Merge pull request #9216 from obsidiansystems/addDrvOutputDependencies-pre
Add `builtins.addDrvOutputDependencies`
This commit is contained in:
John Ericson
GitHub
commit
a58d7f143e
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@ -30,20 +30,27 @@ static RegisterPrimOp primop_hasContext({
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.name = "__hasContext",
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.args = {"s"},
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.doc = R"(
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Return `true` if string *s* has a non-empty context. The
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context can be obtained with
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Return `true` if string *s* has a non-empty context.
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The context can be obtained with
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[`getContext`](#builtins-getContext).
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> **Example**
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>
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> Many operations require a string context to be empty because they are intended only to work with "regular" strings, and also to help users avoid unintentionally loosing track of string context elements.
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> `builtins.hasContext` can help create better domain-specific errors in those case.
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>
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> ```nix
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> name: meta:
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>
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> if builtins.hasContext name
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> then throw "package name cannot contain string context"
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> else { ${name} = meta; }
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> ```
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)",
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.fun = prim_hasContext
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});
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/* Sometimes we want to pass a derivation path (i.e. pkg.drvPath) to a
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builder without causing the derivation to be built (for instance,
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in the derivation that builds NARs in nix-push, when doing
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source-only deployment). This primop marks the string context so
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that builtins.derivation adds the path to drv.inputSrcs rather than
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drv.inputDrvs. */
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static void prim_unsafeDiscardOutputDependency(EvalState & state, const PosIdx pos, Value * * args, Value & v)
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{
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NixStringContext context;
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@ -66,11 +73,83 @@ static void prim_unsafeDiscardOutputDependency(EvalState & state, const PosIdx p
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static RegisterPrimOp primop_unsafeDiscardOutputDependency({
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.name = "__unsafeDiscardOutputDependency",
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.arity = 1,
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.args = {"s"},
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.doc = R"(
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Create a copy of the given string where every "derivation deep" string context element is turned into a constant string context element.
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This is the opposite of [`builtins.addDrvOutputDependencies`](#builtins-addDrvOutputDependencies).
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This is unsafe because it allows us to "forget" store objects we would have otherwise refered to with the string context,
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whereas Nix normally tracks all dependencies consistently.
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Safe operations "grow" but never "shrink" string contexts.
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[`builtins.addDrvOutputDependencies`] in contrast is safe because "derivation deep" string context element always refers to the underlying derivation (among many more things).
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Replacing a constant string context element with a "derivation deep" element is a safe operation that just enlargens the string context without forgetting anything.
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[`builtins.addDrvOutputDependencies`]: #builtins-addDrvOutputDependencies
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)",
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.fun = prim_unsafeDiscardOutputDependency
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});
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static void prim_addDrvOutputDependencies(EvalState & state, const PosIdx pos, Value * * args, Value & v)
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{
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NixStringContext context;
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auto s = state.coerceToString(pos, *args[0], context, "while evaluating the argument passed to builtins.addDrvOutputDependencies");
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auto contextSize = context.size();
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if (contextSize != 1) {
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throw EvalError({
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.msg = hintfmt("context of string '%s' must have exactly one element, but has %d", *s, contextSize),
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.errPos = state.positions[pos]
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});
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}
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NixStringContext context2 {
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(NixStringContextElem { std::visit(overloaded {
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[&](const NixStringContextElem::Opaque & c) -> NixStringContextElem::DrvDeep {
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if (!c.path.isDerivation()) {
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throw EvalError({
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.msg = hintfmt("path '%s' is not a derivation",
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state.store->printStorePath(c.path)),
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.errPos = state.positions[pos],
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});
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}
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return NixStringContextElem::DrvDeep {
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.drvPath = c.path,
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};
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},
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[&](const NixStringContextElem::Built & c) -> NixStringContextElem::DrvDeep {
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throw EvalError({
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.msg = hintfmt("`addDrvOutputDependencies` can only act on derivations, not on a derivation output such as '%1%'", c.output),
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.errPos = state.positions[pos],
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});
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},
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[&](const NixStringContextElem::DrvDeep & c) -> NixStringContextElem::DrvDeep {
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/* Reuse original item because we want this to be idempotent. */
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return std::move(c);
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},
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}, context.begin()->raw) }),
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};
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v.mkString(*s, context2);
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}
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static RegisterPrimOp primop_addDrvOutputDependencies({
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.name = "__addDrvOutputDependencies",
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.args = {"s"},
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.doc = R"(
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Create a copy of the given string where a single consant string context element is turned into a "derivation deep" string context element.
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The store path that is the constant string context element should point to a valid derivation, and end in `.drv`.
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The original string context element must not be empty or have multiple elements, and it must not have any other type of element other than a constant or derivation deep element.
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The latter is supported so this function is idempotent.
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This is the opposite of [`builtins.unsafeDiscardOutputDependency`](#builtins-addDrvOutputDependencies).
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)",
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.fun = prim_addDrvOutputDependencies
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});
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/* Extract the context of a string as a structured Nix value.
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The context is represented as an attribute set whose keys are the
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@ -0,0 +1,10 @@
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error:
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… while calling the 'addDrvOutputDependencies' builtin
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at /pwd/lang/eval-fail-addDrvOutputDependencies-empty-context.nix:1:1:
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1| builtins.addDrvOutputDependencies ""
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| ^
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2|
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error: context of string '' must have exactly one element, but has 0
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@ -0,0 +1 @@
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builtins.addDrvOutputDependencies ""
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@ -0,0 +1,11 @@
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error:
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… while calling the 'addDrvOutputDependencies' builtin
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at /pwd/lang/eval-fail-addDrvOutputDependencies-multi-elem-context.nix:18:4:
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17|
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18| in builtins.addDrvOutputDependencies combo-path
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| ^
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19|
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error: context of string '/nix/store/pg9yqs4yd85yhdm3f4i5dyaqp5jahrsz-fail.drv/nix/store/2dxd5frb715z451vbf7s8birlf3argbk-fail-2.drv' must have exactly one element, but has 2
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@ -0,0 +1,18 @@
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let
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drv0 = derivation {
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name = "fail";
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builder = "/bin/false";
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system = "x86_64-linux";
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outputs = [ "out" "foo" ];
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};
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drv1 = derivation {
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name = "fail-2";
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builder = "/bin/false";
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system = "x86_64-linux";
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outputs = [ "out" "foo" ];
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};
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combo-path = "${drv0.drvPath}${drv1.drvPath}";
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in builtins.addDrvOutputDependencies combo-path
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@ -0,0 +1,11 @@
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error:
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… while calling the 'addDrvOutputDependencies' builtin
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at /pwd/lang/eval-fail-addDrvOutputDependencies-wrong-element-kind.nix:9:4:
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8|
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9| in builtins.addDrvOutputDependencies drv.outPath
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| ^
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10|
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error: `addDrvOutputDependencies` can only act on derivations, not on a derivation output such as 'out'
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@ -0,0 +1,9 @@
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let
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drv = derivation {
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name = "fail";
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builder = "/bin/false";
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system = "x86_64-linux";
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outputs = [ "out" "foo" ];
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};
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in builtins.addDrvOutputDependencies drv.outPath
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@ -1 +1 @@
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[ true true true true true true ]
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[ true true true true true true true true true true true true true ]
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@ -31,11 +31,29 @@ let
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(builtins.unsafeDiscardStringContext str)
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(builtins.getContext str);
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# Only holds true if string context contains both a `DrvDeep` and
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# `Opaque` element.
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almostEtaRule = str:
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str == builtins.addDrvOutputDependencies
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(builtins.unsafeDiscardOutputDependency str);
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addDrvOutputDependencies_idempotent = str:
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builtins.addDrvOutputDependencies str ==
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builtins.addDrvOutputDependencies (builtins.addDrvOutputDependencies str);
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rules = str: [
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(etaRule str)
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(almostEtaRule str)
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(addDrvOutputDependencies_idempotent str)
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];
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in [
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(legit-context == desired-context)
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(reconstructed-path == combo-path)
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(etaRule "foo")
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(etaRule drv.drvPath)
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(etaRule drv.foo.outPath)
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(etaRule (builtins.unsafeDiscardOutputDependency drv.drvPath))
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] ++ builtins.concatMap rules [
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drv.drvPath
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(builtins.addDrvOutputDependencies drv.drvPath)
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(builtins.unsafeDiscardOutputDependency drv.drvPath)
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]
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