $identical_date,
)
);
}

// Add a filter that doesn't modify the SORT clause (returns unchanged).
add_filter(
'get_next_post_sort',
static function ( $sort ) {
// Return unchanged - deterministic ID sort should be applied.
return $sort;
}
);

// Test navigation from the middle post (ID: 3rd post).
$current_post_id = $post_ids[2]; // 3rd post
$this->go_to( get_permalink( $current_post_id ) );

// Next post should be the 4th post (higher ID, same date) - deterministic.
$next = get_adjacent_post( false, '', false );
$this->assertInstanceOf( 'WP_Post', $next );
$this->assertSame( $post_ids[3], $next->ID, 'Next post should be the 4th post (higher ID, same date).' );
}

/**
* Test that deterministic ID sort is NOT applied when SORT filter modifies the clause.
*
* @ticket 64390
*/
public function test_get_adjacent_post_identical_dates_respects_modified_sort_filter() {
$identical_date = '2024-01-01 12:00:00';

// Create posts with identical dates but different IDs.
$post_ids = array();
for ( $i = 1; $i <= 5; $i++ ) {
$post_ids[] = self::factory()->post->create(
array(
'post_title' => "Post $i",
'post_date' => $identical_date,
)
);
}

// Capture what the filter receives and what it returns.
$filter_received = '';
$filter_returned = '';
add_filter(
'get_next_post_sort',
static function ( $sort, $post, $order ) use ( &$filter_received, &$filter_returned ) {
$filter_received = $sort;
// Modify to remove ID - deterministic ID sort should NOT be applied.
$filter_returned = "ORDER BY p.post_date $order LIMIT 1";
return $filter_returned;
},
10,
3
);

// Test navigation from the middle post (ID: 3rd post).
$current_post_id = $post_ids[2]; // 3rd post
$this->go_to( get_permalink( $current_post_id ) );

// Call get_adjacent_post to trigger the filter.
get_adjacent_post( false, '', false );

// Verify the filter received the non-deterministic SORT clause (without ID).
$this->assertNotEmpty( $filter_received, 'Filter should have been called.' );
$this->assertStringNotContainsString( 'p.ID', $filter_received, 'Filter should receive SORT clause without deterministic ID sort.' );
// Verify the filter's modification is preserved (proves deterministic logic wasn't applied on top).
$this->assertStringNotContainsString( 'p.ID', $filter_returned, 'Filter modification should not include ID when filter removes it.' );
$this->assertStringContainsString( 'ORDER BY p.post_date', $filter_returned, 'Filter modification should be preserved.' );
}

/**
* Test that both WHERE and SORT filters work together correctly.
*
* @ticket 64390
*/
public function test_get_adjacent_post_identical_dates_with_both_filters_unmodified() {
$identical_date = '2024-01-01 12:00:00';

// Create posts with identical dates but different IDs.
$post_ids = array();
for ( $i = 1; $i <= 5; $i++ ) {
$post_ids[] = self::factory()->post->create(
array(
'post_title' => "Post $i",
'post_date' => $identical_date,
)
);
}

// Add filters that don't modify the clauses.
add_filter(
'get_previous_post_where',
static function ( $where ) {
return $where;
}
);

add_filter(
'get_previous_post_sort',
static function ( $sort ) {
return $sort;
}
);

// Test navigation from the middle post (ID: 3rd post).
$current_post_id = $post_ids[2]; // 3rd post
$this->go_to( get_permalink( $current_post_id ) );

// Previous post should be the 2nd post (lower ID, same date) - deterministic.
$previous = get_adjacent_post( false, '', true );
$this->assertInstanceOf( 'WP_Post', $previous );
$this->assertSame( $post_ids[1], $previous->ID, 'Previous post should be the 2nd post (lower ID, same date).' );
}

/**
* Test get_adjacent_post with mixed dates and identical dates.
*
Expand Down
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