Fix splat v0 mangling by teor2345 · Pull Request #158890 · rust-lang/rust

teor2345 · 2026-07-07T01:25:32Z

Tracking issue: #153629

Typecheck considers a splatted and non-splatted function as distinct types, so mangling has to include splatting. If it doesn't, we get symbol clashes. See the ticket and the tests in this PR for details.

Demangling PR: rust-lang/rustc-demangle#90

@rustbot label +C-bug +F-splat +T-compiler +A-name-mangling

Fixes #158644

rustbot · 2026-07-07T01:25:36Z

r? @hanna-kruppe

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teor2345 · 2026-07-07T02:51:15Z

Oops, forgot to implement demangling, I'll get to it tomorrow

@rustbobt author

wesleywiser

Just so you know, changes to the mangling scheme typically also have a corresponding PR to https://github.com/rust-lang/rustc-demangle 🙂

View changes since this review

wesleywiser · 2026-07-07T15:32:25Z

+                            // FIXME(splat): this letter is currently completely unused, but for
+                            // efficiently we might want to use a letter that can't occur in any
+                            // type instead
+                            p.push("W");


FYI, "W" is currently used by pattern types

rust/compiler/rustc_symbol_mangling/src/v0.rs

Lines 522 to 523 in f10db29

ty::Pat(ty, pat) => {

self.push("W");

Oops, I meant "w", thanks for picking this up

teor2345 · 2026-07-08T03:21:13Z

+// FIXME(splat): remove this once splat demangling has been added to rustc
+//@ exec-env: RUST_BACKTRACE=0


Hopefully this should skip demangling in panic backtraces, until the demangling impl in rust-lang/rustc-demangle#90 is added to rustc

@rustbot ready

View changes since the review

Just so you know, changes to the mangling scheme typically also have a corresponding PR to rust-lang/rustc-demangle

@wesleywiser, do we usually wait for the demangling PR to merge, or is there another way to disable demangling in backtraces?

Another alternative is dropping or modifying this test until the demangling merges.

@rustbot author

I believe in the past, we've usually sequenced this kind of thing as:

Add new mangling to rustc-demangle (done)

Release new rustc-demangle to crates.io (done, v0.1.28)

Update rust-lang/rust to use new rustc-demangle version

Land the equivalent of this PR

Please also add an item to the tracking issue to update the v0 mangling documentation to include this new form when we stabilize it.

rust-log-analyzer · 2026-07-08T03:55:37Z

The job aarch64-gnu-llvm-21-1 failed! Check out the build log: (web) (plain enhanced) (plain)

Click to see the possible cause of the failure (guessed by this bot)

---- [ui] tests/ui/splat/splat-mangling-issue-158644.rs#default stdout ----

error in revision `default`: test compilation failed although it shouldn't!
status: exit status: 101
command: env -u RUSTC_LOG_COLOR RUSTC_ICE="0" RUST_BACKTRACE="short" "/checkout/obj/build/aarch64-unknown-linux-gnu/stage2/bin/rustc" "/checkout/tests/ui/splat/splat-mangling-issue-158644.rs" "-Zthreads=1" "-Zsimulate-remapped-rust-src-base=/rustc/FAKE_PREFIX" "-Ztranslate-remapped-path-to-local-path=no" "-Z" "ignore-directory-in-diagnostics-source-blocks=/cargo" "-Z" "ignore-directory-in-diagnostics-source-blocks=/checkout/vendor" "--sysroot" "/checkout/obj/build/aarch64-unknown-linux-gnu/stage2" "--target=aarch64-unknown-linux-gnu" "--cfg" "default" "--check-cfg" "cfg(test,FALSE,default,legacy,v0)" "-C" "incremental=/checkout/obj/build/aarch64-unknown-linux-gnu/test/ui/splat/splat-mangling-issue-158644.default/splat-mangling-issue-158644.inc" "-Z" "incremental-verify-ich" "--error-format" "json" "--json" "future-incompat" "-Ccodegen-units=1" "-Zui-testing" "-Zdeduplicate-diagnostics=no" "-Zwrite-long-types-to-disk=no" "-Cstrip=debuginfo" "-C" "prefer-dynamic" "-o" "/checkout/obj/build/aarch64-unknown-linux-gnu/test/ui/splat/splat-mangling-issue-158644.default/a" "-A" "unused" "-W" "unused_attributes" "-A" "internal_features" "-A" "incomplete_features" "-A" "unused_parens" "-A" "unused_braces" "-Crpath" "-Cdebuginfo=0" "-Lnative=/checkout/obj/build/aarch64-unknown-linux-gnu/native/rust-test-helpers" "-C" "opt-level=0"
stdout: none
--- stderr -------------------------------

thread 'rustc' (155444) panicked at compiler/rustc_symbol_mangling/src/lib.rs:332:5:
compute_symbol_name: `_RNvMNtCs9Q54e9i3ovY_4core6optionINtB2_6OptionFwTlEEuE6unwrapCs6xq1pFrxHXi_27splat_mangling_issue_158644` cannot be demangled
stack backtrace:
   0: __rustc::rust_begin_unwind
   1: core::panicking::panic_fmt
   2: rustc_symbol_mangling::symbol_name_provider
      [... omitted 2 frames ...]
   3: <rustc_middle::mono::MonoItem>::symbol_name
   4: <core::iter::adapters::map::Map<core::slice::iter::Iter<rustc_middle::mono::MonoItem>, rustc_monomorphize::partitioning::assert_symbols_are_distinct<core::slice::iter::Iter<rustc_middle::mono::MonoItem>>::{closure#0}> as core::iter::traits::iterator::Iterator>::fold::<(), core::iter::traits::iterator::Iterator::for_each::call<(&rustc_middle::mono::MonoItem, rustc_middle::ty::SymbolName), <alloc::vec::Vec<(&rustc_middle::mono::MonoItem, rustc_middle::ty::SymbolName)>>::extend_trusted<core::iter::adapters::map::Map<core::slice::iter::Iter<rustc_middle::mono::MonoItem>, rustc_monomorphize::partitioning::assert_symbols_are_distinct<core::slice::iter::Iter<rustc_middle::mono::MonoItem>>::{closure#0}>>::{closure#0}>::{closure#0}>
   5: <alloc::vec::Vec<(&rustc_middle::mono::MonoItem, rustc_middle::ty::SymbolName)> as alloc::vec::spec_from_iter::SpecFromIter<(&rustc_middle::mono::MonoItem, rustc_middle::ty::SymbolName), core::iter::adapters::map::Map<core::slice::iter::Iter<rustc_middle::mono::MonoItem>, rustc_monomorphize::partitioning::assert_symbols_are_distinct<core::slice::iter::Iter<rustc_middle::mono::MonoItem>>::{closure#0}>>>::from_iter
   6: rustc_monomorphize::partitioning::assert_symbols_are_distinct::<core::slice::iter::Iter<rustc_middle::mono::MonoItem>>
   7: std::panicking::catch_unwind::<rustc_data_structures::sync::mode::FromDyn<()>, core::panic::unwind_safe::AssertUnwindSafe<rustc_data_structures::sync::parallel::par_join<rustc_monomorphize::partitioning::collect_and_partition_mono_items::{closure#0}::{closure#0}, rustc_monomorphize::partitioning::collect_and_partition_mono_items::{closure#0}::{closure#1}, &[rustc_middle::mono::CodegenUnit], ()>::{closure#0}::{closure#1}::{closure#0}>>
   8: <rustc_session::session::Session>::time::<(&[rustc_middle::mono::CodegenUnit], ()), rustc_monomorphize::partitioning::collect_and_partition_mono_items::{closure#0}>
   9: rustc_monomorphize::partitioning::collect_and_partition_mono_items
      [... omitted 2 frames ...]
  10: rustc_codegen_ssa::base::codegen_crate::<rustc_codegen_llvm::LlvmCodegenBackend, rustc_codegen_llvm::ModuleLlvm>
  11: <rustc_codegen_llvm::LlvmCodegenBackend as rustc_codegen_ssa::traits::backend::CodegenBackend>::codegen_crate
  12: <rustc_session::session::Session>::time::<alloc::boxed::Box<dyn core::any::Any>, rustc_interface::passes::start_codegen::{closure#0}>
  13: rustc_interface::passes::start_codegen
  14: <rustc_interface::queries::Linker>::codegen_and_build_linker
  15: std::panicking::catch_unwind::<core::option::Option<rustc_interface::queries::Linker>, core::panic::unwind_safe::AssertUnwindSafe<rustc_interface::passes::create_and_enter_global_ctxt<core::option::Option<rustc_interface::queries::Linker>, rustc_driver_impl::run_compiler::{closure#0}::{closure#2}>::{closure#2}::{closure#0}>>
  16: <std::thread::local::LocalKey<core::cell::Cell<*const ()>>>::with::<rustc_middle::ty::context::tls::enter_context<<rustc_middle::ty::context::GlobalCtxt>::enter<rustc_interface::passes::create_and_enter_global_ctxt<core::option::Option<rustc_interface::queries::Linker>, rustc_driver_impl::run_compiler::{closure#0}::{closure#2}>::{closure#2}, core::option::Option<rustc_interface::queries::Linker>>::{closure#1}, core::option::Option<rustc_interface::queries::Linker>>::{closure#0}, core::option::Option<rustc_interface::queries::Linker>>
  17: <rustc_middle::ty::context::TyCtxt>::create_global_ctxt::<core::option::Option<rustc_interface::queries::Linker>, rustc_interface::passes::create_and_enter_global_ctxt<core::option::Option<rustc_interface::queries::Linker>, rustc_driver_impl::run_compiler::{closure#0}::{closure#2}>::{closure#2}>
  18: rustc_interface::passes::create_and_enter_global_ctxt::<core::option::Option<rustc_interface::queries::Linker>, rustc_driver_impl::run_compiler::{closure#0}::{closure#2}>
  19: std::panicking::catch_unwind::<(), core::panic::unwind_safe::AssertUnwindSafe<rustc_interface::interface::run_compiler<(), rustc_driver_impl::run_compiler::{closure#0}>::{closure#1}::{closure#0}>>
  20: rustc_interface::interface::run_compiler::<(), rustc_driver_impl::run_compiler::{closure#0}>::{closure#1}
  21: <scoped_tls::ScopedKey<rustc_span::SessionGlobals>>::set::<rustc_interface::util::run_in_thread_with_globals<rustc_interface::util::run_in_thread_pool_with_globals<rustc_interface::interface::run_compiler<(), rustc_driver_impl::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}::{closure#0}, ()>
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.
---
note: please make sure that you have updated to the latest nightly

note: rustc 1.99.0-nightly (c4f74c0db 2026-07-08) running on aarch64-unknown-linux-gnu

note: compiler flags: -Z threads=1 -Z simulate-remapped-rust-src-base=/rustc/FAKE_PREFIX -Z translate-remapped-path-to-local-path=no -Z ignore-directory-in-diagnostics-source-blocks=/cargo -Z ignore-directory-in-diagnostics-source-blocks=/checkout/vendor -C incremental=[REDACTED] -Z incremental-verify-ich -C codegen-units=1 -Z ui-testing -Z deduplicate-diagnostics=no -Z write-long-types-to-disk=no -C strip=debuginfo -C prefer-dynamic -C rpath -C debuginfo=0 -C opt-level=0

query stack during panic:
#0 [symbol_name] computing the symbol for `core::option::Option::<fn(, #[splat](i32,))>::unwrap`
#1 [collect_and_partition_mono_items] collect_and_partition_mono_items
end of query stack
------------------------------------------

---- [ui] tests/ui/splat/splat-mangling-issue-158644.rs#default stdout end ----
---- [ui] tests/ui/splat/splat-mangling-issue-158644.rs#v0 stdout ----

error in revision `v0`: test compilation failed although it shouldn't!
status: exit status: 101
command: env -u RUSTC_LOG_COLOR RUSTC_ICE="0" RUST_BACKTRACE="short" "/checkout/obj/build/aarch64-unknown-linux-gnu/stage2/bin/rustc" "/checkout/tests/ui/splat/splat-mangling-issue-158644.rs" "-Zthreads=1" "-Zsimulate-remapped-rust-src-base=/rustc/FAKE_PREFIX" "-Ztranslate-remapped-path-to-local-path=no" "-Z" "ignore-directory-in-diagnostics-source-blocks=/cargo" "-Z" "ignore-directory-in-diagnostics-source-blocks=/checkout/vendor" "--sysroot" "/checkout/obj/build/aarch64-unknown-linux-gnu/stage2" "--target=aarch64-unknown-linux-gnu" "--cfg" "v0" "--check-cfg" "cfg(test,FALSE,default,legacy,v0)" "-C" "incremental=/checkout/obj/build/aarch64-unknown-linux-gnu/test/ui/splat/splat-mangling-issue-158644.v0/splat-mangling-issue-158644.inc" "-Z" "incremental-verify-ich" "--error-format" "json" "--json" "future-incompat" "-Ccodegen-units=1" "-Zui-testing" "-Zdeduplicate-diagnostics=no" "-Zwrite-long-types-to-disk=no" "-Cstrip=debuginfo" "-C" "prefer-dynamic" "-o" "/checkout/obj/build/aarch64-unknown-linux-gnu/test/ui/splat/splat-mangling-issue-158644.v0/a" "-A" "unused" "-W" "unused_attributes" "-A" "internal_features" "-A" "incomplete_features" "-A" "unused_parens" "-A" "unused_braces" "-Crpath" "-Cdebuginfo=0" "-Lnative=/checkout/obj/build/aarch64-unknown-linux-gnu/native/rust-test-helpers" "-C" "opt-level=0" "-Z" "unstable-options" "-Csymbol-mangling-version=v0"
stdout: none
--- stderr -------------------------------

thread 'rustc' (155451) panicked at compiler/rustc_symbol_mangling/src/lib.rs:332:5:
compute_symbol_name: `_RNvMNtCs9Q54e9i3ovY_4core6optionINtB2_6OptionFwTlEEuE6unwrapCs6xq1pFrxHXi_27splat_mangling_issue_158644` cannot be demangled
stack backtrace:
   0: __rustc::rust_begin_unwind
   1: core::panicking::panic_fmt
   2: rustc_symbol_mangling::symbol_name_provider
      [... omitted 2 frames ...]
   3: <rustc_middle::mono::MonoItem>::symbol_name
   4: <core::iter::adapters::map::Map<core::slice::iter::Iter<rustc_middle::mono::MonoItem>, rustc_monomorphize::partitioning::assert_symbols_are_distinct<core::slice::iter::Iter<rustc_middle::mono::MonoItem>>::{closure#0}> as core::iter::traits::iterator::Iterator>::fold::<(), core::iter::traits::iterator::Iterator::for_each::call<(&rustc_middle::mono::MonoItem, rustc_middle::ty::SymbolName), <alloc::vec::Vec<(&rustc_middle::mono::MonoItem, rustc_middle::ty::SymbolName)>>::extend_trusted<core::iter::adapters::map::Map<core::slice::iter::Iter<rustc_middle::mono::MonoItem>, rustc_monomorphize::partitioning::assert_symbols_are_distinct<core::slice::iter::Iter<rustc_middle::mono::MonoItem>>::{closure#0}>>::{closure#0}>::{closure#0}>
   5: <alloc::vec::Vec<(&rustc_middle::mono::MonoItem, rustc_middle::ty::SymbolName)> as alloc::vec::spec_from_iter::SpecFromIter<(&rustc_middle::mono::MonoItem, rustc_middle::ty::SymbolName), core::iter::adapters::map::Map<core::slice::iter::Iter<rustc_middle::mono::MonoItem>, rustc_monomorphize::partitioning::assert_symbols_are_distinct<core::slice::iter::Iter<rustc_middle::mono::MonoItem>>::{closure#0}>>>::from_iter
   6: rustc_monomorphize::partitioning::assert_symbols_are_distinct::<core::slice::iter::Iter<rustc_middle::mono::MonoItem>>
   7: std::panicking::catch_unwind::<rustc_data_structures::sync::mode::FromDyn<()>, core::panic::unwind_safe::AssertUnwindSafe<rustc_data_structures::sync::parallel::par_join<rustc_monomorphize::partitioning::collect_and_partition_mono_items::{closure#0}::{closure#0}, rustc_monomorphize::partitioning::collect_and_partition_mono_items::{closure#0}::{closure#1}, &[rustc_middle::mono::CodegenUnit], ()>::{closure#0}::{closure#1}::{closure#0}>>
   8: <rustc_session::session::Session>::time::<(&[rustc_middle::mono::CodegenUnit], ()), rustc_monomorphize::partitioning::collect_and_partition_mono_items::{closure#0}>
   9: rustc_monomorphize::partitioning::collect_and_partition_mono_items
      [... omitted 2 frames ...]
  10: rustc_codegen_ssa::base::codegen_crate::<rustc_codegen_llvm::LlvmCodegenBackend, rustc_codegen_llvm::ModuleLlvm>
  11: <rustc_codegen_llvm::LlvmCodegenBackend as rustc_codegen_ssa::traits::backend::CodegenBackend>::codegen_crate
  12: <rustc_session::session::Session>::time::<alloc::boxed::Box<dyn core::any::Any>, rustc_interface::passes::start_codegen::{closure#0}>
  13: rustc_interface::passes::start_codegen
  14: <rustc_interface::queries::Linker>::codegen_and_build_linker
  15: std::panicking::catch_unwind::<core::option::Option<rustc_interface::queries::Linker>, core::panic::unwind_safe::AssertUnwindSafe<rustc_interface::passes::create_and_enter_global_ctxt<core::option::Option<rustc_interface::queries::Linker>, rustc_driver_impl::run_compiler::{closure#0}::{closure#2}>::{closure#2}::{closure#0}>>
  16: <std::thread::local::LocalKey<core::cell::Cell<*const ()>>>::with::<rustc_middle::ty::context::tls::enter_context<<rustc_middle::ty::context::GlobalCtxt>::enter<rustc_interface::passes::create_and_enter_global_ctxt<core::option::Option<rustc_interface::queries::Linker>, rustc_driver_impl::run_compiler::{closure#0}::{closure#2}>::{closure#2}, core::option::Option<rustc_interface::queries::Linker>>::{closure#1}, core::option::Option<rustc_interface::queries::Linker>>::{closure#0}, core::option::Option<rustc_interface::queries::Linker>>
  17: <rustc_middle::ty::context::TyCtxt>::create_global_ctxt::<core::option::Option<rustc_interface::queries::Linker>, rustc_interface::passes::create_and_enter_global_ctxt<core::option::Option<rustc_interface::queries::Linker>, rustc_driver_impl::run_compiler::{closure#0}::{closure#2}>::{closure#2}>
  18: rustc_interface::passes::create_and_enter_global_ctxt::<core::option::Option<rustc_interface::queries::Linker>, rustc_driver_impl::run_compiler::{closure#0}::{closure#2}>
  19: std::panicking::catch_unwind::<(), core::panic::unwind_safe::AssertUnwindSafe<rustc_interface::interface::run_compiler<(), rustc_driver_impl::run_compiler::{closure#0}>::{closure#1}::{closure#0}>>
  20: rustc_interface::interface::run_compiler::<(), rustc_driver_impl::run_compiler::{closure#0}>::{closure#1}
  21: <scoped_tls::ScopedKey<rustc_span::SessionGlobals>>::set::<rustc_interface::util::run_in_thread_with_globals<rustc_interface::util::run_in_thread_pool_with_globals<rustc_interface::interface::run_compiler<(), rustc_driver_impl::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}::{closure#0}, ()>
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.
---
note: please make sure that you have updated to the latest nightly

note: rustc 1.99.0-nightly (c4f74c0db 2026-07-08) running on aarch64-unknown-linux-gnu

note: compiler flags: -Z threads=1 -Z simulate-remapped-rust-src-base=/rustc/FAKE_PREFIX -Z translate-remapped-path-to-local-path=no -Z ignore-directory-in-diagnostics-source-blocks=/cargo -Z ignore-directory-in-diagnostics-source-blocks=/checkout/vendor -C incremental=[REDACTED] -Z incremental-verify-ich -C codegen-units=1 -Z ui-testing -Z deduplicate-diagnostics=no -Z write-long-types-to-disk=no -C strip=debuginfo -C prefer-dynamic -C rpath -C debuginfo=0 -C opt-level=0 -Z unstable-options -C symbol-mangling-version=v0

query stack during panic:
#0 [symbol_name] computing the symbol for `core::option::Option::<fn(, #[splat](i32,))>::unwrap`
#1 [collect_and_partition_mono_items] collect_and_partition_mono_items
end of query stack
------------------------------------------

---- [ui] tests/ui/splat/splat-mangling-issue-158644.rs#v0 stdout end ----
---- [ui] tests/ui/splat/splat-mangling.rs#default stdout ----

error in revision `default`: Error: expected failure status (Some(1)) but received status Some(101).
status: exit status: 101
command: env -u RUSTC_LOG_COLOR RUSTC_ICE="0" RUST_BACKTRACE="short" "/checkout/obj/build/aarch64-unknown-linux-gnu/stage2/bin/rustc" "/checkout/tests/ui/splat/splat-mangling.rs" "-Zthreads=1" "-Zsimulate-remapped-rust-src-base=/rustc/FAKE_PREFIX" "-Ztranslate-remapped-path-to-local-path=no" "-Z" "ignore-directory-in-diagnostics-source-blocks=/cargo" "-Z" "ignore-directory-in-diagnostics-source-blocks=/checkout/vendor" "--sysroot" "/checkout/obj/build/aarch64-unknown-linux-gnu/stage2" "--target=aarch64-unknown-linux-gnu" "--cfg" "default" "--check-cfg" "cfg(test,FALSE,default,legacy,v0)" "--error-format" "json" "--json" "future-incompat" "-Ccodegen-units=1" "-Zui-testing" "-Zdeduplicate-diagnostics=no" "-Zwrite-long-types-to-disk=no" "-Cstrip=debuginfo" "-C" "prefer-dynamic" "--out-dir" "/checkout/obj/build/aarch64-unknown-linux-gnu/test/ui/splat/splat-mangling.default" "-A" "unused" "-W" "unused_attributes" "-A" "internal_features" "-A" "incomplete_features" "-A" "unused_parens" "-A" "unused_braces" "-Crpath" "-Cdebuginfo=0" "-Lnative=/checkout/obj/build/aarch64-unknown-linux-gnu/native/rust-test-helpers" "-C" "opt-level=0"
stdout: none
--- stderr -------------------------------

thread 'rustc' (155468) panicked at compiler/rustc_symbol_mangling/src/lib.rs:332:5:
compute_symbol_name: `_RMNvCsiksvdpJ6Jnj_14splat_mangling4mainINtB0_4TypeFwThmEEuE` cannot be demangled
stack backtrace:
   0: __rustc::rust_begin_unwind
   1: core::panicking::panic_fmt
   2: rustc_symbol_mangling::symbol_name_provider
      [... omitted 2 frames ...]
   3: <std::thread::local::LocalKey<core::cell::Cell<*const ()>>>::with::<rustc_middle::ty::context::tls::enter_context<rustc_symbol_mangling::test::dump_symbol_names_and_def_paths::{closure#0}, ()>::{closure#0}, ()>
   4: rustc_symbol_mangling::test::dump_symbol_names_and_def_paths
   5: rustc_interface::passes::start_codegen
   6: <rustc_interface::queries::Linker>::codegen_and_build_linker
   7: std::panicking::catch_unwind::<core::option::Option<rustc_interface::queries::Linker>, core::panic::unwind_safe::AssertUnwindSafe<rustc_interface::passes::create_and_enter_global_ctxt<core::option::Option<rustc_interface::queries::Linker>, rustc_driver_impl::run_compiler::{closure#0}::{closure#2}>::{closure#2}::{closure#0}>>
   8: <std::thread::local::LocalKey<core::cell::Cell<*const ()>>>::with::<rustc_middle::ty::context::tls::enter_context<<rustc_middle::ty::context::GlobalCtxt>::enter<rustc_interface::passes::create_and_enter_global_ctxt<core::option::Option<rustc_interface::queries::Linker>, rustc_driver_impl::run_compiler::{closure#0}::{closure#2}>::{closure#2}, core::option::Option<rustc_interface::queries::Linker>>::{closure#1}, core::option::Option<rustc_interface::queries::Linker>>::{closure#0}, core::option::Option<rustc_interface::queries::Linker>>
   9: <rustc_middle::ty::context::TyCtxt>::create_global_ctxt::<core::option::Option<rustc_interface::queries::Linker>, rustc_interface::passes::create_and_enter_global_ctxt<core::option::Option<rustc_interface::queries::Linker>, rustc_driver_impl::run_compiler::{closure#0}::{closure#2}>::{closure#2}>
  10: rustc_interface::passes::create_and_enter_global_ctxt::<core::option::Option<rustc_interface::queries::Linker>, rustc_driver_impl::run_compiler::{closure#0}::{closure#2}>
  11: std::panicking::catch_unwind::<(), core::panic::unwind_safe::AssertUnwindSafe<rustc_interface::interface::run_compiler<(), rustc_driver_impl::run_compiler::{closure#0}>::{closure#1}::{closure#0}>>
  12: rustc_interface::interface::run_compiler::<(), rustc_driver_impl::run_compiler::{closure#0}>::{closure#1}
  13: <scoped_tls::ScopedKey<rustc_span::SessionGlobals>>::set::<rustc_interface::util::run_in_thread_with_globals<rustc_interface::util::run_in_thread_pool_with_globals<rustc_interface::interface::run_compiler<(), rustc_driver_impl::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}::{closure#0}, ()>
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.

error: the compiler unexpectedly panicked. This is a bug

note: using internal features is not supported and expected to cause internal compiler errors when used incorrectly

note: rustc 1.99.0-nightly (c4f74c0db 2026-07-08) running on aarch64-unknown-linux-gnu

note: compiler flags: -Z threads=1 -Z simulate-remapped-rust-src-base=/rustc/FAKE_PREFIX -Z translate-remapped-path-to-local-path=no -Z ignore-directory-in-diagnostics-source-blocks=/cargo -Z ignore-directory-in-diagnostics-source-blocks=/checkout/vendor -C codegen-units=1 -Z ui-testing -Z deduplicate-diagnostics=no -Z write-long-types-to-disk=no -C strip=debuginfo -C prefer-dynamic -C rpath -C debuginfo=0 -C opt-level=0

query stack during panic:
#0 [symbol_name] computing the symbol for `main::<impl at /checkout/tests/ui/splat/splat-mangling.rs:23:5: 23:38>`
end of query stack
------------------------------------------

---- [ui] tests/ui/splat/splat-mangling.rs#default stdout end ----
---- [ui] tests/ui/splat/splat-mangling.rs#v0 stdout ----

error in revision `v0`: Error: expected failure status (Some(1)) but received status Some(101).
status: exit status: 101
command: env -u RUSTC_LOG_COLOR RUSTC_ICE="0" RUST_BACKTRACE="short" "/checkout/obj/build/aarch64-unknown-linux-gnu/stage2/bin/rustc" "/checkout/tests/ui/splat/splat-mangling.rs" "-Zthreads=1" "-Zsimulate-remapped-rust-src-base=/rustc/FAKE_PREFIX" "-Ztranslate-remapped-path-to-local-path=no" "-Z" "ignore-directory-in-diagnostics-source-blocks=/cargo" "-Z" "ignore-directory-in-diagnostics-source-blocks=/checkout/vendor" "--sysroot" "/checkout/obj/build/aarch64-unknown-linux-gnu/stage2" "--target=aarch64-unknown-linux-gnu" "--cfg" "v0" "--check-cfg" "cfg(test,FALSE,default,legacy,v0)" "--error-format" "json" "--json" "future-incompat" "-Ccodegen-units=1" "-Zui-testing" "-Zdeduplicate-diagnostics=no" "-Zwrite-long-types-to-disk=no" "-Cstrip=debuginfo" "-C" "prefer-dynamic" "--out-dir" "/checkout/obj/build/aarch64-unknown-linux-gnu/test/ui/splat/splat-mangling.v0" "-A" "unused" "-W" "unused_attributes" "-A" "internal_features" "-A" "incomplete_features" "-A" "unused_parens" "-A" "unused_braces" "-Crpath" "-Cdebuginfo=0" "-Lnative=/checkout/obj/build/aarch64-unknown-linux-gnu/native/rust-test-helpers" "-C" "opt-level=0" "-Z" "unstable-options" "-Csymbol-mangling-version=v0"
stdout: none
--- stderr -------------------------------

thread 'rustc' (155497) panicked at compiler/rustc_symbol_mangling/src/lib.rs:332:5:
compute_symbol_name: `_RMNvCsiksvdpJ6Jnj_14splat_mangling4mainINtB0_4TypeFwThmEEuE` cannot be demangled
stack backtrace:
   0: __rustc::rust_begin_unwind
   1: core::panicking::panic_fmt
   2: rustc_symbol_mangling::symbol_name_provider
      [... omitted 2 frames ...]
   3: <std::thread::local::LocalKey<core::cell::Cell<*const ()>>>::with::<rustc_middle::ty::context::tls::enter_context<rustc_symbol_mangling::test::dump_symbol_names_and_def_paths::{closure#0}, ()>::{closure#0}, ()>
   4: rustc_symbol_mangling::test::dump_symbol_names_and_def_paths
   5: rustc_interface::passes::start_codegen
   6: <rustc_interface::queries::Linker>::codegen_and_build_linker
   7: std::panicking::catch_unwind::<core::option::Option<rustc_interface::queries::Linker>, core::panic::unwind_safe::AssertUnwindSafe<rustc_interface::passes::create_and_enter_global_ctxt<core::option::Option<rustc_interface::queries::Linker>, rustc_driver_impl::run_compiler::{closure#0}::{closure#2}>::{closure#2}::{closure#0}>>
   8: <std::thread::local::LocalKey<core::cell::Cell<*const ()>>>::with::<rustc_middle::ty::context::tls::enter_context<<rustc_middle::ty::context::GlobalCtxt>::enter<rustc_interface::passes::create_and_enter_global_ctxt<core::option::Option<rustc_interface::queries::Linker>, rustc_driver_impl::run_compiler::{closure#0}::{closure#2}>::{closure#2}, core::option::Option<rustc_interface::queries::Linker>>::{closure#1}, core::option::Option<rustc_interface::queries::Linker>>::{closure#0}, core::option::Option<rustc_interface::queries::Linker>>
   9: <rustc_middle::ty::context::TyCtxt>::create_global_ctxt::<core::option::Option<rustc_interface::queries::Linker>, rustc_interface::passes::create_and_enter_global_ctxt<core::option::Option<rustc_interface::queries::Linker>, rustc_driver_impl::run_compiler::{closure#0}::{closure#2}>::{closure#2}>
  10: rustc_interface::passes::create_and_enter_global_ctxt::<core::option::Option<rustc_interface::queries::Linker>, rustc_driver_impl::run_compiler::{closure#0}::{closure#2}>
  11: std::panicking::catch_unwind::<(), core::panic::unwind_safe::AssertUnwindSafe<rustc_interface::interface::run_compiler<(), rustc_driver_impl::run_compiler::{closure#0}>::{closure#1}::{closure#0}>>
  12: rustc_interface::interface::run_compiler::<(), rustc_driver_impl::run_compiler::{closure#0}>::{closure#1}
  13: <scoped_tls::ScopedKey<rustc_span::SessionGlobals>>::set::<rustc_interface::util::run_in_thread_with_globals<rustc_interface::util::run_in_thread_pool_with_globals<rustc_interface::interface::run_compiler<(), rustc_driver_impl::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}::{closure#0}, ()>
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.

error: the compiler unexpectedly panicked. This is a bug

note: using internal features is not supported and expected to cause internal compiler errors when used incorrectly

note: rustc 1.99.0-nightly (c4f74c0db 2026-07-08) running on aarch64-unknown-linux-gnu

note: compiler flags: -Z threads=1 -Z simulate-remapped-rust-src-base=/rustc/FAKE_PREFIX -Z translate-remapped-path-to-local-path=no -Z ignore-directory-in-diagnostics-source-blocks=/cargo -Z ignore-directory-in-diagnostics-source-blocks=/checkout/vendor -C codegen-units=1 -Z ui-testing -Z deduplicate-diagnostics=no -Z write-long-types-to-disk=no -C strip=debuginfo -C prefer-dynamic -C rpath -C debuginfo=0 -C opt-level=0 -Z unstable-options -C symbol-mangling-version=v0

query stack during panic:
#0 [symbol_name] computing the symbol for `main::<impl at /checkout/tests/ui/splat/splat-mangling.rs:23:5: 23:38>`
end of query stack
------------------------------------------

---- [ui] tests/ui/splat/splat-mangling.rs#v0 stdout end ----

rustbot · 2026-07-08T06:14:57Z

Reminder, once the PR becomes ready for a review, use @rustbot ready.

hanna-kruppe · 2026-07-11T12:28:26Z

r? wesleywiser

rustbot · 2026-07-11T12:28:29Z

wesleywiser is currently at their maximum review capacity.
They may take a while to respond.

Add splat mangling bug tests (flaky?)

9ef46b6

rustbot assigned hanna-kruppe Jul 7, 2026

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. labels Jul 7, 2026

rustbot added A-name-mangling Area: Name mangling / decoration aka symbol mangling C-bug Category: This is a bug. F-splat `#![feature(splat)]` labels Jul 7, 2026

teor2345 mentioned this pull request Jul 7, 2026

Fix splat ICEs and ban it in closures #158645

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wesleywiser reviewed Jul 7, 2026

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teor2345 force-pushed the splat-mangling-clash branch from 805f25d to a30c0d8 Compare July 8, 2026 02:45

teor2345 added 2 commits July 8, 2026 13:13

Fix v0 symbol mangling for splat

56a9849

Disable a test backtrace until splat demangling is available

afaae5b

teor2345 force-pushed the splat-mangling-clash branch from a30c0d8 to afaae5b Compare July 8, 2026 03:16

teor2345 mentioned this pull request Jul 8, 2026

Implement demangling for #[splat] rust-lang/rustc-demangle#90

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teor2345 commented Jul 8, 2026

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rustbot added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Jul 8, 2026

rustbot assigned wesleywiser Jul 11, 2026

rustbot unassigned hanna-kruppe Jul 11, 2026

		// FIXME(splat): remove this once splat demangling has been added to rustc
		//@ exec-env: RUST_BACKTRACE=0

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