Support fixed-output derivations depending on impure derivations

src/libstore/build/derivation-goal.cc

@@ -342,9 +342,9 @@ void DerivationGoal::gaveUpOnSubstitution()
     inputDrvOutputs.clear();
     if (useDerivation)
         for (auto & i : dynamic_cast<Derivation *>(drv.get())->inputDrvs) {
-            /* Ensure that pure derivations don't depend on impure
+            /* Ensure that pure, non-fixed-output derivations don't
-               derivations. */
+               depend on impure derivations. */
-            if (drv->type().isPure()) {
+            if (drv->type().isPure() && !drv->type().isFixed()) {
                 auto inputDrv = worker.evalStore.readDerivation(i.first);
                 if (!inputDrv.type().isPure())
                     throw Error("pure derivation '%s' depends on impure derivation '%s'",
@@ -993,6 +993,7 @@ void DerivationGoal::resolvedFinished()
                 auto newRealisation = realisation;
                 newRealisation.id = DrvOutput { initialOutputs.at(wantedOutput).outputHash, wantedOutput };
                 newRealisation.signatures.clear();
+                if (!drv->type().isFixed())
                     newRealisation.dependentRealisations = drvOutputReferences(worker.store, *drv, realisation.outPath);
                 signRealisation(newRealisation);
                 worker.store.registerDrvOutput(newRealisation);

src/libstore/misc.cc

@@ -277,15 +277,15 @@ std::map<DrvOutput, StorePath> drvOutputReferences(
 {
     std::set<Realisation> inputRealisations;
 
-    for (const auto& [inputDrv, outputNames] : drv.inputDrvs) {
+    for (const auto & [inputDrv, outputNames] : drv.inputDrvs) {
         auto outputHashes =
             staticOutputHashes(store, store.readDerivation(inputDrv));
-        for (const auto& outputName : outputNames) {
+        for (const auto & outputName : outputNames) {
             auto thisRealisation = store.queryRealisation(
                 DrvOutput{outputHashes.at(outputName), outputName});
             if (!thisRealisation)
                 throw Error(
-                    "output '%s' of derivation '%s' isn’t built", outputName,
+                    "output '%s' of derivation '%s' isn't built", outputName,
                     store.printStorePath(inputDrv));
             inputRealisations.insert(*thisRealisation);
         }
@@ -295,4 +295,5 @@ std::map<DrvOutput, StorePath> drvOutputReferences(
 
     return drvOutputReferences(Realisation::closure(store, inputRealisations), info->references);
 }
+
 }

tests/impure-derivations.nix

@@ -7,6 +7,7 @@ rec {
     outputs = [ "out" "stuff" ];
     buildCommand =
       ''
+        echo impure
         x=$(< $TEST_ROOT/counter)
         mkdir $out $stuff
         echo $x > $out/n
@@ -23,6 +24,7 @@ rec {
     name = "impure-on-impure";
     buildCommand =
       ''
+        echo impure-on-impure
         x=$(< ${impure}/n)
         mkdir $out
         printf X$x > $out/n
@@ -43,4 +45,24 @@ rec {
       '';
   };
 
+  contentAddressed = mkDerivation {
+    name = "content-addressed";
+    buildCommand =
+      ''
+        echo content-addressed
+        x=$(< ${impureOnImpure}/n)
+        printf ''${x:0:1} > $out
+      '';
+    outputHashAlgo = "sha256";
+    outputHashMode = "recursive";
+    outputHash = "sha256-eBYxcgkuWuiqs4cKNgKwkb3vY/HR0vVsJnqe8itJGcQ=";
+  };
+
+  inputAddressedAfterCA = mkDerivation {
+    name = "input-addressed-after-ca";
+    buildCommand =
+      ''
+        cat ${contentAddressed} > $out
+      '';
+  };
 }

tests/impure-derivations.sh

@@ -21,10 +21,10 @@ path2=$(nix build -L --no-link --json --file ./impure-derivations.nix impure | j
 [[ $(< $path2/n) = 1 ]]
 
 # Test impure derivations that depend on impure derivations.
-path3=$(nix build -L --no-link --json --file ./impure-derivations.nix impureOnImpure -vvvvv | jq -r .[].outputs.out)
+path3=$(nix build -L --no-link --json --file ./impure-derivations.nix impureOnImpure | jq -r .[].outputs.out)
 [[ $(< $path3/n) = X2 ]]
 
-path4=$(nix build -L --no-link --json --file ./impure-derivations.nix impureOnImpure -vvvvv | jq -r .[].outputs.out)
+path4=$(nix build -L --no-link --json --file ./impure-derivations.nix impureOnImpure | jq -r .[].outputs.out)
 [[ $(< $path4/n) = X3 ]]
 
 # Test that (self-)references work.
@@ -37,3 +37,18 @@ nix build -L --no-link --json --file ./impure-derivations.nix inputAddressed 2>&
 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 ]]
+
+# Fixed-output derivations *can* depend on impure derivations.
+path5=$(nix build -L --no-link --json --file ./impure-derivations.nix contentAddressed | jq -r .[].outputs.out)
+[[ $(< $path5) = X ]]
+[[ $(< $TEST_ROOT/counter) = 5 ]]
+
+# And they should not be rebuilt.
+path5=$(nix build -L --no-link --json --file ./impure-derivations.nix contentAddressed | jq -r .[].outputs.out)
+[[ $(< $path5) = X ]]
+[[ $(< $TEST_ROOT/counter) = 5 ]]
+
+# Input-addressed derivations can depend on fixed-output derivations that depend on impure derivations.
+path6=$(nix build -L --no-link --json --file ./impure-derivations.nix inputAddressedAfterCA | jq -r .[].outputs.out)
+[[ $(< $path6) = X ]]
+[[ $(< $TEST_ROOT/counter) = 5 ]]