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43 lines
1.2 KiB
43 lines
1.2 KiB
{ lib, runCommand, emptyFile, nix-diff }:
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/*
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Checks that two packages produce the exact same build instructions.
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This can be used to make sure that a certain difference of configuration,
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such as the presence of an overlay does not cause a cache miss.
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When the derivations are equal, the return value is an empty file.
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Otherwise, the build log explains the difference via `nix-diff`.
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Example:
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testEqualDerivation
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"The hello package must stay the same when enabling checks."
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hello
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(hello.overrideAttrs(o: { doCheck = true; }))
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*/
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assertion: a: b:
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let
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drvA = builtins.unsafeDiscardOutputDependency a.drvPath or (throw "testEqualDerivation second argument must be a package");
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drvB = builtins.unsafeDiscardOutputDependency b.drvPath or (throw "testEqualDerivation third argument must be a package");
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name =
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if a?name
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then "testEqualDerivation-${a.name}"
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else "testEqualDerivation";
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in
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if drvA == drvB then
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emptyFile
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else
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runCommand name
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{
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inherit assertion drvA drvB;
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nativeBuildInputs = [ nix-diff ];
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} ''
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echo "$assertion"
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echo "However, the derivations differ:"
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echo
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echo nix-diff $drvA $drvB
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nix-diff $drvA $drvB
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exit 1
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''
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