1 files changed, 85 insertions, 0 deletions
diff --git a/third_party/nix/src/libexpr/attr-set.hh b/third_party/nix/src/libexpr/attr-set.hh
new file mode 100644
index 000000000000..37e6d5e1ca8f
--- /dev/null
+++ b/third_party/nix/src/libexpr/attr-set.hh
@@ -0,0 +1,85 @@
+// This file implements the underlying structure of Nix attribute sets.
+#pragma once
+
+#include <absl/container/btree_map.h>
+#include <gc/gc_allocator.h>
+
+#include "nixexpr.hh"
+#include "symbol-table.hh"
+#include "types.hh"
+
+namespace nix {  // TODO(tazjin): ::expr
+
+class EvalState;
+struct Value;
+
+/* Map one attribute name to its value. */
+struct Attr {
+  Symbol name;
+  Value* value;  // TODO(tazjin): Who owns this?
+  Pos* pos;      // TODO(tazjin): Who owns this?
+  Attr(Symbol name, Value* value, Pos* pos = &noPos)
+      : name(name), value(value), pos(pos){};
+  Attr() : pos(&noPos){};
+  bool operator<(const Attr& other) const { return name < other.name; }
+};
+
+// TODO: remove this, it only exists briefly while I get rid of the
+// current Attr struct
+inline bool operator==(const Attr& lhs, const Attr& rhs) {
+  return lhs.name == rhs.name;
+}
+
+// Convenience alias for the backing map, with the garbage-collecting
+// allocator explicitly specified.
+using AttributeMap =
+    absl::btree_map<Symbol, Attr, std::less<Symbol>,
+                    gc_allocator<std::pair<const Symbol, Attr>>>;
+
+class Bindings {
+ public:
+  typedef AttributeMap::iterator iterator;
+
+  // Allocate a new attribute set that is visible to the garbage
+  // collector.
+  static Bindings* NewGC();
+
+  // Return the number of contained elements.
+  size_t size();
+
+  // Is this attribute set empty?
+  bool empty();
+
+  // Insert, but do not replace, values in the attribute set.
+  void push_back(const Attr& attr);
+
+  // Insert a value, or replace an existing one.
+  void insert_or_assign(const Attr& attr);
+
+  // Look up a specific element of the attribute set.
+  iterator find(const Symbol& name);
+
+  // TODO
+  iterator begin();
+  iterator end();
+
+  // Merge values from other into the current attribute
+  void merge(const Bindings& other);
+
+  // ???
+  [[deprecated]] size_t capacity();
+
+  // oh no
+  // Attr& operator[](size_t pos); //  { return attrs[pos]; }
+
+  // TODO: can callers just iterate?
+  [[deprecated]] std::vector<const Attr*> lexicographicOrder();
+
+  // oh no
+  friend class EvalState;
+
+ private:
+  AttributeMap attributes_;
+};
+
+}  // namespace nix