Env.exePath returns "/memfd:roc_file_descriptor (deleted)" when running as script

[ScallyGames]

Minimal Reproducible Example:

app [main] {
    pf: platform "https://github.com/roc-lang/basic-cli/releases/download/0.16.0/O00IPk-Krg_diNS2dVWlI0ZQP794Vctxzv0ha96mK0E.tar.br",
}

import pf.Env
import pf.Path

main = 
    exePath = Env.exePath!
    exePathStr = Path.display exePath
    dbg exePathStr
    Task.ok {}

Run as roc test.roc

Expected Behavior:

Output of /home/user/path/to/script/test.roc

Actual Behavior:

Output of /memfd:roc_file_descriptor (deleted)

Environment:

OS: Archlinux
Roc Version: roc nightly pre-release, built from commit 06996d8

Context

Discussed in https://roc.zulipchat.com/#narrow/channel/231634-beginners/topic/basic-cli.20debugging.20Env.2EexePath

Implementation (

basic-cli/crates/roc_host/src/lib.rs

Line 432 in 918c1dc

pub extern "C" fn roc_fx_exePath(_roc_str: &RocStr) -> RocResult<RocList<u8>, ()> {

) just defers to Rust's std::env::current_exe() (https://github.com/rust-lang/rust/blob/a8e75c53d0036b5d012cbc0ee5de17f8991fe60c/library/std/src/sys/pal/unix/os.rs#L406) which reads /proc/self/exe which seems to be invalid when running through roc <file>.

Somewhat related is roc-lang/roc#7172 which fixed argv[0] to be set correctly.

Proposed solution is to use argv[0] and ideally combine with Env.cwd for a full absolute path (similar to https://github.com/rust-lang/rust/blob/a8e75c53d0036b5d012cbc0ee5de17f8991fe60c/library/std/src/sys/pal/unix/os.rs#L253) if /proc/self/exe can't be utilized.

Credit to @jwoudenberg and @lukewilliamboswell who did most of the work of putting this information together.