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 func_id =
  74                     if let ty::FnDef(func_id, _) = func_ty.kind() { Some(func_id) } else { None };
  75                 let sig = func_ty.fn_sig(self.tcx);
  76                 if let hir::Unsafety::Unsafe = sig.unsafety() {
  77                     self.require_unsafe(
  78                         UnsafetyViolationKind::General,
  79                         UnsafetyViolationDetails::CallToUnsafeFunction,
  80                     )
  81                 }
  82
  83                 if let Some(func_id) = func_id {
  84                     self.check_target_features(*func_id);
  85                 }
  86             }
  87
  88             TerminatorKind::InlineAsm { .. } => self.require_unsafe(
  89                 UnsafetyViolationKind::General,
  90                 UnsafetyViolationDetails::UseOfInlineAssembly,
  91             ),
  92         }
  93         self.super_terminator(terminator, location);
  94     }
  95
  96     fn visit_statement(&mut self, statement: &Statement<'tcx>, location: Location) {
  97         self.source_info = statement.source_info;
  98         match statement.kind {
  99             StatementKind::Assign(..)
 100             | StatementKind::FakeRead(..)
 101             | StatementKind::SetDiscriminant { .. }
 102             | StatementKind::Deinit(..)
 103             | StatementKind::StorageLive(..)
 104             | StatementKind::StorageDead(..)
 105             | StatementKind::Retag { .. }
 106             | StatementKind::AscribeUserType(..)
 107             | StatementKind::Coverage(..)
 108             | StatementKind::Nop => {
 109                 // safe (at least as emitted during MIR construction)
 110             }
 111
 112             StatementKind::CopyNonOverlapping(..) => unreachable!(),
 113         }
 114         self.super_statement(statement, location);
 115     }
 116
 117     fn visit_rvalue(&mut self, rvalue: &Rvalue<'tcx>, location: Location) {
 118         match rvalue {
 119             Rvalue::Aggregate(box ref aggregate, _) => match aggregate {
 120                 &AggregateKind::Array(..) | &AggregateKind::Tuple => {}
 121                 &AggregateKind::Adt(adt_did, ..) => {
 122                     match self.tcx.layout_scalar_valid_range(adt_did) {
 123                         (Bound::Unbounded, Bound::Unbounded) => {}
 124                         _ => self.require_unsafe(
 125                             UnsafetyViolationKind::General,
 126                             UnsafetyViolationDetails::InitializingTypeWith,
 127                         ),
 128                     }
 129                 }
 130                 &AggregateKind::Closure(def_id, _) | &AggregateKind::Generator(def_id, _, _) => {
 131                     let UnsafetyCheckResult { violations, used_unsafe_blocks, .. } =
 132                         self.tcx.unsafety_check_result(def_id.expect_local());
 133                     self.register_violations(
 134                         violations,
 135                         used_unsafe_blocks.iter().map(|(&h, &d)| (h, d)),
 136                     );
 137                 }
 138             },
 139             _ => {}
 140         }
 141         self.super_rvalue(rvalue, location);
 142     }
 143
 144     fn visit_place(&mut self, place: &Place<'tcx>, context: PlaceContext, _location: Location) {
 145         // On types with `scalar_valid_range`, prevent
 146         // * `&mut x.field`
 147         // * `x.field = y;`
 148         // * `&x.field` if `field`'s type has interior mutability
 149         // because either of these would allow modifying the layout constrained field and
 150         // insert values that violate the layout constraints.
 151         if context.is_mutating_use() || context.is_borrow() {
 152             self.check_mut_borrowing_layout_constrained_field(*place, context.is_mutating_use());
 153         }
 154
 155         // Some checks below need the extra meta info of the local declaration.
 156         let decl = &self.body.local_decls[place.local];
 157
 158         // Check the base local: it might be an unsafe-to-access static. We only check derefs of the
 159         // temporary holding the static pointer to avoid duplicate errors
 160         // <https://github.com/rust-lang/rust/pull/78068#issuecomment-731753506>.
 161         if decl.internal && place.projection.first() == Some(&ProjectionElem::Deref) {
 162             // If the projection root is an artificial local that we introduced when
 163             // desugaring `static`, give a more specific error message
 164             // (avoid the general "raw pointer" clause below, that would only be confusing).
 165             if let Some(box LocalInfo::StaticRef { def_id, .. }) = decl.local_info {
 166                 if self.tcx.is_mutable_static(def_id) {
 167                     self.require_unsafe(
 168                         UnsafetyViolationKind::General,
 169                         UnsafetyViolationDetails::UseOfMutableStatic,
 170                     );
 171                     return;
 172                 } else if self.tcx.is_foreign_item(def_id) {
 173                     self.require_unsafe(
 174                         UnsafetyViolationKind::General,
 175                         UnsafetyViolationDetails::UseOfExternStatic,
 176                     );
 177                     return;
 178                 }
 179             }
 180         }
 181
 182         // Check for raw pointer `Deref`.
 183         for (base, proj) in place.iter_projections() {
 184             if proj == ProjectionElem::Deref {
 185                 let base_ty = base.ty(self.body, self.tcx).ty;
 186                 if base_ty.is_unsafe_ptr() {
 187                     self.require_unsafe(
 188                         UnsafetyViolationKind::General,
 189                         UnsafetyViolationDetails::DerefOfRawPointer,
 190                     )
 191                 }
 192             }
 193         }
 194
 195         // Check for union fields. For this we traverse right-to-left, as the last `Deref` changes
 196         // whether we *read* the union field or potentially *write* to it (if this place is being assigned to).
 197         let mut saw_deref = false;
 198         for (base, proj) in place.iter_projections().rev() {
 199             if proj == ProjectionElem::Deref {
 200                 saw_deref = true;
 201                 continue;
 202             }
 203
 204             let base_ty = base.ty(self.body, self.tcx).ty;
 205             if base_ty.is_union() {
 206                 // If we did not hit a `Deref` yet and the overall place use is an assignment, the
 207                 // rules are different.
 208                 let assign_to_field = !saw_deref
 209                     && matches!(
 210                         context,
 211                         PlaceContext::MutatingUse(
 212                             MutatingUseContext::Store
 213                                 | MutatingUseContext::Drop
 214                                 | MutatingUseContext::AsmOutput
 215                         )
 216                     );
 217                 // If this is just an assignment, determine if the assigned type needs dropping.
 218                 if assign_to_field {
 219                     // We have to check the actual type of the assignment, as that determines if the
 220                     // old value is being dropped.
 221                     let assigned_ty = place.ty(&self.body.local_decls, self.tcx).ty;
 222                     // To avoid semver hazard, we only consider `Copy` and `ManuallyDrop` non-dropping.
 223                     let manually_drop = assigned_ty
 224                         .ty_adt_def()
 225                         .map_or(false, |adt_def| adt_def.is_manually_drop());
 226                     let nodrop = manually_drop
 227                         || assigned_ty.is_copy_modulo_regions(
 228                             self.tcx.at(self.source_info.span),
 229                             self.param_env,
 230                         );
 231                     if !nodrop {
 232                         self.require_unsafe(
 233                             UnsafetyViolationKind::General,
 234                             UnsafetyViolationDetails::AssignToDroppingUnionField,
 235                         );
 236                     } else {
 237                         // write to non-drop union field, safe
 238                     }
 239                 } else {
 240                     self.require_unsafe(
 241                         UnsafetyViolationKind::General,
 242                         UnsafetyViolationDetails::AccessToUnionField,
 243                     )
 244                 }
 245             }
 246         }
 247     }
 248 }
 249
 250 impl<'tcx> UnsafetyChecker<'_, 'tcx> {
 251     fn require_unsafe(&mut self, kind: UnsafetyViolationKind, details: UnsafetyViolationDetails) {
 252         // Violations can turn out to be `UnsafeFn` during analysis, but they should not start out as such.
 253         assert_ne!(kind, UnsafetyViolationKind::UnsafeFn);
 254
 255         let source_info = self.source_info;
 256         let lint_root = self.body.source_scopes[self.source_info.scope]
 257             .local_data
 258             .as_ref()
 259             .assert_crate_local()
 260             .lint_root;
 261         self.register_violations(
 262             [&UnsafetyViolation { source_info, lint_root, kind, details }],
 263             [],
 264         );
 265     }
 266
 267     fn register_violations<'a>(
 268         &mut self,
 269         violations: impl IntoIterator<Item = &'a UnsafetyViolation>,
 270         new_used_unsafe_blocks: impl IntoIterator<Item = (HirId, UsedUnsafeBlockData)>,
 271     ) {
 272         use UsedUnsafeBlockData::{AllAllowedInUnsafeFn, SomeDisallowedInUnsafeFn};
 273
 274         let update_entry = |this: &mut Self, hir_id, new_usage| {
 275             match this.used_unsafe_blocks.entry(hir_id) {
 276                 hash_map::Entry::Occupied(mut entry) => {
 277                     if new_usage == SomeDisallowedInUnsafeFn {
 278                         *entry.get_mut() = SomeDisallowedInUnsafeFn;
 279                     }
 280                 }
 281                 hash_map::Entry::Vacant(entry) => {
 282                     entry.insert(new_usage);
 283                 }
 284             };
 285         };
 286         let safety = self.body.source_scopes[self.source_info.scope]
 287             .local_data
 288             .as_ref()
 289             .assert_crate_local()
 290             .safety;
 291         match safety {
 292             // `unsafe` blocks are required in safe code
 293             Safety::Safe => violations.into_iter().for_each(|&violation| {
 294                 match violation.kind {
 295                     UnsafetyViolationKind::General => {}
 296                     UnsafetyViolationKind::UnsafeFn => {
 297                         bug!("`UnsafetyViolationKind::UnsafeFn` in an `Safe` context")
 298                     }
 299                 }
 300                 if !self.violations.contains(&violation) {
 301                     self.violations.push(violation)
 302                 }
 303             }),
 304             // With the RFC 2585, no longer allow `unsafe` operations in `unsafe fn`s
 305             Safety::FnUnsafe => violations.into_iter().for_each(|&(mut violation)| {
 306                 violation.kind = UnsafetyViolationKind::UnsafeFn;
 307                 if !self.violations.contains(&violation) {
 308                     self.violations.push(violation)
 309                 }
 310             }),
 311             Safety::BuiltinUnsafe => {}
 312             Safety::ExplicitUnsafe(hir_id) => violations.into_iter().for_each(|violation| {
 313                 update_entry(
 314                     self,
 315                     hir_id,
 316                     match self.tcx.lint_level_at_node(UNSAFE_OP_IN_UNSAFE_FN, violation.lint_root).0
 317                     {
 318                         Level::Allow => AllAllowedInUnsafeFn(violation.lint_root),
 319                         _ => SomeDisallowedInUnsafeFn,
 320                     },
 321                 )
 322             }),
 323         };
 324
 325         new_used_unsafe_blocks
 326             .into_iter()
 327             .for_each(|(hir_id, usage_data)| update_entry(self, hir_id, usage_data));
 328     }
 329     fn check_mut_borrowing_layout_constrained_field(
 330         &mut self,
 331         place: Place<'tcx>,
 332         is_mut_use: bool,
 333     ) {
 334         for (place_base, elem) in place.iter_projections().rev() {
 335             match elem {
 336                 // Modifications behind a dereference don't affect the value of
 337                 // the pointer.
 338                 ProjectionElem::Deref => return,
 339                 ProjectionElem::Field(..) => {
 340                     let ty = place_base.ty(&self.body.local_decls, self.tcx).ty;
 341                     if let ty::Adt(def, _) = ty.kind() {
 342                         if self.tcx.layout_scalar_valid_range(def.did())
 343                             != (Bound::Unbounded, Bound::Unbounded)
 344                         {
 345                             let details = if is_mut_use {
 346                                 UnsafetyViolationDetails::MutationOfLayoutConstrainedField
 347
 348                             // Check `is_freeze` as late as possible to avoid cycle errors
 349                             // with opaque types.
 350                             } else if !place
 351                                 .ty(self.body, self.tcx)
 352                                 .ty
 353                                 .is_freeze(self.tcx.at(self.source_info.span), self.param_env)
 354                             {
 355                                 UnsafetyViolationDetails::BorrowOfLayoutConstrainedField
 356                             } else {
 357                                 continue;
 358                             };
 359                             self.require_unsafe(UnsafetyViolationKind::General, details);
 360                         }
 361                     }
 362                 }
 363                 _ => {}
 364             }
 365         }
 366     }
 367
 368     /// Checks whether calling `func_did` needs an `unsafe` context or not, i.e. whether
 369     /// the called function has target features the calling function hasn't.
 370     fn check_target_features(&mut self, func_did: DefId) {
 371         // Unsafety isn't required on wasm targets. For more information see
 372         // the corresponding check in typeck/src/collect.rs
 373         if self.tcx.sess.target.options.is_like_wasm {
 374             return;
 375         }
 376
 377         let callee_features = &self.tcx.codegen_fn_attrs(func_did).target_features;
 378         // The body might be a constant, so it doesn't have codegen attributes.
 379         let self_features = &self.tcx.body_codegen_attrs(self.body_did.to_def_id()).target_features;
 380
 381         // Is `callee_features` a subset of `calling_features`?
 382         if !callee_features.iter().all(|feature| self_features.contains(feature)) {
 383             self.require_unsafe(
 384                 UnsafetyViolationKind::General,
 385                 UnsafetyViolationDetails::CallToFunctionWith,
 386             )
 387         }
 388     }
 389 }
 390
 391 pub(crate) fn provide(providers: &mut Providers) {
 392     *providers = Providers {
 393         unsafety_check_result: |tcx, def_id| {
 394             if let Some(def) = ty::WithOptConstParam::try_lookup(def_id, tcx) {
 395                 tcx.unsafety_check_result_for_const_arg(def)
 396             } else {
 397                 unsafety_check_result(tcx, ty::WithOptConstParam::unknown(def_id))
 398             }
 399         },
 400         unsafety_check_result_for_const_arg: |tcx, (did, param_did)| {
 401             unsafety_check_result(
 402                 tcx,
 403                 ty::WithOptConstParam { did, const_param_did: Some(param_did) },
 404             )
 405         },
 406         ..*providers
 407     };
 408 }
 409
 410 /// Context information for [`UnusedUnsafeVisitor`] traversal,
 411 /// saves (innermost) relevant context
 412 #[derive(Copy, Clone, Debug)]
 413 enum Context {
 414     Safe,
 415     /// in an `unsafe fn`
 416     UnsafeFn(HirId),
 417     /// in a *used* `unsafe` block
 418     /// (i.e. a block without unused-unsafe warning)
 419     UnsafeBlock(HirId),
 420 }
 421
 422 struct UnusedUnsafeVisitor<'a, 'tcx> {
 423     tcx: TyCtxt<'tcx>,
 424     used_unsafe_blocks: &'a FxHashMap<HirId, UsedUnsafeBlockData>,
 425     context: Context,
 426     unused_unsafes: &'a mut Vec<(HirId, UnusedUnsafe)>,
 427 }
 428
 429 impl<'tcx> intravisit::Visitor<'tcx> for UnusedUnsafeVisitor<'_, 'tcx> {
 430     fn visit_block(&mut self, block: &'tcx hir::Block<'tcx>) {
 431         use UsedUnsafeBlockData::{AllAllowedInUnsafeFn, SomeDisallowedInUnsafeFn};
 432
 433         if let hir::BlockCheckMode::UnsafeBlock(hir::UnsafeSource::UserProvided) = block.rules {
 434             let used = match self.tcx.lint_level_at_node(UNUSED_UNSAFE, block.hir_id) {
 435                 (Level::Allow, _) => Some(SomeDisallowedInUnsafeFn),
 436                 _ => self.used_unsafe_blocks.get(&block.hir_id).copied(),
 437             };
 438             let unused_unsafe = match (self.context, used) {
 439                 (_, None) => UnusedUnsafe::Unused,
 440                 (Context::Safe, Some(_))
 441                 | (Context::UnsafeFn(_), Some(SomeDisallowedInUnsafeFn)) => {
 442                     let previous_context = self.context;
 443                     self.context = Context::UnsafeBlock(block.hir_id);
 444                     intravisit::walk_block(self, block);
 445                     self.context = previous_context;
 446                     return;
 447                 }
 448                 (Context::UnsafeFn(hir_id), Some(AllAllowedInUnsafeFn(lint_root))) => {
 449                     UnusedUnsafe::InUnsafeFn(hir_id, lint_root)
 450                 }
 451                 (Context::UnsafeBlock(hir_id), Some(_)) => UnusedUnsafe::InUnsafeBlock(hir_id),
 452             };
 453             self.unused_unsafes.push((block.hir_id, unused_unsafe));
 454         }
 455         intravisit::walk_block(self, block);
 456     }
 457
 458     fn visit_fn(
 459         &mut self,
 460         fk: intravisit::FnKind<'tcx>,
 461         _fd: &'tcx hir::FnDecl<'tcx>,
 462         b: hir::BodyId,
 463         _s: rustc_span::Span,
 464         _id: HirId,
 465     ) {
 466         if matches!(fk, intravisit::FnKind::Closure) {
 467             self.visit_body(self.tcx.hir().body(b))
 468         }
 469     }
 470 }
 471
 472 fn check_unused_unsafe(
 473     tcx: TyCtxt<'_>,
 474     def_id: LocalDefId,
 475     used_unsafe_blocks: &FxHashMap<HirId, UsedUnsafeBlockData>,
 476 ) -> Vec<(HirId, UnusedUnsafe)> {
 477     let hir_id = tcx.hir().local_def_id_to_hir_id(def_id);
 478     let body_id = tcx.hir().maybe_body_owned_by(hir_id);
 479
 480     let Some(body_id) = body_id else {
 481         debug!("check_unused_unsafe({:?}) - no body found", def_id);
 482         return vec![];
 483     };
 484     let body = tcx.hir().body(body_id);
 485
 486     let context = match tcx.hir().fn_sig_by_hir_id(hir_id) {
 487         Some(sig) if sig.header.unsafety == hir::Unsafety::Unsafe => Context::UnsafeFn(hir_id),
 488         _ => Context::Safe,
 489     };
 490
 491     debug!(
 492         "check_unused_unsafe({:?}, context={:?}, body={:?}, used_unsafe_blocks={:?})",
 493         def_id, body, context, used_unsafe_blocks
 494     );
 495
 496     let mut unused_unsafes = vec![];
 497
 498     let mut visitor = UnusedUnsafeVisitor {
 499         tcx,
 500         used_unsafe_blocks,
 501         context,
 502         unused_unsafes: &mut unused_unsafes,
 503     };
 504     intravisit::Visitor::visit_body(&mut visitor, body);
 505
 506     unused_unsafes
 507 }
 508
 509 fn unsafety_check_result<'tcx>(
 510     tcx: TyCtxt<'tcx>,
 511     def: ty::WithOptConstParam<LocalDefId>,
 512 ) -> &'tcx UnsafetyCheckResult {
 513     debug!("unsafety_violations({:?})", def);
 514
 515     // N.B., this borrow is valid because all the consumers of
 516     // `mir_built` force this.
 517     let body = &tcx.mir_built(def).borrow();
 518
 519     let param_env = tcx.param_env(def.did);
 520
 521     let mut checker = UnsafetyChecker::new(body, def.did, tcx, param_env);
 522     checker.visit_body(&body);
 523
 524     let unused_unsafes = (!tcx.is_closure(def.did.to_def_id()))
 525         .then(|| check_unused_unsafe(tcx, def.did, &checker.used_unsafe_blocks));
 526
 527     tcx.arena.alloc(UnsafetyCheckResult {
 528         violations: checker.violations,
 529         used_unsafe_blocks: checker.used_unsafe_blocks,
 530         unused_unsafes,
 531     })
 532 }
 533
 534 fn report_unused_unsafe(tcx: TyCtxt<'_>, kind: UnusedUnsafe, id: HirId) {
 535     let span = tcx.sess.source_map().guess_head_span(tcx.hir().span(id));
 536     tcx.struct_span_lint_hir(UNUSED_UNSAFE, id, span, |lint| {
 537         let msg = "unnecessary `unsafe` block";
 538         let mut db = lint.build(msg);
 539         db.span_label(span, msg);
 540         match kind {
 541             UnusedUnsafe::Unused => {}
 542             UnusedUnsafe::InUnsafeBlock(id) => {
 543                 db.span_label(
 544                     tcx.sess.source_map().guess_head_span(tcx.hir().span(id)),
 545                     "because it's nested under this `unsafe` block",
 546                 );
 547             }
 548             UnusedUnsafe::InUnsafeFn(id, usage_lint_root) => {
 549                 db.span_label(
 550                     tcx.sess.source_map().guess_head_span(tcx.hir().span(id)),
 551                     "because it's nested under this `unsafe` fn",
 552                 )
 553                 .note(
 554                     "this `unsafe` block does contain unsafe operations, \
 555                     but those are already allowed in an `unsafe fn`",
 556                 );
 557                 let (level, source) =
 558                     tcx.lint_level_at_node(UNSAFE_OP_IN_UNSAFE_FN, usage_lint_root);
 559                 assert_eq!(level, Level::Allow);
 560                 lint::explain_lint_level_source(
 561                     UNSAFE_OP_IN_UNSAFE_FN,
 562                     Level::Allow,
 563                     source,
 564                     &mut db,
 565                 );
 566             }
 567         }
 568
 569         db.emit();
 570     });
 571 }
 572
 573 pub fn check_unsafety(tcx: TyCtxt<'_>, def_id: LocalDefId) {
 574     debug!("check_unsafety({:?})", def_id);
 575
 576     // closures are handled by their parent fn.
 577     if tcx.is_closure(def_id.to_def_id()) {
 578         return;
 579     }
 580
 581     let UnsafetyCheckResult { violations, unused_unsafes, .. } = tcx.unsafety_check_result(def_id);
 582
 583     for &UnsafetyViolation { source_info, lint_root, kind, details } in violations.iter() {
 584         let (description, note) = details.description_and_note();
 585
 586         // Report an error.
 587         let unsafe_fn_msg =
 588             if unsafe_op_in_unsafe_fn_allowed(tcx, lint_root) { " function or" } else { "" };
 589
 590         match kind {
 591             UnsafetyViolationKind::General => {
 592                 // once
 593                 struct_span_err!(
 594                     tcx.sess,
 595                     source_info.span,
 596                     E0133,
 597                     "{} is unsafe and requires unsafe{} block",
 598                     description,
 599                     unsafe_fn_msg,
 600                 )
 601                 .span_label(source_info.span, description)
 602                 .note(note)
 603                 .emit();
 604             }
 605             UnsafetyViolationKind::UnsafeFn => tcx.struct_span_lint_hir(
 606                 UNSAFE_OP_IN_UNSAFE_FN,
 607                 lint_root,
 608                 source_info.span,
 609                 |lint| {
 610                     lint.build(&format!(
 611                         "{} is unsafe and requires unsafe block (error E0133)",
 612                         description,
 613                     ))
 614                     .span_label(source_info.span, description)
 615                     .note(note)
 616                     .emit();
 617                 },
 618             ),
 619         }
 620     }
 621
 622     for &(block_id, kind) in unused_unsafes.as_ref().unwrap() {
 623         report_unused_unsafe(tcx, kind, block_id);
 624     }
 625 }
 626
 627 fn unsafe_op_in_unsafe_fn_allowed(tcx: TyCtxt<'_>, id: HirId) -> bool {
 628     tcx.lint_level_at_node(UNSAFE_OP_IN_UNSAFE_FN, id).0 == Level::Allow
 629 }