python3Packages.setuptools-rust: fix python version inconsistency

[Aleksanaa]

Fixes #467817 (comment)

The default version of python is incorrectly introduced here, instead of the correct one corresponding to python3Packages.
This is causing python312Packages.bcrypt to fail in staging-next, and potentially other packages, because pyo3 tries to use a higher version than current system, resulting in incompatible symbols.

staging-next: #471587

Things done

• Built on platform:
  • x86_64-linux
  • aarch64-linux
  • x86_64-darwin
  • aarch64-darwin
• Tested, as applicable:
  • NixOS tests in nixos/tests.
  • Package tests at passthru.tests.
  • Tests in lib/tests or pkgs/test for functions and "core" functionality.
• Ran nixpkgs-review on this PR. See nixpkgs-review usage.
• Tested basic functionality of all binary files, usually in ./result/bin/.
• Nixpkgs Release Notes
  • Package update: when the change is major or breaking.
• NixOS Release Notes
  • Module addition: when adding a new NixOS module.
  • Module update: when the change is significant.
• Fits CONTRIBUTING.md, pkgs/README.md, maintainers/README.md and other READMEs.

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[Aleksanaa]

nix-repl> pkgsCross.aarch64-multiplatform.buildPackages.targetPackages.python3
«derivation /nix/store/ppqzglhrycgyj5965kc5nrs350j00bhv-python3-aarch64-unknown-linux-gnu-3.13.9.drv»

nix-repl> pkgsCross.aarch64-multiplatform.buildPackages.python3Packages.python.pythonOnTargetForTarget
«derivation /nix/store/zzw607vas5hjvsrfw4xrl2p6ncksldka-python3-aarch64-unknown-linux-gnu-3.13.11.drv»

Should not break cross

[Aleksanaa]

python3.13-word-count is failing for unrelated reason

error: trailing semicolon in macro used in expression position
   --> build.rs:23:87
    |
 23 |     ($fmt: literal $(, $args: expr)+) => { return Err(format!($fmt $(,$args)+).into()); };
    |                                                                                       ^
...
125 |             bail!("{} value of {:?} does not exist", var, path)
    |             --------------------------------------------------- in this macro invocation
    |
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
    = note: for more information, see issue #79813 <https://github.com/rust-lang/rust/issues/79813>
    = note: macro invocations at the end of a block are treated as expressions
    = note: to ignore the value produced by the macro, add a semicolon after the invocation of `bail`
    = note: this error originates in the macro `bail` (in Nightly builds, run with -Z macro-backtrace for more info)
error: trailing semicolon in macro used in expression position
   --> build.rs:23:87
    |
 23 |       ($fmt: literal $(, $args: expr)+) => { return Err(format!($fmt $(,$args)+).into()); };
    |                                                                                         ^
...
383 | /         bail!(
384 | |             "Detected multiple possible python versions, please set the PYO3_PYTHON_VERSION \
385 | |             variable to the wanted version on your system\nsysconfigdata paths = {:?}",
386 | |             sysconfig_paths
387 | |         )
    | |_________- in this macro invocation
    |

[Aleksanaa]

@ofborg build python312Packages.bcrypt python313Packages.bcrypt python314Packages.bcrypt

[trofi]

Bisect says that the change caused the eval failure for pkgsLLVM.python3Packages.setuptools-rust in staging and staging-next as:

$ nix-instantiate -A pkgsLLVM.python3Packages.setuptools-rust
error:
       … while evaluating the attribute 'drvPath'
         at lib/customisation.nix:446:7:
          445|     // {
          446|       drvPath =
             |       ^
          447|         assert condition;

       … while evaluating the attribute 'drvPath'
         at lib/customisation.nix:446:7:
          445|     // {
          446|       drvPath =
             |       ^
          447|         assert condition;

       … while calling the 'derivationStrict' builtin
         at «nix-internal»/derivation-internal.nix:37:12:
           36|
           37|   strict = derivationStrict drvAttrs;
             |            ^
           38|

       (stack trace truncated; use '--show-trace' to show the full, detailed trace)

       error: cannot coerce a set to a string: { }

[Aleksanaa]

It's pkgsLLVM.python3.pythonOnTargetForTarget. I'm looking into why that happens

[Aleksanaa]

Okay I know, for some reasons, pkgsTargetTarget is not empty, but targetPackages is, and pkgsLLVM.pkgsTargetTarget is also empty.

[Aleksanaa]

This is because pkgs is not __splicedPackages... surprise

[Aleksanaa]

The previous workaround is still needed, I'll add it back