Re: Lua 5.3: assert non-string values in #2 cause `(no error message)`-style error message

[Philipp Janda <siffiejoe@...>]

Am 20.10.2014 um 06:46 schröbte Andrew Starks:
> local success, p_res = assert(p(11))
> --> C:\lua.exe: (no error message)
> ```
>
> I don't know if this has broad potential for others, or not, but an error
> would be welcomed here, as well. This time for having any value that is not
> a string or `nil` in assert's second argument would have saved me hours of
> head scratching.

It's not `assert`'s fault. `error{}` without an explicit `pcall` has the 
same "(no error message)" effect. (And some people _want_ to use 
`assert` with non-string error messages ...)

> Not having a line number/file name was very...difficult.

The place where bad things happen is the `msghandler` function in 
`lua.c`. It replaces any non-string errors with strings, but also 
doesn't add a stack trace in this case (which it could since the 
original error value is discarded anyway).

You could add

        msg = lua_tostring(L, -1);
        if (msg)
          luaL_traceback(L, L, msg, 1);

after the `lua_pushliteral` call in `msghandler`. (I'd prefer it that 
`msghandler` leaves all to-string conversions to the `report` function, 
though.)

> --Andrew

Philipp