Fix for #36739: Delete new nodes added via the Add menu or toolbar if the subsequent transform operator is cancelled. This prevents ugly situations where nodes stick "under" the toolbar after clicking a

wrong button.

Works by adding a flag to transform operators "remove_on_cancel". This is currently only used for node transforms, the idea is that if set, the operator will remove the transformed elements when it is
cancelled. It's not possible to do that in the original NODE_OT_add_node operator, because transform is modal and there is no way of reacting to a cancel outside of the transform itself (previous attempt
used a macro operator, but that also doesn't work because subsequent operators don't get executed if the previous transform cancels).

release/scripts/startup/bl_operators/node.py

@@ -123,7 +123,8 @@ class NodeAddOperator():
         result = self.execute(context)
 
         if self.use_transform and ('FINISHED' in result):
-            bpy.ops.transform.translate('INVOKE_DEFAULT')
+            # removes the node again if transform is cancelled
+            bpy.ops.transform.translate('INVOKE_DEFAULT', remove_on_cancel = True)
 
         return result
 

source/blender/editors/transform/transform.c

@@ -1854,7 +1854,7 @@ int initTransform(bContext *C, TransInfo *t, wmOperator *op, const wmEvent *even
 			options |= CTX_TEXTURE;
 		}
 	}
-	
+
 	t->options = options;
 
 	t->mode = mode;

source/blender/editors/transform/transform.h

@@ -341,7 +341,9 @@ typedef struct TransInfo {
 	float		auto_values[4];
 	float		axis[3];
 	float		axis_orig[3];	/* TransCon can change 'axis', store the original value here */
-	
+
+	short		remove_on_cancel; /* remove elements if operator is cancelled */
+
 	void		*view;
 	struct bContext *context; /* Only valid (non null) during an operator called function. */
 	struct ScrArea	*sa;

source/blender/editors/transform/transform_conversions.c

@@ -5323,6 +5323,25 @@ static void special_aftertrans_update__mask(bContext *C, TransInfo *t)
 	}
 }
 
+static void special_aftertrans_update__node(bContext *UNUSED(C), TransInfo *t)
+{
+	int canceled = (t->state == TRANS_CANCEL);
+	
+	if (canceled && t->remove_on_cancel) {
+		/* remove selected nodes on cancel */
+		SpaceNode *snode = (SpaceNode *)t->sa->spacedata.first;
+		bNodeTree *ntree = snode->edittree;
+		if (ntree) {
+			bNode *node, *node_next;
+			for (node = ntree->nodes.first; node; node = node_next) {
+				node_next = node->next;
+				if (node->flag & NODE_SELECT)
+					nodeFreeNode(ntree, node);
+			}
+		}
+	}
+}
+
 static void special_aftertrans_update__mesh(bContext *UNUSED(C), TransInfo *t)
 {
 	/* so automerge supports mirror */
@@ -5434,6 +5453,7 @@ void special_aftertrans_update(bContext *C, TransInfo *t)
 	}
 	else if (t->spacetype == SPACE_NODE) {
 		SpaceNode *snode = (SpaceNode *)t->sa->spacedata.first;
+		special_aftertrans_update__node(C, t);
 		if (canceled == 0) {
 			ED_node_post_apply_transform(C, snode->edittree);
 			

source/blender/editors/transform/transform_generics.c

@@ -1105,6 +1105,12 @@ int initTransInfo(bContext *C, TransInfo *t, wmOperator *op, const wmEvent *even
 		t->options |= CTX_EDGE;
 	}
 
+	t->remove_on_cancel = false;
+	if ((prop = RNA_struct_find_property(op->ptr, "remove_on_cancel")) && RNA_property_is_set(op->ptr, prop)) {
+		if (RNA_property_boolean_get(op->ptr, prop)) {
+			t->remove_on_cancel = true;
+		}
+	}
 
 	/* Assign the space type, some exceptions for running in different mode */
 	if (sa == NULL) {

source/blender/editors/transform/transform_ops.c

@@ -537,6 +537,7 @@ void Transform_Properties(struct wmOperatorType *ot, int flags)
 
 	if (flags & P_OPTIONS) {
 		RNA_def_boolean(ot->srna, "texture_space", 0, "Edit Texture Space", "Edit Object data texture space");
+		RNA_def_boolean(ot->srna, "remove_on_cancel", 0, "Remove on Cancel", "Remove elements on cancel");
 	}
 
 	if (flags & P_CORRECT_UV) {