Fix T44484: Edge-split corrupts mesh

Splitting non-manifold edges could produce duplicate edges.

source/blender/bmesh/operators/bmo_split_edges.c

@@ -48,7 +48,7 @@ void bmo_split_edges_exec(BMesh *bm, BMOperator *op)
 	}
 
 	/* this is where everything happens */
-	BM_mesh_edgesplit(bm, use_verts, true, false);
+	BM_mesh_edgesplit(bm, use_verts, true, true, false);
 
 	BMO_slot_buffer_from_enabled_hflag(bm, op, op->slots_out, "edges.out", BM_EDGE, BM_ELEM_INTERNAL_TAG);
 }

source/blender/bmesh/tools/bmesh_edgesplit.c

@@ -42,7 +42,7 @@
  * un-tag edges not connected to other tagged edges,
  * unless they are on a boundary
  */
-static void bm_edgesplit_validate_seams(BMesh *bm)
+static void bm_edgesplit_validate_seams(BMesh *bm, const bool use_non_manifold)
 {
 	BMIter iter;
 	BMEdge *e;
@@ -72,6 +72,11 @@ static void bm_edgesplit_validate_seams(BMesh *bm)
 			 * the edge its self can't be split */
 			BM_elem_flag_disable(e, BM_ELEM_TAG);
 		}
+		else if ((use_non_manifold == false) &&
+		         (BM_edge_is_manifold(e) == false))
+		{
+			BM_elem_flag_disable(e, BM_ELEM_TAG);
+		}
 	}
 
 	/* single marked edges unconnected to any other marked edges
@@ -98,7 +103,16 @@ static void bm_edgesplit_validate_seams(BMesh *bm)
 	MEM_freeN(vtouch);
 }
 
-void BM_mesh_edgesplit(BMesh *bm, const bool use_verts, const bool tag_only, const bool copy_select)
+/**
+ * \param use_verts  Use flagged verts instead of edges.
+ * \param use_non_manifold  Split non-manifold edges (a little slower, must check for doubles).
+ * \param tag_only  Only split tagged edges.
+ * \param copy_select  Copy selection history.
+ */
+void BM_mesh_edgesplit(
+        BMesh *bm,
+        const bool use_verts, const bool use_non_manifold,
+        const bool tag_only, const bool copy_select)
 {
 	BMIter iter;
 	BMEdge *e;
@@ -142,7 +156,7 @@ void BM_mesh_edgesplit(BMesh *bm, const bool use_verts, const bool tag_only, con
 		}
 	}
 
-	bm_edgesplit_validate_seams(bm);
+	bm_edgesplit_validate_seams(bm, use_non_manifold);
 
 	BM_ITER_MESH (e, &iter, bm, BM_EDGES_OF_MESH) {
 		if (BM_elem_flag_test(e, BM_ELEM_TAG)) {
@@ -204,6 +218,29 @@ void BM_mesh_edgesplit(BMesh *bm, const bool use_verts, const bool tag_only, con
 		}
 	}
 
+	if (use_non_manifold) {
+		/* if we split non-manifold, double edge may remain */
+		BMEdge *e_next;
+		BM_ITER_MESH_MUTABLE (e, e_next, &iter, bm, BM_EDGES_OF_MESH) {
+			if (BM_elem_flag_test(e, BM_ELEM_TAG)) {
+				BMEdge *e_other;
+				if ((e_other = BM_edge_find_double(e))) {
+					BM_edge_splice(bm, e, e_other);
+				}
+			}
+		}
+	}
+	else {
+#ifndef NDEBUG
+		/* ensure we don't have any double edges! */
+		BM_ITER_MESH (e, &iter, bm, BM_EDGES_OF_MESH) {
+			if (BM_elem_flag_test(e, BM_ELEM_TAG)) {
+				BLI_assert(BM_edge_find_double(e) == NULL);
+			}
+		}
+#endif
+	}
+
 	if (use_ese) {
 		BLI_ghash_free(ese_gh, NULL, NULL);
 	}

source/blender/bmesh/tools/bmesh_edgesplit.h

@@ -27,6 +27,9 @@
  *  \ingroup bmesh
  */
 
-void BM_mesh_edgesplit(BMesh *bm, const bool use_verts, const bool tag_only, const bool copy_select);
+void BM_mesh_edgesplit(
+        BMesh *bm,
+        const bool use_verts, const bool use_non_manifold,
+        const bool tag_only, const bool copy_select);
 
 #endif /* __BMESH_EDGESPLIT_H__ */

source/blender/bmesh/tools/bmesh_intersect.c

@@ -1283,7 +1283,7 @@ bool BM_mesh_intersect(
 			BM_elem_flag_enable(e, BM_ELEM_TAG);
 		}
 
-		BM_mesh_edgesplit(bm, false, true, false);
+		BM_mesh_edgesplit(bm, false, false, true, false);
 	}
 #else
 	(void)use_separate;

source/blender/editors/mesh/editmesh_rip.c

@@ -941,7 +941,7 @@ static int edbm_rip_invoke__edge(bContext *C, wmOperator *op, const wmEvent *eve
 		fill_uloop_pairs = edbm_tagged_loop_pairs_to_fill(bm);
 	}
 
-	BM_mesh_edgesplit(em->bm, true, true, true);
+	BM_mesh_edgesplit(em->bm, true, true, true, true);
 
 	/* note: the output of the bmesh operator is ignored, since we built
 	 * the contiguous loop pairs to split already, its possible that some

source/blender/modifiers/intern/MOD_edgesplit.c

@@ -91,7 +91,7 @@ static DerivedMesh *doEdgeSplit(DerivedMesh *dm, EdgeSplitModifierData *emd)
 		}
 	}
 	
-	BM_mesh_edgesplit(bm, false, true, false);
+	BM_mesh_edgesplit(bm, false, false, true, false);
 
 	/* BM_mesh_validate(bm); */ /* for troubleshooting */