BUG: WP_Query::max_num_pages becomes negative when using ep_integrate

[dmitrijCraq]

Describe the bug

Bug: WP_Query::max_num_pages becomes negative when using ep_integrate

Description

While integrating ElasticPress, I noticed an unexpected value for WP_Query::$max_num_pages.

With ep_integrate => true, the query returns:

• found_posts = 17
• max_num_pages = -17

The same query executed without ElasticPress integration does not exhibit this behavior.

A negative value for max_num_pages should never be possible, especially when found_posts is positive.

Query

$query = new WP_Query( [
    // ...
    'ep_integrate' => true,
] );

Observed values

var_dump( [
    'found_posts'    => $query->found_posts,
    'max_num_pages'  => $query->max_num_pages,
    'posts_per_page' => $query->get( 'posts_per_page' ),
] );

Output:

found_posts    => 17
max_num_pages  => -17
posts_per_page => -1

Expected behavior

I would expect either:

• max_num_pages = 17 if posts_per_page is treated as 1, or
• max_num_pages = 0 or 1 when posts_per_page = -1 (no pagination),

but never a negative value.

Additional notes

From debugging, it appears the issue only occurs after ElasticPress populates the WP_Query object with the Elasticsearch response. The initial WP_Query instance does not contain the negative value.

Looking at the code, it seems max_num_pages is calculated directly from found_posts and posts_per_page. Since posts_per_page = -1 is a valid WordPress value meaning "return all posts", I believe this edge case should be handled explicitly to prevent max_num_pages from becoming negative.

I'm not yet sure whether this is caused by ElasticPress itself or by an interaction with WordPress, but I thought it was worth reporting since max_num_pages should never be negative.

Steps to Reproduce

## Steps to reproduce

1. Ensure ElasticPress is active and the index is up to date.
2. Create at least one published post that can be returned by a search query.
3. Run the following query:

```php
$query = new WP_Query( [
    'post_type'      => 'post',
    's'              => '',
    'posts_per_page' => -1,
    'ep_integrate'   => true,
] );
```

4. Inspect the query object:

```php
var_dump( [
    'found_posts'    => $query->found_posts,
    'max_num_pages'  => $query->max_num_pages,
    'posts_per_page' => $query->get( 'posts_per_page' ),
] );
```

5. If the search returns at least one result (for example, `found_posts = 17`), `max_num_pages` is set to `-17`.

## Expected behavior

When `posts_per_page = -1`, `max_num_pages` should not be negative. It should behave consistently with WordPress core, where pagination is effectively disabled.

Screenshots, screen recording, code snippet

No response

Environment information

• PHP: 8.3.30

WordPress and ElasticPress information

• WordPress: 7.0
• ElasticPress: 5.3.3

Code of Conduct

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