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>

1 files changed, 30 insertions, 0 deletions

diff --git a/src/libstore/misc.cc b/src/libstore/misc.cc
index 14160dc8b..2fdf0a68d 100644
--- a/src/libstore/misc.cc
+++ b/src/libstore/misc.cc
@@ -200,6 +200,36 @@ 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()) {
+                experimentalFeatureSettings.require(Xp::CaDerivations);
+
+                // If there are unknown output paths, attempt to find if the
+                // paths are known to substituters through a realisation.
+                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;
+                        found = true;
+                        if (!isValidPath(realisation->outPath))
+                            invalid.insert(realisation->outPath);
+                        break;
+                    }
+                    if (!found) {
+                        // Some paths did not have a realisation, this must be built.
+                        knownOutputPaths = false;
+                        break;
+                    }
+                }
+            }
+
             if (knownOutputPaths && settings.useSubstitutes && parsedDrv.substitutesAllowed()) {
                 auto drvState = make_ref<Sync<DrvState>>(DrvState(invalid.size()));
                 for (auto & output : invalid)