getEntityRecords() returns stale values when subsequent calls reduce the number of records

[johnbillion]

Description

If you call select('core').getEntityRecords( .. ) with an argument which causes the number of results in the set to be reduced from its previous value, for example via the include parameter, unexpected stale values will be present at the end of the array.

Step-by-step reproduction instructions

See below for what seems to be the minimum code to reproduce the issue as a whole by implementing a filter on the Tags panel.

1. Open the post editing screen and add a tag to the post
2. This will trigger the withSelect() callback due to the change. ownProps.terms is an array containing the chosen tag ID. Observe the getEntityRecords() resolver fires off a REST API request to fetch the tag by using the include parameter on the endpoint.
3. Add a second tag and observe the same, with both tag IDs in the include parameter.
4. Remove one of the tags, thus causing the include parameter passed to getEntityRecords() to include one fewer elements that it did previously. Observe the resolver correctly queries for one term ID in the REST API request, but the subsequent return value of getEntityRecords() still contains two values.

What appears to be happening is the getEntityRecords() resolver iterates the values it receives from the REST API but somehow retains stale values for all subsequent elements in the array instead of discarding them.

Code snippet

This is a filter on the Tags panel which calls getEntityRecords() inside the withSelect() callback. You could manually call getEntityRecords() in your console but this demonstrates the problem within the context of withSelect().

const FilterTermSelector = () => {
  return (props) => {
    return (
      <>
        <TaxonomySelector {...props} />
        <CustomSelector {...props} />
      </>
    );
  };
};

wp.hooks.addFilter(
  'editor.PostTaxonomyType',
  'foo',
  FilterTermSelector,
);

class CustomSelector extends React.PureComponent {
  render() {
    return (
      <>
        <p>Terms: {JSON.stringify(this.props.terms)}</p>
        <p>Records: {JSON.stringify(this.props.records)}</p>
      </>
    );
  }
}

export default compose([
  withSelect((select, ownProps) => {
    const records = select('core').getEntityRecords('taxonomy', ownProps.taxonomy.slug, {
      include: ownProps.terms,
      _fields: 'id,name',
    });

    return {
      records,
    };
  }),
])(CustomSelector);

WordPress information

• WordPress version: 5.7
• Gutenberg version: N/A

[Mamaduka]

I think I was able to reproduce the issue with the code @johnbillion provided. However, it's a little inconsistent.

The displayed result happens in specific scenarios and not for all tag combinations.

I also came across this issue while working on #33459, but I couldn't reproduce it, so I ignored it.

Tags are generedet using WP CLI:

wp term generate post_tag --count=50

Screencast

CleanShot.2021-08-11.at.11.53.38.mp4

[Mamaduka]

I was also able to reproduce this via the DevTools console. This method has the same results compared to UI reproduction steps.

Step by step

// Fetch first 10 items
wp.data.select('core').getEntityRecords('taxonomy', 'post_tag', { _fields: 'id,name' } );

// See the resolver fire request

// Fetch specific items by ID.
// The only requirement for `include` is that one of the items shouldn't be a part of the initial request.
wp.data.select('core').getEntityRecords('taxonomy', 'post_tag', { include: [ 5, 14 ], _fields: 'id,name' } );

// Wait for the resolver.

// Check the data. This will include item that was part of the initial response twice.
wp.data.select('core').getEntityRecords('taxonomy', 'post_tag', { include: [ 5, 14 ], _fields: 'id,name' } );

My guess

The source of the issue might be the getMergedItemIds. The following test will fail:

const original = deepFreeze( [ 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 ] );
const result = getMergedItemIds( original, [ 11, 4 ], 1, 10 );

expect( result ).toEqual( [ 11, 2, 3, 4, 5, 6, 7, 8, 9, 10 ] );

Is it expected for getMergedItemIds not to return unique IDs?

[Mamaduka]

Fixed via #34583.