gtk-rs-core: [BUG] Attaching to context panics at 'assertion failed: context.is_owner()'

Bug description

After upgrading to gtk/glib 0.14.0 my application and all integration tests fail at:

thread 'main' panicked at 'assertion failed: context.is_owner()', /home/user/.cargo/registry/src/github.com-1ecc6299db9ec823/glib-0.14.0/src/main_context_channel.rs:507:17

I managed to reproduce it with a simple program:

src/main.rs:

const DEFAULT_CONTEXT : Option<&glib::MainContext> = None;

fn main() {
    let (_sender, receiver) = glib::MainContext::channel(glib::PRIORITY_DEFAULT);
    let handler = move |event: i32| {
        println!("got event: {}", event);
        glib::Continue(true)
    };
    receiver.attach(DEFAULT_CONTEXT, handler);  // panics
}

Cargo.toml:

[package]
name = "glib-context-test"
version = "0.1.0"
edition = "2018"

[dependencies]
glib = "0.14.0"

Tested on: Manjaro 21.0.7 Rust 1.53.0

Backtrace

$ RUST_BACKTRACE=full cargo run
   Compiling proc-macro2 v1.0.27
   Compiling unicode-xid v0.2.2
   Compiling syn v1.0.73
   Compiling serde v1.0.126
   Compiling anyhow v1.0.41
   Compiling unicode-segmentation v1.7.1
   Compiling either v1.6.1
   Compiling smallvec v1.6.1
   Compiling version-compare v0.0.11
   Compiling pkg-config v0.3.19
   Compiling strum v0.21.0
   Compiling version_check v0.9.3
   Compiling futures-core v0.3.15
   Compiling libc v0.2.97
   Compiling futures-task v0.3.15
   Compiling autocfg v1.0.1
   Compiling bitflags v1.2.1
   Compiling futures-channel v0.3.15
   Compiling pin-utils v0.1.0
   Compiling pin-project-lite v0.2.7
   Compiling slab v0.4.3
   Compiling once_cell v1.8.0
   Compiling itertools v0.10.1
   Compiling cfg-expr v0.7.4
   Compiling heck v0.3.3
   Compiling proc-macro-error-attr v1.0.4
   Compiling proc-macro-error v1.0.4
   Compiling futures-util v0.3.15
   Compiling quote v1.0.9
   Compiling futures-executor v0.3.15
   Compiling toml v0.5.8
   Compiling thiserror-impl v1.0.25
   Compiling strum_macros v0.21.1
   Compiling thiserror v1.0.25
   Compiling proc-macro-crate v1.0.0
   Compiling system-deps v3.1.2
   Compiling glib-macros v0.14.0
   Compiling glib-sys v0.14.0
   Compiling gobject-sys v0.14.0
   Compiling glib v0.14.0
   Compiling glib-context-test v0.1.0 (/home/user/dev/project/test/rust/glib-context-test)
    Finished dev [unoptimized + debuginfo] target(s) in 1m 03s
     Running `target/debug/glib-context-test`
thread 'main' panicked at 'assertion failed: context.is_owner()', /home/user/.cargo/registry/src/github.com-1ecc6299db9ec823/glib-0.14.0/src/main_context_channel.rs:507:17
stack backtrace:
   0:     0x564ba96568d0 - std::backtrace_rs::backtrace::libunwind::trace::ha5edb8ba5c6b7a6c
                               at /rustc/53cb7b09b00cbea8754ffb78e7e3cb521cb8af4b/library/std/src/../../backtrace/src/backtrace/libunwind.rs:90:5
   1:     0x564ba96568d0 - std::backtrace_rs::backtrace::trace_unsynchronized::h0de86d320a827db2
                               at /rustc/53cb7b09b00cbea8754ffb78e7e3cb521cb8af4b/library/std/src/../../backtrace/src/backtrace/mod.rs:66:5
   2:     0x564ba96568d0 - std::sys_common::backtrace::_print_fmt::h97b9ad6f0a1380ff
                               at /rustc/53cb7b09b00cbea8754ffb78e7e3cb521cb8af4b/library/std/src/sys_common/backtrace.rs:67:5
   3:     0x564ba96568d0 - <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt::h14be7eb08f97fe80
                               at /rustc/53cb7b09b00cbea8754ffb78e7e3cb521cb8af4b/library/std/src/sys_common/backtrace.rs:46:22
   4:     0x564ba9670e2f - core::fmt::write::h2ca8877d3e0e52de
                               at /rustc/53cb7b09b00cbea8754ffb78e7e3cb521cb8af4b/library/core/src/fmt/mod.rs:1094:17
   5:     0x564ba96550c5 - std::io::Write::write_fmt::h64f5987220b618f4
                               at /rustc/53cb7b09b00cbea8754ffb78e7e3cb521cb8af4b/library/std/src/io/mod.rs:1584:15
   6:     0x564ba965875b - std::sys_common::backtrace::_print::h7f1a4097308f2e0a
                               at /rustc/53cb7b09b00cbea8754ffb78e7e3cb521cb8af4b/library/std/src/sys_common/backtrace.rs:49:5
   7:     0x564ba965875b - std::sys_common::backtrace::print::h1f799fc2ca7f5035
                               at /rustc/53cb7b09b00cbea8754ffb78e7e3cb521cb8af4b/library/std/src/sys_common/backtrace.rs:36:9
   8:     0x564ba965875b - std::panicking::default_hook::{{closure}}::hf38436e8a3ce1071
                               at /rustc/53cb7b09b00cbea8754ffb78e7e3cb521cb8af4b/library/std/src/panicking.rs:208:50
   9:     0x564ba965822d - std::panicking::default_hook::he2f8f3fae11ed1dd
                               at /rustc/53cb7b09b00cbea8754ffb78e7e3cb521cb8af4b/library/std/src/panicking.rs:225:9
  10:     0x564ba9658d6d - std::panicking::rust_panic_with_hook::h79a18548bd90c7d4
                               at /rustc/53cb7b09b00cbea8754ffb78e7e3cb521cb8af4b/library/std/src/panicking.rs:591:17
  11:     0x564ba96588d7 - std::panicking::begin_panic_handler::{{closure}}::h212a72cc08e25126
                               at /rustc/53cb7b09b00cbea8754ffb78e7e3cb521cb8af4b/library/std/src/panicking.rs:495:13
  12:     0x564ba9656d6c - std::sys_common::backtrace::__rust_end_short_backtrace::hbd6897dd42bc0fcd
                               at /rustc/53cb7b09b00cbea8754ffb78e7e3cb521cb8af4b/library/std/src/sys_common/backtrace.rs:141:18
  13:     0x564ba9658869 - rust_begin_unwind
                               at /rustc/53cb7b09b00cbea8754ffb78e7e3cb521cb8af4b/library/std/src/panicking.rs:493:5
  14:     0x564ba963dd91 - core::panicking::panic_fmt::h77ecd04e9b1dd84d
                               at /rustc/53cb7b09b00cbea8754ffb78e7e3cb521cb8af4b/library/core/src/panicking.rs:92:14
  15:     0x564ba963dcdd - core::panicking::panic::h60569d8a39169222
                               at /rustc/53cb7b09b00cbea8754ffb78e7e3cb521cb8af4b/library/core/src/panicking.rs:50:5
  16:     0x564ba963f73a - glib::main_context_channel::Receiver<T>::attach::h594fcf9e7dc84a34
                               at /home/user/.cargo/registry/src/github.com-1ecc6299db9ec823/glib-0.14.0/src/main_context_channel.rs:507:17
  17:     0x564ba964305d - glib_context_test::main::hc555b5f4c0db2dae
                               at /home/user/dev/project/test/rust/glib-context-test/src/main.rs:9:5
  18:     0x564ba9641dcb - core::ops::function::FnOnce::call_once::h17df49f787978c02
                               at /home/user/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/ops/function.rs:227:5
  19:     0x564ba964003e - std::sys_common::backtrace::__rust_begin_short_backtrace::hc9dee5163aee7e43
                               at /home/user/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/std/src/sys_common/backtrace.rs:125:18
  20:     0x564ba96400c1 - std::rt::lang_start::{{closure}}::heeab27af11fe19e8
                               at /home/user/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/std/src/rt.rs:49:18
  21:     0x564ba965916a - core::ops::function::impls::<impl core::ops::function::FnOnce<A> for &F>::call_once::hc4354216bf39217c
                               at /rustc/53cb7b09b00cbea8754ffb78e7e3cb521cb8af4b/library/core/src/ops/function.rs:259:13
  22:     0x564ba965916a - std::panicking::try::do_call::hb68eb312780385cf
                               at /rustc/53cb7b09b00cbea8754ffb78e7e3cb521cb8af4b/library/std/src/panicking.rs:379:40
  23:     0x564ba965916a - std::panicking::try::h22b8e08595060b8b
                               at /rustc/53cb7b09b00cbea8754ffb78e7e3cb521cb8af4b/library/std/src/panicking.rs:343:19
  24:     0x564ba965916a - std::panic::catch_unwind::hc64f1a6a0e71b1fc
                               at /rustc/53cb7b09b00cbea8754ffb78e7e3cb521cb8af4b/library/std/src/panic.rs:431:14
  25:     0x564ba965916a - std::rt::lang_start_internal::h4461fc58637f04f8
                               at /rustc/53cb7b09b00cbea8754ffb78e7e3cb521cb8af4b/library/std/src/rt.rs:34:21
  26:     0x564ba96400a0 - std::rt::lang_start::h6c3d3c3dbe636292
                               at /home/user/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/std/src/rt.rs:48:5
  27:     0x564ba964315c - main
  28:     0x7f3b4857db25 - __libc_start_main
  29:     0x564ba963e48e - _start
  30:                0x0 - <unknown>