This example project demonstrates a strange panic that happens inside
procedural macros when they are compiled as dynamic libraries,
dynamically linked and then called explicitly using
proc_macro::bridge::client.
This example is expected to work only on Linux machines for now.
To get the error you should run the single test from src/main.rs file.
> RUST_BACKTRACE=1 cargo +nightly test -- --nocapture
When you do that, the test will be aborted, and you should see the next stack trace:
thread 'test_getset_expansion' panicked at 'procedural macro API is used outside of a procedural macro', src/libproc_macro/bridge/client.rs:315:17
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.
stack backtrace:
0: std::sys::unix::backtrace::tracing::imp::unwind_backtrace
at src/libstd/sys/unix/backtrace/tracing/gcc_s.rs:39
1: std::sys_common::backtrace::_print
at src/libstd/sys_common/backtrace.rs:71
2: std::panicking::default_hook::{{closure}}
at src/libstd/sys_common/backtrace.rs:59
at src/libstd/panicking.rs:197
3: std::panicking::default_hook
at src/libstd/panicking.rs:211
4: std::panicking::rust_panic_with_hook
at src/libstd/panicking.rs:478
5: std::panicking::begin_panic
at /rustc/a3404557c54ea48fb8efc805d93c450beb3364d4/src/libstd/panicking.rs:408
6: <proc_macro::TokenStream as core::str::FromStr>::from_str
at src/libproc_macro/bridge/client.rs:315
at src/libproc_macro/bridge/client.rs:285
at src/libproc_macro/bridge/scoped_cell.rs:73
at src/libproc_macro/bridge/client.rs:283
at /rustc/a3404557c54ea48fb8efc805d93c450beb3364d4/src/libstd/thread/local.rs:299
at /rustc/a3404557c54ea48fb8efc805d93c450beb3364d4/src/libstd/thread/local.rs:245
at src/libproc_macro/bridge/client.rs:282
at src/libproc_macro/bridge/client.rs:313
at src/libproc_macro/bridge/client.rs:229
at src/libproc_macro/lib.rs:101
7: core::str::<impl str>::parse
at /rustc/a3404557c54ea48fb8efc805d93c450beb3364d4/src/libcore/str/mod.rs:3920
8: test_proc_macro::make_answer_macro
at src/lib.rs:8
9: std::panicking::try::do_call
at src/libproc_macro/bridge/client.rs:358
at src/libproc_macro/bridge/scoped_cell.rs:78
at src/libproc_macro/bridge/scoped_cell.rs:73
at src/libproc_macro/bridge/scoped_cell.rs:78
at src/libproc_macro/bridge/client.rs:309
at /rustc/a3404557c54ea48fb8efc805d93c450beb3364d4/src/libstd/thread/local.rs:299
at /rustc/a3404557c54ea48fb8efc805d93c450beb3364d4/src/libstd/thread/local.rs:245
at src/libproc_macro/bridge/client.rs:309
at src/libproc_macro/bridge/client.rs:351
at /rustc/a3404557c54ea48fb8efc805d93c450beb3364d4/src/libstd/panic.rs:309
at /rustc/a3404557c54ea48fb8efc805d93c450beb3364d4/src/libstd/panicking.rs:293
10: __rust_maybe_catch_panic
at src/libpanic_unwind/lib.rs:85
11: proc_macro::bridge::client::__run_expand1
at /rustc/a3404557c54ea48fb8efc805d93c450beb3364d4/src/libstd/panicking.rs:272
at /rustc/a3404557c54ea48fb8efc805d93c450beb3364d4/src/libstd/panic.rs:388
at src/libproc_macro/bridge/client.rs:350
12: <proc_macro::bridge::server::SameThread as proc_macro::bridge::server::ExecutionStrategy>::run_bridge_and_client
at /rustc/a3404557c54ea48fb8efc805d93c450beb3364d4/src/libproc_macro/bridge/server.rs:151
13: proc_macro::bridge::server::run_server
at /rustc/a3404557c54ea48fb8efc805d93c450beb3364d4/src/libproc_macro/bridge/server.rs:287
14: proc_macro::bridge::server::<impl proc_macro::bridge::client::Client<fn(proc_macro::TokenStream) .> proc_macro::TokenStream>>::run
at /rustc/a3404557c54ea48fb8efc805d93c450beb3364d4/src/libproc_macro/bridge/server.rs:304
15: rust_proc_macro_panic_inside_panic_expample::test_getset_expansion
at src/main.rs:146
16: rust_proc_macro_panic_inside_panic_expample::test_getset_expansion::{{closure}}
at src/main.rs:127
17: core::ops::function::FnOnce::call_once
at /rustc/a3404557c54ea48fb8efc805d93c450beb3364d4/src/libcore/ops/function.rs:231
18: <alloc::boxed::Box<F> as core::ops::function::FnOnce<A>>::call_once
at /rustc/a3404557c54ea48fb8efc805d93c450beb3364d4/src/liballoc/boxed.rs:704
19: __rust_maybe_catch_panic
at src/libpanic_unwind/lib.rs:85
20: test::run_test::run_test_inner::{{closure}}
at /rustc/a3404557c54ea48fb8efc805d93c450beb3364d4/src/libstd/panicking.rs:272
at /rustc/a3404557c54ea48fb8efc805d93c450beb3364d4/src/libstd/panic.rs:388
at src/libtest/lib.rs:1468
thread 'test_getset_expansion' panicked at 'procedural macro API is used outside of a procedural macro', src/libproc_macro/bridge/client.rs:315:17
stack backtrace:
0: 0x5592e3161ae3 - std::sys::unix::backtrace::tracing::imp::unwind_backtrace::h2d6422e3b3d3b496
at src/libstd/sys/unix/backtrace/tracing/gcc_s.rs:39
1: 0x5592e315cbdb - std::sys_common::backtrace::_print::hdcf024b79128e394
at src/libstd/sys_common/backtrace.rs:71
2: 0x5592e3160716 - std::panicking::default_hook::{{closure}}::h65908dc32223ffbc
at src/libstd/sys_common/backtrace.rs:59
at src/libstd/panicking.rs:197
3: 0x5592e31604a9 - std::panicking::default_hook::h8163b58f57533e2a
at src/libstd/panicking.rs:211
4: 0x5592e3160f08 - std::panicking::rust_panic_with_hook::h5afaf61eb853c476
at src/libstd/panicking.rs:478
5: 0x5592e3143f84 - std::panicking::begin_panic::h201a5532d0d32131
at /rustc/a3404557c54ea48fb8efc805d93c450beb3364d4/src/libstd/panicking.rs:408
6: 0x5592e3145a87 - proc_macro::bridge::client::BridgeState::with::{{closure}}::{{closure}}::h43cd42933bf05d3f
at src/libproc_macro/bridge/client.rs:315
at src/libproc_macro/bridge/client.rs:285
7: 0x5592e314c3de - <proc_macro::bridge::client::TokenStream as core::ops::drop::Drop>::drop::h3acf18fccae34825
at src/libproc_macro/bridge/scoped_cell.rs:73
at src/libproc_macro/bridge/client.rs:283
at /rustc/a3404557c54ea48fb8efc805d93c450beb3364d4/src/libstd/thread/local.rs:299
at /rustc/a3404557c54ea48fb8efc805d93c450beb3364d4/src/libstd/thread/local.rs:245
at src/libproc_macro/bridge/client.rs:282
at src/libproc_macro/bridge/client.rs:313
at src/libproc_macro/bridge/client.rs:229
at src/libproc_macro/bridge/client.rs:54
8: 0x7fa36b46956e - core::ptr::real_drop_in_place::hb58c8d7f591e2c59
at /rustc/a3404557c54ea48fb8efc805d93c450beb3364d4/src/libcore/ptr.rs:195
9: 0x7fa36b46955d - core::ptr::real_drop_in_place::h39c30b4f13d1f345
at /rustc/a3404557c54ea48fb8efc805d93c450beb3364d4/src/libcore/ptr.rs:195
10: 0x7fa36b46963a - test_proc_macro::make_answer_macro::hdf69bc05a4e04cef
at src/lib.rs:9
11: 0x7fa36b46a1e3 - std::panicking::try::do_call::h71ee8d644732cdd4
at src/libproc_macro/bridge/client.rs:358
at src/libproc_macro/bridge/scoped_cell.rs:78
at src/libproc_macro/bridge/scoped_cell.rs:73
at src/libproc_macro/bridge/scoped_cell.rs:78
at src/libproc_macro/bridge/client.rs:309
at /rustc/a3404557c54ea48fb8efc805d93c450beb3364d4/src/libstd/thread/local.rs:299
at /rustc/a3404557c54ea48fb8efc805d93c450beb3364d4/src/libstd/thread/local.rs:245
at src/libproc_macro/bridge/client.rs:309
at src/libproc_macro/bridge/client.rs:351
at /rustc/a3404557c54ea48fb8efc805d93c450beb3364d4/src/libstd/panic.rs:309
at /rustc/a3404557c54ea48fb8efc805d93c450beb3364d4/src/libstd/panicking.rs:293
12: 0x5592e3168a59 - __rust_maybe_catch_panic
at src/libpanic_unwind/lib.rs:85
13: 0x7fa36b46fd84 - proc_macro::bridge::client::__run_expand1::h7aa14ea7adb2775b
at /rustc/a3404557c54ea48fb8efc805d93c450beb3364d4/src/libstd/panicking.rs:272
at /rustc/a3404557c54ea48fb8efc805d93c450beb3364d4/src/libstd/panic.rs:388
at src/libproc_macro/bridge/client.rs:350
14: 0x5592e2eebb1a - <proc_macro::bridge::server::SameThread as proc_macro::bridge::server::ExecutionStrategy>::run_bridge_and_client::hf482ceabe96b0313
at /rustc/a3404557c54ea48fb8efc805d93c450beb3364d4/src/libproc_macro/bridge/server.rs:151
15: 0x5592e2eec7e2 - proc_macro::bridge::server::run_server::hd01705c424e0f87a
at /rustc/a3404557c54ea48fb8efc805d93c450beb3364d4/src/libproc_macro/bridge/server.rs:287
16: 0x5592e2ed9905 - proc_macro::bridge::server::<impl proc_macro::bridge::client::Client<fn(proc_macro::TokenStream) .> proc_macro::TokenStream>>::run::h85b859d348785565
at /rustc/a3404557c54ea48fb8efc805d93c450beb3364d4/src/libproc_macro/bridge/server.rs:304
17: 0x5592e2f277b8 - rust_proc_macro_panic_inside_panic_expample::test_getset_expansion::hc04da47dab7f924d
at src/main.rs:146
18: 0x5592e2eea621 - rust_proc_macro_panic_inside_panic_expample::test_getset_expansion::{{closure}}::h1bc35a164ad2a2b7
at src/main.rs:127
19: 0x5592e2ef752d - core::ops::function::FnOnce::call_once::h5ce974b491e02e43
at /rustc/a3404557c54ea48fb8efc805d93c450beb3364d4/src/libcore/ops/function.rs:231
20: 0x5592e2fad89e - <alloc::boxed::Box<F> as core::ops::function::FnOnce<A>>::call_once::he4b816e4551f57f6
at /rustc/a3404557c54ea48fb8efc805d93c450beb3364d4/src/liballoc/boxed.rs:704
21: 0x5592e3168a59 - __rust_maybe_catch_panic
at src/libpanic_unwind/lib.rs:85
22: 0x5592e2fc8227 - test::run_test::run_test_inner::{{closure}}::h3c0a5c57d6a7311e
at /rustc/a3404557c54ea48fb8efc805d93c450beb3364d4/src/libstd/panicking.rs:272
at /rustc/a3404557c54ea48fb8efc805d93c450beb3364d4/src/libstd/panic.rs:388
at src/libtest/lib.rs:1468
23: 0x5592e2fa2be4 - std::sys_common::backtrace::__rust_begin_short_backtrace::he2dc1dc77c2b7d25
at /rustc/a3404557c54ea48fb8efc805d93c450beb3364d4/src/libstd/sys_common/backtrace.rs:136
24: 0x5592e2fa6c34 - std::panicking::try::do_call::hc7daa2c4e69eadc1
at /rustc/a3404557c54ea48fb8efc805d93c450beb3364d4/src/libstd/thread/mod.rs:469
at /rustc/a3404557c54ea48fb8efc805d93c450beb3364d4/src/libstd/panic.rs:309
at /rustc/a3404557c54ea48fb8efc805d93c450beb3364d4/src/libstd/panicking.rs:293
25: 0x5592e3168a59 - __rust_maybe_catch_panic
at src/libpanic_unwind/lib.rs:85
26: 0x5592e2fa7251 - core::ops::function::FnOnce::call_once{{vtable.shim}}::h96e6ceca33de04ae
at /rustc/a3404557c54ea48fb8efc805d93c450beb3364d4/src/libstd/panicking.rs:272
at /rustc/a3404557c54ea48fb8efc805d93c450beb3364d4/src/libstd/panic.rs:388
at /rustc/a3404557c54ea48fb8efc805d93c450beb3364d4/src/libstd/thread/mod.rs:468
at /rustc/a3404557c54ea48fb8efc805d93c450beb3364d4/src/libcore/ops/function.rs:231
27: 0x5592e315361e - <alloc::boxed::Box<F> as core::ops::function::FnOnce<A>>::call_once::hd5bc1c518e080a98
at /rustc/a3404557c54ea48fb8efc805d93c450beb3364d4/src/liballoc/boxed.rs:704
28: 0x5592e316813f - std::sys::unix::thread::Thread::new::thread_start::h5c9e12179bf11e38
at /rustc/a3404557c54ea48fb8efc805d93c450beb3364d4/src/liballoc/boxed.rs:704
at src/libstd/sys_common/thread.rs:13
at src/libstd/sys/unix/thread.rs:79
29: 0x7fa36c2386b9 - start_thread
30: 0x7fa36bd5641c - clone
31: 0x0 - <unknown>
thread panicked while panicking. aborting.
The panic inside panic happens when destructors of TokenStream are running.
However, if you will try and compile tests with the compiler that is different from the current nightly (if your nightly is of 2019-05-06, then 2019-05-05 will do), you will see no such error - the test will be successful.
> RUST_BACKTRACE=1 cargo +nightly-2019-05-06
thread 'test_getset_expansion' panicked at 'not yet implemented', src/rustc_server.rs:229:9
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.
stack backtrace:
0: std::sys::unix::backtrace::tracing::imp::unwind_backtrace
at src/libstd/sys/unix/backtrace/tracing/gcc_s.rs:39
1: std::sys_common::backtrace::_print
at src/libstd/sys_common/backtrace.rs:71
2: std::panicking::default_hook::{{closure}}
at src/libstd/sys_common/backtrace.rs:59
at src/libstd/panicking.rs:197
3: std::panicking::default_hook
at src/libstd/panicking.rs:211
4: std::panicking::rust_panic_with_hook
at src/libstd/panicking.rs:478
5: std::panicking::begin_panic
at /rustc/597f432489f12a3f33419daa039ccef11a12c4fd/src/libstd/panicking.rs:408
6: <rust_proc_macro_panic_inside_panic_expample::rustc_server::Rustc as proc_macro::bridge::server::TokenStream>::from_str
at src/rustc_server.rs:229
7: <proc_macro::bridge::server::MarkedTypes<S> as proc_macro::bridge::server::TokenStream>::from_str
at src/main.rs:1
8: <proc_macro::bridge::server::Dispatcher<proc_macro::bridge::server::MarkedTypes<S>> as proc_macro::bridge::server::DispatcherTrait>::dispatch::{{closure}}
at src/main.rs:1
9: core::ops::function::FnOnce::call_once
at /rustc/597f432489f12a3f33419daa039ccef11a12c4fd/src/libcore/ops/function.rs:231
10: <std::panic::AssertUnwindSafe<F> as core::ops::function::FnOnce<()>>::call_once
at /rustc/597f432489f12a3f33419daa039ccef11a12c4fd/src/libstd/panic.rs:309
11: std::panicking::try::do_call
at /rustc/597f432489f12a3f33419daa039ccef11a12c4fd/src/libstd/panicking.rs:293
12: __rust_maybe_catch_panic
at src/libpanic_unwind/lib.rs:85
13: std::panicking::try
at /rustc/597f432489f12a3f33419daa039ccef11a12c4fd/src/libstd/panicking.rs:272
14: std::panic::catch_unwind
at /rustc/597f432489f12a3f33419daa039ccef11a12c4fd/src/libstd/panic.rs:388
15: <proc_macro::bridge::server::Dispatcher<proc_macro::bridge::server::MarkedTypes<S>> as proc_macro::bridge::server::DispatcherTrait>::dispatch
at /rustc/597f432489f12a3f33419daa039ccef11a12c4fd/src/libproc_macro/bridge/server.rs:113
16: <proc_macro::bridge::server::SameThread as proc_macro::bridge::server::ExecutionStrategy>::run_bridge_and_client::{{closure}}
at /rustc/597f432489f12a3f33419daa039ccef11a12c4fd/src/libproc_macro/bridge/server.rs:149
17: <proc_macro::bridge::closure::Closure<A,R> as core::convert::From<&mut F>>::from::call
at /rustc/597f432489f12a3f33419daa039ccef11a12c4fd/src/libproc_macro/bridge/closure.rs:19
18: <proc_macro::TokenStream as core::str::FromStr>::from_str
at src/libproc_macro/bridge/closure.rs:30
at src/libproc_macro/bridge/client.rs:236
at src/libproc_macro/bridge/client.rs:320
at src/libproc_macro/bridge/client.rs:285
at src/libproc_macro/bridge/scoped_cell.rs:73
at src/libproc_macro/bridge/client.rs:283
at /rustc/a3404557c54ea48fb8efc805d93c450beb3364d4/src/libstd/thread/local.rs:299
at /rustc/a3404557c54ea48fb8efc805d93c450beb3364d4/src/libstd/thread/local.rs:245
at src/libproc_macro/bridge/client.rs:282
at src/libproc_macro/bridge/client.rs:313
at src/libproc_macro/bridge/client.rs:229
at src/libproc_macro/lib.rs:101
19: core::str::<impl str>::parse
at /rustc/a3404557c54ea48fb8efc805d93c450beb3364d4/src/libcore/str/mod.rs:3920
20: test_proc_macro::make_answer_macro
at src/lib.rs:8
21: std::panicking::try::do_call
at src/libproc_macro/bridge/client.rs:358
at src/libproc_macro/bridge/scoped_cell.rs:78
at src/libproc_macro/bridge/scoped_cell.rs:73
at src/libproc_macro/bridge/scoped_cell.rs:78
at src/libproc_macro/bridge/client.rs:309
at /rustc/a3404557c54ea48fb8efc805d93c450beb3364d4/src/libstd/thread/local.rs:299
at /rustc/a3404557c54ea48fb8efc805d93c450beb3364d4/src/libstd/thread/local.rs:245
at src/libproc_macro/bridge/client.rs:309
at src/libproc_macro/bridge/client.rs:351
at /rustc/a3404557c54ea48fb8efc805d93c450beb3364d4/src/libstd/panic.rs:309
at /rustc/a3404557c54ea48fb8efc805d93c450beb3364d4/src/libstd/panicking.rs:293
22: __rust_maybe_catch_panic
at src/libpanic_unwind/lib.rs:85
23: proc_macro::bridge::client::__run_expand1
at /rustc/a3404557c54ea48fb8efc805d93c450beb3364d4/src/libstd/panicking.rs:272
at /rustc/a3404557c54ea48fb8efc805d93c450beb3364d4/src/libstd/panic.rs:388
at src/libproc_macro/bridge/client.rs:350
24: <proc_macro::bridge::server::SameThread as proc_macro::bridge::server::ExecutionStrategy>::run_bridge_and_client
at /rustc/597f432489f12a3f33419daa039ccef11a12c4fd/src/libproc_macro/bridge/server.rs:151
25: proc_macro::bridge::server::run_server
at /rustc/597f432489f12a3f33419daa039ccef11a12c4fd/src/libproc_macro/bridge/server.rs:287
26: proc_macro::bridge::server::<impl proc_macro::bridge::client::Client<fn(proc_macro::TokenStream) .> proc_macro::TokenStream>>::run
at /rustc/597f432489f12a3f33419daa039ccef11a12c4fd/src/libproc_macro/bridge/server.rs:304
27: rust_proc_macro_panic_inside_panic_expample::test_getset_expansion
at src/main.rs:146
28: rust_proc_macro_panic_inside_panic_expample::test_getset_expansion::{{closure}}
at src/main.rs:127
29: core::ops::function::FnOnce::call_once
at /rustc/597f432489f12a3f33419daa039ccef11a12c4fd/src/libcore/ops/function.rs:231
30: <alloc::boxed::Box<F> as core::ops::function::FnOnce<A>>::call_once
at /rustc/597f432489f12a3f33419daa039ccef11a12c4fd/src/liballoc/boxed.rs:704
31: __rust_maybe_catch_panic
at src/libpanic_unwind/lib.rs:85
32: test::run_test::run_test_inner::{{closure}}
at /rustc/597f432489f12a3f33419daa039ccef11a12c4fd/src/libstd/panicking.rs:272
at /rustc/597f432489f12a3f33419daa039ccef11a12c4fd/src/libstd/panic.rs:388
at src/libtest/lib.rs:1468
test test_getset_expansion ... ok
test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out
Now the panic is expected, because, as you can see, src/rustc_server contains no actual implementation of TokenStream
API - it is completely stubbed for the simplicity purpose. Moreover, panic
is correctly caught and returned as an Error from the run method.
I've experimented with different compiler versions, and it seems
that the only thing that triggers such panic is version alignment
between compiler that compiled procedural macro itself, and compiler
that compiled the code that is calling run method.
As long as those compilers have different versions (and they generate
the same ABI for the procedural macros), everything works fine. Moreover,
many popular procedural macros may be called like that (for example serde_derive,
getset, builder_derive etc.).
Unfortunately, I have no idea why this panic happens (maybe it's even supposed to happen), and why it happens only under those strange circumstances.