compiler crash on len of varargs[untyped]

[arnetheduck]

Description

template encodeList*(args: varargs[untyped]): seq[byte] =
  @[byte args.len]

let x = encodeList([22], 43)

Nim Version

2.0.8

Current Output

nim c -r "/home/arnetheduck/status/nimbus-eth1/_exper/testit.nim"
.......................................................................................................................assertions.nim(34)       raiseAssert
Error: unhandled exception: renderer.nim(1313, 7) `n.len == 2` 3 [AssertionDefect]

Expected Output

No response

Known Workarounds

No response

Additional Information

No response

[ringabout]

You probably need to use varargsLen

template encodeList*(args: varargs[untyped]): seq[byte] =
  @[byte varargsLen(args)]

let x = encodeList([22], 43)
echo x

[arnetheduck]

You probably need to use varargsLen

... but why? len is a perfectly fine name for this.

[arnetheduck]

template x(v: varargs[int]) =
  echo v.len

x(2, 3, 4)

for comparison, this works

[ringabout]

In addition to the untyped meta-type that prevents type checking, there is also varargs[untyped] so that not even the number of parameters is fixed:

varargs[int] type checks the parameters, which means 2, 3, 4 are passed as an array form. It equals to len([1, 2, 3]). varargs[untyped] passes the parameters as they are. So it is equal to len(1, 2, 3) which is not valid.

[arnetheduck]

sure, but why a separate name for it? it's conceptually the same thing except for some implementation details.

[ringabout]

I don't know. But in #12907

It said that

IMO len should be made to just work on varargs by making this case behave as the following:

as I mentioned above, it can't, it'd introduce inherent ambiguities due to the way templates work and varargs gets unboxed