ICE: unreachable src/tools/rustfmt/src/expr.rs:407:13

[matthiaskrgr]

fn main() {
    println!("{}", builtin # offset_of(A, 0. 1.1.1));
}

thread 'main' panicked at src/tools/rustfmt/src/expr.rs:407:13:
internal error: entered unreachable code
stack backtrace:
   0:     0x7f5d061634ec - std::backtrace_rs::backtrace::libunwind::trace::h735859f22ae1ae42
                               at /rustc/1b198b3a196442e14fb06978166ab46a4618d131/library/std/src/../../backtrace/src/backtrace/libunwind.rs:93:5
   1:     0x7f5d061634ec - std::backtrace_rs::backtrace::trace_unsynchronized::hf2010d7ee6f90d09
                               at /rustc/1b198b3a196442e14fb06978166ab46a4618d131/library/std/src/../../backtrace/src/backtrace/mod.rs:66:5
   2:     0x7f5d061634ec - std::sys_common::backtrace::_print_fmt::h41f140d22a480669
                               at /rustc/1b198b3a196442e14fb06978166ab46a4618d131/library/std/src/sys_common/backtrace.rs:67:5
   3:     0x7f5d061634ec - <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt::hc0cf8f562aa74991
                               at /rustc/1b198b3a196442e14fb06978166ab46a4618d131/library/std/src/sys_common/backtrace.rs:44:22
   4:     0x7f5d061c8d7c - core::fmt::rt::Argument::fmt::h45214d1bb1360468
                               at /rustc/1b198b3a196442e14fb06978166ab46a4618d131/library/core/src/fmt/rt.rs:138:9
   5:     0x7f5d061c8d7c - core::fmt::write::h0cf0d88bfa21782e
                               at /rustc/1b198b3a196442e14fb06978166ab46a4618d131/library/core/src/fmt/mod.rs:1094:21
   6:     0x7f5d06155e8e - std::io::Write::write_fmt::h0d843d62f88873a3
                               at /rustc/1b198b3a196442e14fb06978166ab46a4618d131/library/std/src/io/mod.rs:1714:15
   7:     0x7f5d061632d4 - std::sys_common::backtrace::_print::h214e31acf5fce41f
                               at /rustc/1b198b3a196442e14fb06978166ab46a4618d131/library/std/src/sys_common/backtrace.rs:47:5
   8:     0x7f5d061632d4 - std::sys_common::backtrace::print::h0be3a8355cde20c1
                               at /rustc/1b198b3a196442e14fb06978166ab46a4618d131/library/std/src/sys_common/backtrace.rs:34:9
   9:     0x7f5d061663ca - std::panicking::panic_hook_with_disk_dump::{{closure}}::h14933742ebca4954
                               at /rustc/1b198b3a196442e14fb06978166ab46a4618d131/library/std/src/panicking.rs:278:22
  10:     0x7f5d061660b7 - std::panicking::panic_hook_with_disk_dump::h934c976f93b38e49
                               at /rustc/1b198b3a196442e14fb06978166ab46a4618d131/library/std/src/panicking.rs:312:9
  11:     0x7f5d093450e9 - <rustc_driver_impl[6be839844fedfd7f]::install_ice_hook::{closure#0} as core[6093bc177ae0b635]::ops::function::FnOnce<(&core[6093bc177ae0b635]::panic::panic_info::PanicInfo,)>>::call_once::{shim:vtable#0}
  12:     0x7f5d06166c70 - <alloc::boxed::Box<F,A> as core::ops::function::Fn<Args>>::call::h17a87ce95b5189e5
                               at /rustc/1b198b3a196442e14fb06978166ab46a4618d131/library/alloc/src/boxed.rs:2021:9
  13:     0x7f5d06166c70 - std::panicking::rust_panic_with_hook::h57165fef3c33fe3c
                               at /rustc/1b198b3a196442e14fb06978166ab46a4618d131/library/std/src/panicking.rs:733:13
  14:     0x7f5d061669b1 - std::panicking::begin_panic_handler::{{closure}}::hd3d74044bc679432
                               at /rustc/1b198b3a196442e14fb06978166ab46a4618d131/library/std/src/panicking.rs:619:13
  15:     0x7f5d06163a16 - std::sys_common::backtrace::__rust_end_short_backtrace::hb0880b96bb7f18bf
                               at /rustc/1b198b3a196442e14fb06978166ab46a4618d131/library/std/src/sys_common/backtrace.rs:170:18
  16:     0x7f5d06166742 - rust_begin_unwind
                               at /rustc/1b198b3a196442e14fb06978166ab46a4618d131/library/std/src/panicking.rs:617:5
  17:     0x7f5d061c5183 - core::panicking::panic_fmt::h1328a2d38b9d4c22
                               at /rustc/1b198b3a196442e14fb06978166ab46a4618d131/library/core/src/panicking.rs:67:14
  18:     0x7f5d061c5213 - core::panicking::panic::h7c6960874348cf53
                               at /rustc/1b198b3a196442e14fb06978166ab46a4618d131/library/core/src/panicking.rs:117:5
  19:     0x55d6a0f22bd5 - rustfmt_nightly[6c3958c54b76f126]::expr::format_expr
  20:     0x55d6a0f3ede1 - <rustfmt_nightly[6c3958c54b76f126]::macros::MacroArg as rustfmt_nightly[6c3958c54b76f126]::rewrite::Rewrite>::rewrite
  21:     0x55d6a0e93fbe - <rustfmt_nightly[6c3958c54b76f126]::overflow::OverflowableItem as rustfmt_nightly[6c3958c54b76f126]::rewrite::Rewrite>::rewrite
  22:     0x55d6a0e97c79 - <rustfmt_nightly[6c3958c54b76f126]::overflow::Context>::rewrite_items
  23:     0x55d6a0e98cb4 - <rustfmt_nightly[6c3958c54b76f126]::overflow::Context>::rewrite
  24:     0x55d6a0e946bb - rustfmt_nightly[6c3958c54b76f126]::overflow::rewrite_with_parens::<rustfmt_nightly[6c3958c54b76f126]::macros::MacroArg, core[6093bc177ae0b635]::slice::iter::Iter<rustfmt_nightly[6c3958c54b76f126]::macros::MacroArg>>
  25:     0x55d6a0f40d4d - rustfmt_nightly[6c3958c54b76f126]::macros::rewrite_macro_inner
  26:     0x55d6a0f3ef2e - rustfmt_nightly[6c3958c54b76f126]::macros::rewrite_macro
  27:     0x55d6a0f8767c - <rustfmt_nightly[6c3958c54b76f126]::visitor::FmtVisitor>::visit_mac
  28:     0x55d6a0f8963b - <rustfmt_nightly[6c3958c54b76f126]::visitor::FmtVisitor>::walk_stmts
  29:     0x55d6a0f80687 - <rustfmt_nightly[6c3958c54b76f126]::visitor::FmtVisitor>::visit_block
  30:     0x55d6a0f83175 - <rustfmt_nightly[6c3958c54b76f126]::visitor::FmtVisitor>::visit_fn
  31:     0x55d6a0f83f41 - <rustfmt_nightly[6c3958c54b76f126]::visitor::FmtVisitor>::visit_item
  32:     0x55d6a0f7eebb - <rustfmt_nightly[6c3958c54b76f126]::visitor::FmtVisitor>::visit_items_with_reordering
  33:     0x55d6a0f89dcd - <rustfmt_nightly[6c3958c54b76f126]::visitor::FmtVisitor>::format_separate_mod
  34:     0x55d6a0e0bb5e - rustfmt_nightly[6c3958c54b76f126]::formatting::format_project::<rustfmt_nightly[6c3958c54b76f126]::Session<std[d5d19527909f28ae]::io::stdio::Stdout>>
  35:     0x55d6a0e065b2 - <scoped_tls[a4738d5243f410f]::ScopedKey<rustc_span[b474a88e3bf3a6a2]::SessionGlobals>>::with::<<rustfmt_nightly[6c3958c54b76f126]::Session<std[d5d19527909f28ae]::io::stdio::Stdout>>::format_input_inner::{closure#0}, core[6093bc177ae0b635]::result::Result<rustfmt_nightly[6c3958c54b76f126]::FormatReport, rustfmt_nightly[6c3958c54b76f126]::ErrorKind>>
  36:     0x55d6a0e03954 - <scoped_tls[a4738d5243f410f]::ScopedKey<rustc_span[b474a88e3bf3a6a2]::SessionGlobals>>::set::<rustc_span[b474a88e3bf3a6a2]::create_session_if_not_set_then<core[6093bc177ae0b635]::result::Result<rustfmt_nightly[6c3958c54b76f126]::FormatReport, rustfmt_nightly[6c3958c54b76f126]::ErrorKind>, <rustfmt_nightly[6c3958c54b76f126]::Session<std[d5d19527909f28ae]::io::stdio::Stdout>>::format_input_inner::{closure#0}>::{closure#0}, core[6093bc177ae0b635]::result::Result<rustfmt_nightly[6c3958c54b76f126]::FormatReport, rustfmt_nightly[6c3958c54b76f126]::ErrorKind>>
  37:     0x55d6a0e08a2f - <rustfmt_nightly[6c3958c54b76f126]::Session<std[d5d19527909f28ae]::io::stdio::Stdout>>::format_input_inner
  38:     0x55d6a0dfb5f7 - rustfmt[f304444a0a4ba634]::format_and_emit_report::<std[d5d19527909f28ae]::io::stdio::Stdout>
  39:     0x55d6a0e07fdb - <rustfmt_nightly[6c3958c54b76f126]::Session<std[d5d19527909f28ae]::io::stdio::Stdout>>::override_config::<rustfmt[f304444a0a4ba634]::format::{closure#0}, ()>
  40:     0x55d6a0dfa3d9 - rustfmt[f304444a0a4ba634]::execute
  41:     0x55d6a0df82b6 - rustfmt[f304444a0a4ba634]::main
  42:     0x55d6a0e088d3 - std[d5d19527909f28ae]::sys_common::backtrace::__rust_begin_short_backtrace::<fn(), ()>
  43:     0x55d6a0e0d1e9 - std[d5d19527909f28ae]::rt::lang_start::<()>::{closure#0}
  44:     0x7f5d0614635b - core::ops::function::impls::<impl core::ops::function::FnOnce<A> for &F>::call_once::hd625ab3f85f394d9
                               at /rustc/1b198b3a196442e14fb06978166ab46a4618d131/library/core/src/ops/function.rs:284:13
  45:     0x7f5d0614635b - std::panicking::try::do_call::hc2a2771195a00054
                               at /rustc/1b198b3a196442e14fb06978166ab46a4618d131/library/std/src/panicking.rs:524:40
  46:     0x7f5d0614635b - std::panicking::try::h0a2a8257c216e1c6
                               at /rustc/1b198b3a196442e14fb06978166ab46a4618d131/library/std/src/panicking.rs:488:19
  47:     0x7f5d0614635b - std::panic::catch_unwind::h0cd317587445f016
                               at /rustc/1b198b3a196442e14fb06978166ab46a4618d131/library/std/src/panic.rs:142:14
  48:     0x7f5d0614635b - std::rt::lang_start_internal::{{closure}}::hf2376de1a4a8bfcd
                               at /rustc/1b198b3a196442e14fb06978166ab46a4618d131/library/std/src/rt.rs:148:48
  49:     0x7f5d0614635b - std::panicking::try::do_call::h5deb927a449cb0ab
                               at /rustc/1b198b3a196442e14fb06978166ab46a4618d131/library/std/src/panicking.rs:524:40
  50:     0x7f5d0614635b - std::panicking::try::h6594b1002feb6499
                               at /rustc/1b198b3a196442e14fb06978166ab46a4618d131/library/std/src/panicking.rs:488:19
  51:     0x7f5d0614635b - std::panic::catch_unwind::h2ea71858371b0c25
                               at /rustc/1b198b3a196442e14fb06978166ab46a4618d131/library/std/src/panic.rs:142:14
  52:     0x7f5d0614635b - std::rt::lang_start_internal::h03d2e46d47e99d1b
                               at /rustc/1b198b3a196442e14fb06978166ab46a4618d131/library/std/src/rt.rs:148:20
  53:     0x55d6a0dfc3b5 - main
  54:     0x7f5d05c27cd0 - <unknown>
  55:     0x7f5d05c27d8a - __libc_start_main
  56:     0x55d6a0de3019 - <unknown>
  57:                0x0 - <unknown>

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

note: we would appreciate a bug report: https://github.com/rust-lang/rustfmt/issues/new?labels=bug

note: please attach the file at `/tmp/fmt/rustc-ice-2023-08-14T21:36:54.460559654Z-52165.txt` to your bug report

query stack during panic:
end of query stack
Diff in /tmp/fmt/93B5BD0690DC27A06716E0D5FDCE8EF7E31E4A69EA999D9797761DC9851406DC.rs at line 1:
 fn main() {
     println!("{}", builtin # offset_of(A, 0. 1.1.1));
-
 }

rustfmt 1.6.0-nightly (1b198b3 2023-08-13)

[eval-exec]

I think this issue is related to https://github.com/rust-lang/rust/pull/106934/files
I'm interested in addressing this matter and am currently in the process of investigating how to do so.

I think we need to handle the branch around ast::ExprKind::OffsetOf:

rustfmt/src/expr.rs

Lines 401 to 406 in 16db2a4

	ast::ExprKind::FormatArgs(..)
	| ast::ExprKind::IncludedBytes(..)
	| ast::ExprKind::OffsetOf(..) => {
	// These do not occur in the AST because macros aren't expanded.
	unreachable!()
	}

[ytmimi]

@eval-exec thanks for offering to help. You can assign yourself to this issue by commenting @rustbot claim.

A little bit about what's going on here; It's technically true that the ast::ExprKind::OffsetOf doesn't appear in the AST of the program when it's initially parsed. The println! macro call appears in the AST and all of it's arguments are unparsed tokens. However, when rustfmt encounters a macro call it invokes the rustc parser to parse the macro's arguments into AST nodes that it can then format.

It's at this point where the rustc parser produces a ast::Expr node with a kind of OffsetOf, and when rustfmt goes to format that expr node it hits the unreachable!() case.

@matthiaskrgr I'm too familiar with the builtin # syntax. Could you link me to some docs that go into more detail about it?

It seems the issue doesn't occur if you don't use builtin #, and instead use theoffset_of!() macro. Most likely because the dubious ast::ExprKind::OffsetOf, isn't produced.

fn main() {
    println!("{}", offset_of!(A, 0. 1.1.1));
}

[eval-exec]

I found this:
https://github.com/rust-lang/rust/blob/9167eea553d00a790c10ebc0a821e3fa1b13d93c/compiler/rustc_parse/src/parser/expr.rs#L2976

and this: https://github.com/rust-lang/rust/blob/36708123c1f73554c7bb5e8a2f0565aa25daef13/compiler/rustc_codegen_cranelift/src/base.rs#L780

It seems that the Kw:Builtin is a newly added keyword.

[ytmimi]

@eval-exec thanks for the info!

[eval-exec]

@rustbot claim

[eval-exec]

I found this: https://github.com/rust-lang/rust/blob/9167eea553d00a790c10ebc0a821e3fa1b13d93c/compiler/rustc_parse/src/parser/expr.rs#L1850

I think we need to treat builtin # offset_of(container, fields) as same as offset_of!(container, fields)

[ytmimi]

Here's the tracking issue for builtin # rust-lang/rust#110680 syntax. From what I can tell this is experimental syntax.

I think we need to treat builtin # offset_of(container, fields) as same as offset_of!(container, fields)

Given that this syntax is experimental it might be simpler to just return Some(context.snippet(expr.span()).to_owned()) or None. Anything but panicking. @calebcartwright do you think it's worth creating a rewrite_builtin function for this case?

[calebcartwright]

I've not looked too closely but based on the description I'd concur that the new builtin syntax is resulting in the AST containing constructs that weren't expected to exist in a pre-expansion context.

I've no objections to doing something quick to avoid the panic, although given some of the idempotence bugs that can easily be triggered in macro contexts I'd like to be able to handle it more directly sooner rather than later