ICE parse_attribute called in non-attribute position

[matthiaskrgr]

cfg_if::cfg_if! {
    if {
    } else if #(&cpus) {
    } else [libc::CTL_HW, libc::HW_NCPU, 0, 0]
}

thread 'main' panicked at 'parse_attribute called in non-attribute position', compiler/rustc_parse/src/parser/attr.rs:122:13
stack backtrace:
   0:     0x7f29d1f65e8a - std::backtrace_rs::backtrace::libunwind::trace::hc07ec51854030801
                               at /rustc/17c11672167827b0dd92c88ef69f24346d1286dd/library/std/src/../../backtrace/src/backtrace/libunwind.rs:93:5
   1:     0x7f29d1f65e8a - std::backtrace_rs::backtrace::trace_unsynchronized::hd5249f53d09c2c41
                               at /rustc/17c11672167827b0dd92c88ef69f24346d1286dd/library/std/src/../../backtrace/src/backtrace/mod.rs:66:5
   2:     0x7f29d1f65e8a - std::sys_common::backtrace::_print_fmt::h7a58bb30aee44196
                               at /rustc/17c11672167827b0dd92c88ef69f24346d1286dd/library/std/src/sys_common/backtrace.rs:65:5
   3:     0x7f29d1f65e8a - <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt::h4f2b7c295e3f8019
                               at /rustc/17c11672167827b0dd92c88ef69f24346d1286dd/library/std/src/sys_common/backtrace.rs:44:22
   4:     0x7f29d1fc9e6f - core::fmt::write::h10777037b979b8b8
                               at /rustc/17c11672167827b0dd92c88ef69f24346d1286dd/library/core/src/fmt/mod.rs:1254:17
   5:     0x7f29d1f58ac5 - std::io::Write::write_fmt::he1dc4aa4bd2563db
                               at /rustc/17c11672167827b0dd92c88ef69f24346d1286dd/library/std/src/io/mod.rs:1698:15
   6:     0x7f29d1f65c55 - std::sys_common::backtrace::_print::h163c7799d3150ce8
                               at /rustc/17c11672167827b0dd92c88ef69f24346d1286dd/library/std/src/sys_common/backtrace.rs:47:5
   7:     0x7f29d1f65c55 - std::sys_common::backtrace::print::h3cf13564ddfd5c0e
                               at /rustc/17c11672167827b0dd92c88ef69f24346d1286dd/library/std/src/sys_common/backtrace.rs:34:9
   8:     0x7f29d1f688fe - std::panicking::default_hook::{{closure}}::h999811fec35f64bf
                               at /rustc/17c11672167827b0dd92c88ef69f24346d1286dd/library/std/src/panicking.rs:269:22
   9:     0x7f29d1f686a5 - std::panicking::default_hook::he182d48ca482e8b2
                               at /rustc/17c11672167827b0dd92c88ef69f24346d1286dd/library/std/src/panicking.rs:288:9
  10:     0x7f29d1f68f6e - std::panicking::rust_panic_with_hook::h2bc066147eaf9845
                               at /rustc/17c11672167827b0dd92c88ef69f24346d1286dd/library/std/src/panicking.rs:690:13
  11:     0x7f29d1f68e22 - std::panicking::begin_panic_handler::{{closure}}::h1e4368c427832fe9
                               at /rustc/17c11672167827b0dd92c88ef69f24346d1286dd/library/std/src/panicking.rs:579:13
  12:     0x7f29d1f662f6 - std::sys_common::backtrace::__rust_end_short_backtrace::h5466480ef33b438e
                               at /rustc/17c11672167827b0dd92c88ef69f24346d1286dd/library/std/src/sys_common/backtrace.rs:150:18
  13:     0x7f29d1f68bc2 - rust_begin_unwind
                               at /rustc/17c11672167827b0dd92c88ef69f24346d1286dd/library/std/src/panicking.rs:577:5
  14:     0x7f29d1fc6273 - core::panicking::panic_fmt::ha28b6d803d12671b
                               at /rustc/17c11672167827b0dd92c88ef69f24346d1286dd/library/core/src/panicking.rs:67:14
  15:     0x7f29d3cfc986 - <rustc_parse[b1dd6c1f496ef2d0]::parser::Parser>::collect_tokens_trailing_token::<rustc_ast[b583ee7534cdfdf7]::ast::Attribute, <rustc_parse[b1dd6c1f496ef2d0]::parser::Parser>::collect_tokens_no_attrs<rustc_ast[b583ee7534cdfdf7]::ast::Attribute, <rustc_parse[b1dd6c1f496ef2d0]::parser::Parser>::parse_attribute::{closure#0}>::{closure#0}>
  16:     0x7f29d5a12f95 - <rustc_parse[b1dd6c1f496ef2d0]::parser::Parser>::parse_attribute
  17:     0x55e3b79ae66d - rustfmt_nightly[e3445ded4feb3b46]::parse::macros::cfg_if::parse_cfg_if_inner
  18:     0x55e3b7a5c219 - <rustfmt_nightly[e3445ded4feb3b46]::modules::visitor::CfgIfVisitor as rustc_ast[b583ee7534cdfdf7]::visit::Visitor>::visit_mac_call
  19:     0x55e3b79ee2f1 - rustc_ast[b583ee7534cdfdf7]::visit::walk_item::<rustfmt_nightly[e3445ded4feb3b46]::modules::visitor::CfgIfVisitor>
  20:     0x55e3b7a8458d - <rustfmt_nightly[e3445ded4feb3b46]::modules::ModResolver>::visit_cfg_if
  21:     0x55e3b7a849c6 - <rustfmt_nightly[e3445ded4feb3b46]::modules::ModResolver>::visit_mod_from_ast
  22:     0x55e3b7a84015 - <rustfmt_nightly[e3445ded4feb3b46]::modules::ModResolver>::visit_crate
  23:     0x55e3b7942533 - rustfmt_nightly[e3445ded4feb3b46]::formatting::format_project::<rustfmt_nightly[e3445ded4feb3b46]::Session<std[6ff7f37a454f70cc]::io::stdio::Stdout>>
  24:     0x55e3b793f9d0 - <scoped_tls[abd3470abb840dd8]::ScopedKey<rustc_span[e810f079a636b72c]::SessionGlobals>>::with::<<rustfmt_nightly[e3445ded4feb3b46]::Session<std[6ff7f37a454f70cc]::io::stdio::Stdout>>::format_input_inner::{closure#0}, core[a19e7c0c634483f1]::result::Result<rustfmt_nightly[e3445ded4feb3b46]::FormatReport, rustfmt_nightly[e3445ded4feb3b46]::ErrorKind>>
  25:     0x55e3b793ca7f - <scoped_tls[abd3470abb840dd8]::ScopedKey<rustc_span[e810f079a636b72c]::SessionGlobals>>::set::<rustc_span[e810f079a636b72c]::create_session_if_not_set_then<core[a19e7c0c634483f1]::result::Result<rustfmt_nightly[e3445ded4feb3b46]::FormatReport, rustfmt_nightly[e3445ded4feb3b46]::ErrorKind>, <rustfmt_nightly[e3445ded4feb3b46]::Session<std[6ff7f37a454f70cc]::io::stdio::Stdout>>::format_input_inner::{closure#0}>::{closure#0}, core[a19e7c0c634483f1]::result::Result<rustfmt_nightly[e3445ded4feb3b46]::FormatReport, rustfmt_nightly[e3445ded4feb3b46]::ErrorKind>>
  26:     0x55e3b7965650 - <rustfmt_nightly[e3445ded4feb3b46]::Session<std[6ff7f37a454f70cc]::io::stdio::Stdout>>::format
  27:     0x55e3b7954b05 - rustfmt[fd29d8685e71f599]::format_and_emit_report::<std[6ff7f37a454f70cc]::io::stdio::Stdout>
  28:     0x55e3b7963b89 - <rustfmt_nightly[e3445ded4feb3b46]::Session<std[6ff7f37a454f70cc]::io::stdio::Stdout>>::override_config::<rustfmt[fd29d8685e71f599]::format::{closure#0}, ()>
  29:     0x55e3b7953865 - rustfmt[fd29d8685e71f599]::execute
  30:     0x55e3b7951221 - rustfmt[fd29d8685e71f599]::main
  31:     0x55e3b7964483 - std[6ff7f37a454f70cc]::sys_common::backtrace::__rust_begin_short_backtrace::<fn(), ()>
  32:     0x55e3b7962cc9 - std[6ff7f37a454f70cc]::rt::lang_start::<()>::{closure#0}
  33:     0x7f29d1f4969e - core::ops::function::impls::<impl core::ops::function::FnOnce<A> for &F>::call_once::hd8ec26e1d0256733
                               at /rustc/17c11672167827b0dd92c88ef69f24346d1286dd/library/core/src/ops/function.rs:287:13
  34:     0x7f29d1f4969e - std::panicking::try::do_call::ha93a022fbffe13f1
                               at /rustc/17c11672167827b0dd92c88ef69f24346d1286dd/library/std/src/panicking.rs:485:40
  35:     0x7f29d1f4969e - std::panicking::try::hb1493baa50505ff7
                               at /rustc/17c11672167827b0dd92c88ef69f24346d1286dd/library/std/src/panicking.rs:449:19
  36:     0x7f29d1f4969e - std::panic::catch_unwind::h68d19a9efbc50ca2
                               at /rustc/17c11672167827b0dd92c88ef69f24346d1286dd/library/std/src/panic.rs:140:14
  37:     0x7f29d1f4969e - std::rt::lang_start_internal::{{closure}}::hfefbc424423bf0ab
                               at /rustc/17c11672167827b0dd92c88ef69f24346d1286dd/library/std/src/rt.rs:148:48
  38:     0x7f29d1f4969e - std::panicking::try::do_call::h33a3e76f78055d3b
                               at /rustc/17c11672167827b0dd92c88ef69f24346d1286dd/library/std/src/panicking.rs:485:40
  39:     0x7f29d1f4969e - std::panicking::try::hf16a19af84a23805
                               at /rustc/17c11672167827b0dd92c88ef69f24346d1286dd/library/std/src/panicking.rs:449:19
  40:     0x7f29d1f4969e - std::panic::catch_unwind::hfd39d2618b0c9350
                               at /rustc/17c11672167827b0dd92c88ef69f24346d1286dd/library/std/src/panic.rs:140:14
  41:     0x7f29d1f4969e - std::rt::lang_start_internal::h8eb39434a671d889
                               at /rustc/17c11672167827b0dd92c88ef69f24346d1286dd/library/std/src/rt.rs:148:20
  42:     0x55e3b79558a5 - main
  43:     0x7f29d1bc3790 - <unknown>
  44:     0x7f29d1bc384a - __libc_start_main
  45:     0x55e3b7938c59 - <unknown>
  46:                0x0 - <unknown>

[matthiaskrgr]

Probably related:

cfg_if::cfg_if! { if # }

error: internal compiler error: the following error was constructed but not emitted

error: expected one of `!` or `[`, found `<eof>`
 --> /tmp/im4/treereduce.out:1:22
  |
1 | cfg_if::cfg_if! { if # }
  |                      ^ expected one of `!` or `[`

thread 'main' panicked at 'error was constructed but not emitted', compiler/rustc_errors/src/diagnostic_builder.rs:780:21
stack backtrace:
   0: rust_begin_unwind
             at /rustc/3a8a131e9509c478ece1c58fe0ea2d49463d2300/library/std/src/panicking.rs:577:5
   1: core::panicking::panic_fmt
             at /rustc/3a8a131e9509c478ece1c58fe0ea2d49463d2300/library/core/src/panicking.rs:67:14
   2: <rustc_errors::diagnostic_builder::DiagnosticBuilderInner as core::ops::drop::Drop>::drop
   3: rustfmt_nightly::parse::macros::cfg_if::parse_cfg_if_inner
   4: <rustfmt_nightly::modules::visitor::CfgIfVisitor as rustc_ast::visit::Visitor>::visit_mac_call
   5: rustc_ast::visit::walk_item::<rustfmt_nightly::modules::visitor::CfgIfVisitor>
   6: <rustfmt_nightly::modules::ModResolver>::visit_cfg_if
   7: <rustfmt_nightly::modules::ModResolver>::visit_mod_from_ast
   8: <rustfmt_nightly::modules::ModResolver>::visit_crate
   9: rustfmt_nightly::formatting::format_project::<rustfmt_nightly::Session<std::io::stdio::Stdout>>
  10: <scoped_tls::ScopedKey<rustc_span::SessionGlobals>>::with::<<rustfmt_nightly::Session<std::io::stdio::Stdout>>::format_input_inner::{closure#0}, core::result::Result<rustfmt_nightly::FormatReport, rustfmt_nightly::ErrorKind>>
  11: <scoped_tls::ScopedKey<rustc_span::SessionGlobals>>::set::<rustc_span::create_session_if_not_set_then<core::result::Result<rustfmt_nightly::FormatReport, rustfmt_nightly::ErrorKind>, <rustfmt_nightly::Session<std::io::stdio::Stdout>>::format_input_inner::{closure#0}>::{closure#0}, core::result::Result<rustfmt_nightly::FormatReport, rustfmt_nightly::ErrorKind>>
  12: <rustfmt_nightly::Session<std::io::stdio::Stdout>>::format
  13: rustfmt::format_and_emit_report::<std::io::stdio::Stdout>
  14: <rustfmt_nightly::Session<std::io::stdio::Stdout>>::override_config::<rustfmt::format::{closure#0}, ()>
  15: rustfmt::execute
  16: rustfmt::main
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace

[ytmimi]

Probably related:

cfg_if::cfg_if! { if # }

I believe this particular case was resolved by #5731, since the error has to do with constructing but not emitting the diagnostic error. Additionally, I'm unable to reproduce this with the latest master a3b2bfc