[ICE]: "warning: error copying object file" damages incremental build cache, induces ICE in subsequent builds unless pruned

$ rustc --version --verbose
rustc 1.96.0 (ac68faa20 2026-05-25)
binary: rustc
commit-hash: ac68faa20c58cbccd01ee7208bf3b6e93a7d7f96
commit-date: 2026-05-25
host: x86_64-pc-windows-gnu
release: 1.96.0
LLVM version: 22.1.2

Starting with target/debug/incremental/cargo* deleted:

$ cargo build
warning: `D:\Users\nabijaczleweli\.cargo\config` is deprecated in favor of `config.toml`
  |
  = help: if you need to support cargo 1.38 or earlier, you can symlink `config` to `config.toml`
   Compiling cargo-update v20.0.0 (P:\Rust\cargo-update)
warning: error copying object file `P:\Rust\cargo-update\target\debug\deps\libcargo_update-e847dae16ed1dcdc.rmeta` to incremental directory as `\\?\V:\Rust-target\debug\incremental\cargo_update-3qbqkuu5iqvls\s-hjbhiioeg6-0au3i45-working\metadata.rmeta`: Access is denied. (os error 5)

warning: `cargo-update` (lib) generated 1 warning
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 6.13s

This build succeeds and produces target/debug/cargo-install-update.exe

With nothing changed:

$ cargo build
warning: `D:\Users\nabijaczleweli\.cargo\config` is deprecated in favor of `config.toml`
  |
  = help: if you need to support cargo 1.38 or earlier, you can symlink `config` to `config.toml`
warning: error copying object file `P:\Rust\cargo-update\target\debug\deps\libcargo_update-e847dae16ed1dcdc.rmeta` to incremental directory as `\\?\V:\Rust-target\debug\incremental\cargo_update-3qbqkuu5iqvls\s-hjbhiioeg6-0au3i45-working\metadata.rmeta`: Access is denied. (os error 5)

warning: `cargo-update` (lib) generated 1 warning
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.43s

(warning appears but doesn't do anything)

After changing main.rs:

$ cargo build
warning: `D:\Users\nabijaczleweli\.cargo\config` is deprecated in favor of `config.toml`
  |
  = help: if you need to support cargo 1.38 or earlier, you can symlink `config` to `config.toml`
   Compiling cargo-update v20.0.0 (P:\Rust\cargo-update)

thread 'rustc' (5872) panicked at /rustc-dev/ac68faa20c58cbccd01ee7208bf3b6e93a7d7f96/compiler\rustc_metadata\src\rmeta\encoder.rs:2448:51:
no entry found for key
stack backtrace:
   0:     0x7ffe89257dbf - std[103871820a823c36]::backtrace_rs::backtrace::win64::trace
                               at /rustc/ac68faa20c58cbccd01ee7208bf3b6e93a7d7f96/library\std\src\..\..\backtrace\src\backtrace/win64.rs:85:14
   1:     0x7ffe89257dbf - std[103871820a823c36]::backtrace_rs::backtrace::trace_unsynchronized::<std[103871820a823c36]::sys::backtrace::_print_fmt::{closure#1}>
                               at /rustc/ac68faa20c58cbccd01ee7208bf3b6e93a7d7f96/library\std\src\..\..\backtrace\src\backtrace/mod.rs:66:14
   2:     0x7ffe89257dbf - std[103871820a823c36]::sys::backtrace::_print_fmt
                               at /rustc/ac68faa20c58cbccd01ee7208bf3b6e93a7d7f96/library\std\src\sys/backtrace.rs:74:9
   3:     0x7ffe89257dbf - <<std[103871820a823c36]::sys::backtrace::BacktraceLock>::print::DisplayBacktrace as core[7eb90ffabe67d87f]::fmt::Display>::fmt
                               at /rustc/ac68faa20c58cbccd01ee7208bf3b6e93a7d7f96/library\std\src\sys/backtrace.rs:44:26
   4:     0x7ffe89297671 - <core[7eb90ffabe67d87f]::fmt::rt::Argument>::fmt
                               at /rustc/ac68faa20c58cbccd01ee7208bf3b6e93a7d7f96/library\core\src\fmt/rt.rs:152:76
   5:     0x7ffe89297671 - core[7eb90ffabe67d87f]::fmt::write
   6:     0x7ffe89267ff2 - std[103871820a823c36]::io::default_write_fmt::<std[103871820a823c36]::sys::stdio::windows::Stderr>
                               at /rustc/ac68faa20c58cbccd01ee7208bf3b6e93a7d7f96/library\std\src\io/mod.rs:621:11
   7:     0x7ffe89267ff2 - <std[103871820a823c36]::sys::stdio::windows::Stderr as std[103871820a823c36]::io::Write>::write_fmt
                               at /rustc/ac68faa20c58cbccd01ee7208bf3b6e93a7d7f96/library\std\src\io/mod.rs:1976:13
   8:     0x7ffe892272b1 - <std[103871820a823c36]::sys::backtrace::BacktraceLock>::print
                               at /rustc/ac68faa20c58cbccd01ee7208bf3b6e93a7d7f96/library\std\src\sys/backtrace.rs:47:9
   9:     0x7ffe892272b1 - std[103871820a823c36]::panicking::default_hook::{closure#0}
                               at /rustc/ac68faa20c58cbccd01ee7208bf3b6e93a7d7f96/library\std\src/panicking.rs:292:27
  10:     0x7ffe89247e8b - std[103871820a823c36]::panicking::default_hook
                               at /rustc/ac68faa20c58cbccd01ee7208bf3b6e93a7d7f96/library\std\src/panicking.rs:319:9
  11:     0x7ffe5229cbba - std[103871820a823c36]::panicking::update_hook::<alloc[83eb0dd09eb55b1c]::boxed::Box<rustc_driver_impl[e175a339f588150f]::install_ice_hook::{closure#1}>>::{closure#0}
  12:     0x7ffe89248209 - <alloc[83eb0dd09eb55b1c]::boxed::Box<dyn for<'a, 'b> core[7eb90ffabe67d87f]::ops::function::Fn<(&'a std[103871820a823c36]::panic::PanicHookInfo<'b>,), Output = ()> + core[7eb90ffabe67d87f]::marker::Sync + core[7eb90ffabe67d87f]::marker::Send> as core[7eb90ffabe67d87f]::ops::function::Fn<(&std[103871820a823c36]::panic::PanicHookInfo,)>>::call
                               at /rustc/ac68faa20c58cbccd01ee7208bf3b6e93a7d7f96/library\alloc\src/boxed.rs:2263:9
  13:     0x7ffe89248209 - std[103871820a823c36]::panicking::panic_with_hook
                               at /rustc/ac68faa20c58cbccd01ee7208bf3b6e93a7d7f96/library\std\src/panicking.rs:833:13
  14:     0x7ffe8922738d - std[103871820a823c36]::panicking::panic_handler::{closure#0}
                               at /rustc/ac68faa20c58cbccd01ee7208bf3b6e93a7d7f96/library\std\src/panicking.rs:698:13
  15:     0x7ffe8921acaf - std[103871820a823c36]::sys::backtrace::__rust_end_short_backtrace::<std[103871820a823c36]::panicking::panic_handler::{closure#0}, !>
                               at /rustc/ac68faa20c58cbccd01ee7208bf3b6e93a7d7f96/library\std\src\sys/backtrace.rs:182:18
  16:     0x7ffe8922807e - __rustc[8068f81614cfe5c]::rust_begin_unwind
                               at /rustc/ac68faa20c58cbccd01ee7208bf3b6e93a7d7f96/library\std\src/panicking.rs:689:5
  17:     0x7ffe8929814d - core[7eb90ffabe67d87f]::panicking::panic_fmt
                               at /rustc/ac68faa20c58cbccd01ee7208bf3b6e93a7d7f96/library\core\src/panicking.rs:80:14
  18:     0x7ffe89297d85 - core[7eb90ffabe67d87f]::panicking::panic_display::<&str>
                               at /rustc/ac68faa20c58cbccd01ee7208bf3b6e93a7d7f96/library\core\src/panicking.rs:259:5
  19:     0x7ffe89297d85 - core[7eb90ffabe67d87f]::option::expect_failed
                               at /rustc/ac68faa20c58cbccd01ee7208bf3b6e93a7d7f96/library\core\src/option.rs:2260:5
  20:     0x7ffe5514d184 - rustc_metadata[354cdd2b2ecdc417]::rmeta::encoder::encode_metadata
  21:     0x7ffe5522505d - rustc_metadata[354cdd2b2ecdc417]::fs::encode_and_write_metadata
  22:     0x7ffe5254a02c - rustc_interface[45e64ae5edd9cc5c]::passes::start_codegen
  23:     0x7ffe524eb686 - <rustc_interface[45e64ae5edd9cc5c]::queries::Linker>::codegen_and_build_linker
  24:     0x7ffe5226dae7 - <std[103871820a823c36]::thread::local::LocalKey<core[7eb90ffabe67d87f]::cell::Cell<*const ()>>>::with::<rustc_middle[e0d897412b502ba6]::ty::context::tls::enter_context<<rustc_middle[e0d897412b502ba6]::ty::context::GlobalCtxt>::enter<rustc_interface[45e64ae5edd9cc5c]::passes::create_and_enter_global_ctxt<core[7eb90ffabe67d87f]::option::Option<rustc_interface[45e64ae5edd9cc5c]::queries::Linker>, rustc_driver_impl[e175a339f588150f]::run_compiler::{closure#0}::{closure#2}>::{closure#2}, core[7eb90ffabe67d87f]::option::Option<rustc_interface[45e64ae5edd9cc5c]::queries::Linker>>::{closure#1}, core[7eb90ffabe67d87f]::option::Option<rustc_interface[45e64ae5edd9cc5c]::queries::Linker>>::{closure#0}, core[7eb90ffabe67d87f]::option::Option<rustc_interface[45e64ae5edd9cc5c]::queries::Linker>>
  25:     0x7ffe522238f5 - <rustc_middle[e0d897412b502ba6]::ty::context::TyCtxt>::create_global_ctxt::<core[7eb90ffabe67d87f]::option::Option<rustc_interface[45e64ae5edd9cc5c]::queries::Linker>, rustc_interface[45e64ae5edd9cc5c]::passes::create_and_enter_global_ctxt<core[7eb90ffabe67d87f]::option::Option<rustc_interface[45e64ae5edd9cc5c]::queries::Linker>, rustc_driver_impl[e175a339f588150f]::run_compiler::{closure#0}::{closure#2}>::{closure#2}>
  26:     0x7ffe52239b30 - rustc_interface[45e64ae5edd9cc5c]::passes::create_and_enter_global_ctxt::<core[7eb90ffabe67d87f]::option::Option<rustc_interface[45e64ae5edd9cc5c]::queries::Linker>, rustc_driver_impl[e175a339f588150f]::run_compiler::{closure#0}::{closure#2}>
  27:     0x7ffe5227bd82 - rustc_span[f226af2a89e9fbaf]::create_session_globals_then::<(), rustc_interface[45e64ae5edd9cc5c]::util::run_in_thread_with_globals<rustc_interface[45e64ae5edd9cc5c]::util::run_in_thread_pool_with_globals<rustc_interface[45e64ae5edd9cc5c]::interface::run_compiler<(), rustc_driver_impl[e175a339f588150f]::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}::{closure#0}>
  28:     0x7ffe522b7194 - std[103871820a823c36]::sys::backtrace::__rust_begin_short_backtrace::<rustc_interface[45e64ae5edd9cc5c]::util::run_in_thread_with_globals<rustc_interface[45e64ae5edd9cc5c]::util::run_in_thread_pool_with_globals<rustc_interface[45e64ae5edd9cc5c]::interface::run_compiler<(), rustc_driver_impl[e175a339f588150f]::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>
  29:     0x7ffe5229d23f - <std[103871820a823c36]::thread::lifecycle::spawn_unchecked<rustc_interface[45e64ae5edd9cc5c]::util::run_in_thread_with_globals<rustc_interface[45e64ae5edd9cc5c]::util::run_in_thread_pool_with_globals<rustc_interface[45e64ae5edd9cc5c]::interface::run_compiler<(), rustc_driver_impl[e175a339f588150f]::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>::{closure#1} as core[7eb90ffabe67d87f]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  30:     0x7ffe8925521d - <alloc[83eb0dd09eb55b1c]::boxed::Box<dyn core[7eb90ffabe67d87f]::ops::function::FnOnce<(), Output = ()> + core[7eb90ffabe67d87f]::marker::Send> as core[7eb90ffabe67d87f]::ops::function::FnOnce<()>>::call_once
                               at /rustc/ac68faa20c58cbccd01ee7208bf3b6e93a7d7f96/library\alloc\src/boxed.rs:2249:9
  31:     0x7ffe8925521d - <std[103871820a823c36]::sys::thread::windows::Thread>::new::thread_start
                               at /rustc/ac68faa20c58cbccd01ee7208bf3b6e93a7d7f96/library\std\src\sys\thread/windows.rs:58:13
  32:     0x7ffef4348364 - <unknown>
  33:     0x7ffef44770d1 - <unknown>

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&template=ice.md

note: rustc 1.96.0 (ac68faa20 2026-05-25) running on x86_64-pc-windows-gnu

note: compiler flags: --crate-type lib -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: could not compile `cargo-update` (lib)

Caused by:
  process didn't exit successfully: `D:\Users\nabijaczleweli\.rustup\toolchains\stable-x86_64-pc-windows-gnu\bin\rustc.exe --crate-name cargo_update --edition=2015 src\lib.rs --error-format=json --json=diagnostic-rendered-ansi,artifacts,future-incompat --crate-type lib --emit=dep-info,metadata,link -C embed-bitcode=no -C debuginfo=2 --cfg "feature=\"default\"" --check-cfg cfg(docsrs,test) --check-cfg "cfg(feature, values(\"default\", \"vendored-libcurl\", \"vendored-libgit2\", \"vendored-openssl\"))" -C metadata=1f77388395f59734 -C extra-filename=-e847dae16ed1dcdc --out-dir P:\Rust\cargo-update\target\debug\deps -C incremental=P:\Rust\cargo-update\target\debug\incremental -L dependency=P:\Rust\cargo-update\target\debug\deps --extern chrono=P:\Rust\cargo-update\target\debug\deps\libchrono-7bfdae7149d302f2.rmeta --extern clap=P:\Rust\cargo-update\target\debug\deps\libclap-5ea6de2e4b806320.rmeta --extern curl=P:\Rust\cargo-update\target\debug\deps\libcurl-9391648b621c1e13.rmeta --extern git2=P:\Rust\cargo-update\target\debug\deps\libgit2-fc3c39bc7f8051f0.rmeta --extern hex=P:\Rust\cargo-update\target\debug\deps\libhex-92af3453014f89e2.rmeta --extern home=P:\Rust\cargo-update\target\debug\deps\libhome-9e6631f89e9dc78e.rmeta --extern jobserver=P:\Rust\cargo-update\target\debug\deps\libjobserver-fe357b099025761e.rmeta --extern semver=P:\Rust\cargo-update\target\debug\deps\libsemver-52c272bbb3aa4bbc.rmeta --extern serde=P:\Rust\cargo-update\target\debug\deps\libserde-1c1a339ebe90e995.rmeta --extern serde_derive=P:\Rust\cargo-update\target\debug\deps\serde_derive-fd023561b10fc953.dll --extern serde_json=P:\Rust\cargo-update\target\debug\deps\libserde_json-175174dd77d4d2ba.rmeta --extern tabwriter=P:\Rust\cargo-update\target\debug\deps\libtabwriter-d26aec6f250a52b9.rmeta --extern toml=P:\Rust\cargo-update\target\debug\deps\libtoml-f2fdd64f8e314611.rmeta --extern url=P:\Rust\cargo-update\target\debug\deps\liburl-122e69c1d2370100.rmeta --extern whoami=P:\Rust\cargo-update\target\debug\deps\libwhoami-815392bd3e97c53c.rmeta --extern windows=P:\Rust\cargo-update\target\debug\deps\libwindows-0e86e46bc1e7bcb7.rmeta -L native=P:\Rust\cargo-update\target\debug\build\curl-sys-44d0f883e8c12bab\out\build -L native=P:\Rust\cargo-update\target\debug\build\libnghttp2-sys-590a71d4580b214f\out\i\lib -L native=P:\Rust\cargo-update\target\debug\build\libz-sys-b08937bd42dba9f7\out\lib -L native=P:\Rust\cargo-update\target\debug\build\libz-sys-b08937bd42dba9f7\out\lib -L native=P:\Rust\cargo-update\target\debug\build\libssh2-sys-58d8342fd041f68c\out\build -L native=D:\Users\nabijaczleweli\.cargo\registry\src\index.crates.io-1949cf8c6b5b557f\windows_x86_64_gnu-0.53.0\lib -L native=/mingw64/lib -L native=D:\Users\nabijaczleweli\.cargo\registry\src\index.crates.io-1949cf8c6b5b557f\windows_x86_64_gnu-0.52.6\lib -L native=/mingw64/lib` (exit code: 101)

The layout of my target directory may be of interest:
P:\Rust\cargo-update\target JUNCTION p:\Rust\target
P:\Rust\target JUNCTION s:\Rust-target
S:\Rust-target JUNCTION v:\Rust-target
v:\Rust-target is a real directory, no internal links

This smells to me like some sort of EXDEV?

The source file (P:\Rust\cargo-update\target\debug\deps\libcargo_update-e847dae16ed1dcdc.rmeta) is still real afterward, the directory containing the target (\?\V:\Rust-target\debug\incremental\cargo_update-3qbqkuu5iqvls\s-hjbhvs6u46-0ouqlsm-working\metadata.rmeta) isn't, but the file does exist in the only similarly-named new directory (V:\Rust-target\debug\incremental\cargo_update-3qbqkuu5iqvls\s-hjbhvs6u46-0ouqlsm-dgr1uuofn17hs3fti5y5oob2k\metadata.rmeta) with the same contents.

Start with the incremental-compilation reproduction using cargo build on x86_64-pc-windows-gnu, then inspect rustc_metadata/src/rmeta/encoder.rs at the reported line 2448:51. Trace how the failed object-file copy leaves the incremental directory before the subsequent metadata-encoding ICE. Done means the copy failure no longer damages later builds or causes the compiler panic.