Anim: prevent pushing down layered Actions onto the NLA

Prevent creating NLA strips from layered Actions via the 'Push Down'
operator.

Maybe in the future the NLA will support layered Actions (as a transitional
phase, before the NLA is replaced with layered Actions itself). For now,
it's better to create stable boundaries to prevent their use in the NLA.
When NLA support is being worked on, those boundaries can be removed again.

Pull Request: https://projects.blender.org/blender/blender/pulls/123467

source/blender/editors/space_action/CMakeLists.txt

@@ -33,6 +33,7 @@ set(SRC
 
 set(LIB
   bf_blenkernel
+  PRIVATE bf::animrig
   PRIVATE bf::blenlib
   PRIVATE bf::depsgraph
   PRIVATE bf::dna
@@ -40,6 +41,9 @@ set(LIB
   PRIVATE bf::animrig
 )
 
+if(WITH_EXPERIMENTAL_FEATURES)
+  add_definitions(-DWITH_ANIM_BAKLAVA)
+endif()
 
 blender_add_lib(bf_editor_space_action "${SRC}" "${INC}" "${INC_SYS}" "${LIB}")
 

source/blender/editors/space_action/action_data.cc

@@ -32,6 +32,8 @@
 #include "BKE_report.hh"
 #include "BKE_scene.hh"
 
+#include "ANIM_action.hh"
+
 #include "ED_anim_api.hh"
 #include "ED_screen.hh"
 
@@ -311,6 +313,14 @@ static bool action_pushdown_poll(bContext *C)
     return false;
   }
 
+#ifdef WITH_ANIM_BAKLAVA
+  blender::animrig::Action &action = saction->action->wrap();
+  if (!action.is_action_legacy()) {
+    CTX_wm_operator_poll_msg_set(C, "Layered Actions cannot be used as NLA strips");
+    return false;
+  }
+#endif
+
   /* NOTE: We check this for the AnimData block in question and not the global flag,
    *       as the global flag may be left dirty by some of the browsing ops here.
    */

source/blender/editors/space_nla/CMakeLists.txt

@@ -32,12 +32,17 @@ set(SRC
 
 set(LIB
   bf_blenkernel
+  PRIVATE bf::animrig
   PRIVATE bf::blenlib
   PRIVATE bf::depsgraph
   PRIVATE bf::dna
   PRIVATE bf::intern::guardedalloc
 )
 
+if(WITH_EXPERIMENTAL_FEATURES)
+  add_definitions(-DWITH_ANIM_BAKLAVA)
+endif()
+
 blender_add_lib(bf_editor_space_nla "${SRC}" "${INC}" "${INC_SYS}" "${LIB}")
 
 # RNA_prototypes.h dna_type_offsets.h

source/blender/editors/space_nla/nla_tracks.cc

@@ -24,6 +24,8 @@
 #include "BKE_nla.h"
 #include "BKE_report.hh"
 
+#include "ANIM_action.hh"
+
 #include "ED_anim_api.hh"
 #include "ED_keyframes_edit.hh"
 #include "ED_object.hh"
@@ -434,6 +436,16 @@ static int nlatracks_pushdown_exec(bContext *C, wmOperator *op)
     return OPERATOR_CANCELLED;
   }
 
+#ifdef WITH_ANIM_BAKLAVA
+  /* Reject layered Actions, until the NLA knows how to handle them.
+   * Ideally this would happen in the poll function, but the way it's determined which Action to
+   * push down is a bit convoluted (see code above). */
+  if (!adt->action->wrap().is_action_legacy()) {
+    BKE_report(op->reports, RPT_ERROR, "Layered Actions cannot be used as NLA strips");
+    return OPERATOR_CANCELLED;
+  }
+#endif  // WITH_ANIM_BAKLAVA
+
   /* 'push-down' action - only usable when not in Tweak-mode. */
   BKE_nla_action_pushdown(adt, ID_IS_OVERRIDE_LIBRARY(id));