Add: [Script] Labels for negative values of a setting

src/script/api/script_info_docs.hpp

@@ -254,13 +254,16 @@ class ScriptInfo {
 	 *  user will see the corresponding name.
 	 * @param setting_name The name of the setting.
 	 * @param value_names A table that maps values to names. The first
-	 *   character of every identifier is ignored and the rest should
+	 *   character of every identifier is ignored, the second character
+	 *   could be '_' to indicate the value is negative, and the rest should
 	 *   be an integer of the value you define a name for. The value
 	 *   is a short description of that value.
 	 * To define labels for a setting named "competition_level" you could
 	 * for example call it like this:
 	 * AddLabels("competition_level", {_0 = "no competition", _1 = "some competition",
 	 * _2 = "a lot of competition"});
+	 * Another example, for a setting with a negative value:
+	 * AddLabels("amount", {__1 = "less than one", _0 = "none", _1 = "more than one"});
 	 *
 	 * @note This is a function provided by OpenTTD, you don't have to
 	 * include it in your Script but should just call it from GetSettings.

src/script/script_info.cpp

@@ -252,7 +252,14 @@ SQInteger ScriptInfo::AddLabels(HSQUIRRELVM vm)
 		if (SQ_FAILED(sq_getstring(vm, -1, &label))) return SQ_ERROR;
 		/* Because squirrel doesn't support identifiers starting with a digit,
 		 * we skip the first character. */
-		int key = atoi(key_string + 1);
+		key_string++;
+		int sign = 1;
+		if (*key_string == '_') {
+			/* When the second character is '_', it indicates the value is negative. */
+			sign = -1;
+			key_string++;
+		}
+		int key = atoi(key_string) * sign;
 		StrMakeValidInPlace(const_cast<char *>(label));
 
 		/* !Contains() prevents stredup from leaking. */