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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.
85 lines
1.7 KiB
C++
85 lines
1.7 KiB
C++
#pragma once
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#include "content-address.hh"
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#include "types.hh"
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namespace nix {
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class Store;
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struct Hash;
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class StorePath
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{
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std::string baseName;
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public:
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/* Size of the hash part of store paths, in base-32 characters. */
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constexpr static size_t HashLen = 32; // i.e. 160 bits
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StorePath() = delete;
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StorePath(std::string_view baseName);
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StorePath(const Hash & hash, std::string_view name);
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std::string_view to_string() const
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{
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return baseName;
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}
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bool operator < (const StorePath & other) const
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{
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return baseName < other.baseName;
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}
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bool operator == (const StorePath & other) const
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{
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return baseName == other.baseName;
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}
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bool operator != (const StorePath & other) const
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{
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return baseName != other.baseName;
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}
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/* Check whether a file name ends with the extension for
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derivations. */
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bool isDerivation() const;
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std::string_view name() const
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{
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return std::string_view(baseName).substr(HashLen + 1);
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}
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std::string_view hashPart() const
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{
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return std::string_view(baseName).substr(0, HashLen);
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}
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static StorePath dummy;
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static StorePath random(std::string_view name);
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};
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typedef std::set<StorePath> StorePathSet;
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typedef std::vector<StorePath> StorePaths;
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typedef std::map<std::string, StorePath> OutputPathMap;
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typedef std::map<StorePath, std::optional<ContentAddress>> StorePathCAMap;
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/* Extension of derivations in the Nix store. */
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const std::string drvExtension = ".drv";
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}
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namespace std {
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template<> struct hash<nix::StorePath> {
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std::size_t operator()(const nix::StorePath & path) const noexcept
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{
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return * (std::size_t *) path.to_string().data();
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}
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};
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}
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