util.debug: Fixes to make coroutine tracebacks work properly

util/debug.lua

@@ -88,7 +88,7 @@ function get_traceback_table(thread, start_level)
 	for level = start_level, math.huge do
 		local info;
 		if thread then
-			info = debug.getinfo(thread, level+1);
+			info = debug.getinfo(thread, level);
 		else
 			info = debug.getinfo(level+1);
 		end
@@ -97,7 +97,7 @@ function get_traceback_table(thread, start_level)
 		levels[(level-start_level)+1] = {
 			level = level;
 			info = info;
-			locals = get_locals_table(level+1);
+			locals = not thread and get_locals_table(level+1);
 			upvalues = get_upvalues_table(info.func);
 		};
 	end
@@ -134,12 +134,12 @@ function _traceback(thread, message, level)
 		return nil; -- debug.traceback() does this
 	end
 
-	level = level or 1;
+	level = level or 0;
 
 	message = message and (message.."\n") or "";
 
-	-- +3 counts for this function, and the pcall() and wrapper above us
-	local levels = get_traceback_table(thread, level+3);
+	-- +3 counts for this function, and the pcall() and wrapper above us, the +1... I don't know.
+	local levels = get_traceback_table(thread, level+(thread == nil and 4 or 0));
 
 	local last_source_desc;
 
@@ -171,9 +171,11 @@ function _traceback(thread, message, level)
 		nlevel = nlevel-1;
 		table.insert(lines, "\t"..(nlevel==0 and ">" or " ")..getstring(styles.level_num, "("..nlevel..") ")..line);
 		local npadding = (" "):rep(#tostring(nlevel));
-		local locals_str = string_from_var_table(level.locals, optimal_line_length, "\t            "..npadding);
-		if locals_str then
-			table.insert(lines, "\t    "..npadding.."Locals: "..locals_str);
+		if level.locals then
+			local locals_str = string_from_var_table(level.locals, optimal_line_length, "\t            "..npadding);
+			if locals_str then
+				table.insert(lines, "\t    "..npadding.."Locals: "..locals_str);
+			end
 		end
 		local upvalues_str = string_from_var_table(level.upvalues, optimal_line_length, "\t            "..npadding);
 		if upvalues_str then