Vyper: Bug report: wrong error message in integer division

[vbuterin]

> from vyper import compiler
> compiler.compile("@public\ndef foo():\n  z:int128 = 5 / 2")
vyper.exceptions.TypeMismatchException: line 3: Invalid type, expected: int128
  z:int128 = 5 / 2

The "expected" type should be decimal, not int128.

[ben-kaufman]

I think the message is correct.
The variable z is an int128 so it expects to receive int128, while 5 / 2 is a decimal. So basically you did try to give an int128 variable a decimal value so the compiler says it expected to receive an int128.

_{Sent with GitHawk}

[fubuloubu]

I thought we changed int/int to return an int. Sounds like there's problems with constants in this regard.

[ben-kaufman]

I think we agreed to change that but it looks like it doesn't work.
Looks like the bug is that int/int returns a decimal instead of an int.

[ben-kaufman]

I checked that out and it looks like the compiler automatically checks if the result is an int.
So if you try the same but with 4 / 2 it will compile to int128 but when the division results in a decimal number it will stay as a decimal (which is good imo).

[fubuloubu]

Nice. Stick a convert in there is you want to avoid there error!

[jacqueswww]

@vbuterin @fubuloubu @ben-kaufman I am not completely sure what we agreed upon with constants/literals case.
The current implementation takes a literal and simplifies it to a single constant :white_check_mark:
But it might be considered inconsistent with the behaviour of using integer division when using variables. :grey_question:
The related accepted VIP is as follows:

https://github.com/ethereum/vyper/issues/775

decimal [op] decimal = decimal (decimal division)
int128 [op] int128 = int128 (signed integer division)
uint256 [op] uint256 = uint256 (unsigned integer division)
decimal [op] integer = COMPILE TIME ERROR
integer [op] decimal = COMPILE TIME ERROR

If we want to keep literals consistent with the above agreed upon VIP.
We should do integer division and return an int128 (if it's in bounds of int 'course)?

[jacqueswww]

^ thumbs up the above comment if you think we should alter to do [literal int] / [literal int] = int128 (using integer division) ?