PHP Fatal error: Class 'Symfony\Component\Yaml\Yaml' not found

I'm experiencing the same issue, can you please explain your solution?

@chriscalip Can you describe how exactly you had phpcs installed the "wrong way"?

I'm getting this same error and am unsure if it has to do with my docker installation, the CodeSniffer config we've got in our project, the local version of CodeSniffer I've got installed through Homebrew, or something else altogether.

I'm not sure if this is more of a bug, or a support request, but when I try to install yaml globally, I get...

Using version ^3.4 for symfony/yaml
./composer.json has been updated
Loading composer repositories with package information
Updating dependencies (including require-dev)
Your requirements could not be resolved to an installable set of packages.

  Problem 1
    - Conclusion: don't install symfony/yaml v3.4.1
    - symfony/console v3.3.13 conflicts with symfony/yaml[v3.4.0].
    - symfony/yaml v3.4.0 conflicts with symfony/console[v3.3.13].
    - symfony/yaml v3.4.0 conflicts with symfony/console[v3.3.13].
    - Installation request for symfony/yaml ^3.4 -> satisfiable by symfony/yaml[v3.4.0, v3.4.1].
    - Installation request for symfony/console (locked at v3.3.13) -> satisfiable by symfony/console[v3.3.13].

Installation failed, reverting ./composer.json to its original content.

I was able to resolve the problem. I'm not sure how. I added the following to the "require" section of my composer.json:

"symfony/yaml": "^3.1"

I also deleted core and vendor and ran composer update. I had to try it a few times.

It also may have helped me to run...

composer global require dealerdirect/phpcodesniffer-composer-installer

I am running into the same issue again:

PHP Fatal error: Uncaught Error: Class 'Symfony\Component\Yaml\Yaml' not found in /root/.composer/vendor/drupal/coder/coder_sniffer/Drupal/Sniffs/InfoFiles/AutoAddedKeysSniff.php:54

I'm getting this too. DrupalPractice works. But Drupal does not.

Works:
phpcs --standard=DrupalPractice .

Fails:
phpcs --standard=Drupal .

PHP Fatal error:  Uncaught Error: Class 'Symfony\Component\Yaml\Yaml' not found in /Users/grayloon/.composer/vendor/drupal/coder/coder_sniffer/Drupal/Sniffs/InfoFiles/AutoAddedKeysSniff.php:54
Stack trace:
#0 phar:///usr/local/bin/phpcs/CodeSniffer/File.php(576): Drupal_Sniffs_InfoFiles_AutoAddedKeysSniff->process(Object(PHP_CodeSniffer_File), 0)
#1 phar:///usr/local/bin/phpcs/CodeSniffer.php(1894): PHP_CodeSniffer_File->start(NULL)
#2 phar:///usr/local/bin/phpcs/CodeSniffer.php(1772): PHP_CodeSniffer->_processFile('/Users/grayloon...', NULL)
#3 phar:///usr/local/bin/phpcs/CodeSniffer.php(653): PHP_CodeSniffer->processFile('/Users/grayloon...', NULL)
#4 phar:///usr/local/bin/phpcs/CodeSniffer/CLI.php(998): PHP_CodeSniffer->processFiles(Array, false)
#5 phar:///usr/local/bin/phpcs/CodeSniffer/CLI.php(113): PHP_CodeSniffer_CLI->process()
#6 /usr/local/bin/phpcs(6): PHP_CodeSniffer_CLI->runphpcs()
#7 {main}
  thrown in /Users/grayloon/.composer/vendor/drupal/coder/coder_sniffer/Drupal/Sniffs/InfoFiles/AutoAddedKeysSniff.php on line 54

Running composer global require symfony/yaml has not helped.

Please verify your installation. We have the Yaml library listed as a required dependency in composer.json so if it is missing you need to make sure it is installed correctly. Also check if any errors might have been output during the installation.

Everything seems ok. Let me add my composer contents. Maybe something is off I don't realize, but like I said "DrupalPractice" works fine. Maybe you'll recognize something off with how I'm trying to do this.

{
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    "authors": [
        {
            "name": "xpersonas",
            "email": "justin.neel@gmail.com"
        }
    ],
    "require": {
        "symfony/yaml": "~3.0",
        "drupal/coder": "^8.2",
        "dealerdirect/phpcodesniffer-composer-installer": "^0.4.4",
        "squizlabs/php_codesniffer": "2.8.1",
        "drush/drush": "~8.0"
    }
}

{
    "_readme": [
        "This file locks the dependencies of your project to a known state",
        "Read more about it at https://getcomposer.org/doc/01-basic-usage.md#composer-lock-the-lock-file",
        "This file is @generated automatically"
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                "MIT"
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            "authors": [
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                }
            ],
            "description": "Format text by applying transformations provided by plug-in formatters.",
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            "require-dev": {
                "composer/composer": "*",
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            "suggest": {
                "dealerdirect/qa-tools": "All the PHP QA tools you'll need"
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        },
        {
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            "require": {
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                "php": ">=5.4.0",
                "squizlabs/php_codesniffer": ">=2.8.1 <3.0",
                "symfony/yaml": ">=2.0.0"
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            "type": "phpcodesniffer-standard",
            "notification-url": "https://packagist.org/downloads/",
            "license": [
                "GPL-2.0+"
            ],
            "description": "Coder is a library to review Drupal code.",
            "homepage": "https://www.drupal.org/project/coder",
            "keywords": [
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                "phpcs",
                "standards"
            ],
            "time": "2017-03-18T10:28:49+00:00"
        },
        {
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            ],
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                {
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                    "homepage": "http://www.php-fig.org/"
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            ],
            "description": "Common interface for logging libraries",
            "homepage": "https://github.com/php-fig/log",
            "keywords": [
                "log",
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        },
        {
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                "ext-intl": "To show region name in time zone dump",
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            },
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                }
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                "MIT"
            ],
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                {
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    ],
    "packages-dev": [],
    "aliases": [],
    "minimum-stability": "stable",
    "stability-flags": [],
    "prefer-stable": false,
    "prefer-lowest": false,
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}

And vendor directory...

autoload.php
bin/
composer/
consolidation/
dealerdirect/
dnoegel/
drupal/
drush/
jakub-onderka/
nikic/
pear/
psr/
psy/
squizlabs/
symfony/
webmozart/

The files you provide look fine to me. The composer.json file contains the reference to symfony/yaml but this is not strictly required, it is normally inherited from Coder. But it 100% fine to put it there and you are expected to do it if you use the Yaml component in your own code.

The composer.lock also looks fine. It contains a reference to symfony/yaml version 3.4.4. I verified this particular release and the file is there and has the correct namespace (ref. v3.4.4/Yaml.php).

I noticed that we have very few instances of calling directly into namespaced code, in fact at first glance it seems that this is the only instance. So I have tried it locally in a fresh installation of my project (ref. https://github.com/ec-europa/joinup-dev):

$ ./vendor/bin/phpcs web/modules/custom/*/*.info.yml
.................................

Time: 93ms; Memory: 4Mb

To be 100% sure that this code is actually running as expected I edited the file AutoAddedKeysSniff.php and changed the line that calls into namespace to something invalid. It fails as expected:

$ ./vendor/bin/phpcs web/modules/custom/*/*.info.yml
PHP Fatal error:  Uncaught Error: Class 'Symfony\Component\Yaml\NonExistingNamespace' not found in /home/pieter/v/joinup/vendor/drupal/coder/coder_sniffer/Drupal/Sniffs/InfoFiles/AutoAddedKeysSniff.php:54
Stack trace:
#0 /home/pieter/v/joinup/vendor/squizlabs/php_codesniffer/CodeSniffer/File.php(576): Drupal_Sniffs_InfoFiles_AutoAddedKeysSniff->process(Object(PHP_CodeSniffer_File), 0)
#1 /home/pieter/v/joinup/vendor/squizlabs/php_codesniffer/CodeSniffer.php(1894): PHP_CodeSniffer_File->start(NULL)
#2 /home/pieter/v/joinup/vendor/squizlabs/php_codesniffer/CodeSniffer.php(1772): PHP_CodeSniffer->_processFile('/home/pieter/v/...', NULL)
#3 /home/pieter/v/joinup/vendor/squizlabs/php_codesniffer/CodeSniffer.php(653): PHP_CodeSniffer->processFile('/home/pieter/v/...', NULL)
#4 /home/pieter/v/joinup/vendor/squizlabs/php_codesniffer/CodeSniffer/CLI.php(998): PHP_CodeSniffer->processFiles(Array, false)
#5 /home/pieter/v/joinup/vendor/squizlabs/php_codesniffer/CodeSniffer/CLI.php(113): PHP_CodeSniffer_CLI->process()
#6 /home/pieter/v/jo in /home/pieter/v/joinup/vendor/drupal/coder/coder_sniffer/Drupal/Sniffs/InfoFiles/AutoAddedKeysSniff.php on line 54

Can you verify that the symfony/yaml package is present in the vendor file? If it is there, maybe you need to rebuild your autoload files, so maybe you can try to run this command?

$ composer dump-autoload

If this doesn't fix it for you I am not sure how I can help you further. You'll need to start debugging it probably, check why the autoloader is not being loaded, maybe it loads the wrong one?

Awesome. $ composer dump-autoload did the trick. Thank you so much. That command wasn't on my radar so I hadn't tried that. I'm all good now!

Wow! Great news! Glad you have it up and running!

This issue occurs when you have phpcs installed globally because in this case phpcs uses its own autoloader instance which is not aware about Coder dependencies.

So I got the same bug.
And looks like @Chi is right it something wrong with phpcs installation.
And my solution to fix it just replaced in the command phpcs to ~/.composer/vendor/bin/phpcs
For example:
~/.composer/vendor/bin/phpcs --standard=Drupal /path/to/code

I have this issue with global installation, but fail DrupalPractice and work Drupal.

Comment #18 work for me, but in my ubuntu the global path is:
~/.config/composer/vendor/bin

My OS version:

Distributor ID:	Ubuntu
Description:	Ubuntu 19.10
Release:	19.10
Codename:	eoan

sudo ln -s ~/.config/composer/vendor/bin/phpcs /usr/local/bin/phpcs
phpcs --standard=Drupal --extensions=php,module,inc,install,test,profile,theme,css,info,txt,md,yml path/to/module

I also have the same problem. Comment #18 worked for me.