wp_maintenance should use wp_die

[spacedmonkey]

When maintenance mode is active, wp_die called, so the output can be filtered by plugins.

[pento]

What kind of plugins would be able to filter this output? wp_maintenance() is called before any plugins or dropins are loaded.

WP-CLI would be able to use it (for example, the enable_loading_advanced_cache_dropin filter was added for WP-CLI), similar custom loaders could do it, too.

[afercia]

Not sure why this ticked focuses accessibility. Going to remove the focus to clean-up the accessibility report. If you feel this issue is related to web content accessibility and universal design, please do feel free to re-add it.

[spacedmonkey]

In 5.1 wp_die received a number of improvements ( #45933 #46026 #46054 #46025 ). So using wp_die add the following improvements here.

• Errors will be displayed in the correct format depending on the request, so xml, json, jsonp, xmlrpc and ajax request, will get the correctly formatted response.
• WP_CLI would be able to use as @pento mentions above.
• Error messages will be styled on look consistent with the rest of core.
• Future improvements to wp_die will be reflected in the maintenance mode.
• Correct cache control headers will be sent. (See #46054 )
• As json request now handles better (see #45933), it means anything use REST API will error my gracefully (including Gutenberg).

The arguments can made for these tickets. #41655 #45975

I am making this as 5.2, in the hopes that is goes in.

[desrosj]

With 5.2 beta in 2 days, let's punt this so it can land early in 5.3 to be properly tested. @SergeyBiryukov if you are comfortable and feel that this is ready for 5.2, feel free to move back and commit.

[SergeyBiryukov]

In 45019:

Bootstrap/Load: Use wp_die() instead of hardcoded HTML in wp_maintenance(), so the output can be filtered by plugins.

Props spacedmonkey.
Fixes #45974.

[SergeyBiryukov]

​With the beta delayed, moving back to 5.2.

[SergeyBiryukov]

In 45022:

PHPCS: Remove extra tab added in [45019].

See #45974.

[desrosj]

Looks like this one never received a dev note. Going to remove needs-dev-note as the ship has already sailed.