Missing XML output when using this plugin

[greg0ire]

Found that issue while working on doctrine/sql-formatter#51 (comment)

With the plugin loaded in psalm.xml:

vendor/bin/psalm --output-format=checkstyle
Scanning files...
Analyzing files...

░░░░░░░░░░░░░

Without:

Scanning files...
Analyzing files...

░░░░░░░░░░░░░
<?xml version="1.0" encoding="UTF-8"?>
<checkstyle>
</checkstyle>

Why is there no checkstyle output in the former?

[weirdan]

I can't seem to be able to reproduce this. E.g. in Psalm repo which itself uses this plugin:

$ ./psalm --output-format=checkstyle 2>/dev/null
<?xml version="1.0" encoding="UTF-8"?>
<checkstyle>
</checkstyle>

$ ./psalm-plugin show
Enabled
-------

 ---------------------- ---------------------------- 
  Package                Class                       
 ---------------------- ---------------------------- 
  psalm/plugin-phpunit   Psalm\PhpUnitPlugin\Plugin  
 ---------------------- ---------------------------- 

Available
---------

 ! [NOTE] No plugins available                                                                                          

$ composer show psalm/plugin-phpunit
name     : psalm/plugin-phpunit
descrip. : Psalm plugin for PHPUnit
keywords : 
versions : * 0.10.0
type     : psalm-plugin
license  : MIT License (MIT) (OSI approved) https://spdx.org/licenses/MIT.html#licenseText
homepage : 
source   : [git] https://github.com/psalm/psalm-plugin-phpunit.git 12b3978cea0e9ad3aa3a127a93d3b8a1ce0eb2af
dist     : [zip] https://api.github.com/repos/psalm/psalm-plugin-phpunit/zipball/12b3978cea0e9ad3aa3a127a93d3b8a1ce0eb2af 12b3978cea0e9ad3aa3a127a93d3b8a1ce0eb2af
path     : /home/weirdan/src/psalm/vendor/psalm/plugin-phpunit
names    : psalm/plugin-phpunit

autoload
psr-4
Psalm\PhpUnitPlugin\ => src

requires
composer/semver ^1.4
ext-simplexml *
ocramius/package-versions ^1.3
php ^7.1.3
phpunit/phpunit ^7.5 || ^8.0 || ^9.0
vimeo/psalm ^3.6.2 || dev-master

requires (dev)
codeception/codeception ^4.0.3
squizlabs/php_codesniffer ^3.3.1
weirdan/codeception-psalm-module ^0.4.0

[greg0ire]

Oh wow that's weird… here is a reproducer:

git clone git@github.com:doctrine/sql-formatter.git 
cd sql-formatter
composer install
vendor/bin/psalm --output-format=checkstyle

[weirdan]

Turns out it's not a problem with the plugin. On the contrary, plugin is doing its job pretty well, and eliminates all issues. Psalm only calls getOutput() [1] if there are some issues to report [2]. So that's a problem with Psalm that went long unnoticed (after all, there's very few projects that Psalm finds no issues in).