Compiler thinks an unused proc is used when an auto parameter is used

[diegomrsantos]

Description

When executing

type
  SomeObj = object
    hey: bool

proc hey() {.deprecated: "Shouldn't use this".} = echo "hey"

proc gen(o: auto) =
  if o.hey:
    echo "bool"

gen(SomeObj(hey: true))

The compiler thinks the hey proc is being called and outputs the warning, but it is not actually being called.

Nim Version

Nim Compiler Version 1.6.12 [MacOSX: amd64]
Compiled at 2023-03-16
Copyright (c) 2006-2023 by Andreas Rumpf

active boot switches: -d:release

Current Output

.................................................................
t.nim(8, 8) Warning: Shouldn't use this; hey is deprecated [Deprecated]
CC: t.nim
Hint:  [Link]
Hint: gc: refc; threads: on; opt: none (DEBUG BUILD, `-d:release` generates faster code)
64653 lines; 0.353s; 75.875MiB peakmem; proj: t; out: t [SuccessX]
Hint: t  [Exec]
bool

Expected Output

.................................................................
t.nim(5, 6) Hint: 'hey' is declared but not used [XDeclaredButNotUsed]
CC: t.nim
Hint:  [Link]
Hint: gc: refc; threads: on; opt: none (DEBUG BUILD, `-d:release` generates faster code)
64653 lines; 0.353s; 75.875MiB peakmem; proj: t; out: t [SuccessX]
Hint: t  [Exec]
bool

Possible Solution

No response

Additional Information

No response

[Menduist]

When using error instead of deprecated, the code doesn't even compile, making this issue more problematic

[beef331]

Could not help but minimize it further, the issue is that closed symbol causes semantic analysis to be done, which means it compiles the deprecated. Swapping bind for mixin causes this deprecation to disappear.

proc hey() {.deprecated: "Shouldn't use this".} = echo "hey"

proc gen(o: auto) =
  bind hey

[beef331]

I assume it's just to do exactly as this issue does but in a sensible way

proc doThing(x: auto) = discard
proc myGen(x: auto) = doThing(x) # We use `doThing` so it's used

Arguably the issue here is really that o.hey does field access instead of invoking the closed symbol and erroring that it expects 0 parameters.