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Consolidate logic choosing where we can/should build a bit

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I want to separate "policy" from "mechanism".

Now the logic to decide how to build (a policy choice, though with some
hard constraints) is all in derivation building goal, and all in the
same spot. build hook, external builder, or local builder --- the choice
between all three is made in the same spot --- pure policy.

Now, if you want to use the external deriation builder, you simply
provide the `ExternalBuilder` you wish to use, and there is no
additional checking --- pure mechanism. It is the responsibility of the
caller to choose an external builder that works for the derivation in
question.

Also, `checkSystem()` was the only thing throwing `BuildError` from
`startBuilder`. Now that that is gone, we can now remove the
`try...catch` around that.
This commit is contained in:
John Ericson 2025-08-16 14:25:28 -04:00
parent 2ff59ec3e0
commit b57caaa1a2
8 changed files with 140 additions and 94 deletions
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38
src/libstore/unix/build/derivation-builder.cc
View file

@ -229,12 +229,6 @@ protected:
return acquireUserLock(1, false);
}
/**
* Throw an exception if we can't do this derivation because of
* missing system features.
*/
virtual void checkSystem();
/**
* Return the paths that should be made available in the sandbox.
* This includes:
@ -672,33 +666,6 @@ static bool checkNotWorldWritable(std::filesystem::path path)
return true;
}
void DerivationBuilderImpl::checkSystem()
{
/* Right platform? */
if (!drvOptions.canBuildLocally(store, drv)) {
auto msg =
fmt("Cannot build '%s'.\n"
"Reason: " ANSI_RED "required system or feature not available" ANSI_NORMAL
"\n"
"Required system: '%s' with features {%s}\n"
"Current system: '%s' with features {%s}",
Magenta(store.printStorePath(drvPath)),
Magenta(drv.platform),
concatStringsSep(", ", drvOptions.getRequiredSystemFeatures(drv)),
Magenta(settings.thisSystem),
concatStringsSep<StringSet>(", ", store.Store::config.systemFeatures));
// since aarch64-darwin has Rosetta 2, this user can actually run x86_64-darwin on their hardware - we should
// tell them to run the command to install Darwin 2
if (drv.platform == "x86_64-darwin" && settings.thisSystem == "aarch64-darwin")
msg +=
fmt("\nNote: run `%s` to run programs for x86_64-darwin",
Magenta("/usr/sbin/softwareupdate --install-rosetta && launchctl stop org.nixos.nix-daemon"));
throw BuildError(BuildResult::Failure::InputRejected, msg);
}
}
std::optional<Descriptor> DerivationBuilderImpl::startBuild()
{
if (useBuildUsers()) {
@ -709,8 +676,6 @@ std::optional<Descriptor> DerivationBuilderImpl::startBuild()
return std::nullopt;
}
checkSystem();
/* Make sure that no other processes are executing under the
sandbox uids. This must be done before any chownToBuilder()
calls. */
@ -1922,9 +1887,6 @@ namespace nix {
std::unique_ptr<DerivationBuilder> makeDerivationBuilder(
LocalStore & store, std::unique_ptr<DerivationBuilderCallbacks> miscMethods, DerivationBuilderParams params)
{
if (auto builder = ExternalDerivationBuilder::newIfSupported(store, miscMethods, params))
return builder;
bool useSandbox = false;
/* Are we doing a sandboxed build? */