bug fix: FileRoot::DirectoryEntries cannot hold std::monostate anymore

DirectoryEntries must be constructed explicitly either via a GitTree*
or an unordered_map<string,ObjectType>. So, the case of an empty
directory, is represented by an empty map. Before this patch, empty
directories were represented by std::monostate and missing checks
on that led to a seg-fault.

2 files changed, 8 insertions, 6 deletions

diff --git a/src/buildtool/build_engine/base_maps/directory_map.cpp b/src/buildtool/build_engine/base_maps/directory_map.cpp
index 1b862386..b8cc4441 100644
--- a/src/buildtool/build_engine/base_maps/directory_map.cpp
+++ b/src/buildtool/build_engine/base_maps/directory_map.cpp
@@ -25,7 +25,8 @@ auto BuildMaps::Base::CreateDirectoryEntriesMap(std::size_t jobs)
         if (not ws_root->IsDirectory(key.module)) {
             // Missing directory is fine (source tree might be incomplete),
             // contains no entries.
-            (*setter)(FileRoot::DirectoryEntries{});
+            (*setter)(FileRoot::DirectoryEntries{
+                FileRoot::DirectoryEntries::pairs_t{}});
             return;
         }
         (*setter)(ws_root->ReadDirectory(key.module));
diff --git a/src/buildtool/file_system/file_root.hpp b/src/buildtool/file_system/file_root.hpp
index c374e937..66ceb68a 100644
--- a/src/buildtool/file_system/file_root.hpp
+++ b/src/buildtool/file_system/file_root.hpp
@@ -84,9 +84,11 @@ class FileRoot {
   public:
     class DirectoryEntries {
         friend class FileRoot;
+
+      public:
         using pairs_t = std::unordered_map<std::string, ObjectType>;
         using tree_t = gsl::not_null<GitTree const*>;
-        using entries_t = std::variant<std::monostate, tree_t, pairs_t>;
+        using entries_t = std::variant<tree_t, pairs_t>;
 
         using fs_iterator_type = typename pairs_t::const_iterator;
         using fs_iterator = FilteredIterator<fs_iterator_type>;
@@ -94,6 +96,7 @@ class FileRoot {
         using git_iterator_type = GitTree::entries_t::const_iterator;
         using git_iterator = FilteredIterator<git_iterator_type>;
 
+      private:
         /// Iterator has two FilteredIterators, one for iterating over pairs_t
         /// and one for tree_t. Each FilteredIterator is constructed with a
         /// proper predicate, allowing for iteration on file-only or
@@ -146,8 +149,6 @@ class FileRoot {
         };
 
       public:
-        DirectoryEntries() noexcept = default;
-
         explicit DirectoryEntries(pairs_t pairs) noexcept
             : data_{std::move(pairs)} {}
 
@@ -226,7 +227,7 @@ class FileRoot {
         }
 
       private:
-        entries_t data_{};
+        entries_t data_;
     };
 
     FileRoot() noexcept = default;
@@ -346,7 +347,7 @@ class FileRoot {
                         dir_path.string(),
                         ex.what());
         }
-        return {};
+        return DirectoryEntries{DirectoryEntries::pairs_t{}};
     }
 
     [[nodiscard]] auto FileType(std::filesystem::path const& file_path)