Try to realise CA derivations during queryMissing

This enables nix to correctly report what will be fetched in the case
that everything is a cache hit.

Note however that if an intermediate build of something which is not
cached could still cause products to end up being substituted if the
intermediate build results in a CA path which is in the cache.

Fixes #8615.

Signed-off-by: Peter Waller <p@pwaller.net>

src/libstore/misc.cc

@@ -200,6 +200,40 @@ void Store::queryMissing(const std::vector<DerivedPath> & targets,
             auto drv = make_ref<Derivation>(derivationFromPath(bfd.drvPath));
             ParsedDerivation parsedDrv(StorePath(bfd.drvPath), *drv);
 
+            if (!knownOutputPaths && settings.useSubstitutes && parsedDrv.substitutesAllowed()) {
+                // Try to realise the static output hashes.
+
+                // TODO: I'm not sure this logic is quite right, how do we
+                // ensure all the needed paths are present?
+
+                // TODO: Should we also do this->queryRealisation?
+
+                // TODO: Originally, this was only done if the drv was a CA drv.
+                // But you could have a non-CA drv with a CA input. So it may be
+                // necessary to gate this on the CA experimental feature?
+                auto outputHashes = staticOutputHashes(*this, *drv);
+                knownOutputPaths = true;
+
+                for (auto [outputName, hash] : outputHashes) {
+                    if (!bfd.outputs.contains(outputName))
+                        continue;
+
+                    bool found = false;
+                    for (auto &sub : getDefaultSubstituters()) {
+                        auto realisation = sub->queryRealisation({hash, outputName});
+                        if (!realisation)
+                            continue;
+                        invalid.insert(realisation->outPath);
+                        found = true;
+                    }
+                    if (!found) {
+                        knownOutputPaths = false;
+                        break;
+                    }
+                }
+            }
+
+
             if (knownOutputPaths && settings.useSubstitutes && parsedDrv.substitutesAllowed()) {
                 auto drvState = make_ref<Sync<DrvState>>(DrvState(invalid.size()));
                 for (auto & output : invalid)

tests/ca/content-addressed.nix

@@ -61,6 +61,14 @@ rec {
       echo ${rootCA}/non-ca-hello > $out/dep
     '';
   };
+  noRuntimeDep = mkDerivation {
+    name = "no-runtime-dep";
+    buildCommand = ''
+      mkdir -p $out
+      echo ${rootCA}
+      touch $out
+    '';
+  };
   dependentFixedOutput = mkDerivation {
     name = "dependent-fixed-output";
     outputHashMode = "recursive";