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                     if assigned_ty.needs_drop(
 223                         self.tcx,
 224                         self.tcx.param_env(base_ty.ty_adt_def().unwrap().did()),
 225                     ) {
 226                         // This would be unsafe, but should be outright impossible since we reject such unions.
 227                         self.tcx.sess.delay_span_bug(
 228                             self.source_info.span,
 229                             "union fields that need dropping should be impossible",
 230                         );
 231                     }
 232                 } else {
 233                     self.require_unsafe(
 234                         UnsafetyViolationKind::General,
 235                         UnsafetyViolationDetails::AccessToUnionField,
 236                     )
 237                 }
 238             }
 239         }
 240     }
 241 }
 242
 243 impl<'tcx> UnsafetyChecker<'_, 'tcx> {
 244     fn require_unsafe(&mut self, kind: UnsafetyViolationKind, details: UnsafetyViolationDetails) {
 245         // Violations can turn out to be `UnsafeFn` during analysis, but they should not start out as such.
 246         assert_ne!(kind, UnsafetyViolationKind::UnsafeFn);
 247
 248         let source_info = self.source_info;
 249         let lint_root = self.body.source_scopes[self.source_info.scope]
 250             .local_data
 251             .as_ref()
 252             .assert_crate_local()
 253             .lint_root;
 254         self.register_violations(
 255             [&UnsafetyViolation { source_info, lint_root, kind, details }],
 256             [],
 257         );
 258     }
 259
 260     fn register_violations<'a>(
 261         &mut self,
 262         violations: impl IntoIterator<Item = &'a UnsafetyViolation>,
 263         new_used_unsafe_blocks: impl IntoIterator<Item = (HirId, UsedUnsafeBlockData)>,
 264     ) {
 265         use UsedUnsafeBlockData::{AllAllowedInUnsafeFn, SomeDisallowedInUnsafeFn};
 266
 267         let update_entry = |this: &mut Self, hir_id, new_usage| {
 268             match this.used_unsafe_blocks.entry(hir_id) {
 269                 hash_map::Entry::Occupied(mut entry) => {
 270                     if new_usage == SomeDisallowedInUnsafeFn {
 271                         *entry.get_mut() = SomeDisallowedInUnsafeFn;
 272                     }
 273                 }
 274                 hash_map::Entry::Vacant(entry) => {
 275                     entry.insert(new_usage);
 276                 }
 277             };
 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                 update_entry(
 307                     self,
 308                     hir_id,
 309                     match self.tcx.lint_level_at_node(UNSAFE_OP_IN_UNSAFE_FN, violation.lint_root).0
 310                     {
 311                         Level::Allow => AllAllowedInUnsafeFn(violation.lint_root),
 312                         _ => SomeDisallowedInUnsafeFn,
 313                     },
 314                 )
 315             }),
 316         };
 317
 318         new_used_unsafe_blocks
 319             .into_iter()
 320             .for_each(|(hir_id, usage_data)| update_entry(self, hir_id, usage_data));
 321     }
 322     fn check_mut_borrowing_layout_constrained_field(
 323         &mut self,
 324         place: Place<'tcx>,
 325         is_mut_use: bool,
 326     ) {
 327         for (place_base, elem) in place.iter_projections().rev() {
 328             match elem {
 329                 // Modifications behind a dereference don't affect the value of
 330                 // the pointer.
 331                 ProjectionElem::Deref => return,
 332                 ProjectionElem::Field(..) => {
 333                     let ty = place_base.ty(&self.body.local_decls, self.tcx).ty;
 334                     if let ty::Adt(def, _) = ty.kind() {
 335                         if self.tcx.layout_scalar_valid_range(def.did())
 336                             != (Bound::Unbounded, Bound::Unbounded)
 337                         {
 338                             let details = if is_mut_use {
 339                                 UnsafetyViolationDetails::MutationOfLayoutConstrainedField
 340
 341                             // Check `is_freeze` as late as possible to avoid cycle errors
 342                             // with opaque types.
 343                             } else if !place
 344                                 .ty(self.body, self.tcx)
 345                                 .ty
 346                                 .is_freeze(self.tcx.at(self.source_info.span), self.param_env)
 347                             {
 348                                 UnsafetyViolationDetails::BorrowOfLayoutConstrainedField
 349                             } else {
 350                                 continue;
 351                             };
 352                             self.require_unsafe(UnsafetyViolationKind::General, details);
 353                         }
 354                     }
 355                 }
 356                 _ => {}
 357             }
 358         }
 359     }
 360
 361     /// Checks whether calling `func_did` needs an `unsafe` context or not, i.e. whether
 362     /// the called function has target features the calling function hasn't.
 363     fn check_target_features(&mut self, func_did: DefId) {
 364         // Unsafety isn't required on wasm targets. For more information see
 365         // the corresponding check in typeck/src/collect.rs
 366         if self.tcx.sess.target.options.is_like_wasm {
 367             return;
 368         }
 369
 370         let callee_features = &self.tcx.codegen_fn_attrs(func_did).target_features;
 371         // The body might be a constant, so it doesn't have codegen attributes.
 372         let self_features = &self.tcx.body_codegen_attrs(self.body_did.to_def_id()).target_features;
 373
 374         // Is `callee_features` a subset of `calling_features`?
 375         if !callee_features.iter().all(|feature| self_features.contains(feature)) {
 376             self.require_unsafe(
 377                 UnsafetyViolationKind::General,
 378                 UnsafetyViolationDetails::CallToFunctionWith,
 379             )
 380         }
 381     }
 382 }
 383
 384 pub(crate) fn provide(providers: &mut Providers) {
 385     *providers = Providers {
 386         unsafety_check_result: |tcx, def_id| {
 387             if let Some(def) = ty::WithOptConstParam::try_lookup(def_id, tcx) {
 388                 tcx.unsafety_check_result_for_const_arg(def)
 389             } else {
 390                 unsafety_check_result(tcx, ty::WithOptConstParam::unknown(def_id))
 391             }
 392         },
 393         unsafety_check_result_for_const_arg: |tcx, (did, param_did)| {
 394             unsafety_check_result(
 395                 tcx,
 396                 ty::WithOptConstParam { did, const_param_did: Some(param_did) },
 397             )
 398         },
 399         ..*providers
 400     };
 401 }
 402
 403 /// Context information for [`UnusedUnsafeVisitor`] traversal,
 404 /// saves (innermost) relevant context
 405 #[derive(Copy, Clone, Debug)]
 406 enum Context {
 407     Safe,
 408     /// in an `unsafe fn`
 409     UnsafeFn(HirId),
 410     /// in a *used* `unsafe` block
 411     /// (i.e. a block without unused-unsafe warning)
 412     UnsafeBlock(HirId),
 413 }
 414
 415 struct UnusedUnsafeVisitor<'a, 'tcx> {
 416     tcx: TyCtxt<'tcx>,
 417     used_unsafe_blocks: &'a FxHashMap<HirId, UsedUnsafeBlockData>,
 418     context: Context,
 419     unused_unsafes: &'a mut Vec<(HirId, UnusedUnsafe)>,
 420 }
 421
 422 impl<'tcx> intravisit::Visitor<'tcx> for UnusedUnsafeVisitor<'_, 'tcx> {
 423     fn visit_block(&mut self, block: &'tcx hir::Block<'tcx>) {
 424         use UsedUnsafeBlockData::{AllAllowedInUnsafeFn, SomeDisallowedInUnsafeFn};
 425
 426         if let hir::BlockCheckMode::UnsafeBlock(hir::UnsafeSource::UserProvided) = block.rules {
 427             let used = match self.tcx.lint_level_at_node(UNUSED_UNSAFE, block.hir_id) {
 428                 (Level::Allow, _) => Some(SomeDisallowedInUnsafeFn),
 429                 _ => self.used_unsafe_blocks.get(&block.hir_id).copied(),
 430             };
 431             let unused_unsafe = match (self.context, used) {
 432                 (_, None) => UnusedUnsafe::Unused,
 433                 (Context::Safe, Some(_))
 434                 | (Context::UnsafeFn(_), Some(SomeDisallowedInUnsafeFn)) => {
 435                     let previous_context = self.context;
 436                     self.context = Context::UnsafeBlock(block.hir_id);
 437                     intravisit::walk_block(self, block);
 438                     self.context = previous_context;
 439                     return;
 440                 }
 441                 (Context::UnsafeFn(hir_id), Some(AllAllowedInUnsafeFn(lint_root))) => {
 442                     UnusedUnsafe::InUnsafeFn(hir_id, lint_root)
 443                 }
 444                 (Context::UnsafeBlock(hir_id), Some(_)) => UnusedUnsafe::InUnsafeBlock(hir_id),
 445             };
 446             self.unused_unsafes.push((block.hir_id, unused_unsafe));
 447         }
 448         intravisit::walk_block(self, block);
 449     }
 450
 451     fn visit_fn(
 452         &mut self,
 453         fk: intravisit::FnKind<'tcx>,
 454         _fd: &'tcx hir::FnDecl<'tcx>,
 455         b: hir::BodyId,
 456         _s: rustc_span::Span,
 457         _id: HirId,
 458     ) {
 459         if matches!(fk, intravisit::FnKind::Closure) {
 460             self.visit_body(self.tcx.hir().body(b))
 461         }
 462     }
 463 }
 464
 465 fn check_unused_unsafe(
 466     tcx: TyCtxt<'_>,
 467     def_id: LocalDefId,
 468     used_unsafe_blocks: &FxHashMap<HirId, UsedUnsafeBlockData>,
 469 ) -> Vec<(HirId, UnusedUnsafe)> {
 470     let hir_id = tcx.hir().local_def_id_to_hir_id(def_id);
 471     let body_id = tcx.hir().maybe_body_owned_by(hir_id);
 472
 473     let Some(body_id) = body_id else {
 474         debug!("check_unused_unsafe({:?}) - no body found", def_id);
 475         return vec![];
 476     };
 477     let body = tcx.hir().body(body_id);
 478
 479     let context = match tcx.hir().fn_sig_by_hir_id(hir_id) {
 480         Some(sig) if sig.header.unsafety == hir::Unsafety::Unsafe => Context::UnsafeFn(hir_id),
 481         _ => Context::Safe,
 482     };
 483
 484     debug!(
 485         "check_unused_unsafe({:?}, context={:?}, body={:?}, used_unsafe_blocks={:?})",
 486         def_id, body, context, used_unsafe_blocks
 487     );
 488
 489     let mut unused_unsafes = vec![];
 490
 491     let mut visitor = UnusedUnsafeVisitor {
 492         tcx,
 493         used_unsafe_blocks,
 494         context,
 495         unused_unsafes: &mut unused_unsafes,
 496     };
 497     intravisit::Visitor::visit_body(&mut visitor, body);
 498
 499     unused_unsafes
 500 }
 501
 502 fn unsafety_check_result<'tcx>(
 503     tcx: TyCtxt<'tcx>,
 504     def: ty::WithOptConstParam<LocalDefId>,
 505 ) -> &'tcx UnsafetyCheckResult {
 506     debug!("unsafety_violations({:?})", def);
 507
 508     // N.B., this borrow is valid because all the consumers of
 509     // `mir_built` force this.
 510     let body = &tcx.mir_built(def).borrow();
 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_closure(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     tcx.struct_span_lint_hir(UNUSED_UNSAFE, id, span, |lint| {
 530         let msg = "unnecessary `unsafe` block";
 531         let mut db = lint.build(msg);
 532         db.span_label(span, msg);
 533         match kind {
 534             UnusedUnsafe::Unused => {}
 535             UnusedUnsafe::InUnsafeBlock(id) => {
 536                 db.span_label(
 537                     tcx.sess.source_map().guess_head_span(tcx.hir().span(id)),
 538                     "because it's nested under this `unsafe` block",
 539                 );
 540             }
 541             UnusedUnsafe::InUnsafeFn(id, usage_lint_root) => {
 542                 db.span_label(
 543                     tcx.sess.source_map().guess_head_span(tcx.hir().span(id)),
 544                     "because it's nested under this `unsafe` fn",
 545                 )
 546                 .note(
 547                     "this `unsafe` block does contain unsafe operations, \
 548                     but those are already allowed in an `unsafe fn`",
 549                 );
 550                 let (level, source) =
 551                     tcx.lint_level_at_node(UNSAFE_OP_IN_UNSAFE_FN, usage_lint_root);
 552                 assert_eq!(level, Level::Allow);
 553                 lint::explain_lint_level_source(
 554                     UNSAFE_OP_IN_UNSAFE_FN,
 555                     Level::Allow,
 556                     source,
 557                     &mut db,
 558                 );
 559             }
 560         }
 561
 562         db.emit();
 563     });
 564 }
 565
 566 pub fn check_unsafety(tcx: TyCtxt<'_>, def_id: LocalDefId) {
 567     debug!("check_unsafety({:?})", def_id);
 568
 569     // closures are handled by their parent fn.
 570     if tcx.is_closure(def_id.to_def_id()) {
 571         return;
 572     }
 573
 574     let UnsafetyCheckResult { violations, unused_unsafes, .. } = tcx.unsafety_check_result(def_id);
 575
 576     for &UnsafetyViolation { source_info, lint_root, kind, details } in violations.iter() {
 577         let (description, note) = details.description_and_note();
 578
 579         // Report an error.
 580         let unsafe_fn_msg =
 581             if unsafe_op_in_unsafe_fn_allowed(tcx, lint_root) { " function or" } else { "" };
 582
 583         match kind {
 584             UnsafetyViolationKind::General => {
 585                 // once
 586                 struct_span_err!(
 587                     tcx.sess,
 588                     source_info.span,
 589                     E0133,
 590                     "{} is unsafe and requires unsafe{} block",
 591                     description,
 592                     unsafe_fn_msg,
 593                 )
 594                 .span_label(source_info.span, description)
 595                 .note(note)
 596                 .emit();
 597             }
 598             UnsafetyViolationKind::UnsafeFn => tcx.struct_span_lint_hir(
 599                 UNSAFE_OP_IN_UNSAFE_FN,
 600                 lint_root,
 601                 source_info.span,
 602                 |lint| {
 603                     lint.build(&format!(
 604                         "{} is unsafe and requires unsafe block (error E0133)",
 605                         description,
 606                     ))
 607                     .span_label(source_info.span, description)
 608                     .note(note)
 609                     .emit();
 610                 },
 611             ),
 612         }
 613     }
 614
 615     for &(block_id, kind) in unused_unsafes.as_ref().unwrap() {
 616         report_unused_unsafe(tcx, kind, block_id);
 617     }
 618 }
 619
 620 fn unsafe_op_in_unsafe_fn_allowed(tcx: TyCtxt<'_>, id: HirId) -> bool {
 621     tcx.lint_level_at_node(UNSAFE_OP_IN_UNSAFE_FN, id).0 == Level::Allow
 622 }