Prevent `update_option()` from updating when the old and new values contain identical objects.

[peterwilsoncc]

When an object is included in an option, passing an unchanged value to update_option will trigger an UPDATE query.

Given the data below, the meta_data will have a different resource ID for the old and new values. $value === $old_value will always evaluate untrue and the database will be updated and the caches cleared.

array(2) {
  ["url"]=>
  string(85) "http://src.wordpress-develop.dev/wp-content/uploads/2016/10/cropped-Blurry-Lights.jpg"
  ["meta_data"]=>
  object(stdClass)#370 (3) {
    ["attachment_id"]=>
    int(292)
    ["height"]=>
    int(708)
    ["width"]=>
    int(1260)
  }
}

Followup from #38866, props due @bradyvercher for finding.

[peterwilsoncc]

In 38903.diff​:

• run the old and new values through maybe_serialize() before comparing.

Bringing this over from a patch in #38866.

I'm not sure of the perfromance implication of serialising in this manner, on the surface it's doesn't seem great, so some data would be helpful here.

[salcode]

Updated patch file to include test

[salcode]

Test written at #wcus 2016 contributor day

[iaaxpage]

@peterwilsoncc I just pulled the patch and ran the option unit tests and they passed.

phpunit tests/phpunit/tests/option/option.php

The method test_the_basics asserts this to false if the value is the same.

$this->assertFalse( update_option( $key, $value ) ); // Value is the same

[peterwilsoncc]

Replying to salcode:

Test written at #wcus 2016 contributor day

Thanks for the tests @salcode.

Rather than using the hook to detect if the function exists early, a more direct test would be to test get_num_queries() returns the same value before and after the function call. It will save a bit of messing around.

Testing the returned value is false would also be ideal.

[salcode]

Ha ha, that is an infinitely better way to test this. Thanks @peterwilsoncc

I've updated the patch.

[peterwilsoncc]

Replying to salcode:

I've updated the patch.

Thanks for the refresh.

One gotcha in the patch, assertFalse isn't available in the version of phpunit WP uses when testing PHP 5.6 and earlier. To test for false, the code is:

$this->assertSame( false, update_option( 'array_w_object', $array_w_object ) );

My intention is to commit the code this weekend, I can update the patch then if you wish.

[peterwilsoncc]

@salcode ignore me, I was thinking of assertNotFalse(). Your patch is great as it. :)

[salcode]

Great, thanks for checking one item off my to do list. :)

[peterwilsoncc]

In 38903.4.diff​:

• avoid the maybe_serialize calls if they are not needed. This is to avoid the performance cost of serialization in most instances.
• minor formatting changes in the unit tests for coding standards

[peterwilsoncc]

In 39564:

Options: Prevent unnecessary SQL updates by update_option.

Previously an option containing an object would trigger an SQL UPDATE on all calls to update_option, even if the old and new values were identical. This was due to the old and new values having differing resource IDs.

This change compares the old and new values as serialized data to remove the resource ID from the comparison.

Props salcode, bradyvercher, peterwilsoncc.
Fixes #38903.