Regression in std/sets: len used before its definition

[ghost]

The title might not be the most descriptive, but I have an example here. Found in https://github.com/mark-summerfield/diff (which uses std/sets)

Example

# first.nim
import std/sets

type
  Diff*[T] = object
    data: T

proc test*[T](diff: Diff[T]) =
  var bPopular = initHashSet[T]()
  for element in bPopular.items():
    echo element

# second.nim
import first

let a = Diff[int]()
a.test()

Current Output

/home/dian/Projects/ircord/tt2.nim(5, 2) template/generic instantiation of `test` from here
/home/dian/Projects/ircord/tt.nim(9, 26) template/generic instantiation of `items` from here
/home/dian/Things/Nim/lib/pure/collections/sets.nim(241, 17) Error: type mismatch: got <HashSet[system.int]>
but expected one of: 
func len(x: (type array) | array): int
  first type mismatch at position: 1
  required type for x: typedesc[array] or array
  but expression 's' is of type: HashSet[system.int]
func len(x: string): int
  first type mismatch at position: 1
  required type for x: string
  but expression 's' is of type: HashSet[system.int]
func len[TOpenArray: openArray | varargs](x: TOpenArray): int
  first type mismatch at position: 1
  required type for x: TOpenArray: openArray or varargs
  but expression 's' is of type: HashSet[system.int]
func len[T](x: seq[T]): int
  first type mismatch at position: 1
  required type for x: seq[T]
  but expression 's' is of type: HashSet[system.int]
func len[T](x: set[T]): int
  first type mismatch at position: 1
  required type for x: set[T]
  but expression 's' is of type: HashSet[system.int]
proc len(w: WideCString): int
  first type mismatch at position: 1
  required type for w: WideCString
  but expression 's' is of type: HashSet[system.int]
proc len(x: cstring): int
  first type mismatch at position: 1
  required type for x: cstring
  but expression 's' is of type: HashSet[system.int]
proc len[U: Ordinal; V: Ordinal](x: HSlice[U, V]): int
  first type mismatch at position: 1
  required type for x: HSlice[len.U, len.V]
  but expression 's' is of type: HashSet[system.int]

expression: len(s)

Expected Output

Successful compilation

Additional Information

Works in 1.4.4

$ nim -v
Nim Compiler Version 1.5.1 [Linux: amd64]
Compiled at 2021-03-15
Copyright (c) 2006-2021 by Andreas Rumpf

git hash: 51a04a3674d62707506774b11a4376a914735aeb
active boot switches: -d:release -d:danger

[ghost]

Sorry, it's not a regression but rather a change in the sets module I think.

[ghost]

updated the example

[narimiran]

Since this seems to be len-related, this might be the PR which introduced the change in the behaviour:

#16959

[ghost]

Caused by #16959

[ghost]

0cf3ba159c97d3aa00bcb408e99cd4bdef33d64f is the first bad commit
commit 0cf3ba159c97d3aa00bcb408e99cd4bdef33d64f
Author: flywind <43030857+xflywind@users.noreply.github.com>
Date:   Mon Feb 8 04:47:28 2021 -0600

    close #15767 (#16959)
    
    * fix some warnings
    
    * close #15767
    
    * Revert "fix some warnings"
    
    This reverts commit 39f2f23b0026d50c42af7be3ad80edf0f1f19610.

 lib/pure/collections/sets.nim | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)
bisect run success

[timotheecour]

@Yardanico I tried the original example you had reported before editing it to add import std/sets etc, where you said it was working in 1.4.4; for me it didn't work on 1.4.4 either, can you double check?

furthermore:

• it did work when moving up len similar to fix #17385, len must be declared before items #17386
• it did not work when adding mixin len above let length = s.len() despite fixes #11225; generic sandwich problems; [backport:1.2] #17255 being merged (which i was hoping would help with generic sandwich issues /cc @Araq )

for reference:

# first.nim
type
  HashSet*[T] = object
    data: T
    counter: int

iterator items*[T](s: HashSet[T]): int = 
  let length = s.len()
  yield length

proc len*[T](hs: HashSet[T]): int =
  result = hs.counter
# second.nim
import first

type
  Other*[T] = object
    data: T

proc test*[T](x: Other[T]) =
  var test = HashSet[T]()
  for x in test.items():
    echo x
# third.nim
import second

var other = Other[int]()
other.test()

[ghost]

@timotheecour well I specifically edited the example because it was a wrong one, see #17385 (comment)

[timotheecour]

ok, that clarifies, thanks! (updated the example didn't imply this :) )