compiler/rustc_hir_analysis/src/coherence/unsafety.rs

//! Unsafety checker: every impl either implements a trait defined in this
//! crate or pertains to a type defined in this crate.

use rustc_errors::struct_span_err;
use rustc_hir as hir;
use rustc_hir::def::DefKind;
use rustc_hir::Unsafety;
use rustc_middle::ty::TyCtxt;
use rustc_span::def_id::LocalDefId;

pub(super) fn check_item(tcx: TyCtxt<'_>, def_id: LocalDefId) {
    debug_assert!(matches!(tcx.def_kind(def_id), DefKind::Impl));
    let item = tcx.hir().expect_item(def_id);
    let hir::ItemKind::Impl(ref impl_) = item.kind else { bug!() };

    if let Some(trait_ref) = tcx.impl_trait_ref(item.owner_id) {
        let trait_def = tcx.trait_def(trait_ref.def_id);
        let unsafe_attr =
            impl_.generics.params.iter().find(|p| p.pure_wrt_drop).map(|_| "may_dangle");
        match (trait_def.unsafety, unsafe_attr, impl_.unsafety, impl_.polarity) {
            (Unsafety::Normal, None, Unsafety::Unsafe, hir::ImplPolarity::Positive) => {
                struct_span_err!(
                    tcx.sess,
                    item.span,
                    E0199,
                    "implementing the trait `{}` is not unsafe",
                    trait_ref.print_only_trait_path()
                )
                .span_suggestion_verbose(
                    item.span.with_hi(item.span.lo() + rustc_span::BytePos(7)),
                    "remove `unsafe` from this trait implementation",
                    "",
                    rustc_errors::Applicability::MachineApplicable,
                )
                .emit();
            }

            (Unsafety::Unsafe, _, Unsafety::Normal, hir::ImplPolarity::Positive) => {
                struct_span_err!(
                    tcx.sess,
                    item.span,
                    E0200,
                    "the trait `{}` requires an `unsafe impl` declaration",
                    trait_ref.print_only_trait_path()
                )
                .note(format!(
                    "the trait `{}` enforces invariants that the compiler can't check. \
                    Review the trait documentation and make sure this implementation \
                    upholds those invariants before adding the `unsafe` keyword",
                    trait_ref.print_only_trait_path()
                ))
                .span_suggestion_verbose(
                    item.span.shrink_to_lo(),
                    "add `unsafe` to this trait implementation",
                    "unsafe ",
                    rustc_errors::Applicability::MaybeIncorrect,
                )
                .emit();
            }

            (Unsafety::Normal, Some(attr_name), Unsafety::Normal, hir::ImplPolarity::Positive) => {
                struct_span_err!(
                    tcx.sess,
                    item.span,
                    E0569,
                    "requires an `unsafe impl` declaration due to `#[{}]` attribute",
                    attr_name
                )
                .note(format!(
                    "the trait `{}` enforces invariants that the compiler can't check. \
                    Review the trait documentation and make sure this implementation \
                    upholds those invariants before adding the `unsafe` keyword",
                    trait_ref.print_only_trait_path()
                ))
                .span_suggestion_verbose(
                    item.span.shrink_to_lo(),
                    "add `unsafe` to this trait implementation",
                    "unsafe ",
                    rustc_errors::Applicability::MaybeIncorrect,
                )
                .emit();
            }

            (_, _, Unsafety::Unsafe, hir::ImplPolarity::Negative(_)) => {
                // Reported in AST validation
                tcx.sess.delay_span_bug(item.span, "unsafe negative impl");
            }
            (_, _, Unsafety::Normal, hir::ImplPolarity::Negative(_))
            | (Unsafety::Unsafe, _, Unsafety::Unsafe, hir::ImplPolarity::Positive)
            | (Unsafety::Normal, Some(_), Unsafety::Unsafe, hir::ImplPolarity::Positive)
            | (Unsafety::Normal, None, Unsafety::Normal, _) => {
                // OK
            }
        }
    }
}