The new, scope-based LLVM is so much nicer to override. There’s still jank, but I don’t have to do anything to handle build vs. host vs. target packages.

(llvmPackages_19.override {
  officialRelease = {
    version = "19.1.5"; # From https://github.com/swiftlang/llvm-project/blob/swift-$swiftVersion-RELEASE/cmake/Modules/LLVMVersion.cmake
  };

  monorepoSrc = fetchFromGitHub {
    owner = "swiftlang";
    repo = "llvm-project";
    tag = "swift-${lib.getVersion swift}-RELEASE";
    hash = "sha256-DahdGT8VMBOXuwfhtXIJGFJmmhzzoQ6NdpU2CDs5B/s=";
  };

  otherSplices = generateSplicesForMkScope [
    "swiftPackages"
    "llvmPackages"
  ];
}).overrideScope
  (
    _: prev: {
      version = "17.0.0"; # From https://github.com/swiftlang/swift/blob/swift-$swiftVersion-RELEASE/utils/build_swift/build_swift/defaults.py#L51
    }
  )

The new, scope-based LLVM is so much nicer to override. There’s still jank, but I don’t have to do anything to handle build vs. host vs. target packages.

let
  swiftlangLlvmVersion = "17.0.0"; # From https://github.com/swiftlang/swift/blob/swift-$swiftVersion-RELEASE/utils/build_swift/build_swift/defaults.py#L51
  llvmVersion = "19.1.5"; # From https://github.com/swiftlang/llvm-project/blob/swift-$swiftVersion-RELEASE/cmake/Modules/LLVMVersion.cmake
in
(llvmPackages_19.override {
  officialRelease = { version = llvmVersion; };

  monorepoSrc = fetchFromGitHub {
    owner = "swiftlang";
    repo = "llvm-project";
    tag = "swift-${lib.getVersion swift}-RELEASE";
    hash = "sha256-DahdGT8VMBOXuwfhtXIJGFJmmhzzoQ6NdpU2CDs5B/s=";
  };

  otherSplices = generateSplicesForMkScope [
    "swiftPackages"
    "llvmPackages"
  ];
}).overrideScope
  (
    _: prev: {
      version = swiftlangLlvmVersion;
      release_version = llvmVersion;
    }
  )

error: derivation 'rj3n6mm11f90ssv0az0aplkiy9b2s48l-python3.13-sentencepiece-0.2.1.drv' may not be deterministic: outputs differ
         output '/nix/store/cpjk1gyzyz6j18jxfpsswdd0rggyzjah-python3.13-sentencepiece-0.2.1' differs

Here's the import crash:

0   ???                           	               0x0 ???
1   libpython3.13.dylib           	       0x103b950d8 state_fini + 228
2   libpython3.13.dylib           	       0x103b92828 _sre_SRE_Pattern_match + 712
3   libpython3.13.dylib           	       0x1038a3cd0 method_vectorcall_FASTCALL_KEYWORDS_METHOD + 188
4   libpython3.13.dylib           	       0x1038938c8 PyObject_VectorcallMethod + 168
5   libpython3.13.dylib           	       0x1039f242c check_matched + 112
6   libpython3.13.dylib           	       0x1039eebb8 warn_explicit + 1368
7   libpython3.13.dylib           	       0x1039f120c do_warn + 176
8   libpython3.13.dylib           	       0x1039ee158 PyErr_WarnFormat + 108
9   libpython3.13.dylib           	       0x10395549c _PyType_FromMetaclass_impl + 3940
10  _sentencepiece.cpython-313-darwin.so	       0x12a79e4a4 SwigPyPacked_TypeOnce() + 104
11  _sentencepiece.cpython-313-darwin.so	       0x12a77e738 PyInit__sentencepiece + 1244
12  libpython3.13.dylib           	       0x103ab0c38 _PyImport_RunModInitFunc + 100
13  libpython3.13.dylib           	       0x103aac6e0 import_run_extension + 192
14  libpython3.13.dylib           	       0x103aaf490 _imp_create_dynamic + 536
15  libpython3.13.dylib           	       0x103916d54 cfunction_vectorcall_FASTCALL + 280
16  libpython3.13.dylib           	       0x103a46eb0 _PyEval_EvalFrameDefault + 13948
-------- RECURSION LEVEL 9
17  libpython3.13.dylib           	       0x103893dc4 object_vacall + 428
18  libpython3.13.dylib           	       0x103893ac4 PyObject_CallMethodObjArgs + 124
19  libpython3.13.dylib           	       0x103aaa164 PyImport_ImportModuleLevelObject + 3048
20  libpython3.13.dylib           	       0x103a3b90c builtin___import__ + 316
21  libpython3.13.dylib           	       0x103916e68 cfunction_vectorcall_FASTCALL_KEYWORDS + 148
22  libpython3.13.dylib           	       0x103a46eb0 _PyEval_EvalFrameDefault + 13948
-------- RECURSION LEVEL 8