1 files changed, 5 insertions, 0 deletions
diff --git a/src/buildtool/build_engine/expression/configuration.hpp b/src/buildtool/build_engine/expression/configuration.hpp
index ec3fde66..dadb71d2 100644
--- a/src/buildtool/build_engine/expression/configuration.hpp
+++ b/src/buildtool/build_engine/expression/configuration.hpp
@@ -16,6 +16,7 @@
 #define INCLUDED_SRC_BUILDTOOL_BUILD_ENGINE_EXPRESSION_CONFIGURATION_HPP
 
 #include <algorithm>
+#include <compare>
 #include <cstddef>
 #include <functional>
 #include <optional>
@@ -92,6 +93,10 @@ class Configuration {
         return expr_ == other.expr_;
     }
 
+    [[nodiscard]] auto operator<(const Configuration& other) const -> bool {
+        return expr_->ToHash() < other.expr_->ToHash();
+    }
+
     [[nodiscard]] auto hash() const noexcept -> std::size_t {
         return std::hash<ExpressionPtr>{}(expr_);
     }