Stack overflow? in parser in some code with syntax errors

[ijackson]

Steps to reproduce

git clone https://salsa.debian.org/iwj/otter.git -b wip.ice
cd otter
cargo build -p otter-webdriver-tests

I'm afraid I haven't minimised this test case.

This doesn't seem to be a very serious problem as the compiler has correctly pointed out syntax errors; fixing those syntax errors makes the ICE go away. But since it suggested filing a bug I repro'd with today's nightly and have done so.

Meta

rustc --version --verbose:

binary: rustc
commit-hash: 257becbfe4987d1f7b12af5a8dd5ed96697cd2e8
commit-date: 2020-12-27
host: x86_64-unknown-linux-gnu
release: 1.51.0-nightly

Error output

   Compiling otter-webdriver-tests v0.0.1 (/home/rustcargo/d/otter/wdriver)
error: expected one of `)`, `+`, `,`, or `::`, found `->`
   --> wdriver/../wdriver.rs:156:38
[more reasonable looking error messages]
    | non-item starts here
    | item list ends here

thread 'rustc' panicked at 'Stack should be empty: final_buf=FrameData { open: wdriver/../wdriver.rs:156:11: 156:12 (#0), inner: [(Token(Token { kind: BinOp(And), span: wdriver/../wdriver.rs:156:12: 156:13 (#0) }), Alone), (Token(Token { kind: Ident("self", false), span: wdriver/../wdriver.rs:156:13: 156:17 (#0) }), Joint), (Token(Token { kind: Comma, span: wdriver/../wdriver.rs:156:17: 156:18 (#0) }), Alone), (Token(Token { kind: Ident("s", false), span: wdriver/../wdriver.rs:156:19: 156:20 (#0) }), Joint), (Token(Token { kind: Colon, span: wdriver/../wdriver.rs:156:20: 156:21 (#0) }), Alone), (Token(Token { kind: BinOp(And), span: wdriver/../wdriver.rs:156:22: 156:23 (#0) }), Alone), (Token(Token { kind: Ident("dyn", false), span: wdriver/../wdriver.rs:156:23
[a very large quantity more like this]
wdriver.rs:177:19: 177:20 (#0) }), Alone)])), Alone)])), Alone)] } stack=[FrameData { open: wdriver/../wdriver.rs:1:1: 1:1 (#0), inner: [(Token(Token { kind: Ident("fn", false), span: wdriver/../wdriver.rs:156:3: 156:5 (#0) }), Alone), (Token(Token { kind: Ident("subst", false), span: wdriver/../wdriver.rs:156:6: 156:11 (#0) }), Alone)] }]', compiler/rustc_parse/src/parser/mod.rs:1409:5
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

error: internal compiler error: unexpected panic

Backtrace

stack backtrace:
   0:     0x7fd92e0877e7 - std::backtrace_rs::backtrace::libunwind::trace::h746c3e9529d524bc
                               at /rustc/257becbfe4987d1f7b12af5a8dd5ed96697cd2e8/library/std/src/../../backtrace/src/backtrace/libunwind.rs:90:5
   1:     0x7fd92e0877e7 - std::backtrace_rs::backtrace::trace_unsynchronized::h84373278bfb39e0c
                               at /rustc/257becbfe4987d1f7b12af5a8dd5ed96697cd2e8/library/std/src/../../backtrace/src/backtrace/mod.rs:66:5
   2:     0x7fd92e0877e7 - std::sys_common::backtrace::_print_fmt::h517324efde750597
                               at /rustc/257becbfe4987d1f7b12af5a8dd5ed96697cd2e8/library/std/src/sys_common/backtrace.rs:67:5
   3:     0x7fd92e0877e7 - <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt::hf594ab77fac89284
                               at /rustc/257becbfe4987d1f7b12af5a8dd5ed96697cd2e8/library/std/src/sys_common/backtrace.rs:46:22
   4:     0x7fd92e0f806c - core::fmt::write::h3868db8542c90941
                               at /rustc/257becbfe4987d1f7b12af5a8dd5ed96697cd2e8/library/core/src/fmt/mod.rs:1078:17
   5:     0x7fd92e079722 - std::io::Write::write_fmt::h3f6656f045fa877f
                               at /rustc/257becbfe4987d1f7b12af5a8dd5ed96697cd2e8/library/std/src/io/mod.rs:1519:15
   6:     0x7fd92e08b4b5 - std::sys_common::backtrace::_print::hda7655c057c24dcc
                               at /rustc/257becbfe4987d1f7b12af5a8dd5ed96697cd2e8/library/std/src/sys_common/backtrace.rs:49:5
   7:     0x7fd92e08b4b5 - std::sys_common::backtrace::print::h546a6c8431d46287
                               at /rustc/257becbfe4987d1f7b12af5a8dd5ed96697cd2e8/library/std/src/sys_common/backtrace.rs:36:9
   8:     0x7fd92e08b4b5 - std::panicking::default_hook::{{closure}}::h006dd083853faf51
                               at /rustc/257becbfe4987d1f7b12af5a8dd5ed96697cd2e8/library/std/src/panicking.rs:208:50
   9:     0x7fd92e08b013 - std::panicking::default_hook::hf0f9afb1017317fc
                               at /rustc/257becbfe4987d1f7b12af5a8dd5ed96697cd2e8/library/std/src/panicking.rs:225:9
  10:     0x7fd92e8eeb8b - rustc_driver::report_ice::h1a7ab7fc7b8fd641
  11:     0x7fd91d4912d6 - <alloc::boxed::Box<F,A> as core::ops::function::Fn<Args>>::call::hf0349c093b90eab1
                               at /volatile/rustcargo/rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/alloc/src/boxed.rs:1342:9
  12:     0x7fd91d4927eb - proc_macro::bridge::client::<impl proc_macro::bridge::Bridge>::enter::{{closure}}::{{closure}}::h6c733668da23e5b0
                               at /volatile/rustcargo/rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/proc_macro/src/bridge/client.rs:320:21
  13:     0x7fd92e08bdb6 - std::panicking::rust_panic_with_hook::hb7a19826c029b1d6
                               at /rustc/257becbfe4987d1f7b12af5a8dd5ed96697cd2e8/library/std/src/panicking.rs:595:17
  14:     0x7fd92e08b8d7 - std::panicking::begin_panic_handler::{{closure}}::hde71edcd925d0c5e
                               at /rustc/257becbfe4987d1f7b12af5a8dd5ed96697cd2e8/library/std/src/panicking.rs:497:13
  15:     0x7fd92e087cac - std::sys_common::backtrace::__rust_end_short_backtrace::h8a3c7d6cea578919
                               at /rustc/257becbfe4987d1f7b12af5a8dd5ed96697cd2e8/library/std/src/sys_common/backtrace.rs:141:18
  16:     0x7fd92e08b839 - rust_begin_unwind
                               at /rustc/257becbfe4987d1f7b12af5a8dd5ed96697cd2e8/library/std/src/panicking.rs:493:5
  17:     0x7fd92e08b7eb - std::panicking::begin_panic_fmt::hee67ce14b77d0396
                               at /rustc/257becbfe4987d1f7b12af5a8dd5ed96697cd2e8/library/std/src/panicking.rs:435:5
  18:     0x7fd931688252 - <rustc_parse::parser::Parser::collect_tokens::LazyTokenStreamImpl as rustc_ast::tokenstream::CreateTokenStream>::create_token_stream::h841bbbdeec5aad6b
  19:     0x7fd9316a2d2e - rustc_parse::prepend_attrs::h63fa2d717369e1c0
  20:     0x7fd9316a0446 - rustc_parse::nt_to_tokenstream::he85c9b61a269d1e9
  21:     0x7fd92f81c201 - rustc_expand::base::Annotatable::into_tokens::hb578d9bf826452e8
  22:     0x7fd9309d503a - rustc_expand::expand::MacroExpander::fully_expand_fragment::he26fff039b78329f
  23:     0x7fd93161b6c3 - rustc_expand::expand::MacroExpander::expand_crate::hd5614e1080b391fe
  24:     0x7fd930e072dc - rustc_session::utils::<impl rustc_session::session::Session>::time::h77ea5bb11cbba8f9
  25:     0x7fd930e188fd - rustc_interface::passes::configure_and_expand_inner::had4f1edaa9e5dcc1
  26:     0x7fd930e031d5 - rustc_interface::passes::configure_and_expand::{{closure}}::h2a8de7b2e7685621
  27:     0x7fd930dfbd5d - rustc_data_structures::box_region::PinnedGenerator<I,A,R>::new::h2350cf4304a58173
  28:     0x7fd930e17f7b - rustc_interface::passes::configure_and_expand::hc2f6a0c4b008d57b
  29:     0x7fd930e2c38d - rustc_interface::queries::Queries::expansion::h541f7763ec81d5df
  30:     0x7fd930dbb420 - rustc_interface::queries::<impl rustc_interface::interface::Compiler>::enter::h27c18adf15a8e2d0
  31:     0x7fd930db0ad4 - rustc_span::with_source_map::ha7a34f5cae8f35d5
  32:     0x7fd930dbc4ba - rustc_interface::interface::create_compiler_and_run::hadd076a85b89b30e
  33:     0x7fd930db1768 - std::sys_common::backtrace::__rust_begin_short_backtrace::h64a4b3a8ddd28b5c
  34:     0x7fd930d943ca - core::ops::function::FnOnce::call_once{{vtable.shim}}::h151269a6222c3e41
  35:     0x7fd92e09bfda - <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once::hea1090dbdcecbf5a
                               at /rustc/257becbfe4987d1f7b12af5a8dd5ed96697cd2e8/library/alloc/src/boxed.rs:1328:9
  36:     0x7fd92e09bfda - <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once::h8d5723d3912bd325
                               at /rustc/257becbfe4987d1f7b12af5a8dd5ed96697cd2e8/library/alloc/src/boxed.rs:1328:9
  37:     0x7fd92e09bfda - std::sys::unix::thread::Thread::new::thread_start::hc17a425ca2995724
                               at /rustc/257becbfe4987d1f7b12af5a8dd5ed96697cd2e8/library/std/src/sys/unix/thread.rs:71:17
  38:     0x7fd92df85fa3 - start_thread
  39:     0x7fd92dea54cf - clone
  40:                0x0 - <unknown>

The panic message in full

Details

thread 'rustc' panicked at 'Stack should be empty: final_buf=FrameData { open: wdriver/../wdriver.rs:156:11: 156:12 (#0), inner: [(Token(Token { kind: BinOp(And), span: wdriver/../wdriver.rs:156:12: 156:13 (#0) }), Alone), (Token(Token { kind: Ident("self", false), span: wdriver/../wdriver.rs:156:13: 156:17 (#0) }), Joint), (Token(Token { kind: Comma, span: wdriver/../wdriver.rs:156:17: 156:18 (#0) }), Alone), (Token(Token { kind: Ident("s", false), span: wdriver/../wdriver.rs:156:19: 156:20 (#0) }), Joint), (Token(Token { kind: Colon, span: wdriver/../wdriver.rs:156:20: 156:21 (#0) }), Alone), (Token(Token { kind: BinOp(And), span: wdriver/../wdriver.rs:156:22: 156:23 (#0) }), Alone), (Token(Token { kind: Ident("dyn", false), span: wdriver/../wdriver.rs:156:23: 156:26 (#0) }), Alone), (Token(Token { kind: Ident("AsRef", false), span: wdriver/../wdriver.rs:156:27: 156:32 (#0) }), Joint), (Token(Token { kind: Lt, span: wdriver/../wdriver.rs:156:32: 156:33 (#0) }), Alone), (Token(Token { kind: Ident("str", false), span: wdriver/../wdriver.rs:156:33: 156:36 (#0) }), Joint), (Token(Token { kind: Gt, span: wdriver/../wdriver.rs:156:36: 156:37 (#0) }), Alone), (Token(Token { kind: RArrow, span: wdriver/../wdriver.rs:156:38: 156:40 (#0) }), Alone), (Token(Token { kind: Ident("String", false), span: wdriver/../wdriver.rs:156:41: 156:47 (#0) }), Alone), (Delimited(DelimSpan { open: wdriver/../wdriver.rs:156:48: 156:49 (#0), close: wdriver/../wdriver.rs:178:3: 178:4 (#0) }, Brace, TokenStream([(Token(Token { kind: Pound, span: wdriver/../wdriver.rs:157:5: 157:6 (#0) }), Alone), (Delimited(DelimSpan { open: wdriver/../wdriver.rs:157:6: 157:7 (#0), close: wdriver/../wdriver.rs:157:17: 157:18 (#0) }, Bracket, TokenStream([(Token(Token { kind: Ident("throws", false), span: wdriver/../wdriver.rs:157:7: 157:13 (#0) }), Alone), (Delimited(DelimSpan { open: wdriver/../wdriver.rs:157:13: 157:14 (#0), close: wdriver/../wdriver.rs:157:16: 157:17 (#0) }, Paren, TokenStream([(Token(Token { kind: Ident("AE", false), span: wdriver/../wdriver.rs:157:14: 157:16 (#0) }), Alone)])), Alone)])), Alone), (Token(Token { kind: Ident("fn", false), span: wdriver/../wdriver.rs:158:5: 158:7 (#0) }), Alone), (Token(Token { kind: Ident("inner", false), span: wdriver/../wdriver.rs:158:8: 158:13 (#0) }), Alone), (Delimited(DelimSpan { open: wdriver/../wdriver.rs:158:13: 158:14 (#0), close: wdriver/../wdriver.rs:178:3: 178:4 (#0) }, Paren, TokenStream([(Token(Token { kind: Ident("self_", false), span: wdriver/../wdriver.rs:158:14: 158:19 (#0) }), Joint), (Token(Token { kind: Colon, span: wdriver/../wdriver.rs:158:19: 158:20 (#0) }), Alone), (Token(Token { kind: BinOp(And), span: wdriver/../wdriver.rs:158:21: 158:22 (#0) }), Alone), (Token(Token { kind: Ident("Self", false), span: wdriver/../wdriver.rs:158:22: 158:26 (#0) }), Joint), (Token(Token { kind: Comma, span: wdriver/../wdriver.rs:158:26: 158:27 (#0) }), Alone), (Token(Token { kind: Ident("s", false), span: wdriver/../wdriver.rs:158:28: 158:29 (#0) }), Joint), (Token(Token { kind: Colon, span: wdriver/../wdriver.rs:158:29: 158:30 (#0) }), Alone), (Token(Token { kind: BinOp(And), span: wdriver/../wdriver.rs:158:31: 158:32 (#0) }), Alone), (Token(Token { kind: Ident("dyn", false), span: wdriver/../wdriver.rs:158:32: 158:35 (#0) }), Alone), (Token(Token { kind: Ident("AsRef", false), span: wdriver/../wdriver.rs:158:36: 158:41 (#0) }), Joint), (Token(Token { kind: Lt, span: wdriver/../wdriver.rs:158:41: 158:42 (#0) }), Alone), (Token(Token { kind: Ident("str", false), span: wdriver/../wdriver.rs:158:42: 158:45 (#0) }), Joint), (Token(Token { kind: Gt, span: wdriver/../wdriver.rs:158:45: 158:46 (#0) }), Alone), (Token(Token { kind: RArrow, span: wdriver/../wdriver.rs:158:47: 158:49 (#0) }), Alone), (Token(Token { kind: Ident("String", false), span: wdriver/../wdriver.rs:158:50: 158:56 (#0) }), Alone), (Delimited(DelimSpan { open: wdriver/../wdriver.rs:158:57: 158:58 (#0), close: wdriver/../wdriver.rs:176:5: 176:6 (#0) }, Brace, TokenStream([(Token(Token { kind: Ident("let", false), span: wdriver/../wdriver.rs:159:7: 159:10 (#0) }), Alone), (Token(Token { kind: Ident("s", false), span: wdriver/../wdriver.rs:159:11: 159:12 (#0) }), Alone), (Token(Token { kind: Eq, span: wdriver/../wdriver.rs:159:13: 159:14 (#0) }), Alone), (Token(Token { kind: Ident("s", false), span: wdriver/../wdriver.rs:159:15: 159:16 (#0) }), Joint), (Token(Token { kind: Dot, span: wdriver/../wdriver.rs:159:16: 159:17 (#0) }), Alone), (Token(Token { kind: Ident("as_ref", false), span: wdriver/../wdriver.rs:159:17: 159:23 (#0) }), Alone), (Delimited(DelimSpan { open: wdriver/../wdriver.rs:159:23: 159:24 (#0), close: wdriver/../wdriver.rs:159:24: 159:25 (#0) }, Paren, TokenStream([])), Alone), (Token(Token { kind: Semi, span: wdriver/../wdriver.rs:159:25: 159:26 (#0) }), Alone), (Token(Token { kind: Ident("let", false), span: wdriver/../wdriver.rs:160:7: 160:10 (#0) }), Alone), (Token(Token { kind: Ident("re", false), span: wdriver/../wdriver.rs:160:11: 160:13 (#0) }), Alone), (Token(Token { kind: Eq, span: wdriver/../wdriver.rs:160:14: 160:15 (#0) }), Alone), (Token(Token { kind: Ident("Regex", false), span: wdriver/../wdriver.rs:160:16: 160:21 (#0) }), Joint), (Token(Token { kind: ModSep, span: wdriver/../wdriver.rs:160:21: 160:23 (#0) }), Alone), (Token(Token { kind: Ident("new", false), span: wdriver/../wdriver.rs:160:23: 160:26 (#0) }), Alone), (Delimited(DelimSpan { open: wdriver/../wdriver.rs:160:26: 160:27 (#0), close: wdriver/../wdriver.rs:160:37: 160:38 (#0) }, Paren, TokenStream([(Token(Token { kind: Literal(Lit { kind: StrRaw(0), symbol: "@(\\w+)@", suffix: None }), span: wdriver/../wdriver.rs:160:27: 160:37 (#0) }), Alone)])), Alone), (Token(Token { kind: Dot, span: wdriver/../wdriver.rs:160:38: 160:39 (#0) }), Alone), (Token(Token { kind: Ident("expect", false), span: wdriver/../wdriver.rs:160:39: 160:45 (#0) }), Alone), (Delimited(DelimSpan { open: wdriver/../wdriver.rs:160:45: 160:46 (#0), close: wdriver/../wdriver.rs:160:55: 160:56 (#0) }, Paren, TokenStream([(Token(Token { kind: Literal(Lit { kind: Str, symbol: "bad re!", suffix: None }), span: wdriver/../wdriver.rs:160:46: 160:55 (#0) }), Alone)])), Alone), (Token(Token { kind: Semi, span: wdriver/../wdriver.rs:160:56: 160:57 (#0) }), Alone), (Token(Token { kind: Ident("let", false), span: wdriver/../wdriver.rs:161:7: 161:10 (#0) }), Alone), (Token(Token { kind: Ident("mut", false), span: wdriver/../wdriver.rs:161:11: 161:14 (#0) }), Alone), (Token(Token { kind: Ident("errs", false), span: wdriver/../wdriver.rs:161:15: 161:19 (#0) }), Alone), (Token(Token { kind: Eq, span: wdriver/../wdriver.rs:161:20: 161:21 (#0) }), Alone), (Token(Token { kind: Ident("vec", false), span: wdriver/../wdriver.rs:161:22: 161:25 (#0) }), Joint), (Token(Token { kind: Not, span: wdriver/../wdriver.rs:161:25: 161:26 (#0) }), Alone), (Delimited(DelimSpan { open: wdriver/../wdriver.rs:161:26: 161:27 (#0), close: wdriver/../wdriver.rs:161:27: 161:28 (#0) }, Bracket, TokenStream([])), Alone), (Token(Token { kind: Semi, span: wdriver/../wdriver.rs:161:28: 161:29 (#0) }), Alone), (Token(Token { kind: Ident("let", false), span: wdriver/../wdriver.rs:162:7: 162:10 (#0) }), Alone), (Token(Token { kind: Ident("out", false), span: wdriver/../wdriver.rs:162:11: 162:14 (#0) }), Alone), (Token(Token { kind: Eq, span: wdriver/../wdriver.rs:162:15: 162:16 (#0) }), Alone), (Token(Token { kind: Ident("re", false), span: wdriver/../wdriver.rs:162:17: 162:19 (#0) }), Joint), (Token(Token { kind: Dot, span: wdriver/../wdriver.rs:162:19: 162:20 (#0) }), Alone), (Token(Token { kind: Ident("replace_all", false), span: wdriver/../wdriver.rs:162:20: 162:31 (#0) }), Alone), (Delimited(DelimSpan { open: wdriver/../wdriver.rs:162:31: 162:32 (#0), close: wdriver/../wdriver.rs:170:8: 170:9 (#0) }, Paren, TokenStream([(Token(Token { kind: Ident("s", false), span: wdriver/../wdriver.rs:162:32: 162:33 (#0) }), Joint), (Token(Token { kind: Comma, span: wdriver/../wdriver.rs:162:33: 162:34 (#0) }), Alone), (Token(Token { kind: BinOp(Or), span: wdriver/../wdriver.rs:162:35: 162:36 (#0) }), Alone), (Token(Token { kind: Ident("caps", false), span: wdriver/../wdriver.rs:162:36: 162:40 (#0) }), Joint), (Token(Token { kind: Colon, span: wdriver/../wdriver.rs:162:40: 162:41 (#0) }), Alone), (Token(Token { kind: BinOp(And), span: wdriver/../wdriver.rs:162:42: 162:43 (#0) }), Alone), (Token(Token { kind: Ident("regex", false), span: wdriver/../wdriver.rs:162:43: 162:48 (#0) }), Joint), (Token(Token { kind: ModSep, span: wdriver/../wdriver.rs:162:48: 162:50 (#0) }), Alone), (Token(Token { kind: Ident("Captures", false), span: wdriver/../wdriver.rs:162:50: 162:58 (#0) }), Joint), (Token(Token { kind: BinOp(Or), span: wdriver/../wdriver.rs:162:58: 162:59 (#0) }), Alone), (Delimited(DelimSpan { open: wdriver/../wdriver.rs:162:60: 162:61 (#0), close: wdriver/../wdriver.rs:170:7: 170:8 (#0) }, Brace, TokenStream([(Token(Token { kind: Ident("let", false), span: wdriver/../wdriver.rs:163:9: 163:12 (#0) }), Alone), (Token(Token { kind: Ident("kw", false), span: wdriver/../wdriver.rs:163:13: 163:15 (#0) }), Alone), (Token(Token { kind: Eq, span: wdriver/../wdriver.rs:163:16: 163:17 (#0) }), Alone), (Token(Token { kind: Ident("caps", false), span: wdriver/../wdriver.rs:163:18: 163:22 (#0) }), Joint), (Token(Token { kind: Dot, span: wdriver/../wdriver.rs:163:22: 163:23 (#0) }), Alone), (Token(Token { kind: Ident("get", false), span: wdriver/../wdriver.rs:163:23: 163:26 (#0) }), Alone), (Delimited(DelimSpan { open: wdriver/../wdriver.rs:163:26: 163:27 (#0), close: wdriver/../wdriver.rs:163:28: 163:29 (#0) }, Paren, TokenStream([(Token(Token { kind: Literal(Lit { kind: Integer, symbol: "1", suffix: None }), span: wdriver/../wdriver.rs:163:27: 163:28 (#0) }), Alone)])), Alone), (Token(Token { kind: Dot, span: wdriver/../wdriver.rs:163:29: 163:30 (#0) }), Alone), (Token(Token { kind: Ident("expect", false), span: wdriver/../wdriver.rs:163:30: 163:36 (#0) }), Alone), (Delimited(DelimSpan { open: wdriver/../wdriver.rs:163:36: 163:37 (#0), close: wdriver/../wdriver.rs:163:50: 163:51 (#0) }, Paren, TokenStream([(Token(Token { kind: Literal(Lit { kind: Str, symbol: "$1 missing!", suffix: None }), span: wdriver/../wdriver.rs:163:37: 163:50 (#0) }), Alone)])), Alone), (Token(Token { kind: Dot, span: wdriver/../wdriver.rs:163:51: 163:52 (#0) }), Alone), (Token(Token { kind: Ident("as_str", false), span: wdriver/../wdriver.rs:163:52: 163:58 (#0) }), Alone), (Delimited(DelimSpan { open: wdriver/../wdriver.rs:163:58: 163:59 (#0), close: wdriver/../wdriver.rs:163:59: 163:60 (#0) }, Paren, TokenStream([])), Alone), (Token(Token { kind: Semi, span: wdriver/../wdriver.rs:163:60: 163:61 (#0) }), Alone), (Token(Token { kind: Ident("if", false), span: wdriver/../wdriver.rs:164:9: 164:11 (#0) }), Alone), (Token(Token { kind: Ident("kw", false), span: wdriver/../wdriver.rs:164:12: 164:14 (#0) }), Alone), (Token(Token { kind: EqEq, span: wdriver/../wdriver.rs:164:15: 164:17 (#0) }), Alone), (Token(Token { kind: Literal(Lit { kind: Str, symbol: "", suffix: None }), span: wdriver/../wdriver.rs:164:18: 164:20 (#0) }), Alone), (Delimited(DelimSpan { open: wdriver/../wdriver.rs:164:21: 164:22 (#0), close: wdriver/../wdriver.rs:164:44: 164:45 (#0) }, Brace, TokenStream([(Token(Token { kind: Ident("return", false), span: wdriver/../wdriver.rs:164:23: 164:29 (#0) }), Alone), (Token(Token { kind: Literal(Lit { kind: Str, symbol: "", suffix: None }), span: wdriver/../wdriver.rs:164:30: 164:32 (#0) }), Joint), (Token(Token { kind: Dot, span: wdriver/../wdriver.rs:164:32: 164:33 (#0) }), Alone), (Token(Token { kind: Ident("to_owned", false), span: wdriver/../wdriver.rs:164:33: 164:41 (#0) }), Alone), (Delimited(DelimSpan { open: wdriver/../wdriver.rs:164:41: 164:42 (#0), close: wdriver/../wdriver.rs:164:42: 164:43 (#0) }, Paren, TokenStream([])), Alone)])), Alone), (Token(Token { kind: Ident("let", false), span: wdriver/../wdriver.rs:165:9: 165:12 (#0) }), Alone), (Token(Token { kind: Ident("v", false), span: wdriver/../wdriver.rs:165:13: 165:14 (#0) }), Alone), (Token(Token { kind: Eq, span: wdriver/../wdriver.rs:165:15: 165:16 (#0) }), Alone), (Token(Token { kind: Ident("self", false), span: wdriver/../wdriver.rs:165:17: 165:21 (#0) }), Joint), (Token(Token { kind: Dot, span: wdriver/../wdriver.rs:165:21: 165:22 (#0) }), Alone), (Token(Token { kind: Ident("get", false), span: wdriver/../wdriver.rs:165:22: 165:25 (#0) }), Alone), (Delimited(DelimSpan { open: wdriver/../wdriver.rs:165:25: 165:26 (#0), close: wdriver/../wdriver.rs:165:28: 165:29 (#0) }, Paren, TokenStream([(Token(Token { kind: Ident("kw", false), span: wdriver/../wdriver.rs:165:26: 165:28 (#0) }), Alone)])), Alone), (Token(Token { kind: Semi, span: wdriver/../wdriver.rs:165:29: 165:30 (#0) }), Alone), (Token(Token { kind: Ident("v", false), span: wdriver/../wdriver.rs:166:9: 166:10 (#0) }), Joint), (Token(Token { kind: Dot, span: wdriver/../wdriver.rs:166:10: 166:11 (#0) }), Alone), (Token(Token { kind: Ident("unwrap_or_else", false), span: wdriver/../wdriver.rs:166:11: 166:25 (#0) }), Alone), (Delimited(DelimSpan { open: wdriver/../wdriver.rs:166:25: 166:26 (#0), close: wdriver/../wdriver.rs:169:10: 169:11 (#0) }, Paren, TokenStream([(Token(Token { kind: OrOr, span: wdriver/../wdriver.rs:166:26: 166:28 (#0) }), Alone), (Delimited(DelimSpan { open: wdriver/../wdriver.rs:166:28: 166:29 (#0), close: wdriver/../wdriver.rs:169:9: 169:10 (#0) }, Brace, TokenStream([(Token(Token { kind: Ident("errs", false), span: wdriver/../wdriver.rs:167:11: 167:15 (#0) }), Joint), (Token(Token { kind: Dot, span: wdriver/../wdriver.rs:167:15: 167:16 (#0) }), Alone), (Token(Token { kind: Ident("push", false), span: wdriver/../wdriver.rs:167:16: 167:20 (#0) }), Alone), (Delimited(DelimSpan { open: wdriver/../wdriver.rs:167:20: 167:21 (#0), close: wdriver/../wdriver.rs:167:34: 167:35 (#0) }, Paren, TokenStream([(Token(Token { kind: Ident("kw", false), span: wdriver/../wdriver.rs:167:21: 167:23 (#0) }), Joint), (Token(Token { kind: Dot, span: wdriver/../wdriver.rs:167:23: 167:24 (#0) }), Alone), (Token(Token { kind: Ident("to_owned", false), span: wdriver/../wdriver.rs:167:24: 167:32 (#0) }), Alone), (Delimited(DelimSpan { open: wdriver/../wdriver.rs:167:32: 167:33 (#0), close: wdriver/../wdriver.rs:167:33: 167:34 (#0) }, Paren, TokenStream([])), Alone)])), Alone), (Token(Token { kind: Semi, span: wdriver/../wdriver.rs:167:35: 167:36 (#0) }), Alone), (Token(Token { kind: Literal(Lit { kind: Str, symbol: "", suffix: None }), span: wdriver/../wdriver.rs:168:11: 168:13 (#0) }), Joint), (Token(Token { kind: Dot, span: wdriver/../wdriver.rs:168:13: 168:14 (#0) }), Alone), (Token(Token { kind: Ident("to_owned", false), span: wdriver/../wdriver.rs:168:14: 168:22 (#0) }), Alone), (Delimited(DelimSpan { open: wdriver/../wdriver.rs:168:22: 168:23 (#0), close: wdriver/../wdriver.rs:168:23: 168:24 (#0) }, Paren, TokenStream([])), Alone)])), Alone)])), Alone)])), Alone)])), Alone), (Token(Token { kind: Semi, span: wdriver/../wdriver.rs:170:9: 170:10 (#0) }), Alone), (Token(Token { kind: Ident("if", false), span: wdriver/../wdriver.rs:171:7: 171:9 (#0) }), Alone), (Token(Token { kind: Not, span: wdriver/../wdriver.rs:171:10: 171:11 (#0) }), Alone), (Token(Token { kind: Ident("errs", false), span: wdriver/../wdriver.rs:171:12: 171:16 (#0) }), Joint), (Token(Token { kind: Dot, span: wdriver/../wdriver.rs:171:16: 171:17 (#0) }), Alone), (Token(Token { kind: Ident("is_empty", false), span: wdriver/../wdriver.rs:171:17: 171:25 (#0) }), Alone), (Delimited(DelimSpan { open: wdriver/../wdriver.rs:171:25: 171:26 (#0), close: wdriver/../wdriver.rs:171:26: 171:27 (#0) }, Paren, TokenStream([])), Alone), (Delimited(DelimSpan { open: wdriver/../wdriver.rs:171:28: 171:29 (#0), close: wdriver/../wdriver.rs:174:7: 174:8 (#0) }, Brace, TokenStream([(Token(Token { kind: Ident("throw", false), span: wdriver/../wdriver.rs:172:9: 172:14 (#0) }), Joint), (Token(Token { kind: Not, span: wdriver/../wdriver.rs:172:14: 172:15 (#0) }), Alone), (Delimited(DelimSpan { open: wdriver/../wdriver.rs:172:15: 172:16 (#0), close: wdriver/../wdriver.rs:173:33: 173:34 (#0) }, Paren, TokenStream([(Token(Token { kind: Ident("anyhow", false), span: wdriver/../wdriver.rs:172:16: 172:22 (#0) }), Joint), (Token(Token { kind: Not, span: wdriver/../wdriver.rs:172:22: 172:23 (#0) }), Alone), (Delimited(DelimSpan { open: wdriver/../wdriver.rs:172:23: 172:24 (#0), close: wdriver/../wdriver.rs:173:32: 173:33 (#0) }, Paren, TokenStream([(Token(Token { kind: Literal(Lit { kind: Str, symbol: "bad substitution(s) {:?} in {:?}", suffix: None }), span: wdriver/../wdriver.rs:172:24: 172:58 (#0) }), Joint), (Token(Token { kind: Comma, span: wdriver/../wdriver.rs:172:58: 172:59 (#0) }), Alone), (Token(Token { kind: BinOp(And), span: wdriver/../wdriver.rs:173:24: 173:25 (#0) }), Alone), (Token(Token { kind: Ident("errs", false), span: wdriver/../wdriver.rs:173:25: 173:29 (#0) }), Joint), (Token(Token { kind: Comma, span: wdriver/../wdriver.rs:173:29: 173:30 (#0) }), Alone), (Token(Token { kind: Ident("s", false), span: wdriver/../wdriver.rs:173:31: 173:32 (#0) }), Alone)])), Alone)])), Alone), (Token(Token { kind: Semi, span: wdriver/../wdriver.rs:173:34: 173:35 (#0) }), Alone)])), Alone), (Token(Token { kind: Ident("out", false), span: wdriver/../wdriver.rs:175:7: 175:10 (#0) }), Joint), (Token(Token { kind: Dot, span: wdriver/../wdriver.rs:175:10: 175:11 (#0) }), Alone), (Token(Token { kind: Ident("into", false), span: wdriver/../wdriver.rs:175:11: 175:15 (#0) }), Alone), (Delimited(DelimSpan { open: wdriver/../wdriver.rs:175:15: 175:16 (#0), close: wdriver/../wdriver.rs:175:16: 175:17 (#0) }, Paren, TokenStream([])), Alone)])), Alone), (Token(Token { kind: Ident("inner", false), span: wdriver/../wdriver.rs:177:5: 177:10 (#0) }), Alone), (Delimited(DelimSpan { open: wdriver/../wdriver.rs:177:10: 177:11 (#0), close: wdriver/../wdriver.rs:177:18: 177:19 (#0) }, Paren, TokenStream([(Token(Token { kind: Ident("self", false), span: wdriver/../wdriver.rs:177:11: 177:15 (#0) }), Joint), (Token(Token { kind: Comma, span: wdriver/../wdriver.rs:177:15: 177:16 (#0) }), Alone), (Token(Token { kind: Ident("s", false), span: wdriver/../wdriver.rs:177:17: 177:18 (#0) }), Alone)])), Alone), (Token(Token { kind: Question, span: wdriver/../wdriver.rs:177:19: 177:20 (#0) }), Alone)])), Alone)])), Alone)] } stack=[FrameData { open: wdriver/../wdriver.rs:1:1: 1:1 (#0), inner: [(Token(Token { kind: Ident("fn", false), span: wdriver/../wdriver.rs:156:3: 156:5 (#0) }), Alone), (Token(Token { kind: Ident("subst", false), span: wdriver/../wdriver.rs:156:6: 156:11 (#0) }), Alone)] }]', compiler/rustc_parse/src/parser/mod.rs:1409:5

[durka]

Minimized:

proc macro

extern crate proc_macro;
use proc_macro::TokenStream;

#[proc_macro_attribute]
pub fn mac(_attrs: TokenStream, input: TokenStream) -> TokenStream {
    input
}

lib.rs

pub trait Crash {
    #[mac::mac]
    fn one(s: () {
    }

    fn two();
}

[ijackson]

@rustbot modify labels -E-needs-mcve +A-proc-macros

[durka]

Is the solution possibly to just remove the offending assertion? The token stream will be nonsense but some other error reporting should catch the mismatched delimiters, I'd assume?

[osa1]

I just quickly tried the suggestion above (removing the assertion) and this is the error I got without it:

error: expected one of `)` or `,`, found `{`
 --> src/lib.rs:3:18
  |
3 |     fn one(s: () {
  |           -     -^
  |           |     |
  |           |     help: `)` may belong here
  |           unclosed delimiter

error: non-item in item list
 --> src/lib.rs:5:1
  |
1 | pub trait Crash {
  |                 - item list starts here
...
5 | }
  | ^
  | |
  | non-item starts here
  | item list ends here

error: expected one of `!` or `::`, found `:`
 --> src/lib.rs:2:5
  |
2 |     #[proc_macro::mac]
  |     ^^^^^^^^^^^^^^^^^^

error: aborting due to 3 previous errors

error: could not compile `issue`

To learn more, run the command again with --verbose.

Note that I tried a slightly simpler version of the small repro above:

pub trait Crash {
    #[proc_macro::mac]
    fn one(s: () {
    }
}

This still fails with ICE with the assertion.

[leftwo]

I think I'm seeing the same issue with code containing a similar syntax error:

use tracing::instrument;

struct al;

impl al {
    #[instrument]
    fn ox(&mut self {
    }
}

The error is the ox fn does not have the closing paren.

I see this on both release and debug builds:
stable: 1.55.0
beta: 1.56.0-beta.2
Nightly: 1.57.0-nightly (c3c0f80d6 2021-09-14)

Here is the error and stack from Rust Playground:

   Compiling playground v0.0.1 (/playground)
error: expected one of `)` or `,`, found `{`
 --> src/lib.rs:7:10
  |
7 |     fn ox(&mut self {
  |          ^         -^
  |          |         |
  |          |         help: `)` may belong here
  |          unclosed delimiter

error: non-item in item list
 --> src/lib.rs:9:1
  |
5 | impl al {
  |         - item list starts here
...
9 | }
  | ^
  | |
  | non-item starts here
  | item list ends here

thread 'rustc' panicked at 'Stack should be empty: final_buf=FrameData { open: src/lib.rs:7:10: 7:11 (#0), open_delim: Paren, inner: [(Token(Token { kind: BinOp(And), span: src/lib.rs:7:11: 7:12 (#0) }), Alone), (Token(Token { kind: Ident("mut", false), span: src/lib.rs:7:12: 7:15 (#0) }), Alone), (Token(Token { kind: Ident("self", false), span: src/lib.rs:7:16: 7:20 (#0) }), Alone), (Delimited(DelimSpan { open: src/lib.rs:7:21: 7:22 (#0), close: src/lib.rs:8:5: 8:6 (#0) }, Brace, AttrAnnotatedTokenStream([])), Alone)] } stack=[FrameData { open: no-location (#0), open_delim: NoDelim, inner: [(Token(Token { kind: Ident("fn", false), span: src/lib.rs:7:5: 7:7 (#0) }), Alone), (Token(Token { kind: Ident("ox", false), span: src/lib.rs:7:8: 7:10 (#0) }), Alone)] }]', compiler/rustc_parse/src/parser/attr_wrapper.rs:501:5
stack backtrace:
   0: rust_begin_unwind
             at /rustc/c3c0f80d6081092faff801542dd82f0e2420152b/library/std/src/panicking.rs:517:5
   1: std::panicking::begin_panic_fmt
             at /rustc/c3c0f80d6081092faff801542dd82f0e2420152b/library/std/src/panicking.rs:460:5
   2: <rustc_parse::parser::attr_wrapper::LazyTokenStreamImpl as rustc_ast::tokenstream::CreateTokenStream>::create_token_stream
   3: rustc_parse::prepend_attrs
   4: rustc_parse::nt_to_tokenstream
   5: rustc_expand::base::Annotatable::into_tokens
   6: rustc_expand::expand::MacroExpander::fully_expand_fragment
   7: rustc_expand::expand::MacroExpander::expand_crate
   8: rustc_session::utils::<impl rustc_session::session::Session>::time
   9: rustc_interface::passes::configure_and_expand
  10: rustc_interface::queries::Queries::expansion
  11: rustc_interface::queries::<impl rustc_interface::interface::Compiler>::enter
  12: rustc_span::with_source_map
  13: 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 1.57.0-nightly (c3c0f80d6 2021-09-14) running on x86_64-unknown-linux-gnu

note: compiler flags: -C opt-level=3 -C embed-bitcode=no -C codegen-units=1 --crate-type lib

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

query stack during panic:
end of query stack