A bizzare static int related error

[dawkot]

When either of the commented lines is uncommented the code compiles, but if both are uncommented an error is returned.

import sugar

type Obj[N: static int] = object

func arr(N: static int, fn: 0..N -> void): Obj[N] =
  for i in (0 ..< N): fn i

func map[N](a: Obj[N], fn: () -> void): Obj[N] =
  arr(N, (i: 0..N) => fn())

static:
  # discard Obj[2]().map(() => nil)
  # discard Obj[3]().map(() => nil)
  discard

error message:

 error2.nim(13, 19) template/generic instantiation from here
 error2.nim(9, 6) Error: type mismatch: got <static[int literal(3)](3), proc (i: range 0..3(int)){.closure, noSideEffect, gcsafe, locks: <unknown>.}>
 but expected one of:
 func arr(N: static int; fn: 0 .. N -> void): Obj[N]
   first type mismatch at position: 2
   required type: proc (i0: range 0..2(int)){.closure.}
   but expression 'proc (i: 0 .. N): auto = fn()' is of type: proc (i: range 0..3(int)){.closure, noSideEffect, gcsafe, locks: <unknown>.}
 
 expression: arr(N, proc (i: 0 .. N): auto = fn())

[mratsim]

Not too sure how to solve that but the relevant part of the error message is this:

required type: proc (i0: range 0..2(int)){.closure.}
expression ... is of type: proc (i: range 0..3(int))

[jangko]

the symptoms looks very much like #8569, #7976

[metagn]

Is the -> macro causing it?

[dawkot]

Is the -> macro causing it?

No. But, sure, I shouldn't use it in the example in the first place. This returns the same error:

type Obj[N: static int] = object

func arr(N: static int, fn: proc(_: 0..N): void): Obj[N] =
  for i in (0 .. N): fn i

func map[N](a: Obj[N], fn: proc()): Obj[N] =
  arr(N, proc(i: 0..N) = fn())

static:
  # discard Obj[2]().map(proc() = discard)
  # discard Obj[3]().map(proc() = discard)
  discard

[LemonBoy]

type Obj[N: static int] = object

func arr[N: static int](fn: proc(_: 0..N): void): Obj[N] =
  for i in (0 .. N): fn i

func map[N](a: Obj[N], fn: proc()): Obj[N] =
  arr[N](proc(i: 0..N) = fn())

static:
  discard Obj[2]().map(proc() = discard)
  discard Obj[3]().map(proc() = discard)

Using a static int parameter makes the compiler instantiate the proc(_: 0..N): void) expression as proc(_: 0..2): void) and doesn't make the arr procedure generic (even though the N parameter is lifted as an implicit generic) so it is only instantiated once.

[krux02]

@dawkot is the question solved?

[dawkot]

@krux02 Sure, but at least the error message should be more clear.

[dawkot]

The code compiles now on

Nim Compiler Version 1.0.2 [Windows: amd64]
Compiled at 2019-10-22