From 82c87208146e11f26c2dbc1aa647bb38c7da7458 Mon Sep 17 00:00:00 2001
From: frosch <frosch@openttd.org>
Date: Sun, 1 Oct 2023 15:21:57 +0200
Subject: [PATCH] Fix #8846: When upgrading NewGRF presets, copy NewGRF
 parameters only if the NewGRF are compatible. Otherwise reset to defaults.

---
 src/newgrf_config.cpp | 10 +++++++++-
 src/newgrf_config.h   |  1 +
 src/newgrf_gui.cpp    |  6 +++++-
 3 files changed, 15 insertions(+), 2 deletions(-)

diff --git a/src/newgrf_config.cpp b/src/newgrf_config.cpp
index 8985f4c181..c45498ee2b 100644
--- a/src/newgrf_config.cpp
+++ b/src/newgrf_config.cpp
@@ -66,6 +66,14 @@ GRFConfig::GRFConfig(const GRFConfig &config) :
 {
 }
 
+/**
+ * Return whether this NewGRF can replace an older version of the same NewGRF.
+ */
+bool GRFConfig::IsCompatible(uint32_t old_version) const
+{
+	return this->min_loadable_version <= old_version && old_version <= this->version;
+}
+
 /**
  * Copy the parameter information from the \a src config.
  * @param src Source config.
@@ -685,7 +693,7 @@ const GRFConfig *FindGRFConfig(uint32_t grfid, FindGRFConfigMode mode, const MD5
 		/* Skip incompatible stuff, unless explicitly allowed */
 		if (mode != FGCM_NEWEST && HasBit(c->flags, GCF_INVALID)) continue;
 		/* check version compatibility */
-		if (mode == FGCM_COMPATIBLE && (c->version < desired_version || c->min_loadable_version > desired_version)) continue;
+		if (mode == FGCM_COMPATIBLE && !c->IsCompatible(desired_version)) continue;
 		/* remember the newest one as "the best" */
 		if (best == nullptr || c->version > best->version) best = c;
 	}
diff --git a/src/newgrf_config.h b/src/newgrf_config.h
index 22706ce025..3620501b19 100644
--- a/src/newgrf_config.h
+++ b/src/newgrf_config.h
@@ -173,6 +173,7 @@ struct GRFConfig : ZeroedMemoryAllocator {
 
 	struct GRFConfig *next; ///< NOSAVE: Next item in the linked list
 
+	bool IsCompatible(uint32_t old_version) const;
 	void CopyParams(const GRFConfig &src);
 
 	std::optional<std::string> GetTextfile(TextfileType type) const;
diff --git a/src/newgrf_gui.cpp b/src/newgrf_gui.cpp
index 9aab5e9b6f..f1ec5e3f7f 100644
--- a/src/newgrf_gui.cpp
+++ b/src/newgrf_gui.cpp
@@ -723,7 +723,11 @@ struct NewGRFWindow : public Window, NewGRFScanCallback {
 			while (*c != iter->second) c = &(*c)->next;
 			GRFConfig *d = new GRFConfig(*a);
 			d->next = (*c)->next;
-			d->CopyParams(**c);
+			if (d->IsCompatible((*c)->version)) {
+				d->CopyParams(**c);
+			} else {
+				d->SetParameterDefaults();
+			}
 			if (this->active_sel == *c) {
 				CloseWindowByClass(WC_GRF_PARAMETERS);
 				CloseWindowByClass(WC_TEXTFILE);