libexpr: Optimize prim_attrNames a bit

Instead of having lexicographicOrder() create a temporary sorted array
of Attr*:s and copying attr names from that, copy the attr names
first and then sort that.

1 files changed, 5 insertions, 2 deletions

diff --git a/src/libexpr/primops.cc b/src/libexpr/primops.cc
index ca97b2b28bb6..89e984d2e589 100644
--- a/src/libexpr/primops.cc
+++ b/src/libexpr/primops.cc
@@ -1138,8 +1138,11 @@ static void prim_attrNames(EvalState & state, const Pos & pos, Value * * args, V
     state.mkList(v, args[0]->attrs->size());
 
     size_t n = 0;
-    for (auto & i : args[0]->attrs->lexicographicOrder())
-        mkString(*(v.listElems()[n++] = state.allocValue()), i->name);
+    for (auto & i : *args[0]->attrs)
+        mkString(*(v.listElems()[n++] = state.allocValue()), i.name);
+
+    std::sort(v.listElems(), v.listElems() + n,
+              [](Value * v1, Value * v2) { return strcmp(v1->string.s, v2->string.s) < 0; });
 }