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         // Check for borrows to packed fields.
 185         // `is_disaligned` already traverses the place to consider all projections after the last
 186         // `Deref`, so this only needs to be called once at the top level.
 187         if context.is_borrow() {
 188             if util::is_disaligned(self.tcx, self.body, self.param_env, *place) {
 189                 self.require_unsafe(
 190                     UnsafetyViolationKind::BorrowPacked,
 191                     UnsafetyViolationDetails::BorrowOfPackedField,
 192                 );
 193             }
 194         }
 195
 196         // Some checks below need the extra metainfo of the local declaration.
 197         let decl = &self.body.local_decls[place.local];
 198
 199         // Check the base local: it might be an unsafe-to-access static. We only check derefs of the
 200         // temporary holding the static pointer to avoid duplicate errors
 201         // <https://github.com/rust-lang/rust/pull/78068#issuecomment-731753506>.
 202         if decl.internal && place.projection.first() == Some(&ProjectionElem::Deref) {
 203             // If the projection root is an artifical local that we introduced when
 204             // desugaring `static`, give a more specific error message
 205             // (avoid the general "raw pointer" clause below, that would only be confusing).
 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             }
 221         }
 222
 223         // Check for raw pointer `Deref`.
 224         for (base, proj) in place.iter_projections() {
 225             if proj == ProjectionElem::Deref {
 226                 let base_ty = base.ty(self.body, self.tcx).ty;
 227                 if base_ty.is_unsafe_ptr() {
 228                     self.require_unsafe(
 229                         UnsafetyViolationKind::GeneralAndConstFn,
 230                         UnsafetyViolationDetails::DerefOfRawPointer,
 231                     )
 232                 }
 233             }
 234         }
 235
 236         // Check for union fields. For this we traverse right-to-left, as the last `Deref` changes
 237         // whether we *read* the union field or potentially *write* to it (if this place is being assigned to).
 238         let mut saw_deref = false;
 239         for (base, proj) in place.iter_projections().rev() {
 240             if proj == ProjectionElem::Deref {
 241                 saw_deref = true;
 242                 continue;
 243             }
 244
 245             let base_ty = base.ty(self.body, self.tcx).ty;
 246             if base_ty.ty_adt_def().map_or(false, |adt| adt.is_union()) {
 247                 // If we did not hit a `Deref` yet and the overall place use is an assignment, the
 248                 // rules are different.
 249                 let assign_to_field = !saw_deref
 250                     && matches!(
 251                         context,
 252                         PlaceContext::MutatingUse(
 253                             MutatingUseContext::Store
 254                                 | MutatingUseContext::Drop
 255                                 | MutatingUseContext::AsmOutput
 256                         )
 257                     );
 258                 // If this is just an assignment, determine if the assigned type needs dropping.
 259                 if assign_to_field {
 260                     // We have to check the actual type of the assignment, as that determines if the
 261                     // old value is being dropped.
 262                     let assigned_ty = place.ty(&self.body.local_decls, self.tcx).ty;
 263                     // To avoid semver hazard, we only consider `Copy` and `ManuallyDrop` non-dropping.
 264                     let manually_drop = assigned_ty
 265                         .ty_adt_def()
 266                         .map_or(false, |adt_def| adt_def.is_manually_drop());
 267                     let nodrop = manually_drop
 268                         || assigned_ty.is_copy_modulo_regions(
 269                             self.tcx.at(self.source_info.span),
 270                             self.param_env,
 271                         );
 272                     if !nodrop {
 273                         self.require_unsafe(
 274                             UnsafetyViolationKind::GeneralAndConstFn,
 275                             UnsafetyViolationDetails::AssignToDroppingUnionField,
 276                         );
 277                     } else {
 278                         // write to non-drop union field, safe
 279                     }
 280                 } else {
 281                     self.require_unsafe(
 282                         UnsafetyViolationKind::GeneralAndConstFn,
 283                         UnsafetyViolationDetails::AccessToUnionField,
 284                     )
 285                 }
 286             }
 287         }
 288     }
 289 }
 290
 291 impl<'a, 'tcx> UnsafetyChecker<'a, 'tcx> {
 292     fn require_unsafe(&mut self, kind: UnsafetyViolationKind, details: UnsafetyViolationDetails) {
 293         let source_info = self.source_info;
 294         let lint_root = self.body.source_scopes[self.source_info.scope]
 295             .local_data
 296             .as_ref()
 297             .assert_crate_local()
 298             .lint_root;
 299         self.register_violations(
 300             &[UnsafetyViolation { source_info, lint_root, kind, details }],
 301             &[],
 302         );
 303     }
 304
 305     fn register_violations(
 306         &mut self,
 307         violations: &[UnsafetyViolation],
 308         unsafe_blocks: &[(hir::HirId, bool)],
 309     ) {
 310         let safety = self.body.source_scopes[self.source_info.scope]
 311             .local_data
 312             .as_ref()
 313             .assert_crate_local()
 314             .safety;
 315         let within_unsafe = match safety {
 316             // `unsafe` blocks are required in safe code
 317             Safety::Safe => {
 318                 for violation in violations {
 319                     let mut violation = *violation;
 320                     match violation.kind {
 321                         UnsafetyViolationKind::GeneralAndConstFn
 322                         | UnsafetyViolationKind::General => {}
 323                         UnsafetyViolationKind::BorrowPacked => {
 324                             if self.min_const_fn {
 325                                 // const fns don't need to be backwards compatible and can
 326                                 // emit these violations as a hard error instead of a backwards
 327                                 // compat lint
 328                                 violation.kind = UnsafetyViolationKind::General;
 329                             }
 330                         }
 331                         UnsafetyViolationKind::UnsafeFn
 332                         | UnsafetyViolationKind::UnsafeFnBorrowPacked => {
 333                             bug!("`UnsafetyViolationKind::UnsafeFn` in an `Safe` context")
 334                         }
 335                     }
 336                     if !self.violations.contains(&violation) {
 337                         self.violations.push(violation)
 338                     }
 339                 }
 340                 false
 341             }
 342             // With the RFC 2585, no longer allow `unsafe` operations in `unsafe fn`s
 343             Safety::FnUnsafe if self.tcx.features().unsafe_block_in_unsafe_fn => {
 344                 for violation in violations {
 345                     let mut violation = *violation;
 346
 347                     if violation.kind == UnsafetyViolationKind::BorrowPacked {
 348                         violation.kind = UnsafetyViolationKind::UnsafeFnBorrowPacked;
 349                     } else {
 350                         violation.kind = UnsafetyViolationKind::UnsafeFn;
 351                     }
 352                     if !self.violations.contains(&violation) {
 353                         self.violations.push(violation)
 354                     }
 355                 }
 356                 false
 357             }
 358             // `unsafe` function bodies allow unsafe without additional unsafe blocks (before RFC 2585)
 359             Safety::BuiltinUnsafe | Safety::FnUnsafe => true,
 360             Safety::ExplicitUnsafe(hir_id) => {
 361                 // mark unsafe block as used if there are any unsafe operations inside
 362                 if !violations.is_empty() {
 363                     self.used_unsafe.insert(hir_id);
 364                 }
 365                 // only some unsafety is allowed in const fn
 366                 if self.min_const_fn {
 367                     for violation in violations {
 368                         match violation.kind {
 369                             // these unsafe things are stable in const fn
 370                             UnsafetyViolationKind::GeneralAndConstFn => {}
 371                             // these things are forbidden in const fns
 372                             UnsafetyViolationKind::General
 373                             | UnsafetyViolationKind::BorrowPacked => {
 374                                 let mut violation = *violation;
 375                                 // const fns don't need to be backwards compatible and can
 376                                 // emit these violations as a hard error instead of a backwards
 377                                 // compat lint
 378                                 violation.kind = UnsafetyViolationKind::General;
 379                                 if !self.violations.contains(&violation) {
 380                                     self.violations.push(violation)
 381                                 }
 382                             }
 383                             UnsafetyViolationKind::UnsafeFn
 384                             | UnsafetyViolationKind::UnsafeFnBorrowPacked => bug!(
 385                                 "`UnsafetyViolationKind::UnsafeFn` in an `ExplicitUnsafe` context"
 386                             ),
 387                         }
 388                     }
 389                 }
 390                 true
 391             }
 392         };
 393         self.inherited_blocks.extend(
 394             unsafe_blocks.iter().map(|&(hir_id, is_used)| (hir_id, is_used && !within_unsafe)),
 395         );
 396     }
 397     fn check_mut_borrowing_layout_constrained_field(
 398         &mut self,
 399         place: Place<'tcx>,
 400         is_mut_use: bool,
 401     ) {
 402         for (place_base, elem) in place.iter_projections().rev() {
 403             match elem {
 404                 // Modifications behind a dereference don't affect the value of
 405                 // the pointer.
 406                 ProjectionElem::Deref => return,
 407                 ProjectionElem::Field(..) => {
 408                     let ty = place_base.ty(&self.body.local_decls, self.tcx).ty;
 409                     if let ty::Adt(def, _) = ty.kind() {
 410                         if self.tcx.layout_scalar_valid_range(def.did)
 411                             != (Bound::Unbounded, Bound::Unbounded)
 412                         {
 413                             let details = if is_mut_use {
 414                                 UnsafetyViolationDetails::MutationOfLayoutConstrainedField
 415
 416                             // Check `is_freeze` as late as possible to avoid cycle errors
 417                             // with opaque types.
 418                             } else if !place
 419                                 .ty(self.body, self.tcx)
 420                                 .ty
 421                                 .is_freeze(self.tcx.at(self.source_info.span), self.param_env)
 422                             {
 423                                 UnsafetyViolationDetails::BorrowOfLayoutConstrainedField
 424                             } else {
 425                                 continue;
 426                             };
 427                             self.require_unsafe(UnsafetyViolationKind::GeneralAndConstFn, details);
 428                         }
 429                     }
 430                 }
 431                 _ => {}
 432             }
 433         }
 434     }
 435
 436     /// Checks whether calling `func_did` needs an `unsafe` context or not, i.e. whether
 437     /// the called function has target features the calling function hasn't.
 438     fn check_target_features(&mut self, func_did: DefId) {
 439         let callee_features = &self.tcx.codegen_fn_attrs(func_did).target_features;
 440         let self_features = &self.tcx.codegen_fn_attrs(self.body_did).target_features;
 441
 442         // Is `callee_features` a subset of `calling_features`?
 443         if !callee_features.iter().all(|feature| self_features.contains(feature)) {
 444             self.require_unsafe(
 445                 UnsafetyViolationKind::GeneralAndConstFn,
 446                 UnsafetyViolationDetails::CallToFunctionWith,
 447             )
 448         }
 449     }
 450 }
 451
 452 pub(crate) fn provide(providers: &mut Providers) {
 453     *providers = Providers {
 454         unsafety_check_result: |tcx, def_id| {
 455             if let Some(def) = ty::WithOptConstParam::try_lookup(def_id, tcx) {
 456                 tcx.unsafety_check_result_for_const_arg(def)
 457             } else {
 458                 unsafety_check_result(tcx, ty::WithOptConstParam::unknown(def_id))
 459             }
 460         },
 461         unsafety_check_result_for_const_arg: |tcx, (did, param_did)| {
 462             unsafety_check_result(
 463                 tcx,
 464                 ty::WithOptConstParam { did, const_param_did: Some(param_did) },
 465             )
 466         },
 467         unsafe_derive_on_repr_packed,
 468         ..*providers
 469     };
 470 }
 471
 472 struct UnusedUnsafeVisitor<'a> {
 473     used_unsafe: &'a FxHashSet<hir::HirId>,
 474     unsafe_blocks: &'a mut Vec<(hir::HirId, bool)>,
 475 }
 476
 477 impl<'a, 'tcx> intravisit::Visitor<'tcx> for UnusedUnsafeVisitor<'a> {
 478     type Map = intravisit::ErasedMap<'tcx>;
 479
 480     fn nested_visit_map(&mut self) -> intravisit::NestedVisitorMap<Self::Map> {
 481         intravisit::NestedVisitorMap::None
 482     }
 483
 484     fn visit_block(&mut self, block: &'tcx hir::Block<'tcx>) {
 485         intravisit::walk_block(self, block);
 486
 487         if let hir::BlockCheckMode::UnsafeBlock(hir::UnsafeSource::UserProvided) = block.rules {
 488             self.unsafe_blocks.push((block.hir_id, self.used_unsafe.contains(&block.hir_id)));
 489         }
 490     }
 491 }
 492
 493 fn check_unused_unsafe(
 494     tcx: TyCtxt<'_>,
 495     def_id: LocalDefId,
 496     used_unsafe: &FxHashSet<hir::HirId>,
 497     unsafe_blocks: &mut Vec<(hir::HirId, bool)>,
 498 ) {
 499     let body_id = tcx.hir().maybe_body_owned_by(tcx.hir().local_def_id_to_hir_id(def_id));
 500
 501     let body_id = match body_id {
 502         Some(body) => body,
 503         None => {
 504             debug!("check_unused_unsafe({:?}) - no body found", def_id);
 505             return;
 506         }
 507     };
 508     let body = tcx.hir().body(body_id);
 509     debug!("check_unused_unsafe({:?}, body={:?}, used_unsafe={:?})", def_id, body, used_unsafe);
 510
 511     let mut visitor = UnusedUnsafeVisitor { used_unsafe, unsafe_blocks };
 512     intravisit::Visitor::visit_body(&mut visitor, body);
 513 }
 514
 515 fn unsafety_check_result<'tcx>(
 516     tcx: TyCtxt<'tcx>,
 517     def: ty::WithOptConstParam<LocalDefId>,
 518 ) -> &'tcx UnsafetyCheckResult {
 519     debug!("unsafety_violations({:?})", def);
 520
 521     // N.B., this borrow is valid because all the consumers of
 522     // `mir_built` force this.
 523     let body = &tcx.mir_built(def).borrow();
 524
 525     let param_env = tcx.param_env(def.did);
 526
 527     let id = tcx.hir().local_def_id_to_hir_id(def.did);
 528     let (const_context, min_const_fn) = match tcx.hir().body_owner_kind(id) {
 529         hir::BodyOwnerKind::Closure => (false, false),
 530         hir::BodyOwnerKind::Fn => {
 531             (tcx.is_const_fn_raw(def.did.to_def_id()), is_min_const_fn(tcx, def.did.to_def_id()))
 532         }
 533         hir::BodyOwnerKind::Const | hir::BodyOwnerKind::Static(_) => (true, false),
 534     };
 535     let mut checker =
 536         UnsafetyChecker::new(const_context, min_const_fn, body, def.did, tcx, param_env);
 537     checker.visit_body(&body);
 538
 539     check_unused_unsafe(tcx, def.did, &checker.used_unsafe, &mut checker.inherited_blocks);
 540
 541     tcx.arena.alloc(UnsafetyCheckResult {
 542         violations: checker.violations.into(),
 543         unsafe_blocks: checker.inherited_blocks.into(),
 544     })
 545 }
 546
 547 fn unsafe_derive_on_repr_packed(tcx: TyCtxt<'_>, def_id: LocalDefId) {
 548     let lint_hir_id = tcx.hir().local_def_id_to_hir_id(def_id);
 549
 550     tcx.struct_span_lint_hir(SAFE_PACKED_BORROWS, lint_hir_id, tcx.def_span(def_id), |lint| {
 551         // FIXME: when we make this a hard error, this should have its
 552         // own error code.
 553         let message = if tcx.generics_of(def_id).own_requires_monomorphization() {
 554             "`#[derive]` can't be used on a `#[repr(packed)]` struct with \
 555              type or const parameters (error E0133)"
 556                 .to_string()
 557         } else {
 558             "`#[derive]` can't be used on a `#[repr(packed)]` struct that \
 559              does not derive Copy (error E0133)"
 560                 .to_string()
 561         };
 562         lint.build(&message).emit()
 563     });
 564 }
 565
 566 /// Returns the `HirId` for an enclosing scope that is also `unsafe`.
 567 fn is_enclosed(
 568     tcx: TyCtxt<'_>,
 569     used_unsafe: &FxHashSet<hir::HirId>,
 570     id: hir::HirId,
 571     unsafe_op_in_unsafe_fn_allowed: bool,
 572 ) -> Option<(&'static str, hir::HirId)> {
 573     let parent_id = tcx.hir().get_parent_node(id);
 574     if parent_id != id {
 575         if used_unsafe.contains(&parent_id) {
 576             Some(("block", parent_id))
 577         } else if let Some(Node::Item(&hir::Item {
 578             kind: hir::ItemKind::Fn(ref sig, _, _), ..
 579         })) = tcx.hir().find(parent_id)
 580         {
 581             if sig.header.unsafety == hir::Unsafety::Unsafe && unsafe_op_in_unsafe_fn_allowed {
 582                 Some(("fn", parent_id))
 583             } else {
 584                 None
 585             }
 586         } else {
 587             is_enclosed(tcx, used_unsafe, parent_id, unsafe_op_in_unsafe_fn_allowed)
 588         }
 589     } else {
 590         None
 591     }
 592 }
 593
 594 fn report_unused_unsafe(tcx: TyCtxt<'_>, used_unsafe: &FxHashSet<hir::HirId>, id: hir::HirId) {
 595     let span = tcx.sess.source_map().guess_head_span(tcx.hir().span(id));
 596     tcx.struct_span_lint_hir(UNUSED_UNSAFE, id, span, |lint| {
 597         let msg = "unnecessary `unsafe` block";
 598         let mut db = lint.build(msg);
 599         db.span_label(span, msg);
 600         if let Some((kind, id)) =
 601             is_enclosed(tcx, used_unsafe, id, unsafe_op_in_unsafe_fn_allowed(tcx, id))
 602         {
 603             db.span_label(
 604                 tcx.sess.source_map().guess_head_span(tcx.hir().span(id)),
 605                 format!("because it's nested under this `unsafe` {}", kind),
 606             );
 607         }
 608         db.emit();
 609     });
 610 }
 611
 612 fn builtin_derive_def_id(tcx: TyCtxt<'_>, def_id: DefId) -> Option<DefId> {
 613     debug!("builtin_derive_def_id({:?})", def_id);
 614     if let Some(impl_def_id) = tcx.impl_of_method(def_id) {
 615         if tcx.has_attr(impl_def_id, sym::automatically_derived) {
 616             debug!("builtin_derive_def_id({:?}) - is {:?}", def_id, impl_def_id);
 617             Some(impl_def_id)
 618         } else {
 619             debug!("builtin_derive_def_id({:?}) - not automatically derived", def_id);
 620             None
 621         }
 622     } else {
 623         debug!("builtin_derive_def_id({:?}) - not a method", def_id);
 624         None
 625     }
 626 }
 627
 628 pub fn check_unsafety(tcx: TyCtxt<'_>, def_id: LocalDefId) {
 629     debug!("check_unsafety({:?})", def_id);
 630
 631     // closures are handled by their parent fn.
 632     if tcx.is_closure(def_id.to_def_id()) {
 633         return;
 634     }
 635
 636     let UnsafetyCheckResult { violations, unsafe_blocks } = tcx.unsafety_check_result(def_id);
 637
 638     for &UnsafetyViolation { source_info, lint_root, kind, details } in violations.iter() {
 639         let (description, note) = details.description_and_note();
 640
 641         // Report an error.
 642         let unsafe_fn_msg =
 643             if unsafe_op_in_unsafe_fn_allowed(tcx, lint_root) { " function or" } else { "" };
 644
 645         match kind {
 646             UnsafetyViolationKind::GeneralAndConstFn | UnsafetyViolationKind::General => {
 647                 // once
 648                 struct_span_err!(
 649                     tcx.sess,
 650                     source_info.span,
 651                     E0133,
 652                     "{} is unsafe and requires unsafe{} block",
 653                     description,
 654                     unsafe_fn_msg,
 655                 )
 656                 .span_label(source_info.span, description)
 657                 .note(note)
 658                 .emit();
 659             }
 660             UnsafetyViolationKind::BorrowPacked => {
 661                 if let Some(impl_def_id) = builtin_derive_def_id(tcx, def_id.to_def_id()) {
 662                     // If a method is defined in the local crate,
 663                     // the impl containing that method should also be.
 664                     tcx.ensure().unsafe_derive_on_repr_packed(impl_def_id.expect_local());
 665                 } else {
 666                     tcx.struct_span_lint_hir(
 667                         SAFE_PACKED_BORROWS,
 668                         lint_root,
 669                         source_info.span,
 670                         |lint| {
 671                             lint.build(&format!(
 672                                 "{} is unsafe and requires unsafe{} block (error E0133)",
 673                                 description, unsafe_fn_msg,
 674                             ))
 675                             .note(note)
 676                             .emit()
 677                         },
 678                     )
 679                 }
 680             }
 681             UnsafetyViolationKind::UnsafeFn => tcx.struct_span_lint_hir(
 682                 UNSAFE_OP_IN_UNSAFE_FN,
 683                 lint_root,
 684                 source_info.span,
 685                 |lint| {
 686                     lint.build(&format!(
 687                         "{} is unsafe and requires unsafe block (error E0133)",
 688                         description,
 689                     ))
 690                     .span_label(source_info.span, description)
 691                     .note(note)
 692                     .emit();
 693                 },
 694             ),
 695             UnsafetyViolationKind::UnsafeFnBorrowPacked => {
 696                 // When `unsafe_op_in_unsafe_fn` is disallowed, the behavior of safe and unsafe functions
 697                 // should be the same in terms of warnings and errors. Therefore, with `#[warn(safe_packed_borrows)]`,
 698                 // a safe packed borrow should emit a warning *but not an error* in an unsafe function,
 699                 // just like in a safe function, even if `unsafe_op_in_unsafe_fn` is `deny`.
 700                 //
 701                 // Also, `#[warn(unsafe_op_in_unsafe_fn)]` can't cause any new errors. Therefore, with
 702                 // `#[deny(safe_packed_borrows)]` and `#[warn(unsafe_op_in_unsafe_fn)]`, a packed borrow
 703                 // should only issue a warning for the sake of backwards compatibility.
 704                 //
 705                 // The solution those 2 expectations is to always take the minimum of both lints.
 706                 // This prevent any new errors (unless both lints are explicitly set to `deny`).
 707                 let lint = if tcx.lint_level_at_node(SAFE_PACKED_BORROWS, lint_root).0
 708                     <= tcx.lint_level_at_node(UNSAFE_OP_IN_UNSAFE_FN, lint_root).0
 709                 {
 710                     SAFE_PACKED_BORROWS
 711                 } else {
 712                     UNSAFE_OP_IN_UNSAFE_FN
 713                 };
 714                 tcx.struct_span_lint_hir(&lint, lint_root, source_info.span, |lint| {
 715                     lint.build(&format!(
 716                         "{} is unsafe and requires unsafe block (error E0133)",
 717                         description,
 718                     ))
 719                     .span_label(source_info.span, description)
 720                     .note(note)
 721                     .emit();
 722                 })
 723             }
 724         }
 725     }
 726
 727     let (mut unsafe_used, mut unsafe_unused): (FxHashSet<_>, Vec<_>) = Default::default();
 728     for &(block_id, is_used) in unsafe_blocks.iter() {
 729         if is_used {
 730             unsafe_used.insert(block_id);
 731         } else {
 732             unsafe_unused.push(block_id);
 733         }
 734     }
 735     // The unused unsafe blocks might not be in source order; sort them so that the unused unsafe
 736     // error messages are properly aligned and the issue-45107 and lint-unused-unsafe tests pass.
 737     unsafe_unused.sort_by_cached_key(|hir_id| tcx.hir().span(*hir_id));
 738
 739     for &block_id in &unsafe_unused {
 740         report_unused_unsafe(tcx, &unsafe_used, block_id);
 741     }
 742 }
 743
 744 fn unsafe_op_in_unsafe_fn_allowed(tcx: TyCtxt<'_>, id: HirId) -> bool {
 745     tcx.lint_level_at_node(UNSAFE_OP_IN_UNSAFE_FN, id).0 == Level::Allow
 746 }