From c79467692812db55bafe6348a73d53d413704818 Mon Sep 17 00:00:00 2001
From: merni-ns <66267867+merni-ns@users.noreply.github.com>
Date: Tue, 3 Oct 2023 18:13:15 +0530
Subject: [PATCH] Fix #10763, Fix #11168: Display variant groups that consist
 only of unavailable sub-groups (#11342)

---
 src/autoreplace_gui.cpp   |  8 +++++++-
 src/build_vehicle_gui.cpp | 16 ++++++++++++++--
 2 files changed, 21 insertions(+), 3 deletions(-)

diff --git a/src/autoreplace_gui.cpp b/src/autoreplace_gui.cpp
index 467e64d4b8..a95c0034c7 100644
--- a/src/autoreplace_gui.cpp
+++ b/src/autoreplace_gui.cpp
@@ -179,7 +179,13 @@ class ReplaceVehicleWindow : public Window {
 			if (side == 1 && eid == this->sel_engine[0]) flags |= EngineDisplayFlags::Shaded;
 			list.emplace_back(eid, e->info.variant_id, flags, 0);
 
-			if (side == 1 && e->info.variant_id != INVALID_ENGINE) variants.push_back(e->info.variant_id);
+			if (side == 1) {
+				EngineID parent = e->info.variant_id;
+				while (parent != INVALID_ENGINE) {
+					variants.push_back(parent);
+					parent = Engine::Get(parent)->info.variant_id;
+				}
+			}
 			if (eid == this->sel_engine[side]) selected_engine = eid; // The selected engine is still in the list
 		}
 
diff --git a/src/build_vehicle_gui.cpp b/src/build_vehicle_gui.cpp
index 9c869426e5..bbe6034f60 100644
--- a/src/build_vehicle_gui.cpp
+++ b/src/build_vehicle_gui.cpp
@@ -1422,7 +1422,14 @@ struct BuildVehicleWindow : Window {
 			list.emplace_back(eid, e->info.variant_id, e->display_flags, 0);
 
 			if (rvi->railveh_type != RAILVEH_WAGON) num_engines++;
-			if (e->info.variant_id != INVALID_ENGINE) variants.push_back(e->info.variant_id);
+
+			/* Add all parent variants of this engine to the variant list */
+			EngineID parent = e->info.variant_id;
+			while (parent != INVALID_ENGINE) {
+				variants.push_back(parent);
+				parent = Engine::Get(parent)->info.variant_id;
+			}
+
 			if (eid == this->sel_engine) sel_id = eid;
 		}
 
@@ -1563,8 +1570,13 @@ struct BuildVehicleWindow : Window {
 		/* ensure primary engine of variant group is in list after filtering */
 		std::vector<EngineID> variants;
 		for (const auto &item : this->eng_list) {
-			if (item.engine_id != item.variant_id && item.variant_id != INVALID_ENGINE) variants.push_back(item.variant_id);
+			EngineID parent = item.variant_id;
+			while (parent != INVALID_ENGINE) {
+				variants.push_back(parent);
+				parent = Engine::Get(parent)->info.variant_id;
+			}
 		}
+
 		for (const auto &variant : variants) {
 			if (std::find(this->eng_list.begin(), this->eng_list.end(), variant) == this->eng_list.end()) {
 				const Engine *e = Engine::Get(variant);