compiler/rustc_mir_transform/src/check_unsafety.rs

   1 use rustc_data_structures::fx::FxHashSet;
   2 use rustc_errors::struct_span_err;
   3 use rustc_hir as hir;
   4 use rustc_hir::def::DefKind;
   5 use rustc_hir::def_id::{DefId, LocalDefId};
   6 use rustc_hir::hir_id::HirId;
   7 use rustc_hir::intravisit;
   8 use rustc_hir::{BlockCheckMode, ExprKind, Node};
   9 use rustc_middle::mir::visit::{MutatingUseContext, PlaceContext, Visitor};
  10 use rustc_middle::mir::*;
  11 use rustc_middle::ty::query::Providers;
  12 use rustc_middle::ty::{self, TyCtxt};
  13 use rustc_session::lint::builtin::{UNSAFE_OP_IN_UNSAFE_FN, UNUSED_UNSAFE};
  14 use rustc_session::lint::Level;
  15
  16 use std::ops::Bound;
  17
  18 pub struct UnsafetyChecker<'a, 'tcx> {
  19     body: &'a Body<'tcx>,
  20     body_did: LocalDefId,
  21     violations: Vec<UnsafetyViolation>,
  22     source_info: SourceInfo,
  23     tcx: TyCtxt<'tcx>,
  24     param_env: ty::ParamEnv<'tcx>,
  25
  26     /// Used `unsafe` blocks in this function. This is used for the "unused_unsafe" lint.
  27     used_unsafe_blocks: FxHashSet<HirId>,
  28 }
  29
  30 impl<'a, 'tcx> UnsafetyChecker<'a, 'tcx> {
  31     fn new(
  32         body: &'a Body<'tcx>,
  33         body_did: LocalDefId,
  34         tcx: TyCtxt<'tcx>,
  35         param_env: ty::ParamEnv<'tcx>,
  36     ) -> Self {
  37         Self {
  38             body,
  39             body_did,
  40             violations: vec![],
  41             source_info: SourceInfo::outermost(body.span),
  42             tcx,
  43             param_env,
  44             used_unsafe_blocks: Default::default(),
  45         }
  46     }
  47 }
  48
  49 impl<'tcx> Visitor<'tcx> for UnsafetyChecker<'_, 'tcx> {
  50     fn visit_terminator(&mut self, terminator: &Terminator<'tcx>, location: Location) {
  51         self.source_info = terminator.source_info;
  52         match terminator.kind {
  53             TerminatorKind::Goto { .. }
  54             | TerminatorKind::SwitchInt { .. }
  55             | TerminatorKind::Drop { .. }
  56             | TerminatorKind::Yield { .. }
  57             | TerminatorKind::Assert { .. }
  58             | TerminatorKind::DropAndReplace { .. }
  59             | TerminatorKind::GeneratorDrop
  60             | TerminatorKind::Resume
  61             | TerminatorKind::Abort
  62             | TerminatorKind::Return
  63             | TerminatorKind::Unreachable
  64             | TerminatorKind::FalseEdge { .. }
  65             | TerminatorKind::FalseUnwind { .. } => {
  66                 // safe (at least as emitted during MIR construction)
  67             }
  68
  69             TerminatorKind::Call { ref func, .. } => {
  70                 let func_ty = func.ty(self.body, self.tcx);
  71                 let func_id =
  72                     if let ty::FnDef(func_id, _) = func_ty.kind() { Some(func_id) } else { None };
  73                 let sig = func_ty.fn_sig(self.tcx);
  74                 if let hir::Unsafety::Unsafe = sig.unsafety() {
  75                     self.require_unsafe(
  76                         UnsafetyViolationKind::General,
  77                         UnsafetyViolationDetails::CallToUnsafeFunction,
  78                     )
  79                 }
  80
  81                 if let Some(func_id) = func_id {
  82                     self.check_target_features(*func_id);
  83                 }
  84             }
  85
  86             TerminatorKind::InlineAsm { .. } => self.require_unsafe(
  87                 UnsafetyViolationKind::General,
  88                 UnsafetyViolationDetails::UseOfInlineAssembly,
  89             ),
  90         }
  91         self.super_terminator(terminator, location);
  92     }
  93
  94     fn visit_statement(&mut self, statement: &Statement<'tcx>, location: Location) {
  95         self.source_info = statement.source_info;
  96         match statement.kind {
  97             StatementKind::Assign(..)
  98             | StatementKind::FakeRead(..)
  99             | StatementKind::SetDiscriminant { .. }
 100             | StatementKind::Deinit(..)
 101             | StatementKind::StorageLive(..)
 102             | StatementKind::StorageDead(..)
 103             | StatementKind::Retag { .. }
 104             | StatementKind::AscribeUserType(..)
 105             | StatementKind::Coverage(..)
 106             | StatementKind::Intrinsic(..)
 107             | StatementKind::Nop => {
 108                 // safe (at least as emitted during MIR construction)
 109             }
 110         }
 111         self.super_statement(statement, location);
 112     }
 113
 114     fn visit_rvalue(&mut self, rvalue: &Rvalue<'tcx>, location: Location) {
 115         match rvalue {
 116             Rvalue::Aggregate(box ref aggregate, _) => match aggregate {
 117                 &AggregateKind::Array(..) | &AggregateKind::Tuple => {}
 118                 &AggregateKind::Adt(adt_did, ..) => {
 119                     match self.tcx.layout_scalar_valid_range(adt_did) {
 120                         (Bound::Unbounded, Bound::Unbounded) => {}
 121                         _ => self.require_unsafe(
 122                             UnsafetyViolationKind::General,
 123                             UnsafetyViolationDetails::InitializingTypeWith,
 124                         ),
 125                     }
 126                 }
 127                 &AggregateKind::Closure(def_id, _) | &AggregateKind::Generator(def_id, _, _) => {
 128                     let UnsafetyCheckResult { violations, used_unsafe_blocks, .. } =
 129                         self.tcx.unsafety_check_result(def_id);
 130                     self.register_violations(violations, used_unsafe_blocks.iter().copied());
 131                 }
 132             },
 133             _ => {}
 134         }
 135         self.super_rvalue(rvalue, location);
 136     }
 137
 138     fn visit_operand(&mut self, op: &Operand<'tcx>, location: Location) {
 139         if let Operand::Constant(constant) = op {
 140             let maybe_uneval = match constant.literal {
 141                 ConstantKind::Val(..) | ConstantKind::Ty(_) => None,
 142                 ConstantKind::Unevaluated(uv, _) => Some(uv),
 143             };
 144
 145             if let Some(uv) = maybe_uneval {
 146                 if uv.promoted.is_none() {
 147                     let def_id = uv.def.def_id_for_type_of();
 148                     if self.tcx.def_kind(def_id) == DefKind::InlineConst {
 149                         let local_def_id = def_id.expect_local();
 150                         let UnsafetyCheckResult { violations, used_unsafe_blocks, .. } =
 151                             self.tcx.unsafety_check_result(local_def_id);
 152                         self.register_violations(violations, used_unsafe_blocks.iter().copied());
 153                     }
 154                 }
 155             }
 156         }
 157         self.super_operand(op, location);
 158     }
 159
 160     fn visit_place(&mut self, place: &Place<'tcx>, context: PlaceContext, _location: Location) {
 161         // On types with `scalar_valid_range`, prevent
 162         // * `&mut x.field`
 163         // * `x.field = y;`
 164         // * `&x.field` if `field`'s type has interior mutability
 165         // because either of these would allow modifying the layout constrained field and
 166         // insert values that violate the layout constraints.
 167         if context.is_mutating_use() || context.is_borrow() {
 168             self.check_mut_borrowing_layout_constrained_field(*place, context.is_mutating_use());
 169         }
 170
 171         // Some checks below need the extra meta info of the local declaration.
 172         let decl = &self.body.local_decls[place.local];
 173
 174         // Check the base local: it might be an unsafe-to-access static. We only check derefs of the
 175         // temporary holding the static pointer to avoid duplicate errors
 176         // <https://github.com/rust-lang/rust/pull/78068#issuecomment-731753506>.
 177         if decl.internal && place.projection.first() == Some(&ProjectionElem::Deref) {
 178             // If the projection root is an artificial local that we introduced when
 179             // desugaring `static`, give a more specific error message
 180             // (avoid the general "raw pointer" clause below, that would only be confusing).
 181             if let Some(box LocalInfo::StaticRef { def_id, .. }) = decl.local_info {
 182                 if self.tcx.is_mutable_static(def_id) {
 183                     self.require_unsafe(
 184                         UnsafetyViolationKind::General,
 185                         UnsafetyViolationDetails::UseOfMutableStatic,
 186                     );
 187                     return;
 188                 } else if self.tcx.is_foreign_item(def_id) {
 189                     self.require_unsafe(
 190                         UnsafetyViolationKind::General,
 191                         UnsafetyViolationDetails::UseOfExternStatic,
 192                     );
 193                     return;
 194                 }
 195             }
 196         }
 197
 198         // Check for raw pointer `Deref`.
 199         for (base, proj) in place.iter_projections() {
 200             if proj == ProjectionElem::Deref {
 201                 let base_ty = base.ty(self.body, self.tcx).ty;
 202                 if base_ty.is_unsafe_ptr() {
 203                     self.require_unsafe(
 204                         UnsafetyViolationKind::General,
 205                         UnsafetyViolationDetails::DerefOfRawPointer,
 206                     )
 207                 }
 208             }
 209         }
 210
 211         // Check for union fields. For this we traverse right-to-left, as the last `Deref` changes
 212         // whether we *read* the union field or potentially *write* to it (if this place is being assigned to).
 213         let mut saw_deref = false;
 214         for (base, proj) in place.iter_projections().rev() {
 215             if proj == ProjectionElem::Deref {
 216                 saw_deref = true;
 217                 continue;
 218             }
 219
 220             let base_ty = base.ty(self.body, self.tcx).ty;
 221             if base_ty.is_union() {
 222                 // If we did not hit a `Deref` yet and the overall place use is an assignment, the
 223                 // rules are different.
 224                 let assign_to_field = !saw_deref
 225                     && matches!(
 226                         context,
 227                         PlaceContext::MutatingUse(
 228                             MutatingUseContext::Store
 229                                 | MutatingUseContext::Drop
 230                                 | MutatingUseContext::AsmOutput
 231                         )
 232                     );
 233                 // If this is just an assignment, determine if the assigned type needs dropping.
 234                 if assign_to_field {
 235                     // We have to check the actual type of the assignment, as that determines if the
 236                     // old value is being dropped.
 237                     let assigned_ty = place.ty(&self.body.local_decls, self.tcx).ty;
 238                     if assigned_ty.needs_drop(self.tcx, self.param_env) {
 239                         // This would be unsafe, but should be outright impossible since we reject such unions.
 240                         self.tcx.sess.delay_span_bug(
 241                             self.source_info.span,
 242                             format!("union fields that need dropping should be impossible: {assigned_ty}")
 243                         );
 244                     }
 245                 } else {
 246                     self.require_unsafe(
 247                         UnsafetyViolationKind::General,
 248                         UnsafetyViolationDetails::AccessToUnionField,
 249                     )
 250                 }
 251             }
 252         }
 253     }
 254 }
 255
 256 impl<'tcx> UnsafetyChecker<'_, 'tcx> {
 257     fn require_unsafe(&mut self, kind: UnsafetyViolationKind, details: UnsafetyViolationDetails) {
 258         // Violations can turn out to be `UnsafeFn` during analysis, but they should not start out as such.
 259         assert_ne!(kind, UnsafetyViolationKind::UnsafeFn);
 260
 261         let source_info = self.source_info;
 262         let lint_root = self.body.source_scopes[self.source_info.scope]
 263             .local_data
 264             .as_ref()
 265             .assert_crate_local()
 266             .lint_root;
 267         self.register_violations(
 268             [&UnsafetyViolation { source_info, lint_root, kind, details }],
 269             [],
 270         );
 271     }
 272
 273     fn register_violations<'a>(
 274         &mut self,
 275         violations: impl IntoIterator<Item = &'a UnsafetyViolation>,
 276         new_used_unsafe_blocks: impl IntoIterator<Item = HirId>,
 277     ) {
 278         let safety = self.body.source_scopes[self.source_info.scope]
 279             .local_data
 280             .as_ref()
 281             .assert_crate_local()
 282             .safety;
 283         match safety {
 284             // `unsafe` blocks are required in safe code
 285             Safety::Safe => violations.into_iter().for_each(|&violation| {
 286                 match violation.kind {
 287                     UnsafetyViolationKind::General => {}
 288                     UnsafetyViolationKind::UnsafeFn => {
 289                         bug!("`UnsafetyViolationKind::UnsafeFn` in an `Safe` context")
 290                     }
 291                 }
 292                 if !self.violations.contains(&violation) {
 293                     self.violations.push(violation)
 294                 }
 295             }),
 296             // With the RFC 2585, no longer allow `unsafe` operations in `unsafe fn`s
 297             Safety::FnUnsafe => violations.into_iter().for_each(|&(mut violation)| {
 298                 violation.kind = UnsafetyViolationKind::UnsafeFn;
 299                 if !self.violations.contains(&violation) {
 300                     self.violations.push(violation)
 301                 }
 302             }),
 303             Safety::BuiltinUnsafe => {}
 304             Safety::ExplicitUnsafe(hir_id) => violations.into_iter().for_each(|_violation| {
 305                 self.used_unsafe_blocks.insert(hir_id);
 306             }),
 307         };
 308
 309         new_used_unsafe_blocks.into_iter().for_each(|hir_id| {
 310             self.used_unsafe_blocks.insert(hir_id);
 311         });
 312     }
 313     fn check_mut_borrowing_layout_constrained_field(
 314         &mut self,
 315         place: Place<'tcx>,
 316         is_mut_use: bool,
 317     ) {
 318         for (place_base, elem) in place.iter_projections().rev() {
 319             match elem {
 320                 // Modifications behind a dereference don't affect the value of
 321                 // the pointer.
 322                 ProjectionElem::Deref => return,
 323                 ProjectionElem::Field(..) => {
 324                     let ty = place_base.ty(&self.body.local_decls, self.tcx).ty;
 325                     if let ty::Adt(def, _) = ty.kind() {
 326                         if self.tcx.layout_scalar_valid_range(def.did())
 327                             != (Bound::Unbounded, Bound::Unbounded)
 328                         {
 329                             let details = if is_mut_use {
 330                                 UnsafetyViolationDetails::MutationOfLayoutConstrainedField
 331
 332                             // Check `is_freeze` as late as possible to avoid cycle errors
 333                             // with opaque types.
 334                             } else if !place
 335                                 .ty(self.body, self.tcx)
 336                                 .ty
 337                                 .is_freeze(self.tcx, self.param_env)
 338                             {
 339                                 UnsafetyViolationDetails::BorrowOfLayoutConstrainedField
 340                             } else {
 341                                 continue;
 342                             };
 343                             self.require_unsafe(UnsafetyViolationKind::General, details);
 344                         }
 345                     }
 346                 }
 347                 _ => {}
 348             }
 349         }
 350     }
 351
 352     /// Checks whether calling `func_did` needs an `unsafe` context or not, i.e. whether
 353     /// the called function has target features the calling function hasn't.
 354     fn check_target_features(&mut self, func_did: DefId) {
 355         // Unsafety isn't required on wasm targets. For more information see
 356         // the corresponding check in typeck/src/collect.rs
 357         if self.tcx.sess.target.options.is_like_wasm {
 358             return;
 359         }
 360
 361         let callee_features = &self.tcx.codegen_fn_attrs(func_did).target_features;
 362         // The body might be a constant, so it doesn't have codegen attributes.
 363         let self_features = &self.tcx.body_codegen_attrs(self.body_did.to_def_id()).target_features;
 364
 365         // Is `callee_features` a subset of `calling_features`?
 366         if !callee_features.iter().all(|feature| self_features.contains(feature)) {
 367             self.require_unsafe(
 368                 UnsafetyViolationKind::General,
 369                 UnsafetyViolationDetails::CallToFunctionWith,
 370             )
 371         }
 372     }
 373 }
 374
 375 pub(crate) fn provide(providers: &mut Providers) {
 376     *providers = Providers {
 377         unsafety_check_result: |tcx, def_id| {
 378             if let Some(def) = ty::WithOptConstParam::try_lookup(def_id, tcx) {
 379                 tcx.unsafety_check_result_for_const_arg(def)
 380             } else {
 381                 unsafety_check_result(tcx, ty::WithOptConstParam::unknown(def_id))
 382             }
 383         },
 384         unsafety_check_result_for_const_arg: |tcx, (did, param_did)| {
 385             unsafety_check_result(
 386                 tcx,
 387                 ty::WithOptConstParam { did, const_param_did: Some(param_did) },
 388             )
 389         },
 390         ..*providers
 391     };
 392 }
 393
 394 /// Context information for [`UnusedUnsafeVisitor`] traversal,
 395 /// saves (innermost) relevant context
 396 #[derive(Copy, Clone, Debug)]
 397 enum Context {
 398     Safe,
 399     /// in an `unsafe fn`
 400     UnsafeFn(HirId),
 401     /// in a *used* `unsafe` block
 402     /// (i.e. a block without unused-unsafe warning)
 403     UnsafeBlock(HirId),
 404 }
 405
 406 struct UnusedUnsafeVisitor<'a, 'tcx> {
 407     tcx: TyCtxt<'tcx>,
 408     used_unsafe_blocks: &'a FxHashSet<HirId>,
 409     context: Context,
 410     unused_unsafes: &'a mut Vec<(HirId, UnusedUnsafe)>,
 411 }
 412
 413 impl<'tcx> intravisit::Visitor<'tcx> for UnusedUnsafeVisitor<'_, 'tcx> {
 414     fn visit_block(&mut self, block: &'tcx hir::Block<'tcx>) {
 415         if let hir::BlockCheckMode::UnsafeBlock(hir::UnsafeSource::UserProvided) = block.rules {
 416             let used = match self.tcx.lint_level_at_node(UNUSED_UNSAFE, block.hir_id) {
 417                 (Level::Allow, _) => true,
 418                 _ => self.used_unsafe_blocks.contains(&block.hir_id),
 419             };
 420             let unused_unsafe = match (self.context, used) {
 421                 (_, false) => UnusedUnsafe::Unused,
 422                 (Context::Safe, true) | (Context::UnsafeFn(_), true) => {
 423                     let previous_context = self.context;
 424                     self.context = Context::UnsafeBlock(block.hir_id);
 425                     intravisit::walk_block(self, block);
 426                     self.context = previous_context;
 427                     return;
 428                 }
 429                 (Context::UnsafeBlock(hir_id), true) => UnusedUnsafe::InUnsafeBlock(hir_id),
 430             };
 431             self.unused_unsafes.push((block.hir_id, unused_unsafe));
 432         }
 433         intravisit::walk_block(self, block);
 434     }
 435
 436     fn visit_anon_const(&mut self, c: &'tcx hir::AnonConst) {
 437         if matches!(self.tcx.def_kind(c.def_id), DefKind::InlineConst) {
 438             self.visit_body(self.tcx.hir().body(c.body))
 439         }
 440     }
 441
 442     fn visit_fn(
 443         &mut self,
 444         fk: intravisit::FnKind<'tcx>,
 445         _fd: &'tcx hir::FnDecl<'tcx>,
 446         b: hir::BodyId,
 447         _s: rustc_span::Span,
 448         _id: HirId,
 449     ) {
 450         if matches!(fk, intravisit::FnKind::Closure) {
 451             self.visit_body(self.tcx.hir().body(b))
 452         }
 453     }
 454 }
 455
 456 fn check_unused_unsafe(
 457     tcx: TyCtxt<'_>,
 458     def_id: LocalDefId,
 459     used_unsafe_blocks: &FxHashSet<HirId>,
 460 ) -> Vec<(HirId, UnusedUnsafe)> {
 461     let body_id = tcx.hir().maybe_body_owned_by(def_id);
 462
 463     let Some(body_id) = body_id else {
 464         debug!("check_unused_unsafe({:?}) - no body found", def_id);
 465         return vec![];
 466     };
 467
 468     let body = tcx.hir().body(body_id);
 469     let hir_id = tcx.hir().local_def_id_to_hir_id(def_id);
 470     let context = match tcx.hir().fn_sig_by_hir_id(hir_id) {
 471         Some(sig) if sig.header.unsafety == hir::Unsafety::Unsafe => Context::UnsafeFn(hir_id),
 472         _ => Context::Safe,
 473     };
 474
 475     debug!(
 476         "check_unused_unsafe({:?}, context={:?}, body={:?}, used_unsafe_blocks={:?})",
 477         def_id, body, context, used_unsafe_blocks
 478     );
 479
 480     let mut unused_unsafes = vec![];
 481
 482     let mut visitor = UnusedUnsafeVisitor {
 483         tcx,
 484         used_unsafe_blocks,
 485         context,
 486         unused_unsafes: &mut unused_unsafes,
 487     };
 488     intravisit::Visitor::visit_body(&mut visitor, body);
 489
 490     unused_unsafes
 491 }
 492
 493 fn unsafety_check_result<'tcx>(
 494     tcx: TyCtxt<'tcx>,
 495     def: ty::WithOptConstParam<LocalDefId>,
 496 ) -> &'tcx UnsafetyCheckResult {
 497     debug!("unsafety_violations({:?})", def);
 498
 499     // N.B., this borrow is valid because all the consumers of
 500     // `mir_built` force this.
 501     let body = &tcx.mir_built(def).borrow();
 502
 503     if body.is_custom_mir() {
 504         return tcx.arena.alloc(UnsafetyCheckResult {
 505             violations: Vec::new(),
 506             used_unsafe_blocks: FxHashSet::default(),
 507             unused_unsafes: Some(Vec::new()),
 508         });
 509     }
 510
 511     let param_env = tcx.param_env(def.did);
 512
 513     let mut checker = UnsafetyChecker::new(body, def.did, tcx, param_env);
 514     checker.visit_body(&body);
 515
 516     let unused_unsafes = (!tcx.is_typeck_child(def.did.to_def_id()))
 517         .then(|| check_unused_unsafe(tcx, def.did, &checker.used_unsafe_blocks));
 518
 519     tcx.arena.alloc(UnsafetyCheckResult {
 520         violations: checker.violations,
 521         used_unsafe_blocks: checker.used_unsafe_blocks,
 522         unused_unsafes,
 523     })
 524 }
 525
 526 fn report_unused_unsafe(tcx: TyCtxt<'_>, kind: UnusedUnsafe, id: HirId) {
 527     let span = tcx.sess.source_map().guess_head_span(tcx.hir().span(id));
 528     let msg = "unnecessary `unsafe` block";
 529     tcx.struct_span_lint_hir(UNUSED_UNSAFE, id, span, msg, |lint| {
 530         lint.span_label(span, msg);
 531         match kind {
 532             UnusedUnsafe::Unused => {}
 533             UnusedUnsafe::InUnsafeBlock(id) => {
 534                 lint.span_label(
 535                     tcx.sess.source_map().guess_head_span(tcx.hir().span(id)),
 536                     "because it's nested under this `unsafe` block",
 537                 );
 538             }
 539         }
 540
 541         lint
 542     });
 543 }
 544
 545 pub fn check_unsafety(tcx: TyCtxt<'_>, def_id: LocalDefId) {
 546     debug!("check_unsafety({:?})", def_id);
 547
 548     // closures and inline consts are handled by their parent fn.
 549     if tcx.is_typeck_child(def_id.to_def_id()) {
 550         return;
 551     }
 552
 553     let UnsafetyCheckResult { violations, unused_unsafes, .. } = tcx.unsafety_check_result(def_id);
 554
 555     for &UnsafetyViolation { source_info, lint_root, kind, details } in violations.iter() {
 556         let (description, note) = details.description_and_note();
 557
 558         match kind {
 559             UnsafetyViolationKind::General => {
 560                 // once
 561                 let unsafe_fn_msg = if unsafe_op_in_unsafe_fn_allowed(tcx, lint_root) {
 562                     " function or"
 563                 } else {
 564                     ""
 565                 };
 566
 567                 let mut err = struct_span_err!(
 568                     tcx.sess,
 569                     source_info.span,
 570                     E0133,
 571                     "{} is unsafe and requires unsafe{} block",
 572                     description,
 573                     unsafe_fn_msg,
 574                 );
 575                 err.span_label(source_info.span, description).note(note);
 576                 let note_non_inherited = tcx.hir().parent_iter(lint_root).find(|(id, node)| {
 577                     if let Node::Expr(block) = node
 578                         && let ExprKind::Block(block, _) = block.kind
 579                         && let BlockCheckMode::UnsafeBlock(_) = block.rules
 580                     {
 581                         true
 582                     }
 583                     else if let Some(sig) = tcx.hir().fn_sig_by_hir_id(*id)
 584                         && sig.header.is_unsafe()
 585                     {
 586                         true
 587                     } else {
 588                         false
 589                     }
 590                 });
 591                 if let Some((id, _)) = note_non_inherited {
 592                     let span = tcx.hir().span(id);
 593                     err.span_label(
 594                         tcx.sess.source_map().guess_head_span(span),
 595                         "items do not inherit unsafety from separate enclosing items",
 596                     );
 597                 }
 598
 599                 err.emit();
 600             }
 601             UnsafetyViolationKind::UnsafeFn => tcx.struct_span_lint_hir(
 602                 UNSAFE_OP_IN_UNSAFE_FN,
 603                 lint_root,
 604                 source_info.span,
 605                 format!("{} is unsafe and requires unsafe block (error E0133)", description,),
 606                 |lint| lint.span_label(source_info.span, description).note(note),
 607             ),
 608         }
 609     }
 610
 611     for &(block_id, kind) in unused_unsafes.as_ref().unwrap() {
 612         report_unused_unsafe(tcx, kind, block_id);
 613     }
 614 }
 615
 616 fn unsafe_op_in_unsafe_fn_allowed(tcx: TyCtxt<'_>, id: HirId) -> bool {
 617     tcx.lint_level_at_node(UNSAFE_OP_IN_UNSAFE_FN, id).0 == Level::Allow
 618 }