forked from lix-project/lix
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"
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#include "util.hh"
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#include "nlohmann/json.hpp"
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namespace nix {
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std::map<ExperimentalFeature, std::string> stringifiedXpFeatures = {
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{ Xp::CaDerivations, "ca-derivations" },
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{ Xp::ImpureDerivations, "impure-derivations" },
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{ Xp::Flakes, "flakes" },
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{ Xp::NixCommand, "nix-command" },
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{ Xp::RecursiveNix, "recursive-nix" },
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{ Xp::NoUrlLiterals, "no-url-literals" },
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{ Xp::FetchClosure, "fetch-closure" },
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};
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const std::optional<ExperimentalFeature> parseExperimentalFeature(const std::string_view & name)
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{
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using ReverseXpMap = std::map<std::string_view, ExperimentalFeature>;
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static auto reverseXpMap = []()
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{
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auto reverseXpMap = std::make_unique<ReverseXpMap>();
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for (auto & [feature, name] : stringifiedXpFeatures)
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(*reverseXpMap)[name] = feature;
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return reverseXpMap;
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}();
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if (auto feature = get(*reverseXpMap, name))
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return *feature;
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else
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return std::nullopt;
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}
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std::string_view showExperimentalFeature(const ExperimentalFeature feature)
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{
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return stringifiedXpFeatures.at(feature);
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}
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std::set<ExperimentalFeature> parseFeatures(const std::set<std::string> & rawFeatures)
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{
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std::set<ExperimentalFeature> res;
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for (auto & rawFeature : rawFeatures) {
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if (auto feature = parseExperimentalFeature(rawFeature))
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res.insert(*feature);
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}
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return res;
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}
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MissingExperimentalFeature::MissingExperimentalFeature(ExperimentalFeature feature)
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: Error("experimental Nix feature '%1%' is disabled; use '--extra-experimental-features %1%' to override", showExperimentalFeature(feature))
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, missingFeature(feature)
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{}
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std::ostream & operator <<(std::ostream & str, const ExperimentalFeature & feature)
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{
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return str << showExperimentalFeature(feature);
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}
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}
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