Add filters and ajax support for personal data erasure

[allendav]

Similar to #43438 but instead of for personal data export, this is for personal data erasure.

Like #43438, plugins (or core concerns) will need to be able to register callbacks which can erase (or at least anonymize) personal data (a "page" at a time) from where they've stored it. How much is processed by a plugin's exporter in the context of a page is up to the plugin but should target to finish in far less than PHP timeout on a typical host.

When a plugin no longer needs more "pages" it indicates it is done with erasure in the same manner as in #43438.

BTW - the rationale for ajax is to allow wp-admin to drive the process without timeouts that could occur on sites with lots of pages of objects to traverse. As with #43438, the ajax exporter-by-exporter, page-by-page approach will also lend itself to REST API endpoints down the road.

[allendav]

Adds personal data eraser filtering and ajax supportr

[allendav]

Requires #43442 to test. For testing instructions, see #43442.

[allendav]

Updated to return the number of items removed, retained and any messages from the erasers

[allendav]

Updated patch. Erasure ajax response now includes how many items were removed, how many were retained, and any messages personal data erasers wants to display to the administrator (e.g. "Personal data for this user was found in order 1324 but was not removed because the order has not yet shipped." )

Requires additional patches to test. Please standby for updated patches for #43442 and #43602 for testing.

cc @azaozz @mikejolley

[ericdaams]

Updated to correct incorrect doc comment for wp_privacy_personal_data_erasers filter

[desrosj]

Moving to the 4.9.6 milestone after consensus was reached in the most recent GDPR chat (​https://wordpress.slack.com/archives/C9695RJBW/p1524063200000304).

[azaozz]

In 42986:

Privacy: add means to erase personal data by username or email address. First run.

Props allendav, coreymckrill, ericdaams, azaozz.
See #43637, #43602.

[coreymckrill]

Should wp_ajax_wp_privacy_erase_personal_data() have a capability check? Seems like it should be delete_users like in https://core.trac.wordpress.org/ticket/43602#comment:21

[azaozz]

Replying to coreymckrill:

Yep, the cap check is there but see https://core.trac.wordpress.org/ticket/43602#comment:26.

[joemcgill]

This depends on functionality from #43438, specifically [42889] to be backported, before this can be merged to the 4.9 branch. Additionally, @ocean90's concerns on the original ticket need to be addressed before this can be completed.

[desrosj]

In 43637.4.diff​:

• Ensure docblock for the wp_privacy_personal_data_erasers filter is properly formatted.
• Change the %d placeholders for array indexes to %s (there was nothing ensuring arrays have numeric indexes only).
• Add missing placeholder descriptions for translators.

[SergeyBiryukov]

Replying to desrosj:

Change the %d placeholders for array indexes to %s (there was nothing ensuring arrays have numeric indexes only).

$eraser_index is specifically cast to int though:

$eraser_index = (int) $_POST['eraser'];

Let's just add translator comments and leave the placeholders as is, I don't see a need for changing them.

[desrosj]

In 43637.5.diff​:

• Ensure docblock for the wp_privacy_personal_data_erasers filter is properly formatted.
• Add missing placeholder descriptions for translators.

[SergeyBiryukov]

In 43075:

Privacy: add means to erase personal data by username or email address. First run.

Props allendav, coreymckrill, ericdaams, azaozz.
Merges [42986] to the 4.9 branch.
See #43637, #43602.

[SergeyBiryukov]

In 43104:

Docs: Correct DocBlock formatting for wp_privacy_personal_data_erasers filter.

See #43637.

[SergeyBiryukov]

In 43106:

Docs: Correct DocBlock formatting for wp_privacy_personal_data_erasers filter.

Merges [43104] to the 4.9 branch.
See #43637.

[SergeyBiryukov]

Looks like the changes from 43637.5.diff​ are already committed in [43060] and backported in [43105].

[desrosj]

Moving to the new Privacy component.