refactor(tvix): Use absl::btree_map for DerivationOutputs r/1610

This container implementation is much faster than std::map. We have
stuck to an ordered container because it's unclear whether the
accesses of this field (of which there are *many*) are actually
ordering dependent.

Also includes an Arbitrary implementation for absl::btree_map (for any
K, V that are also Arbitrary).

Change-Id: I04f58ca0ce32b9ae1759313b01508b0e44bae793
Reviewed-on: https://cl.tvl.fyi/c/depot/+/1683
Reviewed-by: glittershark <grfn@gws.fyi>
Tested-by: BuildkiteCI

1 files changed, 3 insertions, 2 deletions

diff --git a/third_party/nix/src/libstore/derivations.cc b/third_party/nix/src/libstore/derivations.cc
index 007c268bab2a..adfc6fc05fc1 100644
--- a/third_party/nix/src/libstore/derivations.cc
+++ b/third_party/nix/src/libstore/derivations.cc
@@ -40,8 +40,9 @@ BasicDerivation BasicDerivation::from_proto(
   result.builder = proto_derivation->builder().path();
   store.assertStorePath(result.builder);
 
-  result.outputs.insert(proto_derivation->outputs().begin(),
-                        proto_derivation->outputs().end());
+  for (auto [k, v] : proto_derivation->outputs()) {
+    result.outputs.emplace(k, v);
+  }
 
   result.inputSrcs.insert(proto_derivation->input_sources().paths().begin(),
                           proto_derivation->input_sources().paths().end());