Crashes on macro input containing function signature #4101
Description
Minimal case:
m![fn f();];I started hitting this in syn/tests/test_receiver.rs@189aea8 which hasn't been touched since October, so I guess this is a regression.
To reproduce against the current master branch of rustfmt (9124dd8):
$ echo 'm![fn f();];' | RUST_BACKTRACE=1 cargo +nightly-2020-03-22 run --bin rustfmt
thread 'main' panicked at 'internal error: entered unreachable code', rustfmt-core/rustfmt-lib/src/visitor.rs:367:18
stack backtrace:
0: backtrace::backtrace::libunwind::trace
at /cargo/registry/src/github.com-1ecc6299db9ec823/backtrace-0.3.45/src/backtrace/libunwind.rs:86
1: backtrace::backtrace::trace_unsynchronized
at /cargo/registry/src/github.com-1ecc6299db9ec823/backtrace-0.3.45/src/backtrace/mod.rs:66
2: std::sys_common::backtrace::_print_fmt
at src/libstd/sys_common/backtrace.rs:78
3: <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt
at src/libstd/sys_common/backtrace.rs:59
4: core::fmt::write
at src/libcore/fmt/mod.rs:1069
5: std::io::Write::write_fmt
at src/libstd/io/mod.rs:1427
6: std::sys_common::backtrace::_print
at src/libstd/sys_common/backtrace.rs:62
7: std::sys_common::backtrace::print
at src/libstd/sys_common/backtrace.rs:49
8: std::panicking::default_hook::{{closure}}
at src/libstd/panicking.rs:198
9: std::panicking::default_hook
at src/libstd/panicking.rs:218
10: std::panicking::rust_panic_with_hook
at src/libstd/panicking.rs:511
11: std::panicking::begin_panic
at /rustc/38114ff16e7856f98b2b4be7ab4cd29b38bed59a/src/libstd/panicking.rs:438
12: rustfmt_lib::visitor::FmtVisitor::visit_fn
at rustfmt-core/rustfmt-lib/src/visitor.rs:367
13: rustfmt_lib::visitor::FmtVisitor::visit_item
at rustfmt-core/rustfmt-lib/src/visitor.rs:511
14: rustfmt_lib::macros::rewrite_macro_with_items
at rustfmt-core/rustfmt-lib/src/macros.rs:1537
15: rustfmt_lib::macros::rewrite_macro_inner
at rustfmt-core/rustfmt-lib/src/macros.rs:346
16: rustfmt_lib::macros::rewrite_macro::{{closure}}
at rustfmt-core/rustfmt-lib/src/macros.rs:204
17: core::ops::function::FnOnce::call_once
at /rustc/38114ff16e7856f98b2b4be7ab4cd29b38bed59a/src/libcore/ops/function.rs:232
18: <std::panic::AssertUnwindSafe<F> as core::ops::function::FnOnce<()>>::call_once
at /rustc/38114ff16e7856f98b2b4be7ab4cd29b38bed59a/src/libstd/panic.rs:318
19: std::panicking::try::do_call
at /rustc/38114ff16e7856f98b2b4be7ab4cd29b38bed59a/src/libstd/panicking.rs:331
20: __rust_try
21: std::panicking::try
at /rustc/38114ff16e7856f98b2b4be7ab4cd29b38bed59a/src/libstd/panicking.rs:274
22: std::panic::catch_unwind
at /rustc/38114ff16e7856f98b2b4be7ab4cd29b38bed59a/src/libstd/panic.rs:394
23: rustfmt_lib::macros::rewrite_macro
at rustfmt-core/rustfmt-lib/src/macros.rs:203
24: rustfmt_lib::visitor::FmtVisitor::visit_mac::{{closure}}
at rustfmt-core/rustfmt-lib/src/visitor.rs:682
25: rustfmt_lib::visitor::FmtVisitor::with_context
at rustfmt-core/rustfmt-lib/src/visitor.rs:955
26: rustfmt_lib::visitor::FmtVisitor::visit_mac
at rustfmt-core/rustfmt-lib/src/visitor.rs:682
27: rustfmt_lib::visitor::FmtVisitor::visit_item
at rustfmt-core/rustfmt-lib/src/visitor.rs:496
28: rustfmt_lib::reorder::<impl rustfmt_lib::visitor::FmtVisitor>::visit_items_with_reordering
at rustfmt-core/rustfmt-lib/src/reorder.rs:261
29: rustfmt_lib::visitor::FmtVisitor::walk_mod_items
at rustfmt-core/rustfmt-lib/src/visitor.rs:854
30: rustfmt_lib::visitor::FmtVisitor::format_separate_mod
at rustfmt-core/rustfmt-lib/src/visitor.rs:931
31: rustfmt_lib::formatting::FormatContext<T>::format_file
at ./rustfmt-core/rustfmt-lib/src/formatting.rs:182
32: rustfmt_lib::formatting::format_project
at ./rustfmt-core/rustfmt-lib/src/formatting.rs:109
33: rustfmt_lib::formatting::<impl rustfmt_lib::Session<T>>::format_input_inner::{{closure}}
at ./rustfmt-core/rustfmt-lib/src/formatting.rs:44
34: scoped_tls::ScopedKey<T>::set
at /home/david/.cargo/registry/src/github.com-1ecc6299db9ec823/scoped-tls-1.0.0/src/lib.rs:137
35: rustc_ap_syntax::attr::with_globals::{{closure}}
at /home/david/.cargo/registry/src/github.com-1ecc6299db9ec823/rustc-ap-syntax-642.0.0/attr/mod.rs:44
36: scoped_tls::ScopedKey<T>::set
at /home/david/.cargo/registry/src/github.com-1ecc6299db9ec823/scoped-tls-1.0.0/src/lib.rs:137
37: rustc_ap_syntax::attr::with_globals
at /home/david/.cargo/registry/src/github.com-1ecc6299db9ec823/rustc-ap-syntax-642.0.0/attr/mod.rs:44
38: rustfmt_lib::formatting::<impl rustfmt_lib::Session<T>>::format_input_inner
at ./rustfmt-core/rustfmt-lib/src/formatting.rs:32
39: rustfmt_lib::Session<T>::format
at ./rustfmt-core/rustfmt-lib/src/lib.rs:426
40: rustfmt::format_and_emit_report
at rustfmt-core/rustfmt-bin/src/bin/main.rs:530
41: rustfmt::format_string
at rustfmt-core/rustfmt-bin/src/bin/main.rs:415
42: rustfmt::format
at rustfmt-core/rustfmt-bin/src/bin/main.rs:472
43: rustfmt::execute
at rustfmt-core/rustfmt-bin/src/bin/main.rs:364
44: rustfmt::main
at rustfmt-core/rustfmt-bin/src/bin/main.rs:25
45: std::rt::lang_start::{{closure}}
at /rustc/38114ff16e7856f98b2b4be7ab4cd29b38bed59a/src/libstd/rt.rs:67
46: std::rt::lang_start_internal::{{closure}}
at src/libstd/rt.rs:52
47: std::panicking::try::do_call
at src/libstd/panicking.rs:331
48: std::panicking::try
at src/libstd/panicking.rs:274
49: std::panic::catch_unwind
at src/libstd/panic.rs:394
50: std::rt::lang_start_internal
at src/libstd/rt.rs:51
51: std::rt::lang_start
at /rustc/38114ff16e7856f98b2b4be7ab4cd29b38bed59a/src/libstd/rt.rs:67
52: main
53: __libc_start_main
54: _start
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.