copy_dir fails in coping some files in nested dirs

[caraffande]

Tricky, subtle bug!
Let's suppose we do have a folder structure like this:

/folder1/folder2/
/folder1/folder2/file1.txt
/folder1/folder2/subfolder1/
/folder1/folder2/subfolder1/file2.txt
/folder3/

and that we want to move or copy the entire folder2 to folder3 so that the final structure is like this:

/folder1/folder2/
/folder1/folder2/file1.txt
/folder1/folder2/subfolder1/
/folder1/folder2/subfolder1/file1.txt
/folder3/folder2/
/folder3/folder2/file1.txt
/folder3/folder2/subfolder1/
/folder3/folder2/subfolder1/file1.txt

IMPORTANT: Please note that initially the path /folder3/folder2 doesn't exist.
The problem arise based on the order used internally by copy_dir to retieve the source elements.
Let's see it in detail.

command:

copy_dir('/folder1/folder2', '/folder3/folder2')

Result:

First iteration: /folder3/folder2 is created with mkdir.
Second iteration (if copy_dir retrieves first /folder1/folder2/file1.txt): copy(/folder1/folder2/file1.txt, /folder3/folder2/file1.txt) fails because /folder3/folder2 doesn't exist!
Second iteration (if copydir retrieves first /folder1/folder2): /folder3/folder2 is created. Now, by the next iteration, copy(/folder1/folder2/file1.txt, /folder3/folder2/file1.txt) will not fail.

I've discover this bug almost accidentally using the following (buggy) code:

<?php
    function copy_recursive($source, $dest, $merge = true)
    {
        if (is_file($dest) && is_dir($source)) {
            error_log(__("[PPC] - Error: Cannot copy a dir into a file."));
            return;
        }

        if (!$merge) delete_recursive($dest);

        if (is_dir($source)) {
            $iterator = new RecursiveIteratorIterator(
                new RecursiveDirectoryIterator($source, RecursiveDirectoryIterator::SKIP_DOTS),
                RecursiveIteratorIterator::SELF_FIRST
            );

            foreach ($iterator as $file) {
                if ($file->isDir()) {
                    mkdir($dest.DIRECTORY_SEPARATOR.$iterator->getSubPathName(), 0777, true);
                } else {
                    copy($file, $dest.DIRECTORY_SEPARATOR.$iterator->getSubPathName());
                }
            }
        } else {
            copy($source, $dest);
        }
    }

I need a copy_dir (or copy_recursive) function for copying my custom plugin's data (a complex nested structure of file/folders) to wordpress' upload dir. The above code used to fail, apparently randomly, the copy of only some files.
Then I've tried to use wordpress' copy_dir function only to discover, with disappointment, that it used to fail exactly the same way.

The solution, at least for my (buggy) code, is to create the destination folder before any copy command, like this is:

<?php
    function copy_recursive($source, $dest, $merge = true)
    {
        if (is_file($dest) && is_dir($source)) {
            error_log(__("[PPC] - Error: Cannot copy a dir into a file."));
            return;
        }

        if (!$merge) delete_recursive($dest);

        if (!file_exists($dest)) mkdir($dest, 0777, true); // <<<---- Bug Fix!

        if (is_dir($source)) {
            $iterator = new RecursiveIteratorIterator(
                new RecursiveDirectoryIterator($source, RecursiveDirectoryIterator::SKIP_DOTS),
                RecursiveIteratorIterator::SELF_FIRST
            );

            foreach ($iterator as $file) {
                if ($file->isDir()) {
                    mkdir($dest.DIRECTORY_SEPARATOR.$iterator->getSubPathName(), 0777, true);
                } else {
                    copy($file, $dest.DIRECTORY_SEPARATOR.$iterator->getSubPathName());
                }
            }
        } else {
            copy($source, $dest);
        }
    }

This creates the destination directory in copy_dir() if it does not exist.

Trac ticket: https://core.trac.wordpress.org/ticket/41855

[costdev]

​PR 4221 creates the destination directory if it does not exist. Includes a PHPUnit test which demonstrates the issue, proves the fix is successful, and protects backward compatibility going forward.

Milestoning for 6.3.

[costdev]

Plugin for issue reproduction and patch testing.

[costdev]

Testing Instructions

These steps define how to reproduce the issue, and indicate the expected behavior.

Steps to Reproduce or Test

1. Download the attached testing plugin.
2. Navigate to Plugins > Add New.
3. Click Upload Plugin, select test-41855.zip and click Install Now.
4. 🐞 Once installed, click Activate.
5. Apply the patch.
6. ✅ Refresh the page.

Expected Results

When reproducing a bug:

• ❌ An admin notice should appear stating Could not create directory..
• ❌ wp-content/plugins/test-41855/test-result/test-directory should not exist.

When testing a patch to validate it works as expected:

• ✅ An admin notice should appear stating Success! .
• ✅ wp-content/plugins/test-41855/test-result/test-directory should exist with the same contents as wp-content/plugins/test-41855/test-directory.

Test Report Icons:
🐞 <= Indicates where issue ("bug") occurs.
✅ <= Behavior is expected.
❌ <= Behavior is NOT expected.