1 files changed, 30 insertions, 0 deletions
diff --git a/src/buildtool/file_system/git_cas.hpp b/src/buildtool/file_system/git_cas.hpp
index c964a739..051e40f1 100644
--- a/src/buildtool/file_system/git_cas.hpp
+++ b/src/buildtool/file_system/git_cas.hpp
@@ -4,6 +4,8 @@
 #include <filesystem>
 #include <memory>
 #include <optional>
+#include <unordered_map>
+#include <vector>
 
 #include "src/buildtool/file_system/object_type.hpp"
 
@@ -17,6 +19,25 @@ using GitCASPtr = std::shared_ptr<GitCAS const>;
 /// \brief Git CAS that maintains its own libgit2 global state.
 class GitCAS {
   public:
+    // Stores the data for defining a single Git tree entry, which consists of
+    // a name (flat basename) and an object type (file/executable/tree).
+    struct tree_entry_t {
+        tree_entry_t(std::string n, ObjectType t)
+            : name{std::move(n)}, type{t} {}
+        std::string name;
+        ObjectType type;
+        [[nodiscard]] auto operator==(tree_entry_t const& other) const noexcept
+            -> bool {
+            return name == other.name and type == other.type;
+        }
+    };
+
+    // Tree entries by raw id. The same id might refer to multiple entries.
+    // Note that sharding by id is used as this format enables a more efficient
+    // internal implementation for creating trees.
+    using tree_entries_t =
+        std::unordered_map<std::string, std::vector<tree_entry_t>>;
+
     static auto Open(std::filesystem::path const& repo_path) noexcept
         -> GitCASPtr;
 
@@ -47,6 +68,15 @@ class GitCAS {
                                   bool is_hex_id = false) const noexcept
         -> std::optional<std::pair<std::size_t, ObjectType>>;
 
+    /// \brief Read entries from tree in CAS.
+    /// Reading a tree must be backed by an object database. Therefore, a valid
+    /// instance of this class is required.
+    /// \param id         The object id.
+    /// \param is_hex_id  Specify whether `id` is hex string or raw.
+    [[nodiscard]] auto ReadTree(std::string const& id,
+                                bool is_hex_id = false) const noexcept
+        -> std::optional<tree_entries_t>;
+
   private:
     git_odb* odb_{nullptr};
     bool initialized_{false};