Only register drv outputs when it's safe to do so if ca-drvs aren't e…

…nabled

Unless ca drvs are enabled, only allow registering derivation outputs when we
know it's safe to do so, meaning when we can check that the mapping matches
what's defined in the drv file itself

src/libstore/local-store.cc

@@ -623,6 +623,28 @@ void LocalStore::registerDrvOutput(const DrvOutputId& id, const DrvOutputInfo &
 
 void LocalStore::registerDrvOutput_(State & state, const StorePath & deriver, const string & outputName, const StorePath & output)
 {
+    // Ensure that we don't register a boguous derivation output.
+    debug("Checking the validiy of the drv output '%s!%s'", printStorePath(deriver), outputName);
+    if (!isValidPath_(state, deriver))
+        settings.requireExperimentalFeature("ca-derivations");
+    else {
+        // Can't use `readDerivation` here as we already hold the lock on the db
+        auto matchingDrv = parseDerivation(
+            *this,
+            readFile(Store::toRealPath(deriver)),
+            Derivation::nameFromPath(deriver)
+        );
+        auto outputsFromDrv = matchingDrv.outputsAndOptPaths(*this);
+        auto currentOutputFromDrv = outputsFromDrv.find(outputName);
+        assert (currentOutputFromDrv != outputsFromDrv.end());
+        if (!currentOutputFromDrv->second.second.has_value()) {
+            // Floating-ca or dependent thereof
+            settings.requireExperimentalFeature("ca-derivations");
+        } else {
+            assert (*currentOutputFromDrv->second.second == output);
+        }
+    }
+
     retrySQLite<void>([&]() {
         state.stmtAddDerivationOutput.use()
             (printStorePath(deriver))