Allow empty hash in derivations

matthewbauer · matthewbauer · commit 762273f1fd48 · 2020-06-09T01:23:37.000-05:00
follow up of #3544 This allows hash="" so that it can be used for debugging purposes. For instance, this gives you an error message like: warning: found empty hash, assuming you wanted 'sha256:0000000000000000000000000000000000000000000000000000' hash mismatch in fixed-output derivation '/nix/store/asx6qw1r1xk6iak6y6jph4n58h4hdmbm-nix': wanted: sha256:0000000000000000000000000000000000000000000000000000 got: sha256:0fpfhipl9v1mfzw2ffmxiyyzqwlkvww22bh9wcy4qrfslb4jm429
diff --git a/src/libexpr/primops.cc b/src/libexpr/primops.cc
@@ -719,7 +719,13 @@ static void prim_derivationStrict(EvalState & state, const Pos & pos, Value * *
             throw Error(format("multiple outputs are not supported in fixed-output derivations, at %1%") % posDrvName);
 
         HashType ht = outputHashAlgo.empty() ? htUnknown : parseHashType(outputHashAlgo);
-        Hash h(*outputHash, ht);
+
+        Hash h;
+        if (outputHash->empty()) {
+            h = Hash(ht);
+            printError("warning: found empty hash, assuming you wanted '%s'", h.to_string());
+        } else
+            h = Hash(*outputHash, ht);
 
         auto outPath = state.store->makeFixedOutputPath(ingestionMethod, h, drvName);
         if (!jsonObject) drv.env["out"] = state.store->printStorePath(outPath);
