thread 'main' panicked at 'called Result::unwrap() on an Err value: ExpectedString', core/error.rs:202:52

[NetOpWibby]

============================================================
Deno has panicked. This is a bug in Deno. Please report this
at https://github.com/denoland/deno/issues/new.
If you can reliably reproduce this panic, include the
reproduction steps and re-run with the RUST_BACKTRACE=1 env
var set and include the backtrace in your report.

Platform: macos aarch64
Version: 1.21.0
Args: ["deno", "run", "--allow-net", "--allow-read", "--allow-run", "--allow-write", "main.ts"]

thread 'main' panicked at 'called `Result::unwrap()` on an `Err` value: ExpectedString', core/error.rs:202:52
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

Initial backtrace

stack backtrace:
   0: _rust_begin_unwind
   1: core::panicking::panic_fmt
   2: core::result::unwrap_failed
   3: deno_core::error::JsError::inner_from_v8_exception
   4: deno_core::runtime::exception_to_err_result
   5: deno_core::runtime::JsRuntime::check_promise_exceptions
   6: deno_core::runtime::JsRuntime::poll_event_loop
   7: <core::future::from_generator::GenFuture<T> as core::future::future::Future>::poll
   8: <core::future::from_generator::GenFuture<T> as core::future::future::Future>::poll
   9: deno::run_command::{{closure}}
  10: <core::future::from_generator::GenFuture<T> as core::future::future::Future>::poll
  11: deno::main::{{closure}}
  12: <core::future::from_generator::GenFuture<T> as core::future::future::Future>::poll
  13: deno_runtime::tokio_util::run_basic
  14: deno::main
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.

Full backtrace

stack backtrace:
   0:        0x1015314f4 - <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt::hd6a6e3b094c481b1
   1:        0x100e1e614 - core::fmt::write::h55deb439a2fa505d
   2:        0x10151c000 - std::io::Write::write_fmt::hdd0ccc220f7ec3f7
   3:        0x10152806c - std::panicking::default_hook::{{closure}}::haecbbf48cd1ad553
   4:        0x101527cec - std::panicking::default_hook::hdf33d6d87b6673e5
   5:        0x100cb741c - deno::setup_panic_hook::{{closure}}::hfdede1c1d271ae05
   6:        0x101528b58 - std::panicking::rust_panic_with_hook::ha19270fc750e5dcf
   7:        0x101531840 - std::panicking::begin_panic_handler::{{closure}}::h520977148193b087
   8:        0x1015317c0 - std::sys_common::backtrace::__rust_end_short_backtrace::h563c939a775416b3
   9:        0x1015284c4 - _rust_begin_unwind
  10:        0x100e222b8 - core::panicking::panic_fmt::h0908dd8514c30916
  11:        0x100e2a1bc - core::result::unwrap_failed::ha509accbcac71268
  12:        0x100ea56b4 - deno_core::error::JsError::inner_from_v8_exception::h2e88aa9f4d1c2f9d
  13:        0x100ee330c - deno_core::runtime::exception_to_err_result::hbe4add7992e624d1
  14:        0x100ee392c - deno_core::runtime::JsRuntime::check_promise_exceptions::hd9c6e1da42698d34
  15:        0x100edf854 - deno_core::runtime::JsRuntime::poll_event_loop::h25350bb0c322ac31
  16:        0x100d3a9b8 - <core::future::from_generator::GenFuture<T> as core::future::future::Future>::poll::hdfbb04abf6cc0ec8
  17:        0x100d05c08 - <core::future::from_generator::GenFuture<T> as core::future::future::Future>::poll::h54207a51ff039d8e
  18:        0x100cb2b28 - deno::run_command::{{closure}}::hda6f98d1a70307df
  19:        0x100cfcfc8 - <core::future::from_generator::GenFuture<T> as core::future::future::Future>::poll::h38759e15ec531747
  20:        0x100cba9d0 - deno::main::{{closure}}::h51898a97c1e85b1e
  21:        0x100d332f4 - <core::future::from_generator::GenFuture<T> as core::future::future::Future>::poll::hc3e42d1078066fe1
  22:        0x100bfb51c - deno_runtime::tokio_util::run_basic::h6d7feeb5d04db814
  23:        0x100cb75c4 - deno::main::h6a9df70c24fff5e9
  24:        0x100cbe928 - std::sys_common::backtrace::__rust_begin_short_backtrace::h4da7f0cf5a3c7fb5
  25:        0x100d590c0 - _main

Repro

I'm using abc, trying to get a fallback working for 404 pages. Here is the code in question:

const showNotFound: HandlerFunc = async() => {
  return await handlebars.render("index", {
    content: await handlebars.render("page/not-found", {}),
    description: "A blog about the DNS, Handshake, and the internet at large.",
    head: `<link rel="stylesheet" href="/not-found.css"/>`
  });
};

app.pre((next: HandlerFunc) => (context: Context) => {
  try {
    console.log("hey");
    console.log(context);
    return next(context);
  } catch(error) {
    console.error(">>> error");
    console.error(error);
  } finally {
    return showNotFound(context);
  }
});

I saw the code in this issue and obviously, it doesn't work (at least, not in the way I'm using it).

[bartlomieju]

CC @nayeemrmn it seems to be a problem with JS error deserialization, though I can't spot what's exactly wrong

[nayeemrmn]

@AaronO Do you know when serde_v8::from_v8::<NativeJsError>() might fail? https://github.com/denoland/deno/blob/v1.21.0/core/error.rs#L202