src/librustc_mir/transform/check_unsafety.rs

   1 use rustc::hir::map::Map;
   2 use rustc::lint::builtin::{SAFE_PACKED_BORROWS, UNUSED_UNSAFE};
   3 use rustc::mir::visit::{MutatingUseContext, PlaceContext, Visitor};
   4 use rustc::mir::*;
   5 use rustc::ty::cast::CastTy;
   6 use rustc::ty::query::Providers;
   7 use rustc::ty::{self, TyCtxt};
   8 use rustc_data_structures::fx::FxHashSet;
   9 use rustc_errors::struct_span_err;
  10 use rustc_hir as hir;
  11 use rustc_hir::def_id::DefId;
  12 use rustc_hir::intravisit;
  13 use rustc_hir::Node;
  14 use rustc_span::symbol::{sym, Symbol};
  15
  16 use std::ops::Bound;
  17
  18 use crate::const_eval::{is_const_fn, is_min_const_fn};
  19 use crate::util;
  20
  21 use rustc_error_codes::*;
  22
  23 pub struct UnsafetyChecker<'a, 'tcx> {
  24     body: &'a Body<'tcx>,
  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         tcx: TyCtxt<'tcx>,
  42         param_env: ty::ParamEnv<'tcx>,
  43     ) -> Self {
  44         // sanity check
  45         if min_const_fn {
  46             assert!(const_context);
  47         }
  48         Self {
  49             body,
  50             const_context,
  51             min_const_fn,
  52             violations: vec![],
  53             source_info: SourceInfo { span: body.span, scope: OUTERMOST_SOURCE_SCOPE },
  54             tcx,
  55             param_env,
  56             used_unsafe: Default::default(),
  57             inherited_blocks: vec![],
  58         }
  59     }
  60 }
  61
  62 impl<'a, 'tcx> Visitor<'tcx> for UnsafetyChecker<'a, 'tcx> {
  63     fn visit_terminator(&mut self, terminator: &Terminator<'tcx>, location: Location) {
  64         self.source_info = terminator.source_info;
  65         match terminator.kind {
  66             TerminatorKind::Goto { .. }
  67             | TerminatorKind::SwitchInt { .. }
  68             | TerminatorKind::Drop { .. }
  69             | TerminatorKind::Yield { .. }
  70             | TerminatorKind::Assert { .. }
  71             | TerminatorKind::DropAndReplace { .. }
  72             | TerminatorKind::GeneratorDrop
  73             | TerminatorKind::Resume
  74             | TerminatorKind::Abort
  75             | TerminatorKind::Return
  76             | TerminatorKind::Unreachable
  77             | TerminatorKind::FalseEdges { .. }
  78             | TerminatorKind::FalseUnwind { .. } => {
  79                 // safe (at least as emitted during MIR construction)
  80             }
  81
  82             TerminatorKind::Call { ref func, .. } => {
  83                 let func_ty = func.ty(self.body, self.tcx);
  84                 let sig = func_ty.fn_sig(self.tcx);
  85                 if let hir::Unsafety::Unsafe = sig.unsafety() {
  86                     self.require_unsafe(
  87                         "call to unsafe function",
  88                         "consult the function's documentation for information on how to avoid \
  89                          undefined behavior",
  90                         UnsafetyViolationKind::GeneralAndConstFn,
  91                     )
  92                 }
  93             }
  94         }
  95         self.super_terminator(terminator, location);
  96     }
  97
  98     fn visit_statement(&mut self, statement: &Statement<'tcx>, location: Location) {
  99         self.source_info = statement.source_info;
 100         match statement.kind {
 101             StatementKind::Assign(..)
 102             | StatementKind::FakeRead(..)
 103             | StatementKind::SetDiscriminant { .. }
 104             | StatementKind::StorageLive(..)
 105             | StatementKind::StorageDead(..)
 106             | StatementKind::Retag { .. }
 107             | StatementKind::AscribeUserType(..)
 108             | StatementKind::Nop => {
 109                 // safe (at least as emitted during MIR construction)
 110             }
 111
 112             StatementKind::InlineAsm { .. } => self.require_unsafe(
 113                 "use of inline assembly",
 114                 "inline assembly is entirely unchecked and can cause undefined behavior",
 115                 UnsafetyViolationKind::General,
 116             ),
 117         }
 118         self.super_statement(statement, location);
 119     }
 120
 121     fn visit_rvalue(&mut self, rvalue: &Rvalue<'tcx>, location: Location) {
 122         match rvalue {
 123             Rvalue::Aggregate(box ref aggregate, _) => match aggregate {
 124                 &AggregateKind::Array(..) | &AggregateKind::Tuple => {}
 125                 &AggregateKind::Adt(ref def, ..) => {
 126                     match self.tcx.layout_scalar_valid_range(def.did) {
 127                         (Bound::Unbounded, Bound::Unbounded) => {}
 128                         _ => self.require_unsafe(
 129                             "initializing type with `rustc_layout_scalar_valid_range` attr",
 130                             "initializing a layout restricted type's field with a value \
 131                                 outside the valid range is undefined behavior",
 132                             UnsafetyViolationKind::GeneralAndConstFn,
 133                         ),
 134                     }
 135                 }
 136                 &AggregateKind::Closure(def_id, _) | &AggregateKind::Generator(def_id, _, _) => {
 137                     let UnsafetyCheckResult { violations, unsafe_blocks } =
 138                         self.tcx.unsafety_check_result(def_id);
 139                     self.register_violations(&violations, &unsafe_blocks);
 140                 }
 141             },
 142             // casting pointers to ints is unsafe in const fn because the const evaluator cannot
 143             // possibly know what the result of various operations like `address / 2` would be
 144             // pointers during const evaluation have no integral address, only an abstract one
 145             Rvalue::Cast(CastKind::Misc, ref operand, cast_ty)
 146                 if self.const_context && self.tcx.features().const_raw_ptr_to_usize_cast =>
 147             {
 148                 let operand_ty = operand.ty(self.body, self.tcx);
 149                 let cast_in = CastTy::from_ty(operand_ty).expect("bad input type for cast");
 150                 let cast_out = CastTy::from_ty(cast_ty).expect("bad output type for cast");
 151                 match (cast_in, cast_out) {
 152                     (CastTy::Ptr(_), CastTy::Int(_)) | (CastTy::FnPtr, CastTy::Int(_)) => {
 153                         self.register_violations(
 154                             &[UnsafetyViolation {
 155                                 source_info: self.source_info,
 156                                 description: Symbol::intern("cast of pointer to int"),
 157                                 details: Symbol::intern(
 158                                     "casting pointers to integers in constants",
 159                                 ),
 160                                 kind: UnsafetyViolationKind::General,
 161                             }],
 162                             &[],
 163                         );
 164                     }
 165                     _ => {}
 166                 }
 167             }
 168             // raw pointer and fn pointer operations are unsafe as it is not clear whether one
 169             // pointer would be "less" or "equal" to another, because we cannot know where llvm
 170             // or the linker will place various statics in memory. Without this information the
 171             // result of a comparison of addresses would differ between runtime and compile-time.
 172             Rvalue::BinaryOp(_, ref lhs, _)
 173                 if self.const_context && self.tcx.features().const_compare_raw_pointers =>
 174             {
 175                 if let ty::RawPtr(_) | ty::FnPtr(..) = lhs.ty(self.body, self.tcx).kind {
 176                     self.register_violations(
 177                         &[UnsafetyViolation {
 178                             source_info: self.source_info,
 179                             description: Symbol::intern("pointer operation"),
 180                             details: Symbol::intern("operations on pointers in constants"),
 181                             kind: UnsafetyViolationKind::General,
 182                         }],
 183                         &[],
 184                     );
 185                 }
 186             }
 187             _ => {}
 188         }
 189         self.super_rvalue(rvalue, location);
 190     }
 191
 192     fn visit_place(&mut self, place: &Place<'tcx>, context: PlaceContext, _location: Location) {
 193         match place.base {
 194             PlaceBase::Local(..) => {
 195                 // Locals are safe.
 196             }
 197             PlaceBase::Static(box Static { kind: StaticKind::Promoted(_, _), .. }) => {
 198                 bug!("unsafety checking should happen before promotion");
 199             }
 200             PlaceBase::Static(box Static { kind: StaticKind::Static, .. }) => {
 201                 bug!("StaticKind::Static should not exist");
 202             }
 203         }
 204
 205         for (i, elem) in place.projection.iter().enumerate() {
 206             let proj_base = &place.projection[..i];
 207
 208             if context.is_borrow() {
 209                 if util::is_disaligned(self.tcx, self.body, self.param_env, place) {
 210                     let source_info = self.source_info;
 211                     let lint_root = self.body.source_scopes[source_info.scope]
 212                         .local_data
 213                         .as_ref()
 214                         .assert_crate_local()
 215                         .lint_root;
 216                     self.register_violations(
 217                         &[UnsafetyViolation {
 218                             source_info,
 219                             description: Symbol::intern("borrow of packed field"),
 220                             details: Symbol::intern(
 221                                 "fields of packed structs might be misaligned: dereferencing a \
 222                             misaligned pointer or even just creating a misaligned reference \
 223                             is undefined behavior",
 224                             ),
 225                             kind: UnsafetyViolationKind::BorrowPacked(lint_root),
 226                         }],
 227                         &[],
 228                     );
 229                 }
 230             }
 231             let is_borrow_of_interior_mut = context.is_borrow()
 232                 && !Place::ty_from(&place.base, proj_base, self.body, self.tcx).ty.is_freeze(
 233                     self.tcx,
 234                     self.param_env,
 235                     self.source_info.span,
 236                 );
 237             // prevent
 238             // * `&mut x.field`
 239             // * `x.field = y;`
 240             // * `&x.field` if `field`'s type has interior mutability
 241             // because either of these would allow modifying the layout constrained field and
 242             // insert values that violate the layout constraints.
 243             if context.is_mutating_use() || is_borrow_of_interior_mut {
 244                 self.check_mut_borrowing_layout_constrained_field(place, context.is_mutating_use());
 245             }
 246             let old_source_info = self.source_info;
 247             if let (PlaceBase::Local(local), []) = (&place.base, proj_base) {
 248                 let decl = &self.body.local_decls[*local];
 249                 if decl.internal {
 250                     // Internal locals are used in the `move_val_init` desugaring.
 251                     // We want to check unsafety against the source info of the
 252                     // desugaring, rather than the source info of the RHS.
 253                     self.source_info = self.body.local_decls[*local].source_info;
 254                 } else if let LocalInfo::StaticRef { def_id, .. } = decl.local_info {
 255                     if self.tcx.is_mutable_static(def_id) {
 256                         self.require_unsafe(
 257                             "use of mutable static",
 258                             "mutable statics can be mutated by multiple threads: aliasing \
 259                         violations or data races will cause undefined behavior",
 260                             UnsafetyViolationKind::General,
 261                         );
 262                         return;
 263                     } else if self.tcx.is_foreign_item(def_id) {
 264                         self.require_unsafe(
 265                             "use of extern static",
 266                             "extern statics are not controlled by the Rust type system: \
 267                         invalid data, aliasing violations or data races will cause \
 268                         undefined behavior",
 269                             UnsafetyViolationKind::General,
 270                         );
 271                         return;
 272                     }
 273                 }
 274             }
 275             let base_ty = Place::ty_from(&place.base, proj_base, self.body, self.tcx).ty;
 276             match base_ty.kind {
 277                 ty::RawPtr(..) => self.require_unsafe(
 278                     "dereference of raw pointer",
 279                     "raw pointers may be NULL, dangling or unaligned; they can violate \
 280                          aliasing rules and cause data races: all of these are undefined \
 281                          behavior",
 282                     UnsafetyViolationKind::General,
 283                 ),
 284                 ty::Adt(adt, _) => {
 285                     if adt.is_union() {
 286                         if context == PlaceContext::MutatingUse(MutatingUseContext::Store)
 287                             || context == PlaceContext::MutatingUse(MutatingUseContext::Drop)
 288                             || context == PlaceContext::MutatingUse(MutatingUseContext::AsmOutput)
 289                         {
 290                             let elem_ty = match elem {
 291                                 ProjectionElem::Field(_, ty) => ty,
 292                                 _ => span_bug!(
 293                                     self.source_info.span,
 294                                     "non-field projection {:?} from union?",
 295                                     place
 296                                 ),
 297                             };
 298                             if !elem_ty.is_copy_modulo_regions(
 299                                 self.tcx,
 300                                 self.param_env,
 301                                 self.source_info.span,
 302                             ) {
 303                                 self.require_unsafe(
 304                                     "assignment to non-`Copy` union field",
 305                                     "the previous content of the field will be dropped, which \
 306                                      causes undefined behavior if the field was not properly \
 307                                      initialized",
 308                                     UnsafetyViolationKind::GeneralAndConstFn,
 309                                 )
 310                             } else {
 311                                 // write to non-move union, safe
 312                             }
 313                         } else {
 314                             self.require_unsafe(
 315                                 "access to union field",
 316                                 "the field may not be properly initialized: using \
 317                                  uninitialized data will cause undefined behavior",
 318                                 UnsafetyViolationKind::GeneralAndConstFn,
 319                             )
 320                         }
 321                     }
 322                 }
 323                 _ => {}
 324             }
 325             self.source_info = old_source_info;
 326         }
 327     }
 328 }
 329
 330 impl<'a, 'tcx> UnsafetyChecker<'a, 'tcx> {
 331     fn require_unsafe(
 332         &mut self,
 333         description: &'static str,
 334         details: &'static str,
 335         kind: UnsafetyViolationKind,
 336     ) {
 337         let source_info = self.source_info;
 338         self.register_violations(
 339             &[UnsafetyViolation {
 340                 source_info,
 341                 description: Symbol::intern(description),
 342                 details: Symbol::intern(details),
 343                 kind,
 344             }],
 345             &[],
 346         );
 347     }
 348
 349     fn register_violations(
 350         &mut self,
 351         violations: &[UnsafetyViolation],
 352         unsafe_blocks: &[(hir::HirId, bool)],
 353     ) {
 354         let safety = self.body.source_scopes[self.source_info.scope]
 355             .local_data
 356             .as_ref()
 357             .assert_crate_local()
 358             .safety;
 359         let within_unsafe = match safety {
 360             // `unsafe` blocks are required in safe code
 361             Safety::Safe => {
 362                 for violation in violations {
 363                     let mut violation = violation.clone();
 364                     match violation.kind {
 365                         UnsafetyViolationKind::GeneralAndConstFn
 366                         | UnsafetyViolationKind::General => {}
 367                         UnsafetyViolationKind::BorrowPacked(_) => {
 368                             if self.min_const_fn {
 369                                 // const fns don't need to be backwards compatible and can
 370                                 // emit these violations as a hard error instead of a backwards
 371                                 // compat lint
 372                                 violation.kind = UnsafetyViolationKind::General;
 373                             }
 374                         }
 375                     }
 376                     if !self.violations.contains(&violation) {
 377                         self.violations.push(violation)
 378                     }
 379                 }
 380                 false
 381             }
 382             // `unsafe` function bodies allow unsafe without additional unsafe blocks
 383             Safety::BuiltinUnsafe | Safety::FnUnsafe => true,
 384             Safety::ExplicitUnsafe(hir_id) => {
 385                 // mark unsafe block as used if there are any unsafe operations inside
 386                 if !violations.is_empty() {
 387                     self.used_unsafe.insert(hir_id);
 388                 }
 389                 // only some unsafety is allowed in const fn
 390                 if self.min_const_fn {
 391                     for violation in violations {
 392                         match violation.kind {
 393                             // these unsafe things are stable in const fn
 394                             UnsafetyViolationKind::GeneralAndConstFn => {}
 395                             // these things are forbidden in const fns
 396                             UnsafetyViolationKind::General
 397                             | UnsafetyViolationKind::BorrowPacked(_) => {
 398                                 let mut violation = violation.clone();
 399                                 // const fns don't need to be backwards compatible and can
 400                                 // emit these violations as a hard error instead of a backwards
 401                                 // compat lint
 402                                 violation.kind = UnsafetyViolationKind::General;
 403                                 if !self.violations.contains(&violation) {
 404                                     self.violations.push(violation)
 405                                 }
 406                             }
 407                         }
 408                     }
 409                 }
 410                 true
 411             }
 412         };
 413         self.inherited_blocks.extend(
 414             unsafe_blocks.iter().map(|&(hir_id, is_used)| (hir_id, is_used && !within_unsafe)),
 415         );
 416     }
 417     fn check_mut_borrowing_layout_constrained_field(
 418         &mut self,
 419         place: &Place<'tcx>,
 420         is_mut_use: bool,
 421     ) {
 422         let mut cursor = place.projection.as_ref();
 423         while let &[ref proj_base @ .., elem] = cursor {
 424             cursor = proj_base;
 425
 426             match elem {
 427                 ProjectionElem::Field(..) => {
 428                     let ty =
 429                         Place::ty_from(&place.base, proj_base, &self.body.local_decls, self.tcx).ty;
 430                     match ty.kind {
 431                         ty::Adt(def, _) => match self.tcx.layout_scalar_valid_range(def.did) {
 432                             (Bound::Unbounded, Bound::Unbounded) => {}
 433                             _ => {
 434                                 let (description, details) = if is_mut_use {
 435                                     (
 436                                         "mutation of layout constrained field",
 437                                         "mutating layout constrained fields cannot statically be \
 438                                         checked for valid values",
 439                                     )
 440                                 } else {
 441                                     (
 442                                         "borrow of layout constrained field with interior \
 443                                         mutability",
 444                                         "references to fields of layout constrained fields \
 445                                         lose the constraints. Coupled with interior mutability, \
 446                                         the field can be changed to invalid values",
 447                                     )
 448                                 };
 449                                 let source_info = self.source_info;
 450                                 self.register_violations(
 451                                     &[UnsafetyViolation {
 452                                         source_info,
 453                                         description: Symbol::intern(description),
 454                                         details: Symbol::intern(details),
 455                                         kind: UnsafetyViolationKind::GeneralAndConstFn,
 456                                     }],
 457                                     &[],
 458                                 );
 459                             }
 460                         },
 461                         _ => {}
 462                     }
 463                 }
 464                 _ => {}
 465             }
 466         }
 467     }
 468 }
 469
 470 pub(crate) fn provide(providers: &mut Providers<'_>) {
 471     *providers = Providers { unsafety_check_result, unsafe_derive_on_repr_packed, ..*providers };
 472 }
 473
 474 struct UnusedUnsafeVisitor<'a> {
 475     used_unsafe: &'a FxHashSet<hir::HirId>,
 476     unsafe_blocks: &'a mut Vec<(hir::HirId, bool)>,
 477 }
 478
 479 impl<'a, 'tcx> intravisit::Visitor<'tcx> for UnusedUnsafeVisitor<'a> {
 480     type Map = Map<'tcx>;
 481
 482     fn nested_visit_map<'this>(&'this mut self) -> intravisit::NestedVisitorMap<'this, Self::Map> {
 483         intravisit::NestedVisitorMap::None
 484     }
 485
 486     fn visit_block(&mut self, block: &'tcx hir::Block<'tcx>) {
 487         intravisit::walk_block(self, block);
 488
 489         if let hir::BlockCheckMode::UnsafeBlock(hir::UnsafeSource::UserProvided) = block.rules {
 490             self.unsafe_blocks.push((block.hir_id, self.used_unsafe.contains(&block.hir_id)));
 491         }
 492     }
 493 }
 494
 495 fn check_unused_unsafe(
 496     tcx: TyCtxt<'_>,
 497     def_id: DefId,
 498     used_unsafe: &FxHashSet<hir::HirId>,
 499     unsafe_blocks: &mut Vec<(hir::HirId, bool)>,
 500 ) {
 501     let body_id =
 502         tcx.hir().as_local_hir_id(def_id).and_then(|hir_id| tcx.hir().maybe_body_owned_by(hir_id));
 503
 504     let body_id = match body_id {
 505         Some(body) => body,
 506         None => {
 507             debug!("check_unused_unsafe({:?}) - no body found", def_id);
 508             return;
 509         }
 510     };
 511     let body = tcx.hir().body(body_id);
 512     debug!("check_unused_unsafe({:?}, body={:?}, used_unsafe={:?})", def_id, body, used_unsafe);
 513
 514     let mut visitor = UnusedUnsafeVisitor { used_unsafe, unsafe_blocks };
 515     intravisit::Visitor::visit_body(&mut visitor, body);
 516 }
 517
 518 fn unsafety_check_result(tcx: TyCtxt<'_>, def_id: DefId) -> UnsafetyCheckResult {
 519     debug!("unsafety_violations({:?})", def_id);
 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_id).borrow();
 524
 525     let param_env = tcx.param_env(def_id);
 526
 527     let id = tcx.hir().as_local_hir_id(def_id).unwrap();
 528     let (const_context, min_const_fn) = match tcx.hir().body_owner_kind(id) {
 529         hir::BodyOwnerKind::Closure => (false, false),
 530         hir::BodyOwnerKind::Fn => (is_const_fn(tcx, def_id), is_min_const_fn(tcx, def_id)),
 531         hir::BodyOwnerKind::Const | hir::BodyOwnerKind::Static(_) => (true, false),
 532     };
 533     let mut checker = UnsafetyChecker::new(const_context, min_const_fn, body, tcx, param_env);
 534     // mir_built ensures that body has a computed cache, so we don't (and can't) attempt to
 535     // recompute it here.
 536     let body = body.unwrap_read_only();
 537     checker.visit_body(body);
 538
 539     check_unused_unsafe(tcx, def_id, &checker.used_unsafe, &mut checker.inherited_blocks);
 540     UnsafetyCheckResult {
 541         violations: checker.violations.into(),
 542         unsafe_blocks: checker.inherited_blocks.into(),
 543     }
 544 }
 545
 546 fn unsafe_derive_on_repr_packed(tcx: TyCtxt<'_>, def_id: DefId) {
 547     let lint_hir_id = tcx
 548         .hir()
 549         .as_local_hir_id(def_id)
 550         .unwrap_or_else(|| bug!("checking unsafety for non-local def id {:?}", def_id));
 551
 552     // FIXME: when we make this a hard error, this should have its
 553     // own error code.
 554     let message = if tcx.generics_of(def_id).own_requires_monomorphization() {
 555         "`#[derive]` can't be used on a `#[repr(packed)]` struct with \
 556          type or const parameters (error E0133)"
 557             .to_string()
 558     } else {
 559         "`#[derive]` can't be used on a `#[repr(packed)]` struct that \
 560          does not derive Copy (error E0133)"
 561             .to_string()
 562     };
 563     tcx.lint_hir(SAFE_PACKED_BORROWS, lint_hir_id, tcx.def_span(def_id), &message);
 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 ) -> Option<(String, hir::HirId)> {
 572     let parent_id = tcx.hir().get_parent_node(id);
 573     if parent_id != id {
 574         if used_unsafe.contains(&parent_id) {
 575             Some(("block".to_string(), parent_id))
 576         } else if let Some(Node::Item(&hir::Item {
 577             kind: hir::ItemKind::Fn(ref sig, _, _), ..
 578         })) = tcx.hir().find(parent_id)
 579         {
 580             match sig.header.unsafety {
 581                 hir::Unsafety::Unsafe => Some(("fn".to_string(), parent_id)),
 582                 hir::Unsafety::Normal => None,
 583             }
 584         } else {
 585             is_enclosed(tcx, used_unsafe, parent_id)
 586         }
 587     } else {
 588         None
 589     }
 590 }
 591
 592 fn report_unused_unsafe(tcx: TyCtxt<'_>, used_unsafe: &FxHashSet<hir::HirId>, id: hir::HirId) {
 593     let span = tcx.sess.source_map().def_span(tcx.hir().span(id));
 594     let msg = "unnecessary `unsafe` block";
 595     let mut db = tcx.struct_span_lint_hir(UNUSED_UNSAFE, id, span, msg);
 596     db.span_label(span, msg);
 597     if let Some((kind, id)) = is_enclosed(tcx, used_unsafe, id) {
 598         db.span_label(
 599             tcx.sess.source_map().def_span(tcx.hir().span(id)),
 600             format!("because it's nested under this `unsafe` {}", kind),
 601         );
 602     }
 603     db.emit();
 604 }
 605
 606 fn builtin_derive_def_id(tcx: TyCtxt<'_>, def_id: DefId) -> Option<DefId> {
 607     debug!("builtin_derive_def_id({:?})", def_id);
 608     if let Some(impl_def_id) = tcx.impl_of_method(def_id) {
 609         if tcx.has_attr(impl_def_id, sym::automatically_derived) {
 610             debug!("builtin_derive_def_id({:?}) - is {:?}", def_id, impl_def_id);
 611             Some(impl_def_id)
 612         } else {
 613             debug!("builtin_derive_def_id({:?}) - not automatically derived", def_id);
 614             None
 615         }
 616     } else {
 617         debug!("builtin_derive_def_id({:?}) - not a method", def_id);
 618         None
 619     }
 620 }
 621
 622 pub fn check_unsafety(tcx: TyCtxt<'_>, def_id: DefId) {
 623     debug!("check_unsafety({:?})", def_id);
 624
 625     // closures are handled by their parent fn.
 626     if tcx.is_closure(def_id) {
 627         return;
 628     }
 629
 630     let UnsafetyCheckResult { violations, unsafe_blocks } = tcx.unsafety_check_result(def_id);
 631
 632     for &UnsafetyViolation { source_info, description, details, kind } in violations.iter() {
 633         // Report an error.
 634         match kind {
 635             UnsafetyViolationKind::GeneralAndConstFn | UnsafetyViolationKind::General => {
 636                 struct_span_err!(
 637                     tcx.sess,
 638                     source_info.span,
 639                     E0133,
 640                     "{} is unsafe and requires unsafe function or block",
 641                     description
 642                 )
 643                 .span_label(source_info.span, &*description.as_str())
 644                 .note(&details.as_str())
 645                 .emit();
 646             }
 647             UnsafetyViolationKind::BorrowPacked(lint_hir_id) => {
 648                 if let Some(impl_def_id) = builtin_derive_def_id(tcx, def_id) {
 649                     tcx.unsafe_derive_on_repr_packed(impl_def_id);
 650                 } else {
 651                     tcx.lint_node_note(
 652                         SAFE_PACKED_BORROWS,
 653                         lint_hir_id,
 654                         source_info.span,
 655                         &format!(
 656                             "{} is unsafe and requires unsafe function or block \
 657                                             (error E0133)",
 658                             description
 659                         ),
 660                         &details.as_str(),
 661                     );
 662                 }
 663             }
 664         }
 665     }
 666
 667     let mut unsafe_blocks: Vec<_> = unsafe_blocks.into_iter().collect();
 668     unsafe_blocks.sort_by_cached_key(|(hir_id, _)| tcx.hir().hir_to_node_id(*hir_id));
 669     let used_unsafe: FxHashSet<_> =
 670         unsafe_blocks.iter().flat_map(|&&(id, used)| used.then_some(id)).collect();
 671     for &(block_id, is_used) in unsafe_blocks {
 672         if !is_used {
 673             report_unused_unsafe(tcx, &used_unsafe, block_id);
 674         }
 675     }
 676 }