Deserializing to OsString causes strange error about "Unix" and "Windows" variants

[Scripter17]

Edit: And of course the literal second I submit the issue I realize I'm in the json repository, not the main one. Sorry about that.

It's been mentioned that, since not all OsStrings are valid Strings, serializing them to JSON causes problems.

However, since as far as I know all Strings are valid OsStrings, I'd expect serde to deserialize into a String or &str then convert it to an OsString or &OsStr.

Rust version: 1.68.2 stable

Cargo.toml:

[package]
name = "serde_osstring"
version = "0.1.0"
edition = "2021"

# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html

[dependencies]
serde = { version = "1.0.160", features = ["derive"] }
serde_json = "1.0.96"

main.rs:

use serde::Deserialize;
use serde_json;
use std::ffi::OsString;

#[derive(Deserialize)]
struct A {
    x: OsString
}

fn main() {
    serde_json::from_str::<A>("{\"x\": \"y\"}").unwrap();
}

Error with backtrace:

thread 'main' panicked at 'called `Result::unwrap()` on an `Err` value: Error("unknown variant `y`, expected `Unix` or `Windows`", line: 1, column: 9)', src/main.rs:11:49
stack backtrace:
   0:     0x55c6719d55fa - std::backtrace_rs::backtrace::libunwind::trace::ha271a8a7e1f3d4ef
                               at /rustc/9eb3afe9ebe9c7d2b84b71002d44f4a0edac95e0/library/std/src/../../backtrace/src/backtrace/libunwind.rs:93:5
   1:     0x55c6719d55fa - std::backtrace_rs::backtrace::trace_unsynchronized::h85739da0352c791a
                               at /rustc/9eb3afe9ebe9c7d2b84b71002d44f4a0edac95e0/library/std/src/../../backtrace/src/backtrace/mod.rs:66:5
   2:     0x55c6719d55fa - std::sys_common::backtrace::_print_fmt::hbc6ebcfb2910b329
                               at /rustc/9eb3afe9ebe9c7d2b84b71002d44f4a0edac95e0/library/std/src/sys_common/backtrace.rs:65:5
   3:     0x55c6719d55fa - <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt::he1c117e52d53614f
                               at /rustc/9eb3afe9ebe9c7d2b84b71002d44f4a0edac95e0/library/std/src/sys_common/backtrace.rs:44:22
   4:     0x55c6719f2d5e - core::fmt::write::h25eb51b9526b8e0c
                               at /rustc/9eb3afe9ebe9c7d2b84b71002d44f4a0edac95e0/library/core/src/fmt/mod.rs:1213:17
   5:     0x55c6719d3685 - std::io::Write::write_fmt::ha9edec5fb1621933
                               at /rustc/9eb3afe9ebe9c7d2b84b71002d44f4a0edac95e0/library/std/src/io/mod.rs:1682:15
   6:     0x55c6719d53c5 - std::sys_common::backtrace::_print::hf8657cd429fc3452
                               at /rustc/9eb3afe9ebe9c7d2b84b71002d44f4a0edac95e0/library/std/src/sys_common/backtrace.rs:47:5
   7:     0x55c6719d53c5 - std::sys_common::backtrace::print::h41b9b18ed86f86bd
                               at /rustc/9eb3afe9ebe9c7d2b84b71002d44f4a0edac95e0/library/std/src/sys_common/backtrace.rs:34:9
   8:     0x55c6719d6a4f - std::panicking::default_hook::{{closure}}::h22a91871f4454152
                               at /rustc/9eb3afe9ebe9c7d2b84b71002d44f4a0edac95e0/library/std/src/panicking.rs:267:22
   9:     0x55c6719d678b - std::panicking::default_hook::h21ddc36de0cd4ae7
                               at /rustc/9eb3afe9ebe9c7d2b84b71002d44f4a0edac95e0/library/std/src/panicking.rs:286:9
  10:     0x55c6719d7159 - std::panicking::rust_panic_with_hook::h5059419d6d59b3d0
                               at /rustc/9eb3afe9ebe9c7d2b84b71002d44f4a0edac95e0/library/std/src/panicking.rs:688:13
  11:     0x55c6719d6ef9 - std::panicking::begin_panic_handler::{{closure}}::h0f383c291cd78343
                               at /rustc/9eb3afe9ebe9c7d2b84b71002d44f4a0edac95e0/library/std/src/panicking.rs:579:13
  12:     0x55c6719d5aac - std::sys_common::backtrace::__rust_end_short_backtrace::h70ab22f2ad318cdd
                               at /rustc/9eb3afe9ebe9c7d2b84b71002d44f4a0edac95e0/library/std/src/sys_common/backtrace.rs:137:18
  13:     0x55c6719d6c02 - rust_begin_unwind
                               at /rustc/9eb3afe9ebe9c7d2b84b71002d44f4a0edac95e0/library/std/src/panicking.rs:575:5
  14:     0x55c6719a5d73 - core::panicking::panic_fmt::hd1d46bcde3c61d72
                               at /rustc/9eb3afe9ebe9c7d2b84b71002d44f4a0edac95e0/library/core/src/panicking.rs:64:14
  15:     0x55c6719a61c3 - core::result::unwrap_failed::h456a23f68607268c
                               at /rustc/9eb3afe9ebe9c7d2b84b71002d44f4a0edac95e0/library/core/src/result.rs:1790:5
  16:     0x55c6719a66bc - core::result::Result<T,E>::unwrap::h56594b553cab4079
                               at /rustc/9eb3afe9ebe9c7d2b84b71002d44f4a0edac95e0/library/core/src/result.rs:1112:23
  17:     0x55c6719a72b0 - serde_osstring::main::h8c52b5dd0a5f834f
                               at /home/james/Desktop/serde_osstring/src/main.rs:11:5
  18:     0x55c6719a67fb - core::ops::function::FnOnce::call_once::h64223838b298f290
                               at /rustc/9eb3afe9ebe9c7d2b84b71002d44f4a0edac95e0/library/core/src/ops/function.rs:250:5
  19:     0x55c6719a7ece - std::sys_common::backtrace::__rust_begin_short_backtrace::h84f44f7b4c2d9400
                               at /rustc/9eb3afe9ebe9c7d2b84b71002d44f4a0edac95e0/library/std/src/sys_common/backtrace.rs:121:18
  20:     0x55c6719a7381 - std::rt::lang_start::{{closure}}::hf61f028edf677e65
                               at /rustc/9eb3afe9ebe9c7d2b84b71002d44f4a0edac95e0/library/std/src/rt.rs:166:18
  21:     0x55c6719d1a7c - core::ops::function::impls::<impl core::ops::function::FnOnce<A> for &F>::call_once::h203afb3af230319a
                               at /rustc/9eb3afe9ebe9c7d2b84b71002d44f4a0edac95e0/library/core/src/ops/function.rs:287:13
  22:     0x55c6719d1a7c - std::panicking::try::do_call::hf68e87013b70f3c5
                               at /rustc/9eb3afe9ebe9c7d2b84b71002d44f4a0edac95e0/library/std/src/panicking.rs:483:40
  23:     0x55c6719d1a7c - std::panicking::try::h040ea8f298390ba2
                               at /rustc/9eb3afe9ebe9c7d2b84b71002d44f4a0edac95e0/library/std/src/panicking.rs:447:19
  24:     0x55c6719d1a7c - std::panic::catch_unwind::h1e17b198887a05fa
                               at /rustc/9eb3afe9ebe9c7d2b84b71002d44f4a0edac95e0/library/std/src/panic.rs:140:14
  25:     0x55c6719d1a7c - std::rt::lang_start_internal::{{closure}}::hfb902d8927e51b86
                               at /rustc/9eb3afe9ebe9c7d2b84b71002d44f4a0edac95e0/library/std/src/rt.rs:148:48
  26:     0x55c6719d1a7c - std::panicking::try::do_call::h354e6eb41f2e7d42
                               at /rustc/9eb3afe9ebe9c7d2b84b71002d44f4a0edac95e0/library/std/src/panicking.rs:483:40
  27:     0x55c6719d1a7c - std::panicking::try::h4a39749cd018228c
                               at /rustc/9eb3afe9ebe9c7d2b84b71002d44f4a0edac95e0/library/std/src/panicking.rs:447:19
  28:     0x55c6719d1a7c - std::panic::catch_unwind::h30bce83b8de61cca
                               at /rustc/9eb3afe9ebe9c7d2b84b71002d44f4a0edac95e0/library/std/src/panic.rs:140:14
  29:     0x55c6719d1a7c - std::rt::lang_start_internal::h8f7e70b1a2558118
                               at /rustc/9eb3afe9ebe9c7d2b84b71002d44f4a0edac95e0/library/std/src/rt.rs:148:20
  30:     0x55c6719a735a - std::rt::lang_start::h358a865e45ef7ee6
                               at /rustc/9eb3afe9ebe9c7d2b84b71002d44f4a0edac95e0/library/std/src/rt.rs:165:17
  31:     0x55c6719a731e - main
  32:     0x7fc82a829d90 - __libc_start_call_main
                               at ./csu/../sysdeps/nptl/libc_start_call_main.h:58:16
  33:     0x7fc82a829e40 - __libc_start_main_impl
                               at ./csu/../csu/libc-start.c:392:3
  34:     0x55c6719a6305 - _start
  35:                0x0 - <unknown>