which without application param now lists only executables

[xolra0d]

Release notes summary - What our users need to know

The which command now filters files found in $PATH to include only executables.

Tasks after submitting

---

Done:

1. Optimized search on Windows.
2. Add is_executable check for found files in PATH.

Should resolve controversy in #16140

[xolra0d]

I've done some benchmarking and profiling.

Tested on the same device on Linux and Windows. My config:

$ which | length	all files in PATH	only executables in PATH
Linux	4043	4032
Windows	7731	1211

Results:

1. Current which and which --all implementations perform well on Linux, yet suffer drastically on Windows.

   Perf diff	Time
   Linux	5.957ms
   Windows	104.319ms

   This big difference is caused by path.is_file() check, which is extrimely expensive in Windows.

2. After adding is_executable to algorithm and optimizing it, results are:

   Perf diff	Old with path.is_file()	New with path.is_executable()	Percentage difference
   Linux	5.957ms	6.039ms	1.3%
   Windows	104.319ms	11.166ms	−89.2%

   Note: old version with removed path.is_file() check was 12.319ms

Current is_executable implementation is the same as in is_executable crate, but removes another expensive check on Windows: path.exists().

[xolra0d]

With windows crate, timeit {which} is 14ms.

[fdncred]

Please add some text that describes what this does in the release notes section so it can be mentioned in the next release's notes.

[xolra0d]

Please add some text that describes what this does in the release notes section so it can be mentioned in the next release's notes.

Done

[fdncred]

This is what I'm seeing on Windows. Of course, all of this depends on how many files you have in your path and what type of hard drives you have in your machine. I'm fine with this. Thanks!

Before

❯ use std/bench *
❯ bench { which } --rounds 100
╭──────┬────────────────────────╮
│ mean │ 1sec 204ms 295µs 764ns │
│ min  │ 1sec 170ms 6µs 800ns   │
│ max  │ 2sec 279ms 917µs 100ns │
│ std  │ 108ms 936µs 393ns      │
╰──────┴────────────────────────╯

After

❯ use std/bench *
❯ bench { which } --rounds 100
╭──────┬───────────────────╮
│ mean │ 276ms 41µs 368ns  │
│ min  │ 270ms 169µs 400ns │
│ max  │ 360ms 372µs 200ns │
│ std  │ 9ms 478µs 767ns   │
╰──────┴───────────────────╯