refactor(3p/nix): Apply clang-tidy's performance-* fixes r/789

This applies the performance fixes listed here:

https://clang.llvm.org/extra/clang-tidy/checks/list.html

5 files changed, 7 insertions, 4 deletions

diff --git a/third_party/nix/src/nix-store/dotgraph.cc b/third_party/nix/src/nix-store/dotgraph.cc
index 259ecbd74a5e..0186a7b22ebd 100644
--- a/third_party/nix/src/nix-store/dotgraph.cc
+++ b/third_party/nix/src/nix-store/dotgraph.cc
@@ -79,7 +79,7 @@ void printClosure(const Path & nePath, const StoreExpr & fs)
 }
 #endif
 
-void printDotGraph(ref<Store> store, const PathSet& roots) {
+void printDotGraph(const ref<Store>& store, const PathSet& roots) {
   PathSet workList(roots);
   PathSet doneSet;
 
diff --git a/third_party/nix/src/nix-store/dotgraph.hh b/third_party/nix/src/nix-store/dotgraph.hh
index c7069451e114..20fc357b1bd4 100644
--- a/third_party/nix/src/nix-store/dotgraph.hh
+++ b/third_party/nix/src/nix-store/dotgraph.hh
@@ -6,6 +6,6 @@ namespace nix {
 
 class Store;
 
-void printDotGraph(ref<Store> store, const PathSet& roots);
+void printDotGraph(const ref<Store>& store, const PathSet& roots);
 
 }  // namespace nix
diff --git a/third_party/nix/src/nix-store/graphml.cc b/third_party/nix/src/nix-store/graphml.cc
index 6510b328810d..a1a16cc8f28a 100644
--- a/third_party/nix/src/nix-store/graphml.cc
+++ b/third_party/nix/src/nix-store/graphml.cc
@@ -37,7 +37,7 @@ static string makeNode(const ValidPathInfo& info) {
       (isDerivation(info.path) ? "derivation" : "output-path"));
 }
 
-void printGraphML(ref<Store> store, const PathSet& roots) {
+void printGraphML(const ref<Store>& store, const PathSet& roots) {
   PathSet workList(roots);
   PathSet doneSet;
   std::pair<PathSet::iterator, bool> ret;
diff --git a/third_party/nix/src/nix-store/graphml.hh b/third_party/nix/src/nix-store/graphml.hh
index c330dc6abc43..199421acb264 100644
--- a/third_party/nix/src/nix-store/graphml.hh
+++ b/third_party/nix/src/nix-store/graphml.hh
@@ -6,6 +6,6 @@ namespace nix {
 
 class Store;
 
-void printGraphML(ref<Store> store, const PathSet& roots);
+void printGraphML(const ref<Store>& store, const PathSet& roots);
 
 }  // namespace nix
diff --git a/third_party/nix/src/nix-store/nix-store.cc b/third_party/nix/src/nix-store/nix-store.cc
index 802ebd420792..40d6f01cd96c 100644
--- a/third_party/nix/src/nix-store/nix-store.cc
+++ b/third_party/nix/src/nix-store/nix-store.cc
@@ -28,6 +28,9 @@ using namespace nix;
 using std::cin;
 using std::cout;
 
+// TODO(tazjin): clang-tidy's performance lints don't like this, but
+// the automatic fixes fail (it seems that some of the ops want to own
+// the args for whatever reason)
 using Operation = void (*)(Strings, Strings);
 
 static Path gcRoot;