Fix T75128: Select Linked fails when the selection is a delimiter

Starting select linked failed when the selected vertex or edge
was it's self delimiting.

Support using these elements for linked select
as long as they're part of an isolated selection.

3 files changed, 31 insertions, 6 deletions

diff --git a/source/blender/bmesh/intern/bmesh_query.c b/source/blender/bmesh/intern/bmesh_query.c
index e3b6e243906..64950411fed 100644
--- a/source/blender/bmesh/intern/bmesh_query.c
+++ b/source/blender/bmesh/intern/bmesh_query.c
@@ -2431,6 +2431,22 @@ bool BM_edge_is_all_face_flag_test(const BMEdge *e, const char hflag, const bool
   return true;
 }
 
+bool BM_edge_is_any_face_flag_test(const BMEdge *e, const char hflag)
+{
+  if (e->l) {
+    BMLoop *l_iter, *l_first;
+
+    l_iter = l_first = e->l;
+    do {
+      if (BM_elem_flag_test(l_iter->f, hflag)) {
+        return true;
+      }
+    } while ((l_iter = l_iter->radial_next) != l_first);
+  }
+
+  return false;
+}
+
 /* convenience functions for checking flags */
 bool BM_edge_is_any_vert_flag_test(const BMEdge *e, const char hflag)
 {
diff --git a/source/blender/bmesh/intern/bmesh_query.h b/source/blender/bmesh/intern/bmesh_query.h
index fb646b11076..aaf8191c5db 100644
--- a/source/blender/bmesh/intern/bmesh_query.h
+++ b/source/blender/bmesh/intern/bmesh_query.h
@@ -226,6 +226,8 @@ bool BM_edge_is_all_face_flag_test(const BMEdge *e,
 
 bool BM_edge_is_any_vert_flag_test(const BMEdge *e, const char hflag) ATTR_WARN_UNUSED_RESULT
     ATTR_NONNULL();
+bool BM_edge_is_any_face_flag_test(const BMEdge *e, const char hflag) ATTR_WARN_UNUSED_RESULT
+    ATTR_NONNULL();
 bool BM_face_is_any_vert_flag_test(const BMFace *f, const char hflag) ATTR_WARN_UNUSED_RESULT
     ATTR_NONNULL();
 bool BM_face_is_any_edge_flag_test(const BMFace *f, const char hflag) ATTR_WARN_UNUSED_RESULT
diff --git a/source/blender/editors/mesh/editmesh_select.c b/source/blender/editors/mesh/editmesh_select.c
index f01511fa513..3847f32b19a 100644
--- a/source/blender/editors/mesh/editmesh_select.c
+++ b/source/blender/editors/mesh/editmesh_select.c
@@ -3201,8 +3201,12 @@ static int edbm_select_linked_exec(bContext *C, wmOperator *op)
         BMEdge *e;
         BM_ITER_MESH (e, &iter, em->bm, BM_EDGES_OF_MESH) {
           if (!BMO_edge_flag_test(bm, e, BMO_ELE_TAG)) {
-            BM_elem_flag_disable(e->v1, BM_ELEM_TAG);
-            BM_elem_flag_disable(e->v2, BM_ELEM_TAG);
+            /* Check the edge for selected faces,
+             * this supports stepping off isolated vertices which would otherwise be ignored. */
+            if (BM_edge_is_any_face_flag_test(e, BM_ELEM_SELECT)) {
+              BM_elem_flag_disable(e->v1, BM_ELEM_TAG);
+              BM_elem_flag_disable(e->v2, BM_ELEM_TAG);
+            }
           }
         }
       }
@@ -3258,10 +3262,13 @@ static int edbm_select_linked_exec(bContext *C, wmOperator *op)
 
       if (delimit) {
         BM_ITER_MESH (e, &iter, em->bm, BM_EDGES_OF_MESH) {
-          BM_elem_flag_set(
-              e,
-              BM_ELEM_TAG,
-              (BM_elem_flag_test(e, BM_ELEM_SELECT) && BMO_edge_flag_test(bm, e, BMO_ELE_TAG)));
+          /* Check the edge for selected faces,
+           * this supports stepping off isolated edges which would otherwise be ignored. */
+          BM_elem_flag_set(e,
+                           BM_ELEM_TAG,
+                           (BM_elem_flag_test(e, BM_ELEM_SELECT) &&
+                            (BMO_edge_flag_test(bm, e, BMO_ELE_TAG) ||
+                             !BM_edge_is_any_face_flag_test(e, BM_ELEM_SELECT))));
         }
       }
       else {