Local version causes mismatch between candidate and installed package

[tgolsson]

• 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.

Context

This is the reduced case of #1496, but which is actually two different issues masquerading to look like a cache issue.

Steps to reproduce

Repeatedly pdm sync -v here and note that each time the torch package is deleted and reinstalled:

https://github.com/tgolsson/pdm-repros/tree/main/constant-redownload

Actual behavior

The same package is resolved (and reinstalled) each time when it's bitwise the same. This also leads to unearth claiming to download the package, which is what sent me down the cache path.

Note that pdm list recognizes the actual version installed:

╭─────────────────────┬────────────┬─────────────────────────────────────────────────────────╮
│ name                │ version    │ location                                                │
├─────────────────────┼────────────┼─────────────────────────────────────────────────────────┤
│ setuptools          │ 59.5.0     │                                                         │
│ torch               │ 1.10.2+cpu │                                                         │
│ wasteful-redownload │ 0.0.0      │ -e /home/ts/Repositories/pdm-repros/constant-redownload │
│ typing_extensions   │ 4.4.0      │                                                         │
╰─────────────────────┴────────────┴─────────────────────────────────────────────────────────╯

Expected behavior

Something like this is my expected behavior:

Requirement	Installed	Expected outcome
torch==1.10.2	torch==1.10.2	Keep
torch==1.10.2	torch==1.10.2+cpu	Keep
torch==1.10.2+cpu	torch==1.10.2	Update
torch==1.10.2+cpu	torch==1.10.2+cpu	Keep
torch==1.10.2+cpu	torch==1.10.2+gpu	Update

Environment Information

# Paste the output of `pdm info && pdm info --env` below:
# Paste the output of `pdm info && pdm info --env` below:
PDM version:
  2.2.1
Python Interpreter:
  /home/ts/Repositories/pdm-repros/constant-redownload/.venv/bin/python (3.8)
Project Root:
  /home/ts/Repositories/pdm-repros/constant-redownload
Project Packages:
  None
{
  "implementation_name": "cpython",
  "implementation_version": "3.8.10",
  "os_name": "posix",
  "platform_machine": "x86_64",
  "platform_release": "5.15.68.1-microsoft-standard-WSL2",
  "platform_system": "Linux",
  "platform_version": "#1 SMP Mon Sep 19 19:14:52 UTC 2022",
  "python_full_version": "3.8.10",
  "platform_python_implementation": "CPython",
  "python_version": "3.8",
  "sys_platform": "linux"
}

[frostming]

After a little research I found that

• The reinstallation isn't expected and should be fixed
• The cache mismatch is due to lacking of expires or max-age header.

[tgolsson]

@frostming Yepp! I put up a PR to avoid the cache thrashing caused by the headers.

[frostming]

This was fixed in e480d2c, the cache issue is tracked by #1498