Cleanup/refactor: Undosys: Get rid of the magic values for undo direction.

Move `eUndoStepDir` to `BKE_undo_system.h` and use its values
everywhere.

Note that this also introduce the `STEP_INVALID` value in that enum.

Finally, kept the matching struct members in some lower-level readfile
code as an `int` to avoid having to include `BKE_undo_system.h` in a lot
of unrelated files.

2 files changed, 7 insertions, 18 deletions

diff --git a/source/blender/editors/undo/ed_undo.c b/source/blender/editors/undo/ed_undo.c
index 0771d0254e8..baa178a6a94 100644
--- a/source/blender/editors/undo/ed_undo.c
+++ b/source/blender/editors/undo/ed_undo.c
@@ -70,15 +70,6 @@
 /** We only need this locally. */
 static CLG_LogRef LOG = {"ed.undo"};
 
-/**
- * \warning Values are used in #ED_undo_gpencil_step,
- * which should eventually be replaced with the undo-system.
- */
-enum eUndoStepDir {
-  STEP_REDO = 1,
-  STEP_UNDO = -1,
-};
-
 /* -------------------------------------------------------------------- */
 /** \name Generic Undo System Access
  *
@@ -276,7 +267,7 @@ static int ed_undo_step_direction(bContext *C, enum eUndoStepDir step, ReportLis
    * FIXME: However, it seems to never be used in current code (`ED_gpencil_session_active` seems
    * to always return false). */
   if (ED_gpencil_session_active()) {
-    return ED_undo_gpencil_step(C, (int)step);
+    return ED_undo_gpencil_step(C, step);
   }
 
   wmWindowManager *wm = CTX_wm_manager(C);
diff --git a/source/blender/editors/undo/memfile_undo.c b/source/blender/editors/undo/memfile_undo.c
index eea0f29d295..51859b6a555 100644
--- a/source/blender/editors/undo/memfile_undo.c
+++ b/source/blender/editors/undo/memfile_undo.c
@@ -145,19 +145,18 @@ static int memfile_undosys_step_id_reused_cb(LibraryIDLinkCallbackData *cb_data)
 static void memfile_undosys_step_decode(struct bContext *C,
                                         struct Main *bmain,
                                         UndoStep *us_p,
-                                        int undo_direction,
+                                        const eUndoStepDir undo_direction,
                                         bool UNUSED(is_final))
 {
-  BLI_assert(undo_direction != 0);
+  BLI_assert(undo_direction != STEP_INVALID);
 
   bool use_old_bmain_data = true;
 
   if (USER_EXPERIMENTAL_TEST(&U, use_undo_legacy)) {
     use_old_bmain_data = false;
   }
-  else if (undo_direction > 0) {
-    /* Redo case.
-     * The only time we should have to force a complete redo is when current step is tagged as a
+  else if (undo_direction == STEP_REDO) {
+    /* The only time we should have to force a complete redo is when current step is tagged as a
      * redo barrier.
      * If previous step was not a memfile one should not matter here, current data in old bmain
      * should still always be valid for unchanged data-blocks. */
@@ -165,9 +164,8 @@ static void memfile_undosys_step_decode(struct bContext *C,
       use_old_bmain_data = false;
     }
   }
-  else {
-    /* Undo case.
-     * Here we do not care whether current step is an undo barrier, since we are coming from
+  else if (undo_direction == STEP_UNDO) {
+    /* Here we do not care whether current step is an undo barrier, since we are coming from
      * 'the future' we can still re-use old data. However, if *next* undo step
      * (i.e. the one immediately in the future, the one we are coming from)
      * is a barrier, then we have to force a complete undo.