mirror of
https://github.com/NixOS/nix.git
synced 2025-12-14 13:01:05 +01:00
5cd72598fe
Impure derivations are derivations that can produce a different result
every time they're built. Example:
stdenv.mkDerivation {
name = "impure";
__impure = true; # marks this derivation as impure
outputHashAlgo = "sha256";
outputHashMode = "recursive";
buildCommand = "date > $out";
};
Some important characteristics:
* This requires the 'impure-derivations' experimental feature.
* Impure derivations are not "cached". Thus, running "nix-build" on
the example above multiple times will cause a rebuild every time.
* They are implemented similar to CA derivations, i.e. the output is
moved to a content-addressed path in the store. The difference is
that we don't register a realisation in the Nix database.
* Pure derivations are not allowed to depend on impure derivations. In
the future fixed-output derivations will be allowed to depend on
impure derivations, thus forming an "impurity barrier" in the
dependency graph.
* When sandboxing is enabled, impure derivations can access the
network in the same way as fixed-output derivations. In relaxed
sandboxing mode, they can access the local filesystem.
61 lines
1.8 KiB
C++
61 lines
1.8 KiB
C++
#include "experimental-features.hh"
|
|
#include "util.hh"
|
|
|
|
#include "nlohmann/json.hpp"
|
|
|
|
namespace nix {
|
|
|
|
std::map<ExperimentalFeature, std::string> stringifiedXpFeatures = {
|
|
{ Xp::CaDerivations, "ca-derivations" },
|
|
{ Xp::ImpureDerivations, "impure-derivations" },
|
|
{ Xp::Flakes, "flakes" },
|
|
{ Xp::NixCommand, "nix-command" },
|
|
{ Xp::RecursiveNix, "recursive-nix" },
|
|
{ Xp::NoUrlLiterals, "no-url-literals" },
|
|
{ Xp::FetchClosure, "fetch-closure" },
|
|
};
|
|
|
|
const std::optional<ExperimentalFeature> parseExperimentalFeature(const std::string_view & name)
|
|
{
|
|
using ReverseXpMap = std::map<std::string_view, ExperimentalFeature>;
|
|
|
|
static auto reverseXpMap = []()
|
|
{
|
|
auto reverseXpMap = std::make_unique<ReverseXpMap>();
|
|
for (auto & [feature, name] : stringifiedXpFeatures)
|
|
(*reverseXpMap)[name] = feature;
|
|
return reverseXpMap;
|
|
}();
|
|
|
|
if (auto feature = get(*reverseXpMap, name))
|
|
return *feature;
|
|
else
|
|
return std::nullopt;
|
|
}
|
|
|
|
std::string_view showExperimentalFeature(const ExperimentalFeature feature)
|
|
{
|
|
return stringifiedXpFeatures.at(feature);
|
|
}
|
|
|
|
std::set<ExperimentalFeature> parseFeatures(const std::set<std::string> & rawFeatures)
|
|
{
|
|
std::set<ExperimentalFeature> res;
|
|
for (auto & rawFeature : rawFeatures) {
|
|
if (auto feature = parseExperimentalFeature(rawFeature))
|
|
res.insert(*feature);
|
|
}
|
|
return res;
|
|
}
|
|
|
|
MissingExperimentalFeature::MissingExperimentalFeature(ExperimentalFeature feature)
|
|
: Error("experimental Nix feature '%1%' is disabled; use '--extra-experimental-features %1%' to override", showExperimentalFeature(feature))
|
|
, missingFeature(feature)
|
|
{}
|
|
|
|
std::ostream & operator <<(std::ostream & str, const ExperimentalFeature & feature)
|
|
{
|
|
return str << showExperimentalFeature(feature);
|
|
}
|
|
|
|
}
|