dialog: Fix save file chooser with xdg portal

This correctly sets the xdg portal fields for targeting a specific
new filename or existing file.

"current_name" sets the dialogs placeholder name.
"current_file" targets an existing file.
"current_folder" for when the target is a folder.

Author: ColinKinloch

src/dialog/unix/SDL_portaldialog.c

@@ -25,9 +25,11 @@
 
 #ifdef SDL_USE_LIBDBUS
 
+#include <libgen.h>
 #include <errno.h>
 #include <sys/types.h>
 #include <sys/wait.h>
+#include <sys/stat.h>
 #include <unistd.h>
 
 #define PORTAL_DESTINATION "org.freedesktop.portal.Desktop"
@@ -294,7 +296,12 @@ void SDL_Portal_ShowFileDialogWithProperties(SDL_FileDialogType type, SDL_Dialog
     bool allow_many = SDL_GetBooleanProperty(props, SDL_PROP_FILE_DIALOG_MANY_BOOLEAN, false);
     const char* default_location = SDL_GetStringProperty(props, SDL_PROP_FILE_DIALOG_LOCATION_STRING, NULL);
     const char* accept = SDL_GetStringProperty(props, SDL_PROP_FILE_DIALOG_ACCEPT_STRING, NULL);
+    char* location_name = NULL;
+    char* location_folder = NULL;
+    struct stat statbuf;
     bool open_folders = false;
+    bool save_file_existing = false;
+    bool save_file_new_named = false;
 
     switch (type) {
     case SDL_FILEDIALOG_OPENFILE:
@@ -305,6 +312,22 @@ void SDL_Portal_ShowFileDialogWithProperties(SDL_FileDialogType type, SDL_Dialog
     case SDL_FILEDIALOG_SAVEFILE:
         method = "SaveFile";
         method_title = SDL_GetStringProperty(props, SDL_PROP_FILE_DIALOG_TITLE_STRING, "Save File");
+        if (default_location) {
+            if (stat(default_location, &statbuf) == 0) {
+                save_file_existing = S_ISREG(statbuf.st_mode) || S_ISLNK(statbuf.st_mode);
+            } else if (errno == ENOENT) {
+                char *dirc = SDL_strdup(default_location);
+                location_folder = SDL_strdup(dirname(dirc));
+                SDL_free(dirc);
+                save_file_new_named = (stat(location_folder, &statbuf) == 0) && S_ISDIR(statbuf.st_mode);
+            }
+
+            if (save_file_existing || save_file_new_named) {
+                char *basec = SDL_strdup(default_location);
+                location_name = SDL_strdup(basename(basec));
+                SDL_free(basec);
+            }
+        }
         break;
 
     case SDL_FILEDIALOG_OPENFOLDER:
@@ -410,8 +433,26 @@ void SDL_Portal_ShowFileDialogWithProperties(SDL_FileDialogType type, SDL_Dialog
         DBus_AppendFilters(dbus, &options, filters, nfilters);
     }
     if (default_location) {
-        DBus_AppendByteArray(dbus, &options, "current_folder", default_location);
+        if (save_file_existing) {
+            SDL_LogDebug(SDL_LOG_CATEGORY_SYSTEM, "Create save dialog for existing file");
+            DBus_AppendByteArray(dbus, &options, "current_file", default_location);
+            /* Setting "current_name" should not be necessary however the kde-desktop-portal sets the filename without an extension.
+             * An alternative would be to match the extension to a filter and set "current_filter".
+             */
+            DBus_AppendStringOption(dbus, &options, "current_name", location_name);
+        } else if (save_file_new_named) {
+            SDL_LogDebug(SDL_LOG_CATEGORY_SYSTEM, "Create save dialog for new file");
+            DBus_AppendByteArray(dbus, &options, "current_folder", location_folder);
+            DBus_AppendStringOption(dbus, &options, "current_name", location_name);
+        } else {
+            SDL_LogDebug(SDL_LOG_CATEGORY_SYSTEM, "Create dialog at folder");
+            DBus_AppendByteArray(dbus, &options, "current_folder", default_location);
+        }
+
+        SDL_free(location_name);
+        SDL_free(location_folder);
     }
+
     if (accept) {
         DBus_AppendStringOption(dbus, &options, "accept_label", accept);
     }

test/testdialog.c

@@ -14,6 +14,9 @@
 #include <SDL3/SDL.h>
 #include <SDL3/SDL_main.h>
 #include <SDL3/SDL_test.h>
+#include <fcntl.h>
+#include <sys/stat.h>
+#include <unistd.h>
 
 const SDL_DialogFileFilter filters[] = {
     { "All files", "*" },
@@ -23,6 +26,8 @@ const SDL_DialogFileFilter filters[] = {
 };
 
 static void SDLCALL callback(void *userdata, const char * const *files, int filter) {
+    char **saved_path = userdata;
+
     if (files) {
         const char* filter_name = "(filter fetching unsupported)";
 
@@ -36,6 +41,12 @@ static void SDLCALL callback(void *userdata, const char * const *files, int filt
 
         SDL_Log("Filter used: '%s'", filter_name);
 
+        if (*files && saved_path) {
+            *saved_path = SDL_strdup(*files);
+            int32_t fd = open(*saved_path, O_RDWR | O_CREAT | O_TRUNC, S_IRWXU | S_IRWXG | S_IRWXO );
+            close(fd);
+        }
+
         while (*files) {
             SDL_Log("'%s'", *files);
             files++;
@@ -55,6 +66,7 @@ int main(int argc, char *argv[])
     const SDL_FRect open_folder_rect = { 370, 50, 220, 140 };
     int i;
     const char *initial_path = NULL;
+    char *saved_path = NULL;
 
     /* Initialize test framework */
     state = SDLTest_CommonCreateState(argv, 0);
@@ -116,7 +128,19 @@ int main(int argc, char *argv[])
                 } else if (SDL_PointInRectFloat(&p, &open_folder_rect)) {
                     SDL_ShowOpenFolderDialog(callback, NULL, w, initial_path, 1);
                 } else if (SDL_PointInRectFloat(&p, &save_file_rect)) {
-                    SDL_ShowSaveFileDialog(callback, NULL, w, filters, SDL_arraysize(filters), initial_path);
+                    const char *default_filename = "Untitled.index";
+                    const size_t save_path_total_length = SDL_strlen(initial_path) + SDL_strlen(default_filename) + 1;
+                    char *save_path;
+                    if (saved_path) {
+                        save_path = SDL_strdup(saved_path);
+                    } else {
+                        save_path = (char *)SDL_malloc(save_path_total_length);
+                        *save_path = '\0';
+                        SDL_strlcat(save_path, initial_path, save_path_total_length);
+                        SDL_strlcat(save_path, default_filename, save_path_total_length);
+                    }
+                    SDL_ShowSaveFileDialog(callback, &saved_path, w, filters, SDL_arraysize(filters), save_path);
+                    SDL_free(save_path);
                 }
             }
         }