Rustc panic caused by invalid identifier in proc-macro

[snorrwe]

Brief

The panic is generated when I output a new struct in a proc macro that has an invalid identifier via the Quote crate.
In this case the proc-macro will panic, and in turn rustc panics as well.

I setup up a repository to reproduce the issue.

I also set up GitHub Actions to test a couple variations here.
The panic only seems to happen on Windowns and MacOS

Code

#![crate_type = "proc-macro"]

use proc_macro::TokenStream;
use quote::quote;

#[proc_macro_derive(Problematic)]
pub fn problematic(_input: TokenStream) -> TokenStream {
    let rogue_ident = quote::format_ident!(",");
    let result = quote! {
        struct Aux {
            #rogue_ident : i32
        }
    };
    TokenStream::from(result)
}

Meta

rustc --version --verbose:

$ rustc --version --verbose
rustc 1.47.0 (18bf6b4f0 2020-10-07)
binary: rustc
commit-hash: 18bf6b4f01a6feaf7259ba7cdae58031af1b7b39
commit-date: 2020-10-07
host: x86_64-pc-windows-msvc
release: 1.47.0
LLVM version: 11.0

Error output

Setting RUST_BACKTRACE to 1 produces no backtrace on Windows, but does procude backtrace on MacOS.

thread 'rustc' panicked at '`","` is not a valid identifier', src\librustc_expand\proc_macro_server.rs:332:13
stack backtrace:
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.

error: internal compiler error: unexpected panic

note: the compiler unexpectedly panicked. this is a bug.

note: we would appreciate a bug report: https://github.com/rust-lang/rust/issues/new?labels=C-bug%2C+I-ICE%2C+T-compiler&template=ice.md

note: rustc 1.47.0 (18bf6b4f0 2020-10-07) running on x86_64-pc-windows-msvc

note: compiler flags: -C embed-bitcode=no -C debuginfo=2 -C incremental --crate-type lib

note: some of the compiler flags provided by cargo are hidden

query stack during panic:
end of query stack
error: proc-macro derive panicked
 --> boi\src\lib.rs:2:10
  |
2 | #[derive(proc_boi::Problematic)]
  |          ^^^^^^^^^^^^^^^^^^^^^
  |
  = help: message: `","` is not a valid identifier

error: aborting due to previous error

Backtrace

thread 'rustc' panicked at '`","` is not a valid identifier', compiler/rustc_expand/src/proc_macro_server.rs:332:13
stack backtrace:
   0: _rust_begin_unwind
   1: std::panicking::begin_panic_fmt
   2: rustc_expand::proc_macro_server::Ident::new
   3: <proc_macro::bridge::server::Dispatcher<proc_macro::bridge::server::MarkedTypes<S>> as proc_macro::bridge::server::DispatcherTrait>::dispatch
   4: <proc_macro::bridge::closure::Closure<A,R> as core::convert::From<&mut F>>::from::call
   5: proc_macro::bridge::closure::Closure<A,R>::call
             at /rustc/ffa2e7ae8fbf9badc035740db949b9dae271c29f/library/proc_macro/src/bridge/closure.rs:27:18
   6: proc_macro::bridge::client::Ident::new::{{closure}}
             at /rustc/ffa2e7ae8fbf9badc035740db949b9dae271c29f/library/proc_macro/src/bridge/client.rs:244:25
   7: proc_macro::bridge::client::<impl proc_macro::bridge::Bridge>::with::{{closure}}
             at /rustc/ffa2e7ae8fbf9badc035740db949b9dae271c29f/library/proc_macro/src/bridge/client.rs:336:47
   8: proc_macro::bridge::client::BridgeState::with::{{closure}}::{{closure}}
             at /rustc/ffa2e7ae8fbf9badc035740db949b9dae271c29f/library/proc_macro/src/bridge/client.rs:293:17
   9: proc_macro::bridge::scoped_cell::ScopedCell<T>::replace
             at /rustc/ffa2e7ae8fbf9badc035740db949b9dae271c29f/library/proc_macro/src/bridge/scoped_cell.rs:75:9
  10: proc_macro::bridge::client::BridgeState::with::{{closure}}
             at /rustc/ffa2e7ae8fbf9badc035740db949b9dae271c29f/library/proc_macro/src/bridge/client.rs:291:13
  11: std::thread::local::LocalKey<T>::try_with
             at /rustc/ffa2e7ae8fbf9badc035740db949b9dae271c29f/library/std/src/thread/local.rs:272:16
  12: std::thread::local::LocalKey<T>::with
             at /rustc/ffa2e7ae8fbf9badc035740db949b9dae271c29f/library/std/src/thread/local.rs:248:9
  13: proc_macro::bridge::client::BridgeState::with
             at /rustc/ffa2e7ae8fbf9badc035740db949b9dae271c29f/library/proc_macro/src/bridge/client.rs:290:9
  14: proc_macro::bridge::client::<impl proc_macro::bridge::Bridge>::with
             at /rustc/ffa2e7ae8fbf9badc035740db949b9dae271c29f/library/proc_macro/src/bridge/client.rs:329:9
  15: proc_macro::bridge::client::Ident::new
             at /rustc/ffa2e7ae8fbf9badc035740db949b9dae271c29f/library/proc_macro/src/bridge/client.rs:237:17
  16: proc_macro2::imp::Ident::new
             at /Users/runner/.cargo/registry/src/github.com-1ecc6299db9ec823/proc-macro2-1.0.24/src/wrapper.rs:668:50
  17: proc_macro2::Ident::new
             at /Users/runner/.cargo/registry/src/github.com-1ecc6299db9ec823/proc-macro2-1.0.24/src/lib.rs:895:21
  18: quote::__private::mk_ident
             at /Users/runner/.cargo/registry/src/github.com-1ecc6299db9ec823/quote-1.0.7/src/runtime.rs:336:17
  19: proc_boi::problematic
             at ./proc-boi/src/lib.rs:8:23
  20: core::ops::function::FnOnce::call_once
             at /rustc/ffa2e7ae8fbf9badc035740db949b9dae271c29f/library/core/src/ops/function.rs:227:5
  21: proc_macro::bridge::client::Client<fn(proc_macro::TokenStream) .> proc_macro::TokenStream>::expand1::run::{{closure}}
             at /rustc/ffa2e7ae8fbf9badc035740db949b9dae271c29f/library/proc_macro/src/bridge/client.rs:410:40
  22: proc_macro::bridge::client::run_client::{{closure}}::{{closure}}
             at /rustc/ffa2e7ae8fbf9badc035740db949b9dae271c29f/library/proc_macro/src/bridge/client.rs:377:26
  23: proc_macro::bridge::scoped_cell::ScopedCell<T>::set::{{closure}}
             at /rustc/ffa2e7ae8fbf9badc035740db949b9dae271c29f/library/proc_macro/src/bridge/scoped_cell.rs:80:33
  24: proc_macro::bridge::scoped_cell::ScopedCell<T>::replace
             at /rustc/ffa2e7ae8fbf9badc035740db949b9dae271c29f/library/proc_macro/src/bridge/scoped_cell.rs:75:9
  25: proc_macro::bridge::scoped_cell::ScopedCell<T>::set
             at /rustc/ffa2e7ae8fbf9badc035740db949b9dae271c29f/library/proc_macro/src/bridge/scoped_cell.rs:80:9
  26: proc_macro::bridge::client::<impl proc_macro::bridge::Bridge>::enter::{{closure}}
             at /rustc/ffa2e7ae8fbf9badc035740db949b9dae271c29f/library/proc_macro/src/bridge/client.rs:325:35
  27: std::thread::local::LocalKey<T>::try_with
             at /rustc/ffa2e7ae8fbf9badc035740db949b9dae271c29f/library/std/src/thread/local.rs:272:16
  28: std::thread::local::LocalKey<T>::with
             at /rustc/ffa2e7ae8fbf9badc035740db949b9dae271c29f/library/std/src/thread/local.rs:248:9
  29: proc_macro::bridge::client::<impl proc_macro::bridge::Bridge>::enter
             at /rustc/ffa2e7ae8fbf9badc035740db949b9dae271c29f/library/proc_macro/src/bridge/client.rs:325:9
  30: proc_macro::bridge::client::run_client::{{closure}}
             at /rustc/ffa2e7ae8fbf9badc035740db949b9dae271c29f/library/proc_macro/src/bridge/client.rs:370:9
  31: <std::panic::AssertUnwindSafe<F> as core::ops::function::FnOnce<()>>::call_once
             at /rustc/ffa2e7ae8fbf9badc035740db949b9dae271c29f/library/std/src/panic.rs:308:9
  32: std::panicking::try::do_call
             at /rustc/ffa2e7ae8fbf9badc035740db949b9dae271c29f/library/std/src/panicking.rs:381:40
  33: ___rust_try
  34: std::panicking::try
             at /rustc/ffa2e7ae8fbf9badc035740db949b9dae271c29f/library/std/src/panicking.rs:345:19
  35: std::panic::catch_unwind
             at /rustc/ffa2e7ae8fbf9badc035740db949b9dae271c29f/library/std/src/panic.rs:382:14
  36: proc_macro::bridge::client::run_client
             at /rustc/ffa2e7ae8fbf9badc035740db949b9dae271c29f/library/proc_macro/src/bridge/client.rs:369:5
  37: proc_macro::bridge::client::Client<fn(proc_macro::TokenStream) .> proc_macro::TokenStream>::expand1::run
             at /rustc/ffa2e7ae8fbf9badc035740db949b9dae271c29f/library/proc_macro/src/bridge/client.rs:410:13
  38: proc_macro::bridge::server::run_server
  39: <rustc_expand::proc_macro::ProcMacroDerive as rustc_expand::base::MultiItemModifier>::expand
  40: rustc_expand::expand::MacroExpander::fully_expand_fragment
  41: rustc_expand::expand::MacroExpander::expand_crate
  42: rustc_interface::passes::configure_and_expand_inner
  43: rustc_interface::passes::configure_and_expand::{{closure}}
  44: rustc_data_structures::box_region::PinnedGenerator<I,A,R>::new
  45: rustc_interface::passes::configure_and_expand
  46: rustc_interface::queries::Queries::expansion
  47: rustc_interface::queries::<impl rustc_interface::interface::Compiler>::enter
  48: rustc_span::with_source_map
  49: rustc_interface::interface::create_compiler_and_run
  50: scoped_tls::ScopedKey<T>::set
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.

error: internal compiler error: unexpected panic

note: the compiler unexpectedly panicked. this is a bug.

note: we would appreciate a bug report: https://github.com/rust-lang/rust/issues/new?labels=C-bug%2C+I-ICE%2C+T-compiler&template=ice.md

note: rustc 1.49.0-nightly (ffa2e7ae8 2020-10-24) running on x86_64-apple-darwin

note: compiler flags: -C embed-bitcode=no -C debuginfo=2 -C incremental --crate-type lib

note: some of the compiler flags provided by cargo are hidden

query stack during panic:
end of query stack
error: proc-macro derive panicked

[jyn514]

@snorrwe this is a panic from the proc-macro, not from the compiler (If it were a compiler panic, it would say 'internal compiler error'). It looks like you're intentionally generating an invalid identifier, so I don't know there's anything to fix here - at best, you could ask proc_boi to give better error messages.

[snorrwe]

Yes, the proc-macro is panicking, which is handled correctly on Linux. However on other platforms this leads to an internal panic. See here for example.

[jyn514]

Ah ok, I missed the rustc panic because it was hidden under 'backtrace'.

[snorrwe]

My bad.