Build failed for python 3.14.5

[mildc055ee]

I thought it would be appropriate to report this here rather than in cachix/devenv, so I'm reporting this here.

When I try to use latest python 3.14 with devenv, it failed to build python.

Pinning to "3.14.4" is the current workaround.

• devenv.nix

{
  languages.python = {
    enable = true;
    version = "3.14";
  };
}

• devenv.yaml

inputs:
  nixpkgs:
    url: github:cachix/devenv-nixpkgs/rolling
  nixpkgs-python:
    url: github:cachix/nixpkgs-python
    inputs:
      nixpkgs:
        follows: nixpkgs

• build log
  To get this log, run devenv shell

❯ devenv shell
✓ Validating lock                                                                                                                                                                          0ms
✓ Configuring shell                                                                                                                                                                       4.9s
  └ ✓ Configuring cachix                                                                                                                                                                   1ms
  └ ✗ Evaluating shell 3895 files                                                                                                                                                         4.8s
  │ evaluating file '/nix/store/klzydr6a4fwr1vbg734dppjg8cy9hgy9-source/pkgs/development/compilers/llvm/common/patches.nix'
  │ devenv path: '/nix/store/klzydr6a4fwr1vbg734dppjg8cy9hgy9-source/pkgs/development/compilers/llvm/20/llvm/gnu-install-dirs-polly.patch'
  │ evaluating file '/nix/store/klzydr6a4fwr1vbg734dppjg8cy9hgy9-source/pkgs/development/compilers/llvm/common/patches.nix'
  │ devenv path: '/nix/store/klzydr6a4fwr1vbg734dppjg8cy9hgy9-source/pkgs/development/compilers/llvm/18/llvm/polly-lit-cfg-add-libs-to-dylib-path.patch'
  │ devenv readFile: '/nix/store/klzydr6a4fwr1vbg734dppjg8cy9hgy9-source/pkgs/build-support/rust/fetch-cargo-vendor-util-v2.py'
  │ evaluating file '/nix/store/klzydr6a4fwr1vbg734dppjg8cy9hgy9-source/pkgs/tools/package-management/nix-prefetch-scripts/default.nix'
  │ devenv path: '/nix/store/klzydr6a4fwr1vbg734dppjg8cy9hgy9-source/pkgs/build-support/node/prefetch-npm-deps'
  │ evaluating file '/nix/store/klzydr6a4fwr1vbg734dppjg8cy9hgy9-source/pkgs/pkgs-lib/default.nix'
  │ evaluating file '/nix/store/klzydr6a4fwr1vbg734dppjg8cy9hgy9-source/pkgs/pkgs-lib/formats.nix'
  │ evaluating file '/nix/store/0m0iyr1l1k93r6cvhrc7n6jljg94vwp9-source/src/modules/lib/listen.nix'
  │ evaluating file '/nix/store/0m0iyr1l1k93r6cvhrc7n6jljg94vwp9-source/src/modules/lib/ready.nix'
  │ evaluating file '/nix/store/klzydr6a4fwr1vbg734dppjg8cy9hgy9-source/pkgs/build-support/lib/cmake.nix'
  │ evaluating file '/nix/store/klzydr6a4fwr1vbg734dppjg8cy9hgy9-source/pkgs/build-support/lib/meson.nix'
  │ devenv pathExists: '/Users/********/build-devenv/backend/.env'
  │ devenv readFile: '/nix/store/0m0iyr1l1k93r6cvhrc7n6jljg94vwp9-source/src/modules/latest-version'
  │ error: Cannot build '/nix/store/i9i8cys83pcwrad1cy6jz5nwmijddz3d-python3-3.14.5.drv'.
  │ error: Cannot build '/nix/store/x6a230mms1nsibz2d4fb3chbgskj61m9-python3-3.14.5-env.drv'.
  │ error: Build failed due to failed dependency
  │ error: Cannot build '/nix/store/7l37g6qywynss4ysjj06d81697h2mzdz-devenv-profile.drv'.
  │ error: Cannot build '/nix/store/bqmfn5y04x6w2fkwlhbssv5xsl900gf2-devenv-shell.drv'.
    ✗ error: Cannot build '/nix/store/i9i8cys83pcwrad1cy6jz5nwmijddz3d-python3-3.14.5.drv'.
    ✗ error: Cannot build '/nix/store/x6a230mms1nsibz2d4fb3chbgskj61m9-python3-3.14.5-env.drv'.
    ✗ error: Build failed due to failed dependency
    ✗ error: Cannot build '/nix/store/7l37g6qywynss4ysjj06d81697h2mzdz-devenv-profile.drv'.
    ✗ error: Cannot build '/nix/store/bqmfn5y04x6w2fkwlhbssv5xsl900gf2-devenv-shell.drv'.

error: Cannot build '/nix/store/i9i8cys83pcwrad1cy6jz5nwmijddz3d-python3-3.14.5.drv'.
       Reason: builder failed with exit code 1.
       Output paths:
         /nix/store/lbs4a2c145lpz186s5xx2y0gzinv5fh9-python3-3.14.5
       Last 25 log lines:
       > source root is Python-3.14.5
       > setting SOURCE_DATE_EPOCH to timestamp 1778408494 of file "Python-3.14.5/pyconfig.h.in"
       > Running phase: patchPhase
       > applying patch /nix/store/liwkqspbznysbancwm2bf13spslr50n7-3.14-no-ldconfig.patch
       > patching file Lib/ctypes/util.py
       > Hunk #1 succeeded at 212 with fuzz 1 (offset 112 lines).
       > Hunk #2 succeeded at 334 (offset 112 lines).
       > applying patch /nix/store/73bwxvdmw63kgb1x27nqr7hh227nz04g-virtualenv-permissions.patch
       > patching file Lib/venv/__init__.py
       > Hunk #1 succeeded at 593 (offset 71 lines).
       > applying patch /nix/store/lpfs02z2i2hamz9f50p4bz6v0fs0600j-mimetypes.patch
       > patching file Lib/mimetypes.py
       > Hunk #1 succeeded at 41 (offset 1 line).
       > applying patch /nix/store/b43fwpm05xq99q0np7s78cjvpyra9vyh-hacl-static-ldeps-for-static-modules.patch
       > patching file Misc/NEWS.d/next/Build/2026-03-21-18-51-31.gh-issue-146264.Q9Ej4m.rst
       > patching file configure
       > Reversed (or previously applied) patch detected!  Assume -R? [n]
       > Apply anyway? [n]
       > Skipping patch.
       > 1 out of 1 hunk ignored -- saving rejects to file configure.rej
       > patching file configure.ac
       > Reversed (or previously applied) patch detected!  Assume -R? [n]
       > Apply anyway? [n]
       > Skipping patch.
       > 1 out of 1 hunk ignored -- saving rejects to file configure.ac.rej
       For full logs, run:
         nix log /nix/store/i9i8cys83pcwrad1cy6jz5nwmijddz3d-python3-3.14.5.drv
error: Cannot build '/nix/store/x6a230mms1nsibz2d4fb3chbgskj61m9-python3-3.14.5-env.drv'.
       Reason: 1 dependency failed.
       Output paths:
         /nix/store/yk42x749815sfghnywj3j02xlhim0p4c-python3-3.14.5-env
error: Build failed due to failed dependency
error: Cannot build '/nix/store/bqmfn5y04x6w2fkwlhbssv5xsl900gf2-devenv-shell.drv'.
       Reason: 1 dependency failed.
       Output paths:
         /nix/store/yv2v0s775xyh76jjd5fjksya04sfgx3g-devenv-shell
error: Cannot build '/nix/store/7l37g6qywynss4ysjj06d81697h2mzdz-devenv-profile.drv'.
       Reason: 1 dependency failed.
       Output paths:
         /nix/store/nc7nnbzp9x2ms8qbp9zrks4pl7jh9qj3-devenv-profile
  × Failed to realize shell derivation: error: Cannot build '/nix/store/bqmfn5y04x6w2fkwlhbssv5xsl900gf2-devenv-shell.drv'.
    Reason: 1 dependency failed.
    Output paths:
      /nix/store/yv2v0s775xyh76jjd5fjksya04sfgx3g-devenv-shell

• nix log /nix/store/i9i8cys83pcwrad1cy6jz5nwmijddz3d-python3-3.14.5.drv

structuredAttrs is enabled
Running phase: unpackPhase
@nix { "action": "setPhase", "phase": "unpackPhase" }
unpacking source archive /nix/store/dr6l7kbsh18gar801zwgnijgg2907ykw-Python-3.14.5.tgz
source root is Python-3.14.5
setting SOURCE_DATE_EPOCH to timestamp 1778408494 of file "Python-3.14.5/pyconfig.h.in"
Running phase: patchPhase
@nix { "action": "setPhase", "phase": "patchPhase" }
applying patch /nix/store/liwkqspbznysbancwm2bf13spslr50n7-3.14-no-ldconfig.patch
patching file Lib/ctypes/util.py
Hunk #1 succeeded at 212 with fuzz 1 (offset 112 lines).
Hunk #2 succeeded at 334 (offset 112 lines).
applying patch /nix/store/73bwxvdmw63kgb1x27nqr7hh227nz04g-virtualenv-permissions.patch
patching file Lib/venv/__init__.py
Hunk #1 succeeded at 593 (offset 71 lines).
applying patch /nix/store/lpfs02z2i2hamz9f50p4bz6v0fs0600j-mimetypes.patch
patching file Lib/mimetypes.py
Hunk #1 succeeded at 41 (offset 1 line).
applying patch /nix/store/b43fwpm05xq99q0np7s78cjvpyra9vyh-hacl-static-ldeps-for-static-modules.patch
patching file Misc/NEWS.d/next/Build/2026-03-21-18-51-31.gh-issue-146264.Q9Ej4m.rst
patching file configure
Reversed (or previously applied) patch detected!  Assume -R? [n]
Apply anyway? [n]
Skipping patch.
1 out of 1 hunk ignored -- saving rejects to file configure.rej
patching file configure.ac
Reversed (or previously applied) patch detected!  Assume -R? [n]
Apply anyway? [n]
Skipping patch.
1 out of 1 hunk ignored -- saving rejects to file configure.ac.rej

[domenkozar]

A fix is up in #129. If you can verify, point your devenv.yaml at the branch:

inputs:
  nixpkgs-python:
    url: github:cachix/nixpkgs-python/fix/python-3.10-3.14.5-build

Then devenv update nixpkgs-python && devenv shell should build 3.14.5.

[mildc055ee]

Thank you. Now it build successfully.

❯ devenv shell
✓ Validating lock 1 files                                                                                                                         1ms
✓ Configuring shell                                                                                                                            4m 35s
  └ ✓ Configuring cachix                                                                                                                          3ms
  └ ✓ Evaluating shell 3293 files                                                                                                              4m 34s
    └ ✓ Building  devenv-shell 1 lines                                                                                                          127ms
    └ ✓ Querying  devenv-shell-env from cache.nixos.org                                                                                         293ms
    └ ✓ Querying  devenv-shell-env from cachix.cachix.org                                                                                       338ms
    └ ✓ Querying  devenv-shell-env from nix-community.cachix.org                                                                                357ms
    └ ✓ Building  devenv-shell-env                                                                                                              256ms
✓ Evaluating bash                                                                                                                                 2ms
✓ Loading tasks                                                                                                                                   5ms
  └ ✓ Evaluating devenv.config.task.config                                                                                                        3ms
✓ Running tasks                                                                                                                                 893ms
  └ ✓ devenv:enterShell                                                                                                                         331ms
    └ ✓ devenv:files:cleanup                                                                                                                    558ms
  └ ✓ devenv:enterTest skipped                                                                                                                    0ms
hello from devenv
git version 2.53.0
Welcome to fish, the friendly interactive shell
Type help for instructions on how to use fish
~/priv/playground/devenv/repl
❯ python --version
Python 3.14.5