mirror of
https://github.com/NixOS/nix
synced 2024-09-20 23:28:26 -04:00
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.
59 lines
1.3 KiB
C++
59 lines
1.3 KiB
C++
#pragma once
|
||
|
||
#include "comparator.hh"
|
||
#include "error.hh"
|
||
#include "nlohmann/json_fwd.hpp"
|
||
#include "types.hh"
|
||
|
||
namespace nix {
|
||
|
||
/**
|
||
* The list of available experimental features.
|
||
*
|
||
* If you update this, don’t forget to also change the map defining their
|
||
* string representation in the corresponding `.cc` file.
|
||
**/
|
||
enum struct ExperimentalFeature
|
||
{
|
||
CaDerivations,
|
||
ImpureDerivations,
|
||
Flakes,
|
||
NixCommand,
|
||
RecursiveNix,
|
||
NoUrlLiterals,
|
||
FetchClosure,
|
||
};
|
||
|
||
/**
|
||
* Just because writing `ExperimentalFeature::CaDerivations` is way too long
|
||
*/
|
||
using Xp = ExperimentalFeature;
|
||
|
||
const std::optional<ExperimentalFeature> parseExperimentalFeature(
|
||
const std::string_view & name);
|
||
std::string_view showExperimentalFeature(const ExperimentalFeature);
|
||
|
||
std::ostream & operator<<(
|
||
std::ostream & str,
|
||
const ExperimentalFeature & feature);
|
||
|
||
/**
|
||
* Parse a set of strings to the corresponding set of experimental features,
|
||
* ignoring (but warning for) any unkwown feature.
|
||
*/
|
||
std::set<ExperimentalFeature> parseFeatures(const std::set<std::string> &);
|
||
|
||
class MissingExperimentalFeature : public Error
|
||
{
|
||
public:
|
||
ExperimentalFeature missingFeature;
|
||
|
||
MissingExperimentalFeature(ExperimentalFeature);
|
||
virtual const char * sname() const override
|
||
{
|
||
return "MissingExperimentalFeature";
|
||
}
|
||
};
|
||
|
||
}
|