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