Repository: rust
Issue: rustc won't compile after error
Labels: I-ICE,T-compiler,A-incr-comp,C-bug,S-needs-repro

I was going through the online Rust book and I was modifying the provided code examples to see the types of error messages I could receive.

I tried to compile with this code 

```rs
std::io::stdin()
    .read_line(&mut guess)
```

and I received this error:

```
warning: unused `Result` that must be used
  --> src\main.rs:9:5
   |
9  | /     std::io::stdin()
10 | |         .read_line(&mut guess);
   | |______________________________^
   |
   = note: this `Result` may be an `Err` variant, which should be handled
   = note: `#[warn(unused_must_use)]` on by default
help: use `let _ = ...` to ignore the resulting value
   |
9  |     let _ = std::io::stdin()
   |     +++++++

warning: error copying object file `C:\Binyamin\projects\guessing_game\target\debug\deps\guessing_game.06ft8sozyh5gkeuqf47wn33fq
.rcgu.o` to incremental directory as `\\?\C:\Binyamin\projects\guessing_game\target\debug\incremental\guessing_game-2np01ccfpwk3
q\s-h3n858d5d7-0bhp2xt-working\06ft8sozyh5gkeuqf47wn33fq.o`: Access is denied. (os error 5)

warning: error copying object file `C:\Binyamin\projects\guessing_game\target\debug\deps\guessing_game.0bacoeif7vu57vzgx0itycv8y
.rcgu.o` to incremental directory as `\\?\C:\Binyamin\projects\guessing_game\target\debug\incremental\guessing_game-2np01ccfpwk3
q\s-h3n858d5d7-0bhp2xt-working\0bacoeif7vu57vzgx0itycv8y.o`: Access is denied. (os error 5)

warning: `guessing_game` (bin "guessing_game") generated 3 warnings
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 1.03s
     Running `target\debug\guessing_game.exe`
```

Based on the error hint, I changed the code to:

```rs
let _ = std::io::stdin()
    .read_line(&mut guess);
```

and I got this error:

```
 Compiling guessing_game v0.1.0 (C:\Binyamin\projects\guessing_game)
thread 'coordinator' panicked at /rustc/9fc6b43126469e3858e2fe86cafb4f0fd5068869\compiler\rustc_codegen_ssa\src\back\write.rs:16
62:29:
/rustc/9fc6b43126469e3858e2fe86cafb4f0fd5068869\compiler\rustc_codegen_ssa\src\back\write.rs:1662:29: worker thread panicked
stack backtrace:
   0:     0x7ffe61b6ba41 - std::backtrace_rs::backtrace::dbghelp64::trace
                               at /rustc/9fc6b43126469e3858e2fe86cafb4f0fd5068869\library/std\src\..\..\backtrace\src\backtrace\
dbghelp64.rs:91
   1:     0x7ffe61b6ba41 - std::backtrace_rs::backtrace::trace_unsynchronized
                               at /rustc/9fc6b43126469e3858e2fe86cafb4f0fd5068869\library/std\src\..\..\backtrace\src\backtrace\
mod.rs:66
   2:     0x7ffe61b6ba41 - std::sys::backtrace::_print_fmt
                               at /rustc/9fc6b43126469e3858e2fe86cafb4f0fd5068869\library/std\src\sys\backtrace.rs:66
   3:     0x7ffe61b6ba41 - std::sys::backtrace::impl$0::print::impl$0::fmt
                               at /rustc/9fc6b43126469e3858e2fe86cafb4f0fd5068869\library/std\src\sys\backtrace.rs:39
   4:     0x7ffe61b9dd1a - core::fmt::rt::Argument::fmt
                               at /rustc/9fc6b43126469e3858e2fe86cafb4f0fd5068869\library/core\src\fmt\rt.rs:177
   5:     0x7ffe61b9dd1a - core::fmt::write
                               at /rustc/9fc6b43126469e3858e2fe86cafb4f0fd5068869\library/core\src\fmt\mod.rs:1189
   6:     0x7ffe61b61de7 - std::io::Write::write_fmt<std::sys::pal::windows::stdio::Stderr>
                               at /rustc/9fc6b43126469e3858e2fe86cafb4f0fd5068869\library/std\src\io\mod.rs:1884
   7:     0x7ffe61b6b885 - std::sys::backtrace::BacktraceLock::print
                               at /rustc/9fc6b43126469e3858e2fe86cafb4f0fd5068869\library/std\src\sys\backtrace.rs:42
   8:     0x7ffe61b6e7a3 - std::panicking::default_hook::closure$1
                               at /rustc/9fc6b43126469e3858e2fe86cafb4f0fd5068869\library/std\src\panicking.rs:268
   9:     0x7ffe61b6e582 - std::panicking::default_hook
                               at /rustc/9fc6b43126469e3858e2fe86cafb4f0fd5068869\library/std\src\panicking.rs:295
  10:     0x7ffe6314ab1e - strncpy
  11:     0x7ffe61b6eee2 - alloc::boxed::impl$30::call
                               at /rustc/9fc6b43126469e3858e2fe86cafb4f0fd5068869\library/alloc\src\boxed.rs:1986
  12:     0x7ffe61b6eee2 - std::panicking::rust_panic_with_hook
                               at /rustc/9fc6b43126469e3858e2fe86cafb4f0fd5068869\library/std\src\panicking.rs:809
  13:     0x7ffe647bbfdf - ar_archive_writer[5ad4fe434effa9d8]::object_reader::get_member_alignment
  14:     0x7ffe647b6b29 - ar_archive_writer[5ad4fe434effa9d8]::object_reader::get_member_alignment
  15:     0x7ffe647b516c - ar_archive_writer[5ad4fe434effa9d8]::object_reader::get_member_alignment
  16:     0x7ffe64850eed - rustc_middle[87d6ac0499a2eaf7]::util::bug::bug_fmt
  17:     0x7ffe648318bd - <rustc_middle[87d6ac0499a2eaf7]::ty::consts::Const>::to_valtree
  18:     0x7ffe648316d6 - <rustc_middle[87d6ac0499a2eaf7]::ty::consts::Const>::to_valtree
  19:     0x7ffe64850e22 - rustc_middle[87d6ac0499a2eaf7]::util::bug::bug_fmt
  20:     0x7ffe61c3822a - rustc_interface[c014954558e9d384]::proc_macro_decls::proc_macro_decls_static
  21:     0x7ffe5ebf33ad - llvm::DenseMap<llvm::StructType * __ptr64,llvm::detail::DenseSetEmpty,llvm::IRMover::StructTypeKeyInf
o,llvm::detail::DenseSetPair<llvm::StructType * __ptr64> >::~DenseMap<llvm::StructType * __ptr64,llvm::detail::DenseSetEmpty,llv
m::IRMover::StructTypeKeyIn
  22:     0x7ffe5ec04d8a - llvm::DenseMap<llvm::StructType * __ptr64,llvm::detail::DenseSetEmpty,llvm::IRMover::StructTypeKeyInf
o,llvm::detail::DenseSetPair<llvm::StructType * __ptr64> >::~DenseMap<llvm::StructType * __ptr64,llvm::detail::DenseSetEmpty,llv
m::IRMover::StructTypeKeyIn
  23:     0x7ffe61b80bad - alloc::boxed::impl$28::call_once
                               at /rustc/9fc6b43126469e3858e2fe86cafb4f0fd5068869\library/alloc\src\boxed.rs:1972
  24:     0x7ffe61b80bad - alloc::boxed::impl$28::call_once
                               at /rustc/9fc6b43126469e3858e2fe86cafb4f0fd5068869\library/alloc\src\boxed.rs:1972
  25:     0x7ffe61b80bad - std::sys::pal::windows::thread::impl$0::new::thread_start
                               at /rustc/9fc6b43126469e3858e2fe86cafb4f0fd5068869\library/std\src\sys\pal\windows\thread.rs:55
  26:     0x7ffec3f081f4 - BaseThreadInitThunk
  27:     0x7ffec676a251 - RtlUserThreadStart

error: 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&templat
e=ice.md

note: rustc 1.84.0 (9fc6b4312 2025-01-07) running on x86_64-pc-windows-msvc

note: compiler flags: --crate-type bin -C embed-bitcode=no -C debuginfo=2 -C incremental=[REDACTED]

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

query stack during panic:
end of query stack
error: cached cgu 0bacoeif7vu57vzgx0itycv8y should have an object file, but doesn't

error: could not compile `guessing_game` (bin "guessing_game") due to 1 previous error
```

Not sure what's going on here. I just created a new project with cargo and moved on, but I would like to know how to fix this in the future.