CPython2 support for macOS Big Sur

Issue

After creating a virtualenv with python2 from the Command Line Tools, running the python executable from that virtualenv fails:

% python virtualenv.pyz venv   
created virtual environment CPython2.7.16.final.0-64 in 221ms
  creator CPython2macOsFramework(dest=/Users/glandium/venv, clear=False, no_vcs_ignore=False, global=False)
  seeder FromAppData(download=False, pip=bundle, wheel=bundle, setuptools=bundle, via=copy, app_data_dir=/Users/glandium/Library/Application Support/virtualenv)
    added seed packages: pip==20.2.2, pip==20.2.4, setuptools==44.1.1, wheel==0.35.1
  activators PythonActivator,CShellActivator,FishActivator,PowerShellActivator,BashActivator
% venv/bin/python
zsh: killed     venv/bin/python

The problem comes from code signature not matching:

% codesign -v venv/bin/python
venv/bin/python: invalid Info.plist (plist or signature have been modified)
In architecture: x86_64

This doesn’t happen with python3.

[glandium]

codesign -s - -f venv/bin/python works, until it doesn’t and says the codesign_allocate helper tool cannot be found or used, which I’m not sure under which circumstances it happens (although it seems to involve Rosetta), but it does:

% python virtualenv.pyz venv      
created virtual environment CPython2.7.16.final.0-64 in 192ms
  creator CPython2macOsFramework(dest=/Users/glandium/venv, clear=False, no_vcs_ignore=False, global=False)
  seeder FromAppData(download=False, pip=bundle, wheel=bundle, setuptools=bundle, via=copy, app_data_dir=/Users/glandium/Library/Application Support/virtualenv)
    added seed packages: pip==20.2.4, setuptools==44.1.1, wheel==0.35.1
  activators PythonActivator,CShellActivator,FishActivator,PowerShellActivator,BashActivator
% arch --x86_64 venv/bin/python   
zsh: killed     arch --x86_64 venv/bin/python
% codesign -s - -f venv/bin/python
venv/bin/python: replacing existing signature
venv/bin/python: the codesign_allocate helper tool cannot be found or used

Another one:

% arch --x86_64 python virtualenv.pyz venv
created virtual environment CPython2.7.16.final.0-64 in 263ms
  creator CPython2macOsFramework(dest=/Users/glandium/venv, clear=False, no_vcs_ignore=False, global=False)
  seeder FromAppData(download=False, pip=bundle, wheel=bundle, setuptools=bundle, via=copy, app_data_dir=/Users/glandium/Library/Application Support/virtualenv)
    added seed packages: pip==20.2.4, setuptools==44.1.1, wheel==0.35.1
  activators PythonActivator,CShellActivator,FishActivator,PowerShellActivator,BashActivator
% venv/bin/python
zsh: killed     venv/bin/python
% codesign -s - -f venv/bin/python        
venv/bin/python: replacing existing signature
venv/bin/python: the codesign_allocate helper tool cannot be found or used

But it doesn’t happen here:

% arch --x86_64 python virtualenv.pyz venv
created virtual environment CPython2.7.16.final.0-64 in 263ms
  creator CPython2macOsFramework(dest=/Users/glandium/venv, clear=False, no_vcs_ignore=False, global=False)
  seeder FromAppData(download=False, pip=bundle, wheel=bundle, setuptools=bundle, via=copy, app_data_dir=/Users/glandium/Library/Application Support/virtualenv)
    added seed packages: pip==20.2.4, setuptools==44.1.1, wheel==0.35.1
  activators PythonActivator,CShellActivator,FishActivator,PowerShellActivator,BashActivator
% codesign -s - -f venv/bin/python        
venv/bin/python: replacing existing signature

So I guess if virtualenv itself would do the code signing, it would work™.

But the arm64e problem is unsolvable if virtualenv can’t be made to work with symbolic links. That said, after codesign -s - -f venv/bin/python succeeds, arch --x86_64 venv/bin/python does work.

It really sucks that the failure mode is that the process is killed rather than a more useful error message directly on the command line (instead of hidden in the console log).

[glandium]

The problem is virtualenv is editing the executable to change its dependencies to use @executable_path, invalidating the signature.