WP_Filesystem_*::dirlist() may create invalid path

[afragen]

WP_Filesystem_*::dirlist() creates a nested array of files and subdirectories. If the directory path sent to the function contains a trailing slash, the recursion in the function will send something like path_to_directroy//subdirectory this may emit a PHP Warning though this doesn't seem to effect the results.

This is because line 650 of the function,

$struc['files'] = $this->dirlist( $path . '/' . $struc['name'], $include_hidden, $recursive );

should probably be

$struc['files'] = $this->dirlist( trailingslashit( $path )  . $struc['name'], $include_hidden, $recursive );

to avoid any possible errors.

[afragen]

This change might need to be made throughout.

WP_Filesystem_*::dirlist() uses $path . '/' in several places. For /path/, this will produce /path//.

This PR replaces $path = '/' with trailingslashit( $path ).

Trac ticket: https://core.trac.wordpress.org/ticket/57516

[costdev]

Introduced in [6779].

Looks good.

[costdev]

I've submitted ​PR 3877.

There's an additional benefit for the filesystem classes that by using $path = trailingslashit( $path ) before the while()/foreach() loops, the code is easier to read, and unnecessary concatenation isn't done in every iteration of the loops.

All uses of $path after the PR's $path = trailingslashit( $path ) were previously concatenated, so this doesn't cause any issues later.

[mukesh27]

Thanks @costdev for the ticket and PR.

Set 6.2 milestone for visibility.

Using trailingslashit( $path ) instead of $path . '/' makes sense and seems very unlikely to cause any problems.

Fixed in https://core.trac.wordpress.org/changeset/55354.

[azaozz]

In [55354]: Filesystem API: Use trailingslashit( $path ) instead of $path . '/'. Fixes a warning when $path already ends with a slash.

Props: costdev, afragen, mukesh27.
Fixes: #57516.