LAST phaser fires for some loops that never ran

[sorpigal]

The Problem

While experimenting with loop phasers I found that the LAST phaser will fire for at least some loops when FIRST did not fire and indeed the loop was never entered.

The phaser documentation at https://github.com/Raku/doc/blob/main/doc/Language/phasers.rakudoc says this about loop phasers:

FIRST {...} # at loop initialization time, before any ENTER
NEXT {...} # at loop continuation time, before any LEAVE
LAST {...} # at loop termination time, after any LEAVE

It also says this about LAST:

Runs when a loop is finished because the condition is met, or when it exits
using last or return; it is executed after LEAVE.

For a loop where the condition is never met, or where there is no condition, this implies that LAST will not fire.

Suspiciously, there is no test case for LAST at https://github.com/Raku/roast/tree/master/S04-phasers where the tests for FIRST/ENTER/LEAVE are found.

Expected Behavior

The behavior of the for and while loops should match in terms of what phasers fire when the loop is never entered. Either LAST should fire for both, or for neither. A plain reading of the documentation suggests that "neither" is correct. For the loop case you could argue that the condition is met because the test must have evaluated to False once, but it seems more logical to never run LAST if the loop body executed zero times.

If the current behavior is intended then I will re-file this as a documentation issue so it can become more clear that LAST will fire in this case, and why.

Actual Behavior

The LAST phaser fired even though the loop was never run (and no matching FIRST phaser fired).

Steps to Reproduce

Expected:

$ raku -e "my @a; for () { FIRST @a.push: 'first'; ENTER @a.push: 'enter'; NEXT @a.push: 'next'; LEAVE @a.push: 'leave'; LAST @a.push: 'last'; }; @a.say"
[]

Unexpected:

$ raku -e "my @a; while () { FIRST @a.push: 'first'; ENTER @a.push: 'enter'; NEXT @a.push: 'next'; LEAVE @a.push: 'leave'; LAST @a.push: 'last'; }; @a.say"
[last]

$ raku -e "my @a; loop (;False;) { FIRST @a.push: 'first'; ENTER @a.push: 'enter'; NEXT @a.push: 'next'; LEAVE @a.push: 'leave'; LAST @a.push: 'last'; }; @a.say"
[last]

[lizmat]

It looks like these issues have been fixed in RakuAST.