Same composer.json, same composer.lock but different result - symfony

Question

I'm working on a project hosted on a private github. I'm cloning the repo and run composer install
I'm getting
Loading composer repositories with package information
Installing dependencies (including require-dev) from lock file
Your requirements could not be resolved to an installable set of packages.
Problem 1
- Installation request for symfony/symfony v2.7.38 -> satisfiable by symfony/symfony[v2.7.38].
- don't install symfony/var-dumper v3.3.6|don't install symfony/symfony v2.7.38
- Installation request for symfony/var-dumper v3.3.6 -> satisfiable by symfony/var-dumper[v3.3.6].
I'm not sure I understand what it means.
Here my composer.json
{
"name": "…",
"license": "…",
"type": "…",
"description": "…",
"autoload": {
"psr-0": { "": "src/" }
},
"require": {
"php": ">=5.4",
"symfony/symfony": "2.7.*",
"doctrine/orm": "^2.4.8",
"doctrine/doctrine-bundle": "~1.4",
"symfony/assetic-bundle": "~2.3",
"symfony/swiftmailer-bundle": "~2.3",
"symfony/monolog-bundle": "~2.4",
"sensio/distribution-bundle": "~4.0",
"sensio/framework-extra-bundle": "^3.0.2",
"incenteev/composer-parameter-handler": "~2.0",
"twig/extensions": "1.0.*",
"sonata-project/doctrine-orm-admin-bundle": "2.3.*",
"sonata-project/admin-bundle": "2.3.*",
"sonata-project/user-bundle": "2.2.*",
"sonata-project/media-bundle": "2.3.*",
"sonata-project/translation-bundle": "~1.0",
"friendsofsymfony/jsrouting-bundle": "^2.0#dev",
"friendsofsymfony/user-bundle": "1.3.*",
"stof/doctrine-extensions-bundle": "~1.2",
"doctrine/doctrine-migrations-bundle": "~1.1",
"richsage/rms-push-notifications-bundle": "dev-master",
"components/jquery": "2.1.1",
"ckeditor/ckeditor": "4.4.5",
"hwi/oauth-bundle": "0.3.*",
"guzzlehttp/guzzle": "~5.0",
"guzzlehttp/guzzle-services": "0.5.*",
"mixpanel/mixpanel-php" : "2.*",
"league/csv": "7.2.0",
"friendsofsymfony/rest-bundle": "^1.7",
"jms/serializer-bundle": "^1.1",
"appventus/alertify-bundle":"dev-master",
"dzunke/slack-bundle": "1.4.0",
"algolia/algolia-search-bundle": "~1.0",
"userscape/customerio": "^1.0",
"dubture/customerio-bundle": "^0.0.1",
"minube/amplitude-php": "dev-master",
"stripe/stripe-php": "^3.11",
"suncat/mobile-detect-bundle": "1.0.*",
"willdurand/js-translation-bundle": "^2.5",
"sentry/sentry-symfony": "^0.3.0",
"jms/di-extra-bundle": "dev-master",
"abraham/twitteroauth": "^0.7.1",
"gos/web-socket-bundle": "dev-master",
"phpoffice/phpexcel": "^1.8",
"nelmio/api-doc-bundle": "~2.11",
"liip/url-auto-converter-bundle": "dev-master",
"dizda/onesignal-api-bundle": "^0.1.5",
"slot/mandrill-bundle": "1.0.10"
},
"require-dev": {
"phpunit/phpunit": "4.8.*#stable",
"sensio/generator-bundle": "2.3.*",
"symfony/var-dumper": "3.3.6",
"doctrine/doctrine-fixtures-bundle": "^2.3",
"deployer/deployer": "^5.0"
},
"scripts": {
"post-install-cmd": [
"Incenteev\\ParameterHandler\\ScriptHandler::buildParameters",
"Sensio\\Bundle\\DistributionBundle\\Composer\\ScriptHandler::buildBootstrap",
"Sensio\\Bundle\\DistributionBundle\\Composer\\ScriptHandler::clearCache",
"Sensio\\Bundle\\DistributionBundle\\Composer\\ScriptHandler::installAssets",
"Sensio\\Bundle\\DistributionBundle\\Composer\\ScriptHandler::installRequirementsFile"
],
"post-update-cmd": [
"Incenteev\\ParameterHandler\\ScriptHandler::buildParameters",
"Sensio\\Bundle\\DistributionBundle\\Composer\\ScriptHandler::buildBootstrap",
"Sensio\\Bundle\\DistributionBundle\\Composer\\ScriptHandler::clearCache",
"Sensio\\Bundle\\DistributionBundle\\Composer\\ScriptHandler::installAssets",
"Sensio\\Bundle\\DistributionBundle\\Composer\\ScriptHandler::installRequirementsFile"
]
},
"config": {
"bin-dir": "bin"
},
"minimum-stability": "stable",
"extra": {
"symfony-app-dir": "app",
"symfony-web-dir": "web",
"incenteev-parameters": {
"file": "app/config/parameters.yml"
},
"branch-alias": {
"dev-master": "2.3-dev"
}
}
}
One of my coworker is doing the exact same thing and it's working. I would be really glad to get some explanations about the composer error that I don't understand at all.

Answer 1

Often issues that arise while comparing the run of a composer command, can be generated by the usage of different version.
As a lot of changes are made on each release (for example different glob sorting order, that gives different filepaths as well as slightly different regex to match version of the packages),
the best option is to compare your version to the one your peer is using by running a composer -v on your shell (check the link for more in depth examples and info), and as always i suggest to keep everyone aligned on the latest version by running a composer self-update if there aren't strict requirement that requires a lower version.