VarAction2: Fix detection of callback handlers which don't inspect var C

src/newgrf_optimiser.cpp

@@ -2482,6 +2482,10 @@ void OptimiseVarAction2DeterministicSpriteGroup(VarAction2OptimiseState &state,
 					group->dsg_flags |= DSGF_CB_HANDLER;
 					state.have_cb_handler = true;
 				}
+				if ((dsg->dsg_flags & DSGF_CB_RESULT) && !state.ignore_cb_handler) {
+					group->dsg_flags |= DSGF_CB_RESULT;
+					state.have_cb_handler = true;
+				}
 			}
 			if (sg != nullptr && sg->type == SGT_RANDOMIZED) {
 				const RandomizedSpriteGroup *rsg = (const RandomizedSpriteGroup*)sg;
@@ -2532,6 +2536,12 @@ void OptimiseVarAction2DeterministicSpriteGroup(VarAction2OptimiseState &state,
 					bits.set(ipsg->again, true);
 				}
 			}
+			if (sg != nullptr && sg->type == SGT_CALLBACK) {
+				if (!state.ignore_cb_handler) {
+					group->dsg_flags |= DSGF_CB_RESULT;
+					state.have_cb_handler = true;
+				}
+			}
 		});
 
 		HandleGroupState default_group_state;
@@ -2573,6 +2583,8 @@ void OptimiseVarAction2DeterministicSpriteGroup(VarAction2OptimiseState &state,
 			}
 			state.GetVarTracking(group)->in |= in_bits;
 		}
+	} else {
+		group->dsg_flags |= DSGF_CB_RESULT;
 	}
 	if (possible_callback_handler) group->dsg_flags |= DSGF_CB_HANDLER;
 

src/newgrf_spritegroup.cpp

@@ -658,6 +658,7 @@ void SpriteGroupDumper::DumpSpriteGroup(const SpriteGroup *sg, const char *paddi
 				if (dsg->dsg_flags & DSGF_REQUIRES_VAR1C) p += seprintf(p, lastof(this->buffer), ", REQ_1C");
 				if (dsg->dsg_flags & DSGF_CHECK_EXPENSIVE_VARS) p += seprintf(p, lastof(this->buffer), ", CHECK_EXP_VAR");
 				if (dsg->dsg_flags & DSGF_CHECK_INSERT_JUMP) p += seprintf(p, lastof(this->buffer), ", CHECK_INS_JMP");
+				if (dsg->dsg_flags & DSGF_CB_RESULT) p += seprintf(p, lastof(this->buffer), ", CB_RESULT");
 				if (dsg->dsg_flags & DSGF_CB_HANDLER) p += seprintf(p, lastof(this->buffer), ", CB_HANDLER");
 				if (dsg->dsg_flags & DSGF_INLINE_CANDIDATE) p += seprintf(p, lastof(this->buffer), ", INLINE_CANDIDATE");
 			}

src/newgrf_spritegroup.h

@@ -442,6 +442,7 @@ struct DeterministicSpriteGroupRange {
 enum DeterministicSpriteGroupFlags : uint8 {
 	DSGF_NONE                    = 0,
 	DSGF_NO_DSE                  = 1 << 0,
+	DSGF_CB_RESULT               = 1 << 1,
 	DSGF_VAR_TRACKING_PENDING    = 1 << 2,
 	DSGF_REQUIRES_VAR1C          = 1 << 3,
 	DSGF_CHECK_EXPENSIVE_VARS    = 1 << 4,