proc macro returned error: Cannot perform expansion for Deserialize: error Unknown

[tomjakubowski]

It seems there's been a recent regression in derive proc macros on the nightly channel. I'm on v0.3.367-nightly
and see red squigglies on these entire structs (along with any comments), and a corresponding proc macro error.

Sometimes the error message instead says "Empty result", or "Server closed".

Unsure when this might have been introduced, but I have been on the nightly channel for some time, and wasn't seeing this last week Wednesday in a project that uses proc macros, but do see it today.

I have "rust-analyzer.procMacro.enable and rust-analyzer.cargo.loadOutDirsFromCheck both set to true.

I've attached the testcase I used for the screenshots: testcase.tar.gz

[tomjakubowski]

Downgrading the extension on my Mac to the latest stable version (v0.2.400) resolves the issue. Weirdly, on one Linux box, I needed to downgrade to v0.2.392; I still see rust-analyzer crashing on v0.2.400.

Attached are server trace logs, and here's the panic message, from the "output" tab:

thread 'main' panicked at 'internal error: entered unreachable code', crates/proc_macro_srv/src/proc_macro/bridge/mod.rs:256:5
stack backtrace:
   0: std::panicking::begin_panic
   1: <proc_macro_srv::proc_macro::bridge::api_tags::Method as proc_macro_srv::proc_macro::bridge::rpc::DecodeMut<S>>::decode
   2: <proc_macro_srv::proc_macro::bridge::server::Dispatcher<proc_macro_srv::proc_macro::bridge::server::MarkedTypes<S>> as proc_macro_srv::proc_macro::bridge::server::DispatcherTrait>::dispatch
   3: <proc_macro_srv::proc_macro::bridge::closure::Closure<A,R> as core::convert::From<&mut F>>::from::call
   4: proc_macro::bridge::closure::Closure<A,R>::call
             at /rustc/c7087fe00d2ba919df1d813c040a5d47e43b0fe7/src/libproc_macro/bridge/closure.rs:27
   5: proc_macro::bridge::client::TokenStream::into_iter::{{closure}}
             at /rustc/c7087fe00d2ba919df1d813c040a5d47e43b0fe7/src/libproc_macro/bridge/client.rs:237
   6: proc_macro::bridge::client::<impl proc_macro::bridge::Bridge>::with::{{closure}}
             at /rustc/c7087fe00d2ba919df1d813c040a5d47e43b0fe7/src/libproc_macro/bridge/client.rs:321
   7: proc_macro::bridge::client::BridgeState::with::{{closure}}::{{closure}}
             at /rustc/c7087fe00d2ba919df1d813c040a5d47e43b0fe7/src/libproc_macro/bridge/client.rs:286
   8: proc_macro::bridge::scoped_cell::ScopedCell<T>::replace
             at /rustc/c7087fe00d2ba919df1d813c040a5d47e43b0fe7/src/libproc_macro/bridge/scoped_cell.rs:74
   9: proc_macro::bridge::client::BridgeState::with::{{closure}}
             at /rustc/c7087fe00d2ba919df1d813c040a5d47e43b0fe7/src/libproc_macro/bridge/client.rs:284
  10: std::thread::local::LocalKey<T>::try_with
             at /rustc/c7087fe00d2ba919df1d813c040a5d47e43b0fe7/src/libstd/thread/local.rs:263
  11: std::thread::local::LocalKey<T>::with
             at /rustc/c7087fe00d2ba919df1d813c040a5d47e43b0fe7/src/libstd/thread/local.rs:239
  12: proc_macro::bridge::client::BridgeState::with
             at /rustc/c7087fe00d2ba919df1d813c040a5d47e43b0fe7/src/libproc_macro/bridge/client.rs:283
  13: proc_macro::bridge::client::<impl proc_macro::bridge::Bridge>::with
             at /rustc/c7087fe00d2ba919df1d813c040a5d47e43b0fe7/src/libproc_macro/bridge/client.rs:314
  14: proc_macro::bridge::client::TokenStream::into_iter
             at /rustc/c7087fe00d2ba919df1d813c040a5d47e43b0fe7/src/libproc_macro/bridge/client.rs:230
  15: proc_macro::token_stream::<impl core::iter::traits::collect::IntoIterator for proc_macro::TokenStream>::into_iter
             at /rustc/c7087fe00d2ba919df1d813c040a5d47e43b0fe7/src/libproc_macro/lib.rs:226
  16: <proc_macro2::imp::TokenStream as core::iter::traits::collect::IntoIterator>::into_iter
             at /home/dev/.cargo/registry/src/github.com-1ecc6299db9ec823/proc-macro2-1.0.24/src/wrapper.rs:292
  17: proc_macro2::token_stream::<impl core::iter::traits::collect::IntoIterator for proc_macro2::TokenStream>::into_iter
             at /home/dev/.cargo/registry/src/github.com-1ecc6299db9ec823/proc-macro2-1.0.24/src/lib.rs:1229
  18: syn::buffer::TokenBuffer::inner_new
             at /home/dev/.cargo/registry/src/github.com-1ecc6299db9ec823/syn-1.0.53/src/buffer.rs:53
  19: syn::buffer::TokenBuffer::new2
             at /home/dev/.cargo/registry/src/github.com-1ecc6299db9ec823/syn-1.0.53/src/buffer.rs:112
  20: <F as syn::parse::Parser>::parse2
             at /home/dev/.cargo/registry/src/github.com-1ecc6299db9ec823/syn-1.0.53/src/parse.rs:1210
  21: syn::parse::Parser::parse
             at /home/dev/.cargo/registry/src/github.com-1ecc6299db9ec823/syn-1.0.53/src/parse.rs:1164
  22: syn::parse_macro_input::parse
             at /home/dev/.cargo/registry/src/github.com-1ecc6299db9ec823/syn-1.0.53/src/parse_macro_input.rs:139
  23: serde_derive::derive_deserialize
             at /home/dev/.cargo/registry/src/github.com-1ecc6299db9ec823/serde_derive-1.0.117/src/lib.rs:89
  24: core::ops::function::FnOnce::call_once
             at /home/dev/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/src/libcore/ops/function.rs:232
  25: proc_macro::bridge::client::Client<fn(proc_macro::TokenStream) .> proc_macro::TokenStream>::expand1::run::{{closure}}
             at /home/dev/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/src/libproc_macro/bridge/client.rs:394
  26: proc_macro::bridge::client::run_client::{{closure}}::{{closure}}
             at /home/dev/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/src/libproc_macro/bridge/client.rs:362
  27: proc_macro::bridge::scoped_cell::ScopedCell<T>::set::{{closure}}
             at /home/dev/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/src/libproc_macro/bridge/scoped_cell.rs:79
  28: proc_macro::bridge::scoped_cell::ScopedCell<T>::replace
             at /home/dev/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/src/libproc_macro/bridge/scoped_cell.rs:74
  29: proc_macro::bridge::scoped_cell::ScopedCell<T>::set
             at /home/dev/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/src/libproc_macro/bridge/scoped_cell.rs:79
  30: proc_macro::bridge::client::<impl proc_macro::bridge::Bridge>::enter::{{closure}}
             at /home/dev/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/src/libproc_macro/bridge/client.rs:310
  31: std::thread::local::LocalKey<T>::try_with
             at /home/dev/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/src/libstd/thread/local.rs:263
  32: std::thread::local::LocalKey<T>::with
             at /home/dev/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/src/libstd/thread/local.rs:239
  33: proc_macro::bridge::client::<impl proc_macro::bridge::Bridge>::enter
             at /home/dev/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/src/libproc_macro/bridge/client.rs:310
  34: proc_macro::bridge::client::run_client::{{closure}}
             at /home/dev/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/src/libproc_macro/bridge/client.rs:355
  35: <std::panic::AssertUnwindSafe<F> as core::ops::function::FnOnce<()>>::call_once
             at /home/dev/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/src/libstd/panic.rs:318
  36: std::panicking::try::do_call
             at /home/dev/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/src/libstd/panicking.rs:331
  37: __rust_try
  38: std::panicking::try
             at /home/dev/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/src/libstd/panicking.rs:274
  39: std::panic::catch_unwind
             at /home/dev/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/src/libstd/panic.rs:394
  40: proc_macro::bridge::client::run_client
             at /home/dev/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/src/libproc_macro/bridge/client.rs:354
  41: proc_macro::bridge::client::Client<fn(proc_macro::TokenStream) .> proc_macro::TokenStream>::expand1::run
             at /home/dev/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/src/libproc_macro/bridge/client.rs:394
  42: proc_macro_srv::proc_macro::bridge::server::run_server
  43: proc_macro_srv::dylib::Expander::expand
  44: proc_macro_srv::cli::run
  45: rust_analyzer::main
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.

trace.txt

[bjorn3]

This kind of error is usually caused by an incompatibility between the libproc_macro version of rustc and rust-analyzer. If this is the case, the fix will have to wait until the current rustc nightly hits stable.

[flodiebold]

This is not a regression, the macro-error diagnostic is just new. This was probably already happening in the older versions as well, just not reported.

[kjeremy]

I'm not seeing a diagnostic for this error but hover shows that it fails.

proc macro Deserialize not expanded

[edwin0cheng]

Triage: can't reproduce.

@tomjakubowski do you see any errors now ?

[lnicola]

Seems fixed, probably by #7047.