UX: Readfile: Libraries error messages: avoid wall of warnings.

When a lot of libraries or linked IDs were missing/not found when
loading a .blend file, Blender used to show one warning report for each
missing item, potentially covering the user's screen with a giant
unuable popup.

Now it will instead generate a single warning with amount of missing lib
files and linked IDs. Each missing item is still reported individually,
but only as `INFO`, so it will still show up in the console or Info editor.

2 files changed, 20 insertions, 2 deletions

diff --git a/source/blender/blenloader/intern/readfile.c b/source/blender/blenloader/intern/readfile.c
index bea05699579..dd855ebae0b 100644
--- a/source/blender/blenloader/intern/readfile.c
+++ b/source/blender/blenloader/intern/readfile.c
@@ -5273,12 +5273,13 @@ static void read_library_linked_id(
   }
   else {
     BLO_reportf_wrap(reports,
-                     RPT_WARNING,
+                     RPT_INFO,
                      TIP_("LIB: %s: '%s' missing from '%s', parent '%s'"),
                      BKE_idtype_idcode_to_name(GS(id->name)),
                      id->name + 2,
                      mainvar->curlib->filepath_abs,
                      library_parent_filepath(mainvar->curlib));
+    fd->library_id_missing_count++;
 
     /* Generate a placeholder for this ID (simplified version of read_libblock actually...). */
     if (r_id) {
@@ -5432,7 +5433,8 @@ static FileData *read_library_file_data(FileData *basefd,
 
   if (fd == NULL) {
     BLO_reportf_wrap(
-        basefd->reports, RPT_WARNING, TIP_("Cannot find lib '%s'"), mainptr->curlib->filepath_abs);
+        basefd->reports, RPT_INFO, TIP_("Cannot find lib '%s'"), mainptr->curlib->filepath_abs);
+    fd->library_file_missing_count++;
   }
 
   return fd;
@@ -5481,6 +5483,9 @@ static void read_libraries(FileData *basefd, ListBase *mainlist)
         /* Test if linked data-locks need to read further linked data-locks
          * and create link placeholders for them. */
         BLO_expand_main(fd, mainptr);
+
+        basefd->library_file_missing_count += fd->library_file_missing_count;
+        basefd->library_id_missing_count += fd->library_id_missing_count;
       }
     }
   }
@@ -5526,6 +5531,15 @@ static void read_libraries(FileData *basefd, ListBase *mainlist)
     mainptr->curlib->filedata = NULL;
   }
   BKE_main_free(main_newid);
+
+  if (basefd->library_file_missing_count != 0 || basefd->library_id_missing_count != 0) {
+    BKE_reportf(basefd->reports,
+                RPT_WARNING,
+                "LIB: %d libraries and %d linked data-blocks are missing, please check the "
+                "Info and Outliner editors for details",
+                basefd->library_file_missing_count,
+                basefd->library_id_missing_count);
+  }
 }
 
 void *BLO_read_get_new_data_address(BlendDataReader *reader, const void *old_address)
diff --git a/source/blender/blenloader/intern/readfile.h b/source/blender/blenloader/intern/readfile.h
index 425932498f1..b81d8bd9a2b 100644
--- a/source/blender/blenloader/intern/readfile.h
+++ b/source/blender/blenloader/intern/readfile.h
@@ -138,6 +138,10 @@ typedef struct FileData {
   struct IDNameLib_Map *old_idmap;
 
   struct ReportList *reports;
+  /* Counters for amount of missing libraries, and missing IDs in libraries.
+   * Used to generate a synthetic report in the UI. */
+  int library_file_missing_count;
+  int library_id_missing_count;
 } FileData;
 
 #define SIZEOFBLENDERHEADER 12