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 pub struct UnsafetyChecker<'a, 'tcx> {
  22     body: &'a Body<'tcx>,
  23     const_context: bool,
  24     min_const_fn: bool,
  25     violations: Vec<UnsafetyViolation>,
  26     source_info: SourceInfo,
  27     tcx: TyCtxt<'tcx>,
  28     param_env: ty::ParamEnv<'tcx>,
  29     /// Mark an `unsafe` block as used, so we don't lint it.
  30     used_unsafe: FxHashSet<hir::HirId>,
  31     inherited_blocks: Vec<(hir::HirId, bool)>,
  32 }
  33
  34 impl<'a, 'tcx> UnsafetyChecker<'a, 'tcx> {
  35     fn new(
  36         const_context: bool,
  37         min_const_fn: bool,
  38         body: &'a Body<'tcx>,
  39         tcx: TyCtxt<'tcx>,
  40         param_env: ty::ParamEnv<'tcx>,
  41     ) -> Self {
  42         // sanity check
  43         if min_const_fn {
  44             assert!(const_context);
  45         }
  46         Self {
  47             body,
  48             const_context,
  49             min_const_fn,
  50             violations: vec![],
  51             source_info: SourceInfo { span: body.span, scope: OUTERMOST_SOURCE_SCOPE },
  52             tcx,
  53             param_env,
  54             used_unsafe: Default::default(),
  55             inherited_blocks: vec![],
  56         }
  57     }
  58 }
  59
  60 impl<'a, 'tcx> Visitor<'tcx> for UnsafetyChecker<'a, 'tcx> {
  61     fn visit_terminator(&mut self, terminator: &Terminator<'tcx>, location: Location) {
  62         self.source_info = terminator.source_info;
  63         match terminator.kind {
  64             TerminatorKind::Goto { .. }
  65             | TerminatorKind::SwitchInt { .. }
  66             | TerminatorKind::Drop { .. }
  67             | TerminatorKind::Yield { .. }
  68             | TerminatorKind::Assert { .. }
  69             | TerminatorKind::DropAndReplace { .. }
  70             | TerminatorKind::GeneratorDrop
  71             | TerminatorKind::Resume
  72             | TerminatorKind::Abort
  73             | TerminatorKind::Return
  74             | TerminatorKind::Unreachable
  75             | TerminatorKind::FalseEdges { .. }
  76             | TerminatorKind::FalseUnwind { .. } => {
  77                 // safe (at least as emitted during MIR construction)
  78             }
  79
  80             TerminatorKind::Call { ref func, .. } => {
  81                 let func_ty = func.ty(self.body, self.tcx);
  82                 let sig = func_ty.fn_sig(self.tcx);
  83                 if let hir::Unsafety::Unsafe = sig.unsafety() {
  84                     self.require_unsafe(
  85                         "call to unsafe function",
  86                         "consult the function's documentation for information on how to avoid \
  87                          undefined behavior",
  88                         UnsafetyViolationKind::GeneralAndConstFn,
  89                     )
  90                 }
  91             }
  92         }
  93         self.super_terminator(terminator, location);
  94     }
  95
  96     fn visit_statement(&mut self, statement: &Statement<'tcx>, location: Location) {
  97         self.source_info = statement.source_info;
  98         match statement.kind {
  99             StatementKind::Assign(..)
 100             | StatementKind::FakeRead(..)
 101             | StatementKind::SetDiscriminant { .. }
 102             | StatementKind::StorageLive(..)
 103             | StatementKind::StorageDead(..)
 104             | StatementKind::Retag { .. }
 105             | StatementKind::AscribeUserType(..)
 106             | StatementKind::Nop => {
 107                 // safe (at least as emitted during MIR construction)
 108             }
 109
 110             StatementKind::InlineAsm { .. } => self.require_unsafe(
 111                 "use of inline assembly",
 112                 "inline assembly is entirely unchecked and can cause undefined behavior",
 113                 UnsafetyViolationKind::General,
 114             ),
 115         }
 116         self.super_statement(statement, location);
 117     }
 118
 119     fn visit_rvalue(&mut self, rvalue: &Rvalue<'tcx>, location: Location) {
 120         match rvalue {
 121             Rvalue::Aggregate(box ref aggregate, _) => match aggregate {
 122                 &AggregateKind::Array(..) | &AggregateKind::Tuple => {}
 123                 &AggregateKind::Adt(ref def, ..) => {
 124                     match self.tcx.layout_scalar_valid_range(def.did) {
 125                         (Bound::Unbounded, Bound::Unbounded) => {}
 126                         _ => self.require_unsafe(
 127                             "initializing type with `rustc_layout_scalar_valid_range` attr",
 128                             "initializing a layout restricted type's field with a value \
 129                                 outside the valid range is undefined behavior",
 130                             UnsafetyViolationKind::GeneralAndConstFn,
 131                         ),
 132                     }
 133                 }
 134                 &AggregateKind::Closure(def_id, _) | &AggregateKind::Generator(def_id, _, _) => {
 135                     let UnsafetyCheckResult { violations, unsafe_blocks } =
 136                         self.tcx.unsafety_check_result(def_id);
 137                     self.register_violations(&violations, &unsafe_blocks);
 138                 }
 139             },
 140             // casting pointers to ints is unsafe in const fn because the const evaluator cannot
 141             // possibly know what the result of various operations like `address / 2` would be
 142             // pointers during const evaluation have no integral address, only an abstract one
 143             Rvalue::Cast(CastKind::Misc, ref operand, cast_ty)
 144                 if self.const_context && self.tcx.features().const_raw_ptr_to_usize_cast =>
 145             {
 146                 let operand_ty = operand.ty(self.body, self.tcx);
 147                 let cast_in = CastTy::from_ty(operand_ty).expect("bad input type for cast");
 148                 let cast_out = CastTy::from_ty(cast_ty).expect("bad output type for cast");
 149                 match (cast_in, cast_out) {
 150                     (CastTy::Ptr(_), CastTy::Int(_)) | (CastTy::FnPtr, CastTy::Int(_)) => {
 151                         self.require_unsafe(
 152                             "cast of pointer to int",
 153                             "casting pointers to integers in constants",
 154                             UnsafetyViolationKind::General,
 155                         );
 156                     }
 157                     _ => {}
 158                 }
 159             }
 160             // raw pointer and fn pointer operations are unsafe as it is not clear whether one
 161             // pointer would be "less" or "equal" to another, because we cannot know where llvm
 162             // or the linker will place various statics in memory. Without this information the
 163             // result of a comparison of addresses would differ between runtime and compile-time.
 164             Rvalue::BinaryOp(_, ref lhs, _)
 165                 if self.const_context && self.tcx.features().const_compare_raw_pointers =>
 166             {
 167                 if let ty::RawPtr(_) | ty::FnPtr(..) = lhs.ty(self.body, self.tcx).kind {
 168                     self.require_unsafe(
 169                         "pointer operation",
 170                         "operations on pointers in constants",
 171                         UnsafetyViolationKind::General,
 172                     );
 173                 }
 174             }
 175             _ => {}
 176         }
 177         self.super_rvalue(rvalue, location);
 178     }
 179
 180     fn visit_place(&mut self, place: &Place<'tcx>, context: PlaceContext, _location: Location) {
 181         // prevent
 182         // * `&mut x.field`
 183         // * `x.field = y;`
 184         // * `&x.field` if `field`'s type has interior mutability
 185         // because either of these would allow modifying the layout constrained field and
 186         // insert values that violate the layout constraints.
 187         if context.is_mutating_use() || context.is_borrow() {
 188             self.check_mut_borrowing_layout_constrained_field(place, context.is_mutating_use());
 189         }
 190
 191         for (i, elem) in place.projection.iter().enumerate() {
 192             let proj_base = &place.projection[..i];
 193
 194             if context.is_borrow() {
 195                 if util::is_disaligned(self.tcx, self.body, self.param_env, place) {
 196                     let source_info = self.source_info;
 197                     let lint_root = self.body.source_scopes[source_info.scope]
 198                         .local_data
 199                         .as_ref()
 200                         .assert_crate_local()
 201                         .lint_root;
 202                     self.require_unsafe(
 203                         "borrow of packed field",
 204                         "fields of packed structs might be misaligned: dereferencing a \
 205                         misaligned pointer or even just creating a misaligned reference \
 206                         is undefined behavior",
 207                         UnsafetyViolationKind::BorrowPacked(lint_root),
 208                     );
 209                 }
 210             }
 211             let old_source_info = self.source_info;
 212             if let [] = proj_base {
 213                 let decl = &self.body.local_decls[place.local];
 214                 if decl.internal {
 215                     if let LocalInfo::StaticRef { def_id, .. } = decl.local_info {
 216                         if self.tcx.is_mutable_static(def_id) {
 217                             self.require_unsafe(
 218                                 "use of mutable static",
 219                                 "mutable statics can be mutated by multiple threads: aliasing \
 220                             violations or data races will cause undefined behavior",
 221                                 UnsafetyViolationKind::General,
 222                             );
 223                             return;
 224                         } else if self.tcx.is_foreign_item(def_id) {
 225                             self.require_unsafe(
 226                                 "use of extern static",
 227                                 "extern statics are not controlled by the Rust type system: \
 228                             invalid data, aliasing violations or data races will cause \
 229                             undefined behavior",
 230                                 UnsafetyViolationKind::General,
 231                             );
 232                             return;
 233                         }
 234                     } else {
 235                         // Internal locals are used in the `move_val_init` desugaring.
 236                         // We want to check unsafety against the source info of the
 237                         // desugaring, rather than the source info of the RHS.
 238                         self.source_info = self.body.local_decls[place.local].source_info;
 239                     }
 240                 }
 241             }
 242             let base_ty = Place::ty_from(place.local, proj_base, self.body, self.tcx).ty;
 243             match base_ty.kind {
 244                 ty::RawPtr(..) => self.require_unsafe(
 245                     "dereference of raw pointer",
 246                     "raw pointers may be NULL, dangling or unaligned; they can violate \
 247                          aliasing rules and cause data races: all of these are undefined \
 248                          behavior",
 249                     UnsafetyViolationKind::General,
 250                 ),
 251                 ty::Adt(adt, _) => {
 252                     if adt.is_union() {
 253                         if context == PlaceContext::MutatingUse(MutatingUseContext::Store)
 254                             || context == PlaceContext::MutatingUse(MutatingUseContext::Drop)
 255                             || context == PlaceContext::MutatingUse(MutatingUseContext::AsmOutput)
 256                         {
 257                             let elem_ty = match elem {
 258                                 ProjectionElem::Field(_, ty) => ty,
 259                                 _ => span_bug!(
 260                                     self.source_info.span,
 261                                     "non-field projection {:?} from union?",
 262                                     place
 263                                 ),
 264                             };
 265                             if !elem_ty.is_copy_modulo_regions(
 266                                 self.tcx,
 267                                 self.param_env,
 268                                 self.source_info.span,
 269                             ) {
 270                                 self.require_unsafe(
 271                                     "assignment to non-`Copy` union field",
 272                                     "the previous content of the field will be dropped, which \
 273                                      causes undefined behavior if the field was not properly \
 274                                      initialized",
 275                                     UnsafetyViolationKind::GeneralAndConstFn,
 276                                 )
 277                             } else {
 278                                 // write to non-move union, safe
 279                             }
 280                         } else {
 281                             self.require_unsafe(
 282                                 "access to union field",
 283                                 "the field may not be properly initialized: using \
 284                                  uninitialized data will cause undefined behavior",
 285                                 UnsafetyViolationKind::GeneralAndConstFn,
 286                             )
 287                         }
 288                     }
 289                 }
 290                 _ => {}
 291             }
 292             self.source_info = old_source_info;
 293         }
 294     }
 295 }
 296
 297 impl<'a, 'tcx> UnsafetyChecker<'a, 'tcx> {
 298     fn require_unsafe(
 299         &mut self,
 300         description: &'static str,
 301         details: &'static str,
 302         kind: UnsafetyViolationKind,
 303     ) {
 304         let source_info = self.source_info;
 305         self.register_violations(
 306             &[UnsafetyViolation {
 307                 source_info,
 308                 description: Symbol::intern(description),
 309                 details: Symbol::intern(details),
 310                 kind,
 311             }],
 312             &[],
 313         );
 314     }
 315
 316     fn register_violations(
 317         &mut self,
 318         violations: &[UnsafetyViolation],
 319         unsafe_blocks: &[(hir::HirId, bool)],
 320     ) {
 321         let safety = self.body.source_scopes[self.source_info.scope]
 322             .local_data
 323             .as_ref()
 324             .assert_crate_local()
 325             .safety;
 326         let within_unsafe = match safety {
 327             // `unsafe` blocks are required in safe code
 328             Safety::Safe => {
 329                 for violation in violations {
 330                     let mut violation = *violation;
 331                     match violation.kind {
 332                         UnsafetyViolationKind::GeneralAndConstFn
 333                         | UnsafetyViolationKind::General => {}
 334                         UnsafetyViolationKind::BorrowPacked(_) => {
 335                             if self.min_const_fn {
 336                                 // const fns don't need to be backwards compatible and can
 337                                 // emit these violations as a hard error instead of a backwards
 338                                 // compat lint
 339                                 violation.kind = UnsafetyViolationKind::General;
 340                             }
 341                         }
 342                     }
 343                     if !self.violations.contains(&violation) {
 344                         self.violations.push(violation)
 345                     }
 346                 }
 347                 false
 348             }
 349             // `unsafe` function bodies allow unsafe without additional unsafe blocks
 350             Safety::BuiltinUnsafe | Safety::FnUnsafe => true,
 351             Safety::ExplicitUnsafe(hir_id) => {
 352                 // mark unsafe block as used if there are any unsafe operations inside
 353                 if !violations.is_empty() {
 354                     self.used_unsafe.insert(hir_id);
 355                 }
 356                 // only some unsafety is allowed in const fn
 357                 if self.min_const_fn {
 358                     for violation in violations {
 359                         match violation.kind {
 360                             // these unsafe things are stable in const fn
 361                             UnsafetyViolationKind::GeneralAndConstFn => {}
 362                             // these things are forbidden in const fns
 363                             UnsafetyViolationKind::General
 364                             | UnsafetyViolationKind::BorrowPacked(_) => {
 365                                 let mut violation = *violation;
 366                                 // const fns don't need to be backwards compatible and can
 367                                 // emit these violations as a hard error instead of a backwards
 368                                 // compat lint
 369                                 violation.kind = UnsafetyViolationKind::General;
 370                                 if !self.violations.contains(&violation) {
 371                                     self.violations.push(violation)
 372                                 }
 373                             }
 374                         }
 375                     }
 376                 }
 377                 true
 378             }
 379         };
 380         self.inherited_blocks.extend(
 381             unsafe_blocks.iter().map(|&(hir_id, is_used)| (hir_id, is_used && !within_unsafe)),
 382         );
 383     }
 384     fn check_mut_borrowing_layout_constrained_field(
 385         &mut self,
 386         place: &Place<'tcx>,
 387         is_mut_use: bool,
 388     ) {
 389         let mut cursor = place.projection.as_ref();
 390         while let &[ref proj_base @ .., elem] = cursor {
 391             cursor = proj_base;
 392
 393             match elem {
 394                 // Modifications behind a dereference don't affect the value of
 395                 // the pointer.
 396                 ProjectionElem::Deref => return,
 397                 ProjectionElem::Field(..) => {
 398                     let ty =
 399                         Place::ty_from(place.local, proj_base, &self.body.local_decls, self.tcx).ty;
 400                     match ty.kind {
 401                         ty::Adt(def, _) => match self.tcx.layout_scalar_valid_range(def.did) {
 402                             (Bound::Unbounded, Bound::Unbounded) => {}
 403                             _ => {
 404                                 let (description, details) = if is_mut_use {
 405                                     (
 406                                         "mutation of layout constrained field",
 407                                         "mutating layout constrained fields cannot statically be \
 408                                         checked for valid values",
 409                                     )
 410
 411                                 // Check `is_freeze` as late as possible to avoid cycle errors
 412                                 // with opaque types.
 413                                 } else if !place.ty(self.body, self.tcx).ty.is_freeze(
 414                                     self.tcx,
 415                                     self.param_env,
 416                                     self.source_info.span,
 417                                 ) {
 418                                     (
 419                                         "borrow of layout constrained field with interior \
 420                                         mutability",
 421                                         "references to fields of layout constrained fields \
 422                                         lose the constraints. Coupled with interior mutability, \
 423                                         the field can be changed to invalid values",
 424                                     )
 425                                 } else {
 426                                     continue;
 427                                 };
 428                                 self.require_unsafe(
 429                                     description,
 430                                     details,
 431                                     UnsafetyViolationKind::GeneralAndConstFn,
 432                                 );
 433                             }
 434                         },
 435                         _ => {}
 436                     }
 437                 }
 438                 _ => {}
 439             }
 440         }
 441     }
 442 }
 443
 444 pub(crate) fn provide(providers: &mut Providers<'_>) {
 445     *providers = Providers { unsafety_check_result, unsafe_derive_on_repr_packed, ..*providers };
 446 }
 447
 448 struct UnusedUnsafeVisitor<'a> {
 449     used_unsafe: &'a FxHashSet<hir::HirId>,
 450     unsafe_blocks: &'a mut Vec<(hir::HirId, bool)>,
 451 }
 452
 453 impl<'a, 'tcx> intravisit::Visitor<'tcx> for UnusedUnsafeVisitor<'a> {
 454     type Map = Map<'tcx>;
 455
 456     fn nested_visit_map(&mut self) -> intravisit::NestedVisitorMap<'_, Self::Map> {
 457         intravisit::NestedVisitorMap::None
 458     }
 459
 460     fn visit_block(&mut self, block: &'tcx hir::Block<'tcx>) {
 461         intravisit::walk_block(self, block);
 462
 463         if let hir::BlockCheckMode::UnsafeBlock(hir::UnsafeSource::UserProvided) = block.rules {
 464             self.unsafe_blocks.push((block.hir_id, self.used_unsafe.contains(&block.hir_id)));
 465         }
 466     }
 467 }
 468
 469 fn check_unused_unsafe(
 470     tcx: TyCtxt<'_>,
 471     def_id: DefId,
 472     used_unsafe: &FxHashSet<hir::HirId>,
 473     unsafe_blocks: &mut Vec<(hir::HirId, bool)>,
 474 ) {
 475     let body_id =
 476         tcx.hir().as_local_hir_id(def_id).and_then(|hir_id| tcx.hir().maybe_body_owned_by(hir_id));
 477
 478     let body_id = match body_id {
 479         Some(body) => body,
 480         None => {
 481             debug!("check_unused_unsafe({:?}) - no body found", def_id);
 482             return;
 483         }
 484     };
 485     let body = tcx.hir().body(body_id);
 486     debug!("check_unused_unsafe({:?}, body={:?}, used_unsafe={:?})", def_id, body, used_unsafe);
 487
 488     let mut visitor = UnusedUnsafeVisitor { used_unsafe, unsafe_blocks };
 489     intravisit::Visitor::visit_body(&mut visitor, body);
 490 }
 491
 492 fn unsafety_check_result(tcx: TyCtxt<'_>, def_id: DefId) -> UnsafetyCheckResult {
 493     debug!("unsafety_violations({:?})", def_id);
 494
 495     // N.B., this borrow is valid because all the consumers of
 496     // `mir_built` force this.
 497     let body = &tcx.mir_built(def_id).borrow();
 498
 499     let param_env = tcx.param_env(def_id);
 500
 501     let id = tcx.hir().as_local_hir_id(def_id).unwrap();
 502     let (const_context, min_const_fn) = match tcx.hir().body_owner_kind(id) {
 503         hir::BodyOwnerKind::Closure => (false, false),
 504         hir::BodyOwnerKind::Fn => (is_const_fn(tcx, def_id), is_min_const_fn(tcx, def_id)),
 505         hir::BodyOwnerKind::Const | hir::BodyOwnerKind::Static(_) => (true, false),
 506     };
 507     let mut checker = UnsafetyChecker::new(const_context, min_const_fn, body, tcx, param_env);
 508     // mir_built ensures that body has a computed cache, so we don't (and can't) attempt to
 509     // recompute it here.
 510     let body = body.unwrap_read_only();
 511     checker.visit_body(body);
 512
 513     check_unused_unsafe(tcx, def_id, &checker.used_unsafe, &mut checker.inherited_blocks);
 514     UnsafetyCheckResult {
 515         violations: checker.violations.into(),
 516         unsafe_blocks: checker.inherited_blocks.into(),
 517     }
 518 }
 519
 520 fn unsafe_derive_on_repr_packed(tcx: TyCtxt<'_>, def_id: DefId) {
 521     let lint_hir_id = tcx
 522         .hir()
 523         .as_local_hir_id(def_id)
 524         .unwrap_or_else(|| bug!("checking unsafety for non-local def id {:?}", def_id));
 525
 526     tcx.struct_span_lint_hir(SAFE_PACKED_BORROWS, lint_hir_id, tcx.def_span(def_id), |lint| {
 527         // FIXME: when we make this a hard error, this should have its
 528         // own error code.
 529         let message = if tcx.generics_of(def_id).own_requires_monomorphization() {
 530             "`#[derive]` can't be used on a `#[repr(packed)]` struct with \
 531              type or const parameters (error E0133)"
 532                 .to_string()
 533         } else {
 534             "`#[derive]` can't be used on a `#[repr(packed)]` struct that \
 535              does not derive Copy (error E0133)"
 536                 .to_string()
 537         };
 538         lint.build(&message).emit()
 539     });
 540 }
 541
 542 /// Returns the `HirId` for an enclosing scope that is also `unsafe`.
 543 fn is_enclosed(
 544     tcx: TyCtxt<'_>,
 545     used_unsafe: &FxHashSet<hir::HirId>,
 546     id: hir::HirId,
 547 ) -> Option<(String, hir::HirId)> {
 548     let parent_id = tcx.hir().get_parent_node(id);
 549     if parent_id != id {
 550         if used_unsafe.contains(&parent_id) {
 551             Some(("block".to_string(), parent_id))
 552         } else if let Some(Node::Item(&hir::Item {
 553             kind: hir::ItemKind::Fn(ref sig, _, _), ..
 554         })) = tcx.hir().find(parent_id)
 555         {
 556             match sig.header.unsafety {
 557                 hir::Unsafety::Unsafe => Some(("fn".to_string(), parent_id)),
 558                 hir::Unsafety::Normal => None,
 559             }
 560         } else {
 561             is_enclosed(tcx, used_unsafe, parent_id)
 562         }
 563     } else {
 564         None
 565     }
 566 }
 567
 568 fn report_unused_unsafe(tcx: TyCtxt<'_>, used_unsafe: &FxHashSet<hir::HirId>, id: hir::HirId) {
 569     let span = tcx.sess.source_map().def_span(tcx.hir().span(id));
 570     tcx.struct_span_lint_hir(UNUSED_UNSAFE, id, span, |lint| {
 571         let msg = "unnecessary `unsafe` block";
 572         let mut db = lint.build(msg);
 573         db.span_label(span, msg);
 574         if let Some((kind, id)) = is_enclosed(tcx, used_unsafe, id) {
 575             db.span_label(
 576                 tcx.sess.source_map().def_span(tcx.hir().span(id)),
 577                 format!("because it's nested under this `unsafe` {}", kind),
 578             );
 579         }
 580         db.emit();
 581     });
 582 }
 583
 584 fn builtin_derive_def_id(tcx: TyCtxt<'_>, def_id: DefId) -> Option<DefId> {
 585     debug!("builtin_derive_def_id({:?})", def_id);
 586     if let Some(impl_def_id) = tcx.impl_of_method(def_id) {
 587         if tcx.has_attr(impl_def_id, sym::automatically_derived) {
 588             debug!("builtin_derive_def_id({:?}) - is {:?}", def_id, impl_def_id);
 589             Some(impl_def_id)
 590         } else {
 591             debug!("builtin_derive_def_id({:?}) - not automatically derived", def_id);
 592             None
 593         }
 594     } else {
 595         debug!("builtin_derive_def_id({:?}) - not a method", def_id);
 596         None
 597     }
 598 }
 599
 600 pub fn check_unsafety(tcx: TyCtxt<'_>, def_id: DefId) {
 601     debug!("check_unsafety({:?})", def_id);
 602
 603     // closures are handled by their parent fn.
 604     if tcx.is_closure(def_id) {
 605         return;
 606     }
 607
 608     let UnsafetyCheckResult { violations, unsafe_blocks } = tcx.unsafety_check_result(def_id);
 609
 610     for &UnsafetyViolation { source_info, description, details, kind } in violations.iter() {
 611         // Report an error.
 612         match kind {
 613             UnsafetyViolationKind::GeneralAndConstFn | UnsafetyViolationKind::General => {
 614                 struct_span_err!(
 615                     tcx.sess,
 616                     source_info.span,
 617                     E0133,
 618                     "{} is unsafe and requires unsafe function or block",
 619                     description
 620                 )
 621                 .span_label(source_info.span, &*description.as_str())
 622                 .note(&details.as_str())
 623                 .emit();
 624             }
 625             UnsafetyViolationKind::BorrowPacked(lint_hir_id) => {
 626                 if let Some(impl_def_id) = builtin_derive_def_id(tcx, def_id) {
 627                     tcx.unsafe_derive_on_repr_packed(impl_def_id);
 628                 } else {
 629                     tcx.struct_span_lint_hir(
 630                         SAFE_PACKED_BORROWS,
 631                         lint_hir_id,
 632                         source_info.span,
 633                         |lint| {
 634                             lint.build(&format!(
 635                                 "{} is unsafe and requires unsafe function or block (error E0133)",
 636                                 description
 637                             ))
 638                             .note(&details.as_str())
 639                             .emit()
 640                         },
 641                     )
 642                 }
 643             }
 644         }
 645     }
 646
 647     let mut unsafe_blocks: Vec<_> = unsafe_blocks.iter().collect();
 648     unsafe_blocks.sort_by_cached_key(|(hir_id, _)| tcx.hir().hir_to_node_id(*hir_id));
 649     let used_unsafe: FxHashSet<_> =
 650         unsafe_blocks.iter().flat_map(|&&(id, used)| used.then_some(id)).collect();
 651     for &(block_id, is_used) in unsafe_blocks {
 652         if !is_used {
 653             report_unused_unsafe(tcx, &used_unsafe, block_id);
 654         }
 655     }
 656 }