2 files changed, 73 insertions, 2 deletions

diff --git a/src/buildtool/file_system/precomputed_root.cpp b/src/buildtool/file_system/precomputed_root.cpp
index 8e20f2f0..f62bab64 100644
--- a/src/buildtool/file_system/precomputed_root.cpp
+++ b/src/buildtool/file_system/precomputed_root.cpp
@@ -86,6 +86,25 @@ template <>
                         .target_name = std::string{root[3]},
                         .config = root[4]};
 }
+
+template <>
+[[nodiscard]] auto ParseImpl<TreeStructureRoot>(nlohmann::json const& root)
+    -> expected<TreeStructureRoot, std::string> {
+    if (root.size() != TreeStructureRoot::kSchemeLength) {
+        return unexpected{
+            fmt::format("The root has a wrong number of arguments: {}\nThe "
+                        "scheme requires [<scheme>, <root>]",
+                        root.dump())};
+    }
+
+    if (not root[1].is_string()) {
+        return unexpected{fmt::format(
+            "The root has a wrong type of <root>. Expected a string, got {}",
+            root[1].dump())};
+    }
+
+    return TreeStructureRoot{.repository = std::string{root[1]}};
+}
 }  // namespace
 
 auto ComputedRoot::operator==(ComputedRoot const& other) const noexcept
@@ -126,6 +145,27 @@ auto ComputedRoot::ComputeHash() const -> std::size_t {
     return seed;
 }
 
+auto TreeStructureRoot::operator==(
+    TreeStructureRoot const& other) const noexcept -> bool {
+    return repository == other.repository;
+}
+
+auto TreeStructureRoot::operator<(TreeStructureRoot const& other) const noexcept
+    -> bool {
+    return repository < other.repository;
+}
+
+auto TreeStructureRoot::ToString() const -> std::string {
+    return fmt::format("[\"tree structure\", {}]",
+                       nlohmann::json(repository).dump());
+}
+auto TreeStructureRoot::ComputeHash() const -> std::size_t {
+    std::size_t seed{};
+    hash_combine<std::string>(&seed, kMarker);
+    hash_combine<std::string>(&seed, repository);
+    return seed;
+}
+
 auto PrecomputedRoot::Parse(nlohmann::json const& root) noexcept
     -> expected<PrecomputedRoot, std::string> {
     if ((not root.is_array()) or root.empty()) {
@@ -137,6 +177,9 @@ auto PrecomputedRoot::Parse(nlohmann::json const& root) noexcept
     if (root[0] == ComputedRoot::kMarker) {
         return ParsePrecomputed<ComputedRoot>(root);
     }
+    if (root[0] == TreeStructureRoot::kMarker) {
+        return ParsePrecomputed<TreeStructureRoot>(root);
+    }
 
     return unexpected{
         fmt::format("Unknown precomputed type of the root {}", root.dump())};
diff --git a/src/buildtool/file_system/precomputed_root.hpp b/src/buildtool/file_system/precomputed_root.hpp
index 8261b94c..6df59bc9 100644
--- a/src/buildtool/file_system/precomputed_root.hpp
+++ b/src/buildtool/file_system/precomputed_root.hpp
@@ -42,6 +42,22 @@ struct ComputedRoot final {
     [[nodiscard]] auto ComputeHash() const -> std::size_t;
 };
 
+struct TreeStructureRoot final {
+    static constexpr auto kMarker = "tree structure";
+    static constexpr std::size_t kSchemeLength = 2;
+
+    std::string repository;
+
+    [[nodiscard]] auto operator==(TreeStructureRoot const& other) const noexcept
+        -> bool;
+
+    [[nodiscard]] auto operator<(TreeStructureRoot const& other) const noexcept
+        -> bool;
+
+    [[nodiscard]] auto ToString() const -> std::string;
+    [[nodiscard]] auto ComputeHash() const -> std::size_t;
+};
+
 namespace std {
 template <typename>
 struct hash;
@@ -51,7 +67,7 @@ struct hash;
 /// real build starts.
 class PrecomputedRoot final {
   public:
-    using root_t = std::variant<ComputedRoot>;
+    using root_t = std::variant<ComputedRoot, TreeStructureRoot>;
     explicit PrecomputedRoot() : PrecomputedRoot(ComputedRoot{}) {}
     explicit PrecomputedRoot(root_t root)
         : root_{std::move(root)}, hash_{ComputeHash(root_)} {}
@@ -61,7 +77,8 @@ class PrecomputedRoot final {
 
     [[nodiscard]] static auto IsPrecomputedMarker(
         std::string const& marker) noexcept -> bool {
-        return marker == ComputedRoot::kMarker;
+        return marker == ComputedRoot::kMarker or
+               marker == TreeStructureRoot::kMarker;
     }
 
     [[nodiscard]] auto operator==(PrecomputedRoot const& other) const noexcept
@@ -86,6 +103,17 @@ class PrecomputedRoot final {
         return std::nullopt;
     }
 
+    [[nodiscard]] auto IsTreeStructure() const noexcept -> bool {
+        return std::holds_alternative<TreeStructureRoot>(root_);
+    }
+    [[nodiscard]] auto AsTreeStructure() const noexcept
+        -> std::optional<TreeStructureRoot> {
+        if (auto const* root = std::get_if<TreeStructureRoot>(&root_)) {
+            return *root;
+        }
+        return std::nullopt;
+    }
+
   private:
     root_t root_;
     std::size_t hash_;