Link is not defined if not TYPE_CHECKING but it's used

[alkuzad]

• [*] I have searched the issue tracker and believe that this is not a duplicate.

Make sure you run commands with -v flag before pasting the output.

Steps to reproduce

1. install 2.8.2
2. Init project
3. pdm add --dev black
4. Error happens:

File "/nix/store/5a457g4zr7q11b4mz0ifc9z88kwcp8g7-python3-3.10.12/lib/python3.10/concurrent/futures/thread.py", line 58, in run
result = self.fn(*self.args, **self.kwargs)
File "/home/dgoslawski/.local/pipx/venvs/pdm/lib/python3.10/site-packages/pdm/installers/synchronizers.py", line 277, in install_candidate
self.manager.install(can)
File "/home/dgoslawski/.local/pipx/venvs/pdm/lib/python3.10/site-packages/pdm/installers/manager.py", line 33, in install
installer(str(prepared.build()), self.environment, prepared.direct_url())
File "/home/dgoslawski/.local/pipx/venvs/pdm/lib/python3.10/site-packages/pdm/models/candidates.py", line 379, in build
self.obtain(allow_all=False)
File "/home/dgoslawski/.local/pipx/venvs/pdm/lib/python3.10/site-packages/pdm/models/candidates.py", line 413, in obtain
self.link = _find_best_match_link(
File "/home/dgoslawski/.local/pipx/venvs/pdm/lib/python3.10/site-packages/pdm/models/candidates.py", line 88, in _find_best_match_link
links = [Link(f["url"]) for f in files if "url" in f]
File "/home/dgoslawski/.local/pipx/venvs/pdm/lib/python3.10/site-packages/pdm/models/candidates.py", line 88, in
links = [Link(f["url"]) for f in files if "url" in f]
NameError: name 'Link' is not defined

Actual behavior

pdm refuses to install. Installs when candidates.py is modified to move from unearth import Link, Package, PackageFinder outside the TYPE_CHECKING condition

Expected behavior

pdm installs

Environment Information

# Paste the output of `pdm info && pdm info --env` below:
λ pdm info && pdm info --env
PDM version:
  2.8.2
Python Interpreter:
  /home/dgoslawski/projects/pre-commit-semver/.venv/bin/python (3.10)
Project Root:
  /home/dgoslawski/projects/pre-commit-semver
Local Packages:

{
  "implementation_name": "cpython",
  "implementation_version": "3.10.7",
  "os_name": "posix",
  "platform_machine": "x86_64",
  "platform_release": "5.15.90.1-microsoft-standard-WSL2",
  "platform_system": "Linux",
  "platform_version": "#1 SMP Fri Jan 27 02:56:13 UTC 2023",
  "python_full_version": "3.10.7",
  "platform_python_implementation": "CPython",
  "python_version": "3.10",
  "sys_platform": "linux"
}

[frostming]

Can you submit a fix?

[alkuzad]

Can you submit a fix?

Technically yes but I do not understand the details of the problem :) Why it is inside condition in the first place? This code seems preety common, am I only one getting this error, maybe due to some nix/pdx shenaningans?

[frostming]

Can you submit a fix?

Technically yes but I do not understand the details of the problem :) Why it is inside condition in the first place? This code seems preety common, am I only one getting this error, maybe due to some nix/pdx shenaningans?

You already found the cause, didn't you?

What you need to do is add a line in this function to import Link from unearth:

pdm/src/pdm/models/candidates.py

Lines 76 to 89 in fa34573

	def _find_best_match_link(
	finder: PackageFinder,
	req: Requirement,
	files: list[FileHash],
	ignore_compatibility: bool = False,
	) -> Link | None:
	"""Get the best matching link for a requirement"""
	# This function is called when a lock file candidate is given or incompatible wheel
	# In this case, the requirement must be pinned, so no need to pass allow_prereleases
	# If links are not empty, find the best match from the links, otherwise find from
	# the package sources.
	links = [Link(f["url"]) for f in files if "url" in f]
	hashes = convert_hashes(files)

Others don't encounter this because they never enter the loop, because url field is missing, which is the default behavior. Your lockfile is generated with --static-urls option, right?

[alkuzad]

yes it is using static_links because that is the easiest method to enforce the internal packages to be resolved from internal PyPi and others from public one without using the --extra-index-url shenanigans that are a vulnerability.

I wouldn't add import inside a function, it is a correct syntax-wise but imports inside functions seems hacky. Can we move it just 2 lines above to skip the type checking condition?

[frostming]

I wouldn't add import inside a function, it is a correct syntax-wise but imports inside functions seems hacky. Can we move it just 2 lines above to skip the type checking condition?

No, that is an intended change, because unearth is a heavy module and importing it will significantly affect the startup time of CLI.