First step to handle missing libs/datablocks when reading a file.

Idea is, instead of ignoring completely missing linked datablocks, to
create void placeholders for them.

That way, you can work on your file, save it, and find again your missing data once
lib becomes available again. Or you can edit missing lib's path (in Outliner),
save and reload the file, and you are done.

Also, Outliner now shows broken libraries (and placeholders) with a 'broken lib' icon.

Future plans are also to be able to relocate missing libs and reload them at runtime.

Code notes:
    - Placeholder ID is just a regular datablock of same type as expected linked one,
      with 'default' data, and a LIB_MISSING bitflag set.
    - To allow creation of such datablocks, creation of datablocks in BKE was split in two step:
        + Allocation of memory itself.
        + Setting of all internal data to default values.

See also the design task (T43351).

Reviewed by @campbellbarton, thanks a bunch!

Differential Revision: https://developer.blender.org/D1394

1 files changed, 67 insertions, 33 deletions

diff --git a/source/blender/blenloader/intern/readfile.c b/source/blender/blenloader/intern/readfile.c
index 2e7969637a3..6545a3b0e67 100644
--- a/source/blender/blenloader/intern/readfile.c
+++ b/source/blender/blenloader/intern/readfile.c
@@ -7937,7 +7937,7 @@ static BHead *read_libblock(FileData *fd, Main *main, BHead *bhead, int flag, ID
 	if (id->flag & LIB_FAKEUSER) id->us= 1;
 	else id->us = 0;
 	id->icon_id = 0;
-	id->flag &= ~(LIB_ID_RECALC|LIB_ID_RECALC_DATA|LIB_DOIT);
+	id->flag &= ~(LIB_ID_RECALC | LIB_ID_RECALC_DATA | LIB_DOIT | LIB_MISSING);
 	
 	/* this case cannot be direct_linked: it's just the ID part */
 	if (bhead->code == ID_ID) {
@@ -9615,6 +9615,25 @@ static void give_base_to_groups(
 	}
 }
 
+static ID *create_placeholder(Main *mainvar, const char *idname, const short flag)
+{
+	const short idcode = GS(idname);
+	ListBase *lb = which_libbase(mainvar, idcode);
+	ID *ph_id = BKE_libblock_alloc_notest(idcode);
+
+	memcpy(ph_id->name, idname, sizeof(ph_id->name));
+	BKE_libblock_init_empty(ph_id);
+	ph_id->lib = mainvar->curlib;
+	ph_id->flag = flag | LIB_MISSING;
+	ph_id->us = (flag & LIB_FAKEUSER) ? 1 : 0;
+	ph_id->icon_id = 0;
+
+	BLI_addtail(lb, ph_id);
+	id_sort_by_name(lb, ph_id);
+
+	return ph_id;
+}
+
 /* returns true if the item was found
  * but it may already have already been appended/linked */
 static ID *link_named_part(Main *mainl, FileData *fd, const short idcode, const char *name)
@@ -9758,16 +9777,35 @@ ID *BLO_library_link_named_part_ex(
 	return link_named_part_ex(mainl, fd, idcode, name, flag, scene, v3d);
 }
 
-static void link_id_part(FileData *fd, Main *mainvar, ID *id, ID **r_id)
+static void link_id_part(ReportList *reports, FileData *fd, Main *mainvar, ID *id, ID **r_id)
 {
-	BHead *bhead = find_bhead_from_idname(fd, id->name);
+	BHead *bhead = NULL;
+
+	if (fd) {
+		bhead = find_bhead_from_idname(fd, id->name);
+	}
+
+	id->flag &= ~LIB_READ;
 
 	if (bhead) {
-		id->flag &= ~LIB_READ;
 		id->flag |= LIB_NEED_EXPAND;
 		// printf("read lib block %s\n", id->name);
 		read_libblock(fd, mainvar, bhead, id->flag, r_id);
 	}
+	else {
+		blo_reportf_wrap(
+		        reports, RPT_WARNING,
+		        TIP_("LIB ERROR: %s: '%s' missing from '%s', parent '%s'"),
+		        BKE_idcode_to_name(GS(id->name)),
+		        id->name + 2,
+		        mainvar->curlib->filepath,
+		        library_parent_filepath(mainvar->curlib));
+
+		/* Generate a placeholder for this ID (simplified version of read_libblock actually...). */
+		if (r_id) {
+			*r_id = create_placeholder(mainvar, id->name, id->flag);
+		}
+	}
 }
 
 /* common routine to append/link something from a library */
@@ -10012,6 +10050,7 @@ static void read_libraries(FileData *basefd, ListBase *mainlist)
 					}
 					else {
 						mainptr->curlib->filedata = NULL;
+						mainptr->curlib->id.flag |= LIB_MISSING;
 					}
 					
 					if (fd == NULL) {
@@ -10021,37 +10060,29 @@ static void read_libraries(FileData *basefd, ListBase *mainlist)
 				}
 				if (fd) {
 					do_it = true;
-					a = set_listbasepointers(mainptr, lbarray);
-					while (a--) {
-						ID *id = lbarray[a]->first;
-						
-						while (id) {
-							ID *idn = id->next;
-							if (id->flag & LIB_READ) {
-								ID *realid = NULL;
-								BLI_remlink(lbarray[a], id);
-								
-								link_id_part(fd, mainptr, id, &realid);
-								if (!realid) {
-									blo_reportf_wrap(
-									        fd->reports, RPT_WARNING,
-									        TIP_("LIB ERROR: %s: '%s' missing from '%s', parent '%s'"),
-									        BKE_idcode_to_name(GS(id->name)),
-									        id->name + 2,
-									        mainptr->curlib->filepath,
-									        library_parent_filepath(mainptr->curlib));
-								}
-								
-								change_idid_adr(mainlist, basefd, id, realid);
-								
-								MEM_freeN(id);
-							}
-							id = idn;
+				}
+				a = set_listbasepointers(mainptr, lbarray);
+				while (a--) {
+					ID *id = lbarray[a]->first;
+
+					while (id) {
+						ID *idn = id->next;
+						if (id->flag & LIB_READ) {
+							ID *realid = NULL;
+							BLI_remlink(lbarray[a], id);
+
+							link_id_part(basefd->reports, fd, mainptr, id, &realid);
+
+							BLI_assert(realid != NULL);
+
+							change_idid_adr(mainlist, basefd, id, realid);
+
+							MEM_freeN(id);
 						}
+						id = idn;
 					}
-					
-					BLO_expand_main(fd, mainptr);
 				}
+				BLO_expand_main(fd, mainptr);
 			}
 			
 			mainptr = mainptr->next;
@@ -10059,6 +10090,7 @@ static void read_libraries(FileData *basefd, ListBase *mainlist)
 	}
 	
 	/* test if there are unread libblocks */
+	/* XXX This code block is kept for 2.77, until we are sure it never gets reached anymore. Can be removed later. */
 	for (mainptr = mainl->next; mainptr; mainptr = mainptr->next) {
 		a = set_listbasepointers(mainptr, lbarray);
 		while (a--) {
@@ -10067,10 +10099,12 @@ static void read_libraries(FileData *basefd, ListBase *mainlist)
 			for (id = lbarray[a]->first; id; id = idn) {
 				idn = id->next;
 				if (id->flag & LIB_READ) {
+					BLI_assert(0);
 					BLI_remlink(lbarray[a], id);
 					blo_reportf_wrap(
 					        basefd->reports, RPT_WARNING,
-					        TIP_("LIB ERROR: %s: '%s' unread lib block missing from '%s', parent '%s'"),
+					        TIP_("LIB ERROR: %s: '%s' unread lib block missing from '%s', parent '%s' - "
+					             "Please file a bug report if you see this message"),
 					        BKE_idcode_to_name(GS(id->name)),
 					        id->name + 2,
 					        mainptr->curlib->filepath,