filesystem.cpp: Use reused path buffer for directory recursion. Use...

filesystem.cpp: Use reused path buffer for directory recursion. Use std::string_view for input directory name type, and std::string for returned filename type. Remove common_types.hpp.

.clang-tidy

 ---
 Checks: '*,
          -llvm-header-guard,
-         -fuchsia-default-arguments,
-         -fuchsia-trailing-return,
          -cppcoreguidelines-pro-bounds-constant-array-index,
          -cppcoreguidelines-pro-bounds-array-to-pointer-decay,
+         -fuchsia-default-arguments,
+         -fuchsia-trailing-return,
+         -google-runtime-references,
          -hicpp-no-array-decay'
 
 # -cppcoreguidelines-pro-bounds-array-to-pointer-decay

src/megadep/common_types.hpp

-#ifndef MEGADEP_COMMON_TYPES_HPP
-#define MEGADEP_COMMON_TYPES_HPP
-
-#include <cstdint>
-#include <string>
-
-namespace megadep {
-
-using FileName = std::string;
-using DirectoryName = std::string;
-
-using FileHash = uint32_t;
-
-} // namespace megadep
-
-#endif // MEGADEP_COMMON_TYPES_HPP

src/megadep/filesystem.cpp

-#include <megadep/common_types.hpp>
 #include <megadep/config.hpp>
 #include <megadep/filesystem.hpp>
 
@@ -14,23 +13,45 @@
 
 namespace megadep {
 
-std::vector<FileName> list_files(const DirectoryName &directory) {
-  std::vector<FileName> file_names;
+static void list_files_impl(char *path_begin, char *path_end,
+                            std::vector<std::string> &file_names);
 
-  DIR *dir_ptr = opendir(directory.c_str());
+std::vector<std::string> list_files(std::string_view directory) {
+  std::vector<std::string> file_names;
+  std::array<char, filename_max> path_buffer{};
+
+  directory.copy(path_buffer.begin(), path_buffer.size());
+
+  list_files_impl(path_buffer.begin(), path_buffer.begin() + directory.size(),
+                  file_names);
+
+  return file_names;
+}
+
+// This implimentation takes advantage of recursing into directories only
+// needing to append values to the current directory path.
+// The function only ever reads the region [path_begin, path_end], and
+// edits the region [path_end, path_max) for recursive calls, bumping the
+// `path_end` pointer along to recursive calls.
+static void list_files_impl(char *path_begin, char *path_end,
+                            std::vector<std::string> &file_names) {
+  *path_end = '\0';
+  DIR *dir_ptr = opendir(path_begin);
 
   // Directory is a file, return the directory name
   if (dir_ptr == nullptr) {
     if (errno == ENOTDIR || errno == ENOENT) {
-      return {directory};
+      file_names.emplace_back(path_begin);
+      return;
     }
 
-    return {};
+    return;
   }
 
   dirent *entity_ptr;
   while ((entity_ptr = readdir(dir_ptr)) != nullptr) {
     const char *entity_name = static_cast<const char *>(entity_ptr->d_name);
+    const size_t entity_name_size = strlen(entity_name);
 
     // Skip . and ..
     if (strcmp(entity_name, ".") == 0) {
@@ -40,17 +61,20 @@ std::vector<FileName> list_files(const DirectoryName &directory) {
       continue;
     }
 
-    // Try recursing
-    auto sub_files = list_files(directory + '/' + entity_name);
+    // Copy the entity to the end of the current path and recurse.
+    assert(path_end - path_begin + entity_name_size + 2 < filename_max &&
+           "Filename is too big for filename buffer!");
 
-    for (auto &sub_file : sub_files) {
-      file_names.emplace_back(std::move(sub_file));
-    }
+    *path_end = '/';
+
+    auto new_entity_start = std::next(path_end);
+    std::copy_n(entity_name, entity_name_size, new_entity_start);
+    auto new_entity_end = std::next(new_entity_start, entity_name_size);
+
+    list_files_impl(path_begin, new_entity_end, file_names);
   }
 
   closedir(dir_ptr);
-
-  return file_names;
 }
 
 namespace {

src/megadep/filesystem.hpp

 #ifndef MEGADEP_FILESYSTEM_HPP
 #define MEGADEP_FILESYSTEM_HPP
 
-#include <megadep/common_types.hpp>
-
 #include <string>
 #include <string_view>
 #include <vector>
@@ -11,7 +9,7 @@
 
 namespace megadep {
 
-std::vector<FileName> list_files(const DirectoryName &directory);
+std::vector<std::string> list_files(std::string_view directory);
 
 std::vector<std::string> read_includes(std::string_view file_name);