a Seq's first .iterator call shall be recorded with backtrace to be outputted when .iterator is called a second time ("seq already had its iterator taken and got consumed" or whatever)

01-output.txt

making patch
will create seq
seq has which Seq|66864704
0
first user:
0.5
1
1.5
second user:
iterator already taken for this seq:
      in method map at SETTING::src/core.c/Any-iterable-methods.pm6 line 40
      in sub first-user at /tmp/wraptest.raku line 47
      in block <unit> at /tmp/wraptest.raku line 56


--> encountered when this code tried to take the iterator another time:
      in method map at SETTING::src/core.c/Any-iterable-methods.pm6 line 40
      in sub second-user at /tmp/wraptest.raku line 50
      in block <unit> at /tmp/wraptest.raku line 58


(btw this Seq is iterating a Rakudo::Iterator::ReifiedListIterator|66867248)

  in sub second-user at /tmp/wraptest.raku line 50
  in block <unit> at /tmp/wraptest.raku line 58

02-implementation.rakumod

my $in-patch = 0;
role TappedSeq {
    has $.introducer is rw;
    has $.iterator-at-the-time is rw;
    method iterator is hidden-from-backtrace {
        $in-patch++;
        #say "entering trouble reporting";
        my $second-call = Backtrace.new(3).full;
        my $text = $.introducer.full;
        die qq:to/ERROR/;
        iterator already taken for this seq:
        $text.indent(4)

        --> encountered when this code tried to take the iterator another time:
        $second-call.indent(4)

        (btw this Seq is iterating a $!iterator-at-the-time)
        ERROR
        LEAVE $in-patch--;
    }
};

say "making patch";
Seq.^find_method("iterator").wrap(
    sub wrapper( $self ) is hidden-from-backtrace {
        #if $in-patch >= 2 { say "not patching " ~ $self.WHICH; LEAVE { $in-patch--; }; nextsame; say "oh my?" }
        if $in-patch >= 2 { LEAVE { $in-patch--; }; nextsame; }
        my $result := callwith($self);
        $self does TappedSeq;
        $self.introducer = Backtrace.new(7);
        $self.iterator-at-the-time = $result.WHICH;
        ENTER { $in-patch++; }
        LEAVE { $in-patch--; }
        return $result
    });

say "will create seq";
my $s = (1, 2, 3).Seq;
say "seq has which " ~ $s.WHICH;

            #if $me ~~ TappedSeq { note "this seq was already grabbed here:\n" ~ $me.introducer; } else { $me does TappedSeq; $me.introducer = Backtrace.new.full; callsame; LEAVE { $in-patch = 0 } } } } }); }; do-patch();

my $i1;
my $i2;

sub first-user  {
    .say for $s.map(* / 2)
}
sub second-user {
    .say for $s.map(*+1)
}

say $in-patch;

say "first user:";
first-user();
say "second user:";
second-user();