src/librustc_mir/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::Nop => {
 118                 // safe (at least as emitted during MIR construction)
 119             }
 120
 121             StatementKind::LlvmInlineAsm { .. } => self.require_unsafe(
 122                 UnsafetyViolationKind::General,
 123                 UnsafetyViolationDetails::UseOfInlineAssembly,
 124             ),
 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         if context.is_borrow() {
 184             if util::is_disaligned(self.tcx, self.body, self.param_env, *place) {
 185                 self.require_unsafe(
 186                     UnsafetyViolationKind::BorrowPacked,
 187                     UnsafetyViolationDetails::BorrowOfPackedField,
 188                 );
 189             }
 190         }
 191
 192         for (i, elem) in place.projection.iter().enumerate() {
 193             let proj_base = &place.projection[..i];
 194             if context.is_borrow() {
 195                 if util::is_disaligned(self.tcx, self.body, self.param_env, *place) {
 196                     self.require_unsafe(
 197                         UnsafetyViolationKind::BorrowPacked,
 198                         UnsafetyViolationDetails::BorrowOfPackedField,
 199                     );
 200                 }
 201             }
 202             let source_info = self.source_info;
 203             if let [] = proj_base {
 204                 let decl = &self.body.local_decls[place.local];
 205                 if decl.internal {
 206                     if let Some(box LocalInfo::StaticRef { def_id, .. }) = decl.local_info {
 207                         if self.tcx.is_mutable_static(def_id) {
 208                             self.require_unsafe(
 209                                 UnsafetyViolationKind::General,
 210                                 UnsafetyViolationDetails::UseOfMutableStatic,
 211                             );
 212                             return;
 213                         } else if self.tcx.is_foreign_item(def_id) {
 214                             self.require_unsafe(
 215                                 UnsafetyViolationKind::General,
 216                                 UnsafetyViolationDetails::UseOfExternStatic,
 217                             );
 218                             return;
 219                         }
 220                     } else {
 221                         // Internal locals are used in the `move_val_init` desugaring.
 222                         // We want to check unsafety against the source info of the
 223                         // desugaring, rather than the source info of the RHS.
 224                         self.source_info = self.body.local_decls[place.local].source_info;
 225                     }
 226                 }
 227             }
 228             let base_ty = Place::ty_from(place.local, proj_base, self.body, self.tcx).ty;
 229             match base_ty.kind {
 230                 ty::RawPtr(..) => self.require_unsafe(
 231                     UnsafetyViolationKind::General,
 232                     UnsafetyViolationDetails::DerefOfRawPointer,
 233                 ),
 234                 ty::Adt(adt, _) => {
 235                     if adt.is_union() {
 236                         if context == PlaceContext::MutatingUse(MutatingUseContext::Store)
 237                             || context == PlaceContext::MutatingUse(MutatingUseContext::Drop)
 238                             || context == PlaceContext::MutatingUse(MutatingUseContext::AsmOutput)
 239                         {
 240                             let elem_ty = match elem {
 241                                 ProjectionElem::Field(_, ty) => ty,
 242                                 _ => span_bug!(
 243                                     self.source_info.span,
 244                                     "non-field projection {:?} from union?",
 245                                     place
 246                                 ),
 247                             };
 248                             if !elem_ty.is_copy_modulo_regions(
 249                                 self.tcx.at(self.source_info.span),
 250                                 self.param_env,
 251                             ) {
 252                                 self.require_unsafe(
 253                                     UnsafetyViolationKind::GeneralAndConstFn,
 254                                     UnsafetyViolationDetails::AssignToNonCopyUnionField,
 255                                 )
 256                             } else {
 257                                 // write to non-move union, safe
 258                             }
 259                         } else {
 260                             self.require_unsafe(
 261                                 UnsafetyViolationKind::GeneralAndConstFn,
 262                                 UnsafetyViolationDetails::AccessToUnionField,
 263                             )
 264                         }
 265                     }
 266                 }
 267                 _ => {}
 268             }
 269             self.source_info = source_info;
 270         }
 271     }
 272 }
 273
 274 impl<'a, 'tcx> UnsafetyChecker<'a, 'tcx> {
 275     fn require_unsafe(&mut self, kind: UnsafetyViolationKind, details: UnsafetyViolationDetails) {
 276         let source_info = self.source_info;
 277         let lint_root = self.body.source_scopes[self.source_info.scope]
 278             .local_data
 279             .as_ref()
 280             .assert_crate_local()
 281             .lint_root;
 282         self.register_violations(
 283             &[UnsafetyViolation { source_info, lint_root, kind, details }],
 284             &[],
 285         );
 286     }
 287
 288     fn register_violations(
 289         &mut self,
 290         violations: &[UnsafetyViolation],
 291         unsafe_blocks: &[(hir::HirId, bool)],
 292     ) {
 293         let safety = self.body.source_scopes[self.source_info.scope]
 294             .local_data
 295             .as_ref()
 296             .assert_crate_local()
 297             .safety;
 298         let within_unsafe = match safety {
 299             // `unsafe` blocks are required in safe code
 300             Safety::Safe => {
 301                 for violation in violations {
 302                     let mut violation = *violation;
 303                     match violation.kind {
 304                         UnsafetyViolationKind::GeneralAndConstFn
 305                         | UnsafetyViolationKind::General => {}
 306                         UnsafetyViolationKind::BorrowPacked => {
 307                             if self.min_const_fn {
 308                                 // const fns don't need to be backwards compatible and can
 309                                 // emit these violations as a hard error instead of a backwards
 310                                 // compat lint
 311                                 violation.kind = UnsafetyViolationKind::General;
 312                             }
 313                         }
 314                         UnsafetyViolationKind::UnsafeFn
 315                         | UnsafetyViolationKind::UnsafeFnBorrowPacked => {
 316                             bug!("`UnsafetyViolationKind::UnsafeFn` in an `Safe` context")
 317                         }
 318                     }
 319                     if !self.violations.contains(&violation) {
 320                         self.violations.push(violation)
 321                     }
 322                 }
 323                 false
 324             }
 325             // With the RFC 2585, no longer allow `unsafe` operations in `unsafe fn`s
 326             Safety::FnUnsafe if self.tcx.features().unsafe_block_in_unsafe_fn => {
 327                 for violation in violations {
 328                     let mut violation = *violation;
 329
 330                     if violation.kind == UnsafetyViolationKind::BorrowPacked {
 331                         violation.kind = UnsafetyViolationKind::UnsafeFnBorrowPacked;
 332                     } else {
 333                         violation.kind = UnsafetyViolationKind::UnsafeFn;
 334                     }
 335                     if !self.violations.contains(&violation) {
 336                         self.violations.push(violation)
 337                     }
 338                 }
 339                 false
 340             }
 341             // `unsafe` function bodies allow unsafe without additional unsafe blocks (before RFC 2585)
 342             Safety::BuiltinUnsafe | Safety::FnUnsafe => true,
 343             Safety::ExplicitUnsafe(hir_id) => {
 344                 // mark unsafe block as used if there are any unsafe operations inside
 345                 if !violations.is_empty() {
 346                     self.used_unsafe.insert(hir_id);
 347                 }
 348                 // only some unsafety is allowed in const fn
 349                 if self.min_const_fn {
 350                     for violation in violations {
 351                         match violation.kind {
 352                             // these unsafe things are stable in const fn
 353                             UnsafetyViolationKind::GeneralAndConstFn => {}
 354                             // these things are forbidden in const fns
 355                             UnsafetyViolationKind::General
 356                             | UnsafetyViolationKind::BorrowPacked => {
 357                                 let mut violation = *violation;
 358                                 // const fns don't need to be backwards compatible and can
 359                                 // emit these violations as a hard error instead of a backwards
 360                                 // compat lint
 361                                 violation.kind = UnsafetyViolationKind::General;
 362                                 if !self.violations.contains(&violation) {
 363                                     self.violations.push(violation)
 364                                 }
 365                             }
 366                             UnsafetyViolationKind::UnsafeFn
 367                             | UnsafetyViolationKind::UnsafeFnBorrowPacked => bug!(
 368                                 "`UnsafetyViolationKind::UnsafeFn` in an `ExplicitUnsafe` context"
 369                             ),
 370                         }
 371                     }
 372                 }
 373                 true
 374             }
 375         };
 376         self.inherited_blocks.extend(
 377             unsafe_blocks.iter().map(|&(hir_id, is_used)| (hir_id, is_used && !within_unsafe)),
 378         );
 379     }
 380     fn check_mut_borrowing_layout_constrained_field(
 381         &mut self,
 382         place: Place<'tcx>,
 383         is_mut_use: bool,
 384     ) {
 385         let mut cursor = place.projection.as_ref();
 386         while let &[ref proj_base @ .., elem] = cursor {
 387             cursor = proj_base;
 388
 389             match elem {
 390                 // Modifications behind a dereference don't affect the value of
 391                 // the pointer.
 392                 ProjectionElem::Deref => return,
 393                 ProjectionElem::Field(..) => {
 394                     let ty =
 395                         Place::ty_from(place.local, proj_base, &self.body.local_decls, self.tcx).ty;
 396                     if let ty::Adt(def, _) = ty.kind {
 397                         if self.tcx.layout_scalar_valid_range(def.did)
 398                             != (Bound::Unbounded, Bound::Unbounded)
 399                         {
 400                             let details = if is_mut_use {
 401                                 UnsafetyViolationDetails::MutationOfLayoutConstrainedField
 402
 403                             // Check `is_freeze` as late as possible to avoid cycle errors
 404                             // with opaque types.
 405                             } else if !place
 406                                 .ty(self.body, self.tcx)
 407                                 .ty
 408                                 .is_freeze(self.tcx.at(self.source_info.span), self.param_env)
 409                             {
 410                                 UnsafetyViolationDetails::BorrowOfLayoutConstrainedField
 411                             } else {
 412                                 continue;
 413                             };
 414                             self.require_unsafe(UnsafetyViolationKind::GeneralAndConstFn, details);
 415                         }
 416                     }
 417                 }
 418                 _ => {}
 419             }
 420         }
 421     }
 422
 423     /// Checks whether calling `func_did` needs an `unsafe` context or not, i.e. whether
 424     /// the called function has target features the calling function hasn't.
 425     fn check_target_features(&mut self, func_did: DefId) {
 426         let callee_features = &self.tcx.codegen_fn_attrs(func_did).target_features;
 427         let self_features = &self.tcx.codegen_fn_attrs(self.body_did).target_features;
 428
 429         // Is `callee_features` a subset of `calling_features`?
 430         if !callee_features.iter().all(|feature| self_features.contains(feature)) {
 431             self.require_unsafe(
 432                 UnsafetyViolationKind::GeneralAndConstFn,
 433                 UnsafetyViolationDetails::CallToFunctionWith,
 434             )
 435         }
 436     }
 437 }
 438
 439 pub(crate) fn provide(providers: &mut Providers) {
 440     *providers = Providers {
 441         unsafety_check_result: |tcx, def_id| {
 442             if let Some(def) = ty::WithOptConstParam::try_lookup(def_id, tcx) {
 443                 tcx.unsafety_check_result_for_const_arg(def)
 444             } else {
 445                 unsafety_check_result(tcx, ty::WithOptConstParam::unknown(def_id))
 446             }
 447         },
 448         unsafety_check_result_for_const_arg: |tcx, (did, param_did)| {
 449             unsafety_check_result(
 450                 tcx,
 451                 ty::WithOptConstParam { did, const_param_did: Some(param_did) },
 452             )
 453         },
 454         unsafe_derive_on_repr_packed,
 455         ..*providers
 456     };
 457 }
 458
 459 struct UnusedUnsafeVisitor<'a> {
 460     used_unsafe: &'a FxHashSet<hir::HirId>,
 461     unsafe_blocks: &'a mut Vec<(hir::HirId, bool)>,
 462 }
 463
 464 impl<'a, 'tcx> intravisit::Visitor<'tcx> for UnusedUnsafeVisitor<'a> {
 465     type Map = intravisit::ErasedMap<'tcx>;
 466
 467     fn nested_visit_map(&mut self) -> intravisit::NestedVisitorMap<Self::Map> {
 468         intravisit::NestedVisitorMap::None
 469     }
 470
 471     fn visit_block(&mut self, block: &'tcx hir::Block<'tcx>) {
 472         intravisit::walk_block(self, block);
 473
 474         if let hir::BlockCheckMode::UnsafeBlock(hir::UnsafeSource::UserProvided) = block.rules {
 475             self.unsafe_blocks.push((block.hir_id, self.used_unsafe.contains(&block.hir_id)));
 476         }
 477     }
 478 }
 479
 480 fn check_unused_unsafe(
 481     tcx: TyCtxt<'_>,
 482     def_id: LocalDefId,
 483     used_unsafe: &FxHashSet<hir::HirId>,
 484     unsafe_blocks: &mut Vec<(hir::HirId, bool)>,
 485 ) {
 486     let body_id = tcx.hir().maybe_body_owned_by(tcx.hir().as_local_hir_id(def_id));
 487
 488     let body_id = match body_id {
 489         Some(body) => body,
 490         None => {
 491             debug!("check_unused_unsafe({:?}) - no body found", def_id);
 492             return;
 493         }
 494     };
 495     let body = tcx.hir().body(body_id);
 496     debug!("check_unused_unsafe({:?}, body={:?}, used_unsafe={:?})", def_id, body, used_unsafe);
 497
 498     let mut visitor = UnusedUnsafeVisitor { used_unsafe, unsafe_blocks };
 499     intravisit::Visitor::visit_body(&mut visitor, body);
 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 id = tcx.hir().as_local_hir_id(def.did);
 515     let (const_context, min_const_fn) = match tcx.hir().body_owner_kind(id) {
 516         hir::BodyOwnerKind::Closure => (false, false),
 517         hir::BodyOwnerKind::Fn => {
 518             (tcx.is_const_fn_raw(def.did.to_def_id()), is_min_const_fn(tcx, def.did.to_def_id()))
 519         }
 520         hir::BodyOwnerKind::Const | hir::BodyOwnerKind::Static(_) => (true, false),
 521     };
 522     let mut checker =
 523         UnsafetyChecker::new(const_context, min_const_fn, body, def.did, tcx, param_env);
 524     checker.visit_body(&body);
 525
 526     check_unused_unsafe(tcx, def.did, &checker.used_unsafe, &mut checker.inherited_blocks);
 527
 528     tcx.arena.alloc(UnsafetyCheckResult {
 529         violations: checker.violations.into(),
 530         unsafe_blocks: checker.inherited_blocks.into(),
 531     })
 532 }
 533
 534 fn unsafe_derive_on_repr_packed(tcx: TyCtxt<'_>, def_id: LocalDefId) {
 535     let lint_hir_id = tcx.hir().as_local_hir_id(def_id);
 536
 537     tcx.struct_span_lint_hir(SAFE_PACKED_BORROWS, lint_hir_id, tcx.def_span(def_id), |lint| {
 538         // FIXME: when we make this a hard error, this should have its
 539         // own error code.
 540         let message = if tcx.generics_of(def_id).own_requires_monomorphization() {
 541             "`#[derive]` can't be used on a `#[repr(packed)]` struct with \
 542              type or const parameters (error E0133)"
 543                 .to_string()
 544         } else {
 545             "`#[derive]` can't be used on a `#[repr(packed)]` struct that \
 546              does not derive Copy (error E0133)"
 547                 .to_string()
 548         };
 549         lint.build(&message).emit()
 550     });
 551 }
 552
 553 /// Returns the `HirId` for an enclosing scope that is also `unsafe`.
 554 fn is_enclosed(
 555     tcx: TyCtxt<'_>,
 556     used_unsafe: &FxHashSet<hir::HirId>,
 557     id: hir::HirId,
 558 ) -> Option<(String, hir::HirId)> {
 559     let parent_id = tcx.hir().get_parent_node(id);
 560     if parent_id != id {
 561         if used_unsafe.contains(&parent_id) {
 562             Some(("block".to_string(), parent_id))
 563         } else if let Some(Node::Item(&hir::Item {
 564             kind: hir::ItemKind::Fn(ref sig, _, _), ..
 565         })) = tcx.hir().find(parent_id)
 566         {
 567             if sig.header.unsafety == hir::Unsafety::Unsafe
 568                 && !tcx.features().unsafe_block_in_unsafe_fn
 569             {
 570                 Some(("fn".to_string(), parent_id))
 571             } else {
 572                 None
 573             }
 574         } else {
 575             is_enclosed(tcx, used_unsafe, parent_id)
 576         }
 577     } else {
 578         None
 579     }
 580 }
 581
 582 fn report_unused_unsafe(tcx: TyCtxt<'_>, used_unsafe: &FxHashSet<hir::HirId>, id: hir::HirId) {
 583     let span = tcx.sess.source_map().guess_head_span(tcx.hir().span(id));
 584     tcx.struct_span_lint_hir(UNUSED_UNSAFE, id, span, |lint| {
 585         let msg = "unnecessary `unsafe` block";
 586         let mut db = lint.build(msg);
 587         db.span_label(span, msg);
 588         if let Some((kind, id)) = is_enclosed(tcx, used_unsafe, id) {
 589             db.span_label(
 590                 tcx.sess.source_map().guess_head_span(tcx.hir().span(id)),
 591                 format!("because it's nested under this `unsafe` {}", kind),
 592             );
 593         }
 594         db.emit();
 595     });
 596 }
 597
 598 fn builtin_derive_def_id(tcx: TyCtxt<'_>, def_id: DefId) -> Option<DefId> {
 599     debug!("builtin_derive_def_id({:?})", def_id);
 600     if let Some(impl_def_id) = tcx.impl_of_method(def_id) {
 601         if tcx.has_attr(impl_def_id, sym::automatically_derived) {
 602             debug!("builtin_derive_def_id({:?}) - is {:?}", def_id, impl_def_id);
 603             Some(impl_def_id)
 604         } else {
 605             debug!("builtin_derive_def_id({:?}) - not automatically derived", def_id);
 606             None
 607         }
 608     } else {
 609         debug!("builtin_derive_def_id({:?}) - not a method", def_id);
 610         None
 611     }
 612 }
 613
 614 pub fn check_unsafety(tcx: TyCtxt<'_>, def_id: LocalDefId) {
 615     debug!("check_unsafety({:?})", def_id);
 616
 617     // closures are handled by their parent fn.
 618     if tcx.is_closure(def_id.to_def_id()) {
 619         return;
 620     }
 621
 622     let UnsafetyCheckResult { violations, unsafe_blocks } = tcx.unsafety_check_result(def_id);
 623
 624     for &UnsafetyViolation { source_info, lint_root, kind, details } in violations.iter() {
 625         let (description, note) = details.description_and_note();
 626
 627         // Report an error.
 628         let unsafe_fn_msg =
 629             if unsafe_op_in_unsafe_fn_allowed(tcx, lint_root) { " function or" } else { "" };
 630
 631         match kind {
 632             UnsafetyViolationKind::GeneralAndConstFn | UnsafetyViolationKind::General => {
 633                 // once
 634                 struct_span_err!(
 635                     tcx.sess,
 636                     source_info.span,
 637                     E0133,
 638                     "{} is unsafe and requires unsafe{} block",
 639                     description,
 640                     unsafe_fn_msg,
 641                 )
 642                 .span_label(source_info.span, description)
 643                 .note(note)
 644                 .emit();
 645             }
 646             UnsafetyViolationKind::BorrowPacked => {
 647                 if let Some(impl_def_id) = builtin_derive_def_id(tcx, def_id.to_def_id()) {
 648                     // If a method is defined in the local crate,
 649                     // the impl containing that method should also be.
 650                     tcx.ensure().unsafe_derive_on_repr_packed(impl_def_id.expect_local());
 651                 } else {
 652                     tcx.struct_span_lint_hir(
 653                         SAFE_PACKED_BORROWS,
 654                         lint_root,
 655                         source_info.span,
 656                         |lint| {
 657                             lint.build(&format!(
 658                                 "{} is unsafe and requires unsafe{} block (error E0133)",
 659                                 description, unsafe_fn_msg,
 660                             ))
 661                             .note(note)
 662                             .emit()
 663                         },
 664                     )
 665                 }
 666             }
 667             UnsafetyViolationKind::UnsafeFn => tcx.struct_span_lint_hir(
 668                 UNSAFE_OP_IN_UNSAFE_FN,
 669                 lint_root,
 670                 source_info.span,
 671                 |lint| {
 672                     lint.build(&format!(
 673                         "{} is unsafe and requires unsafe block (error E0133)",
 674                         description,
 675                     ))
 676                     .span_label(source_info.span, description)
 677                     .note(note)
 678                     .emit();
 679                 },
 680             ),
 681             UnsafetyViolationKind::UnsafeFnBorrowPacked => {
 682                 // When `unsafe_op_in_unsafe_fn` is disallowed, the behavior of safe and unsafe functions
 683                 // should be the same in terms of warnings and errors. Therefore, with `#[warn(safe_packed_borrows)]`,
 684                 // a safe packed borrow should emit a warning *but not an error* in an unsafe function,
 685                 // just like in a safe function, even if `unsafe_op_in_unsafe_fn` is `deny`.
 686                 //
 687                 // Also, `#[warn(unsafe_op_in_unsafe_fn)]` can't cause any new errors. Therefore, with
 688                 // `#[deny(safe_packed_borrows)]` and `#[warn(unsafe_op_in_unsafe_fn)]`, a packed borrow
 689                 // should only issue a warning for the sake of backwards compatibility.
 690                 //
 691                 // The solution those 2 expectations is to always take the minimum of both lints.
 692                 // This prevent any new errors (unless both lints are explicitely set to `deny`).
 693                 let lint = if tcx.lint_level_at_node(SAFE_PACKED_BORROWS, lint_root).0
 694                     <= tcx.lint_level_at_node(UNSAFE_OP_IN_UNSAFE_FN, lint_root).0
 695                 {
 696                     SAFE_PACKED_BORROWS
 697                 } else {
 698                     UNSAFE_OP_IN_UNSAFE_FN
 699                 };
 700                 tcx.struct_span_lint_hir(&lint, lint_root, source_info.span, |lint| {
 701                     lint.build(&format!(
 702                         "{} is unsafe and requires unsafe block (error E0133)",
 703                         description,
 704                     ))
 705                     .span_label(source_info.span, description)
 706                     .note(note)
 707                     .emit();
 708                 })
 709             }
 710         }
 711     }
 712
 713     let (mut unsafe_used, mut unsafe_unused): (FxHashSet<_>, Vec<_>) = Default::default();
 714     for &(block_id, is_used) in unsafe_blocks.iter() {
 715         if is_used {
 716             unsafe_used.insert(block_id);
 717         } else {
 718             unsafe_unused.push(block_id);
 719         }
 720     }
 721     // The unused unsafe blocks might not be in source order; sort them so that the unused unsafe
 722     // error messages are properly aligned and the issue-45107 and lint-unused-unsafe tests pass.
 723     unsafe_unused.sort_by_cached_key(|hir_id| tcx.hir().span(*hir_id));
 724
 725     for &block_id in &unsafe_unused {
 726         report_unused_unsafe(tcx, &unsafe_used, block_id);
 727     }
 728 }
 729
 730 fn unsafe_op_in_unsafe_fn_allowed(tcx: TyCtxt<'_>, id: HirId) -> bool {
 731     tcx.lint_level_at_node(UNSAFE_OP_IN_UNSAFE_FN, id).0 == Level::Allow
 732 }