local build root layout: collect all ephemeral directories

... under a common root in the youngest generation. This will allow
a simple way of cleaning them up during garbage collection.

2 files changed, 9 insertions, 3 deletions

diff --git a/src/buildtool/storage/config.hpp b/src/buildtool/storage/config.hpp
index 069daed2..92358d12 100644
--- a/src/buildtool/storage/config.hpp
+++ b/src/buildtool/storage/config.hpp
@@ -170,11 +170,18 @@ class StorageConfig {
         }
     }
 
+    /// \brief Root directory for all ephemeral directories, i.e., directories
+    /// that can (and should) be removed immediately by garbage collection.
+    [[nodiscard]] static auto EphemeralRoot() noexcept
+        -> std::filesystem::path {
+        return GenerationCacheRoot(0) / "ephemeral";
+    }
+
     /// \brief Root directory for local action executions; individual actions
     /// create a working directory below this root.
     [[nodiscard]] static auto ExecutionRoot() noexcept
         -> std::filesystem::path {
-        return GenerationCacheRoot(0) / "exec_root";
+        return EphemeralRoot() / "exec_root";
     }
 
   private:
diff --git a/src/buildtool/storage/fs_utils.cpp b/src/buildtool/storage/fs_utils.cpp
index 83167181..5cc3d8a0 100644
--- a/src/buildtool/storage/fs_utils.cpp
+++ b/src/buildtool/storage/fs_utils.cpp
@@ -51,8 +51,7 @@ auto GetGitRoot(LocalPathsPtr const& just_mr_paths,
 
 auto CreateTypedTmpDir(std::string const& type) noexcept -> TmpDirPtr {
     // try to create parent dir
-    auto parent_path =
-        StorageConfig::GenerationCacheRoot(0) / "tmp-workspaces" / type;
+    auto parent_path = StorageConfig::EphemeralRoot() / "tmp-workspaces" / type;
     return TmpDir::Create(parent_path);
 }