Cleanup: Forward declare some classes in mesh headers

Aiming to reduce cases of including headers in headers,
when the final definition might be unnecessary.

source/blender/blenkernel/BKE_mesh.h

@@ -14,7 +14,6 @@
 #include "DNA_mesh_types.h"
 #include "DNA_meshdata_types.h"
 
-
 struct BMesh;
 struct BMeshCreateParams;
 struct BMeshFromMeshParams;

source/blender/blenkernel/BKE_mesh.hh

@@ -8,7 +8,14 @@
  * \ingroup bke
  */
 
-#include "BLI_index_mask.hh"
+namespace blender {
+namespace index_mask {
+class IndexMask;
+}
+using index_mask::IndexMask;
+}  // namespace blender
+
+#include "BLI_offset_indices.hh"
 
 #include "BKE_mesh.h"
 #include "BKE_mesh_types.hh"

source/blender/blenkernel/BKE_subdiv_ccg.hh

@@ -10,6 +10,13 @@
 
 #include <memory>
 
+namespace blender {
+namespace index_mask {
+class IndexMask;
+}
+using index_mask::IndexMask;
+}  // namespace blender
+
 #include "BLI_array.hh"
 #include "BLI_bit_group_vector.hh"
 #include "BLI_offset_indices.hh"

source/blender/blenkernel/intern/subdiv_ccg.cc

@@ -14,6 +14,7 @@
 #include "MEM_guardedalloc.h"
 
 #include "BLI_enumerable_thread_specific.hh"
+#include "BLI_index_mask.hh"
 #include "BLI_math_bits.h"
 #include "BLI_math_geom.h"
 #include "BLI_math_vector.h"

source/blender/blenlib/BLI_offset_indices.hh

@@ -6,7 +6,13 @@
 
 #include <algorithm>
 
-#include "BLI_index_mask.hh"
+namespace blender {
+namespace index_mask {
+class IndexMask;
+}
+using index_mask::IndexMask;
+}  // namespace blender
+
 #include "BLI_index_range.hh"
 #include "BLI_span.hh"
 

source/blender/draw/engines/eevee_next/eevee_pipeline.hh

@@ -12,6 +12,8 @@
 
 #pragma once
 
+#include "BLI_math_bits.h"
+
 #include "DRW_render.h"
 #include "draw_shader_shared.h"
 

source/blender/io/wavefront_obj/exporter/obj_export_mesh.hh

@@ -11,6 +11,7 @@
 #include <optional>
 
 #include "BLI_math_vector_types.hh"
+#include "BLI_offset_indices.hh"
 #include "BLI_utility_mixins.hh"
 #include "BLI_vector.hh"
 #include "BLI_virtual_array.hh"

source/blender/makesdna/DNA_mesh_types.h

@@ -11,7 +11,6 @@
 #include "DNA_ID.h"
 #include "DNA_customdata_types.h"
 #include "DNA_defs.h"
-#include "DNA_meshdata_types.h"
 #include "DNA_session_uuid_types.h"
 
 /** Workaround to forward-declare C++ type in C header. */
@@ -19,13 +18,18 @@
 
 #  include <optional>
 
-#  include "BLI_bounds_types.hh"
 #  include "BLI_math_vector_types.hh"
-#  include "BLI_offset_indices.hh"
 
 namespace blender {
-template<typename T> class Span;
+template<typename T> class Bounds;
+namespace offset_indices {
+template<typename T> class GroupedSpan;
+template<typename T> class OffsetIndices;
+}  // namespace offset_indices
+using offset_indices::GroupedSpan;
+using offset_indices::OffsetIndices;
 template<typename T> class MutableSpan;
+template<typename T> class Span;
 namespace bke {
 struct MeshRuntime;
 class AttributeAccessor;