Environment

• pip version: 19.1.1
• Python version: 3.7
• OS: MacOS Mojave

Description
I'm not sure if this is a six bug or a Pip bug. Excuse me if it belongs to six.

Pip seems to allow local paths in install_requires via name @ ./some/path, but the URL parsing is terribly broken.

https://github.com/pypa/pip/blob/a38a0eacd4650a7d9af4e6831a2c0aed0b6a0329/src/pip/_internal/download.py#L670-L690

In this function, it uses urlsplit to get the individual components of the incoming URL.

Here's what that looks like with a few pieces of input:

./foo/bar -> SplitResult(scheme='', netloc='', path='./foo/bar', query='', fragment='')
file:./foo/bar -> SplitResult(scheme='file', netloc='', path='./foo/bar', query='', fragment='')
file://./foo/bar -> SplitResult(scheme='file', netloc='.', path='/foo/bar', query='', fragment='')

Notice the last one results in the netloc being . instead of empty and the path being absolute, not local. This trips the error regarding non-local paths. That's all fine and well - I can use the second form to satisfy the conditional logic (though it really ought to support the first as well).

However, there's conflicting logic elsewhere...

https://github.com/pypa/pip/blob/169eebdb6e36a31e545804228cad94902a1ec8e9/src/pip/_vendor/packaging/requirements.py#L103-L106

This is the logic that fails even though we satisfy the prior logic.

Here's a test function that shows the problem:

from six.moves.urllib import parse as urllib_parse

def tryparse(url):
    print(url)
    parsed = urllib_parse.urlparse(url)
    unparsed = urllib_parse.urlunparse(parsed)
    parsed_again = urllib_parse.urlparse(unparsed)
    print(parsed)
    print(unparsed)
    print(parsed_again)

Here's the output for ./foo/bar:

>>> tryparse('./foo/bar')
./foo/bar
ParseResult(scheme='', netloc='', path='./foo/bar', params='', query='', fragment='')
./foo/bar
ParseResult(scheme='', netloc='', path='./foo/bar', params='', query='', fragment='')

All good, though it doesn't satisfy the first function's logic of requiring a scheme of file:.

Here's the output for file:./foo/bar:

>>> tryparse('file:./foo/bar')
file:./foo/bar
ParseResult(scheme='file', netloc='', path='./foo/bar', params='', query='', fragment='')
file:///./foo/bar
ParseResult(scheme='file', netloc='', path='/./foo/bar', params='', query='', fragment='')

Oops! Notice how, when we "unparse" the result from the first parse call, our path becomes absolute file:///....

This is why the second mentioned check fails - the path is not local. I believe this to be a bug in six but can be mitigated in Pip by allowing scheme in ['file', ''] and instructing users to use the ./foo/bar URI form.

Given these two contradictory pieces of logic, it's impossible to use local paths in install_requires keys in either distutils or setuptools configurations.

Expected behavior
I should be able to do name @ ./some/path (or, honestly, simply ./some/path) to specify a vendored package local to my codebase.

How to Reproduce

#!/usr/bin/env bash
mkdir /tmp/pip-uri-repro && cd /tmp/pip-uri-repro

mkdir -p foo/bar

cat > requirements.txt <<EOF
./foo
EOF

cat > foo/setup.py <<EOF
#!/usr/bin/env python
from setuptools import setup
setup(
    name="foo",
    version="0.1",
    install_requires=[
        "bar @ file:./bar"
    ]
)
EOF

cat > foo/bar/setup.py <<EOF
#!/usr/bin/env python
from setuptools import setup
setup(
    name="bar",
    version="0.1"
)
EOF

# (OUTPUT 1)
pip install -r requirements.txt

cat > foo/setup.py <<EOF
#!/usr/bin/env python
from setuptools import setup
setup(
    name="foo",
    version="0.1",
    install_requires=[
        # we're forced to use an absolute path
        # to make the "Invalid URL" error go
        # away, which isn't right anyway (the
        # error that is raised as a result
        # is justified)
        "bar @ file://./bar"
    ]
)
EOF

# (OUTPUT 2)
pip install -r requirements.txt

Output

From the first pip install:

Processing ./foo
    ERROR: Complete output from command python setup.py egg_info:
    ERROR: error in foo setup command: 'install_requires' must be a string or list of strings containing valid project/version requirement specifiers; Invalid URL given

From the second pip install:

Processing ./foo
ERROR: Exception:
Traceback (most recent call last):
  File "/private/tmp/repro-pip-egg/env3/lib/python3.7/site-packages/pip/_internal/cli/base_command.py", line 178, in main
    status = self.run(options, args)
  File "/private/tmp/repro-pip-egg/env3/lib/python3.7/site-packages/pip/_internal/commands/install.py", line 352, in run
    resolver.resolve(requirement_set)
  File "/private/tmp/repro-pip-egg/env3/lib/python3.7/site-packages/pip/_internal/resolve.py", line 131, in resolve
    self._resolve_one(requirement_set, req)
  File "/private/tmp/repro-pip-egg/env3/lib/python3.7/site-packages/pip/_internal/resolve.py", line 294, in _resolve_one
    abstract_dist = self._get_abstract_dist_for(req_to_install)
  File "/private/tmp/repro-pip-egg/env3/lib/python3.7/site-packages/pip/_internal/resolve.py", line 242, in _get_abstract_dist_for
    self.require_hashes
  File "/private/tmp/repro-pip-egg/env3/lib/python3.7/site-packages/pip/_internal/operations/prepare.py", line 256, in prepare_linked_requirement
    path = url_to_path(req.link.url)
  File "/private/tmp/repro-pip-egg/env3/lib/python3.7/site-packages/pip/_internal/download.py", line 521, in url_to_path
    % url
ValueError: non-local file URIs are not supported on this platform: 'file://./bar'

EDIT:

Just found out that RFC 3986 specifies that relative path URIs are not permitted with the file: scheme, so technically six should be erroring out on file:./foo/bar.

However, that means, technically, I should be able to do the following in my setup.py:

PKG_DIR = os.path.dirname(os.path.abspath(__file__))
install_requires = [
    f"name @ file://{PKG_DIR}/foo/bar"
]

However, pip seems to be creating a "clean" copy of the package in /tmp, so we get something like file:///tmp/pip-req-build-9u3z545j/foo/bar.

Running that through our test function, we satisfy the second function's conditional:

>>> tryparse('file:///tmp/pip-req-build-9u3z545j/foo/bar')
file:///tmp/pip-req-build-9u3z545j/foo/bar
ParseResult(scheme='file', netloc='', path='/tmp/pip-req-build-9u3z545j/foo/bar', params='', query='', fragment='')
file:///tmp/pip-req-build-9u3z545j/foo/bar
ParseResult(scheme='file', netloc='', path='/tmp/pip-req-build-9u3z545j/foo/bar', params='', query='', fragment='')

Everything is good there. The "unparse" yields the same result, and the netloc requirements are met for the first function's conditional.

However, we're still met with an Invalid URL error, even though the second function's logic is satisfied.

Since pip (or distutils or setuptools or whatever) swallows output, I went ahead and did the following in my setup.py

import os
PKG_DIR = os.path.dirname(os.path.abspath(__file__))
assert False, os.system(f"find {PKG_DIR}")

Which verifies that all of the files are there, as expected - so it can't be a file missing or something. The line above that has "Invalid URL given" is the only place in the codebase that string shows up.

At this point, I'm not sure what the problem is.