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-rw-r--r--src/libexpr/primops.cc9
1 files changed, 5 insertions, 4 deletions
diff --git a/src/libexpr/primops.cc b/src/libexpr/primops.cc
index 615cc8138..cc23827a1 100644
--- a/src/libexpr/primops.cc
+++ b/src/libexpr/primops.cc
@@ -534,7 +534,8 @@ static void prim_derivationStrict(EvalState & state, const Pos & pos, Value * *
PathSet context;
- string outputHash, outputHashAlgo;
+ std::experimental::optional<std::string> outputHash;
+ std::string outputHashAlgo;
bool outputHashRecursive = false;
StringSet outputs;
@@ -703,7 +704,7 @@ static void prim_derivationStrict(EvalState & state, const Pos & pos, Value * *
throw EvalError(format("derivation names are not allowed to end in ‘%1%’, at %2%")
% drvExtension % posDrvName);
- if (outputHash != "") {
+ if (outputHash) {
/* Handle fixed-output derivations. */
if (outputs.size() != 1 || *(outputs.begin()) != "out")
throw Error(format("multiple outputs are not supported in fixed-output derivations, at %1%") % posDrvName);
@@ -711,13 +712,13 @@ static void prim_derivationStrict(EvalState & state, const Pos & pos, Value * *
HashType ht = parseHashType(outputHashAlgo);
if (ht == htUnknown)
throw EvalError(format("unknown hash algorithm ‘%1%’, at %2%") % outputHashAlgo % posDrvName);
- Hash h = parseHash16or32(ht, outputHash);
+ Hash h = parseHash16or32(ht, *outputHash);
outputHash = printHash(h);
if (outputHashRecursive) outputHashAlgo = "r:" + outputHashAlgo;
Path outPath = state.store->makeFixedOutputPath(outputHashRecursive, h, drvName);
drv.env["out"] = outPath;
- drv.outputs["out"] = DerivationOutput(outPath, outputHashAlgo, outputHash);
+ drv.outputs["out"] = DerivationOutput(outPath, outputHashAlgo, *outputHash);
}
else {