ID-Remap - Step one: core work (cleanup and rework of generic ID datablock handling).

This commit changes a lot of how IDs are handled internally, especially the unlinking/freeing
processes. So far, this was very fuzy, to summarize cleanly deleting or replacing a datablock
was pretty much impossible, except for a few special cases.

Also, unlinking was handled by each datatype, in a rather messy and prone-to-errors way (quite
a few ID usages were missed or wrongly handled that way).

One of the main goal of id-remap branch was to cleanup this, and fatorize ID links handling
by using library_query utils to allow generic handling of those, which is now the case
(now, generic ID links handling is only "knwon" from readfile.c and library_query.c).

This commit also adds backends to allow live replacement and deletion of datablocks in Blender
(so-called 'remapping' process, where we replace all usages of a given ID pointer by a new one,
or NULL one in case of unlinking).

This will allow nice new features, like ability to easily reload or relocate libraries, real immediate
deletion of datablocks in blender, replacement of one datablock by another, etc.
Some of those are for next commits.

A word of warning: this commit is highly risky, because it affects potentially a lot in Blender core.
Though it was tested rather deeply, being totally impossible to check all possible ID usage cases,
it's likely there are some remaining issues and bugs in new code... Please report them! ;)

Review task: D2027 (https://developer.blender.org/D2027).
Reviewed by campbellbarton, thanks a bunch.

2 files changed, 37 insertions, 28 deletions

diff --git a/source/blender/editors/space_node/node_edit.c b/source/blender/editors/space_node/node_edit.c
index 6ae72e2a164..ffe510016ff 100644
--- a/source/blender/editors/space_node/node_edit.c
+++ b/source/blender/editors/space_node/node_edit.c
@@ -740,34 +740,6 @@ void ED_node_set_active(Main *bmain, bNodeTree *ntree, bNode *node)
 	}
 }
 
-void ED_node_id_unref(SpaceNode *snode, const ID *id)
-{
-	if (GS(id->name) == ID_SCE) {
-		if (snode->id == id) {
-			/* nasty DNA logic for SpaceNode:
-			 * ideally should be handled by editor code, but would be bad level call
-			 */
-			bNodeTreePath *path, *path_next;
-			for (path = snode->treepath.first; path; path = path_next) {
-				path_next = path->next;
-				MEM_freeN(path);
-			}
-			BLI_listbase_clear(&snode->treepath);
-
-			snode->id = NULL;
-			snode->from = NULL;
-			snode->nodetree = NULL;
-			snode->edittree = NULL;
-		}
-	}
-	else if (GS(id->name) == ID_OB) {
-		if (snode->from == id) {
-			snode->flag &= ~SNODE_PIN;
-			snode->from = NULL;
-		}
-	}
-}
-
 void ED_node_post_apply_transform(bContext *UNUSED(C), bNodeTree *UNUSED(ntree))
 {
 	/* XXX This does not work due to layout functions relying on node->block,
diff --git a/source/blender/editors/space_node/space_node.c b/source/blender/editors/space_node/space_node.c
index df484724fc5..4ef703c8994 100644
--- a/source/blender/editors/space_node/space_node.c
+++ b/source/blender/editors/space_node/space_node.c
@@ -28,6 +28,7 @@
  *  \ingroup spnode
  */
 
+#include "DNA_gpencil_types.h"
 #include "DNA_lamp_types.h"
 #include "DNA_material_types.h"
 #include "DNA_node_types.h"
@@ -821,6 +822,41 @@ static int node_context(const bContext *C, const char *member, bContextDataResul
 	return 0;
 }
 
+static void node_id_remap(ScrArea *UNUSED(sa), SpaceLink *slink, ID *old_id, ID *new_id)
+{
+	SpaceNode *snode = (SpaceNode *)slink;
+
+	if (GS(old_id->name) == ID_SCE) {
+		if (snode->id == old_id) {
+			/* nasty DNA logic for SpaceNode:
+			 * ideally should be handled by editor code, but would be bad level call
+			 */
+			BLI_freelistN(&snode->treepath);
+
+			/* XXX Untested in case new_id != NULL... */
+			snode->id = new_id;
+			snode->from = NULL;
+			snode->nodetree = NULL;
+			snode->edittree = NULL;
+		}
+	}
+	else if (GS(old_id->name) == ID_OB) {
+		if (snode->from == old_id) {
+			if (new_id == NULL) {
+				snode->flag &= ~SNODE_PIN;
+			}
+			snode->from = new_id;
+		}
+	}
+	else if (GS(old_id->name) == ID_GD) {
+		if ((ID *)snode->gpd == old_id) {
+			snode->gpd = (bGPdata *)new_id;
+			id_us_min(old_id);
+			id_us_plus(new_id);
+		}
+	}
+}
+
 /* only called once, from space/spacetypes.c */
 void ED_spacetype_node(void)
 {
@@ -840,6 +876,7 @@ void ED_spacetype_node(void)
 	st->refresh = node_area_refresh;
 	st->context = node_context;
 	st->dropboxes = node_dropboxes;
+	st->id_remap = node_id_remap;
 
 	/* regions: main window */
 	art = MEM_callocN(sizeof(ARegionType), "spacetype node region");