Refactor ScanDirectoryTreeAndCallback to separate errors and retvals

ScanDirectoryTreeAndCallback, before this change, coupled error/return
codes and actual return values (number of entries found). This caused
confusion and difficulty interpreting the precise way the function
worked.

Supersedes, and closes #1255.

3 files changed, 62 insertions, 57 deletions

diff --git a/src/citra_qt/game_list.cpp b/src/citra_qt/game_list.cpp
index e925f08a7..1f8d69a03 100644
--- a/src/citra_qt/game_list.cpp
+++ b/src/citra_qt/game_list.cpp
@@ -119,13 +119,14 @@ void GameList::LoadInterfaceLayout(QSettings& settings)
 
 void GameListWorker::AddFstEntriesToGameList(const std::string& dir_path, bool deep_scan)
 {
-    const auto callback = [&](const std::string& directory,
-                                     const std::string& virtual_name) -> int {
+    const auto callback = [&](unsigned* num_entries_out,
+                              const std::string& directory,
+                              const std::string& virtual_name) -> bool {
 
         std::string physical_name = directory + DIR_SEP + virtual_name;
 
         if (stop_processing)
-            return -1; // A negative return value breaks the callback loop.
+            return false; // Breaks the callback loop.
 
         if (deep_scan && FileUtil::IsDirectory(physical_name)) {
             AddFstEntriesToGameList(physical_name, true);
@@ -135,11 +136,11 @@ void GameListWorker::AddFstEntriesToGameList(const std::string& dir_path, bool d
 
             Loader::FileType guessed_filetype = Loader::GuessFromExtension(filename_extension);
             if (guessed_filetype == Loader::FileType::Unknown)
-                return 0;
+                return true;
             Loader::FileType filetype = Loader::IdentifyFile(physical_name);
             if (filetype == Loader::FileType::Unknown) {
                 LOG_WARNING(Frontend, "File %s is of indeterminate type and is possibly corrupted.", physical_name.c_str());
-                return 0;
+                return true;
             }
             if (guessed_filetype != filetype) {
                 LOG_WARNING(Frontend, "Filetype and extension of file %s do not match.", physical_name.c_str());
@@ -152,9 +153,10 @@ void GameListWorker::AddFstEntriesToGameList(const std::string& dir_path, bool d
             });
         }
 
-        return 0; // We don't care about the found entries
+        return true;
     };
-    FileUtil::ScanDirectoryTreeAndCallback(dir_path, callback);
+
+    FileUtil::ForeachDirectoryEntry(nullptr, dir_path, callback);
 }
 
 void GameListWorker::run()
diff --git a/src/common/file_util.cpp b/src/common/file_util.cpp
index 1e0d33313..4c7113390 100644
--- a/src/common/file_util.cpp
+++ b/src/common/file_util.cpp
@@ -420,11 +420,13 @@ bool CreateEmptyFile(const std::string &filename)
 }
 
 
-int ScanDirectoryTreeAndCallback(const std::string &directory, std::function<int(const std::string&, const std::string&)> callback)
+bool ForeachDirectoryEntry(unsigned* num_entries_out, const std::string &directory, DirectoryEntryCallable callback)
 {
     LOG_TRACE(Common_Filesystem, "directory %s", directory.c_str());
+
     // How many files + directories we found
-    int found_entries = 0;
+    unsigned found_entries = 0;
+
 #ifdef _WIN32
     // Find the first file in the directory.
     WIN32_FIND_DATA ffd;
@@ -432,7 +434,7 @@ int ScanDirectoryTreeAndCallback(const std::string &directory, std::function<int
     HANDLE handle_find = FindFirstFile(Common::UTF8ToTStr(directory + "\\*").c_str(), &ffd);
     if (handle_find == INVALID_HANDLE_VALUE) {
         FindClose(handle_find);
-        return found_entries;
+        return false;
     }
     // windows loop
     do {
@@ -442,25 +444,20 @@ int ScanDirectoryTreeAndCallback(const std::string &directory, std::function<int
 
     DIR *dirp = opendir(directory.c_str());
     if (!dirp)
-        return 0;
+        return false;
 
     // non windows loop
     while (!readdir_r(dirp, &dirent, &result) && result) {
         const std::string virtual_name(result->d_name);
 #endif
-        // check for "." and ".."
-        if (((virtual_name[0] == '.') && (virtual_name[1] == '\0')) ||
-                ((virtual_name[0] == '.') && (virtual_name[1] == '.') &&
-                 (virtual_name[2] == '\0')))
+
+        if (virtual_name == "." || virtual_name == "..")
             continue;
 
-        int ret = callback(directory, virtual_name);
-        if (ret < 0) {
-            if (ret != -1)
-                found_entries = ret;
+        unsigned ret_entries;
+        if (!callback(&ret_entries, directory, virtual_name))
             break;
-        }
-        found_entries += ret;
+        found_entries += ret_entries;
 
 #ifdef _WIN32
     } while (FindNextFile(handle_find, &ffd) != 0);
@@ -469,16 +466,18 @@ int ScanDirectoryTreeAndCallback(const std::string &directory, std::function<int
     }
     closedir(dirp);
 #endif
-    // Return number of entries found.
-    return found_entries;
+
+    // num_entries_out is allowed to be specified nullptr, in which case we shouldn't try to set it
+    if (num_entries_out != nullptr)
+        *num_entries_out = found_entries;
 }
 
-int ScanDirectoryTree(const std::string &directory, FSTEntry& parent_entry)
+unsigned ScanDirectoryTree(const std::string &directory, FSTEntry& parent_entry)
 {
-    const auto callback = [&parent_entry](const std::string& directory,
-                                          const std::string& virtual_name) -> int {
+    const auto callback = [&parent_entry](unsigned* num_entries_out,
+                                          const std::string& directory,
+                                          const std::string& virtual_name) -> bool {
         FSTEntry entry;
-        int found_entries = 0;
         entry.virtualName = virtual_name;
         entry.physicalName = directory + DIR_SEP + virtual_name;
 
@@ -486,41 +485,40 @@ int ScanDirectoryTree(const std::string &directory, FSTEntry& parent_entry)
             entry.isDirectory = true;
             // is a directory, lets go inside
             entry.size = ScanDirectoryTree(entry.physicalName, entry);
-            found_entries += (int)entry.size;
+            *num_entries_out += (int)entry.size;
         } else { // is a file
             entry.isDirectory = false;
             entry.size = GetSize(entry.physicalName);
         }
-        ++found_entries;
+        (*num_entries_out)++;
+
         // Push into the tree
         parent_entry.children.push_back(entry);
-        return found_entries;
+        return true;
     };
 
-    return ScanDirectoryTreeAndCallback(directory, callback);
+    unsigned num_entries;
+    return ForeachDirectoryEntry(&num_entries, directory, callback) ? num_entries : 0;
 }
 
 
 bool DeleteDirRecursively(const std::string &directory)
 {
-    const static auto callback = [](const std::string& directory,
-                                    const std::string& virtual_name) -> int {
+    const static auto callback = [](unsigned* num_entries_out,
+                                    const std::string& directory,
+                                    const std::string& virtual_name) -> bool {
         std::string new_path = directory + DIR_SEP_CHR + virtual_name;
-        if (IsDirectory(new_path)) {
-            if (!DeleteDirRecursively(new_path)) {
-                return -2;
-            }
-        } else if (!Delete(new_path)) {
-            return -2;
-        }
-        return 0;
+        if (IsDirectory(new_path))
+            return DeleteDirRecursively(new_path);
+
+        return Delete(new_path);
     };
 
-    if (ScanDirectoryTreeAndCallback(directory, callback) == -2) {
+    if (!ForeachDirectoryEntry(nullptr, directory, callback))
         return false;
-    }
-    FileUtil::DeleteDir(directory);
 
+    // Delete the outermost directory
+    FileUtil::DeleteDir(directory);
     return true;
 }
 
diff --git a/src/common/file_util.h b/src/common/file_util.h
index 3d617f573..a85121aa6 100644
--- a/src/common/file_util.h
+++ b/src/common/file_util.h
@@ -98,19 +98,24 @@ bool Copy(const std::string &srcFilename, const std::string &destFilename);
 bool CreateEmptyFile(const std::string &filename);
 
 /**
- * Scans the directory tree, calling the callback for each file/directory found.
- * The callback must return the number of files and directories which the provided path contains.
- * If the callback's return value is -1, the callback loop is broken immediately.
- * If the callback's return value is otherwise negative, the callback loop is broken immediately
- * and the callback's return value is returned from this function (to allow for error handling).
- * @param directory the parent directory to start scanning from
- * @param callback The callback which will be called for each file/directory. It is called
- *     with the arguments (const std::string& directory, const std::string& virtual_name).
- *     The `directory `parameter is the path to the directory which contains the file/directory.
- *     The `virtual_name` parameter is the incomplete file path, without any directory info.
- * @return the total number of files/directories found
+ * @param num_entries_out to be assigned by the callable with the number of iterated directory entries, never null
+ * @param directory the path to the enclosing directory
+ * @param virtual_name the entry name, without any preceding directory info
+ * @return whether handling the entry succeeded
+ */
+using DirectoryEntryCallable = std::function<bool(unsigned* num_entries_out,
+                                                 const std::string& directory,
+                                                 const std::string& virtual_name)>;
+
+/**
+ * Scans a directory, calling the callback for each file/directory contained within.
+ * If the callback returns failure, scanning halts and this function returns failure as well
+ * @param num_entries_out assigned by the function with the number of iterated directory entries, can be null
+ * @param directory the directory to scan
+ * @param callback The callback which will be called for each entry
+ * @return whether scanning the directory succeeded
  */
-int ScanDirectoryTreeAndCallback(const std::string &directory, std::function<int(const std::string&, const std::string&)> callback);
+bool ForeachDirectoryEntry(unsigned* num_entries_out, const std::string &directory, DirectoryEntryCallable callback);
 
 /**
  * Scans the directory tree, storing the results.
@@ -118,7 +123,7 @@ int ScanDirectoryTreeAndCallback(const std::string &directory, std::function<int
  * @param parent_entry FSTEntry where the filesystem tree results will be stored.
  * @return the total number of files/directories found
  */
-int ScanDirectoryTree(const std::string &directory, FSTEntry& parent_entry);
+unsigned ScanDirectoryTree(const std::string &directory, FSTEntry& parent_entry);
 
 // deletes the given directory and anything under it. Returns true on success.
 bool DeleteDirRecursively(const std::string &directory);