"conflict with the backend dependencies" with pip 19

• I am on the latest Poetry version.

• I have searched the issues of this repo and believe that this is not a duplicate.

• If an exception occurs when executing a command, I executed it again in debug mode (-vvv option).

• OS version and name: Linux, RHEL7.5

• Poetry version: 0.12.11

• Link of a Gist with the contents of your pyproject.toml file: https://gist.github.com/danmur/fe1b9685b8f6fa87fad4764be892f9f9

$ ~/pythons/poetry2/bin/poetry install -vvvv
Using virtualenv: /home/daniel.j.murray/git/testapp/.venv
Installing dependencies from lock file

Nothing to install or update

  - Skipping scandir (1.9.0) Already installed
  - Skipping six (1.12.0) Already installed
  - Skipping atomicwrites (1.2.1) Already installed
  - Skipping attrs (18.2.0) Already installed
  - Skipping certifi (2018.11.29) Already installed
  - Skipping chardet (3.0.4) Already installed
  - Skipping colorama (0.4.1) Not needed for the current environment
  - Skipping funcsigs (1.0.2) Already installed
  - Skipping idna (2.5) Already installed
  - Skipping more-itertools (5.0.0) Already installed
  - Skipping pathlib2 (2.3.3) Already installed
  - Skipping pluggy (0.8.1) Already installed
  - Skipping py (1.7.0) Already installed
  - Skipping urllib3 (1.22) Already installed
  - Skipping pytest (3.10.1) Already installed
  - Skipping requests (2.18.3) Already installed
  - Installing testapp (0.1.0)
                                                                                                                                                                   
[EnvCommandError]                                                                                                                                   
Command ['/home/daniel.j.murray/git/testapp/.venv/bin/pip', 'install', '-e', '/home/daniel.j.murray/git/testapp', '--no-deps'] errored with the followi        
ng output:                                                                                                                                                       
DEPRECATION: Python 2.7 will reach the end of its life on January 1st, 2020. Please upgrade your Python as Python 2.7 won't be maintained after that date. A fu  
ture version of pip will drop support for Python 2.7.                                                                                                            
Looking in indexes: xxx                                                                                                
Obtaining file:///home/daniel.j.murray/git/testapp                                                                                                           
  Installing build dependencies: started                                                                                                                         
  Installing build dependencies: finished with status 'done'                                                                                                     
  Getting requirements to build wheel: started                                                                                                                   
  Getting requirements to build wheel: finished with status 'done'                                                                                               
Some build dependencies for file:///home/daniel.j.murray/git/testapp conflict with the backend dependencies: requests==2.21.0 is incompatible with requests  
==2.18.3.                                                                                                                                                        
                                                                                                                                                                   
Exception trace:
 /home/daniel.j.murray/pythons/poetry2/lib/python2.7/site-packages/cleo/application.py in run() at line 94
   status_code = self.do_run(input_, output_)
 /home/daniel.j.murray/pythons/poetry2/lib/python2.7/site-packages/poetry/console/application.py in do_run() at line 88
   return super(Application, self).do_run(i, o)
 /home/daniel.j.murray/pythons/poetry2/lib/python2.7/site-packages/cleo/application.py in do_run() at line 197
   status_code = command.run(input_, output_)
 /home/daniel.j.murray/pythons/poetry2/lib/python2.7/site-packages/poetry/console/commands/command.py in run() at line 77
   return super(BaseCommand, self).run(i, o)
 /home/daniel.j.murray/pythons/poetry2/lib/python2.7/site-packages/cleo/commands/base_command.py in run() at line 146
   status_code = self.execute(input_, output_)
 /home/daniel.j.murray/pythons/poetry2/lib/python2.7/site-packages/cleo/commands/command.py in execute() at line 107
   return self.handle()
 /home/daniel.j.murray/pythons/poetry2/lib/python2.7/site-packages/poetry/console/commands/install.py in handle() at line 89
   self.env.run("pip", "install", "-e", str(setup.parent), "--no-deps")
 /home/daniel.j.murray/pythons/poetry2/lib/python2.7/site-packages/poetry/utils/env.py in run() at line 492
   return super(VirtualEnv, self).run(bin, *args, **kwargs)
 /home/daniel.j.murray/pythons/poetry2/lib/python2.7/site-packages/poetry/utils/env.py in run() at line 354
   raise EnvCommandError(e)

install [--no-dev] [--dry-run] [-E|--extras EXTRAS] [--develop DEVELOP]

The issue seems to be having requirements on poetry dependencies with this new version of pip. I have a dependency on requests 2.18.3, which I imagine poetry does too but for a different version, and pip is trying to treat this as a conflict here: https://github.com/pypa/pip/blob/8ff8e1fa9e9c70b1fa285a8c02223e92a53d05ef/src/pip/_internal/operations/prepare.py#L151

Commenting out the [build-system] bit in pyproject.toml works around it.

I am not sure if this is a poetry issue or a pip issue; if it seems more like a pip issue let me know and I’ll file it there 😃

[pmav99]

Downgrading pip to 18.1 also seems to be a valid workaround.

[MRigal]

Hi @sdispater This is really critical! The easiest way to reproduce this is to run with pip 19:

poetry new foobar
poetry add cleo  # Actual version 0.7.X
poetry install

Since poetry itself is sticked to cleo 0.6.X, any packages willing to use cleo 0.7.X will result in raising an exception