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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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39
tests/impure-derivations.sh Normal file
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source common.sh
requireDaemonNewerThan "2.8pre20220311"
enableFeatures "ca-derivations ca-references impure-derivations"
clearStore
# Basic test of impure derivations: building one a second time should not use the previous result.
printf 0 > $TEST_ROOT/counter
json=$(nix build -L --no-link --json --file ./impure-derivations.nix impure)
path1=$(echo $json | jq -r .[].outputs.out)
path1_stuff=$(echo $json | jq -r .[].outputs.stuff)
[[ $(< $path1/n) = 0 ]]
[[ $(< $path1_stuff/bla) = 0 ]]
[[ $(nix path-info --json $path1 | jq .[].ca) =~ fixed:r:sha256: ]]
path2=$(nix build -L --no-link --json --file ./impure-derivations.nix impure | jq -r .[].outputs.out)
[[ $(< $path2/n) = 1 ]]
# Test impure derivations that depend on impure derivations.
path3=$(nix build -L --no-link --json --file ./impure-derivations.nix impureOnImpure -vvvvv | jq -r .[].outputs.out)
[[ $(< $path3/n) = X2 ]]
path4=$(nix build -L --no-link --json --file ./impure-derivations.nix impureOnImpure -vvvvv | jq -r .[].outputs.out)
[[ $(< $path4/n) = X3 ]]
# Test that (self-)references work.
[[ $(< $path4/symlink/bla) = 3 ]]
[[ $(< $path4/self/n) = X3 ]]
# Input-addressed derivations cannot depend on impure derivations directly.
nix build -L --no-link --json --file ./impure-derivations.nix inputAddressed 2>&1 | grep 'depends on impure derivation'
drvPath=$(nix eval --json --file ./impure-derivations.nix impure.drvPath | jq -r .)
[[ $(nix show-derivation $drvPath | jq ".[\"$drvPath\"].outputs.out.impure") = true ]]
[[ $(nix show-derivation $drvPath | jq ".[\"$drvPath\"].outputs.stuff.impure") = true ]]