Compiler can't find generic items when iterating over a field in a generic object

[ghost]

This code works only if you replace cache.order with items(cache.order). Title may not be fully correct so feel free to edit it. Found by @PMunch in their https://github.com/PMunch/nim-cache project

Example

# a.nim
type
  Data[T] = object
    data: seq[T]
  
  Cache*[X: static[int]] = ref object
    order: Data[string]

iterator items[T](x: Data[T]): T = 
  for x in x.data:
    yield x

proc initCache*[X: static[int]](): Cache[X] =
  Cache[X](order: Data[string](data: @["hello"]))

iterator items*[X: static[int]](cache: Cache[X]): string =
  # works if you replace cache.order with items(cache.order)
  for item in cache.order:
    yield item

# b.nim
import a

var c = initCache[5]()
for entry in c:
  echo entry

Current Output

/home/dian/Projects/nim-mathexpr/nim-cache/a.nim(17, 20) Error: type mismatch: got <Data[system.string]>
but expected one of: 
iterator items(E: typedesc[enum]): E:type
  first type mismatch at position: 1
  required type for E: type enum
  but expression 'cache.order' is of type: Data[system.string]
iterator items(a: cstring): char
  first type mismatch at position: 1
  required type for a: cstring
  but expression 'cache.order' is of type: Data[system.string]
iterator items(a: string): char
  first type mismatch at position: 1
  required type for a: string
  but expression 'cache.order' is of type: Data[system.string]
iterator items[IX, T](a: array[IX, T]): T
  first type mismatch at position: 1
  required type for a: array[IX, T]
  but expression 'cache.order' is of type: Data[system.string]
iterator items[T](a: openArray[T]): T
  first type mismatch at position: 1
  required type for a: openArray[T]
  but expression 'cache.order' is of type: Data[system.string]
iterator items[T](a: seq[T]): T
  first type mismatch at position: 1
  required type for a: seq[T]
  but expression 'cache.order' is of type: Data[system.string]
iterator items[T](a: set[T]): T
  first type mismatch at position: 1
  required type for a: set[T]
  but expression 'cache.order' is of type: Data[system.string]
iterator items[T](s: HSlice[T, T]): T
  first type mismatch at position: 1
  required type for s: HSlice[items.T, items.T]
  but expression 'cache.order' is of type: Data[system.string]
iterator items[X: static[int]](cache: Cache[X]): string
  first type mismatch at position: 1
  required type for cache: Cache[items.X]
  but expression 'cache.order' is of type: Data[system.string]

expression: items(cache.order)

Expected Output

hello

Nim Compiler Version 1.3.5 [Linux: amd64]
Compiled at 2020-05-26
Copyright (c) 2006-2020 by Andreas Rumpf

git hash: dadc97d91e6ece6387195bdaad54baa9d3f0fc12
active boot switches: -d:release

[nc-x]

Same as #4773, #11167, #4722 i think

[timotheecour]

ya it's a duplicate; closing but feel free to reopen if you disagree