Eelco Dolstra
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.
59 lines
1.3 KiB
C++
59 lines
1.3 KiB
C++
#pragma once
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#include "comparator.hh"
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#include "error.hh"
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#include "nlohmann/json_fwd.hpp"
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#include "types.hh"
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namespace nix {
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/**
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* The list of available experimental features.
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*
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* If you update this, don’t forget to also change the map defining their
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* string representation in the corresponding `.cc` file.
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**/
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enum struct ExperimentalFeature
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{
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CaDerivations,
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ImpureDerivations,
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Flakes,
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NixCommand,
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RecursiveNix,
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NoUrlLiterals,
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FetchClosure,
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};
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/**
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* Just because writing `ExperimentalFeature::CaDerivations` is way too long
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*/
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using Xp = ExperimentalFeature;
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const std::optional<ExperimentalFeature> parseExperimentalFeature(
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const std::string_view & name);
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std::string_view showExperimentalFeature(const ExperimentalFeature);
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std::ostream & operator<<(
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std::ostream & str,
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const ExperimentalFeature & feature);
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/**
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* Parse a set of strings to the corresponding set of experimental features,
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* ignoring (but warning for) any unkwown feature.
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*/
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std::set<ExperimentalFeature> parseFeatures(const std::set<std::string> &);
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class MissingExperimentalFeature : public Error
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{
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public:
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ExperimentalFeature missingFeature;
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MissingExperimentalFeature(ExperimentalFeature);
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virtual const char * sname() const override
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{
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return "MissingExperimentalFeature";
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}
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};
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}
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