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Add support for impure derivations

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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.
This commit is contained in:
Eelco Dolstra 2022-03-30 16:31:01 +02:00
parent 28309352d9
commit 5cd72598fe
17 changed files with 486 additions and 154 deletions
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9
src/libstore/path.cc
View file

@ -1,5 +1,7 @@
#include "store-api.hh"
#include <sodium.h>
namespace nix {
static void checkName(std::string_view path, std::string_view name)
@ -41,6 +43,13 @@ bool StorePath::isDerivation() const
StorePath StorePath::dummy("ffffffffffffffffffffffffffffffff-x");
StorePath StorePath::random(std::string_view name)
{
Hash hash(htSHA1);
randombytes_buf(hash.hash, hash.hashSize);
return StorePath(hash, name);
}
StorePath Store::parseStorePath(std::string_view path) const
{
auto p = canonPath(std::string(path));