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::{SAFE_PACKED_BORROWS, UNSAFE_OP_IN_UNSAFE_FN, UNUSED_UNSAFE};
  14 use rustc_session::lint::Level;
  15 use rustc_span::symbol::sym;
  16
  17 use std::ops::Bound;
  18
  19 use crate::const_eval::is_min_const_fn;
  20 use crate::util;
  21
  22 pub struct UnsafetyChecker<'a, 'tcx> {
  23     body: &'a Body<'tcx>,
  24     body_did: LocalDefId,
  25     const_context: bool,
  26     min_const_fn: bool,
  27     violations: Vec<UnsafetyViolation>,
  28     source_info: SourceInfo,
  29     tcx: TyCtxt<'tcx>,
  30     param_env: ty::ParamEnv<'tcx>,
  31     /// Mark an `unsafe` block as used, so we don't lint it.
  32     used_unsafe: FxHashSet<hir::HirId>,
  33     inherited_blocks: Vec<(hir::HirId, bool)>,
  34 }
  35
  36 impl<'a, 'tcx> UnsafetyChecker<'a, 'tcx> {
  37     fn new(
  38         const_context: bool,
  39         min_const_fn: bool,
  40         body: &'a Body<'tcx>,
  41         body_did: LocalDefId,
  42         tcx: TyCtxt<'tcx>,
  43         param_env: ty::ParamEnv<'tcx>,
  44     ) -> Self {
  45         // sanity check
  46         if min_const_fn {
  47             assert!(const_context);
  48         }
  49         Self {
  50             body,
  51             body_did,
  52             const_context,
  53             min_const_fn,
  54             violations: vec![],
  55             source_info: SourceInfo::outermost(body.span),
  56             tcx,
  57             param_env,
  58             used_unsafe: Default::default(),
  59             inherited_blocks: vec![],
  60         }
  61     }
  62 }
  63
  64 impl<'a, 'tcx> Visitor<'tcx> for UnsafetyChecker<'a, 'tcx> {
  65     fn visit_terminator(&mut self, terminator: &Terminator<'tcx>, location: Location) {
  66         self.source_info = terminator.source_info;
  67         match terminator.kind {
  68             TerminatorKind::Goto { .. }
  69             | TerminatorKind::SwitchInt { .. }
  70             | TerminatorKind::Drop { .. }
  71             | TerminatorKind::Yield { .. }
  72             | TerminatorKind::Assert { .. }
  73             | TerminatorKind::DropAndReplace { .. }
  74             | TerminatorKind::GeneratorDrop
  75             | TerminatorKind::Resume
  76             | TerminatorKind::Abort
  77             | TerminatorKind::Return
  78             | TerminatorKind::Unreachable
  79             | TerminatorKind::FalseEdge { .. }
  80             | TerminatorKind::FalseUnwind { .. } => {
  81                 // safe (at least as emitted during MIR construction)
  82             }
  83
  84             TerminatorKind::Call { ref func, .. } => {
  85                 let func_ty = func.ty(self.body, self.tcx);
  86                 let sig = func_ty.fn_sig(self.tcx);
  87                 if let hir::Unsafety::Unsafe = sig.unsafety() {
  88                     self.require_unsafe(
  89                         UnsafetyViolationKind::GeneralAndConstFn,
  90                         UnsafetyViolationDetails::CallToUnsafeFunction,
  91                     )
  92                 }
  93
  94                 if let ty::FnDef(func_id, _) = func_ty.kind() {
  95                     self.check_target_features(*func_id);
  96                 }
  97             }
  98
  99             TerminatorKind::InlineAsm { .. } => self.require_unsafe(
 100                 UnsafetyViolationKind::General,
 101                 UnsafetyViolationDetails::UseOfInlineAssembly,
 102             ),
 103         }
 104         self.super_terminator(terminator, location);
 105     }
 106
 107     fn visit_statement(&mut self, statement: &Statement<'tcx>, location: Location) {
 108         self.source_info = statement.source_info;
 109         match statement.kind {
 110             StatementKind::Assign(..)
 111             | StatementKind::FakeRead(..)
 112             | StatementKind::SetDiscriminant { .. }
 113             | StatementKind::StorageLive(..)
 114             | StatementKind::StorageDead(..)
 115             | StatementKind::Retag { .. }
 116             | StatementKind::AscribeUserType(..)
 117             | StatementKind::Coverage(..)
 118             | StatementKind::Nop => {
 119                 // safe (at least as emitted during MIR construction)
 120             }
 121
 122             StatementKind::LlvmInlineAsm { .. } => self.require_unsafe(
 123                 UnsafetyViolationKind::General,
 124                 UnsafetyViolationDetails::UseOfInlineAssembly,
 125             ),
 126         }
 127         self.super_statement(statement, location);
 128     }
 129
 130     fn visit_rvalue(&mut self, rvalue: &Rvalue<'tcx>, location: Location) {
 131         match rvalue {
 132             Rvalue::Aggregate(box ref aggregate, _) => match aggregate {
 133                 &AggregateKind::Array(..) | &AggregateKind::Tuple => {}
 134                 &AggregateKind::Adt(ref def, ..) => {
 135                     match self.tcx.layout_scalar_valid_range(def.did) {
 136                         (Bound::Unbounded, Bound::Unbounded) => {}
 137                         _ => self.require_unsafe(
 138                             UnsafetyViolationKind::GeneralAndConstFn,
 139                             UnsafetyViolationDetails::InitializingTypeWith,
 140                         ),
 141                     }
 142                 }
 143                 &AggregateKind::Closure(def_id, _) | &AggregateKind::Generator(def_id, _, _) => {
 144                     let UnsafetyCheckResult { violations, unsafe_blocks } =
 145                         self.tcx.unsafety_check_result(def_id.expect_local());
 146                     self.register_violations(&violations, &unsafe_blocks);
 147                 }
 148             },
 149             // casting pointers to ints is unsafe in const fn because the const evaluator cannot
 150             // possibly know what the result of various operations like `address / 2` would be
 151             // pointers during const evaluation have no integral address, only an abstract one
 152             Rvalue::Cast(CastKind::Misc, ref operand, cast_ty)
 153                 if self.const_context && self.tcx.features().const_raw_ptr_to_usize_cast =>
 154             {
 155                 let operand_ty = operand.ty(self.body, self.tcx);
 156                 let cast_in = CastTy::from_ty(operand_ty).expect("bad input type for cast");
 157                 let cast_out = CastTy::from_ty(cast_ty).expect("bad output type for cast");
 158                 match (cast_in, cast_out) {
 159                     (CastTy::Ptr(_) | CastTy::FnPtr, CastTy::Int(_)) => {
 160                         self.require_unsafe(
 161                             UnsafetyViolationKind::General,
 162                             UnsafetyViolationDetails::CastOfPointerToInt,
 163                         );
 164                     }
 165                     _ => {}
 166                 }
 167             }
 168             _ => {}
 169         }
 170         self.super_rvalue(rvalue, location);
 171     }
 172
 173     fn visit_place(&mut self, place: &Place<'tcx>, context: PlaceContext, _location: Location) {
 174         // On types with `scalar_valid_range`, prevent
 175         // * `&mut x.field`
 176         // * `x.field = y;`
 177         // * `&x.field` if `field`'s type has interior mutability
 178         // because either of these would allow modifying the layout constrained field and
 179         // insert values that violate the layout constraints.
 180         if context.is_mutating_use() || context.is_borrow() {
 181             self.check_mut_borrowing_layout_constrained_field(*place, context.is_mutating_use());
 182         }
 183
 184         if context.is_borrow() {
 185             if util::is_disaligned(self.tcx, self.body, self.param_env, *place) {
 186                 self.require_unsafe(
 187                     UnsafetyViolationKind::BorrowPacked,
 188                     UnsafetyViolationDetails::BorrowOfPackedField,
 189                 );
 190             }
 191         }
 192
 193         for (i, elem) in place.projection.iter().enumerate() {
 194             let proj_base = &place.projection[..i];
 195             if context.is_borrow() {
 196                 if util::is_disaligned(self.tcx, self.body, self.param_env, *place) {
 197                     self.require_unsafe(
 198                         UnsafetyViolationKind::BorrowPacked,
 199                         UnsafetyViolationDetails::BorrowOfPackedField,
 200                     );
 201                 }
 202             }
 203             let source_info = self.source_info;
 204             if let [] = proj_base {
 205                 let decl = &self.body.local_decls[place.local];
 206                 if decl.internal {
 207                     if let Some(box LocalInfo::StaticRef { def_id, .. }) = decl.local_info {
 208                         if self.tcx.is_mutable_static(def_id) {
 209                             self.require_unsafe(
 210                                 UnsafetyViolationKind::General,
 211                                 UnsafetyViolationDetails::UseOfMutableStatic,
 212                             );
 213                             return;
 214                         } else if self.tcx.is_foreign_item(def_id) {
 215                             self.require_unsafe(
 216                                 UnsafetyViolationKind::General,
 217                                 UnsafetyViolationDetails::UseOfExternStatic,
 218                             );
 219                             return;
 220                         }
 221                     } else {
 222                         // Internal locals are used in the `move_val_init` desugaring.
 223                         // We want to check unsafety against the source info of the
 224                         // desugaring, rather than the source info of the RHS.
 225                         self.source_info = self.body.local_decls[place.local].source_info;
 226                     }
 227                 }
 228             }
 229             let base_ty = Place::ty_from(place.local, proj_base, self.body, self.tcx).ty;
 230             match base_ty.kind() {
 231                 ty::RawPtr(..) => self.require_unsafe(
 232                     UnsafetyViolationKind::GeneralAndConstFn,
 233                     UnsafetyViolationDetails::DerefOfRawPointer,
 234                 ),
 235                 ty::Adt(adt, _) => {
 236                     if adt.is_union() {
 237                         if context == PlaceContext::MutatingUse(MutatingUseContext::Store)
 238                             || context == PlaceContext::MutatingUse(MutatingUseContext::Drop)
 239                             || context == PlaceContext::MutatingUse(MutatingUseContext::AsmOutput)
 240                         {
 241                             let elem_ty = match elem {
 242                                 ProjectionElem::Field(_, ty) => ty,
 243                                 _ => span_bug!(
 244                                     self.source_info.span,
 245                                     "non-field projection {:?} from union?",
 246                                     place
 247                                 ),
 248                             };
 249                             if !elem_ty.is_copy_modulo_regions(
 250                                 self.tcx.at(self.source_info.span),
 251                                 self.param_env,
 252                             ) {
 253                                 self.require_unsafe(
 254                                     UnsafetyViolationKind::GeneralAndConstFn,
 255                                     UnsafetyViolationDetails::AssignToNonCopyUnionField,
 256                                 )
 257                             } else {
 258                                 // write to non-move union, safe
 259                             }
 260                         } else {
 261                             self.require_unsafe(
 262                                 UnsafetyViolationKind::GeneralAndConstFn,
 263                                 UnsafetyViolationDetails::AccessToUnionField,
 264                             )
 265                         }
 266                     }
 267                 }
 268                 _ => {}
 269             }
 270             self.source_info = source_info;
 271         }
 272     }
 273 }
 274
 275 impl<'a, 'tcx> UnsafetyChecker<'a, 'tcx> {
 276     fn require_unsafe(&mut self, kind: UnsafetyViolationKind, details: UnsafetyViolationDetails) {
 277         let source_info = self.source_info;
 278         let lint_root = self.body.source_scopes[self.source_info.scope]
 279             .local_data
 280             .as_ref()
 281             .assert_crate_local()
 282             .lint_root;
 283         self.register_violations(
 284             &[UnsafetyViolation { source_info, lint_root, kind, details }],
 285             &[],
 286         );
 287     }
 288
 289     fn register_violations(
 290         &mut self,
 291         violations: &[UnsafetyViolation],
 292         unsafe_blocks: &[(hir::HirId, bool)],
 293     ) {
 294         let safety = self.body.source_scopes[self.source_info.scope]
 295             .local_data
 296             .as_ref()
 297             .assert_crate_local()
 298             .safety;
 299         let within_unsafe = match safety {
 300             // `unsafe` blocks are required in safe code
 301             Safety::Safe => {
 302                 for violation in violations {
 303                     let mut violation = *violation;
 304                     match violation.kind {
 305                         UnsafetyViolationKind::GeneralAndConstFn
 306                         | UnsafetyViolationKind::General => {}
 307                         UnsafetyViolationKind::BorrowPacked => {
 308                             if self.min_const_fn {
 309                                 // const fns don't need to be backwards compatible and can
 310                                 // emit these violations as a hard error instead of a backwards
 311                                 // compat lint
 312                                 violation.kind = UnsafetyViolationKind::General;
 313                             }
 314                         }
 315                         UnsafetyViolationKind::UnsafeFn
 316                         | UnsafetyViolationKind::UnsafeFnBorrowPacked => {
 317                             bug!("`UnsafetyViolationKind::UnsafeFn` in an `Safe` context")
 318                         }
 319                     }
 320                     if !self.violations.contains(&violation) {
 321                         self.violations.push(violation)
 322                     }
 323                 }
 324                 false
 325             }
 326             // With the RFC 2585, no longer allow `unsafe` operations in `unsafe fn`s
 327             Safety::FnUnsafe if self.tcx.features().unsafe_block_in_unsafe_fn => {
 328                 for violation in violations {
 329                     let mut violation = *violation;
 330
 331                     if violation.kind == UnsafetyViolationKind::BorrowPacked {
 332                         violation.kind = UnsafetyViolationKind::UnsafeFnBorrowPacked;
 333                     } else {
 334                         violation.kind = UnsafetyViolationKind::UnsafeFn;
 335                     }
 336                     if !self.violations.contains(&violation) {
 337                         self.violations.push(violation)
 338                     }
 339                 }
 340                 false
 341             }
 342             // `unsafe` function bodies allow unsafe without additional unsafe blocks (before RFC 2585)
 343             Safety::BuiltinUnsafe | Safety::FnUnsafe => true,
 344             Safety::ExplicitUnsafe(hir_id) => {
 345                 // mark unsafe block as used if there are any unsafe operations inside
 346                 if !violations.is_empty() {
 347                     self.used_unsafe.insert(hir_id);
 348                 }
 349                 // only some unsafety is allowed in const fn
 350                 if self.min_const_fn {
 351                     for violation in violations {
 352                         match violation.kind {
 353                             // these unsafe things are stable in const fn
 354                             UnsafetyViolationKind::GeneralAndConstFn => {}
 355                             // these things are forbidden in const fns
 356                             UnsafetyViolationKind::General
 357                             | UnsafetyViolationKind::BorrowPacked => {
 358                                 let mut violation = *violation;
 359                                 // const fns don't need to be backwards compatible and can
 360                                 // emit these violations as a hard error instead of a backwards
 361                                 // compat lint
 362                                 violation.kind = UnsafetyViolationKind::General;
 363                                 if !self.violations.contains(&violation) {
 364                                     self.violations.push(violation)
 365                                 }
 366                             }
 367                             UnsafetyViolationKind::UnsafeFn
 368                             | UnsafetyViolationKind::UnsafeFnBorrowPacked => bug!(
 369                                 "`UnsafetyViolationKind::UnsafeFn` in an `ExplicitUnsafe` context"
 370                             ),
 371                         }
 372                     }
 373                 }
 374                 true
 375             }
 376         };
 377         self.inherited_blocks.extend(
 378             unsafe_blocks.iter().map(|&(hir_id, is_used)| (hir_id, is_used && !within_unsafe)),
 379         );
 380     }
 381     fn check_mut_borrowing_layout_constrained_field(
 382         &mut self,
 383         place: Place<'tcx>,
 384         is_mut_use: bool,
 385     ) {
 386         let mut cursor = place.projection.as_ref();
 387         while let &[ref proj_base @ .., elem] = cursor {
 388             cursor = proj_base;
 389
 390             match elem {
 391                 // Modifications behind a dereference don't affect the value of
 392                 // the pointer.
 393                 ProjectionElem::Deref => return,
 394                 ProjectionElem::Field(..) => {
 395                     let ty =
 396                         Place::ty_from(place.local, proj_base, &self.body.local_decls, self.tcx).ty;
 397                     if let ty::Adt(def, _) = ty.kind() {
 398                         if self.tcx.layout_scalar_valid_range(def.did)
 399                             != (Bound::Unbounded, Bound::Unbounded)
 400                         {
 401                             let details = if is_mut_use {
 402                                 UnsafetyViolationDetails::MutationOfLayoutConstrainedField
 403
 404                             // Check `is_freeze` as late as possible to avoid cycle errors
 405                             // with opaque types.
 406                             } else if !place
 407                                 .ty(self.body, self.tcx)
 408                                 .ty
 409                                 .is_freeze(self.tcx.at(self.source_info.span), self.param_env)
 410                             {
 411                                 UnsafetyViolationDetails::BorrowOfLayoutConstrainedField
 412                             } else {
 413                                 continue;
 414                             };
 415                             self.require_unsafe(UnsafetyViolationKind::GeneralAndConstFn, details);
 416                         }
 417                     }
 418                 }
 419                 _ => {}
 420             }
 421         }
 422     }
 423
 424     /// Checks whether calling `func_did` needs an `unsafe` context or not, i.e. whether
 425     /// the called function has target features the calling function hasn't.
 426     fn check_target_features(&mut self, func_did: DefId) {
 427         let callee_features = &self.tcx.codegen_fn_attrs(func_did).target_features;
 428         let self_features = &self.tcx.codegen_fn_attrs(self.body_did).target_features;
 429
 430         // Is `callee_features` a subset of `calling_features`?
 431         if !callee_features.iter().all(|feature| self_features.contains(feature)) {
 432             self.require_unsafe(
 433                 UnsafetyViolationKind::GeneralAndConstFn,
 434                 UnsafetyViolationDetails::CallToFunctionWith,
 435             )
 436         }
 437     }
 438 }
 439
 440 pub(crate) fn provide(providers: &mut Providers) {
 441     *providers = Providers {
 442         unsafety_check_result: |tcx, def_id| {
 443             if let Some(def) = ty::WithOptConstParam::try_lookup(def_id, tcx) {
 444                 tcx.unsafety_check_result_for_const_arg(def)
 445             } else {
 446                 unsafety_check_result(tcx, ty::WithOptConstParam::unknown(def_id))
 447             }
 448         },
 449         unsafety_check_result_for_const_arg: |tcx, (did, param_did)| {
 450             unsafety_check_result(
 451                 tcx,
 452                 ty::WithOptConstParam { did, const_param_did: Some(param_did) },
 453             )
 454         },
 455         unsafe_derive_on_repr_packed,
 456         ..*providers
 457     };
 458 }
 459
 460 struct UnusedUnsafeVisitor<'a> {
 461     used_unsafe: &'a FxHashSet<hir::HirId>,
 462     unsafe_blocks: &'a mut Vec<(hir::HirId, bool)>,
 463 }
 464
 465 impl<'a, 'tcx> intravisit::Visitor<'tcx> for UnusedUnsafeVisitor<'a> {
 466     type Map = intravisit::ErasedMap<'tcx>;
 467
 468     fn nested_visit_map(&mut self) -> intravisit::NestedVisitorMap<Self::Map> {
 469         intravisit::NestedVisitorMap::None
 470     }
 471
 472     fn visit_block(&mut self, block: &'tcx hir::Block<'tcx>) {
 473         intravisit::walk_block(self, block);
 474
 475         if let hir::BlockCheckMode::UnsafeBlock(hir::UnsafeSource::UserProvided) = block.rules {
 476             self.unsafe_blocks.push((block.hir_id, self.used_unsafe.contains(&block.hir_id)));
 477         }
 478     }
 479 }
 480
 481 fn check_unused_unsafe(
 482     tcx: TyCtxt<'_>,
 483     def_id: LocalDefId,
 484     used_unsafe: &FxHashSet<hir::HirId>,
 485     unsafe_blocks: &mut Vec<(hir::HirId, bool)>,
 486 ) {
 487     let body_id = tcx.hir().maybe_body_owned_by(tcx.hir().local_def_id_to_hir_id(def_id));
 488
 489     let body_id = match body_id {
 490         Some(body) => body,
 491         None => {
 492             debug!("check_unused_unsafe({:?}) - no body found", def_id);
 493             return;
 494         }
 495     };
 496     let body = tcx.hir().body(body_id);
 497     debug!("check_unused_unsafe({:?}, body={:?}, used_unsafe={:?})", def_id, body, used_unsafe);
 498
 499     let mut visitor = UnusedUnsafeVisitor { used_unsafe, unsafe_blocks };
 500     intravisit::Visitor::visit_body(&mut visitor, body);
 501 }
 502
 503 fn unsafety_check_result<'tcx>(
 504     tcx: TyCtxt<'tcx>,
 505     def: ty::WithOptConstParam<LocalDefId>,
 506 ) -> &'tcx UnsafetyCheckResult {
 507     debug!("unsafety_violations({:?})", def);
 508
 509     // N.B., this borrow is valid because all the consumers of
 510     // `mir_built` force this.
 511     let body = &tcx.mir_built(def).borrow();
 512
 513     let param_env = tcx.param_env(def.did);
 514
 515     let id = tcx.hir().local_def_id_to_hir_id(def.did);
 516     let (const_context, min_const_fn) = match tcx.hir().body_owner_kind(id) {
 517         hir::BodyOwnerKind::Closure => (false, false),
 518         hir::BodyOwnerKind::Fn => {
 519             (tcx.is_const_fn_raw(def.did.to_def_id()), is_min_const_fn(tcx, def.did.to_def_id()))
 520         }
 521         hir::BodyOwnerKind::Const | hir::BodyOwnerKind::Static(_) => (true, false),
 522     };
 523     let mut checker =
 524         UnsafetyChecker::new(const_context, min_const_fn, body, def.did, tcx, param_env);
 525     checker.visit_body(&body);
 526
 527     check_unused_unsafe(tcx, def.did, &checker.used_unsafe, &mut checker.inherited_blocks);
 528
 529     tcx.arena.alloc(UnsafetyCheckResult {
 530         violations: checker.violations.into(),
 531         unsafe_blocks: checker.inherited_blocks.into(),
 532     })
 533 }
 534
 535 fn unsafe_derive_on_repr_packed(tcx: TyCtxt<'_>, def_id: LocalDefId) {
 536     let lint_hir_id = tcx.hir().local_def_id_to_hir_id(def_id);
 537
 538     tcx.struct_span_lint_hir(SAFE_PACKED_BORROWS, lint_hir_id, tcx.def_span(def_id), |lint| {
 539         // FIXME: when we make this a hard error, this should have its
 540         // own error code.
 541         let message = if tcx.generics_of(def_id).own_requires_monomorphization() {
 542             "`#[derive]` can't be used on a `#[repr(packed)]` struct with \
 543              type or const parameters (error E0133)"
 544                 .to_string()
 545         } else {
 546             "`#[derive]` can't be used on a `#[repr(packed)]` struct that \
 547              does not derive Copy (error E0133)"
 548                 .to_string()
 549         };
 550         lint.build(&message).emit()
 551     });
 552 }
 553
 554 /// Returns the `HirId` for an enclosing scope that is also `unsafe`.
 555 fn is_enclosed(
 556     tcx: TyCtxt<'_>,
 557     used_unsafe: &FxHashSet<hir::HirId>,
 558     id: hir::HirId,
 559 ) -> Option<(String, hir::HirId)> {
 560     let parent_id = tcx.hir().get_parent_node(id);
 561     if parent_id != id {
 562         if used_unsafe.contains(&parent_id) {
 563             Some(("block".to_string(), parent_id))
 564         } else if let Some(Node::Item(&hir::Item {
 565             kind: hir::ItemKind::Fn(ref sig, _, _), ..
 566         })) = tcx.hir().find(parent_id)
 567         {
 568             if sig.header.unsafety == hir::Unsafety::Unsafe
 569                 && !tcx.features().unsafe_block_in_unsafe_fn
 570             {
 571                 Some(("fn".to_string(), parent_id))
 572             } else {
 573                 None
 574             }
 575         } else {
 576             is_enclosed(tcx, used_unsafe, parent_id)
 577         }
 578     } else {
 579         None
 580     }
 581 }
 582
 583 fn report_unused_unsafe(tcx: TyCtxt<'_>, used_unsafe: &FxHashSet<hir::HirId>, id: hir::HirId) {
 584     let span = tcx.sess.source_map().guess_head_span(tcx.hir().span(id));
 585     tcx.struct_span_lint_hir(UNUSED_UNSAFE, id, span, |lint| {
 586         let msg = "unnecessary `unsafe` block";
 587         let mut db = lint.build(msg);
 588         db.span_label(span, msg);
 589         if let Some((kind, id)) = is_enclosed(tcx, used_unsafe, id) {
 590             db.span_label(
 591                 tcx.sess.source_map().guess_head_span(tcx.hir().span(id)),
 592                 format!("because it's nested under this `unsafe` {}", kind),
 593             );
 594         }
 595         db.emit();
 596     });
 597 }
 598
 599 fn builtin_derive_def_id(tcx: TyCtxt<'_>, def_id: DefId) -> Option<DefId> {
 600     debug!("builtin_derive_def_id({:?})", def_id);
 601     if let Some(impl_def_id) = tcx.impl_of_method(def_id) {
 602         if tcx.has_attr(impl_def_id, sym::automatically_derived) {
 603             debug!("builtin_derive_def_id({:?}) - is {:?}", def_id, impl_def_id);
 604             Some(impl_def_id)
 605         } else {
 606             debug!("builtin_derive_def_id({:?}) - not automatically derived", def_id);
 607             None
 608         }
 609     } else {
 610         debug!("builtin_derive_def_id({:?}) - not a method", def_id);
 611         None
 612     }
 613 }
 614
 615 pub fn check_unsafety(tcx: TyCtxt<'_>, def_id: LocalDefId) {
 616     debug!("check_unsafety({:?})", def_id);
 617
 618     // closures are handled by their parent fn.
 619     if tcx.is_closure(def_id.to_def_id()) {
 620         return;
 621     }
 622
 623     let UnsafetyCheckResult { violations, unsafe_blocks } = tcx.unsafety_check_result(def_id);
 624
 625     for &UnsafetyViolation { source_info, lint_root, kind, details } in violations.iter() {
 626         let (description, note) = details.description_and_note();
 627
 628         // Report an error.
 629         let unsafe_fn_msg =
 630             if unsafe_op_in_unsafe_fn_allowed(tcx, lint_root) { " function or" } else { "" };
 631
 632         match kind {
 633             UnsafetyViolationKind::GeneralAndConstFn | UnsafetyViolationKind::General => {
 634                 // once
 635                 struct_span_err!(
 636                     tcx.sess,
 637                     source_info.span,
 638                     E0133,
 639                     "{} is unsafe and requires unsafe{} block",
 640                     description,
 641                     unsafe_fn_msg,
 642                 )
 643                 .span_label(source_info.span, description)
 644                 .note(note)
 645                 .emit();
 646             }
 647             UnsafetyViolationKind::BorrowPacked => {
 648                 if let Some(impl_def_id) = builtin_derive_def_id(tcx, def_id.to_def_id()) {
 649                     // If a method is defined in the local crate,
 650                     // the impl containing that method should also be.
 651                     tcx.ensure().unsafe_derive_on_repr_packed(impl_def_id.expect_local());
 652                 } else {
 653                     tcx.struct_span_lint_hir(
 654                         SAFE_PACKED_BORROWS,
 655                         lint_root,
 656                         source_info.span,
 657                         |lint| {
 658                             lint.build(&format!(
 659                                 "{} is unsafe and requires unsafe{} block (error E0133)",
 660                                 description, unsafe_fn_msg,
 661                             ))
 662                             .note(note)
 663                             .emit()
 664                         },
 665                     )
 666                 }
 667             }
 668             UnsafetyViolationKind::UnsafeFn => tcx.struct_span_lint_hir(
 669                 UNSAFE_OP_IN_UNSAFE_FN,
 670                 lint_root,
 671                 source_info.span,
 672                 |lint| {
 673                     lint.build(&format!(
 674                         "{} is unsafe and requires unsafe block (error E0133)",
 675                         description,
 676                     ))
 677                     .span_label(source_info.span, description)
 678                     .note(note)
 679                     .emit();
 680                 },
 681             ),
 682             UnsafetyViolationKind::UnsafeFnBorrowPacked => {
 683                 // When `unsafe_op_in_unsafe_fn` is disallowed, the behavior of safe and unsafe functions
 684                 // should be the same in terms of warnings and errors. Therefore, with `#[warn(safe_packed_borrows)]`,
 685                 // a safe packed borrow should emit a warning *but not an error* in an unsafe function,
 686                 // just like in a safe function, even if `unsafe_op_in_unsafe_fn` is `deny`.
 687                 //
 688                 // Also, `#[warn(unsafe_op_in_unsafe_fn)]` can't cause any new errors. Therefore, with
 689                 // `#[deny(safe_packed_borrows)]` and `#[warn(unsafe_op_in_unsafe_fn)]`, a packed borrow
 690                 // should only issue a warning for the sake of backwards compatibility.
 691                 //
 692                 // The solution those 2 expectations is to always take the minimum of both lints.
 693                 // This prevent any new errors (unless both lints are explicitely set to `deny`).
 694                 let lint = if tcx.lint_level_at_node(SAFE_PACKED_BORROWS, lint_root).0
 695                     <= tcx.lint_level_at_node(UNSAFE_OP_IN_UNSAFE_FN, lint_root).0
 696                 {
 697                     SAFE_PACKED_BORROWS
 698                 } else {
 699                     UNSAFE_OP_IN_UNSAFE_FN
 700                 };
 701                 tcx.struct_span_lint_hir(&lint, lint_root, source_info.span, |lint| {
 702                     lint.build(&format!(
 703                         "{} is unsafe and requires unsafe block (error E0133)",
 704                         description,
 705                     ))
 706                     .span_label(source_info.span, description)
 707                     .note(note)
 708                     .emit();
 709                 })
 710             }
 711         }
 712     }
 713
 714     let (mut unsafe_used, mut unsafe_unused): (FxHashSet<_>, Vec<_>) = Default::default();
 715     for &(block_id, is_used) in unsafe_blocks.iter() {
 716         if is_used {
 717             unsafe_used.insert(block_id);
 718         } else {
 719             unsafe_unused.push(block_id);
 720         }
 721     }
 722     // The unused unsafe blocks might not be in source order; sort them so that the unused unsafe
 723     // error messages are properly aligned and the issue-45107 and lint-unused-unsafe tests pass.
 724     unsafe_unused.sort_by_cached_key(|hir_id| tcx.hir().span(*hir_id));
 725
 726     for &block_id in &unsafe_unused {
 727         report_unused_unsafe(tcx, &unsafe_used, block_id);
 728     }
 729 }
 730
 731 fn unsafe_op_in_unsafe_fn_allowed(tcx: TyCtxt<'_>, id: HirId) -> bool {
 732     tcx.lint_level_at_node(UNSAFE_OP_IN_UNSAFE_FN, id).0 == Level::Allow
 733 }