We are nearing the replacement of core:os, this issue outlines todos and nice to haves.

Todos:

• core:os/os2 read_entire_file creates infinite loop #3279
• os2.pipe() -> Assert error #4712
• @gingerBill needs to look at the env API, env_posix.odin has a bunch of NOTE(laytan): comments outlining potential improvements, same thing on the directory iterator, these comments are mostly about surfacing errors instead of ignoring them or returning just a boolean (which core:os famously does a lot and we should avoid) (b3bbb00 & 7994405)
• the IMPORTANT NOTE saying the package is a mockup needs to be removed from doc.odin
• write on linux needs to loop until everything is written, just like windows and posix implementations (os/os2: bring Linux to other impls standards by looping writes and maxing one shot RW sizes #4730)
• linux does not do the MAX_RW thing other implementations do but afaik it does have the same restriction (os/os2: bring Linux to other impls standards by looping writes and maxing one shot RW sizes #4730)
• remove on posix needs to handle directories, just like the other implementations (it already did, whoops)
• unused File_Flag cases should be removed, .Sparse, .Unbuffered_IO
• core:path needs to be looked over and possibly removed/merged into os2 (Add new path API for os2 #4954)
• Flysand: create() does not allow to set the permission bits or specify the behavior when the file exists (.Trunc or .Excl). I would like to see truncate parameter to that procedure that is false by default. If it's not specified, .Excl is the behavior on existing files, otherwise existing file is truncated.
• atomic bulk operations
• bulk operations errors with more info on what actually went wrong and where, so instead of Permission_Denied, get a path back or something too

Targets supported in core:os but not yet in core:os/os2:

• wasi (os/os2: wasi target support #4716)
• js - just os.write is implemented, maybe it should just be dropped entirely for os2
• haiku - should be pretty easy to use the posix implementation at first, can go "native" later

Non blocking but can have api consequences:

• buffered file mode/flag (needs testing to see if it's beneficial)
• Jeroen: Virtual File System - file possibly backed by not actual files

Packages that use core:os and need to be updated:

• core:compress/gzip

• core:crypto

• core:encoding/csv

• core:encoding/hxa

• core:encoding/ini

• core:encoding/xml

• core:flags

• core:fmt (JS impl needs rewrite to not use core:os at all)

• core:image/bmp

• core:image/netpbm

• core:image/png

• core:image/qoi

• core:image/tga

• core:image

• core:log

• core:math/big

• core:mem/virtual

• core:net

• core:odin/parser

• core:path/filepath

• core:prof/spall

• core:testing

• core:text/i18n

• core:text/regex

• core:text/table

• core:time/timezone

• core:unicode/tools

• tests/core/encoding/hxa

• tests/core/flags

• tests/core/io

• tests/documentation

• vendor:fontstash

• vendor:libc

• vendor:opengl

• odin-lang/examples repo needs to be updated

Nice to have, but not blocking the replacement of core:os:

• more tests
• docs additions, dir.odin, file.odin, etc. don't have any docs
• docs unification, doc style differs between files and procs
• linux process_info should query /proc/pid/exe instead of the way it's done now to get executable paths
• netbsd, openbsd, freebsd targets implementation for _process_info_by_pid, _process_list, _process_open, _process_handle_still_valid, _process_state_update_times for full process API coverage (decided to make non blocking because it is a new API)
• current_executable_path(allocator: runtime.Allocator) -> (string, Error) returning the full absolute executable path of the program, useful for loading things relative to this path. You can already do this in a round about way with: current_process_info({.Executable_Path}, context.allocator) but a more direct way with the native APIs for each target would be nice (os/os2: add get_executable_path and get_executable_directory #4733)
• wrapper api over the process API that handles the details of processes and just allows easy communication, similar to this idea: https://gist.github.com/laytan/68be38614d9274663a48fd3d710fefc2
• a heap allocator that does not rely on any system libraries, ideally this goes into base: though, so it can be the default allocator in general (Add native lock-free dynamic heap allocator #4749)
• core:testing to replace os2.stdout and os2.stderr with an implementation that synchronises between tests (currently writing to stdout or stderr in tests doesn't work well because the terminal renders progress and clears it out)
• Flysand: There is no procedure to free a file handle without closing it (which can be used in tandem with new_file, if i.e. a library returned a handle, and that library is responsible for closing the file).
• Flysand: It would be nice to have unlink :: remove alias.

After replacement the following can be closed:

• Spawning a process #3325
• core:os package read_entire_file_xxx procedures don't work on /proc filesystem even if on a Linux system #4264
• Implement os.environ() on Linux #3154
• copy_file implemented for Windows, Linux and Darwin #3186