wp import --authors=<file>.csv fails with DivisionByZeroError instead of creating the mapping file #111

Bug Report

• Yes, I reviewed the contribution guidelines.
• Yes, more specifically, I reviewed the guidelines on how to write clear bug reports.

Describe the current, buggy behavior

The help for --authors says the command will "read author mapping associations from a CSV, or create a CSV for editing if the file path doesn't exist".

When the CSV file does not exist yet, wp import now stops with a fatal error instead of writing the file:

$ wp import export.xml --authors=mapping.csv
Starting the import process...
Fatal error: Uncaught DivisionByZeroError: Division by zero in phar:///tmp/wp.phar/vendor/wp-cli/import-command/src/Import_Command.php:732
Stack trace:
#0 phar:///tmp/wp.phar/vendor/wp-cli/import-command/src/Import_Command.php(617): Import_Command->suggest_user('admin', 'admin@example.c...')
#1 phar:///tmp/wp.phar/vendor/wp-cli/import-command/src/Import_Command.php(566): Import_Command->create_author_mapping_file('mapping.csv', Array)
#2 phar:///tmp/wp.phar/vendor/wp-cli/import-command/src/Import_Command.php(290): Import_Command->process_author_mapping('mapping.csv', Array)
...
$ echo $?
1

mapping.csv is created, but it is empty:

$ wc -c mapping.csv
0 mapping.csv

If I run the same command again, it reads the empty file and imports everything without any author mapping. There is no warning.

The cause is in suggest_user(). It loads the site users only when ! isset( $this->blog_users ). Since a50c132 (#94) the property is declared as private $blog_users = [];, so isset() is always true. get_users() never runs, the loop over the users never runs, and array_sum( $shortestavg ) / count( $shortestavg ) divides by zero.

WP-CLI 2.12.0 (the current stable phar, saved as /tmp/stable.phar) still works on the same site. It writes the file and stops as expected:

$ php /tmp/stable.phar import /tmp/repro/export.xml --authors=/tmp/repro/mapping.csv
Starting the import process...
Error: Please update author mapping file before continuing: /tmp/repro/mapping.csv
$ cat /tmp/repro/mapping.csv
old_user_login,new_user_login
admin,admin

Describe how other contributors can replicate this bug

• Use a site with at least one post, for example a fresh install with "Hello world!".
• wp plugin install wordpress-importer --activate
• wp export --filename_format=export.xml
• wp import export.xml --authors=mapping.csv (the file mapping.csv must not exist yet)
• The command ends with Fatal error: Uncaught DivisionByZeroError: Division by zero and leaves an empty mapping.csv.

Describe what you would expect as the correct outcome

The mapping file is written with a suggestion for each author, and the command stops so I can edit it:

$ wp import export.xml --authors=mapping.csv
Starting the import process...
Error: Please update author mapping file before continuing: mapping.csv
$ cat mapping.csv
old_user_login,new_user_login
admin,admin

Let us know what environment you are running this on

OS:	Linux 6.18.33.2-microsoft-standard-WSL2 #1 SMP PREEMPT_DYNAMIC Thu Jun 18 21:54:43 UTC 2026 x86_64
Shell:	
PHP binary:	/usr/local/bin/php
PHP version:	8.5.9
PHP memory limit:	-1
php.ini used:	/usr/local/etc/php/php-cli.ini
MySQL binary:	/usr/bin/mariadb
MySQL version:	mariadb from 11.8.9-MariaDB, client 15.2 for Linux (x86_64) using readline 5.1
SQL modes:	
WP-CLI root dir:	phar://wp-cli.phar/vendor/wp-cli/wp-cli
WP-CLI vendor dir:	phar://wp-cli.phar/vendor
WP_CLI phar path:	phar:///tmp/wp.phar
WP-CLI packages dir:	/tmp/.wp-cli/packages/
WP-CLI cache dir:	/tmp/.wp-cli/cache
WP-CLI global config:	
WP-CLI project config:	
WP-CLI version:	3.0.0-alpha-836ccac

WordPress 7.2-beta1-64691 (nightly), WordPress Importer 0.9.7, WP_DEBUG true. In the commands above, wp is the nightly phar run as php -d error_reporting=-1 -d display_errors=stderr /tmp/wp.phar. I also reproduced it with a Behat scenario on the import-command main branch (60399a0).

Provide a possible solution

• Declare $blog_users without a default value, so it is null until suggest_user() loads the users.
• Only compare with the average when $shortestavg is not empty. Otherwise the same error happens when the first site user matches the imported login exactly but has a different email: the loop breaks before anything is added to $shortestavg.

I have a pull request with both changes and a Behat scenario ready.

Provide additional context/Screenshots

• The isset() check is old. The property declaration came with PHPStan level 9 #94 (PHPStan level 9), which is in v2.0.15 and later, including v3.0.0. WP-CLI 2.12.0 bundles an older version and shows a "Creation of dynamic property Import_Command::$blog_users" deprecation on PHP 8.5 instead of the fatal error.
• No Behat scenario uses --authors=<file>.csv today, so the tests did not catch it.