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build: also throw hash-mismatch errors if buildMode == bmCheck

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This actually bit me quite recently in `nixpkgs` because I assumed that
`nix-build --check` would also error out if hashes don't match anymore[1]
and so I wrongly assumed that I couldn't reproduce the mismatch error.

The fix is rather simple, during the output registration a so-called
`delayedException` is instantiated e.g. if a FOD hash-mismatch occurs.
However, in case of `nix-build --check` (or `--rebuild` in case of `nix
build`), the code-path where this exception is thrown will never be
reached.

By adding that check to the if-clause that causes an early exit in case
of `bmCheck`, the issue is gone. Also added a (previously failing)
test-case to demonstrate the problem.

[1] https://github.com/NixOS/nixpkgs/pull/139238, the underlying issue
    was that `nix-prefetch-git` returns different hashes than `fetchgit`
    because the latter one fetches submodules by default.
This commit is contained in:
Maximilian Bosch 2021-09-26 15:20:36 +02:00
parent a0bb5c4130
commit bb1a851bcf
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GPG key ID: 091DBF4D1FC46B8E
3 changed files with 20 additions and 1 deletions
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8
src/libstore/build/local-derivation-goal.cc
View file

@ -2474,7 +2474,13 @@ void LocalDerivationGoal::registerOutputs()
infos.emplace(outputName, std::move(newInfo));
}
if (buildMode == bmCheck) return;
if (buildMode == bmCheck) {
// In case of FOD mismatches on `--check` an error must be thrown as this is also
// a source for non-determinism.
if (delayedException)
std::rethrow_exception(delayedException);
return;
}
/* Apply output checks. */
checkOutputs(infos);

8
tests/fixed.nix
View file

@ -21,6 +21,14 @@ rec {
(f ./fixed.builder2.sh "recursive" "sha1" "vw46m23bizj4n8afrc0fj19wrp7mj3c0")
];
# Expression to test that `nix-build --check` also throws an error if the hash of
# fixed-output derivation has changed even if the hash exists in the store (in this
# case the hash exists because of `fixed.builder2.sh`, but building a derivation
# with the same hash and a different result must throw an error).
check = [
(f ./fixed.builder1.sh "recursive" "md5" "3670af73070fa14077ad74e0f5ea4e42")
];
good2 = [
# Yes, this looks fscked up: builder2 doesn't have that result.
# But Nix sees that an output with the desired hash already

5
tests/fixed.sh
View file

@ -15,6 +15,11 @@ nix path-info --json $path | grep fixed:md5:2qk15sxzzjlnpjk9brn7j8ppcd
echo 'testing good...'
nix-build fixed.nix -A good --no-out-link
if isDaemonNewer "2.4pre20210927"; then
echo 'testing --check...'
nix-build fixed.nix -A check --check && fail "should fail"
fi
echo 'testing good2...'
nix-build fixed.nix -A good2 --no-out-link