Update: New Solution

Skip to the tldr; section below for direct solution. Otherwise, enjoy:

I had to accept that there were no php-cs-fixer vscode plugins that would work with solving the path difference between my host machine and docker container.

I got deep into the weeds and I forked Simple PHP CS FIXER adding a few more configuration options:

• executablePath - relative to my host machine so I could use a script in my project. eg. /Users/me/myproject/docker-phpcs - this project was originally hardcoding php-cs-fixer here. That is still the default in my version.

  Here's an example script:

  #!/bin/bash
  
  docker exec -t "mycontainer" /var/www/site/app/vendor/bin/php-cs-fixer $@
  

  Note: I made sure to chmod +x on my script to make it executable

• hostPath - so I could tell it my project path eg. "/Users/me/code/myproject/"

• dockerPath - so I could tell it my docker container path eg. "/var/www/site"

Then I modified the extension.js to replace the hostName with the dockerPath in the following files:

• the config file, if one is set.
• the document-being-saved's fileName.

So when using this, I create my settings per-folder like this:

"simple-php-cs-fixer.executablePath": "/Users/me/code/myproject/docker-phpcs",
"simple-php-cs-fixer.config": ".php_cs",
"simple-php-cs-fixer.hostPath": "/Users/me/code/myproject",
"simple-php-cs-fixer.dockerPath": "/var/www/site",

And I purposefully do not force this on save - and instead made a key-binding for the plugin's command (ctrl+s, instead of cmd + s), so I can control when I want to completely obliterate my file.

tldr;

I forked the plugin to provide options for docker-relative paths and custom executable path to php-cs-fixer - I also did make a PR to the plugin - but if that does not get accepted... you can side load the extension like so:

1. "install" the plugin using marketplace as normal
2. go to your extensions folder (on my mac it was $HOME/.vscode/extensions
3. git clone git@github.com:amurrell/simple-php-cs-fixer.git
4. remove the one installed by marketplace like: calebporzio.simple-php-cs-fixer-x.x.x

Hopefully PR gets accepted...

In the meantime, with ctrl+s key-binding and this modified plugin with extra settings, I now get a fixed file according to my configuration, using my docker-container.

Another Close Solution

Update: This was not really accurately solving my problem - my script would trigger when saving but it wasn't actually processing the current document file being edited/saved - it was triggering the script which would scan all my files defined in my configuration file. This means the plugin wasn't getting to control the configuration file either.

I got what I wanted! Assuming the context I have in my question (eg. your project has friendsofphp/php-cs-fixer required in composer):

1. Make an edit to your .zshrc or .bashrc file with snippet below
2. Install the Simple PHP CS Fixer extension & update with desired settings

Make Edit to your .zshrc or .bashrc

This source gave me the idea to store php-cs-fixer in my .zshrc or .bashrc file like this:

php-cs-fixer () {
  docker run -it --rm --net host -v `pwd`:/app  ypereirareis/php-cs-fixer fix --level=psr2 --verbose $@
}

Adapted to my circumstance:

I pasted this into the bottom of my .zshrc file:

php-cs-fixer () {
    docker exec -t "mycontainername" /var/www/site/app/vendor/bin/php-cs-fixer fix --verbose --config=/var/www/site/.php_cs $@
}

• mycontainername can be retrieved by: docker ps and looking at last column "Names"
• /var/www/site/app/ is the container's path to my project's app folder where my composer.json file is
• /var/www/site/.php_cs is the container's path to my project's .php_cs file which is at the root of my project eg. ~/code/project/.php_cs

Install Simple PHP CS FIXER

This extension for vscode makes it easy. I assume it will just call "php-cs-fixer" and the edit your profile will find that function and run the docker stuff for you.

Here are my setting changes:

"simple-php-cs-fixer.config": ".php_cs",
"simple-php-cs-fixer.save": true,

BONUS Note:

My .php_cs file in case anyone is curious - I did make my project_path relative to the container and not my host machine.

<?php

use PhpCsFixer\Config;
use PhpCsFixer\Finder;

$rules = [
    'array_syntax' => ['syntax' => 'short'],
    'binary_operator_spaces' => [
        'default' => 'single_space',
        'operators' => ['=>' => null],
    ],
    'blank_line_after_namespace' => false,
    'blank_line_after_opening_tag' => false,
    // 'blank_line_before_statement' => [
    //     'statements' => ['return'],
    // ],
    'braces' => true,
    'cast_spaces' => true,
    'class_attributes_separation' => [
        'elements' => ['method'],
    ],
    'class_definition' => true,
    'concat_space' => [
        'spacing' => 'one',
    ],
    'declare_equal_normalize' => true,
    'elseif' => true,
    'encoding' => true,
    'full_opening_tag' => true,
    'fully_qualified_strict_types' => true, // added by Shift
    'function_declaration' => true,
    'function_typehint_space' => true,
    'heredoc_to_nowdoc' => true,
    'include' => true,
    'increment_style' => ['style' => 'post'],
    'indentation_type' => true,
    'linebreak_after_opening_tag' => false,
    'line_ending' => true,
    'lowercase_cast' => true,
    'lowercase_constants' => true,
    'lowercase_keywords' => true,
    'lowercase_static_reference' => true, // added from Symfony
    'magic_method_casing' => true, // added from Symfony
    'magic_constant_casing' => true,
    'method_argument_space' => true,
    'native_function_casing' => true,
    'no_alias_functions' => true,
    'no_extra_blank_lines' => [
        'tokens' => [
            'extra',
            'throw',
            'use',
            'use_trait',
        ],
    ],
    'no_blank_lines_after_class_opening' => false,
    'no_blank_lines_after_phpdoc' => true,
    'no_closing_tag' => true,
    'no_empty_phpdoc' => true,
    'no_empty_statement' => true,
    'no_leading_import_slash' => true,
    'no_leading_namespace_whitespace' => true,
    'no_mixed_echo_print' => [
        'use' => 'echo',
    ],
    'no_multiline_whitespace_around_double_arrow' => true,
    'multiline_whitespace_before_semicolons' => [
        'strategy' => 'no_multi_line',
    ],
    'no_short_bool_cast' => true,
    'no_singleline_whitespace_before_semicolons' => true,
    'no_spaces_after_function_name' => true,
    'no_spaces_around_offset' => true,
    'no_spaces_inside_parenthesis' => true,
    'no_trailing_comma_in_list_call' => true,
    'no_trailing_comma_in_singleline_array' => true,
    'no_trailing_whitespace' => true,
    'no_trailing_whitespace_in_comment' => true,
    'no_unneeded_control_parentheses' => true,
    'no_unreachable_default_argument_value' => true,
    'no_useless_return' => true,
    'no_whitespace_before_comma_in_array' => true,
    'no_whitespace_in_blank_line' => true,
    'normalize_index_brace' => true,
    'not_operator_with_successor_space' => true,
    'object_operator_without_whitespace' => true,
    'ordered_imports' => ['sortAlgorithm' => 'alpha'],
    'phpdoc_indent' => true,
    'phpdoc_inline_tag' => true,
    'phpdoc_no_access' => true,
    'phpdoc_no_package' => true,
    'phpdoc_no_useless_inheritdoc' => true,
    'phpdoc_scalar' => true,
    'phpdoc_single_line_var_spacing' => true,
    'phpdoc_summary' => true,
    'phpdoc_to_comment' => true,
    'phpdoc_trim' => true,
    'phpdoc_types' => true,
    'phpdoc_var_without_name' => true,
    'psr4' => true,
    'self_accessor' => true,
    'short_scalar_cast' => true,
    'simplified_null_return' => false, // disabled by Shift
    'single_blank_line_at_eof' => true,
    'single_blank_line_before_namespace' => false,
    'single_class_element_per_statement' => true,
    'single_import_per_statement' => true,
    'single_line_after_imports' => true,
    'single_line_comment_style' => [
        'comment_types' => ['hash'],
    ],
    'single_quote' => true,
    'space_after_semicolon' => true,
    'standardize_not_equals' => true,
    'switch_case_semicolon_to_colon' => true,
    'switch_case_space' => true,
    'ternary_operator_spaces' => true,
    'trailing_comma_in_multiline_array' => true,
    'trim_array_spaces' => true,
    'unary_operator_spaces' => true,
    'visibility_required' => [
        'elements' => ['method', 'property'],
    ],
    'whitespace_after_comma_in_array' => true,
];

$project_path = '/var/www/site/app';
$finder = Finder::create()
    ->in([
        $project_path . '/app',
        $project_path . '/config',
        $project_path . '/database',
        $project_path . '/resources',
        $project_path . '/routes',
        $project_path . '/tests',
    ])
    ->name('*.php')
    ->notName('*.blade.php')
    ->ignoreDotFiles(true)
    ->ignoreVCS(true);

return Config::create()
    ->setFinder($finder)
    ->setRules($rules)
    ->setRiskyAllowed(true)
    ->setUsingCache(false);

As part of a package solution for overall application code quality control (interitty/code-checker), I solved the situation of running a php-cs-fixer inside a docker container from NetBeans IDE on a guest machine.

So, I created a bash script that emulates the php-cs-fixer interface and passes the parameters to the specified container.

Related documentation can be found in the readme

I hope that this should help you too.

I come with my 2 cents for vscode, as I gave up on using any php-cs-fixer related extension.

Install this extensions https://marketplace.visualstudio.com/items?itemName=emeraldwalk.RunOnSave.

Basically, it allows you to run any command when saving a file; it is not targeted specifically to php fixer

Then, in workspace's or folder's settings, setup a command to forward instruction on saved file, using extension's placeholder. {containerName} is the name of the container you want to forward command to, ${relativeFile} is the extension's placeholder for the relative path of the saved file.

"emeraldwalk.runonsave": {
    "commands": [
        {
            "match": ".php",
            "cmd": "docker exec -i {containerName} /var/www/html/tools/php-cs-fixer/vendor/friendsofphp/php-cs-fixer/php-cs-fixer --format=json fix ${relativeFile}"
        },
    ]
}

Make sure to set the appropriate path (inside the container) of php-cs-fixer executable.