Add const_param_ty_unchecked gate

[zedddie]

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Add const_param_ty_unchecked internal feature gate to skip ConstParamTy_ trait enforcement on type. Provides an escape hatch for writing tests and examples that use const generics without needing to ensure all fields implement ConstParamTy_.

r? BoxyUwU

[rustbot]

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[rustbot]

changes to the core type system

cc @lcnr

[BoxyUwU]

thx yeah this is what i was looking for :3

View changes since this review

[rustbot]

This PR was rebased onto a different main commit. Here's a range-diff highlighting what actually changed.

Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers.

[rust-log-analyzer]

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)

Executing "/scripts/stage_2_test_set1.sh"
+ /scripts/stage_2_test_set1.sh
PR_CI_JOB set; skipping tidy
+ '[' 1 == 1 ']'
+ echo 'PR_CI_JOB set; skipping tidy'
+ SKIP_TIDY='--skip tidy'
+ ../x.py --stage 2 test --skip tidy --skip compiler --skip src
##[group]Building bootstrap
    Finished `dev` profile [unoptimized] target(s) in 0.04s
##[endgroup]
downloading https://static.rust-lang.org/dist/2026-03-05/rustfmt-nightly-aarch64-unknown-linux-gnu.tar.xz
---
To only update this specific test, also pass `--test-args cfg/suggest-alternative-name-on-target.rs`

error: 1 errors occurred comparing output.
status: exit status: 1
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/cfg/suggest-alternative-name-on-target.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" "--check-cfg" "cfg(test,FALSE)" "--error-format" "json" "--json" "future-incompat" "-Ccodegen-units=1" "-Zui-testing" "-Zdeduplicate-diagnostics=no" "-Zwrite-long-types-to-disk=no" "-Cstrip=debuginfo" "--emit" "metadata" "-C" "prefer-dynamic" "--out-dir" "/checkout/obj/build/aarch64-unknown-linux-gnu/test/ui/cfg/suggest-alternative-name-on-target" "-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"
stdout: none
--- stderr -------------------------------
error: unexpected `cfg` condition value: `arm`
##[error]  --> /checkout/tests/ui/cfg/suggest-alternative-name-on-target.rs:5:7
   |
---
LL | #![deny(unexpected_cfgs)]
   |         ^^^^^^^^^^^^^^^
help: `arm` is an expected value for `target_arch`
   |
LL - #[cfg(target_abi = "arm")]
LL + #[cfg(target_arch = "arm")]
   |

error: unexpected `cfg` condition value: `gnu`
##[error]  --> /checkout/tests/ui/cfg/suggest-alternative-name-on-target.rs:12:7
   |
LL | #[cfg(target_arch = "gnu")]
   |       ^^^^^^^^^^^^^^^^^^^
   |
   = note: see <https://doc.rust-lang.org/nightly/rustc/check-cfg.html> for more information about checking conditional configuration
help: `gnu` is an expected value for `target_env`
   |
LL - #[cfg(target_arch = "gnu")]
LL + #[cfg(target_env = "gnu")]
   |

error: unexpected `cfg` condition value: `openbsd`
##[error]  --> /checkout/tests/ui/cfg/suggest-alternative-name-on-target.rs:19:7
   |

[zedddie]

its fine locally... :_<

[BoxyUwU]

retriggering CI 🤔

[BoxyUwU]

@bors r+

thank you :)

[rust-bors]

📌 Commit 335585b has been approved by BoxyUwU

It is now in the queue for this repository.

[rust-log-analyzer]

The job x86_64-gnu-nopt 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/const-generics/adt_const_params/const_param_ty_unchecked.rs stdout ----

error: 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/x86_64-unknown-linux-gnu/stage2/bin/rustc" "/checkout/tests/ui/const-generics/adt_const_params/const_param_ty_unchecked.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/x86_64-unknown-linux-gnu/stage2" "--target=x86_64-unknown-linux-gnu" "--check-cfg" "cfg(test,FALSE)" "--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/x86_64-unknown-linux-gnu/test/ui/const-generics/adt_const_params/const_param_ty_unchecked/a" "-A" "internal_features" "-A" "incomplete_features" "-A" "unused_parens" "-A" "unused_braces" "-Crpath" "-Cdebuginfo=0" "-Lnative=/checkout/obj/build/x86_64-unknown-linux-gnu/native/rust-test-helpers"
stdout: none
--- stderr -------------------------------
##[error]error: internal compiler error: compiler/rustc_symbol_mangling/src/v0.rs:829:17: symbol_names: unsupported constant of type `f64` (1f64)


thread 'rustc' (105470) panicked at compiler/rustc_symbol_mangling/src/v0.rs:829:17:
Box<dyn Any>
stack backtrace:
   0: std::panicking::begin_panic::<rustc_errors::ExplicitBug>
   1: <rustc_errors::diagnostic::BugAbort as rustc_errors::diagnostic::EmissionGuarantee>::emit_producing_guarantee
   2: rustc_middle::util::bug::opt_span_bug_fmt::<rustc_span::span_encoding::Span>::{closure#0}
   3: rustc_middle::ty::context::tls::with_opt::<rustc_middle::util::bug::opt_span_bug_fmt<rustc_span::span_encoding::Span>::{closure#0}, !>::{closure#0}
   4: rustc_middle::ty::context::tls::with_context_opt::<rustc_middle::ty::context::tls::with_opt<rustc_middle::util::bug::opt_span_bug_fmt<rustc_span::span_encoding::Span>::{closure#0}, !>::{closure#0}, !>
   5: rustc_middle::util::bug::bug_fmt
   6: <rustc_symbol_mangling::v0::V0SymbolMangler as rustc_middle::ty::print::Printer>::print_const
   7: <rustc_symbol_mangling::v0::V0SymbolMangler as rustc_middle::ty::print::Printer>::print_path_with_generic_args::<<rustc_symbol_mangling::v0::V0SymbolMangler as rustc_middle::ty::print::Printer>::default_print_def_path::{closure#0}>
   8: <rustc_symbol_mangling::v0::V0SymbolMangler as rustc_middle::ty::print::Printer>::print_def_path
   9: rustc_symbol_mangling::v0::mangle
  10: rustc_symbol_mangling::symbol_name_provider
      [... omitted 1 frame ...]
  11: <rustc_middle::mono::MonoItem>::symbol_name
  12: <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}>
  13: <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
  14: rustc_monomorphize::partitioning::assert_symbols_are_distinct::<core::slice::iter::Iter<rustc_middle::mono::MonoItem>>
  15: <rustc_session::session::Session>::time::<(&[rustc_middle::mono::CodegenUnit], ()), rustc_monomorphize::partitioning::collect_and_partition_mono_items::{closure#0}>
  16: rustc_monomorphize::partitioning::collect_and_partition_mono_items
      [... omitted 1 frame ...]
  17: <rustc_codegen_llvm::LlvmCodegenBackend as rustc_codegen_ssa::traits::backend::CodegenBackend>::codegen_crate
  18: <rustc_session::session::Session>::time::<alloc::boxed::Box<dyn core::any::Any>, rustc_interface::passes::start_codegen::{closure#0}>
  19: rustc_interface::passes::start_codegen
  20: <rustc_interface::queries::Linker>::codegen_and_build_linker
  21: <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>>
  22: <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}>
  23: rustc_interface::passes::create_and_enter_global_ctxt::<core::option::Option<rustc_interface::queries::Linker>, rustc_driver_impl::run_compiler::{closure#0}::{closure#2}>
  24: 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}>>
  25: rustc_interface::interface::run_compiler::<(), rustc_driver_impl::run_compiler::{closure#0}>::{closure#1}
  26: rustc_span::create_session_globals_then::<(), 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: using internal features is not supported and expected to cause internal compiler errors when used incorrectly

note: rustc 1.97.0-nightly (e15118494 2026-04-15) running on x86_64-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

query stack during panic:
#0 [symbol_name] computing the symbol for `something::<ValTree(Leaf(0x3ff0000000000000): f64)>`
#1 [collect_and_partition_mono_items] collect_and_partition_mono_items
end of query stack
error: aborting due to 1 previous error
------------------------------------------

---- [ui] tests/ui/const-generics/adt_const_params/const_param_ty_unchecked.rs stdout end ----

[rust-bors]

💔 Test for e151184 failed: CI. Failed job:

• auto - x86_64-gnu-nopt (web logs, enhanced plaintext logs)

[JonathanBrouwer]

@bors r-
#155309

[rust-bors]

This PR was contained in a rollup (#155309), which was unapproved.