Search-replace of uploads paths is innefective when importing from multi-site into single-site

[drebs]

Describe the bug

If a blog is exported from a multi-site installation without passing --blog_id and then imported into a single-site installation with a --new_url, then the search-replace command for uploads paths does not effectivelly replace wp-content/uploads/sites/$blog_id for wp-content/uploads.

Steps to Reproduce

Export the website from a multi-site installation using exactly the following command line options:

wp mu-migration export all myblog.zip --url=myblog.example.com

Then import it into a single-site installation using exactly the following command line options:

wp mu-migration import all myblog.zip --new_url=example.com/myblog

In our case, we noticed that the logo was not showing up after migration. It so happens that the theme we're using stores logo info in the wp_options table and the path was not replaced at all (note that the URL was replaced correctly):

MariaDB [myblog]> select option_name, option_value from wp_options where option_name = 'theme_mods_morning';
+--------------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| option_name        | option_value                                                                                                                                                                                                                                |
+--------------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| theme_mods_morning | a:5:{i:0;b:0;s:18:"nav_menu_locations";a:1:{s:7:"primary";i:2;}s:11:"logo_upload";s:71:"https://example.com/myblog/wp-content/uploads/sites/30/2019/10/mama.png";s:10:"search_bar";s:4:"show";s:18:"custom_css_post_id";i:-1;} |
+--------------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)

Expected behavior

Uploads paths should have been replaced correctly throughout the database (and the logo should appear in our blog).

Environment information

• Plugin and version: MU-Migration 0.3.2
• Theme and version: Morning 1.02 (https://www.competethemes.com/morning)

Additional context

I did some investigation and I found that:

• Despite in the original installation blog_id = 30, the exported .json file contains blog_id = 1, and thus this line was never executed when importing.
• The above happens because if --blog_id is not passed when exporting, this line is never executed and then the .json file ends up with blog_id = 1.
• I don't really understand if this is an expected behavior of the export command (and then passing --blog_id when exporting is "mandatory" for the export/import case described here) or if it is a bug and this whole bug report should've actually been about this specific behavior.
• If I add --blog_id=30 to the command line when exporting, the issue described in this bug report does not manifest itself.

[wpbullet]

FWIW when I made a script using this amazing package I worked around this with:

wp search-replace "/wp-content/uploads/" "/wp-content/uploads/sites/${SITEID}/" --url=${SITEURL} --report-changed-only