使用laravelcomposer install出现版本问题

在新部署laravel项目时报了如下的错误

D:\WWW\laravel-bjyblog>composer install
Loading composer repositories with package information
Installing dependencies (including require-dev) from lock file
Warning: The lock file is not up to date with the latest changes in composer.json. You may be getting outdated dependencies. Run update to update them.
Your requirements could not be resolved to an installable set of packages.

  Problem 1
    - Installation request for phpunit/php-code-coverage 7.0.3 -> satisfiable by phpunit/php-code-coverage[7.0.3].
    - phpunit/php-code-coverage 7.0.3 requires php ^7.2 -> your PHP version (7.1.13) does not satisfy that requirement.
  Problem 2
    - Installation request for phpunit/phpunit 8.0.6 -> satisfiable by phpunit/phpunit[8.0.6].
    - phpunit/phpunit 8.0.6 requires php ^7.2 -> your PHP version (7.1.13) does not satisfy that requirement.
  Problem 3
    - Installation request for sebastian/global-state 3.0.0 -> satisfiable by sebastian/global-state[3.0.0].
    - sebastian/global-state 3.0.0 requires php ^7.2 -> your PHP version (7.1.13) does not satisfy that requirement.
  Problem 4
    - Installation request for spatie/laravel-backup 6.1.2 -> satisfiable by spatie/laravel-backup[6.1.2].
    - spatie/laravel-backup 6.1.2 requires php ^7.2 -> your PHP version (7.1.13) does not satisfy that requirement.
  Problem 5
    - phpunit/phpunit 8.0.6 requires php ^7.2 -> your PHP version (7.1.13) does not satisfy that requirement.
    - baijunyao/laravel-test-support v2.0.0 requires phpunit/phpunit 7.0 - 8.0 -> satisfiable by phpunit/phpunit[8.0.6].
    - Installation request for baijunyao/laravel-test-support v2.0.0 -> satisfiable by baijunyao/laravel-test-support[v2.0.0].

    - phpunit/phpunit 8.0.6 requires php ^7.2 -> your PHP version (7.1.13) does not satisfy that requirement.
    - baijunyao/laravel-test-support v2.0.0 requires phpunit/phpunit 7.0 - 8.0 -> satisfiable by phpunit/phpunit[8.0.6].
    - Installation request for baijunyao/laravel-test-support v2.0.0 -> satisfiable by baijunyao/laravel-test-support[v2.0.0].

出现这个问题的主要原因就是因为composer时引入的文件所需要的环境版本和你的环境不符合

因此只要将相应的package降低版本然后再进行composer install（composer包版本对应PHP环境信息在这边查看https://packagist.org/explore/）

在这需要强调的是composer install时走的文件是composer.lock，如果composer.lock 不存在才会去走composer.json

你可以试着删掉composer.lock然后修改composer.json中的package的版本号，然后composer install一下，完成后会生成新的composer.lock