Requirements file which contains `-e` with a relative local path, is only installable from a specific directory

[Thiel]

Environment

• pip version: 18.1
• Python version: 2.7.14
• OS: Windows (but I don't think it's restricted to a specific platform)

Description
I would like to be able to call pip install -r path/to/requirements.txt from any directory. However usage of --editable/-e with a relative path inside of a requirements.txt assume that the path is relative the current directory I'm currently in, rather than the directory where the file is located.

My specific use case, involve usage of multiple independent requirements.txt in a directory hierarchy where they can reference each other. And seems to exhibit the same issue.

Expected behavior
Expected behavior would be to not require being in a specific directory in order to call pip install -r path/to/requirements.txt when --editable/-e is being used with relative local path.

How to Reproduce

#! /bin/bash

mkdir dir/
echo '-e .' > dir/requirements.txt
cat - > dir/setup.py <<EOF
from distutils.core import setup, Extension
setup(name='foo', version='1.0')
EOF

pip install -r dir/requirements.txt # FAIL

cd dir
pip install -r requirements.txt # PASS

Output

Directory '.' is not installable. File 'setup.py' not found.
Obtaining file:///C:/project/repro_github/pip_change_dir_r/dir (from -r requirements.txt (line 1))
Installing collected packages: foo
  Found existing installation: foo 1.0
    Uninstalling foo-1.0:
      Successfully uninstalled foo-1.0
  Running setup.py develop for foo
Successfully installed foo

Potential solution
I assume that pip is missing a chdir when the requirements is being interpreted. And doing so would fix all mentioned issue.
Would there be a reason that prevent us to do that?

[cjerdonek]

I wonder how this could be rolled out if people are relying on the cwd behavior for relative paths. Would we need a mechanism to warn people of the change in advance (e.g. triggered by the appearance of relative paths inside a requirements file)?

[piotr-dobrogost]

Duplicate of issue #3772
Some history around relative paths in requirements files can be found in issue #328.

[pradyunsg]

Thanks (again!) for looking up the duplicate issue that would have been difficult to find otherwise @piotr-dobrogost! :)

@cjerdonek I agree with the closing comment on #3772 that this should be handled in Requirements 2.0.

[Thiel]

@cjerdonek Good point. In order keep backward compatibly there would have to be a hint to distinguish the 2 cases. The only ideas that come to mind are having a distinguishable syntax in the requirements.txt or in the command line flag. I have to admit I'm not a big fan of either solution.

@pradyunsg By requirements 2.0 do you mean Pipfile ?

[pradyunsg]

@Thiel Yes. That's what it has become now. :)

[kevincantu]

We could use a / like .gitignore and .gitattributes do to indicate a path relative to the repository root, or some other symbol like that.

So ../other/requirements.txt would still go wherever it goes today. But /my/other/requirements.txt would go to the same file no matter which directory I attempted to install it from.