Codechange: [Script] rework how compat-scripts work and are loaded (#13504)

- compat_NNN.nut files now only defines what is needed to downgrade from API NNN + 1 to NNN.
- Automatically load all required compatibility files based on the API version of the script, starting with the latest.

src/ai/ai_info.cpp

@@ -24,8 +24,7 @@
  */
 static bool CheckAPIVersion(const std::string &api_version)
 {
-	static const std::set<std::string> versions = { "0.7", "1.0", "1.1", "1.2", "1.3", "1.4", "1.5", "1.6", "1.7", "1.8", "1.9", "1.10", "1.11", "12", "13", "14", "15" };
-	return versions.find(api_version) != versions.end();
+	return std::ranges::find(AIInfo::ApiVersions, api_version) != AIInfo::ApiVersions.end();
 }
 
 #if defined(_WIN32)

src/ai/ai_info.hpp

@@ -15,6 +15,9 @@
 /** All static information from an AI like name, version, etc. */
 class AIInfo : public ScriptInfo {
 public:
+	/* All valid AI API versions, in order. */
+	static constexpr std::initializer_list<std::string_view> ApiVersions{ "0.7", "1.0", "1.1", "1.2", "1.3", "1.4", "1.5", "1.6", "1.7", "1.8", "1.9", "1.10", "1.11", "12", "13", "14", "15" };
+
 	AIInfo();
 
 	/**

src/ai/ai_instance.cpp

@@ -54,7 +54,7 @@ void AIInstance::RegisterAPI()
 	/* Register all classes */
 	SQAI_RegisterAll(this->engine);
 
-	if (!this->LoadCompatibilityScripts(this->versionAPI, AI_DIR)) this->Died();
+	if (!this->LoadCompatibilityScripts(AI_DIR, AIInfo::ApiVersions)) this->Died();
 }
 
 void AIInstance::Died()

src/game/game_info.cpp

@@ -22,8 +22,7 @@
  */
 static bool CheckAPIVersion(const std::string &api_version)
 {
-	static const std::set<std::string> versions = { "1.2", "1.3", "1.4", "1.5", "1.6", "1.7", "1.8", "1.9", "1.10", "1.11", "12", "13", "14", "15" };
-	return versions.find(api_version) != versions.end();
+	return std::ranges::find(GameInfo::ApiVersions, api_version) != GameInfo::ApiVersions.end();
 }
 
 #if defined(_WIN32)

src/game/game_info.hpp

@@ -15,6 +15,9 @@
 /** All static information from an Game like name, version, etc. */
 class GameInfo : public ScriptInfo {
 public:
+	/* All valid GameScript API versions, in order. */
+	static constexpr std::initializer_list<std::string_view> ApiVersions{ "1.2", "1.3", "1.4", "1.5", "1.6", "1.7", "1.8", "1.9", "1.10", "1.11", "12", "13", "14", "15" };
+
 	GameInfo();
 
 	/**

src/game/game_instance.cpp

@@ -50,7 +50,7 @@ void GameInstance::RegisterAPI()
 
 	RegisterGameTranslation(this->engine);
 
-	if (!this->LoadCompatibilityScripts(this->versionAPI, GAME_DIR)) this->Died();
+	if (!this->LoadCompatibilityScripts(GAME_DIR, GameInfo::ApiVersions)) this->Died();
 }
 
 int GameInstance::GetSetting(const std::string &name)

src/script/script_instance.cpp

@@ -116,9 +116,10 @@ void ScriptInstance::RegisterAPI()
 	squirrel_register_std(this->engine);
 }
 
-bool ScriptInstance::LoadCompatibilityScripts(const std::string &api_version, Subdirectory dir)
+bool ScriptInstance::LoadCompatibilityScript(std::string_view api_version, Subdirectory dir)
 {
 	std::string script_name = fmt::format("compat_{}.nut", api_version);
+
 	for (Searchpath sp : _valid_searchpaths) {
 		std::string buf = FioGetDirectory(sp, dir);
 		buf += script_name;
@@ -126,12 +127,30 @@ bool ScriptInstance::LoadCompatibilityScripts(const std::string &api_version, Su
 
 		if (this->engine->LoadScript(buf)) return true;
 
-		ScriptLog::Error("Failed to load API compatibility script");
+		ScriptLog::Error(fmt::format("Failed to load API compatibility script for {}", api_version));
 		Debug(script, 0, "Error compiling / running API compatibility script: {}", buf);
 		return false;
 	}
 
-	ScriptLog::Warning("API compatibility script not found");
+	ScriptLog::Warning(fmt::format("API compatibility script for {} not found", api_version));
+	return true;
+}
+
+bool ScriptInstance::LoadCompatibilityScripts(Subdirectory dir, std::span<const std::string_view> api_versions)
+{
+	/* Don't try to load compatibility scripts for the current version. */
+	if (this->versionAPI == std::rbegin(api_versions)->data()) return true;
+
+	ScriptLog::Info(fmt::format("Downgrading API to be compatible with version {}", this->versionAPI));
+
+	/* Downgrade the API till we are the same version as the script. The last
+	 * entry in the list is always the current version, so skip that one. */
+	for (auto it = std::rbegin(api_versions) + 1; it != std::rend(api_versions); ++it) {
+		if (!this->LoadCompatibilityScript(*it, dir)) return false;
+
+		if (*it == this->versionAPI) break;
+	}
+
 	return true;
 }
 

src/script/script_instance.hpp

@@ -261,11 +261,11 @@ protected:
 
 	/**
 	 * Load squirrel scripts to emulate an older API.
-	 * @param api_version: API version to load scripts for
-	 * @param dir Subdirectory to find the scripts in
-	 * @return true iff script loading should proceed
+	 * @param dir Subdirectory to find the scripts in.
+	 * @param api_versions List of available versions of the script type.
+	 * @return true iff script loading should proceed.
 	 */
-	bool LoadCompatibilityScripts(const std::string &api_version, Subdirectory dir);
+	bool LoadCompatibilityScripts(Subdirectory dir, std::span<const std::string_view> api_versions);
 
 	/**
 	 * Tell the script it died.
@@ -302,6 +302,14 @@ private:
 	 */
 	bool CallLoad();
 
+	/**
+	 * Load squirrel script for a specific version to emulate an older API.
+	 * @param api_version: API version to load scripts for.
+	 * @param dir Subdirectory to find the scripts in.
+	 * @return true iff script loading should proceed.
+	 */
+	bool LoadCompatibilityScript(std::string_view api_version, Subdirectory dir);
+
 	/**
 	 * Save one object (int / string / array / table) to the savegame.
 	 * @param vm The virtual machine to get all the data from.