Codechange: use setting name instead of index for HandleOldDiffCustom() (#9311)

src/settings.cpp

@@ -22,6 +22,7 @@
  */
 
 #include "stdafx.h"
+#include <array>
 #include <limits>
 #include "currency.h"
 #include "screenshot.h"
@@ -1227,7 +1228,9 @@ static void PrepareOldDiffCustom()
  */
 static void HandleOldDiffCustom(bool savegame)
 {
-	uint options_to_load = GAME_DIFFICULTY_NUM - ((savegame && IsSavegameVersionBefore(SLV_4)) ? 1 : 0);
+	/* Savegames before v4 didn't have "town_council_tolerance" in savegame yet. */
+	bool has_no_town_council_tolerance = savegame && IsSavegameVersionBefore(SLV_4);
+	uint options_to_load = GAME_DIFFICULTY_NUM - (has_no_town_council_tolerance ? 1 : 0);
 
 	if (!savegame) {
 		/* If we did read to old_diff_custom, then at least one value must be non 0. */
@@ -1239,11 +1242,21 @@ static void HandleOldDiffCustom(bool savegame)
 		if (!old_diff_custom_used) return;
 	}
 
-	for (uint i = 0; i < options_to_load; i++) {
-		const SettingDesc *sd = GetSettingDescription(i);
-		/* Skip deprecated options */
-		if (!SlIsObjectCurrentlyValid(sd->save.version_from, sd->save.version_to)) continue;
-		int32 value = (int32)((i == 4 ? 1000 : 1) * _old_diff_custom[i]);
+	/* Iterate over all the old difficulty settings, and convert the list-value to the new setting. */
+	uint i = 0;
+	for (const auto &name : _old_diff_settings) {
+		if (has_no_town_council_tolerance && name == "town_council_tolerance") continue;
+
+		std::string fullname = "difficulty." + name;
+		const SettingDesc *sd = GetSettingFromName(fullname.c_str());
+
+		/* Some settings are no longer in use; skip reading those. */
+		if (sd == nullptr) {
+			i++;
+			continue;
+		}
+
+		int32 value = (int32)((name == "max_loan" ? 1000 : 1) * _old_diff_custom[i++]);
 		sd->AsIntSetting()->MakeValueValidAndWrite(savegame ? &_settings_game : &_settings_newgame, value);
 	}
 }

src/settings_type.h

@@ -61,6 +61,9 @@ enum IndustryDensity {
 
 /** Settings related to the difficulty of the game */
 struct DifficultySettings {
+	byte   competitor_start_time;            ///< Unused value, used to load old savegames.
+	byte   competitor_intelligence;          ///< Unused value, used to load old savegames.
+
 	byte   max_no_competitors;               ///< the number of competitors (AIs)
 	byte   number_towns;                     ///< the amount of towns
 	byte   industry_density;                 ///< The industry density. @see IndustryDensity

src/table/settings/gameopt_settings.ini

@@ -15,6 +15,7 @@
 
 [pre-amble]
 static const uint GAME_DIFFICULTY_NUM = 18;
+static const std::array<std::string, GAME_DIFFICULTY_NUM> _old_diff_settings{"max_no_competitors", "competitor_start_time", "number_towns", "industry_density", "max_loan", "initial_interest", "vehicle_costs", "competitor_speed", "competitor_intelligence", "vehicle_breakdowns", "subsidy_multiplier", "construction_cost", "terrain_type", "quantity_sea_lakes", "economy", "line_reverse_mode", "disasters", "town_council_tolerance"};
 static uint16 _old_diff_custom[GAME_DIFFICULTY_NUM];
 uint8 _old_diff_level;                                 ///< Old difficulty level from old savegames
 uint8 _old_units;                                      ///< Old units from old savegames

src/table/settings/settings.ini

@@ -94,7 +94,7 @@ startup  = false
 
 
 ; Saved settings variables.
-; Do not ADD or REMOVE something in this "difficulty.XXX" table or before it. It breaks savegame compatibility.
+; The next 18 entries are important for savegame compatibility. Do NOT remove those. See HandleOldDiffCustom() for more details.
 [SDT_VAR]
 var      = difficulty.max_no_competitors
 type     = SLE_UINT8
@@ -106,10 +106,14 @@ interval = 1
 post_cb  = MaxNoAIsChange
 cat      = SC_BASIC
 
-[SDT_NULL]
-length   = 1
+[SDT_VAR]
+var      = difficulty.competitor_start_time
+type     = SLE_UINT8
 from     = SLV_97
 to       = SLV_110
+def      = 2
+min      = 0
+max      = 3
 
 [SDT_VAR]
 var      = difficulty.number_towns
@@ -192,10 +196,14 @@ strhelp  = STR_CONFIG_SETTING_CONSTRUCTION_SPEED_HELPTEXT
 strval   = STR_AI_SPEED_VERY_SLOW
 cat      = SC_BASIC
 
-[SDT_NULL]
-length   = 1
+[SDT_VAR]
+var      = difficulty.competitor_intelligence
+type     = SLE_UINT8
 from     = SLV_97
 to       = SLV_110
+def      = 0
+min      = 0
+max      = 2
 
 [SDT_VAR]
 var      = difficulty.vehicle_breakdowns