BM_mesh_create will now add mesh_id customdata layers when asked,

instead of leaving that to the client.

Also semi-fixed uninitialized memory bug in bmesh unit test (dunno
how best to memset a C struct in C++ won't won't run afoul of some
random compiler somewhere).

source/blender/blenkernel/intern/customdata.c

@@ -3866,9 +3866,10 @@ static void CustomData_bmesh_set_default_n(CustomData *data, void **block, int n
   int offset = data->layers[n].offset;
   const LayerTypeInfo *typeInfo = layerType_getInfo(data->layers[n].type);
 
+  /*
   if (data->layers[n].flag & CD_FLAG_ELEM_NOCOPY) {
     return;
-  }
+  }*/
 
   if (typeInfo->set_default) {
     typeInfo->set_default(POINTER_OFFSET(*block, offset), 1);

source/blender/bmesh/intern/bmesh_mesh.c

@@ -184,6 +184,23 @@ BMesh *BM_mesh_create(const BMAllocTemplate *allocsize, const struct BMeshCreate
   CustomData_reset(&bm->ldata);
   CustomData_reset(&bm->pdata);
 
+  if (params->use_unique_ids) {
+    bm_init_idmap_cdlayers(bm);
+
+    if (bm->vdata.totlayer) {
+      CustomData_bmesh_init_pool(&bm->vdata, 0, BM_VERT);
+    }
+    if (bm->edata.totlayer) {
+      CustomData_bmesh_init_pool(&bm->edata, 0, BM_EDGE);
+    }
+    if (bm->ldata.totlayer) {
+      CustomData_bmesh_init_pool(&bm->ldata, 0, BM_LOOP);
+    }
+    if (bm->pdata.totlayer) {
+      CustomData_bmesh_init_pool(&bm->pdata, 0, BM_FACE);
+    }
+  }
+
   return bm;
 }
 

source/blender/bmesh/tests/bmesh_core_test.cc

@@ -12,6 +12,8 @@ TEST(bmesh_core, BMVertCreate)
 
   BMeshCreateParams bm_params;
   bm_params.use_toolflags = true;
+  bm_params.use_unique_ids = false;
+
   bm = BM_mesh_create(&bm_mesh_allocsize_default, &bm_params);
   EXPECT_EQ(bm->totvert, 0);
   /* make a custom layer so we can see if it is copied properly */

source/blender/editors/sculpt_paint/sculpt_dyntopo.c

@@ -468,6 +468,11 @@ BMesh *BM_mesh_bm_from_me_threaded(BMesh *bm,
                                    const Mesh *me,
                                    const struct BMeshFromMeshParams *params);
 
+#define EXPECT_EQ(a, b) \
+  if ((a) != (b)) { \
+    printf("error\n"); \
+  }
+
 void SCULPT_dynamic_topology_enable_ex(Main *bmain, Depsgraph *depsgraph, Scene *scene, Object *ob)
 {
   SculptSession *ss = ob->sculpt;