Python: buildPythonPackage and overridePythonAttrs should support final: prev: style overrides

[RuRo]

After #119942, mkDerivation supports recursive definition of package attributes with

foo = mkDerivation (final: { });
foo_v2 = foo.overrideAttrs (final: prev: { });

# instead of
foo = mkDerivation rec { };
foo_v2 = foo.overrideAttrs (prev: { });

The buildPythonPackage.overridePythonAttrs functionality originally introduced in #26155 should also support this style of overrides (to avoid the rec antipattern and make the overrides more composable).

pyfoo = buildPythonPackage (final: { });
pyfoo_v2 = pyfoo.overridePythonAttrs (final: prev: { });

# instead of
pyfoo = buildPythonPackage rec { };
pyfoo_v2 = pyfoo.overridePythonAttrs (prev: { });

Also, this probably belongs in #1819.

[ShamrockLee]

#234651 addresses this issue with new functions lib.extendMkDerivation and lib.extendMkDerivationModified to defined build helpers with fixed-point arguments based on existing ones. Please take a look!

[uninsane]

for simple packages, a stopgap fix is to use toPythonModule (stdenv.mkDerivation (finalAttrs: { ... })). you'll have to add the appropriate setup hooks to native{Build,Check}Inputs which buildPythonPackage would ordinarily takes care of though.

not the best ergonomics, but if you need it, at least it is possible.