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, 57 insertions, 31 deletions

diff --git a/source/blender/editors/space_buttons/buttons_context.c b/source/blender/editors/space_buttons/buttons_context.c
index 42e2d6b90f0..5b03bdd7761 100644
--- a/source/blender/editors/space_buttons/buttons_context.c
+++ b/source/blender/editors/space_buttons/buttons_context.c
@@ -1180,33 +1180,3 @@ ID *buttons_context_id_path(const bContext *C)
 
 	return NULL;
 }
-
-void ED_buttons_id_unref(SpaceButs *sbuts, const ID *id)
-{
-	if (sbuts->pinid == id) {
-		sbuts->pinid = NULL;
-		sbuts->flag &= ~SB_PIN_CONTEXT;
-	}
-
-	if (sbuts->path) {
-		ButsContextPath *path = sbuts->path;
-		int i;
-
-		for (i = 0; i < path->len; i++) {
-			if (path->ptr[i].id.data == id) {
-				break;
-			}
-		}
-
-		if (i == path->len) {
-			/* pass */
-		}
-		else if (i == 0) {
-			MEM_SAFE_FREE(sbuts->path);
-		}
-		else {
-			memset(&path->ptr[i], 0, sizeof(path->ptr[i]) * (path->len - i));
-			path->len = i;
-		}
-	}
-}
diff --git a/source/blender/editors/space_buttons/space_buttons.c b/source/blender/editors/space_buttons/space_buttons.c
index 126a27c36cb..e4c23ad74f8 100644
--- a/source/blender/editors/space_buttons/space_buttons.c
+++ b/source/blender/editors/space_buttons/space_buttons.c
@@ -45,6 +45,8 @@
 #include "WM_api.h"
 #include "WM_types.h"
 
+#include "RNA_access.h"
+
 #include "buttons_intern.h"  /* own include */
 
 /* ******************** default callbacks for buttons space ***************** */
@@ -389,6 +391,59 @@ static void buttons_area_listener(bScreen *UNUSED(sc), ScrArea *sa, wmNotifier *
 		ED_area_tag_redraw(sa);
 }
 
+static void buttons_id_remap(ScrArea *UNUSED(sa), SpaceLink *slink, ID *old_id, ID *new_id)
+{
+	SpaceButs *sbuts = (SpaceButs *)slink;
+
+	if (sbuts->pinid == old_id) {
+		sbuts->pinid = new_id;
+		if (new_id == NULL) {
+			sbuts->flag &= ~SB_PIN_CONTEXT;
+		}
+	}
+
+	if (sbuts->path) {
+		ButsContextPath *path = sbuts->path;
+		int i;
+
+		for (i = 0; i < path->len; i++) {
+			if (path->ptr[i].id.data == old_id) {
+				break;
+			}
+		}
+
+		if (i == path->len) {
+			/* pass */
+		}
+		else if (new_id == NULL) {
+			if (i == 0) {
+				MEM_SAFE_FREE(sbuts->path);
+			}
+			else {
+				memset(&path->ptr[i], 0, sizeof(path->ptr[i]) * (path->len - i));
+				path->len = i;
+			}
+		}
+		else {
+			RNA_id_pointer_create(new_id, &path->ptr[i]);
+			/* There is no easy way to check/make path downwards valid, just nullify it.
+			 * Next redraw will rebuild this anyway. */
+			i++;
+			memset(&path->ptr[i], 0, sizeof(path->ptr[i]) * (path->len - i));
+			path->len = i;
+		}
+	}
+
+	if (sbuts->texuser) {
+		ButsContextTexture *ct = sbuts->texuser;
+		if ((ID *)ct->texture == old_id) {
+			ct->texture = (Tex *)new_id;
+		}
+		BLI_freelistN(&ct->users);
+		ct->user = NULL;
+	}
+}
+
 /* only called once, from space/spacetypes.c */
 void ED_spacetype_buttons(void)
 {
@@ -406,7 +461,8 @@ void ED_spacetype_buttons(void)
 	st->keymap = buttons_keymap;
 	st->listener = buttons_area_listener;
 	st->context = buttons_context;
-	
+	st->id_remap = buttons_id_remap;
+
 	/* regions: main window */
 	art = MEM_callocN(sizeof(ARegionType), "spacetype buttons region");
 	art->regionid = RGN_TYPE_WINDOW;