Fix: Incorrects filepaths on drag and drop with recursive option enabled

Currently drag and drop expects to selection to be in the same folder,
but blender internal file browser allows to select files from different
folders when recursion is active.

When writing to operator properties the `directory` is taken now from
the first file provided, and `files` are now relative to this
`directory` instead of just taking the file name.
When reading from operator properties filepaths are normalized.

I notice this issue while reading about #140942, the issue would
require a proper fix too.

Pull Request: https://projects.blender.org/blender/blender/pulls/140948

source/blender/editors/include/ED_fileselect.hh

@@ -8,6 +8,10 @@
 
 #pragma once
 
+#include <string>
+
+#include "BLI_vector.hh"
+
 #include "DNA_uuid_types.h"
 
 struct ARegion;
@@ -203,6 +207,8 @@ ScrArea *ED_fileselect_handler_area_find_any_with_op(const wmWindow *win);
  */
 void ED_fileselect_ensure_default_filepath(bContext *C, wmOperator *op, const char *extension);
 
+blender::Vector<std::string> ED_fileselect_selected_files_full_paths(const SpaceFile *sfile);
+
 /* TODO: Maybe we should move this to BLI?
  * On the other hand, it's using defines from space-file area, so not sure... */
 int ED_path_extension_type(const char *path);

source/blender/editors/io/io_drop_import_file.cc

@@ -3,6 +3,7 @@
  * SPDX-License-Identifier: GPL-2.0-or-later */
 
 #include "BLI_path_utils.hh"
+#include "BLI_string.h"
 
 #include "BLT_translation.hh"
 
@@ -60,9 +61,9 @@ static void file_handler_import_operator_write_ptr(
   }
 
   PropertyRNA *directory_prop = RNA_struct_find_property_check(props, "directory", PROP_STRING);
+  char dir[FILE_MAX];
+  BLI_path_split_dir_part(paths[0].c_str(), dir, sizeof(dir));
   if (directory_prop) {
-    char dir[FILE_MAX];
-    BLI_path_split_dir_part(paths[0].c_str(), dir, sizeof(dir));
     RNA_property_string_set(&props, directory_prop, dir);
   }
 
@@ -72,7 +73,8 @@ static void file_handler_import_operator_write_ptr(
     RNA_property_collection_clear(&props, files_prop);
     for (const auto &index : supported_paths) {
       char file[FILE_MAX];
-      BLI_path_split_file_part(paths[index].c_str(), file, sizeof(file));
+      STRNCPY(file, paths[index].c_str());
+      BLI_path_rel(file, dir);
 
       PointerRNA item_ptr{};
       RNA_property_collection_add(&props, files_prop, &item_ptr);

source/blender/editors/io/io_utils.cc

@@ -5,6 +5,7 @@
 #include <fmt/format.h>
 
 #include "BLI_path_utils.hh"
+#include "BLI_string.h"
 
 #include "BLT_translation.hh"
 
@@ -96,6 +97,7 @@ Vector<std::string> paths_from_operator_properties(PointerRNA *ptr)
       RNA_string_get(&file_ptr, "name", name);
       char path[FILE_MAX];
       BLI_path_join(path, sizeof(path), directory, name);
+      BLI_path_normalize(path);
       paths.append_non_duplicates(path);
     }
     RNA_PROP_END;
@@ -121,7 +123,8 @@ void paths_to_operator_properties(PointerRNA *ptr, const Span<std::string> paths
   RNA_collection_clear(ptr, "files");
   for (const auto &path : paths) {
     char file[FILE_MAX];
-    BLI_path_split_file_part(path.c_str(), file, sizeof(file));
+    STRNCPY(file, path.c_str());
+    BLI_path_rel(file, dir);
 
     PointerRNA itemptr{};
     RNA_collection_add(ptr, "files", &itemptr);

source/blender/editors/space_file/filesel.cc

@@ -1502,3 +1502,17 @@ void ED_fileselect_ensure_default_filepath(bContext *C, wmOperator *op, const ch
     RNA_string_set(op->ptr, "filepath", filepath);
   }
 }
+
+blender::Vector<std::string> ED_fileselect_selected_files_full_paths(const SpaceFile *sfile)
+{
+  blender::Vector<std::string> paths;
+  char path[FILE_MAX_LIBEXTRA];
+  for (const int i : blender::IndexRange(filelist_files_ensure(sfile->files))) {
+    if (filelist_entry_is_selected(sfile->files, i)) {
+      const FileDirEntry *entry = filelist_file(sfile->files, i);
+      filelist_file_get_full_path(sfile->files, entry, path);
+      paths.append(path);
+    }
+  }
+  return paths;
+}

source/blender/windowmanager/intern/wm_dragdrop.cc

@@ -21,7 +21,6 @@
 
 #include "BLT_translation.hh"
 
-#include "BLI_linear_allocator.hh"
 #include "BLI_listbase.h"
 #include "BLI_math_color.h"
 #include "BLI_path_utils.hh"
@@ -365,21 +364,15 @@ void WM_event_drag_image(wmDrag *drag, const ImBuf *imb, float scale)
 void WM_event_drag_path_override_poin_data_with_space_file_paths(const bContext *C, wmDrag *drag)
 {
   BLI_assert(drag->type == WM_DRAG_PATH);
-  if (!CTX_wm_space_file(C)) {
+  const SpaceFile *sfile = CTX_wm_space_file(C);
+  if (!sfile) {
     return;
   }
-  char dirpath[FILE_MAX];
-  BLI_path_split_dir_part(WM_drag_get_single_path(drag), dirpath, FILE_MAX);
-
-  blender::LinearAllocator<> allocator;
+  const blender::Vector<std::string> selected_paths = ED_fileselect_selected_files_full_paths(
+      sfile);
   blender::Vector<const char *> paths;
-  const blender::Vector<PointerRNA> files = CTX_data_collection_get(C, "selected_files");
-  for (const PointerRNA &file_ptr : files) {
-    const FileDirEntry *file = static_cast<const FileDirEntry *>(file_ptr.data);
-    char filepath[FILE_MAX];
-    BLI_path_join(filepath, sizeof(filepath), dirpath, file->name);
-
-    paths.append(allocator.copy_string(filepath).c_str());
+  for (const std::string &path : selected_paths) {
+    paths.append(path.c_str());
   }
   if (paths.is_empty()) {
     return;