compiler/rustc_mir_transform/src/check_unsafety.rs

   1 use rustc_data_structures::fx::FxHashMap;
   2 use rustc_errors::struct_span_err;
   3 use rustc_hir as hir;
   4 use rustc_hir::def_id::{DefId, LocalDefId};
   5 use rustc_hir::hir_id::HirId;
   6 use rustc_hir::intravisit;
   7 use rustc_middle::mir::visit::{MutatingUseContext, PlaceContext, Visitor};
   8 use rustc_middle::ty::query::Providers;
   9 use rustc_middle::ty::{self, TyCtxt};
  10 use rustc_middle::{lint, mir::*};
  11 use rustc_session::lint::builtin::{UNSAFE_OP_IN_UNSAFE_FN, UNUSED_UNSAFE};
  12 use rustc_session::lint::Level;
  13
  14 use std::collections::hash_map;
  15 use std::ops::Bound;
  16
  17 pub struct UnsafetyChecker<'a, 'tcx> {
  18     body: &'a Body<'tcx>,
  19     body_did: LocalDefId,
  20     violations: Vec<UnsafetyViolation>,
  21     source_info: SourceInfo,
  22     tcx: TyCtxt<'tcx>,
  23     param_env: ty::ParamEnv<'tcx>,
  24
  25     /// Used `unsafe` blocks in this function. This is used for the "unused_unsafe" lint.
  26     ///
  27     /// The keys are the used `unsafe` blocks, the UnusedUnsafeKind indicates whether
  28     /// or not any of the usages happen at a place that doesn't allow `unsafe_op_in_unsafe_fn`.
  29     used_unsafe_blocks: FxHashMap<HirId, UsedUnsafeBlockData>,
  30 }
  31
  32 impl<'a, 'tcx> UnsafetyChecker<'a, 'tcx> {
  33     fn new(
  34         body: &'a Body<'tcx>,
  35         body_did: LocalDefId,
  36         tcx: TyCtxt<'tcx>,
  37         param_env: ty::ParamEnv<'tcx>,
  38     ) -> Self {
  39         Self {
  40             body,
  41             body_did,
  42             violations: vec![],
  43             source_info: SourceInfo::outermost(body.span),
  44             tcx,
  45             param_env,
  46             used_unsafe_blocks: Default::default(),
  47         }
  48     }
  49 }
  50
  51 impl<'tcx> Visitor<'tcx> for UnsafetyChecker<'_, 'tcx> {
  52     fn visit_terminator(&mut self, terminator: &Terminator<'tcx>, location: Location) {
  53         self.source_info = terminator.source_info;
  54         match terminator.kind {
  55             TerminatorKind::Goto { .. }
  56             | TerminatorKind::SwitchInt { .. }
  57             | TerminatorKind::Drop { .. }
  58             | TerminatorKind::Yield { .. }
  59             | TerminatorKind::Assert { .. }
  60             | TerminatorKind::DropAndReplace { .. }
  61             | TerminatorKind::GeneratorDrop
  62             | TerminatorKind::Resume
  63             | TerminatorKind::Abort
  64             | TerminatorKind::Return
  65             | TerminatorKind::Unreachable
  66             | TerminatorKind::FalseEdge { .. }
  67             | TerminatorKind::FalseUnwind { .. } => {
  68                 // safe (at least as emitted during MIR construction)
  69             }
  70
  71             TerminatorKind::Call { ref func, .. } => {
  72                 let func_ty = func.ty(self.body, self.tcx);
  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 ty::FnDef(func_id, _) = func_ty.kind() {
  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::Nop => {
 107                 // safe (at least as emitted during MIR construction)
 108             }
 109
 110             StatementKind::CopyNonOverlapping(..) => unreachable!(),
 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.expect_local());
 131                     self.register_violations(
 132                         violations,
 133                         used_unsafe_blocks.iter().map(|(&h, &d)| (h, d)),
 134                     );
 135                 }
 136             },
 137             _ => {}
 138         }
 139         self.super_rvalue(rvalue, location);
 140     }
 141
 142     fn visit_place(&mut self, place: &Place<'tcx>, context: PlaceContext, _location: Location) {
 143         // On types with `scalar_valid_range`, prevent
 144         // * `&mut x.field`
 145         // * `x.field = y;`
 146         // * `&x.field` if `field`'s type has interior mutability
 147         // because either of these would allow modifying the layout constrained field and
 148         // insert values that violate the layout constraints.
 149         if context.is_mutating_use() || context.is_borrow() {
 150             self.check_mut_borrowing_layout_constrained_field(*place, context.is_mutating_use());
 151         }
 152
 153         // Some checks below need the extra meta info of the local declaration.
 154         let decl = &self.body.local_decls[place.local];
 155
 156         // Check the base local: it might be an unsafe-to-access static. We only check derefs of the
 157         // temporary holding the static pointer to avoid duplicate errors
 158         // <https://github.com/rust-lang/rust/pull/78068#issuecomment-731753506>.
 159         if decl.internal && place.projection.first() == Some(&ProjectionElem::Deref) {
 160             // If the projection root is an artificial local that we introduced when
 161             // desugaring `static`, give a more specific error message
 162             // (avoid the general "raw pointer" clause below, that would only be confusing).
 163             if let Some(box LocalInfo::StaticRef { def_id, .. }) = decl.local_info {
 164                 if self.tcx.is_mutable_static(def_id) {
 165                     self.require_unsafe(
 166                         UnsafetyViolationKind::General,
 167                         UnsafetyViolationDetails::UseOfMutableStatic,
 168                     );
 169                     return;
 170                 } else if self.tcx.is_foreign_item(def_id) {
 171                     self.require_unsafe(
 172                         UnsafetyViolationKind::General,
 173                         UnsafetyViolationDetails::UseOfExternStatic,
 174                     );
 175                     return;
 176                 }
 177             }
 178         }
 179
 180         // Check for raw pointer `Deref`.
 181         for (base, proj) in place.iter_projections() {
 182             if proj == ProjectionElem::Deref {
 183                 let base_ty = base.ty(self.body, self.tcx).ty;
 184                 if base_ty.is_unsafe_ptr() {
 185                     self.require_unsafe(
 186                         UnsafetyViolationKind::General,
 187                         UnsafetyViolationDetails::DerefOfRawPointer,
 188                     )
 189                 }
 190             }
 191         }
 192
 193         // Check for union fields. For this we traverse right-to-left, as the last `Deref` changes
 194         // whether we *read* the union field or potentially *write* to it (if this place is being assigned to).
 195         let mut saw_deref = false;
 196         for (base, proj) in place.iter_projections().rev() {
 197             if proj == ProjectionElem::Deref {
 198                 saw_deref = true;
 199                 continue;
 200             }
 201
 202             let base_ty = base.ty(self.body, self.tcx).ty;
 203             if base_ty.is_union() {
 204                 // If we did not hit a `Deref` yet and the overall place use is an assignment, the
 205                 // rules are different.
 206                 let assign_to_field = !saw_deref
 207                     && matches!(
 208                         context,
 209                         PlaceContext::MutatingUse(
 210                             MutatingUseContext::Store
 211                                 | MutatingUseContext::Drop
 212                                 | MutatingUseContext::AsmOutput
 213                         )
 214                     );
 215                 // If this is just an assignment, determine if the assigned type needs dropping.
 216                 if assign_to_field {
 217                     // We have to check the actual type of the assignment, as that determines if the
 218                     // old value is being dropped.
 219                     let assigned_ty = place.ty(&self.body.local_decls, self.tcx).ty;
 220                     // To avoid semver hazard, we only consider `Copy` and `ManuallyDrop` non-dropping.
 221                     let manually_drop = assigned_ty
 222                         .ty_adt_def()
 223                         .map_or(false, |adt_def| adt_def.is_manually_drop());
 224                     let nodrop = manually_drop
 225                         || assigned_ty.is_copy_modulo_regions(
 226                             self.tcx.at(self.source_info.span),
 227                             self.param_env,
 228                         );
 229                     if !nodrop {
 230                         self.require_unsafe(
 231                             UnsafetyViolationKind::General,
 232                             UnsafetyViolationDetails::AssignToDroppingUnionField,
 233                         );
 234                     } else {
 235                         // write to non-drop union field, safe
 236                     }
 237                 } else {
 238                     self.require_unsafe(
 239                         UnsafetyViolationKind::General,
 240                         UnsafetyViolationDetails::AccessToUnionField,
 241                     )
 242                 }
 243             }
 244         }
 245     }
 246 }
 247
 248 impl<'tcx> UnsafetyChecker<'_, 'tcx> {
 249     fn require_unsafe(&mut self, kind: UnsafetyViolationKind, details: UnsafetyViolationDetails) {
 250         // Violations can turn out to be `UnsafeFn` during analysis, but they should not start out as such.
 251         assert_ne!(kind, UnsafetyViolationKind::UnsafeFn);
 252
 253         let source_info = self.source_info;
 254         let lint_root = self.body.source_scopes[self.source_info.scope]
 255             .local_data
 256             .as_ref()
 257             .assert_crate_local()
 258             .lint_root;
 259         self.register_violations(
 260             [&UnsafetyViolation { source_info, lint_root, kind, details }],
 261             [],
 262         );
 263     }
 264
 265     fn register_violations<'a>(
 266         &mut self,
 267         violations: impl IntoIterator<Item = &'a UnsafetyViolation>,
 268         new_used_unsafe_blocks: impl IntoIterator<Item = (HirId, UsedUnsafeBlockData)>,
 269     ) {
 270         use UsedUnsafeBlockData::{AllAllowedInUnsafeFn, SomeDisallowedInUnsafeFn};
 271
 272         let update_entry = |this: &mut Self, hir_id, new_usage| {
 273             match this.used_unsafe_blocks.entry(hir_id) {
 274                 hash_map::Entry::Occupied(mut entry) => {
 275                     if new_usage == SomeDisallowedInUnsafeFn {
 276                         *entry.get_mut() = SomeDisallowedInUnsafeFn;
 277                     }
 278                 }
 279                 hash_map::Entry::Vacant(entry) => {
 280                     entry.insert(new_usage);
 281                 }
 282             };
 283         };
 284         let safety = self.body.source_scopes[self.source_info.scope]
 285             .local_data
 286             .as_ref()
 287             .assert_crate_local()
 288             .safety;
 289         match safety {
 290             // `unsafe` blocks are required in safe code
 291             Safety::Safe => violations.into_iter().for_each(|&violation| {
 292                 match violation.kind {
 293                     UnsafetyViolationKind::General => {}
 294                     UnsafetyViolationKind::UnsafeFn => {
 295                         bug!("`UnsafetyViolationKind::UnsafeFn` in an `Safe` context")
 296                     }
 297                 }
 298                 if !self.violations.contains(&violation) {
 299                     self.violations.push(violation)
 300                 }
 301             }),
 302             // With the RFC 2585, no longer allow `unsafe` operations in `unsafe fn`s
 303             Safety::FnUnsafe => violations.into_iter().for_each(|&(mut violation)| {
 304                 violation.kind = UnsafetyViolationKind::UnsafeFn;
 305                 if !self.violations.contains(&violation) {
 306                     self.violations.push(violation)
 307                 }
 308             }),
 309             Safety::BuiltinUnsafe => {}
 310             Safety::ExplicitUnsafe(hir_id) => violations.into_iter().for_each(|violation| {
 311                 update_entry(
 312                     self,
 313                     hir_id,
 314                     match self.tcx.lint_level_at_node(UNSAFE_OP_IN_UNSAFE_FN, violation.lint_root).0
 315                     {
 316                         Level::Allow => AllAllowedInUnsafeFn(violation.lint_root),
 317                         _ => SomeDisallowedInUnsafeFn,
 318                     },
 319                 )
 320             }),
 321         };
 322
 323         new_used_unsafe_blocks
 324             .into_iter()
 325             .for_each(|(hir_id, usage_data)| update_entry(self, hir_id, usage_data));
 326     }
 327     fn check_mut_borrowing_layout_constrained_field(
 328         &mut self,
 329         place: Place<'tcx>,
 330         is_mut_use: bool,
 331     ) {
 332         for (place_base, elem) in place.iter_projections().rev() {
 333             match elem {
 334                 // Modifications behind a dereference don't affect the value of
 335                 // the pointer.
 336                 ProjectionElem::Deref => return,
 337                 ProjectionElem::Field(..) => {
 338                     let ty = place_base.ty(&self.body.local_decls, self.tcx).ty;
 339                     if let ty::Adt(def, _) = ty.kind() {
 340                         if self.tcx.layout_scalar_valid_range(def.did())
 341                             != (Bound::Unbounded, Bound::Unbounded)
 342                         {
 343                             let details = if is_mut_use {
 344                                 UnsafetyViolationDetails::MutationOfLayoutConstrainedField
 345
 346                             // Check `is_freeze` as late as possible to avoid cycle errors
 347                             // with opaque types.
 348                             } else if !place
 349                                 .ty(self.body, self.tcx)
 350                                 .ty
 351                                 .is_freeze(self.tcx.at(self.source_info.span), self.param_env)
 352                             {
 353                                 UnsafetyViolationDetails::BorrowOfLayoutConstrainedField
 354                             } else {
 355                                 continue;
 356                             };
 357                             self.require_unsafe(UnsafetyViolationKind::General, details);
 358                         }
 359                     }
 360                 }
 361                 _ => {}
 362             }
 363         }
 364     }
 365
 366     /// Checks whether calling `func_did` needs an `unsafe` context or not, i.e. whether
 367     /// the called function has target features the calling function hasn't.
 368     fn check_target_features(&mut self, func_did: DefId) {
 369         // Unsafety isn't required on wasm targets. For more information see
 370         // the corresponding check in typeck/src/collect.rs
 371         if self.tcx.sess.target.options.is_like_wasm {
 372             return;
 373         }
 374
 375         let callee_features = &self.tcx.codegen_fn_attrs(func_did).target_features;
 376         let self_features = &self.tcx.codegen_fn_attrs(self.body_did).target_features;
 377
 378         // Is `callee_features` a subset of `calling_features`?
 379         if !callee_features.iter().all(|feature| self_features.contains(feature)) {
 380             self.require_unsafe(
 381                 UnsafetyViolationKind::General,
 382                 UnsafetyViolationDetails::CallToFunctionWith,
 383             )
 384         }
 385     }
 386 }
 387
 388 pub(crate) fn provide(providers: &mut Providers) {
 389     *providers = Providers {
 390         unsafety_check_result: |tcx, def_id| {
 391             if let Some(def) = ty::WithOptConstParam::try_lookup(def_id, tcx) {
 392                 tcx.unsafety_check_result_for_const_arg(def)
 393             } else {
 394                 unsafety_check_result(tcx, ty::WithOptConstParam::unknown(def_id))
 395             }
 396         },
 397         unsafety_check_result_for_const_arg: |tcx, (did, param_did)| {
 398             unsafety_check_result(
 399                 tcx,
 400                 ty::WithOptConstParam { did, const_param_did: Some(param_did) },
 401             )
 402         },
 403         ..*providers
 404     };
 405 }
 406
 407 /// Context information for [`UnusedUnsafeVisitor`] traversal,
 408 /// saves (innermost) relevant context
 409 #[derive(Copy, Clone, Debug)]
 410 enum Context {
 411     Safe,
 412     /// in an `unsafe fn`
 413     UnsafeFn(HirId),
 414     /// in a *used* `unsafe` block
 415     /// (i.e. a block without unused-unsafe warning)
 416     UnsafeBlock(HirId),
 417 }
 418
 419 struct UnusedUnsafeVisitor<'a, 'tcx> {
 420     tcx: TyCtxt<'tcx>,
 421     used_unsafe_blocks: &'a FxHashMap<HirId, UsedUnsafeBlockData>,
 422     context: Context,
 423     unused_unsafes: &'a mut Vec<(HirId, UnusedUnsafe)>,
 424 }
 425
 426 impl<'tcx> intravisit::Visitor<'tcx> for UnusedUnsafeVisitor<'_, 'tcx> {
 427     fn visit_block(&mut self, block: &'tcx hir::Block<'tcx>) {
 428         use UsedUnsafeBlockData::{AllAllowedInUnsafeFn, SomeDisallowedInUnsafeFn};
 429
 430         if let hir::BlockCheckMode::UnsafeBlock(hir::UnsafeSource::UserProvided) = block.rules {
 431             let used = match self.tcx.lint_level_at_node(UNUSED_UNSAFE, block.hir_id) {
 432                 (Level::Allow, _) => Some(SomeDisallowedInUnsafeFn),
 433                 _ => self.used_unsafe_blocks.get(&block.hir_id).copied(),
 434             };
 435             let unused_unsafe = match (self.context, used) {
 436                 (_, None) => UnusedUnsafe::Unused,
 437                 (Context::Safe, Some(_))
 438                 | (Context::UnsafeFn(_), Some(SomeDisallowedInUnsafeFn)) => {
 439                     let previous_context = self.context;
 440                     self.context = Context::UnsafeBlock(block.hir_id);
 441                     intravisit::walk_block(self, block);
 442                     self.context = previous_context;
 443                     return;
 444                 }
 445                 (Context::UnsafeFn(hir_id), Some(AllAllowedInUnsafeFn(lint_root))) => {
 446                     UnusedUnsafe::InUnsafeFn(hir_id, lint_root)
 447                 }
 448                 (Context::UnsafeBlock(hir_id), Some(_)) => UnusedUnsafe::InUnsafeBlock(hir_id),
 449             };
 450             self.unused_unsafes.push((block.hir_id, unused_unsafe));
 451         }
 452         intravisit::walk_block(self, block);
 453     }
 454
 455     fn visit_fn(
 456         &mut self,
 457         fk: intravisit::FnKind<'tcx>,
 458         _fd: &'tcx hir::FnDecl<'tcx>,
 459         b: hir::BodyId,
 460         _s: rustc_span::Span,
 461         _id: HirId,
 462     ) {
 463         if matches!(fk, intravisit::FnKind::Closure) {
 464             self.visit_body(self.tcx.hir().body(b))
 465         }
 466     }
 467 }
 468
 469 fn check_unused_unsafe(
 470     tcx: TyCtxt<'_>,
 471     def_id: LocalDefId,
 472     used_unsafe_blocks: &FxHashMap<HirId, UsedUnsafeBlockData>,
 473 ) -> Vec<(HirId, UnusedUnsafe)> {
 474     let hir_id = tcx.hir().local_def_id_to_hir_id(def_id);
 475     let body_id = tcx.hir().maybe_body_owned_by(hir_id);
 476
 477     let Some(body_id) = body_id else {
 478         debug!("check_unused_unsafe({:?}) - no body found", def_id);
 479         return vec![];
 480     };
 481     let body = tcx.hir().body(body_id);
 482
 483     let context = match tcx.hir().fn_sig_by_hir_id(hir_id) {
 484         Some(sig) if sig.header.unsafety == hir::Unsafety::Unsafe => Context::UnsafeFn(hir_id),
 485         _ => Context::Safe,
 486     };
 487
 488     debug!(
 489         "check_unused_unsafe({:?}, context={:?}, body={:?}, used_unsafe_blocks={:?})",
 490         def_id, body, context, used_unsafe_blocks
 491     );
 492
 493     let mut unused_unsafes = vec![];
 494
 495     let mut visitor = UnusedUnsafeVisitor {
 496         tcx,
 497         used_unsafe_blocks,
 498         context,
 499         unused_unsafes: &mut unused_unsafes,
 500     };
 501     intravisit::Visitor::visit_body(&mut visitor, body);
 502
 503     unused_unsafes
 504 }
 505
 506 fn unsafety_check_result<'tcx>(
 507     tcx: TyCtxt<'tcx>,
 508     def: ty::WithOptConstParam<LocalDefId>,
 509 ) -> &'tcx UnsafetyCheckResult {
 510     debug!("unsafety_violations({:?})", def);
 511
 512     // N.B., this borrow is valid because all the consumers of
 513     // `mir_built` force this.
 514     let body = &tcx.mir_built(def).borrow();
 515
 516     let param_env = tcx.param_env(def.did);
 517
 518     let mut checker = UnsafetyChecker::new(body, def.did, tcx, param_env);
 519     checker.visit_body(&body);
 520
 521     let unused_unsafes = (!tcx.is_closure(def.did.to_def_id()))
 522         .then(|| check_unused_unsafe(tcx, def.did, &checker.used_unsafe_blocks));
 523
 524     tcx.arena.alloc(UnsafetyCheckResult {
 525         violations: checker.violations,
 526         used_unsafe_blocks: checker.used_unsafe_blocks,
 527         unused_unsafes,
 528     })
 529 }
 530
 531 fn report_unused_unsafe(tcx: TyCtxt<'_>, kind: UnusedUnsafe, id: HirId) {
 532     let span = tcx.sess.source_map().guess_head_span(tcx.hir().span(id));
 533     tcx.struct_span_lint_hir(UNUSED_UNSAFE, id, span, |lint| {
 534         let msg = "unnecessary `unsafe` block";
 535         let mut db = lint.build(msg);
 536         db.span_label(span, msg);
 537         match kind {
 538             UnusedUnsafe::Unused => {}
 539             UnusedUnsafe::InUnsafeBlock(id) => {
 540                 db.span_label(
 541                     tcx.sess.source_map().guess_head_span(tcx.hir().span(id)),
 542                     format!("because it's nested under this `unsafe` block"),
 543                 );
 544             }
 545             UnusedUnsafe::InUnsafeFn(id, usage_lint_root) => {
 546                 db.span_label(
 547                     tcx.sess.source_map().guess_head_span(tcx.hir().span(id)),
 548                     format!("because it's nested under this `unsafe` fn"),
 549                 )
 550                 .note(
 551                     "this `unsafe` block does contain unsafe operations, \
 552                     but those are already allowed in an `unsafe fn`",
 553                 );
 554                 let (level, source) =
 555                     tcx.lint_level_at_node(UNSAFE_OP_IN_UNSAFE_FN, usage_lint_root);
 556                 assert_eq!(level, Level::Allow);
 557                 lint::explain_lint_level_source(
 558                     UNSAFE_OP_IN_UNSAFE_FN,
 559                     Level::Allow,
 560                     source,
 561                     &mut db,
 562                 );
 563             }
 564         }
 565
 566         db.emit();
 567     });
 568 }
 569
 570 pub fn check_unsafety(tcx: TyCtxt<'_>, def_id: LocalDefId) {
 571     debug!("check_unsafety({:?})", def_id);
 572
 573     // closures are handled by their parent fn.
 574     if tcx.is_closure(def_id.to_def_id()) {
 575         return;
 576     }
 577
 578     let UnsafetyCheckResult { violations, unused_unsafes, .. } = tcx.unsafety_check_result(def_id);
 579
 580     for &UnsafetyViolation { source_info, lint_root, kind, details } in violations.iter() {
 581         let (description, note) = details.description_and_note();
 582
 583         // Report an error.
 584         let unsafe_fn_msg =
 585             if unsafe_op_in_unsafe_fn_allowed(tcx, lint_root) { " function or" } else { "" };
 586
 587         match kind {
 588             UnsafetyViolationKind::General => {
 589                 // once
 590                 struct_span_err!(
 591                     tcx.sess,
 592                     source_info.span,
 593                     E0133,
 594                     "{} is unsafe and requires unsafe{} block",
 595                     description,
 596                     unsafe_fn_msg,
 597                 )
 598                 .span_label(source_info.span, description)
 599                 .note(note)
 600                 .emit();
 601             }
 602             UnsafetyViolationKind::UnsafeFn => tcx.struct_span_lint_hir(
 603                 UNSAFE_OP_IN_UNSAFE_FN,
 604                 lint_root,
 605                 source_info.span,
 606                 |lint| {
 607                     lint.build(&format!(
 608                         "{} is unsafe and requires unsafe block (error E0133)",
 609                         description,
 610                     ))
 611                     .span_label(source_info.span, description)
 612                     .note(note)
 613                     .emit();
 614                 },
 615             ),
 616         }
 617     }
 618
 619     for &(block_id, kind) in unused_unsafes.as_ref().unwrap() {
 620         report_unused_unsafe(tcx, kind, block_id);
 621     }
 622 }
 623
 624 fn unsafe_op_in_unsafe_fn_allowed(tcx: TyCtxt<'_>, id: HirId) -> bool {
 625     tcx.lint_level_at_node(UNSAFE_OP_IN_UNSAFE_FN, id).0 == Level::Allow
 626 }