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don't include derivation name in temporary build directories #207

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Merged
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Sep 17, 2025
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don't include derivation name in temporary build directories #207

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6 changes: 6 additions & 0 deletions doc/manual/rl-next/shorter-build-dir-names.md
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Original file line number Diff line number Diff line change
@@ -0,0 +1,6 @@
---
synopsis: "Temporary build directories no longer include derivation names"
prs: [13839]
---

Temporary build directories created during derivation builds no longer include the derivation name in their path to avoid build failures when the derivation name is too long. This change ensures predictable prefix lengths for build directories under `/nix/var/nix/builds`.
2 changes: 1 addition & 1 deletion src/libstore/unix/build/derivation-builder.cc
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Expand Up @@ -717,7 +717,7 @@ void DerivationBuilderImpl::startBuilder()

/* Create a temporary directory where the build will take
place. */
topTmpDir = createTempDir(buildDir, "nix-build-" + std::string(drvPath.name()), 0700);
topTmpDir = createTempDir(buildDir, "nix", 0700);
setBuildTmpDir();
assert(!tmpDir.empty());

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6 changes: 3 additions & 3 deletions tests/functional/check.sh
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Expand Up @@ -52,10 +52,10 @@ test_custom_build_dir() {
nix-build check.nix -A failed --argstr checkBuildId "$checkBuildId" \
--no-out-link --keep-failed --option build-dir "$TEST_ROOT/custom-build-dir" 2> "$TEST_ROOT/log" || status=$?
[ "$status" = "100" ]
[[ 1 == "$(count "$customBuildDir/nix-build-"*)" ]]
local buildDir=("$customBuildDir/nix-build-"*)
[[ 1 == "$(count "$customBuildDir/nix-"*)" ]]
local buildDir=("$customBuildDir/nix-"*)
if [[ "${#buildDir[@]}" -ne 1 ]]; then
echo "expected one nix-build-* directory, got: ${buildDir[*]}" >&2
echo "expected one nix-* directory, got: ${buildDir[*]}" >&2
exit 1
fi
if [[ -e ${buildDir[*]}/build ]]; then
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8 changes: 4 additions & 4 deletions tests/nixos/user-sandboxing/default.nix
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Expand Up @@ -104,8 +104,8 @@ in

# Wait for the build to be ready
# This is OK because it runs as root, so we can access everything
machine.wait_until_succeeds("stat /nix/var/nix/builds/nix-build-open-build-dir.drv-*/build/syncPoint")
dir = machine.succeed("ls -d /nix/var/nix/builds/nix-build-open-build-dir.drv-*").strip()
machine.wait_until_succeeds("stat /nix/var/nix/builds/nix-*/build/syncPoint")
dir = machine.succeed("ls -d /nix/var/nix/builds/nix-*").strip()

# But Alice shouldn't be able to access the build directory
machine.fail(f"su alice -c 'ls {dir}/build'")
Expand All @@ -125,8 +125,8 @@ in
args = [ (builtins.storePath "${create-hello-world}") ];
}' >&2 &
""".strip())
machine.wait_until_succeeds("stat /nix/var/nix/builds/nix-build-innocent.drv-*/build/syncPoint")
dir = machine.succeed("ls -d /nix/var/nix/builds/nix-build-innocent.drv-*").strip()
machine.wait_until_succeeds("stat /nix/var/nix/builds/nix-*/build/syncPoint")
dir = machine.succeed("ls -d /nix/var/nix/builds/nix-*").strip()

# The build ran as `nixbld1` (which is the only build user on the
# machine), but a process running as `nixbld1` outside the sandbox
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