term: obtain the cursor position via termios.h

[onerbs]

This PR solves a TODO:
Use termios.h, C.tcgetattr and C.tcsetattr directly, instead of using stty

...But I have a couple of doubts:

1. The code inside a defer block is called on panic?
   'cuz this implementation assumes a yes, a no might cause unwanted results
   (i.e. not restoring the initial terminal state)
2. Would it be better to use C.printf('\e[6n'.str) instead of print('\e[6n')? (L63)
   according to my tests it doesn't seem to make a difference, but I am not an expert.
   ('m thinking about performance here, but I think no one will call this function so many times to notice 🤷🏻)

Cheers !
😺

[spytheman]

It would be better to make the function return an ?Coord and use return error('description') instead of the panic() calls.

[spytheman]

The code inside a defer block is called on panic?

Currently it is not.

[spytheman]

Would it be better to use C.printf('\e[6n'.str) instead of print('\e[6n')? (L63)

Pure V is cleaner imho.

[onerbs]

So, by making the get_cursor_position return an optional for *NIX it leaves the same function for Windows with a different signature. A possible solution would be:

pub fn get_cursor_position() ?Coord {
	if os.is_atty(1) <= 0 && os.getenv('TERM') != 'dumb' {
		return Coord{}
	}
	info := C.CONSOLE_SCREEN_BUFFER_INFO{}
	if !C.GetConsoleScreenBufferInfo(C.GetStdHandle(C.STD_OUTPUT_HANDLE), &info) {
		return error(os.get_error_msg(int(C.GetLastError())))
	}
	return Coord{
		x: info.dwCursorPosition.X
		y: info.dwCursorPosition.Y
	}
}

But there are more functions that use the GetConsoleScreenBufferInfo function. When making the change above, should all other functions be updated as well? (I'm thinking of a no)

Also,

In term.ui there's a function called get_cursor_position. I understand that the module was developed independently and then got merged... I think term.ui should import term, but that's another topic.

[awmorgan]

cc -std=gnu99 -w -o ./v ./vc/v.c -lm -lpthread
./vc/v.c:30104:84: error: field designator 'c_line' does not refer to any field in type 'struct termios'
old_state = (struct termios){.c_iflag = 0,.c_oflag = 0,.c_cflag = 0,.c_lflag = 0,.c_line = 0,.c_cc = {0},};
^
./vc/v.c:30109:95: error: field designator 'c_line' does not refer to any field in type 'struct termios'
struct termios state = (struct termios){.c_iflag = 0,.c_oflag = 0,.c_cflag = 0,.c_lflag = 0,.c_line = 0,.c_cc = {0},};
^