Composer error while updating symfony 2.8 to 3.0

Question

I have successfully updated my Symfony version from 2.5 to 2.8 and deleted all my calls to deprecated methos. So now, I want to update to 3.0.*. So I updated my composer.json with "symfony/symfony": "3.0.*" and runned composer update symfony/symfony, but I get the following error in the console :

λ composer update symfony/symfony
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/symfony v3.0.9
    - Conclusion: don't install symfony/symfony v3.0.8
    - Conclusion: don't install symfony/symfony v3.0.7
    - Conclusion: don't install symfony/symfony v3.0.6
    - Conclusion: don't install symfony/symfony v3.0.5
    - Conclusion: don't install symfony/symfony v3.0.4
    - Conclusion: don't install symfony/symfony v3.0.3
    - Conclusion: don't install symfony/symfony v3.0.2
    - Conclusion: don't install symfony/symfony v3.0.1
    - sensio/generator-bundle v2.5.3 requires symfony/framework-bundle ~2.2 -> satisfiable by symfony/symfony[v2.8.8], symfony/framework-bundle[v2.2.0, v2.2.1, v2.2.10, v2.2.11, v2.2.2, v2.2.3, v2.2.4, v2.2.5, v2.2.6, v2.2.7, v2.2.8, v2.2.9, v2.3.0, v2.3.1, v2.3.10, v2.3.11, v2.3.12, v2.3.13, v2.3.14, v2.3.15, v2.3.16, v2.3.17, v2.3.18, v2.3.19, v2.3.2, v2.3.20, v2.3.21, v2.3.22, v2.3.23, v2.3.24, v2.3.25, v2.3.26, v2.3.27, v2.3.28, v2.3.29, v2.3.3, v2.3.30, v2.3.31, v2.3.32, v2.3.33, v2.3.34, v2.3.35, v2.3.36, v2.3.37, v2.3.38, v2.3.39, v2.3.4, v2.3.40, v2.3.41, v2.3.42, v2.3.5, v2.3.6, v2.3.7, v2.3.8, v2.3.9, v2.4.0, v2.4.1, v2.4.10, v2.4.2, v2.4.3, v2.4.4, v2.4.5, v2.4.6, v2.4.7, v2.4.8, v2.4.9, v2.5.0, v2.5.1, v2.5.10, v2.5.11, v2.5.12, v2.5.2, v2.5.3, v2.5.4, v2.5.5, v2.5.6, v2.5.7, v2.5.8, v2.5.9, v2.6.0, v2.6.1, v2.6.10, v2.6.11, v2.6.12, v2.6.13, v2.6.2, v2.6.3, v2.6.4, v2.6.5, v2.6.6, v2.6.7, v2.6.8, v2.6.9, v2.7.0, v2.7.1, v2.7.10, v2.7.11, v2.7.12, v2.7.13, v2.7.14, v2.7.15, v2.7.16, v2.7.2, v2.7.3, v2.7.4, v2.7.5, v2.7.6, v2.7.7, v2.7.8, v2.7.9, v2.8.0, v2.8.1, v2.8.2, v2.8.3, v2.8.4, v2.8.5, v2.8.6, v2.8.7, v2.8.8, v2.8.9].
    - sensio/generator-bundle v2.5.3 requires symfony/console ~2.5 -> satisfiable by symfony/symfony[v2.8.8], symfony/console[v2.5.0, v2.5.1, v2.5.10, v2.5.11, v2.5.12, v2.5.2, v2.5.3, v2.5.4, v2.5.5, v2.5.6, v2.5.7, v2.5.8, v2.5.9, v2.6.0, v2.6.1, v2.6.10, v2.6.11, v2.6.12, v2.6.13, v2.6.2, v2.6.3, v2.6.4, v2.6.5, v2.6.6, v2.6.7, v2.6.8, v2.6.9, v2.7.0, v2.7.1, v2.7.10, v2.7.11, v2.7.12, v2.7.13, v2.7.14, v2.7.15, v2.7.16, v2.7.2, v2.7.3, v2.7.4, v2.7.5, v2.7.6, v2.7.7, v2.7.8, v2.7.9, v2.8.0, v2.8.1, v2.8.2, v2.8.3, v2.8.4, v2.8.5, v2.8.6, v2.8.7, v2.8.8, v2.8.9].
    - sensio/generator-bundle v2.5.3 requires symfony/framework-bundle ~2.2 -> satisfiable by symfony/symfony[v2.8.8], symfony/framework-bundle[v2.2.0, v2.2.1, v2.2.10, v2.2.11, v2.2.2, v2.2.3, v2.2.4, v2.2.5, v2.2.6, v2.2.7, v2.2.8, v2.2.9, v2.3.0, v2.3.1, v2.3.10, v2.3.11, v2.3.12, v2.3.13, v2.3.14, v2.3.15, v2.3.16, v2.3.17, v2.3.18, v2.3.19, v2.3.2, v2.3.20, v2.3.21, v2.3.22, v2.3.23, v2.3.24, v2.3.25, v2.3.26, v2.3.27, v2.3.28, v2.3.29, v2.3.3, v2.3.30, v2.3.31, v2.3.32, v2.3.33, v2.3.34, v2.3.35, v2.3.36, v2.3.37, v2.3.38, v2.3.39, v2.3.4, v2.3.40, v2.3.41, v2.3.42, v2.3.5, v2.3.6, v2.3.7, v2.3.8, v2.3.9, v2.4.0, v2.4.1, v2.4.10, v2.4.2, v2.4.3, v2.4.4, v2.4.5, v2.4.6, v2.4.7, v2.4.8, v2.4.9, v2.5.0, v2.5.1, v2.5.10, v2.5.11, v2.5.12, v2.5.2, v2.5.3, v2.5.4, v2.5.5, v2.5.6, v2.5.7, v2.5.8, v2.5.9, v2.6.0, v2.6.1, v2.6.10, v2.6.11, v2.6.12, v2.6.13, v2.6.2, v2.6.3, v2.6.4, v2.6.5, v2.6.6, v2.6.7, v2.6.8, v2.6.9, v2.7.0, v2.7.1, v2.7.10, v2.7.11, v2.7.12, v2.7.13, v2.7.14, v2.7.15, v2.7.16, v2.7.2, v2.7.3, v2.7.4, v2.7.5, v2.7.6, v2.7.7, v2.7.8, v2.7.9, v2.8.0, v2.8.1, v2.8.2, v2.8.3, v2.8.4, v2.8.5, v2.8.6, v2.8.7, v2.8.8, v2.8.9].
    - don't install symfony/symfony v3.0.0|don't install symfony/framework-bundle v2.2.0
    - don't install symfony/symfony v3.0.0|don't install symfony/framework-bundle v2.2.1
    - don't install symfony/symfony v3.0.0|don't install symfony/framework-bundle v2.2.10
    - don't install symfony/symfony v3.0.0|don't install symfony/framework-bundle v2.2.11
    - don't install symfony/symfony v3.0.0|don't install symfony/framework-bundle v2.2.2
    - don't install symfony/symfony v3.0.0|don't install symfony/framework-bundle v2.2.3
    - don't install symfony/symfony v3.0.0|don't install symfony/framework-bundle v2.2.4
    - don't install symfony/symfony v3.0.0|don't install symfony/framework-bundle v2.2.5
    - don't install symfony/symfony v3.0.0|don't install symfony/framework-bundle v2.2.6
    - don't install symfony/symfony v3.0.0|don't install symfony/framework-bundle v2.2.7
    - don't install symfony/symfony v3.0.0|don't install symfony/framework-bundle v2.2.8
    - don't install symfony/symfony v3.0.0|don't install symfony/framework-bundle v2.2.9
    - don't install symfony/symfony v3.0.0|don't install symfony/framework-bundle v2.3.0
    - don't install symfony/symfony v3.0.0|don't install symfony/framework-bundle v2.3.1
    - don't install symfony/symfony v3.0.0|don't install symfony/framework-bundle v2.3.10
    - don't install symfony/symfony v3.0.0|don't install symfony/framework-bundle v2.3.11
    - don't install symfony/symfony v3.0.0|don't install symfony/framework-bundle v2.3.12
    - don't install symfony/symfony v3.0.0|don't install symfony/framework-bundle v2.3.13
    - don't install symfony/symfony v3.0.0|don't install symfony/framework-bundle v2.3.14
    - don't install symfony/symfony v3.0.0|don't install symfony/framework-bundle v2.3.15
    - don't install symfony/symfony v3.0.0|don't install symfony/framework-bundle v2.3.16
    - don't install symfony/symfony v3.0.0|don't install symfony/framework-bundle v2.3.17
    - don't install symfony/symfony v3.0.0|don't install symfony/framework-bundle v2.3.18
    - don't install symfony/symfony v3.0.0|don't install symfony/framework-bundle v2.3.19
    - don't install symfony/symfony v3.0.0|don't install symfony/framework-bundle v2.3.2
    - don't install symfony/symfony v3.0.0|don't install symfony/framework-bundle v2.3.20
    - don't install symfony/symfony v3.0.0|don't install symfony/framework-bundle v2.3.21
    - don't install symfony/symfony v3.0.0|don't install symfony/framework-bundle v2.3.22
    - don't install symfony/symfony v3.0.0|don't install symfony/framework-bundle v2.3.23
    - don't install symfony/symfony v3.0.0|don't install symfony/framework-bundle v2.3.24
    - don't install symfony/symfony v3.0.0|don't install symfony/framework-bundle v2.3.25
    - don't install symfony/symfony v3.0.0|don't install symfony/framework-bundle v2.3.26
    - don't install symfony/symfony v3.0.0|don't install symfony/framework-bundle v2.3.27
    - don't install symfony/symfony v3.0.0|don't install symfony/framework-bundle v2.3.28
    - don't install symfony/symfony v3.0.0|don't install symfony/framework-bundle v2.3.29
    - don't install symfony/symfony v3.0.0|don't install symfony/framework-bundle v2.3.3
    - don't install symfony/symfony v3.0.0|don't install symfony/framework-bundle v2.3.30
    - don't install symfony/symfony v3.0.0|don't install symfony/framework-bundle v2.3.31
    - don't install symfony/symfony v3.0.0|don't install symfony/framework-bundle v2.3.32
    - don't install symfony/symfony v3.0.0|don't install symfony/framework-bundle v2.3.33
    - don't install symfony/symfony v3.0.0|don't install symfony/framework-bundle v2.3.34
    - don't install symfony/symfony v3.0.0|don't install symfony/framework-bundle v2.3.35
    - don't install symfony/symfony v3.0.0|don't install symfony/framework-bundle v2.3.36
    - don't install symfony/symfony v3.0.0|don't install symfony/framework-bundle v2.3.37
    - don't install symfony/symfony v3.0.0|don't install symfony/framework-bundle v2.3.38
    - don't install symfony/symfony v3.0.0|don't install symfony/framework-bundle v2.3.39
    - don't install symfony/symfony v3.0.0|don't install symfony/framework-bundle v2.3.4
    - don't install symfony/symfony v3.0.0|don't install symfony/framework-bundle v2.3.40
    - don't install symfony/symfony v3.0.0|don't install symfony/framework-bundle v2.3.41
    - don't install symfony/symfony v3.0.0|don't install symfony/framework-bundle v2.3.42
    - don't install symfony/symfony v3.0.0|don't install symfony/framework-bundle v2.3.5
    - don't install symfony/symfony v3.0.0|don't install symfony/framework-bundle v2.3.6
    - don't install symfony/symfony v3.0.0|don't install symfony/framework-bundle v2.3.7
    - don't install symfony/symfony v3.0.0|don't install symfony/framework-bundle v2.3.8
    - don't install symfony/symfony v3.0.0|don't install symfony/framework-bundle v2.3.9
    - don't install symfony/symfony v3.0.0|don't install symfony/framework-bundle v2.4.0
    - don't install symfony/symfony v3.0.0|don't install symfony/framework-bundle v2.4.1
    - don't install symfony/symfony v3.0.0|don't install symfony/framework-bundle v2.4.10
    - don't install symfony/symfony v3.0.0|don't install symfony/framework-bundle v2.4.2
    - don't install symfony/symfony v3.0.0|don't install symfony/framework-bundle v2.4.3
    - don't install symfony/symfony v3.0.0|don't install symfony/framework-bundle v2.4.4
    - don't install symfony/symfony v3.0.0|don't install symfony/framework-bundle v2.4.5
    - don't install symfony/symfony v3.0.0|don't install symfony/framework-bundle v2.4.6
    - don't install symfony/symfony v3.0.0|don't install symfony/framework-bundle v2.4.7
    - don't install symfony/symfony v3.0.0|don't install symfony/framework-bundle v2.4.8
    - don't install symfony/symfony v3.0.0|don't install symfony/framework-bundle v2.4.9
    - don't install symfony/symfony v3.0.0|don't install symfony/framework-bundle v2.5.0
    - don't install symfony/symfony v3.0.0|don't install symfony/framework-bundle v2.5.1
    - don't install symfony/symfony v3.0.0|don't install symfony/framework-bundle v2.5.10
    - don't install symfony/symfony v3.0.0|don't install symfony/framework-bundle v2.5.11
    - don't install symfony/symfony v3.0.0|don't install symfony/framework-bundle v2.5.12
    - don't install symfony/symfony v3.0.0|don't install symfony/framework-bundle v2.5.2
    - don't install symfony/symfony v3.0.0|don't install symfony/framework-bundle v2.5.3
    - don't install symfony/symfony v3.0.0|don't install symfony/framework-bundle v2.5.4
    - don't install symfony/symfony v3.0.0|don't install symfony/framework-bundle v2.5.5
    - don't install symfony/symfony v3.0.0|don't install symfony/framework-bundle v2.5.6
    - don't install symfony/symfony v3.0.0|don't install symfony/framework-bundle v2.5.7
    - don't install symfony/symfony v3.0.0|don't install symfony/framework-bundle v2.5.8
    - don't install symfony/symfony v3.0.0|don't install symfony/framework-bundle v2.5.9
    - don't install symfony/symfony v3.0.0|don't install symfony/framework-bundle v2.6.0
    - don't install symfony/symfony v3.0.0|don't install symfony/framework-bundle v2.6.1
    - don't install symfony/symfony v3.0.0|don't install symfony/framework-bundle v2.6.10
    - don't install symfony/symfony v3.0.0|don't install symfony/framework-bundle v2.6.11
    - don't install symfony/symfony v3.0.0|don't install symfony/framework-bundle v2.6.12
    - don't install symfony/symfony v3.0.0|don't install symfony/framework-bundle v2.6.13
    - don't install symfony/symfony v3.0.0|don't install symfony/framework-bundle v2.6.2
    - don't install symfony/symfony v3.0.0|don't install symfony/framework-bundle v2.6.3
    - don't install symfony/symfony v3.0.0|don't install symfony/framework-bundle v2.6.4
    - don't install symfony/symfony v3.0.0|don't install symfony/framework-bundle v2.6.5
    - don't install symfony/symfony v3.0.0|don't install symfony/framework-bundle v2.6.6
    - don't install symfony/symfony v3.0.0|don't install symfony/framework-bundle v2.6.7
    - don't install symfony/symfony v3.0.0|don't install symfony/framework-bundle v2.6.8
    - don't install symfony/symfony v3.0.0|don't install symfony/framework-bundle v2.6.9
    - don't install symfony/symfony v3.0.0|don't install symfony/framework-bundle v2.7.0
    - don't install symfony/symfony v3.0.0|don't install symfony/framework-bundle v2.7.1
    - don't install symfony/symfony v3.0.0|don't install symfony/framework-bundle v2.7.10
    - don't install symfony/symfony v3.0.0|don't install symfony/framework-bundle v2.7.11
    - don't install symfony/symfony v3.0.0|don't install symfony/framework-bundle v2.7.12
    - don't install symfony/symfony v3.0.0|don't install symfony/framework-bundle v2.7.13
    - don't install symfony/symfony v3.0.0|don't install symfony/framework-bundle v2.7.14
    - don't install symfony/symfony v3.0.0|don't install symfony/framework-bundle v2.7.15
    - don't install symfony/symfony v3.0.0|don't install symfony/framework-bundle v2.7.16
    - don't install symfony/symfony v3.0.0|don't install symfony/framework-bundle v2.7.2
    - don't install symfony/symfony v3.0.0|don't install symfony/framework-bundle v2.7.3
    - don't install symfony/symfony v3.0.0|don't install symfony/framework-bundle v2.7.4
    - don't install symfony/symfony v3.0.0|don't install symfony/framework-bundle v2.7.5
    - don't install symfony/symfony v3.0.0|don't install symfony/framework-bundle v2.7.6
    - don't install symfony/symfony v3.0.0|don't install symfony/framework-bundle v2.7.7
    - don't install symfony/symfony v3.0.0|don't install symfony/framework-bundle v2.7.8
    - don't install symfony/symfony v3.0.0|don't install symfony/framework-bundle v2.7.9
    - don't install symfony/symfony v3.0.0|don't install symfony/framework-bundle v2.8.0
    - don't install symfony/symfony v3.0.0|don't install symfony/framework-bundle v2.8.1
    - don't install symfony/symfony v3.0.0|don't install symfony/framework-bundle v2.8.2
    - don't install symfony/symfony v3.0.0|don't install symfony/framework-bundle v2.8.3
    - don't install symfony/symfony v3.0.0|don't install symfony/framework-bundle v2.8.4
    - don't install symfony/symfony v3.0.0|don't install symfony/framework-bundle v2.8.5
    - don't install symfony/symfony v3.0.0|don't install symfony/framework-bundle v2.8.6
    - don't install symfony/symfony v3.0.0|don't install symfony/framework-bundle v2.8.7
    - don't install symfony/symfony v3.0.0|don't install symfony/framework-bundle v2.8.8
    - don't install symfony/symfony v3.0.0|don't install symfony/framework-bundle v2.8.9
    - Can only install one of: symfony/symfony[v3.0.0, v2.8.8].
    - don't install symfony/console v2.5.0|don't install symfony/symfony v3.0.0
    - don't install symfony/console v2.5.1|don't install symfony/symfony v3.0.0
    - don't install symfony/console v2.5.10|don't install symfony/symfony v3.0.0
    - don't install symfony/console v2.5.11|don't install symfony/symfony v3.0.0
    - don't install symfony/console v2.5.12|don't install symfony/symfony v3.0.0
    - don't install symfony/console v2.5.2|don't install symfony/symfony v3.0.0
    - don't install symfony/console v2.5.3|don't install symfony/symfony v3.0.0
    - don't install symfony/console v2.5.4|don't install symfony/symfony v3.0.0
    - don't install symfony/console v2.5.5|don't install symfony/symfony v3.0.0
    - don't install symfony/console v2.5.6|don't install symfony/symfony v3.0.0
    - don't install symfony/console v2.5.7|don't install symfony/symfony v3.0.0
    - don't install symfony/console v2.5.8|don't install symfony/symfony v3.0.0
    - don't install symfony/console v2.5.9|don't install symfony/symfony v3.0.0
    - don't install symfony/console v2.6.0|don't install symfony/symfony v3.0.0
    - don't install symfony/console v2.6.1|don't install symfony/symfony v3.0.0
    - don't install symfony/console v2.6.10|don't install symfony/symfony v3.0.0
    - don't install symfony/console v2.6.11|don't install symfony/symfony v3.0.0
    - don't install symfony/console v2.6.12|don't install symfony/symfony v3.0.0
    - don't install symfony/console v2.6.13|don't install symfony/symfony v3.0.0
    - don't install symfony/console v2.6.2|don't install symfony/symfony v3.0.0
    - don't install symfony/console v2.6.3|don't install symfony/symfony v3.0.0
    - don't install symfony/console v2.6.4|don't install symfony/symfony v3.0.0
    - don't install symfony/console v2.6.5|don't install symfony/symfony v3.0.0
    - don't install symfony/console v2.6.6|don't install symfony/symfony v3.0.0
    - don't install symfony/console v2.6.7|don't install symfony/symfony v3.0.0
    - don't install symfony/console v2.6.8|don't install symfony/symfony v3.0.0
    - don't install symfony/console v2.6.9|don't install symfony/symfony v3.0.0
    - don't install symfony/console v2.7.0|don't install symfony/symfony v3.0.0
    - don't install symfony/console v2.7.1|don't install symfony/symfony v3.0.0
    - don't install symfony/console v2.7.10|don't install symfony/symfony v3.0.0
    - don't install symfony/console v2.7.11|don't install symfony/symfony v3.0.0
    - don't install symfony/console v2.7.12|don't install symfony/symfony v3.0.0
    - don't install symfony/console v2.7.13|don't install symfony/symfony v3.0.0
    - don't install symfony/console v2.7.14|don't install symfony/symfony v3.0.0
    - don't install symfony/console v2.7.15|don't install symfony/symfony v3.0.0
    - don't install symfony/console v2.7.16|don't install symfony/symfony v3.0.0
    - don't install symfony/console v2.7.2|don't install symfony/symfony v3.0.0
    - don't install symfony/console v2.7.3|don't install symfony/symfony v3.0.0
    - don't install symfony/console v2.7.4|don't install symfony/symfony v3.0.0
    - don't install symfony/console v2.7.5|don't install symfony/symfony v3.0.0
    - don't install symfony/console v2.7.6|don't install symfony/symfony v3.0.0
    - don't install symfony/console v2.7.7|don't install symfony/symfony v3.0.0
    - don't install symfony/console v2.7.8|don't install symfony/symfony v3.0.0
    - don't install symfony/console v2.7.9|don't install symfony/symfony v3.0.0
    - don't install symfony/console v2.8.0|don't install symfony/symfony v3.0.0
    - don't install symfony/console v2.8.1|don't install symfony/symfony v3.0.0
    - don't install symfony/console v2.8.2|don't install symfony/symfony v3.0.0
    - don't install symfony/console v2.8.3|don't install symfony/symfony v3.0.0
    - don't install symfony/console v2.8.4|don't install symfony/symfony v3.0.0
    - don't install symfony/console v2.8.5|don't install symfony/symfony v3.0.0
    - don't install symfony/console v2.8.6|don't install symfony/symfony v3.0.0
    - don't install symfony/console v2.8.7|don't install symfony/symfony v3.0.0
    - don't install symfony/console v2.8.8|don't install symfony/symfony v3.0.0
    - don't install symfony/console v2.8.9|don't install symfony/symfony v3.0.0
    - Installation request for symfony/symfony 3.0.* -> satisfiable by symfony/symfony[v3.0.0, v3.0.1, v3.0.2, v3.0.3, v3.0.4, v3.0.5, v3.0.6, v3.0.7, v3.0.8, v3.0.9].
    - Installation request for sensio/generator-bundle (locked at v2.5.3, required as ~2.3) -> satisfiable by sensio/generator-bundle[v2.5.3].

Here is my composer.json :

{
    "name": "symfony/framework-standard-edition",
    "license": "MIT",
    "type": "project",
    "description": "The \"Symfony Standard Edition\" distribution",
    "autoload": {
        "psr-0": { "": "src/", "SymfonyStandard": "app/" }
    },
    "require": {
        "php": ">=5.3.3",
        "symfony/symfony": "3.0.*",
        "doctrine/orm": "~2.2,>=2.2.3",
        "doctrine/doctrine-bundle": "~1.2",
        "twig/extensions": "~1.0",
        "symfony/assetic-bundle": "~2.3",
        "symfony/swiftmailer-bundle": "~2.3",
        "symfony/monolog-bundle": "~2.4",
        "sensio/distribution-bundle": "~3.0",
        "sensio/framework-extra-bundle": "~3.0",
        "incenteev/composer-parameter-handler": "~2.0",
        "stof/doctrine-extensions-bundle": "dev-master",
        "oh/instagram-bundle" : "dev-master",
        "knplabs/knp-paginator-bundle": "~2.4",
        "imagine/imagine": "0.6.*",
        "excelwebzone/recaptcha-bundle": "2.6.*@dev"
    },
    "require-dev": {
        "sensio/generator-bundle": "~2.3"
    },
    "scripts": {
        "post-root-package-install": [
            "SymfonyStandard\\Composer::hookRootPackageInstall"
        ],
        "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",
            "Sensio\\Bundle\\DistributionBundle\\Composer\\ScriptHandler::removeSymfonyStandardFiles"
        ],
        "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",
            "Sensio\\Bundle\\DistributionBundle\\Composer\\ScriptHandler::removeSymfonyStandardFiles"
        ]
    },
    "config": {
        "bin-dir": "bin"
    },
    "extra": {
        "symfony-app-dir": "app",
        "symfony-web-dir": "web",
        "symfony-var-dir": "var",
        "symfony-bin-dir": "bin",
        "incenteev-parameters": {
            "file": "app/config/parameters.yml",
            "keep-outdated": true
        },
        "branch-alias": {
            "dev-master": "2.5-dev"
        }
    }
}

Does anybody find what's wrong with my setup ?

Thank you very much !

Answer 1

Like in the upgrade from Symfony 2.3 to 2.7, you have to update all the dependencies, not the symfony/symfony package only.

We can use GitHub in order to generate the diff between Symfony 2.8 and 3.0 (if the diff for the composer.json file is not displayed, click on Files changed tab, then 26 changed files and finally composer.json):

         "psr-4": { "": "src/" },
         "classmap": [ "app/AppKernel.php", "app/AppCache.php" ]
     },
+    "autoload-dev": {
+        "psr-4": { "Tests\\": "tests/" }
+    },
     "require": {
-        "php": ">=5.3.9",
-        "symfony/symfony": "2.8.*",
-        "doctrine/orm": "^2.4.8",
-        "doctrine/doctrine-bundle": "~1.4",
-        "symfony/swiftmailer-bundle": "~2.3",
-        "symfony/monolog-bundle": "~2.4",
-        "sensio/distribution-bundle": "~5.0",
+        "php": ">=5.5.9",
+        "symfony/symfony": "3.0.*",
+        "doctrine/orm": "^2.5",
+        "doctrine/doctrine-bundle": "^1.6",
+        "doctrine/doctrine-cache-bundle": "^1.2",
+        "symfony/swiftmailer-bundle": "^2.3",
+        "symfony/monolog-bundle": "^2.8",
+        "sensio/distribution-bundle": "^5.0",
         "sensio/framework-extra-bundle": "^3.0.2",
-        "incenteev/composer-parameter-handler": "~2.0"
+        "incenteev/composer-parameter-handler": "^2.0"
     },
     "require-dev": {
-        "sensio/generator-bundle": "~3.0",
-        "symfony/phpunit-bridge": "~2.7"
+        "sensio/generator-bundle": "^3.0",
+        "symfony/phpunit-bridge": "^3.0"
     },
     "scripts": {
         "post-install-cmd": [

So you should use a composer.json like this:

    "require": {
        "php": ">=5.3.9",
        "symfony/symfony": "3.0.*",
        "doctrine/orm": "^2.5",
        "doctrine/doctrine-bundle": "^1.6",
        "doctrine/doctrine-cache-bundle": "^1.2",
        "twig/extensions": "~1.0",
        "symfony/swiftmailer-bundle": "^2.3",
        "symfony/monolog-bundle": "^2.8",
        "sensio/distribution-bundle": "^5.0",
        "sensio/framework-extra-bundle": "^3.0.2",
        "incenteev/composer-parameter-handler": "^2.0",
        …
    },
    "require-dev": {
        "sensio/generator-bundle": "^3.0"
    },

And conflicts between packages should not appear anymore.

Answer 2

You have to change this line:

"require-dev": {
    "sensio/generator-bundle": "~2.3"
},

to

"require-dev": {
    "sensio/generator-bundle": "^3.0"
},

Generator bundle version 2.3 is incompatible with Symfony 3.0