update-po: Doesn't preserve / create X-Domain header of .pot file

[FabianKielmann]

Bug Report

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

Describe the current, buggy behavior

When creating a pot file from your wordpress files and then use wp i18n update-po to update your .po files: In case your .po file is empty, the update-process in general works, but the X-Domain header present in the .pot file will not be included.

Describe how other contributors can replicate this bug

• create an empty .po file in your language folder
• create a .pot file with wp i18n make-pot and make sure it added an X-Domain header containing your text-domain
• update your empty .po file from your .pot file you just created with wp i18n update-po

Describe what you would expect as the correct outcome

I would expect the X-Domain header to be present in the updated .po file in case that the .pot file included it.

Let us know what environment you are running this on

OS:     Linux 5.15.49-linuxkit-pr #1 SMP PREEMPT Thu May 25 07:27:39 UTC 2023 aarch64
Shell:
PHP binary:     /usr/local/bin/php
PHP version:    8.0.29
php.ini used:
MySQL binary:   /usr/bin/mysql
MySQL version:  mysql  Ver 15.1 Distrib 10.6.14-MariaDB, for Linux (aarch64) 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:       /var/www/html
WP-CLI packages dir:
WP-CLI cache dir:       /home/www-data/.wp-cli/cache
WP-CLI global config:
WP-CLI project config:
WP-CLI version: 2.8.1

Provide a possible solution

I took a look inside the code and found that the update-po command may use a "wrong" strategy or might just not tell mergewith how to handle the headers:

https://github.com/wp-cli/i18n-command/blob/main/src/UpdatePoCommand.php#L71

[swissspidy]

Curious: What‘s a use case where the po file doesn‘t have that header but the pot file does? How are you generating the po file?

[FabianKielmann]

In our case, we just create an empty one.

As far as I know there is no default way of creating a .po file, right? So the first file we ever create (for a plugin for example) would be just an empty .po file which will then get updates from the .pot file that we generate via wp i18n make-json.

[swissspidy]

As far as I know there is no default way of creating a .po file, right?

You could just copy yourcatalog.pot to yournewpofile.po and you have one :-)

Afterwards, whenever the .pot file is updated, that's when you'd want to use the update-po command.