compiler/rustc_mir/src/transform/check_unsafety.rs

   1 use rustc_data_structures::fx::FxHashSet;
   2 use rustc_errors::struct_span_err;
   3 use rustc_hir as hir;
   4 use rustc_hir::def_id::{DefId, LocalDefId};
   5 use rustc_hir::hir_id::HirId;
   6 use rustc_hir::intravisit;
   7 use rustc_hir::Node;
   8 use rustc_middle::mir::visit::{MutatingUseContext, PlaceContext, Visitor};
   9 use rustc_middle::mir::*;
  10 use rustc_middle::ty::cast::CastTy;
  11 use rustc_middle::ty::query::Providers;
  12 use rustc_middle::ty::{self, TyCtxt};
  13 use rustc_session::lint::builtin::{UNSAFE_OP_IN_UNSAFE_FN, UNUSED_UNSAFE};
  14 use rustc_session::lint::Level;
  15
  16 use std::ops::Bound;
  17
  18 use crate::const_eval::is_min_const_fn;
  19
  20 pub struct UnsafetyChecker<'a, 'tcx> {
  21     body: &'a Body<'tcx>,
  22     body_did: LocalDefId,
  23     const_context: bool,
  24     min_const_fn: bool,
  25     violations: Vec<UnsafetyViolation>,
  26     source_info: SourceInfo,
  27     tcx: TyCtxt<'tcx>,
  28     param_env: ty::ParamEnv<'tcx>,
  29     /// Mark an `unsafe` block as used, so we don't lint it.
  30     used_unsafe: FxHashSet<hir::HirId>,
  31     inherited_blocks: Vec<(hir::HirId, bool)>,
  32 }
  33
  34 impl<'a, 'tcx> UnsafetyChecker<'a, 'tcx> {
  35     fn new(
  36         const_context: bool,
  37         min_const_fn: bool,
  38         body: &'a Body<'tcx>,
  39         body_did: LocalDefId,
  40         tcx: TyCtxt<'tcx>,
  41         param_env: ty::ParamEnv<'tcx>,
  42     ) -> Self {
  43         // sanity check
  44         if min_const_fn {
  45             assert!(const_context);
  46         }
  47         Self {
  48             body,
  49             body_did,
  50             const_context,
  51             min_const_fn,
  52             violations: vec![],
  53             source_info: SourceInfo::outermost(body.span),
  54             tcx,
  55             param_env,
  56             used_unsafe: Default::default(),
  57             inherited_blocks: vec![],
  58         }
  59     }
  60 }
  61
  62 impl<'a, 'tcx> Visitor<'tcx> for UnsafetyChecker<'a, 'tcx> {
  63     fn visit_terminator(&mut self, terminator: &Terminator<'tcx>, location: Location) {
  64         self.source_info = terminator.source_info;
  65         match terminator.kind {
  66             TerminatorKind::Goto { .. }
  67             | TerminatorKind::SwitchInt { .. }
  68             | TerminatorKind::Drop { .. }
  69             | TerminatorKind::Yield { .. }
  70             | TerminatorKind::Assert { .. }
  71             | TerminatorKind::DropAndReplace { .. }
  72             | TerminatorKind::GeneratorDrop
  73             | TerminatorKind::Resume
  74             | TerminatorKind::Abort
  75             | TerminatorKind::Return
  76             | TerminatorKind::Unreachable
  77             | TerminatorKind::FalseEdge { .. }
  78             | TerminatorKind::FalseUnwind { .. } => {
  79                 // safe (at least as emitted during MIR construction)
  80             }
  81
  82             TerminatorKind::Call { ref func, .. } => {
  83                 let func_ty = func.ty(self.body, self.tcx);
  84                 let sig = func_ty.fn_sig(self.tcx);
  85                 if let hir::Unsafety::Unsafe = sig.unsafety() {
  86                     self.require_unsafe(
  87                         UnsafetyViolationKind::GeneralAndConstFn,
  88                         UnsafetyViolationDetails::CallToUnsafeFunction,
  89                     )
  90                 }
  91
  92                 if let ty::FnDef(func_id, _) = func_ty.kind() {
  93                     self.check_target_features(*func_id);
  94                 }
  95             }
  96
  97             TerminatorKind::InlineAsm { .. } => self.require_unsafe(
  98                 UnsafetyViolationKind::General,
  99                 UnsafetyViolationDetails::UseOfInlineAssembly,
 100             ),
 101         }
 102         self.super_terminator(terminator, location);
 103     }
 104
 105     fn visit_statement(&mut self, statement: &Statement<'tcx>, location: Location) {
 106         self.source_info = statement.source_info;
 107         match statement.kind {
 108             StatementKind::Assign(..)
 109             | StatementKind::FakeRead(..)
 110             | StatementKind::SetDiscriminant { .. }
 111             | StatementKind::StorageLive(..)
 112             | StatementKind::StorageDead(..)
 113             | StatementKind::Retag { .. }
 114             | StatementKind::AscribeUserType(..)
 115             | StatementKind::Coverage(..)
 116             | StatementKind::Nop => {
 117                 // safe (at least as emitted during MIR construction)
 118             }
 119
 120             StatementKind::LlvmInlineAsm { .. } => self.require_unsafe(
 121                 UnsafetyViolationKind::General,
 122                 UnsafetyViolationDetails::UseOfInlineAssembly,
 123             ),
 124             StatementKind::CopyNonOverlapping(..) => unreachable!(),
 125         }
 126         self.super_statement(statement, location);
 127     }
 128
 129     fn visit_rvalue(&mut self, rvalue: &Rvalue<'tcx>, location: Location) {
 130         match rvalue {
 131             Rvalue::Aggregate(box ref aggregate, _) => match aggregate {
 132                 &AggregateKind::Array(..) | &AggregateKind::Tuple => {}
 133                 &AggregateKind::Adt(ref def, ..) => {
 134                     match self.tcx.layout_scalar_valid_range(def.did) {
 135                         (Bound::Unbounded, Bound::Unbounded) => {}
 136                         _ => self.require_unsafe(
 137                             UnsafetyViolationKind::GeneralAndConstFn,
 138                             UnsafetyViolationDetails::InitializingTypeWith,
 139                         ),
 140                     }
 141                 }
 142                 &AggregateKind::Closure(def_id, _) | &AggregateKind::Generator(def_id, _, _) => {
 143                     let UnsafetyCheckResult { violations, unsafe_blocks } =
 144                         self.tcx.unsafety_check_result(def_id.expect_local());
 145                     self.register_violations(&violations, &unsafe_blocks);
 146                 }
 147             },
 148             // casting pointers to ints is unsafe in const fn because the const evaluator cannot
 149             // possibly know what the result of various operations like `address / 2` would be
 150             // pointers during const evaluation have no integral address, only an abstract one
 151             Rvalue::Cast(CastKind::Misc, ref operand, cast_ty)
 152                 if self.const_context && self.tcx.features().const_raw_ptr_to_usize_cast =>
 153             {
 154                 let operand_ty = operand.ty(self.body, self.tcx);
 155                 let cast_in = CastTy::from_ty(operand_ty).expect("bad input type for cast");
 156                 let cast_out = CastTy::from_ty(cast_ty).expect("bad output type for cast");
 157                 match (cast_in, cast_out) {
 158                     (CastTy::Ptr(_) | CastTy::FnPtr, CastTy::Int(_)) => {
 159                         self.require_unsafe(
 160                             UnsafetyViolationKind::General,
 161                             UnsafetyViolationDetails::CastOfPointerToInt,
 162                         );
 163                     }
 164                     _ => {}
 165                 }
 166             }
 167             _ => {}
 168         }
 169         self.super_rvalue(rvalue, location);
 170     }
 171
 172     fn visit_place(&mut self, place: &Place<'tcx>, context: PlaceContext, _location: Location) {
 173         // On types with `scalar_valid_range`, prevent
 174         // * `&mut x.field`
 175         // * `x.field = y;`
 176         // * `&x.field` if `field`'s type has interior mutability
 177         // because either of these would allow modifying the layout constrained field and
 178         // insert values that violate the layout constraints.
 179         if context.is_mutating_use() || context.is_borrow() {
 180             self.check_mut_borrowing_layout_constrained_field(*place, context.is_mutating_use());
 181         }
 182
 183         // Some checks below need the extra metainfo of the local declaration.
 184         let decl = &self.body.local_decls[place.local];
 185
 186         // Check the base local: it might be an unsafe-to-access static. We only check derefs of the
 187         // temporary holding the static pointer to avoid duplicate errors
 188         // <https://github.com/rust-lang/rust/pull/78068#issuecomment-731753506>.
 189         if decl.internal && place.projection.first() == Some(&ProjectionElem::Deref) {
 190             // If the projection root is an artifical local that we introduced when
 191             // desugaring `static`, give a more specific error message
 192             // (avoid the general "raw pointer" clause below, that would only be confusing).
 193             if let Some(box LocalInfo::StaticRef { def_id, .. }) = decl.local_info {
 194                 if self.tcx.is_mutable_static(def_id) {
 195                     self.require_unsafe(
 196                         UnsafetyViolationKind::General,
 197                         UnsafetyViolationDetails::UseOfMutableStatic,
 198                     );
 199                     return;
 200                 } else if self.tcx.is_foreign_item(def_id) {
 201                     self.require_unsafe(
 202                         UnsafetyViolationKind::General,
 203                         UnsafetyViolationDetails::UseOfExternStatic,
 204                     );
 205                     return;
 206                 }
 207             }
 208         }
 209
 210         // Check for raw pointer `Deref`.
 211         for (base, proj) in place.iter_projections() {
 212             if proj == ProjectionElem::Deref {
 213                 let base_ty = base.ty(self.body, self.tcx).ty;
 214                 if base_ty.is_unsafe_ptr() {
 215                     self.require_unsafe(
 216                         UnsafetyViolationKind::GeneralAndConstFn,
 217                         UnsafetyViolationDetails::DerefOfRawPointer,
 218                     )
 219                 }
 220             }
 221         }
 222
 223         // Check for union fields. For this we traverse right-to-left, as the last `Deref` changes
 224         // whether we *read* the union field or potentially *write* to it (if this place is being assigned to).
 225         let mut saw_deref = false;
 226         for (base, proj) in place.iter_projections().rev() {
 227             if proj == ProjectionElem::Deref {
 228                 saw_deref = true;
 229                 continue;
 230             }
 231
 232             let base_ty = base.ty(self.body, self.tcx).ty;
 233             if base_ty.ty_adt_def().map_or(false, |adt| adt.is_union()) {
 234                 // If we did not hit a `Deref` yet and the overall place use is an assignment, the
 235                 // rules are different.
 236                 let assign_to_field = !saw_deref
 237                     && matches!(
 238                         context,
 239                         PlaceContext::MutatingUse(
 240                             MutatingUseContext::Store
 241                                 | MutatingUseContext::Drop
 242                                 | MutatingUseContext::AsmOutput
 243                         )
 244                     );
 245                 // If this is just an assignment, determine if the assigned type needs dropping.
 246                 if assign_to_field {
 247                     // We have to check the actual type of the assignment, as that determines if the
 248                     // old value is being dropped.
 249                     let assigned_ty = place.ty(&self.body.local_decls, self.tcx).ty;
 250                     // To avoid semver hazard, we only consider `Copy` and `ManuallyDrop` non-dropping.
 251                     let manually_drop = assigned_ty
 252                         .ty_adt_def()
 253                         .map_or(false, |adt_def| adt_def.is_manually_drop());
 254                     let nodrop = manually_drop
 255                         || assigned_ty.is_copy_modulo_regions(
 256                             self.tcx.at(self.source_info.span),
 257                             self.param_env,
 258                         );
 259                     if !nodrop {
 260                         self.require_unsafe(
 261                             UnsafetyViolationKind::GeneralAndConstFn,
 262                             UnsafetyViolationDetails::AssignToDroppingUnionField,
 263                         );
 264                     } else {
 265                         // write to non-drop union field, safe
 266                     }
 267                 } else {
 268                     self.require_unsafe(
 269                         UnsafetyViolationKind::GeneralAndConstFn,
 270                         UnsafetyViolationDetails::AccessToUnionField,
 271                     )
 272                 }
 273             }
 274         }
 275     }
 276 }
 277
 278 impl<'a, 'tcx> UnsafetyChecker<'a, 'tcx> {
 279     fn require_unsafe(&mut self, kind: UnsafetyViolationKind, details: UnsafetyViolationDetails) {
 280         let source_info = self.source_info;
 281         let lint_root = self.body.source_scopes[self.source_info.scope]
 282             .local_data
 283             .as_ref()
 284             .assert_crate_local()
 285             .lint_root;
 286         self.register_violations(
 287             &[UnsafetyViolation { source_info, lint_root, kind, details }],
 288             &[],
 289         );
 290     }
 291
 292     fn register_violations(
 293         &mut self,
 294         violations: &[UnsafetyViolation],
 295         unsafe_blocks: &[(hir::HirId, bool)],
 296     ) {
 297         let safety = self.body.source_scopes[self.source_info.scope]
 298             .local_data
 299             .as_ref()
 300             .assert_crate_local()
 301             .safety;
 302         let within_unsafe = match safety {
 303             // `unsafe` blocks are required in safe code
 304             Safety::Safe => {
 305                 for violation in violations {
 306                     match violation.kind {
 307                         UnsafetyViolationKind::GeneralAndConstFn
 308                         | UnsafetyViolationKind::General => {}
 309                         UnsafetyViolationKind::UnsafeFn => {
 310                             bug!("`UnsafetyViolationKind::UnsafeFn` in an `Safe` context")
 311                         }
 312                     }
 313                     if !self.violations.contains(violation) {
 314                         self.violations.push(*violation)
 315                     }
 316                 }
 317                 false
 318             }
 319             // With the RFC 2585, no longer allow `unsafe` operations in `unsafe fn`s
 320             Safety::FnUnsafe => {
 321                 for violation in violations {
 322                     let mut violation = *violation;
 323
 324                     violation.kind = UnsafetyViolationKind::UnsafeFn;
 325                     if !self.violations.contains(&violation) {
 326                         self.violations.push(violation)
 327                     }
 328                 }
 329                 false
 330             }
 331             Safety::BuiltinUnsafe => true,
 332             Safety::ExplicitUnsafe(hir_id) => {
 333                 // mark unsafe block as used if there are any unsafe operations inside
 334                 if !violations.is_empty() {
 335                     self.used_unsafe.insert(hir_id);
 336                 }
 337                 // only some unsafety is allowed in const fn
 338                 if self.min_const_fn {
 339                     for violation in violations {
 340                         match violation.kind {
 341                             // these unsafe things are stable in const fn
 342                             UnsafetyViolationKind::GeneralAndConstFn => {}
 343                             // these things are forbidden in const fns
 344                             UnsafetyViolationKind::General => {
 345                                 let mut violation = *violation;
 346                                 // const fns don't need to be backwards compatible and can
 347                                 // emit these violations as a hard error instead of a backwards
 348                                 // compat lint
 349                                 violation.kind = UnsafetyViolationKind::General;
 350                                 if !self.violations.contains(&violation) {
 351                                     self.violations.push(violation)
 352                                 }
 353                             }
 354                             UnsafetyViolationKind::UnsafeFn => bug!(
 355                                 "`UnsafetyViolationKind::UnsafeFn` in an `ExplicitUnsafe` context"
 356                             ),
 357                         }
 358                     }
 359                 }
 360                 true
 361             }
 362         };
 363         self.inherited_blocks.extend(
 364             unsafe_blocks.iter().map(|&(hir_id, is_used)| (hir_id, is_used && !within_unsafe)),
 365         );
 366     }
 367     fn check_mut_borrowing_layout_constrained_field(
 368         &mut self,
 369         place: Place<'tcx>,
 370         is_mut_use: bool,
 371     ) {
 372         for (place_base, elem) in place.iter_projections().rev() {
 373             match elem {
 374                 // Modifications behind a dereference don't affect the value of
 375                 // the pointer.
 376                 ProjectionElem::Deref => return,
 377                 ProjectionElem::Field(..) => {
 378                     let ty = place_base.ty(&self.body.local_decls, self.tcx).ty;
 379                     if let ty::Adt(def, _) = ty.kind() {
 380                         if self.tcx.layout_scalar_valid_range(def.did)
 381                             != (Bound::Unbounded, Bound::Unbounded)
 382                         {
 383                             let details = if is_mut_use {
 384                                 UnsafetyViolationDetails::MutationOfLayoutConstrainedField
 385
 386                             // Check `is_freeze` as late as possible to avoid cycle errors
 387                             // with opaque types.
 388                             } else if !place
 389                                 .ty(self.body, self.tcx)
 390                                 .ty
 391                                 .is_freeze(self.tcx.at(self.source_info.span), self.param_env)
 392                             {
 393                                 UnsafetyViolationDetails::BorrowOfLayoutConstrainedField
 394                             } else {
 395                                 continue;
 396                             };
 397                             self.require_unsafe(UnsafetyViolationKind::GeneralAndConstFn, details);
 398                         }
 399                     }
 400                 }
 401                 _ => {}
 402             }
 403         }
 404     }
 405
 406     /// Checks whether calling `func_did` needs an `unsafe` context or not, i.e. whether
 407     /// the called function has target features the calling function hasn't.
 408     fn check_target_features(&mut self, func_did: DefId) {
 409         let callee_features = &self.tcx.codegen_fn_attrs(func_did).target_features;
 410         let self_features = &self.tcx.codegen_fn_attrs(self.body_did).target_features;
 411
 412         // Is `callee_features` a subset of `calling_features`?
 413         if !callee_features.iter().all(|feature| self_features.contains(feature)) {
 414             self.require_unsafe(
 415                 UnsafetyViolationKind::GeneralAndConstFn,
 416                 UnsafetyViolationDetails::CallToFunctionWith,
 417             )
 418         }
 419     }
 420 }
 421
 422 pub(crate) fn provide(providers: &mut Providers) {
 423     *providers = Providers {
 424         unsafety_check_result: |tcx, def_id| {
 425             if let Some(def) = ty::WithOptConstParam::try_lookup(def_id, tcx) {
 426                 tcx.unsafety_check_result_for_const_arg(def)
 427             } else {
 428                 unsafety_check_result(tcx, ty::WithOptConstParam::unknown(def_id))
 429             }
 430         },
 431         unsafety_check_result_for_const_arg: |tcx, (did, param_did)| {
 432             unsafety_check_result(
 433                 tcx,
 434                 ty::WithOptConstParam { did, const_param_did: Some(param_did) },
 435             )
 436         },
 437         ..*providers
 438     };
 439 }
 440
 441 struct UnusedUnsafeVisitor<'a> {
 442     used_unsafe: &'a FxHashSet<hir::HirId>,
 443     unsafe_blocks: &'a mut Vec<(hir::HirId, bool)>,
 444 }
 445
 446 impl<'a, 'tcx> intravisit::Visitor<'tcx> for UnusedUnsafeVisitor<'a> {
 447     type Map = intravisit::ErasedMap<'tcx>;
 448
 449     fn nested_visit_map(&mut self) -> intravisit::NestedVisitorMap<Self::Map> {
 450         intravisit::NestedVisitorMap::None
 451     }
 452
 453     fn visit_block(&mut self, block: &'tcx hir::Block<'tcx>) {
 454         intravisit::walk_block(self, block);
 455
 456         if let hir::BlockCheckMode::UnsafeBlock(hir::UnsafeSource::UserProvided) = block.rules {
 457             self.unsafe_blocks.push((block.hir_id, self.used_unsafe.contains(&block.hir_id)));
 458         }
 459     }
 460 }
 461
 462 fn check_unused_unsafe(
 463     tcx: TyCtxt<'_>,
 464     def_id: LocalDefId,
 465     used_unsafe: &FxHashSet<hir::HirId>,
 466     unsafe_blocks: &mut Vec<(hir::HirId, bool)>,
 467 ) {
 468     let body_id = tcx.hir().maybe_body_owned_by(tcx.hir().local_def_id_to_hir_id(def_id));
 469
 470     let body_id = match body_id {
 471         Some(body) => body,
 472         None => {
 473             debug!("check_unused_unsafe({:?}) - no body found", def_id);
 474             return;
 475         }
 476     };
 477     let body = tcx.hir().body(body_id);
 478     debug!("check_unused_unsafe({:?}, body={:?}, used_unsafe={:?})", def_id, body, used_unsafe);
 479
 480     let mut visitor = UnusedUnsafeVisitor { used_unsafe, unsafe_blocks };
 481     intravisit::Visitor::visit_body(&mut visitor, body);
 482 }
 483
 484 fn unsafety_check_result<'tcx>(
 485     tcx: TyCtxt<'tcx>,
 486     def: ty::WithOptConstParam<LocalDefId>,
 487 ) -> &'tcx UnsafetyCheckResult {
 488     debug!("unsafety_violations({:?})", def);
 489
 490     // N.B., this borrow is valid because all the consumers of
 491     // `mir_built` force this.
 492     let body = &tcx.mir_built(def).borrow();
 493
 494     let param_env = tcx.param_env(def.did);
 495
 496     let id = tcx.hir().local_def_id_to_hir_id(def.did);
 497     let (const_context, min_const_fn) = match tcx.hir().body_owner_kind(id) {
 498         hir::BodyOwnerKind::Closure => (false, false),
 499         hir::BodyOwnerKind::Fn => {
 500             (tcx.is_const_fn_raw(def.did.to_def_id()), is_min_const_fn(tcx, def.did.to_def_id()))
 501         }
 502         hir::BodyOwnerKind::Const | hir::BodyOwnerKind::Static(_) => (true, false),
 503     };
 504     let mut checker =
 505         UnsafetyChecker::new(const_context, min_const_fn, body, def.did, tcx, param_env);
 506     checker.visit_body(&body);
 507
 508     check_unused_unsafe(tcx, def.did, &checker.used_unsafe, &mut checker.inherited_blocks);
 509
 510     tcx.arena.alloc(UnsafetyCheckResult {
 511         violations: checker.violations.into(),
 512         unsafe_blocks: checker.inherited_blocks.into(),
 513     })
 514 }
 515
 516 /// Returns the `HirId` for an enclosing scope that is also `unsafe`.
 517 fn is_enclosed(
 518     tcx: TyCtxt<'_>,
 519     used_unsafe: &FxHashSet<hir::HirId>,
 520     id: hir::HirId,
 521     unsafe_op_in_unsafe_fn_allowed: bool,
 522 ) -> Option<(&'static str, hir::HirId)> {
 523     let parent_id = tcx.hir().get_parent_node(id);
 524     if parent_id != id {
 525         if used_unsafe.contains(&parent_id) {
 526             Some(("block", parent_id))
 527         } else if let Some(Node::Item(&hir::Item {
 528             kind: hir::ItemKind::Fn(ref sig, _, _), ..
 529         })) = tcx.hir().find(parent_id)
 530         {
 531             if sig.header.unsafety == hir::Unsafety::Unsafe && unsafe_op_in_unsafe_fn_allowed {
 532                 Some(("fn", parent_id))
 533             } else {
 534                 None
 535             }
 536         } else {
 537             is_enclosed(tcx, used_unsafe, parent_id, unsafe_op_in_unsafe_fn_allowed)
 538         }
 539     } else {
 540         None
 541     }
 542 }
 543
 544 fn report_unused_unsafe(tcx: TyCtxt<'_>, used_unsafe: &FxHashSet<hir::HirId>, id: hir::HirId) {
 545     let span = tcx.sess.source_map().guess_head_span(tcx.hir().span(id));
 546     tcx.struct_span_lint_hir(UNUSED_UNSAFE, id, span, |lint| {
 547         let msg = "unnecessary `unsafe` block";
 548         let mut db = lint.build(msg);
 549         db.span_label(span, msg);
 550         if let Some((kind, id)) =
 551             is_enclosed(tcx, used_unsafe, id, unsafe_op_in_unsafe_fn_allowed(tcx, id))
 552         {
 553             db.span_label(
 554                 tcx.sess.source_map().guess_head_span(tcx.hir().span(id)),
 555                 format!("because it's nested under this `unsafe` {}", kind),
 556             );
 557         }
 558         db.emit();
 559     });
 560 }
 561
 562 pub fn check_unsafety(tcx: TyCtxt<'_>, def_id: LocalDefId) {
 563     debug!("check_unsafety({:?})", def_id);
 564
 565     // closures are handled by their parent fn.
 566     if tcx.is_closure(def_id.to_def_id()) {
 567         return;
 568     }
 569
 570     let UnsafetyCheckResult { violations, unsafe_blocks } = tcx.unsafety_check_result(def_id);
 571
 572     for &UnsafetyViolation { source_info, lint_root, kind, details } in violations.iter() {
 573         let (description, note) = details.description_and_note();
 574
 575         // Report an error.
 576         let unsafe_fn_msg =
 577             if unsafe_op_in_unsafe_fn_allowed(tcx, lint_root) { " function or" } else { "" };
 578
 579         match kind {
 580             UnsafetyViolationKind::GeneralAndConstFn | UnsafetyViolationKind::General => {
 581                 // once
 582                 struct_span_err!(
 583                     tcx.sess,
 584                     source_info.span,
 585                     E0133,
 586                     "{} is unsafe and requires unsafe{} block",
 587                     description,
 588                     unsafe_fn_msg,
 589                 )
 590                 .span_label(source_info.span, description)
 591                 .note(note)
 592                 .emit();
 593             }
 594             UnsafetyViolationKind::UnsafeFn => tcx.struct_span_lint_hir(
 595                 UNSAFE_OP_IN_UNSAFE_FN,
 596                 lint_root,
 597                 source_info.span,
 598                 |lint| {
 599                     lint.build(&format!(
 600                         "{} is unsafe and requires unsafe block (error E0133)",
 601                         description,
 602                     ))
 603                     .span_label(source_info.span, description)
 604                     .note(note)
 605                     .emit();
 606                 },
 607             ),
 608         }
 609     }
 610
 611     let (mut unsafe_used, mut unsafe_unused): (FxHashSet<_>, Vec<_>) = Default::default();
 612     for &(block_id, is_used) in unsafe_blocks.iter() {
 613         if is_used {
 614             unsafe_used.insert(block_id);
 615         } else {
 616             unsafe_unused.push(block_id);
 617         }
 618     }
 619     // The unused unsafe blocks might not be in source order; sort them so that the unused unsafe
 620     // error messages are properly aligned and the issue-45107 and lint-unused-unsafe tests pass.
 621     unsafe_unused.sort_by_cached_key(|hir_id| tcx.hir().span(*hir_id));
 622
 623     for &block_id in &unsafe_unused {
 624         report_unused_unsafe(tcx, &unsafe_used, block_id);
 625     }
 626 }
 627
 628 fn unsafe_op_in_unsafe_fn_allowed(tcx: TyCtxt<'_>, id: HirId) -> bool {
 629     tcx.lint_level_at_node(UNSAFE_OP_IN_UNSAFE_FN, id).0 == Level::Allow
 630 }