Use the hash modulo in the derivation outputs

Rather than storing the derivation outputs as `drvPath!outputName` internally,
store them as `drvHashModulo!outputName` (or `outputHash!outputName` for
fixed-output derivations).

This makes the storage slightly more opaque, but enables an earlier
cutoff in cases where a fixed-output dependency changes (but keeps the
same output hash) − same as what we already do for input-addressed
derivations.

1 files changed, 5 insertions, 5 deletions

diff --git a/src/libstore/realisation.cc b/src/libstore/realisation.cc
index 47db1ec9f..47ad90eee 100644
--- a/src/libstore/realisation.cc
+++ b/src/libstore/realisation.cc
@@ -7,18 +7,18 @@ namespace nix {
 MakeError(InvalidDerivationOutputId, Error);
 
 DrvOutput DrvOutput::parse(const std::string &strRep) {
-    const auto &[rawPath, outputs] = parsePathWithOutputs(strRep);
-    if (outputs.size() != 1)
+    size_t n = strRep.find("!");
+    if (n == strRep.npos)
         throw InvalidDerivationOutputId("Invalid derivation output id %s", strRep);
 
     return DrvOutput{
-        .drvPath = StorePath(rawPath),
-        .outputName = *outputs.begin(),
+        .drvHash = Hash::parseAnyPrefixed(strRep.substr(0, n)),
+        .outputName = strRep.substr(n+1),
     };
 }
 
 std::string DrvOutput::to_string() const {
-    return std::string(drvPath.to_string()) + "!" + outputName;
+    return strHash() + "!" + outputName;
 }
 
 nlohmann::json Realisation::toJSON() const {