ICE when forwarding `$item` with inner attr through a proc-macro layer

[danielhenrymantilla]

Code

macro_rules! foo {(
    #[fake_attr]
    $item:item
) => (
    $item
)}

macro_rules! outer {($item:item) => (
    ::paste::paste! { // Identity proc-macro
        foo! {
            #[fake_attr]
            $item
        }
    }
)}
outer! {
    mod bar {
        //! Foo
    }
}

Meta

rustc --version --verbose:

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

Error output

thread 'rustc' panicked at 'assertion failed: `(left == right)`
  left: `Inner`,
 right: `Outer`: inner attributes should prevent cached tokens from existing', compiler/rustc_parse/src/lib.rs:613:9

Backtrace

stack backtrace:
   0: _rust_begin_unwind
   1: std::panicking::begin_panic_fmt
   2: rustc_parse::prepend_attrs
   3: rustc_parse::nt_to_tokenstream
   4: <proc_macro::bridge::TokenTree<rustc_expand::proc_macro_server::Group,rustc_expand::proc_macro_server::Punct,rustc_expand::proc_macro_server::Ident,rustc_expand::proc_macro_server::Literal> as rustc_expand::proc_macro_server::FromInternal<((rustc_ast::tokenstream::TokenTree,rustc_ast::tokenstream::Spacing),&rustc_session::parse::ParseSess,&mut alloc::vec::Vec<proc_macro::bridge::TokenTree<rustc_expand::proc_macro_server::Group,rustc_expand::proc_macro_server::Punct,rustc_expand::proc_macro_server::Ident,rustc_expand::proc_macro_server::Literal>>)>>::from_internal
   5: <rustc_expand::proc_macro_server::Rustc as proc_macro::bridge::server::TokenStreamIter>::next
   6: <std::panic::AssertUnwindSafe<F> as core::ops::function::FnOnce<()>>::call_once
   7: std::panicking::try
   8: <proc_macro::bridge::server::Dispatcher<proc_macro::bridge::server::MarkedTypes<S>> as proc_macro::bridge::server::DispatcherTrait>::dispatch
   9: <proc_macro::bridge::closure::Closure<A,R> as core::convert::From<&mut F>>::from::call
  10: proc_macro::bridge::closure::Closure<A,R>::call
             at /rustc/ffa2e7ae8fbf9badc035740db949b9dae271c29f/library/proc_macro/src/bridge/closure.rs:27:18
  11: proc_macro::bridge::client::TokenStreamIter::next::{{closure}}
             at /rustc/ffa2e7ae8fbf9badc035740db949b9dae271c29f/library/proc_macro/src/bridge/client.rs:244:25
  12: proc_macro::bridge::client::<impl proc_macro::bridge::Bridge>::with::{{closure}}
             at /rustc/ffa2e7ae8fbf9badc035740db949b9dae271c29f/library/proc_macro/src/bridge/client.rs:336:47
  13: proc_macro::bridge::client::BridgeState::with::{{closure}}::{{closure}}
             at /rustc/ffa2e7ae8fbf9badc035740db949b9dae271c29f/library/proc_macro/src/bridge/client.rs:293:17
  14: proc_macro::bridge::scoped_cell::ScopedCell<T>::replace
             at /rustc/ffa2e7ae8fbf9badc035740db949b9dae271c29f/library/proc_macro/src/bridge/scoped_cell.rs:75:9
  15: proc_macro::bridge::client::BridgeState::with::{{closure}}
             at /rustc/ffa2e7ae8fbf9badc035740db949b9dae271c29f/library/proc_macro/src/bridge/client.rs:291:13
  16: std::thread::local::LocalKey<T>::try_with
             at /rustc/ffa2e7ae8fbf9badc035740db949b9dae271c29f/library/std/src/thread/local.rs:272:16
  17: std::thread::local::LocalKey<T>::with
             at /rustc/ffa2e7ae8fbf9badc035740db949b9dae271c29f/library/std/src/thread/local.rs:248:9
  18: proc_macro::bridge::client::BridgeState::with
             at /rustc/ffa2e7ae8fbf9badc035740db949b9dae271c29f/library/proc_macro/src/bridge/client.rs:290:9
  19: proc_macro::bridge::client::<impl proc_macro::bridge::Bridge>::with
             at /rustc/ffa2e7ae8fbf9badc035740db949b9dae271c29f/library/proc_macro/src/bridge/client.rs:329:9
  20: proc_macro::bridge::client::TokenStreamIter::next
             at /rustc/ffa2e7ae8fbf9badc035740db949b9dae271c29f/library/proc_macro/src/bridge/client.rs:237:17
  21: <proc_macro::token_stream::IntoIter as core::iter::traits::iterator::Iterator>::next
             at /rustc/ffa2e7ae8fbf9badc035740db949b9dae271c29f/library/proc_macro/src/lib.rs:239:13
  22: <proc_macro2::imp::TokenTreeIter as core::iter::traits::iterator::Iterator>::next
             at /Users/dhm/.cargo/registry/src/github.com-1ecc6299db9ec823/proc-macro2-1.0.24/src/wrapper.rs:304:46
  23: <proc_macro2::token_stream::IntoIter as core::iter::traits::iterator::Iterator>::next
             at /Users/dhm/.cargo/registry/src/github.com-1ecc6299db9ec823/proc-macro2-1.0.24/src/lib.rs:1213:13
  24: syn::buffer::TokenBuffer::inner_new
             at /Users/dhm/.cargo/registry/src/github.com-1ecc6299db9ec823/syn-1.0.48/src/buffer.rs:53:19
  25: syn::buffer::TokenBuffer::inner_new
             at /Users/dhm/.cargo/registry/src/github.com-1ecc6299db9ec823/syn-1.0.48/src/buffer.rs:89:25
  26: syn::buffer::TokenBuffer::inner_new
             at /Users/dhm/.cargo/registry/src/github.com-1ecc6299db9ec823/syn-1.0.48/src/buffer.rs:89:25
  27: syn::buffer::TokenBuffer::new2
             at /Users/dhm/.cargo/registry/src/github.com-1ecc6299db9ec823/syn-1.0.48/src/buffer.rs:112:9
  28: <F as syn::parse::Parser>::parse2
             at /Users/dhm/.cargo/registry/src/github.com-1ecc6299db9ec823/syn-1.0.48/src/parse.rs:1184:19
  29: syn::parse::Parser::parse
             at /Users/dhm/.cargo/registry/src/github.com-1ecc6299db9ec823/syn-1.0.48/src/parse.rs:1138:9
  30: syn::parse_macro_input::parse
             at /Users/dhm/.cargo/registry/src/github.com-1ecc6299db9ec823/syn-1.0.48/src/parse_macro_input.rs:138:5
  31: with_builtin_macros_proc_macros::with_builtin
             at /Users/dhm/git/dhm/with_builtin_macros.rs/src/lib.rs:54:9
  32: core::ops::function::FnOnce::call_once
             at /Users/dhm/.rustup/toolchains/nightly-x86_64-apple-darwin/lib/rustlib/src/rust/library/core/src/ops/function.rs:227:5
  33: proc_macro::bridge::client::Client<fn(proc_macro::TokenStream) .> proc_macro::TokenStream>::expand1::run::{{closure}}
             at /Users/dhm/.rustup/toolchains/nightly-x86_64-apple-darwin/lib/rustlib/src/rust/library/proc_macro/src/bridge/client.rs:410:40
  34: proc_macro::bridge::client::run_client::{{closure}}::{{closure}}
             at /Users/dhm/.rustup/toolchains/nightly-x86_64-apple-darwin/lib/rustlib/src/rust/library/proc_macro/src/bridge/client.rs:377:26
  35: proc_macro::bridge::scoped_cell::ScopedCell<T>::set::{{closure}}
             at /Users/dhm/.rustup/toolchains/nightly-x86_64-apple-darwin/lib/rustlib/src/rust/library/proc_macro/src/bridge/scoped_cell.rs:80:33
  36: proc_macro::bridge::scoped_cell::ScopedCell<T>::replace
             at /Users/dhm/.rustup/toolchains/nightly-x86_64-apple-darwin/lib/rustlib/src/rust/library/proc_macro/src/bridge/scoped_cell.rs:75:9
  37: proc_macro::bridge::scoped_cell::ScopedCell<T>::set
             at /Users/dhm/.rustup/toolchains/nightly-x86_64-apple-darwin/lib/rustlib/src/rust/library/proc_macro/src/bridge/scoped_cell.rs:80:9
  38: proc_macro::bridge::client::<impl proc_macro::bridge::Bridge>::enter::{{closure}}
             at /Users/dhm/.rustup/toolchains/nightly-x86_64-apple-darwin/lib/rustlib/src/rust/library/proc_macro/src/bridge/client.rs:325:35
  39: std::thread::local::LocalKey<T>::try_with
             at /Users/dhm/.rustup/toolchains/nightly-x86_64-apple-darwin/lib/rustlib/src/rust/library/std/src/thread/local.rs:272:16
  40: std::thread::local::LocalKey<T>::with
             at /Users/dhm/.rustup/toolchains/nightly-x86_64-apple-darwin/lib/rustlib/src/rust/library/std/src/thread/local.rs:248:9
  41: proc_macro::bridge::client::<impl proc_macro::bridge::Bridge>::enter
             at /Users/dhm/.rustup/toolchains/nightly-x86_64-apple-darwin/lib/rustlib/src/rust/library/proc_macro/src/bridge/client.rs:325:9
  42: proc_macro::bridge::client::run_client::{{closure}}
             at /Users/dhm/.rustup/toolchains/nightly-x86_64-apple-darwin/lib/rustlib/src/rust/library/proc_macro/src/bridge/client.rs:370:9
  43: <std::panic::AssertUnwindSafe<F> as core::ops::function::FnOnce<()>>::call_once
             at /Users/dhm/.rustup/toolchains/nightly-x86_64-apple-darwin/lib/rustlib/src/rust/library/std/src/panic.rs:308:9
  44: std::panicking::try::do_call
             at /Users/dhm/.rustup/toolchains/nightly-x86_64-apple-darwin/lib/rustlib/src/rust/library/std/src/panicking.rs:381:40
  45: ___rust_try
  46: std::panicking::try
             at /Users/dhm/.rustup/toolchains/nightly-x86_64-apple-darwin/lib/rustlib/src/rust/library/std/src/panicking.rs:345:19
  47: std::panic::catch_unwind
             at /Users/dhm/.rustup/toolchains/nightly-x86_64-apple-darwin/lib/rustlib/src/rust/library/std/src/panic.rs:382:14
  48: proc_macro::bridge::client::run_client
             at /Users/dhm/.rustup/toolchains/nightly-x86_64-apple-darwin/lib/rustlib/src/rust/library/proc_macro/src/bridge/client.rs:369:5
  49: proc_macro::bridge::client::Client<fn(proc_macro::TokenStream) .> proc_macro::TokenStream>::expand1::run
             at /Users/dhm/.rustup/toolchains/nightly-x86_64-apple-darwin/lib/rustlib/src/rust/library/proc_macro/src/bridge/client.rs:410:13
  50: proc_macro::bridge::server::run_server
  51: <rustc_expand::proc_macro::BangProcMacro as rustc_expand::base::ProcMacro>::expand
  52: rustc_expand::expand::MacroExpander::fully_expand_fragment
  53: rustc_expand::expand::MacroExpander::expand_crate
  54: rustc_interface::passes::configure_and_expand_inner
  55: rustc_interface::passes::configure_and_expand::{{closure}}
  56: rustc_data_structures::box_region::PinnedGenerator<I,A,R>::new
  57: rustc_interface::passes::configure_and_expand
  58: rustc_interface::queries::Queries::expansion
  59: rustc_interface::queries::<impl rustc_interface::interface::Compiler>::enter
  60: rustc_span::with_source_map
  61: rustc_interface::interface::create_compiler_and_run
  62: scoped_tls::ScopedKey<T>::set
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.

cc @Aaron1011

[danielhenrymantilla]

Also note that on 1.45.0 there is no ICE, so this is a regression (EDIT: it ICEs starting from 1.46.0)

@rustbot modify labels: +regression-from-stable-to-stable

[camelid]

searched nightlies: from nightly-2020-03-01 to nightly-2020-11-02
regressed nightly: nightly-2020-06-25
searched commits: from ff5b446 to 67100f6
regressed commit: 3c90ae8

bisected with cargo-bisect-rustc v0.6.0

Host triple: x86_64-apple-darwin
Reproduce with:

cargo bisect-rustc --regress=ice --start=2020-03-01 --preserve