[pip 25.1] `assert req.source_dir` fails with the legacy resolver enabled

[ramannanda9]

Description

Seeing build failures because of this function, my guess is this function was supposed to check whether the stuff needs to be built, but the commit 5b20593
is causing assertion failures, we will need to pin pip till this is resolved.

Expected behavior

The assertion should not be there, a check was fine.

pip version

25.1

Python version

3.9

OS

Al2023

How to Reproduce

Try installing certifi,

I will add more details soon.

Output

File "/usr/local/lib/python3.9/site-packages/pip/_internal
/wheel_builder.py", line 53, in _should_build
2025-04-27 12:03:18,230:INFO:__main__:deploy_model: 24.64
assert req.source_dir

Code of Conduct

• I agree to follow the PSF Code of Conduct.

[ichard26]

We can't do anything unless we have reproduction steps. Please do update your issue with reproduction information.

Installing certifi from source on Python 3.9 does result in the bdist_wheel deprecation warning, but it builds just fine.

[andreaschiappacasse]

Hi everyone, currently don't have time to fully reproduce the bug, but I am experiencing the same error while installing a custom package as well in our environment.

Pinned requirements used to build just fine with pip 25.0.1, but after our build environment migrated to pip 25.1 we started experiencing build failures at the same line mentioned by @ramannanda9 (assertion error while loonking for source_dir).

[ichard26]

Given that there is only two reports of this bug, there still isn't anything we can do. We could revert the commit as it was simply a refactoring change, but I don't want to do that unless we know why it's broken and the severity of the bug (which for all we can tell is rather limited).

If anyone else is affected by this crash, please send in a minimum reproduction example. We cannot do anything otherwise.

[pfmoore]

One particular thing that could shed light on this issue - are the people experiencing this bug just using pip as a command line tool, or are they using code that imports pip in some way? Because we changed the test to an assert because pip should never be passing a requirement without a source_dir to _should_build. If it is, we need a reproducer to find out where that is occurring (and fix that, rather than just remove the check and accept that we don't know what pip is doing internally 🙁).

If the issue is triggered by importing pip and using internals somehow, then such usage is not supported, as people will be aware. We may still be able to help, but not without understanding what people are trying to do (and of course, as it's unsupported usage, there are no guarantees).

Either way, we can do nothing without a description of how to trigger the issue.

[sbidoul]

I'd be in favor of leaving the assert in place until we receive a reproducer, which I'll be happy to investigate rapidly.

The reason I made this an assert is that while I thought it could never happen, I had doubts, and it is critical to understand in which circumstances this req.source_dir can be falsy, because _should_build will be changed to return always True soon (then be removed), and we need to clarify that edge case beforehand.

[Rahlir]

I have stumbled upon this issue as well. Simple way to reproduce it:

1. Use fresh virtualenv and python 3.11.9
2. Upgrade pip with pip install --upgrade pip
3. Running pip --version returns pip 25.1
4. Run pip install aiohttp[speedups] == 3.11.16 and you will get AssertionError on assert req.source_dir.

[sbidoul]

@Rahlir thanks! I tried this but it does not reproduce:

#!/bin/bash
set -eaux
venv=$(mktemp -d)
python3.9 -m venv $venv
$venv/bin/pip install --upgrade pip
$venv/bin/pip install aiohttp[speedups]==3.11.16

Can you provide additional information? Maybe pip config debug.

Edit: same with python 3.11.12, and 3.11.9.

[avengersassemble]

Facing the same issue, @sbidoul

Attaching Dockerfile and requirements.txt to reproduce this issue.

requirements.txt

Dockerfile.txt

[notatallshaw]

@avengersassemble I'm not near a computer right now but can you please check without --Use-deprecated=legacy-resolver

[Rahlir]

@Rahlir thanks! I tried this but it does not reproduce:

#!/bin/bash
set -eaux
venv=$(mktemp -d)
python3.9 -m venv $venv
$venv/bin/pip install --upgrade pip
$venv/bin/pip install aiohttp[speedups]==3.11.16

Can you provide additional information? Maybe pip config debug.

Edit: same with python 3.11.12, and 3.11.9.

Ups, you are right, this is due to the --use-deprecated=legacy-resolver, forgot that that was included in our company's default pip.conf. So, you can also reproduce the issue with my example by running the last command with --use-deprecated=legacy-resolver. So, my guess is that the Docker example has the assertion error also due to the legacy-resolver (I am unable to run it right now).

Is there a reason this fails with the legacy-resolver? I guess I will remove it from our config for now (not sure what was the original reason that we used it).

[ramannanda9]

Yep it has to do with deprecated resolver flag, something not easy to switch out.

bash-5.2# pip install --use-deprecated=legacy-resolver "certifi"
Looking in indexes: https://artifactory.vertigo.stitchfix.com/artifactory/api/pypi/stitchpy/simple
Requirement already satisfied: certifi in /usr/local/lib/python3.11/site-packages (2025.4.26)
ERROR: Exception:
Traceback (most recent call last):
  File "/usr/local/lib/python3.11/site-packages/pip/_internal/cli/base_command.py", line 105, in _run_wrapper
    status = _inner_run()
             ^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/site-packages/pip/_internal/cli/base_command.py", line 96, in _inner_run
    return self.run(options, args)
           ^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/site-packages/pip/_internal/cli/req_command.py", line 68, in wrapper
    return func(self, options, args)
           ^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/site-packages/pip/_internal/commands/install.py", line 421, in run
    reqs_to_build = [
                    ^
  File "/usr/local/lib/python3.11/site-packages/pip/_internal/commands/install.py", line 424, in <listcomp>
    if should_build_for_install_command(r)
       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/site-packages/pip/_internal/wheel_builder.py", line 65, in should_build_for_install_command
    return _should_build(req)
           ^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/site-packages/pip/_internal/wheel_builder.py", line 53, in _should_build
    assert req.source_dir
           ^^^^^^^^^^^^^^
AssertionError