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         }
 198
 199         for (i, elem) in place.projection.iter().enumerate() {
 200             let proj_base = &place.projection[..i];
 201
 202             if context.is_borrow() {
 203                 if util::is_disaligned(self.tcx, self.body, self.param_env, place) {
 204                     let source_info = self.source_info;
 205                     let lint_root = self.body.source_scopes[source_info.scope]
 206                         .local_data
 207                         .as_ref()
 208                         .assert_crate_local()
 209                         .lint_root;
 210                     self.register_violations(
 211                         &[UnsafetyViolation {
 212                             source_info,
 213                             description: Symbol::intern("borrow of packed field"),
 214                             details: Symbol::intern(
 215                                 "fields of packed structs might be misaligned: dereferencing a \
 216                             misaligned pointer or even just creating a misaligned reference \
 217                             is undefined behavior",
 218                             ),
 219                             kind: UnsafetyViolationKind::BorrowPacked(lint_root),
 220                         }],
 221                         &[],
 222                     );
 223                 }
 224             }
 225             let is_borrow_of_interior_mut = context.is_borrow()
 226                 && !Place::ty_from(&place.base, proj_base, self.body, self.tcx).ty.is_freeze(
 227                     self.tcx,
 228                     self.param_env,
 229                     self.source_info.span,
 230                 );
 231             // prevent
 232             // * `&mut x.field`
 233             // * `x.field = y;`
 234             // * `&x.field` if `field`'s type has interior mutability
 235             // because either of these would allow modifying the layout constrained field and
 236             // insert values that violate the layout constraints.
 237             if context.is_mutating_use() || is_borrow_of_interior_mut {
 238                 self.check_mut_borrowing_layout_constrained_field(place, context.is_mutating_use());
 239             }
 240             let old_source_info = self.source_info;
 241             if let (PlaceBase::Local(local), []) = (&place.base, proj_base) {
 242                 let decl = &self.body.local_decls[*local];
 243                 if decl.internal {
 244                     // Internal locals are used in the `move_val_init` desugaring.
 245                     // We want to check unsafety against the source info of the
 246                     // desugaring, rather than the source info of the RHS.
 247                     self.source_info = self.body.local_decls[*local].source_info;
 248                 } else if let LocalInfo::StaticRef { def_id, .. } = decl.local_info {
 249                     if self.tcx.is_mutable_static(def_id) {
 250                         self.require_unsafe(
 251                             "use of mutable static",
 252                             "mutable statics can be mutated by multiple threads: aliasing \
 253                         violations or data races will cause undefined behavior",
 254                             UnsafetyViolationKind::General,
 255                         );
 256                         return;
 257                     } else if self.tcx.is_foreign_item(def_id) {
 258                         self.require_unsafe(
 259                             "use of extern static",
 260                             "extern statics are not controlled by the Rust type system: \
 261                         invalid data, aliasing violations or data races will cause \
 262                         undefined behavior",
 263                             UnsafetyViolationKind::General,
 264                         );
 265                         return;
 266                     }
 267                 }
 268             }
 269             let base_ty = Place::ty_from(&place.base, proj_base, self.body, self.tcx).ty;
 270             match base_ty.kind {
 271                 ty::RawPtr(..) => self.require_unsafe(
 272                     "dereference of raw pointer",
 273                     "raw pointers may be NULL, dangling or unaligned; they can violate \
 274                          aliasing rules and cause data races: all of these are undefined \
 275                          behavior",
 276                     UnsafetyViolationKind::General,
 277                 ),
 278                 ty::Adt(adt, _) => {
 279                     if adt.is_union() {
 280                         if context == PlaceContext::MutatingUse(MutatingUseContext::Store)
 281                             || context == PlaceContext::MutatingUse(MutatingUseContext::Drop)
 282                             || context == PlaceContext::MutatingUse(MutatingUseContext::AsmOutput)
 283                         {
 284                             let elem_ty = match elem {
 285                                 ProjectionElem::Field(_, ty) => ty,
 286                                 _ => span_bug!(
 287                                     self.source_info.span,
 288                                     "non-field projection {:?} from union?",
 289                                     place
 290                                 ),
 291                             };
 292                             if !elem_ty.is_copy_modulo_regions(
 293                                 self.tcx,
 294                                 self.param_env,
 295                                 self.source_info.span,
 296                             ) {
 297                                 self.require_unsafe(
 298                                     "assignment to non-`Copy` union field",
 299                                     "the previous content of the field will be dropped, which \
 300                                      causes undefined behavior if the field was not properly \
 301                                      initialized",
 302                                     UnsafetyViolationKind::GeneralAndConstFn,
 303                                 )
 304                             } else {
 305                                 // write to non-move union, safe
 306                             }
 307                         } else {
 308                             self.require_unsafe(
 309                                 "access to union field",
 310                                 "the field may not be properly initialized: using \
 311                                  uninitialized data will cause undefined behavior",
 312                                 UnsafetyViolationKind::GeneralAndConstFn,
 313                             )
 314                         }
 315                     }
 316                 }
 317                 _ => {}
 318             }
 319             self.source_info = old_source_info;
 320         }
 321     }
 322 }
 323
 324 impl<'a, 'tcx> UnsafetyChecker<'a, 'tcx> {
 325     fn require_unsafe(
 326         &mut self,
 327         description: &'static str,
 328         details: &'static str,
 329         kind: UnsafetyViolationKind,
 330     ) {
 331         let source_info = self.source_info;
 332         self.register_violations(
 333             &[UnsafetyViolation {
 334                 source_info,
 335                 description: Symbol::intern(description),
 336                 details: Symbol::intern(details),
 337                 kind,
 338             }],
 339             &[],
 340         );
 341     }
 342
 343     fn register_violations(
 344         &mut self,
 345         violations: &[UnsafetyViolation],
 346         unsafe_blocks: &[(hir::HirId, bool)],
 347     ) {
 348         let safety = self.body.source_scopes[self.source_info.scope]
 349             .local_data
 350             .as_ref()
 351             .assert_crate_local()
 352             .safety;
 353         let within_unsafe = match safety {
 354             // `unsafe` blocks are required in safe code
 355             Safety::Safe => {
 356                 for violation in violations {
 357                     let mut violation = violation.clone();
 358                     match violation.kind {
 359                         UnsafetyViolationKind::GeneralAndConstFn
 360                         | UnsafetyViolationKind::General => {}
 361                         UnsafetyViolationKind::BorrowPacked(_) => {
 362                             if self.min_const_fn {
 363                                 // const fns don't need to be backwards compatible and can
 364                                 // emit these violations as a hard error instead of a backwards
 365                                 // compat lint
 366                                 violation.kind = UnsafetyViolationKind::General;
 367                             }
 368                         }
 369                     }
 370                     if !self.violations.contains(&violation) {
 371                         self.violations.push(violation)
 372                     }
 373                 }
 374                 false
 375             }
 376             // `unsafe` function bodies allow unsafe without additional unsafe blocks
 377             Safety::BuiltinUnsafe | Safety::FnUnsafe => true,
 378             Safety::ExplicitUnsafe(hir_id) => {
 379                 // mark unsafe block as used if there are any unsafe operations inside
 380                 if !violations.is_empty() {
 381                     self.used_unsafe.insert(hir_id);
 382                 }
 383                 // only some unsafety is allowed in const fn
 384                 if self.min_const_fn {
 385                     for violation in violations {
 386                         match violation.kind {
 387                             // these unsafe things are stable in const fn
 388                             UnsafetyViolationKind::GeneralAndConstFn => {}
 389                             // these things are forbidden in const fns
 390                             UnsafetyViolationKind::General
 391                             | UnsafetyViolationKind::BorrowPacked(_) => {
 392                                 let mut violation = violation.clone();
 393                                 // const fns don't need to be backwards compatible and can
 394                                 // emit these violations as a hard error instead of a backwards
 395                                 // compat lint
 396                                 violation.kind = UnsafetyViolationKind::General;
 397                                 if !self.violations.contains(&violation) {
 398                                     self.violations.push(violation)
 399                                 }
 400                             }
 401                         }
 402                     }
 403                 }
 404                 true
 405             }
 406         };
 407         self.inherited_blocks.extend(
 408             unsafe_blocks.iter().map(|&(hir_id, is_used)| (hir_id, is_used && !within_unsafe)),
 409         );
 410     }
 411     fn check_mut_borrowing_layout_constrained_field(
 412         &mut self,
 413         place: &Place<'tcx>,
 414         is_mut_use: bool,
 415     ) {
 416         let mut cursor = place.projection.as_ref();
 417         while let &[ref proj_base @ .., elem] = cursor {
 418             cursor = proj_base;
 419
 420             match elem {
 421                 ProjectionElem::Field(..) => {
 422                     let ty =
 423                         Place::ty_from(&place.base, proj_base, &self.body.local_decls, self.tcx).ty;
 424                     match ty.kind {
 425                         ty::Adt(def, _) => match self.tcx.layout_scalar_valid_range(def.did) {
 426                             (Bound::Unbounded, Bound::Unbounded) => {}
 427                             _ => {
 428                                 let (description, details) = if is_mut_use {
 429                                     (
 430                                         "mutation of layout constrained field",
 431                                         "mutating layout constrained fields cannot statically be \
 432                                         checked for valid values",
 433                                     )
 434                                 } else {
 435                                     (
 436                                         "borrow of layout constrained field with interior \
 437                                         mutability",
 438                                         "references to fields of layout constrained fields \
 439                                         lose the constraints. Coupled with interior mutability, \
 440                                         the field can be changed to invalid values",
 441                                     )
 442                                 };
 443                                 let source_info = self.source_info;
 444                                 self.register_violations(
 445                                     &[UnsafetyViolation {
 446                                         source_info,
 447                                         description: Symbol::intern(description),
 448                                         details: Symbol::intern(details),
 449                                         kind: UnsafetyViolationKind::GeneralAndConstFn,
 450                                     }],
 451                                     &[],
 452                                 );
 453                             }
 454                         },
 455                         _ => {}
 456                     }
 457                 }
 458                 _ => {}
 459             }
 460         }
 461     }
 462 }
 463
 464 pub(crate) fn provide(providers: &mut Providers<'_>) {
 465     *providers = Providers { unsafety_check_result, unsafe_derive_on_repr_packed, ..*providers };
 466 }
 467
 468 struct UnusedUnsafeVisitor<'a> {
 469     used_unsafe: &'a FxHashSet<hir::HirId>,
 470     unsafe_blocks: &'a mut Vec<(hir::HirId, bool)>,
 471 }
 472
 473 impl<'a, 'tcx> intravisit::Visitor<'tcx> for UnusedUnsafeVisitor<'a> {
 474     type Map = Map<'tcx>;
 475
 476     fn nested_visit_map<'this>(&'this mut self) -> intravisit::NestedVisitorMap<'this, Self::Map> {
 477         intravisit::NestedVisitorMap::None
 478     }
 479
 480     fn visit_block(&mut self, block: &'tcx hir::Block<'tcx>) {
 481         intravisit::walk_block(self, block);
 482
 483         if let hir::BlockCheckMode::UnsafeBlock(hir::UnsafeSource::UserProvided) = block.rules {
 484             self.unsafe_blocks.push((block.hir_id, self.used_unsafe.contains(&block.hir_id)));
 485         }
 486     }
 487 }
 488
 489 fn check_unused_unsafe(
 490     tcx: TyCtxt<'_>,
 491     def_id: DefId,
 492     used_unsafe: &FxHashSet<hir::HirId>,
 493     unsafe_blocks: &mut Vec<(hir::HirId, bool)>,
 494 ) {
 495     let body_id =
 496         tcx.hir().as_local_hir_id(def_id).and_then(|hir_id| tcx.hir().maybe_body_owned_by(hir_id));
 497
 498     let body_id = match body_id {
 499         Some(body) => body,
 500         None => {
 501             debug!("check_unused_unsafe({:?}) - no body found", def_id);
 502             return;
 503         }
 504     };
 505     let body = tcx.hir().body(body_id);
 506     debug!("check_unused_unsafe({:?}, body={:?}, used_unsafe={:?})", def_id, body, used_unsafe);
 507
 508     let mut visitor = UnusedUnsafeVisitor { used_unsafe, unsafe_blocks };
 509     intravisit::Visitor::visit_body(&mut visitor, body);
 510 }
 511
 512 fn unsafety_check_result(tcx: TyCtxt<'_>, def_id: DefId) -> UnsafetyCheckResult {
 513     debug!("unsafety_violations({:?})", def_id);
 514
 515     // N.B., this borrow is valid because all the consumers of
 516     // `mir_built` force this.
 517     let body = &tcx.mir_built(def_id).borrow();
 518
 519     let param_env = tcx.param_env(def_id);
 520
 521     let id = tcx.hir().as_local_hir_id(def_id).unwrap();
 522     let (const_context, min_const_fn) = match tcx.hir().body_owner_kind(id) {
 523         hir::BodyOwnerKind::Closure => (false, false),
 524         hir::BodyOwnerKind::Fn => (is_const_fn(tcx, def_id), is_min_const_fn(tcx, def_id)),
 525         hir::BodyOwnerKind::Const | hir::BodyOwnerKind::Static(_) => (true, false),
 526     };
 527     let mut checker = UnsafetyChecker::new(const_context, min_const_fn, body, tcx, param_env);
 528     // mir_built ensures that body has a computed cache, so we don't (and can't) attempt to
 529     // recompute it here.
 530     let body = body.unwrap_read_only();
 531     checker.visit_body(body);
 532
 533     check_unused_unsafe(tcx, def_id, &checker.used_unsafe, &mut checker.inherited_blocks);
 534     UnsafetyCheckResult {
 535         violations: checker.violations.into(),
 536         unsafe_blocks: checker.inherited_blocks.into(),
 537     }
 538 }
 539
 540 fn unsafe_derive_on_repr_packed(tcx: TyCtxt<'_>, def_id: DefId) {
 541     let lint_hir_id = tcx
 542         .hir()
 543         .as_local_hir_id(def_id)
 544         .unwrap_or_else(|| bug!("checking unsafety for non-local def id {:?}", def_id));
 545
 546     // FIXME: when we make this a hard error, this should have its
 547     // own error code.
 548     let message = if tcx.generics_of(def_id).own_requires_monomorphization() {
 549         "`#[derive]` can't be used on a `#[repr(packed)]` struct with \
 550          type or const parameters (error E0133)"
 551             .to_string()
 552     } else {
 553         "`#[derive]` can't be used on a `#[repr(packed)]` struct that \
 554          does not derive Copy (error E0133)"
 555             .to_string()
 556     };
 557     tcx.lint_hir(SAFE_PACKED_BORROWS, lint_hir_id, tcx.def_span(def_id), &message);
 558 }
 559
 560 /// Returns the `HirId` for an enclosing scope that is also `unsafe`.
 561 fn is_enclosed(
 562     tcx: TyCtxt<'_>,
 563     used_unsafe: &FxHashSet<hir::HirId>,
 564     id: hir::HirId,
 565 ) -> Option<(String, hir::HirId)> {
 566     let parent_id = tcx.hir().get_parent_node(id);
 567     if parent_id != id {
 568         if used_unsafe.contains(&parent_id) {
 569             Some(("block".to_string(), parent_id))
 570         } else if let Some(Node::Item(&hir::Item {
 571             kind: hir::ItemKind::Fn(ref sig, _, _), ..
 572         })) = tcx.hir().find(parent_id)
 573         {
 574             match sig.header.unsafety {
 575                 hir::Unsafety::Unsafe => Some(("fn".to_string(), parent_id)),
 576                 hir::Unsafety::Normal => None,
 577             }
 578         } else {
 579             is_enclosed(tcx, used_unsafe, parent_id)
 580         }
 581     } else {
 582         None
 583     }
 584 }
 585
 586 fn report_unused_unsafe(tcx: TyCtxt<'_>, used_unsafe: &FxHashSet<hir::HirId>, id: hir::HirId) {
 587     let span = tcx.sess.source_map().def_span(tcx.hir().span(id));
 588     let msg = "unnecessary `unsafe` block";
 589     let mut db = tcx.struct_span_lint_hir(UNUSED_UNSAFE, id, span, msg);
 590     db.span_label(span, msg);
 591     if let Some((kind, id)) = is_enclosed(tcx, used_unsafe, id) {
 592         db.span_label(
 593             tcx.sess.source_map().def_span(tcx.hir().span(id)),
 594             format!("because it's nested under this `unsafe` {}", kind),
 595         );
 596     }
 597     db.emit();
 598 }
 599
 600 fn builtin_derive_def_id(tcx: TyCtxt<'_>, def_id: DefId) -> Option<DefId> {
 601     debug!("builtin_derive_def_id({:?})", def_id);
 602     if let Some(impl_def_id) = tcx.impl_of_method(def_id) {
 603         if tcx.has_attr(impl_def_id, sym::automatically_derived) {
 604             debug!("builtin_derive_def_id({:?}) - is {:?}", def_id, impl_def_id);
 605             Some(impl_def_id)
 606         } else {
 607             debug!("builtin_derive_def_id({:?}) - not automatically derived", def_id);
 608             None
 609         }
 610     } else {
 611         debug!("builtin_derive_def_id({:?}) - not a method", def_id);
 612         None
 613     }
 614 }
 615
 616 pub fn check_unsafety(tcx: TyCtxt<'_>, def_id: DefId) {
 617     debug!("check_unsafety({:?})", def_id);
 618
 619     // closures are handled by their parent fn.
 620     if tcx.is_closure(def_id) {
 621         return;
 622     }
 623
 624     let UnsafetyCheckResult { violations, unsafe_blocks } = tcx.unsafety_check_result(def_id);
 625
 626     for &UnsafetyViolation { source_info, description, details, kind } in violations.iter() {
 627         // Report an error.
 628         match kind {
 629             UnsafetyViolationKind::GeneralAndConstFn | UnsafetyViolationKind::General => {
 630                 struct_span_err!(
 631                     tcx.sess,
 632                     source_info.span,
 633                     E0133,
 634                     "{} is unsafe and requires unsafe function or block",
 635                     description
 636                 )
 637                 .span_label(source_info.span, &*description.as_str())
 638                 .note(&details.as_str())
 639                 .emit();
 640             }
 641             UnsafetyViolationKind::BorrowPacked(lint_hir_id) => {
 642                 if let Some(impl_def_id) = builtin_derive_def_id(tcx, def_id) {
 643                     tcx.unsafe_derive_on_repr_packed(impl_def_id);
 644                 } else {
 645                     tcx.lint_node_note(
 646                         SAFE_PACKED_BORROWS,
 647                         lint_hir_id,
 648                         source_info.span,
 649                         &format!(
 650                             "{} is unsafe and requires unsafe function or block \
 651                                             (error E0133)",
 652                             description
 653                         ),
 654                         &details.as_str(),
 655                     );
 656                 }
 657             }
 658         }
 659     }
 660
 661     let mut unsafe_blocks: Vec<_> = unsafe_blocks.into_iter().collect();
 662     unsafe_blocks.sort_by_cached_key(|(hir_id, _)| tcx.hir().hir_to_node_id(*hir_id));
 663     let used_unsafe: FxHashSet<_> =
 664         unsafe_blocks.iter().flat_map(|&&(id, used)| used.then_some(id)).collect();
 665     for &(block_id, is_used) in unsafe_blocks {
 666         if !is_used {
 667             report_unused_unsafe(tcx, &used_unsafe, block_id);
 668         }
 669     }
 670 }