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::ConstEvalCounter
 108             | StatementKind::Nop => {
 109                 // safe (at least as emitted during MIR construction)
 110             }
 111         }
 112         self.super_statement(statement, location);
 113     }
 114
 115     fn visit_rvalue(&mut self, rvalue: &Rvalue<'tcx>, location: Location) {
 116         match rvalue {
 117             Rvalue::Aggregate(box ref aggregate, _) => match aggregate {
 118                 &AggregateKind::Array(..) | &AggregateKind::Tuple => {}
 119                 &AggregateKind::Adt(adt_did, ..) => {
 120                     match self.tcx.layout_scalar_valid_range(adt_did) {
 121                         (Bound::Unbounded, Bound::Unbounded) => {}
 122                         _ => self.require_unsafe(
 123                             UnsafetyViolationKind::General,
 124                             UnsafetyViolationDetails::InitializingTypeWith,
 125                         ),
 126                     }
 127                 }
 128                 &AggregateKind::Closure(def_id, _) | &AggregateKind::Generator(def_id, _, _) => {
 129                     let UnsafetyCheckResult { violations, used_unsafe_blocks, .. } =
 130                         self.tcx.unsafety_check_result(def_id);
 131                     self.register_violations(violations, used_unsafe_blocks.iter().copied());
 132                 }
 133             },
 134             _ => {}
 135         }
 136         self.super_rvalue(rvalue, location);
 137     }
 138
 139     fn visit_operand(&mut self, op: &Operand<'tcx>, location: Location) {
 140         if let Operand::Constant(constant) = op {
 141             let maybe_uneval = match constant.literal {
 142                 ConstantKind::Val(..) | ConstantKind::Ty(_) => None,
 143                 ConstantKind::Unevaluated(uv, _) => Some(uv),
 144             };
 145
 146             if let Some(uv) = maybe_uneval {
 147                 if uv.promoted.is_none() {
 148                     let def_id = uv.def.def_id_for_type_of();
 149                     if self.tcx.def_kind(def_id) == DefKind::InlineConst {
 150                         let local_def_id = def_id.expect_local();
 151                         let UnsafetyCheckResult { violations, used_unsafe_blocks, .. } =
 152                             self.tcx.unsafety_check_result(local_def_id);
 153                         self.register_violations(violations, used_unsafe_blocks.iter().copied());
 154                     }
 155                 }
 156             }
 157         }
 158         self.super_operand(op, location);
 159     }
 160
 161     fn visit_place(&mut self, place: &Place<'tcx>, context: PlaceContext, _location: Location) {
 162         // On types with `scalar_valid_range`, prevent
 163         // * `&mut x.field`
 164         // * `x.field = y;`
 165         // * `&x.field` if `field`'s type has interior mutability
 166         // because either of these would allow modifying the layout constrained field and
 167         // insert values that violate the layout constraints.
 168         if context.is_mutating_use() || context.is_borrow() {
 169             self.check_mut_borrowing_layout_constrained_field(*place, context.is_mutating_use());
 170         }
 171
 172         // Some checks below need the extra meta info of the local declaration.
 173         let decl = &self.body.local_decls[place.local];
 174
 175         // Check the base local: it might be an unsafe-to-access static. We only check derefs of the
 176         // temporary holding the static pointer to avoid duplicate errors
 177         // <https://github.com/rust-lang/rust/pull/78068#issuecomment-731753506>.
 178         if decl.internal && place.projection.first() == Some(&ProjectionElem::Deref) {
 179             // If the projection root is an artificial local that we introduced when
 180             // desugaring `static`, give a more specific error message
 181             // (avoid the general "raw pointer" clause below, that would only be confusing).
 182             if let Some(box LocalInfo::StaticRef { def_id, .. }) = decl.local_info {
 183                 if self.tcx.is_mutable_static(def_id) {
 184                     self.require_unsafe(
 185                         UnsafetyViolationKind::General,
 186                         UnsafetyViolationDetails::UseOfMutableStatic,
 187                     );
 188                     return;
 189                 } else if self.tcx.is_foreign_item(def_id) {
 190                     self.require_unsafe(
 191                         UnsafetyViolationKind::General,
 192                         UnsafetyViolationDetails::UseOfExternStatic,
 193                     );
 194                     return;
 195                 }
 196             }
 197         }
 198
 199         // Check for raw pointer `Deref`.
 200         for (base, proj) in place.iter_projections() {
 201             if proj == ProjectionElem::Deref {
 202                 let base_ty = base.ty(self.body, self.tcx).ty;
 203                 if base_ty.is_unsafe_ptr() {
 204                     self.require_unsafe(
 205                         UnsafetyViolationKind::General,
 206                         UnsafetyViolationDetails::DerefOfRawPointer,
 207                     )
 208                 }
 209             }
 210         }
 211
 212         // Check for union fields. For this we traverse right-to-left, as the last `Deref` changes
 213         // whether we *read* the union field or potentially *write* to it (if this place is being assigned to).
 214         let mut saw_deref = false;
 215         for (base, proj) in place.iter_projections().rev() {
 216             if proj == ProjectionElem::Deref {
 217                 saw_deref = true;
 218                 continue;
 219             }
 220
 221             let base_ty = base.ty(self.body, self.tcx).ty;
 222             if base_ty.is_union() {
 223                 // If we did not hit a `Deref` yet and the overall place use is an assignment, the
 224                 // rules are different.
 225                 let assign_to_field = !saw_deref
 226                     && matches!(
 227                         context,
 228                         PlaceContext::MutatingUse(
 229                             MutatingUseContext::Store
 230                                 | MutatingUseContext::Drop
 231                                 | MutatingUseContext::AsmOutput
 232                         )
 233                     );
 234                 // If this is just an assignment, determine if the assigned type needs dropping.
 235                 if assign_to_field {
 236                     // We have to check the actual type of the assignment, as that determines if the
 237                     // old value is being dropped.
 238                     let assigned_ty = place.ty(&self.body.local_decls, self.tcx).ty;
 239                     if assigned_ty.needs_drop(self.tcx, self.param_env) {
 240                         // This would be unsafe, but should be outright impossible since we reject such unions.
 241                         self.tcx.sess.delay_span_bug(
 242                             self.source_info.span,
 243                             format!("union fields that need dropping should be impossible: {assigned_ty}")
 244                         );
 245                     }
 246                 } else {
 247                     self.require_unsafe(
 248                         UnsafetyViolationKind::General,
 249                         UnsafetyViolationDetails::AccessToUnionField,
 250                     )
 251                 }
 252             }
 253         }
 254     }
 255 }
 256
 257 impl<'tcx> UnsafetyChecker<'_, 'tcx> {
 258     fn require_unsafe(&mut self, kind: UnsafetyViolationKind, details: UnsafetyViolationDetails) {
 259         // Violations can turn out to be `UnsafeFn` during analysis, but they should not start out as such.
 260         assert_ne!(kind, UnsafetyViolationKind::UnsafeFn);
 261
 262         let source_info = self.source_info;
 263         let lint_root = self.body.source_scopes[self.source_info.scope]
 264             .local_data
 265             .as_ref()
 266             .assert_crate_local()
 267             .lint_root;
 268         self.register_violations(
 269             [&UnsafetyViolation { source_info, lint_root, kind, details }],
 270             [],
 271         );
 272     }
 273
 274     fn register_violations<'a>(
 275         &mut self,
 276         violations: impl IntoIterator<Item = &'a UnsafetyViolation>,
 277         new_used_unsafe_blocks: impl IntoIterator<Item = HirId>,
 278     ) {
 279         let safety = self.body.source_scopes[self.source_info.scope]
 280             .local_data
 281             .as_ref()
 282             .assert_crate_local()
 283             .safety;
 284         match safety {
 285             // `unsafe` blocks are required in safe code
 286             Safety::Safe => violations.into_iter().for_each(|&violation| {
 287                 match violation.kind {
 288                     UnsafetyViolationKind::General => {}
 289                     UnsafetyViolationKind::UnsafeFn => {
 290                         bug!("`UnsafetyViolationKind::UnsafeFn` in an `Safe` context")
 291                     }
 292                 }
 293                 if !self.violations.contains(&violation) {
 294                     self.violations.push(violation)
 295                 }
 296             }),
 297             // With the RFC 2585, no longer allow `unsafe` operations in `unsafe fn`s
 298             Safety::FnUnsafe => violations.into_iter().for_each(|&(mut violation)| {
 299                 violation.kind = UnsafetyViolationKind::UnsafeFn;
 300                 if !self.violations.contains(&violation) {
 301                     self.violations.push(violation)
 302                 }
 303             }),
 304             Safety::BuiltinUnsafe => {}
 305             Safety::ExplicitUnsafe(hir_id) => violations.into_iter().for_each(|_violation| {
 306                 self.used_unsafe_blocks.insert(hir_id);
 307             }),
 308         };
 309
 310         new_used_unsafe_blocks.into_iter().for_each(|hir_id| {
 311             self.used_unsafe_blocks.insert(hir_id);
 312         });
 313     }
 314     fn check_mut_borrowing_layout_constrained_field(
 315         &mut self,
 316         place: Place<'tcx>,
 317         is_mut_use: bool,
 318     ) {
 319         for (place_base, elem) in place.iter_projections().rev() {
 320             match elem {
 321                 // Modifications behind a dereference don't affect the value of
 322                 // the pointer.
 323                 ProjectionElem::Deref => return,
 324                 ProjectionElem::Field(..) => {
 325                     let ty = place_base.ty(&self.body.local_decls, self.tcx).ty;
 326                     if let ty::Adt(def, _) = ty.kind() {
 327                         if self.tcx.layout_scalar_valid_range(def.did())
 328                             != (Bound::Unbounded, Bound::Unbounded)
 329                         {
 330                             let details = if is_mut_use {
 331                                 UnsafetyViolationDetails::MutationOfLayoutConstrainedField
 332
 333                             // Check `is_freeze` as late as possible to avoid cycle errors
 334                             // with opaque types.
 335                             } else if !place
 336                                 .ty(self.body, self.tcx)
 337                                 .ty
 338                                 .is_freeze(self.tcx, self.param_env)
 339                             {
 340                                 UnsafetyViolationDetails::BorrowOfLayoutConstrainedField
 341                             } else {
 342                                 continue;
 343                             };
 344                             self.require_unsafe(UnsafetyViolationKind::General, details);
 345                         }
 346                     }
 347                 }
 348                 _ => {}
 349             }
 350         }
 351     }
 352
 353     /// Checks whether calling `func_did` needs an `unsafe` context or not, i.e. whether
 354     /// the called function has target features the calling function hasn't.
 355     fn check_target_features(&mut self, func_did: DefId) {
 356         // Unsafety isn't required on wasm targets. For more information see
 357         // the corresponding check in typeck/src/collect.rs
 358         if self.tcx.sess.target.options.is_like_wasm {
 359             return;
 360         }
 361
 362         let callee_features = &self.tcx.codegen_fn_attrs(func_did).target_features;
 363         // The body might be a constant, so it doesn't have codegen attributes.
 364         let self_features = &self.tcx.body_codegen_attrs(self.body_did.to_def_id()).target_features;
 365
 366         // Is `callee_features` a subset of `calling_features`?
 367         if !callee_features.iter().all(|feature| self_features.contains(feature)) {
 368             self.require_unsafe(
 369                 UnsafetyViolationKind::General,
 370                 UnsafetyViolationDetails::CallToFunctionWith,
 371             )
 372         }
 373     }
 374 }
 375
 376 pub(crate) fn provide(providers: &mut Providers) {
 377     *providers = Providers {
 378         unsafety_check_result: |tcx, def_id| {
 379             if let Some(def) = ty::WithOptConstParam::try_lookup(def_id, tcx) {
 380                 tcx.unsafety_check_result_for_const_arg(def)
 381             } else {
 382                 unsafety_check_result(tcx, ty::WithOptConstParam::unknown(def_id))
 383             }
 384         },
 385         unsafety_check_result_for_const_arg: |tcx, (did, param_did)| {
 386             unsafety_check_result(
 387                 tcx,
 388                 ty::WithOptConstParam { did, const_param_did: Some(param_did) },
 389             )
 390         },
 391         ..*providers
 392     };
 393 }
 394
 395 /// Context information for [`UnusedUnsafeVisitor`] traversal,
 396 /// saves (innermost) relevant context
 397 #[derive(Copy, Clone, Debug)]
 398 enum Context {
 399     Safe,
 400     /// in an `unsafe fn`
 401     UnsafeFn(HirId),
 402     /// in a *used* `unsafe` block
 403     /// (i.e. a block without unused-unsafe warning)
 404     UnsafeBlock(HirId),
 405 }
 406
 407 struct UnusedUnsafeVisitor<'a, 'tcx> {
 408     tcx: TyCtxt<'tcx>,
 409     used_unsafe_blocks: &'a FxHashSet<HirId>,
 410     context: Context,
 411     unused_unsafes: &'a mut Vec<(HirId, UnusedUnsafe)>,
 412 }
 413
 414 impl<'tcx> intravisit::Visitor<'tcx> for UnusedUnsafeVisitor<'_, 'tcx> {
 415     fn visit_block(&mut self, block: &'tcx hir::Block<'tcx>) {
 416         if let hir::BlockCheckMode::UnsafeBlock(hir::UnsafeSource::UserProvided) = block.rules {
 417             let used = match self.tcx.lint_level_at_node(UNUSED_UNSAFE, block.hir_id) {
 418                 (Level::Allow, _) => true,
 419                 _ => self.used_unsafe_blocks.contains(&block.hir_id),
 420             };
 421             let unused_unsafe = match (self.context, used) {
 422                 (_, false) => UnusedUnsafe::Unused,
 423                 (Context::Safe, true) | (Context::UnsafeFn(_), true) => {
 424                     let previous_context = self.context;
 425                     self.context = Context::UnsafeBlock(block.hir_id);
 426                     intravisit::walk_block(self, block);
 427                     self.context = previous_context;
 428                     return;
 429                 }
 430                 (Context::UnsafeBlock(hir_id), true) => UnusedUnsafe::InUnsafeBlock(hir_id),
 431             };
 432             self.unused_unsafes.push((block.hir_id, unused_unsafe));
 433         }
 434         intravisit::walk_block(self, block);
 435     }
 436
 437     fn visit_anon_const(&mut self, c: &'tcx hir::AnonConst) {
 438         if matches!(self.tcx.def_kind(c.def_id), DefKind::InlineConst) {
 439             self.visit_body(self.tcx.hir().body(c.body))
 440         }
 441     }
 442
 443     fn visit_fn(
 444         &mut self,
 445         fk: intravisit::FnKind<'tcx>,
 446         _fd: &'tcx hir::FnDecl<'tcx>,
 447         b: hir::BodyId,
 448         _s: rustc_span::Span,
 449         _id: LocalDefId,
 450     ) {
 451         if matches!(fk, intravisit::FnKind::Closure) {
 452             self.visit_body(self.tcx.hir().body(b))
 453         }
 454     }
 455 }
 456
 457 fn check_unused_unsafe(
 458     tcx: TyCtxt<'_>,
 459     def_id: LocalDefId,
 460     used_unsafe_blocks: &FxHashSet<HirId>,
 461 ) -> Vec<(HirId, UnusedUnsafe)> {
 462     let body_id = tcx.hir().maybe_body_owned_by(def_id);
 463
 464     let Some(body_id) = body_id else {
 465         debug!("check_unused_unsafe({:?}) - no body found", def_id);
 466         return vec![];
 467     };
 468
 469     let body = tcx.hir().body(body_id);
 470     let hir_id = tcx.hir().local_def_id_to_hir_id(def_id);
 471     let context = match tcx.hir().fn_sig_by_hir_id(hir_id) {
 472         Some(sig) if sig.header.unsafety == hir::Unsafety::Unsafe => Context::UnsafeFn(hir_id),
 473         _ => Context::Safe,
 474     };
 475
 476     debug!(
 477         "check_unused_unsafe({:?}, context={:?}, body={:?}, used_unsafe_blocks={:?})",
 478         def_id, body, context, used_unsafe_blocks
 479     );
 480
 481     let mut unused_unsafes = vec![];
 482
 483     let mut visitor = UnusedUnsafeVisitor {
 484         tcx,
 485         used_unsafe_blocks,
 486         context,
 487         unused_unsafes: &mut unused_unsafes,
 488     };
 489     intravisit::Visitor::visit_body(&mut visitor, body);
 490
 491     unused_unsafes
 492 }
 493
 494 fn unsafety_check_result(
 495     tcx: TyCtxt<'_>,
 496     def: ty::WithOptConstParam<LocalDefId>,
 497 ) -> &UnsafetyCheckResult {
 498     debug!("unsafety_violations({:?})", def);
 499
 500     // N.B., this borrow is valid because all the consumers of
 501     // `mir_built` force this.
 502     let body = &tcx.mir_built(def).borrow();
 503
 504     if body.is_custom_mir() {
 505         return tcx.arena.alloc(UnsafetyCheckResult {
 506             violations: Vec::new(),
 507             used_unsafe_blocks: FxHashSet::default(),
 508             unused_unsafes: Some(Vec::new()),
 509         });
 510     }
 511
 512     let param_env = tcx.param_env(def.did);
 513
 514     let mut checker = UnsafetyChecker::new(body, def.did, tcx, param_env);
 515     checker.visit_body(&body);
 516
 517     let unused_unsafes = (!tcx.is_typeck_child(def.did.to_def_id()))
 518         .then(|| check_unused_unsafe(tcx, def.did, &checker.used_unsafe_blocks));
 519
 520     tcx.arena.alloc(UnsafetyCheckResult {
 521         violations: checker.violations,
 522         used_unsafe_blocks: checker.used_unsafe_blocks,
 523         unused_unsafes,
 524     })
 525 }
 526
 527 fn report_unused_unsafe(tcx: TyCtxt<'_>, kind: UnusedUnsafe, id: HirId) {
 528     let span = tcx.sess.source_map().guess_head_span(tcx.hir().span(id));
 529     let msg = "unnecessary `unsafe` block";
 530     tcx.struct_span_lint_hir(UNUSED_UNSAFE, id, span, msg, |lint| {
 531         lint.span_label(span, msg);
 532         match kind {
 533             UnusedUnsafe::Unused => {}
 534             UnusedUnsafe::InUnsafeBlock(id) => {
 535                 lint.span_label(
 536                     tcx.sess.source_map().guess_head_span(tcx.hir().span(id)),
 537                     "because it's nested under this `unsafe` block",
 538                 );
 539             }
 540         }
 541
 542         lint
 543     });
 544 }
 545
 546 pub fn check_unsafety(tcx: TyCtxt<'_>, def_id: LocalDefId) {
 547     debug!("check_unsafety({:?})", def_id);
 548
 549     // closures and inline consts are handled by their parent fn.
 550     if tcx.is_typeck_child(def_id.to_def_id()) {
 551         return;
 552     }
 553
 554     let UnsafetyCheckResult { violations, unused_unsafes, .. } = tcx.unsafety_check_result(def_id);
 555
 556     for &UnsafetyViolation { source_info, lint_root, kind, details } in violations.iter() {
 557         let (description, note) = details.description_and_note();
 558
 559         match kind {
 560             UnsafetyViolationKind::General => {
 561                 // once
 562                 let unsafe_fn_msg = if unsafe_op_in_unsafe_fn_allowed(tcx, lint_root) {
 563                     " function or"
 564                 } else {
 565                     ""
 566                 };
 567
 568                 let mut err = struct_span_err!(
 569                     tcx.sess,
 570                     source_info.span,
 571                     E0133,
 572                     "{} is unsafe and requires unsafe{} block",
 573                     description,
 574                     unsafe_fn_msg,
 575                 );
 576                 err.span_label(source_info.span, description).note(note);
 577                 let note_non_inherited = tcx.hir().parent_iter(lint_root).find(|(id, node)| {
 578                     if let Node::Expr(block) = node
 579                         && let ExprKind::Block(block, _) = block.kind
 580                         && let BlockCheckMode::UnsafeBlock(_) = block.rules
 581                     {
 582                         true
 583                     }
 584                     else if let Some(sig) = tcx.hir().fn_sig_by_hir_id(*id)
 585                         && sig.header.is_unsafe()
 586                     {
 587                         true
 588                     } else {
 589                         false
 590                     }
 591                 });
 592                 if let Some((id, _)) = note_non_inherited {
 593                     let span = tcx.hir().span(id);
 594                     err.span_label(
 595                         tcx.sess.source_map().guess_head_span(span),
 596                         "items do not inherit unsafety from separate enclosing items",
 597                     );
 598                 }
 599
 600                 err.emit();
 601             }
 602             UnsafetyViolationKind::UnsafeFn => tcx.struct_span_lint_hir(
 603                 UNSAFE_OP_IN_UNSAFE_FN,
 604                 lint_root,
 605                 source_info.span,
 606                 format!("{} is unsafe and requires unsafe block (error E0133)", description,),
 607                 |lint| lint.span_label(source_info.span, description).note(note),
 608             ),
 609         }
 610     }
 611
 612     for &(block_id, kind) in unused_unsafes.as_ref().unwrap() {
 613         report_unused_unsafe(tcx, kind, block_id);
 614     }
 615 }
 616
 617 fn unsafe_op_in_unsafe_fn_allowed(tcx: TyCtxt<'_>, id: HirId) -> bool {
 618     tcx.lint_level_at_node(UNSAFE_OP_IN_UNSAFE_FN, id).0 == Level::Allow
 619 }