source tree service: Ensure the Git cache exists

Similarly to just-mr, each SourceTree RPC must ensure that the Git
cache folder exists and the Git cache repository is initialized
before using it.

While there, fix missing shared locks on the Git cache root.

1 files changed, 6 insertions, 0 deletions

diff --git a/src/buildtool/serve_api/serve_service/source_tree.hpp b/src/buildtool/serve_api/serve_service/source_tree.hpp
index 7b3d3cac..2b08a26f 100644
--- a/src/buildtool/serve_api/serve_service/source_tree.hpp
+++ b/src/buildtool/serve_api/serve_service/source_tree.hpp
@@ -23,6 +23,7 @@
 #include <type_traits>
 #include <unordered_map>
 #include <utility>
+#include <variant>
 
 #include <grpcpp/grpcpp.h>
 
@@ -142,6 +143,11 @@ class SourceTreeService final
     // symlinks resolver map
     ResolveSymlinksMap resolve_symlinks_map_{CreateResolveSymlinksMap()};
 
+    /// \brief Ensure that the Git cache repository exists.
+    /// \returns Error message on failure.
+    [[nodiscard]] auto EnsureGitCacheRoot()
+        -> expected<std::monostate, std::string>;
+
     /// \brief Check if commit exists and tries to get the subtree if found.
     /// \returns The subtree hash on success or an unexpected error (fatal or
     /// commit was not found).