False positive "this equal statement has no effect" warning

[volsa]

Describe the bug
The following code

{external}
FUNCTION printf : DINT
  VAR_INPUT {ref}
    format : STRING;
  END_VAR
  VAR_INPUT
    args : ...;
  END_VAR
END_FUNCTION

FUNCTION main
  VAR
    a : DINT;
  END_VAR

  printf('%d', a = 1);
END_FUNCTION

will return

warning[E023]: This equal statement has no effect, did you mean `a := 1`?
   ┌─ target/demo.st:16:16
   │
16 │   printf('%d', a = 1);
   │                ^^^^^ This equal statement has no effect, did you mean `a := 1`?

I just wanted this to be documented with a simple reproducible example, however this needs further investigation.