Parens in (very!) long expression cause stack overflow

[yupferris]

The following causes rustc to overflow its stack:

Code

fn main() {
    let i = true;
    let o = (!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(!(i))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))));

    println!("i: {}, o: {}", i, o);
}

Meta

rustc --version --verbose:

rustc 1.50.0-nightly (e792288df 2020-12-05)
binary: rustc
commit-hash: e792288df31636ca28108516c63a00ce4267063a
commit-date: 2020-12-05
host: x86_64-apple-darwin
release: 1.50.0-nightly

Error output

thread 'rustc' has overflowed its stack
fatal runtime error: stack overflow
error: could not compile `kaze-sim-tests`

Caused by:
  process didn't exit successfully: `rustc --crate-name kaze_sim_tests --edition=2018 kaze-sim-tests/src/lib.rs --error-format=json --json=diagnostic-rendered-ansi --emit=dep-info,link -C opt-level=3 -C embed-bitcode=no --test -C metadata=91881571569f64d4 -C extra-filename=-91881571569f64d4 --out-dir /Users/jaket/dev/misc/kaze/target/release/deps -L dependency=/Users/jaket/dev/misc/kaze/target/release/deps --extern kaze=/Users/jaket/dev/misc/kaze/target/release/deps/libkaze-8ee187787d5eca6b.rlib` (signal: 6, SIGABRT: process abort signal)

Backtrace cannot be provided, as the stack has overflowed.

Interestingly, removing all parens from the above expression works as expected:

fn main() {
    let i = true;
    let o = !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!i;

    println!("i: {}, o: {}", i, o);
}

i: true, o: false

[jyn514]

Backtrace cannot be provided, as the stack has overflowed.

You can get a backtrace by running gdb (or another debugger).

Backtrace

Thread 2 "rustc" received signal SIGSEGV, Segmentation fault.
[Switching to Thread 0x7fffed9ff700 (LWP 10618)]
0x00007ffff5dc6b21 in rustc_parse::parser::TokenCursor::next ()
   from /home/joshua/.local/lib/rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/librustc_driver-4f0cc9f50e53f0ba.so
(gdb) where
#0  0x00007ffff5dc6b21 in rustc_parse::parser::TokenCursor::next ()
   from /home/joshua/.local/lib/rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/librustc_driver-4f0cc9f50e53f0ba.so
#1  0x00007ffff5dd13c6 in rustc_parse::parser::Parser::bump ()
   from /home/joshua/.local/lib/rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/librustc_driver-4f0cc9f50e53f0ba.so
#2  0x00007ffff5dc8462 in rustc_parse::parser::Parser::expect_one_of ()
   from /home/joshua/.local/lib/rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/librustc_driver-4f0cc9f50e53f0ba.so
#3  0x00007ffff5dc7cc9 in rustc_parse::parser::Parser::expect ()
   from /home/joshua/.local/lib/rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/librustc_driver-4f0cc9f50e53f0ba.so
#4  0x00007ffff5d7f059 in rustc_parse::parser::expr::<impl rustc_parse::parser::Parser>::parse_bottom_expr ()
   from /home/joshua/.local/lib/rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/librustc_driver-4f0cc9f50e53f0ba.so
#5  0x00007ffff5d79a92 in rustc_parse::parser::expr::<impl rustc_parse::parser::Parser>::parse_prefix_expr::{{closure}} ()
   from /home/joshua/.local/lib/rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/librustc_driver-4f0cc9f50e53f0ba.so
#6  0x00007ffff5d78798 in rustc_parse::parser::expr::<impl rustc_parse::parser::Parser>::parse_prefix_expr ()
   from /home/joshua/.local/lib/rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/librustc_driver-4f0cc9f50e53f0ba.so
#7  0x00007ffff5d78d52 in rustc_parse::parser::expr::<impl rustc_parse::parser::Parser>::parse_prefix_expr::{{closure}} ()
   from /home/joshua/.local/lib/rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/librustc_driver-4f0cc9f50e53f0ba.so
#8  0x00007ffff5d78798 in rustc_parse::parser::expr::<impl rustc_parse::parser::Parser>::parse_prefix_expr ()
   from /home/joshua/.local/lib/rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/librustc_driver-4f0cc9f50e53f0ba.so
#9  0x00007ffff5d757a8 in rustc_parse::parser::expr::<impl rustc_parse::parser::Parser>::parse_assoc_expr_with ()
   from /home/joshua/.local/lib/rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/librustc_driver-4f0cc9f50e53f0ba.so
#10 0x00007ffff5d75363 in rustc_parse::parser::expr::<impl rustc_parse::parser::Parser>::parse_expr_catch_underscore ()
   from /home/joshua/.local/lib/rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/librustc_driver-4f0cc9f50e53f0ba.so
#11 0x00007ffff5dcc794 in rustc_parse::parser::Parser::parse_seq_to_before_tokens ()
   from /home/joshua/.local/lib/rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/librustc_driver-4f0cc9f50e53f0ba.so
#12 0x00007ffff5d7f0f8 in rustc_parse::parser::expr::<impl rustc_parse::parser::Parser>::parse_bottom_expr ()

After that it repeats for 17000 more stackframes, then

#17780 0x00007ffff5d7f0f8 in rustc_parse::parser::expr::<impl rustc_parse::parser::Parser>::parse_bottom_expr () from /home/joshua/.local/lib/rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/librustc_driver-4f0cc9f50e53f0ba.so
#17781 0x00007ffff5d79a92 in rustc_parse::parser::expr::<impl rustc_parse::parser::Parser>::parse_prefix_expr::{{closure}} () from /home/joshua/.local/lib/rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/librustc_driver-4f0cc9f50e53f0ba.so
#17782 0x00007ffff5d78798 in rustc_parse::parser::expr::<impl rustc_parse::parser::Parser>::parse_prefix_expr () from /home/joshua/.local/lib/rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/librustc_driver-4f0cc9f50e53f0ba.so
#17783 0x00007ffff5d757a8 in rustc_parse::parser::expr::<impl rustc_parse::parser::Parser>::parse_assoc_expr_with () from /home/joshua/.local/lib/rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/librustc_driver-4f0cc9f50e53f0ba.so
#17784 0x00007ffff5dbc934 in rustc_parse::parser::stmt::<impl rustc_parse::parser::Parser>::parse_local () from /home/joshua/.local/lib/rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/librustc_driver-4f0cc9f50e53f0ba.so
#17785 0x00007ffff5dba70f in rustc_parse::parser::stmt::<impl rustc_parse::parser::Parser>::parse_stmt_without_recovery::{{closure}} () from /home/joshua/.local/lib/rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/librustc_driver-4f0cc9f50e53f0ba.so
#17786 0x00007ffff5db9e80 in rustc_parse::parser::stmt::<impl rustc_parse::parser::Parser>::parse_stmt_without_recovery () from /home/joshua/.local/lib/rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/librustc_driver-4f0cc9f50e53f0ba.so
#17787 0x00007ffff5dbe12b in rustc_parse::parser::stmt::<impl rustc_parse::parser::Parser>::parse_full_stmt () from /home/joshua/.local/lib/rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/librustc_driver-4f0cc9f50e53f0ba.so
#17788 0x00007ffff5dbdd7f in rustc_parse::parser::stmt::<impl rustc_parse::parser::Parser>::parse_block_tail () from /home/joshua/.local/lib/rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/librustc_driver-4f0cc9f50e53f0ba.so
#17789 0x00007ffff5dbd421 in rustc_parse::parser::stmt::<impl rustc_parse::parser::Parser>::parse_block_common () from /home/joshua/.local/lib/rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/librustc_driver-4f0cc9f50e53f0ba.so
#17790 0x00007ffff5d94c3f in rustc_parse::parser::item::<impl rustc_parse::parser::Parser>::parse_item_kind () from /home/joshua/.local/lib/rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/librustc_driver-4f0cc9f50e53f0ba.so
#17791 0x00007ffff5d92d17 in rustc_parse::parser::item::<impl rustc_parse::parser::Parser>::parse_item_common_ () from /home/joshua/.local/lib/rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/librustc_driver-4f0cc9f50e53f0ba.so
#17792 0x00007ffff5d922be in rustc_parse::parser::item::<impl rustc_parse::parser::Parser>::parse_item_common () from /home/joshua/.local/lib/rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/librustc_driver-4f0cc9f50e53f0ba.so
#17793 0x00007ffff5d91d6f in rustc_parse::parser::item::<impl rustc_parse::parser::Parser>::parse_item () from /home/joshua/.local/lib/rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/librustc_driver-4f0cc9f50e53f0ba.so
#17794 0x00007ffff5d917ca in rustc_parse::parser::item::<impl rustc_parse::parser::Parser>::parse_mod () from /home/joshua/.local/lib/rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/librustc_driver-4f0cc9f50e53f0ba.so
#17795 0x00007ffff5e35d57 in rustc_parse::parse_crate_from_file () from /home/joshua/.local/lib/rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/librustc_driver-4f0cc9f50e53f0ba.so
#17796 0x00007ffff3dd25aa in rustc_session::utils::<impl rustc_session::session::Session>::time () from /home/joshua/.local/lib/rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/librustc_driver-4f0cc9f50e53f0ba.so
#17797 0x00007ffff3e09112 in rustc_interface::queries::Queries::parse () from /home/joshua/.local/lib/rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/librustc_driver-4f0cc9f50e53f0ba.so
#17798 0x00007ffff3c01ee6 in rustc_interface::queries::<impl rustc_interface::interface::Compiler>::enter () from /home/joshua/.local/lib/rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/librustc_driver-4f0cc9f50e53f0ba.so
#17799 0x00007ffff3bd08f7 in rustc_span::with_source_map () from /home/joshua/.local/lib/rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/librustc_driver-4f0cc9f50e53f0ba.so
#17800 0x00007ffff3bfea5c in scoped_tls::ScopedKey<T>::set () from /home/joshua/.local/lib/rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/librustc_driver-4f0cc9f50e53f0ba.so
#17801 0x00007ffff3c05b75 in std::sys_common::backtrace::__rust_begin_short_backtrace () from /home/joshua/.local/lib/rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/librustc_driver-4f0cc9f50e53f0ba.so
#17802 0x00007ffff3b6eb5a in core::ops::function::FnOnce::call_once{{vtable-shim}} () from /home/joshua/.local/lib/rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/librustc_driver-4f0cc9f50e53f0ba.so
#17803 0x00007ffff332499a in <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once () at /rustc/f4db9ffb22dfcb702dbdb2e0607cb91791866b57/library/alloc/src/boxed.rs:1327
#17804 <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once () at /rustc/f4db9ffb22dfcb702dbdb2e0607cb91791866b57/library/alloc/src/boxed.rs:1327
#17805 std::sys::unix::thread::Thread::new::thread_start () at library/std/src/sys/unix/thread.rs:71
#17806 0x00007ffff3255fa3 in start_thread (arg=<optimized out>) at pthread_create.c:486
#17807 0x00007ffff31754cf in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:95

[jyn514]

That said, I think this is kind of expected behavior in that I don't think there's a way to avoid recursion on parentheses without switching away from a recursive descent parser to something auto generated, which would hurt diagnostics a lot.

Relevant code:

rust/compiler/rustc_parse/src/parser/expr.rs

Line 1014 in d577c53

fn parse_bottom_expr(&mut self) -> PResult<'a, P<Expr>> {

[yupferris]

That said, I think this is kind of expected behavior

I would have expected the compiler not to overflow its stack on any input, but I can certainly understand/accept if the compiler team decides it's not practical to make that happen due to current implementation details (either for the time being, or forever), especially for these kinds of (admittedly synthetic) cases that I'm generating to smoke out/fix such problems in another compiler that's relying on rustc as a backend.

[jyn514]

Actually now that I think about it, maybe we could use https://docs.rs/stacker/0.1.12/stacker/fn.maybe_grow.html for the parser as well as the query engine?

[yupferris]

Actually now that I think about it, maybe we could use https://docs.rs/stacker/0.1.12/stacker/fn.maybe_grow.html for the parser as well as the query engine?

Ah, I hadn’t seen this crate before, interesting!

[camelid]

I think this should probably be closed as wontfix. Unless there's a real-world use case for extremely-deep nesting of parentheses, I don't think it's worth it to try to mitigate this.

[nagisa]

Actually now that I think about it, maybe we could use https://docs.rs/stacker/0.1.12/stacker/fn.maybe_grow.html for the parser as well as the query engine?

Compiler internals already have https://doc.rust-lang.org/nightly/nightly-rustc/rustc_data_structures/stack/fn.ensure_sufficient_stack.html. Not sure if it can be used in the parser (i.e. if rustc_parser can depend on rustc_data_structures), but yeah we do support deeply recursive inputs like these, we just haven't annotated all of the locations in the compiler with ensure_sufficient_stack.

[osa1]

Not sure if it can be used in the parser (i.e. if rustc_parser can depend on rustc_data_structures),

Not sure when this was added but rustc_parser already depends on rustc_data_structures today.

I think a problem is recursion in the parser happens indirectly after many calls. In the repro for this issue it happens after 15 calls:

parse_expr () at /home/omer/rust/rust/compiler/rustc_parse/src/parser/expr.rs:92
parse_expr_catch_underscore () at /home/omer/rust/rust/compiler/rustc_parse/src/parser/expr.rs:100
parse_tuple_parens_expr::{{closure}} () at /home/omer/rust/rust/compiler/rustc_parse/src/parser/expr.rs:1189
parse_seq_to_before_tokens () at /home/omer/rust/rust/compiler/rustc_parse/src/parser/mod.rs:765
parse_seq_to_before_end () at /home/omer/rust/rust/compiler/rustc_parse/src/parser/mod.rs:781
parse_seq_to_end () at /home/omer/rust/rust/compiler/rustc_parse/src/parser/mod.rs:793
parse_tuple_parens_expr () at /home/omer/rust/rust/compiler/rustc_parse/src/parser/expr.rs:1186
parse_bottom_expr () at /home/omer/rust/rust/compiler/rustc_parse/src/parser/expr.rs:1077
parse_dot_or_call_expr () at /home/omer/rust/rust/compiler/rustc_parse/src/parser/expr.rs:810
parse_prefix_expr::{{closure}} () at /home/omer/rust/rust/compiler/rustc_parse/src/parser/expr.rs:493
parse_prefix_expr () at /home/omer/rust/rust/compiler/rustc_parse/src/parser/expr.rs:497
parse_assoc_expr_with () at /home/omer/rust/rust/compiler/rustc_parse/src/parser/expr.rs:156
parse_assoc_expr () at /home/omer/rust/rust/compiler/rustc_parse/src/parser/expr.rs:137
parse_expr_res::{{closure}} () at /home/omer/rust/rust/compiler/rustc_parse/src/parser/expr.rs:128
with_res () at /home/omer/rust/rust/compiler/rustc_parse/src/parser/mod.rs:1076
parse_expr_res () at /home/omer/rust/rust/compiler/rustc_parse/src/parser/expr.rs:128
parse_expr () at /home/omer/rust/rust/compiler/rustc_parse/src/parser/expr.rs:92

So it's a bit unclear where to add ensure_sufficient_stacks and how much stack space to demand.

I'm also curious about potential performance impact of having too many ensure_sufficient_stacks..