<p>尽管约束不兼容，pip 仍成功退出</p>

环境

• 点子版本：19.2.3
• Python版本：3.7.4
• 操作系统：macOS 18.7.0

这也是使用docker run python:3复制的。

描述

如果约束文件指定了不兼容的版本，pip 会安装一个依赖项损坏的包。 显示错误消息，但退出代码为0 。

例如， environs 5.2.1需要marshmallow>=2.7.0 ，但如果后者在约束文件中指定，pip 会使用marshmallow 2.6.0安装它。

预期行为

pip 不应安装该软件包，并以失败退出。

如何繁殖

1. 使用marshmallow==2.6.0创建约束
2. 使用environs==5.2.1创建 requirements.txt
3. 运行pip install -r requirements.txt -c constraints.txt

输出

$ docker run --rm -ti python:3 sh
# python -V
Python 3.7.4
# pip -V
pip 19.2.3 from /usr/local/lib/python3.7/site-packages/pip (python 3.7)
# uname -a
Linux 4d4f16cc965f 4.9.184-linuxkit #1 SMP Tue Jul 2 22:58:16 UTC 2019 x86_64 GNU/Linux
# echo marshmallow==2.6.0 > constraints.txt
# echo environs==5.2.1 > requirements.txt
# pip install -r requirements.txt -c constraints.txt
Collecting environs==5.2.1 (from -r requirements.txt (line 1))
  Downloading https://files.pythonhosted.org/packages/5f/c9/6b576b8b374dfe78d9435988e6a53497822f31b9da5bdd446343ad1a4d1b/environs-5.2.1-py2.py3-none-any.whl
Collecting marshmallow==2.6.0 (from -c constraints.txt (line 1))
  Downloading https://files.pythonhosted.org/packages/33/44/c3bdd4222909b6452ebe5c028ea5dbe7e9409307b3b933026218c677fcf1/marshmallow-2.6.0-py2.py3-none-any.whl (44kB)
     |████████████████████████████████| 51kB 729kB/s
Collecting python-dotenv (from environs==5.2.1->-r requirements.txt (line 1))
  Downloading https://files.pythonhosted.org/packages/57/c8/5b14d5cffe7bb06bedf9d66c4562bf90330d3d35e7f0266928c370d9dd6d/python_dotenv-0.10.3-py2.py3-none-any.whl
ERROR: environs 5.2.1 has requirement marshmallow>=2.7.0, but you'll have marshmallow 2.6.0 which is incompatible.
Installing collected packages: marshmallow, python-dotenv, environs
Successfully installed environs-5.2.1 marshmallow-2.6.0 python-dotenv-0.10.3
# echo $?
0