1 files changed, 69 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..5d77e0907cd6
--- /dev/null
+++ b/third_party/nix/src/libexpr/attr-set.hh
@@ -0,0 +1,69 @@
+// This file implements the underlying structure of Nix attribute sets.
+#pragma once
+
+#include <absl/container/btree_map.h>
+
+#include "libexpr/nixexpr.hh"
+#include "libexpr/symbol-table.hh"
+#include "libutil/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){};
+};
+
+using AttributeMap = absl::btree_map<Symbol, Attr>;
+
+class Bindings {
+ public:
+  using iterator = AttributeMap::iterator;
+  using const_iterator = AttributeMap::const_iterator;
+
+  // Allocate a new attribute set that is visible to the garbage
+  // collector.
+  static std::unique_ptr<Bindings> New(size_t capacity = 0);
+
+  // Create a new attribute set by merging two others. This is used to
+  // implement the `//` operator in Nix.
+  static std::unique_ptr<Bindings> Merge(const Bindings& lhs,
+                                         const Bindings& rhs);
+
+  // Return the number of contained elements.
+  size_t size() const;
+
+  // Is this attribute set empty?
+  bool empty();
+
+  // Insert, but do not replace, values in the attribute set.
+  void push_back(const Attr& attr);
+
+  // Are these two attribute sets deeply equal?
+  // Note: Does not special-case derivations. Use state.eqValues() to check
+  // attrsets that may be derivations.
+  bool Equal(const Bindings* other, EvalState& state) const;
+
+  // Look up a specific element of the attribute set.
+  iterator find(const Symbol& name);
+
+  iterator begin();
+  const_iterator cbegin() const;
+  iterator end();
+  const_iterator cend() const;
+
+  // oh no
+  friend class EvalState;
+
+ private:
+  AttributeMap attributes_;
+};
+
+}  // namespace nix