2.34.4 on MacOS patch causes OOM

[bvsn]

Describe the bug

Nix 2.34.4 on macOS causes patch: **** out of memory errors during patchPhase for packages that apply diffs (e.g. gz-transport14, freeimage, libdart). The patches themselves are valid and apply successfully outside the Nix build environment.

https://github.com/devbrom/gazebo-sim-overlay/tree/darwin-support

The issue does not occur on Nix 2.31.2 with an identical system configuration, same macOS version, same flake, and same nixpkgs pin.

Nix 2.34.x appears to result in nixbld build users running with a stack size soft limit of 8176 KB, which is insufficient for patch to process multi-chunk diffs. Running sudo -u _nixbld1 ulimit -s confirms this value.

Steps To Reproduce

1. Install Nix 2.34.4 on macOS (arm64, darwin25)
2. Run nix develop github:devbrom/gazebo-sim-overlay/darwin-support#default -c $SHELL
3. Observe patch: **** out of memory during patchPhase
4. Confirm the patch applies successfully outside the sandbox:
5. Confirm nixbld stack limit: sudo -u _nixbld1 ulimit -s # returns 8176
6. Downgrade to Nix 2.31.2 - builds succeed without any other changes

Expected behavior

nixbld build users should have sufficient stack size to run standard POSIX tools like patch. The stack limit applied to build processes should not regress between Nix versions on macOS.

Metadata

nix (Nix) 2.34.4
nix (Nix) 2.31.2  # works

nix log /nix/store/m6bsabwxy7ylr1rw79425fhabb9pr36k-gz-transport14-14.1.0.drv
Running phase: qtPreHook
@nix { "action": "setPhase", "phase": "qtPreHook" }
Running phase: unpackPhase
@nix { "action": "setPhase", "phase": "unpackPhase" }
unpacking source archive /nix/store/4kynmimn3yfdr358r77a1ik067w83dgg-gz-transport14_14.1.0-source
source root is gz-transport14_14.1.0-source
Running phase: patchPhase
@nix { "action": "setPhase", "phase": "patchPhase" }
applying patch /nix/store/d281scad7p61mqdiw87zfpc6x4dczg4f-cmd.patch
patch: **** out of memory

Additional context

• sandbox = false does not resolve the issue - the stack limit is applied at the nixbld process level, not the sandbox
• Raising the nix-daemon's launchd SoftResourceLimits.Stack also does not resolve it - the limit applies to child nixbld processes, not the daemon itself
• The only working fixes are: downgrade to 2.31.2
• Patches as small as 4 lines fail, ruling out patch file size as the cause - the issue is purely the stack constraint on the build user

Checklist

• checked [latest Nix manual] ([source])
• checked [open bug issues and pull requests] for possible duplicates

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[cyraxjoe]

Also getting the same error in the context of building an old cython build for python 3.9

nix-store --realise /nix/store/i2yqddy6irzc3c4vwjbpzqxczdg74bxn-python3.9-cython-0.29.36.drv
this derivation will be built:
  /nix/store/i2yqddy6irzc3c4vwjbpzqxczdg74bxn-python3.9-cython-0.29.36.drv
building '/nix/store/i2yqddy6irzc3c4vwjbpzqxczdg74bxn-python3.9-cython-0.29.36.drv'...
Sourcing python-remove-tests-dir-hook
Sourcing python-catch-conflicts-hook.sh
Sourcing python-remove-bin-bytecode-hook.sh
Sourcing setuptools-build-hook
Using setuptoolsBuildPhase
Using setuptoolsShellHook
Sourcing pypa-install-hook
Using pypaInstallPhase
Sourcing python-imports-check-hook.sh
Using pythonImportsCheckPhase
Sourcing python-namespaces-hook
Sourcing python-catch-conflicts-hook.sh
Running phase: unpackPhase
unpacking source archive /nix/store/lhbv18s721s0w223as3iwph424db1w11-Cython-0.29.36.tar.gz
source root is Cython-0.29.36
setting SOURCE_DATE_EPOCH to timestamp 1688498448 of file Cython-0.29.36/PKG-INFO
Running phase: patchPhase
applying patch /nix/store/53f259gg3r5807ck0xl3yc9yyvmmh381-trashcan.patch
patch: **** out of memory
error: Cannot build '/nix/store/i2yqddy6irzc3c4vwjbpzqxczdg74bxn-python3.9-cython-0.29.36.drv'.
       Reason: builder failed with exit code 2.
       Output paths:
         /nix/store/j3gh5vsdbcryhm5jgk5iqqdcvsf0iamk-python3.9-cython-0.29.36-dist
         /nix/store/rcdb4zqir05qkqbvqwdhjph0gdyklqag-python3.9-cython-0.29.36
       Last 19 log lines:
       > Sourcing python-remove-tests-dir-hook
       > Sourcing python-catch-conflicts-hook.sh
       > Sourcing python-remove-bin-bytecode-hook.sh
       > Sourcing setuptools-build-hook
       > Using setuptoolsBuildPhase
       > Using setuptoolsShellHook
       > Sourcing pypa-install-hook
       > Using pypaInstallPhase
       > Sourcing python-imports-check-hook.sh
       > Using pythonImportsCheckPhase
       > Sourcing python-namespaces-hook
       > Sourcing python-catch-conflicts-hook.sh
       > Running phase: unpackPhase
       > unpacking source archive /nix/store/lhbv18s721s0w223as3iwph424db1w11-Cython-0.29.36.tar.gz
       > source root is Cython-0.29.36
       > setting SOURCE_DATE_EPOCH to timestamp 1688498448 of file Cython-0.29.36/PKG-INFO
       > Running phase: patchPhase
       > applying patch /nix/store/53f259gg3r5807ck0xl3yc9yyvmmh381-trashcan.patch
       > patch: **** out of memory
       For full logs, run:
         nix-store -l /nix/store/i2yqddy6irzc3c4vwjbpzqxczdg74bxn-python3.9-cython-0.29.36.drv

This is on a M4 Pro running MacOS 26.4 with nix 2.34.4

[xokdvium]

Yeah I was able to repro this on my macos machine. Seems quite unfortunate, I'll try to run a bisect on this and see what pops up.