tools.modtrace: Library for tracing/debugging Lua module and method calls

tools/modtrace.lua

@@ -0,0 +1,152 @@
+-- Trace module calls and method calls on created objects
+--
+-- Very rough and for debugging purposes only. It makes many
+-- assumptions and there are many ways it could fail.
+--
+-- Example use:
+--
+--   local dbuffer = require "tools.modtrace".trace("util.dbuffer");
+--
+
+local t_pack = require "util.table".pack;
+local serialize = require "util.serialization".serialize;
+local unpack = table.unpack or unpack; --luacheck: ignore 113
+local set = require "util.set";
+
+local function stringify_value(v)
+	if type(v) == "string" and #v > 20 then
+		return ("<string(%d)>"):format(#v);
+	elseif type(v) == "function" then
+		return tostring(v);
+	end
+	return serialize(v, "debug");
+end
+
+local function stringify_params(...)
+	local n = select("#", ...);
+	local r = {};
+	for i = 1, n do
+		table.insert(r, stringify_value((select(i, ...))));
+	end
+	return table.concat(r, ", ");
+end
+
+local function stringify_result(ret)
+	local r = {};
+	for i = 1, ret.n do
+		table.insert(r, stringify_value(ret[i]));
+	end
+	return table.concat(r, ", ");
+end
+
+local function stringify_call(method_name, ...)
+	return ("%s(%s)"):format(method_name, stringify_params(...));
+end
+
+local function wrap_method(original_obj, original_method, method_name)
+	method_name = ("<%s>:%s"):format(getmetatable(original_obj).__name or "object", method_name);
+	return function (new_obj_self, ...)
+		local opts = new_obj_self._modtrace_opts;
+		local f = opts.output or io.stderr;
+		f:write(stringify_call(method_name, ...));
+		local ret = t_pack(original_method(original_obj, ...));
+		if ret.n > 0 then
+			f:write(" = ", stringify_result(ret), "\n");
+		else
+			f:write("\n");
+		end
+		return unpack(ret, 1, ret.n);
+	end;
+end
+
+local function wrap_function(original_function, function_name, opts)
+	local f = opts.output or io.stderr;
+	return function (...)
+		f:write(stringify_call(function_name, ...));
+		local ret = t_pack(original_function(...));
+		if ret.n > 0 then
+			f:write(" = ", stringify_result(ret), "\n");
+		else
+			f:write("\n");
+		end
+		return unpack(ret, 1, ret.n);
+	end;
+end
+
+local function wrap_metamethod(name, method)
+	if name == "__index" then
+		return function (new_obj, k)
+			local original_method;
+			if type(method) == "table" then
+				original_method = new_obj._modtrace_original_obj[k];
+			else
+				original_method = method(new_obj._modtrace_original_obj, k);
+			end
+			if original_method == nil then
+				return nil;
+			end
+			return wrap_method(new_obj._modtrace_original_obj, original_method, k);
+		end;
+	end
+	return function (new_obj, ...)
+		return method(new_obj._modtrace_original_obj, ...);
+	end;
+end
+
+local function wrap_mt(original_mt)
+	local new_mt = {};
+	for k, v in pairs(original_mt) do
+		new_mt[k] = wrap_metamethod(k, v);
+	end
+	return new_mt;
+end
+
+local function wrap_obj(original_obj, opts)
+	local new_mt = wrap_mt(getmetatable(original_obj));
+	return setmetatable({_modtrace_original_obj = original_obj, _modtrace_opts = opts}, new_mt);
+end
+
+local function wrap_new(original_new, function_name, opts)
+	local f = opts.output or io.stderr;
+	return function (...)
+		f:write(stringify_call(function_name, ...));
+		local ret = t_pack(original_new(...));
+		local obj = ret[1];
+
+		if ret.n == 1 and type(ret[1]) == "table" then
+			f:write(" = <", getmetatable(ret[1]).__name or "object", ">", "\n");
+		elseif ret.n > 0 then
+			f:write(" = ", stringify_result(ret), "\n");
+		else
+			f:write("\n");
+		end
+
+		if obj then
+			ret[1] = wrap_obj(obj, opts);
+		end
+		return unpack(ret, 1, ret.n);
+	end;
+end
+
+local function trace(module, opts)
+	if type(module) == "string" then
+		module = require(module);
+	end
+	opts = opts or {};
+	local new_methods = set.new(opts.new_methods or {"new"});
+	local fake_module = setmetatable({}, {
+		__index = function (_, k)
+			if new_methods:contains(k) then
+				return wrap_new(module[k], k, opts);
+			else
+				return wrap_function(module[k], k, opts);
+			end
+		end;
+	});
+	return fake_module;
+end
+
+return {
+	wrap = trace;
+	trace = trace;
+}