Fix #112423: Recover Autosave breaks library paths.

Trying to 'recover' a normal (non-auto-saved) blendfile would break any
relative paths.

Caused by 88b24bc6bb, it looks like this commit did not take into
account readfile side of the code?

Pull Request: https://projects.blender.org/blender/blender/pulls/115048

source/blender/blenkernel/intern/blendfile.cc

@@ -900,7 +900,8 @@ static void setup_app_data(bContext *C,
     bmain->filepath[0] = '\0';
   }
   else if (recover) {
-    /* In case of auto-save or quit.blend, use original filepath instead. */
+    /* In case of auto-save or quit.blend, use original filepath instead (see also #read_global in
+     * `readfile.cc`). */
     bmain->recovered = true;
     STRNCPY(bmain->filepath, bfd->filepath);
   }

source/blender/blenloader/BLO_readfile.h

@@ -57,6 +57,11 @@ typedef struct BlendFileData {
 
   int fileflags;
   int globalf;
+  /** Typically the actual filepath of the read blendfile, except when recovering
+   * save-on-exit/autosave files. In the latter case, it will be the path of the file that
+   * generated the auto-saved one being recovered.
+   *
+   * NOTE: Currently expected to be the same path as #BlendFileData.filepath. */
   char filepath[1024]; /* 1024 = FILE_MAX */
 
   /** TODO: think this isn't needed anymore? */

source/blender/blenloader/intern/readfile.cc

@@ -3109,25 +3109,21 @@ static BHead *read_global(BlendFileData *bfd, FileData *fd, BHead *bhead)
 
   bfd->fileflags = fg->fileflags;
   bfd->globalf = fg->globalf;
-  STRNCPY(bfd->filepath, fg->filepath);
-
-  /* Error in 2.65 and older: `main->filepath` was not set if you save from startup
-   * (not after loading file). */
-  if (bfd->filepath[0] == 0) {
-    if (fd->fileversion < 265 || (fd->fileversion == 265 && fg->subversion < 1)) {
-      if ((G.fileflags & G_FILE_RECOVER_READ) == 0) {
-        STRNCPY(bfd->filepath, BKE_main_blendfile_path(bfd->main));
-      }
-    }
-
-    /* early 2.50 version patch - filepath not in FileGlobal struct at all */
-    if (fd->fileversion <= 250) {
-      STRNCPY(bfd->filepath, BKE_main_blendfile_path(bfd->main));
-    }
-  }
 
+  /* Note: since 88b24bc6bb, `fg->filepath` is only written for crash recovery and autosave files,
+   * so only overwrite `fd->relabase` if it is not empty, in case a regular blendfile is opened
+   * through one of the 'recover' operators.
+   *
+   * In all other cases, the path is just set to the current path of the blendfile being read, so
+   * there is no need to handle anymore older files (pre-2.65) that did not store (correctly) their
+   * path. */
   if (G.fileflags & G_FILE_RECOVER_READ) {
-    STRNCPY(fd->relabase, fg->filepath);
+    if (fg->filepath[0] != '\0') {
+      STRNCPY(fd->relabase, fg->filepath);
+      /* Used to set expected original filepath in read Main, instead of the path of the recovery
+       * file itself. */
+      STRNCPY(bfd->filepath, fg->filepath);
+    }
   }
 
   bfd->curscreen = fg->curscreen;
@@ -3589,6 +3585,7 @@ BlendFileData *blo_read_file_internal(FileData *fd, const char *filepath)
 
   bfd->main = BKE_main_new();
   bfd->main->versionfile = fd->fileversion;
+  STRNCPY(bfd->filepath, filepath);
 
   bfd->type = BLENFILETYPE_BLEND;
 

source/blender/blenloader/intern/readfile.hh

@@ -65,7 +65,13 @@ struct FileData {
    * to detect unchanged data from memfile. */
   int undo_direction; /* eUndoStepDir */
 
-  /** Now only in use for library appending. */
+  /** Used for relative paths handling.
+   *
+   * Typically the actual filepath of the read blendfile, except when recovering
+   * save-on-exit/autosave files. In the latter case, it will be the path of the file that
+   * generated the auto-saved one being recovered.
+   *
+   * NOTE: Currently expected to be the same path as #BlendFileData.filepath. */
   char relabase[FILE_MAX];
 
   /** General reading variables. */