Speed up, fix fish_status_to_signal

[IlanCosman]

Description

Some super small changes to fish_status_to_signal that grant a massive speed boost.
Running (count $signals) is slow, and silly considering that we know the number already.
And this list of signals is never, ever going to change, so it won't waste any developer time in the future.

# In config.fish
set -g list (seq 255)

function new_status_to_signal
    for arg in $argv
        if test $arg -gt 128
            set -l sigix (math $arg - 128)
            if test $sigix -le 31
                set -l signals SIGHUP SIGINT SIGQUIT SIGILL SIGTRAP SIGABRT SIGBUS \
                    SIGFPE SIGKILL SIGUSR1 SIGSEGV SIGUSR2 SIGPIPE SIGALRM \
                    SIGTERM SIGSTKFLT SIGCHLD SIGCONT SIGSTOP SIGTSTP \
                    SIGTTIN SIGTTOU SIGURG SIGXCPU SIGXFSZ SIGVTALRM \
                    SIGPROF SIGWINCH SIGIO SIGPWR SIGSYS
                echo $signals[$sigix]
            else
                echo $arg
            end
        else
            echo $arg
        end
    end
    return 0
end

ilan@arch ~> hyperfine --shell=fish "fish_status_to_signal \$list" "new_status_to_signal \$list"
Benchmark 1: fish_status_to_signal $list
  Time (mean ± σ):      23.4 ms ±   3.0 ms    [User: 15.6 ms, System: 10.0 ms]
  Range (min … max):    12.9 ms …  37.4 ms    103 runs
 
Benchmark 2: new_status_to_signal $list
  Time (mean ± σ):      11.7 ms ±   0.9 ms    [User: 7.3 ms, System: 6.0 ms]
  Range (min … max):     6.7 ms …  14.5 ms    177 runs
 
Summary
  'new_status_to_signal $list' ran
    1.99 ± 0.30 times faster than 'fish_status_to_signal $list'

[floam]

Yikes! This speedup is nice but this function is no bueno! For starters, SIGBUS (10, not 7) comes after SIGKILL and before SIGSEGV on my system.

signal 7 is SIGEMT here. This hardcoded list idea is trouble.

[floam]

Would you like to also fix that while you are improving this function? We actually cache these - see the completions for kill/killall. What you want to do is check for $__kill_signals otherwise run __fish_make_completion_signals.

[IlanCosman]

Can do 👍

[IlanCosman]

Should be good now, hope I did things right 😄