inconsistent handling of plugin_folder in get_plugins()

[wpmuguru]

If you pass the name of a folder to get_plugins, it needs to have a leading slash which then stores the plugin list from that folder in $wp_plugins['/folder-name'].

Secondly, the plugin file/path does not include folder-name passed to get_plugins, so the returned data has to have the 'folder-name/' added to the key of each plugin's information before it can be used throughout WP. The code I'm currently using to work around the issue is

			$my_plugins = get_plugins( '/extra' );
			$extra = array();
			if( !empty( $my_plugins ) ) {
				foreach( $my_plugins as $k => $v )
					$extra['extra/' . $k] = $v;
			}

related #15906

[sterlo]

Possibly related? #15853

[wonderboymusic]

Refreshed against trunk

[MikeHansenMe]

Refreshed relative to root.

[DrewAPicture]

15907.4.diff​ fixes spacing in the changed code, uses clearer concat for $plugin_files[].

[wonderboymusic]

Latest patch applies cleanly

[dd32]

• Backwards incompatible change
• The function returns data relative to WP_PLUGINS_DIR, or, optionally, relative to WP_PLUGINS_DIR/$folder in the event one is passed

Anyone calling it with a folder name will know the prefix if they require it for something.

Closing as wontfix for now, but if someone can come up with an actual use-case we can re-evaluate it, I can think of no reason why a change here is needed.