Display unexpected plugin output during activation with --debug

[Copilot]

When a plugin generates output during activation, WordPress returns a WP_Error with code unexpected_output and the captured output as error data. Currently, WP-CLI shows the error message but not the actual output, making debugging difficult.

Changes

• src/Plugin_Command.php: Check for unexpected_output error code and display captured output via WP_CLI::debug() with 'plugin' group
• features/plugin-activate.feature: Add test scenario verifying debug output appears with --debug flag

Example

# Before: no visibility into what was output
$ wp plugin activate broken-plugin
Warning: Failed to activate plugin. The plugin generated unexpected output.

# After: see the actual output with --debug
$ wp plugin activate broken-plugin --debug
Warning: Failed to activate plugin. The plugin generated unexpected output.
Debug (plugin): Unexpected output: echo "initialization started";

The output only appears when --debug is used, keeping normal operation unchanged.

Warning

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• https://api.github.com/repos/Behat/Behat/zipball/1b6b08efa995fe4135901b862d112adc7e95ecbb
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• https://api.github.com/repos/PHPCSStandards/PHP_CodeSniffer/zipball/0ca86845ce43291e8f5692c7356fccf3bcf02bf4
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If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to the custom allowlist in this repository's Copilot coding agent settings (admins only)

Original prompt

---

This section details on the original issue you should resolve

<issue_title>wp plugin activate should show what unexpected output the plugin generated</issue_title>
<issue_description>If a plugin generates output during activation, activate_plugin will return an WP_Error object configured like this:

$output = ob_get_clean();
return new WP_Error( 'unexpected_output', __( 'The plugin generated unexpected output.' ), $output );

As you can see, the output is passed as the third parameter, and the error has code "unexpected_output".

I have a use-case where I need the output that was generated for logging reasons.

Relevant code that should print the output:

extension-command/src/Plugin_Command.php

Lines 347 to 354 in 409b3f6

	$result = activate_plugin( $plugin->file, '', $network_wide );
	if ( is_wp_error( $result ) ) {
	$message = $result->get_error_message();
	$message = preg_replace( '/<a\s[^>]+>.*<\/a>/im', '', $message );
	$message = wp_strip_all_tags( $message );
	$message = str_replace( 'Error: ', '', $message );
	WP_CLI::warning( "Failed to activate plugin. {$message}" );

</issue_description>

Comments on the Issue (you are @copilot in this section)

@danielbachhuber Hey @Luc45,

Thanks for the suggestion!

I have a use-case where I need the output that was generated for logging reasons.

I'm a little hesitant about changing the output solely for this use case.

What do you think about instead running the $result through an action, so your custom code can capture and report the output however you need?</comment_new>
<comment_new>@swissspidy
I think it's useful to include the output just to make debugging easier. Could be in a debug() statement though.</comment_new>

• Fixes wp plugin activate should show what unexpected output the plugin generated #329

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