wp plugin verify-checksums inconsistent output in JSON format #160

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

wp plugin verify-checksums as documented in version 2.12.0 support a --format=json option (same problem with yaml, I did not test others formats)

When running, the output is not always JSON, and some of the output is done on STDERR:

Here are the ouput for success and fail:

$ wp plugin verify-checksums hello --format=json
On STDOUT: [{"plugin_name":"hello","file":"hello.php","message":"Checksum does not match"}]
On STDERR: Error: No plugins verified (1 failed).
Return code 1

$ wp plugin verify-checksums akismet --format=json
On STDOUT: Success: Verified 1 of 1 plugins.
Nothing on STDERR
return code 0

Describe what you would expect as the correct outcome

As the command run without error (it perform the test I asked), I expect nothing on STDERR, and I expect the result as JSON in both cases.

If the checksums are correct, I expect a JSON document with a key/value telling me if the plugin's checksums are OK or not. For example: {"plugin_name":"akismet","result":"OK"} (or an empty list that I can interpret as an empty of error, but it's less easy to work with)

If there is an error, I expect a list of errors, as it is currently. Or a list of errors as a child of the plugin.

For example

$ wp plugin verify-checksums --all --format=json
[
    {"plugin_name":"akismet","result":"OK"},
    {"plugin_name":"hello","result":"Failed", "errors": 
        [
            {"file":"hello.php","message":"Checksum does not match"}
        ]
    }
]

Let us know what environment you are running this on

OS:     Linux 6.1.0-52-amd64 wp-cli/builds#1 SMP PREEMPT_DYNAMIC Debian 6.1.180-1 (2026-08-03) x86_64
Shell:  /bin/bash
PHP binary:     /usr/bin/php8.2
PHP version:    8.2.33
php.ini used:   /etc/php/8.2/cli/php.ini
MySQL binary:   /usr/bin/mariadb
MySQL version:  mariadb  Ver 15.1 Distrib 10.11.18-MariaDB, for debian-linux-gnu (x86_64) using  EditLine wrapper
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:///usr/bin/wp
WP-CLI packages dir:
WP-CLI cache dir:       /home/xxx/.wp-cli/cache
WP-CLI global config:   
WP-CLI project config:  
WP-CLI version: 2.12.0

Provide a possible solution

Sorry, I do not have the skill to help you on code.