Upgrade Rust toolchain to nightly-2026-03-01

[feliperodri]

Advance from nightly-2026-02-18 to nightly-2026-03-01. Several source changes are required to track rustc and rustc_public API changes.

• Rvalue::ShallowInitBox was removed. Box::new is now lowered as an ordinary library call rather than a box-expression that produced this variant, so exchange_malloc/ShallowInitBox no longer exist in either rustc_public or internal MIR. Remove the now-unmatchable arms in analysis, points-to, check_values, body visitor, internal_mir, the gotoc rvalue codegen, and the llbc backend. Box/Vec/dyn codegen still verifies.

• IntoQueryParam<DefId> no longer has a blanket impl for &DefId; only the owned type implements it. Dereference &DefId to the Copy DefId at the generics_of, coerce_unsized_info, def_kind, def_path_str, and associated_item_def_ids call sites.

• VariantDef::idx is now private with no accessor. variants_iter yields variants in declaration order, so reconstruct the VariantIdx from the enumeration index via VariantIdx::to_val in the automatic Arbitrary pass, the Option builders, and the llbc backend.

• CrateDefItems was removed; its associated_items method is now inherent on TraitDef/ImplDef. Drop the unused import.

• rustc_driver::default_translator was removed and JsonEmitter::new no longer takes a translator argument. Drop both.

• TyCtxt::get_all_attrs is now #[deprecated] in favor of rustc_hir::find_attr!, which only matches parsed built-in attributes. Kani inspects unparsed kanitool::* tool attributes, so get_all_attrs remains the correct API; add scoped #[allow(deprecated)] with a comment.

• Fix new clippy lints on pre-existing code that CI's -D warnings now rejects: an if-in-match guard, iterating a map's keys, an explicit loop counter, and a redundant .into_iter().

Test fixtures:

• tests/cargo-kani/vecdeque-cve: the rustc_allow_const_fn_unstable feature gate was removed (the #[rustc_allow_const_fn_unstable] attribute still works under rustc_attrs). Drop the #![feature(...)] line.
• tests/ui/unsupported-annotation: rustc reworded E0433 from "failed to resolve: could not find" to "cannot find".

The charon submodule is left unchanged. It builds against this nightly once scripts/charon-patch.diff is applied, which the llbc CI job already does; cargo build-dev --features cprover --features llbc and ./scripts/kani-llbc-regression.sh (9/9) both pass with the patch applied.

Resolves #4703 and #4707

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 and MIT licenses.

[Copilot]

🟡 Human review recommended

It upgrades the pinned nightly and touches multiple compiler-internals-facing translation paths (MIR transforms and both backends), which warrants final human verification despite the changes being mostly mechanical.

Pull request overview

Updates Kani’s Rust nightly toolchain to nightly-2026-03-01 and applies the corresponding mechanical source/test adjustments needed to track upstream rustc / rustc_public API and lint changes (notably removal of Rvalue::ShallowInitBox, IntoQueryParam<DefId> reference behavior changes, and VariantDef::idx privacy).

Changes:

• Bump toolchain to nightly-2026-03-01 and update UI / cargo-kani test fixtures for upstream diagnostic/feature-gate changes.
• Remove now-unreachable ShallowInitBox handling across MIR transforms and codegen paths.
• Adapt to API changes around DefId query parameters and variant indexing by reconstructing VariantIdx from enumeration order; address newly-enforced Clippy warnings.

File summaries

File	Description
rust-toolchain.toml	Bumps pinned nightly from 2026-02-18 to 2026-03-01.
kani-driver/src/list/collect_metadata.rs	Removes redundant .into_iter() to satisfy linting / idiomatic iteration.
kani-driver/src/cbmc_property_renderer.rs	Reworks property indexing to avoid an explicit loop counter (Clippy).
kani-compiler/src/session.rs	Updates JSON emitter construction after default_translator / signature changes.
kani-compiler/src/kani_middle/transform/kani_intrinsics.rs	Reconstructs VariantIdx via enumeration index (since VariantDef::idx is private).
kani-compiler/src/kani_middle/transform/internal_mir.rs	Drops internal MIR conversion for removed Rvalue::ShallowInitBox.
kani-compiler/src/kani_middle/transform/check_values.rs	Removes unreachable ShallowInitBox visitor handling.
kani-compiler/src/kani_middle/transform/body.rs	Removes unreachable ShallowInitBox operand visitation.
kani-compiler/src/kani_middle/transform/automatic.rs	Reconstructs VariantIdx for enum/struct Arbitrary generation; updates helper signature accordingly.
kani-compiler/src/kani_middle/resolve.rs	Adjusts imports and dereferences &DefId at query call sites; drops removed CrateDefItems.
kani-compiler/src/kani_middle/points_to/points_to_analysis.rs	Removes unreachable ShallowInitBox handling in points-to analysis match.
kani-compiler/src/kani_middle/coercion.rs	Dereferences &DefId at coerce_unsized_info call site.
kani-compiler/src/kani_middle/attributes.rs	Adds scoped #[allow(deprecated)] for get_all_attrs (tool attrs), derefs &DefId, and fixes map-key iteration lint.
kani-compiler/src/kani_middle/analysis.rs	Removes unreachable ShallowInitBox key classification.
kani-compiler/src/codegen_cprover_gotoc/context/current_fn.rs	Refactors match arm to satisfy Clippy (if-in-match guard).
kani-compiler/src/codegen_cprover_gotoc/codegen/rvalue.rs	Removes ShallowInitBox rvalue codegen path (no longer produced).
kani-compiler/src/codegen_aeneas_llbc/mir_to_ullbc/mod.rs	Reconstructs VariantIdx during variant translation and removes ShallowInitBox TODO arm.
tests/cargo-kani/vecdeque-cve/src/harness.rs	Removes obsolete #![feature(rustc_allow_const_fn_unstable)] gate from fixture.
tests/ui/unsupported-annotation/expected	Updates expected diagnostic wording to match new rustc E0433 message.

Review details

• Files reviewed: 19/19 changed files
• Comments generated: 0
• Review effort level: Lite

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