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