src/librustc_mir/transform/check_unsafety.rs

   1 use rustc::mir::visit::{MutatingUseContext, PlaceContext, Visitor};
   2 use rustc::mir::*;
   3 use rustc::ty::cast::CastTy;
   4 use rustc::ty::query::Providers;
   5 use rustc::ty::{self, TyCtxt};
   6 use rustc_data_structures::fx::FxHashSet;
   7 use rustc_errors::struct_span_err;
   8 use rustc_hir as hir;
   9 use rustc_hir::def_id::DefId;
  10 use rustc_hir::intravisit;
  11 use rustc_hir::Node;
  12 use rustc_session::lint::builtin::{SAFE_PACKED_BORROWS, UNUSED_UNSAFE};
  13 use rustc_span::symbol::{sym, Symbol};
  14
  15 use std::ops::Bound;
  16
  17 use crate::const_eval::{is_const_fn, is_min_const_fn};
  18 use crate::util;
  19
  20 pub struct UnsafetyChecker<'a, 'tcx> {
  21     body: &'a Body<'tcx>,
  22     const_context: bool,
  23     min_const_fn: bool,
  24     violations: Vec<UnsafetyViolation>,
  25     source_info: SourceInfo,
  26     tcx: TyCtxt<'tcx>,
  27     param_env: ty::ParamEnv<'tcx>,
  28     /// Mark an `unsafe` block as used, so we don't lint it.
  29     used_unsafe: FxHashSet<hir::HirId>,
  30     inherited_blocks: Vec<(hir::HirId, bool)>,
  31 }
  32
  33 impl<'a, 'tcx> UnsafetyChecker<'a, 'tcx> {
  34     fn new(
  35         const_context: bool,
  36         min_const_fn: bool,
  37         body: &'a Body<'tcx>,
  38         tcx: TyCtxt<'tcx>,
  39         param_env: ty::ParamEnv<'tcx>,
  40     ) -> Self {
  41         // sanity check
  42         if min_const_fn {
  43             assert!(const_context);
  44         }
  45         Self {
  46             body,
  47             const_context,
  48             min_const_fn,
  49             violations: vec![],
  50             source_info: SourceInfo { span: body.span, scope: OUTERMOST_SOURCE_SCOPE },
  51             tcx,
  52             param_env,
  53             used_unsafe: Default::default(),
  54             inherited_blocks: vec![],
  55         }
  56     }
  57 }
  58
  59 impl<'a, 'tcx> Visitor<'tcx> for UnsafetyChecker<'a, 'tcx> {
  60     fn visit_terminator(&mut self, terminator: &Terminator<'tcx>, location: Location) {
  61         self.source_info = terminator.source_info;
  62         match terminator.kind {
  63             TerminatorKind::Goto { .. }
  64             | TerminatorKind::SwitchInt { .. }
  65             | TerminatorKind::Drop { .. }
  66             | TerminatorKind::Yield { .. }
  67             | TerminatorKind::Assert { .. }
  68             | TerminatorKind::DropAndReplace { .. }
  69             | TerminatorKind::GeneratorDrop
  70             | TerminatorKind::Resume
  71             | TerminatorKind::Abort
  72             | TerminatorKind::Return
  73             | TerminatorKind::Unreachable
  74             | TerminatorKind::FalseEdges { .. }
  75             | TerminatorKind::FalseUnwind { .. } => {
  76                 // safe (at least as emitted during MIR construction)
  77             }
  78
  79             TerminatorKind::Call { ref func, .. } => {
  80                 let func_ty = func.ty(self.body, self.tcx);
  81                 let sig = func_ty.fn_sig(self.tcx);
  82                 if let hir::Unsafety::Unsafe = sig.unsafety() {
  83                     self.require_unsafe(
  84                         "call to unsafe function",
  85                         "consult the function's documentation for information on how to avoid \
  86                          undefined behavior",
  87                         UnsafetyViolationKind::GeneralAndConstFn,
  88                     )
  89                 }
  90             }
  91         }
  92         self.super_terminator(terminator, location);
  93     }
  94
  95     fn visit_statement(&mut self, statement: &Statement<'tcx>, location: Location) {
  96         self.source_info = statement.source_info;
  97         match statement.kind {
  98             StatementKind::Assign(..)
  99             | StatementKind::FakeRead(..)
 100             | StatementKind::SetDiscriminant { .. }
 101             | StatementKind::StorageLive(..)
 102             | StatementKind::StorageDead(..)
 103             | StatementKind::Retag { .. }
 104             | StatementKind::AscribeUserType(..)
 105             | StatementKind::Nop => {
 106                 // safe (at least as emitted during MIR construction)
 107             }
 108
 109             StatementKind::InlineAsm { .. } => self.require_unsafe(
 110                 "use of inline assembly",
 111                 "inline assembly is entirely unchecked and can cause undefined behavior",
 112                 UnsafetyViolationKind::General,
 113             ),
 114         }
 115         self.super_statement(statement, location);
 116     }
 117
 118     fn visit_rvalue(&mut self, rvalue: &Rvalue<'tcx>, location: Location) {
 119         match rvalue {
 120             Rvalue::Aggregate(box ref aggregate, _) => match aggregate {
 121                 &AggregateKind::Array(..) | &AggregateKind::Tuple => {}
 122                 &AggregateKind::Adt(ref def, ..) => {
 123                     match self.tcx.layout_scalar_valid_range(def.did) {
 124                         (Bound::Unbounded, Bound::Unbounded) => {}
 125                         _ => self.require_unsafe(
 126                             "initializing type with `rustc_layout_scalar_valid_range` attr",
 127                             "initializing a layout restricted type's field with a value \
 128                                 outside the valid range is undefined behavior",
 129                             UnsafetyViolationKind::GeneralAndConstFn,
 130                         ),
 131                     }
 132                 }
 133                 &AggregateKind::Closure(def_id, _) | &AggregateKind::Generator(def_id, _, _) => {
 134                     let UnsafetyCheckResult { violations, unsafe_blocks } =
 135                         self.tcx.unsafety_check_result(def_id);
 136                     self.register_violations(&violations, &unsafe_blocks);
 137                 }
 138             },
 139             // casting pointers to ints is unsafe in const fn because the const evaluator cannot
 140             // possibly know what the result of various operations like `address / 2` would be
 141             // pointers during const evaluation have no integral address, only an abstract one
 142             Rvalue::Cast(CastKind::Misc, ref operand, cast_ty)
 143                 if self.const_context && self.tcx.features().const_raw_ptr_to_usize_cast =>
 144             {
 145                 let operand_ty = operand.ty(self.body, self.tcx);
 146                 let cast_in = CastTy::from_ty(operand_ty).expect("bad input type for cast");
 147                 let cast_out = CastTy::from_ty(cast_ty).expect("bad output type for cast");
 148                 match (cast_in, cast_out) {
 149                     (CastTy::Ptr(_), CastTy::Int(_)) | (CastTy::FnPtr, CastTy::Int(_)) => {
 150                         self.require_unsafe(
 151                             "cast of pointer to int",
 152                             "casting pointers to integers in constants",
 153                             UnsafetyViolationKind::General,
 154                         );
 155                     }
 156                     _ => {}
 157                 }
 158             }
 159             // raw pointer and fn pointer operations are unsafe as it is not clear whether one
 160             // pointer would be "less" or "equal" to another, because we cannot know where llvm
 161             // or the linker will place various statics in memory. Without this information the
 162             // result of a comparison of addresses would differ between runtime and compile-time.
 163             Rvalue::BinaryOp(_, ref lhs, _)
 164                 if self.const_context && self.tcx.features().const_compare_raw_pointers =>
 165             {
 166                 if let ty::RawPtr(_) | ty::FnPtr(..) = lhs.ty(self.body, self.tcx).kind {
 167                     self.require_unsafe(
 168                         "pointer operation",
 169                         "operations on pointers in constants",
 170                         UnsafetyViolationKind::General,
 171                     );
 172                 }
 173             }
 174             _ => {}
 175         }
 176         self.super_rvalue(rvalue, location);
 177     }
 178
 179     fn visit_place(&mut self, place: &Place<'tcx>, context: PlaceContext, _location: Location) {
 180         // prevent
 181         // * `&mut x.field`
 182         // * `x.field = y;`
 183         // * `&x.field` if `field`'s type has interior mutability
 184         // because either of these would allow modifying the layout constrained field and
 185         // insert values that violate the layout constraints.
 186         if context.is_mutating_use() || context.is_borrow() {
 187             self.check_mut_borrowing_layout_constrained_field(place, context.is_mutating_use());
 188         }
 189
 190         for (i, elem) in place.projection.iter().enumerate() {
 191             let proj_base = &place.projection[..i];
 192
 193             if context.is_borrow() {
 194                 if util::is_disaligned(self.tcx, self.body, self.param_env, place) {
 195                     let source_info = self.source_info;
 196                     let lint_root = self.body.source_scopes[source_info.scope]
 197                         .local_data
 198                         .as_ref()
 199                         .assert_crate_local()
 200                         .lint_root;
 201                     self.require_unsafe(
 202                         "borrow of packed field",
 203                         "fields of packed structs might be misaligned: dereferencing a \
 204                         misaligned pointer or even just creating a misaligned reference \
 205                         is undefined behavior",
 206                         UnsafetyViolationKind::BorrowPacked(lint_root),
 207                     );
 208                 }
 209             }
 210             let old_source_info = self.source_info;
 211             if let [] = proj_base {
 212                 let decl = &self.body.local_decls[place.local];
 213                 if decl.internal {
 214                     if let LocalInfo::StaticRef { def_id, .. } = decl.local_info {
 215                         if self.tcx.is_mutable_static(def_id) {
 216                             self.require_unsafe(
 217                                 "use of mutable static",
 218                                 "mutable statics can be mutated by multiple threads: aliasing \
 219                             violations or data races will cause undefined behavior",
 220                                 UnsafetyViolationKind::General,
 221                             );
 222                             return;
 223                         } else if self.tcx.is_foreign_item(def_id) {
 224                             self.require_unsafe(
 225                                 "use of extern static",
 226                                 "extern statics are not controlled by the Rust type system: \
 227                             invalid data, aliasing violations or data races will cause \
 228                             undefined behavior",
 229                                 UnsafetyViolationKind::General,
 230                             );
 231                             return;
 232                         }
 233                     } else {
 234                         // Internal locals are used in the `move_val_init` desugaring.
 235                         // We want to check unsafety against the source info of the
 236                         // desugaring, rather than the source info of the RHS.
 237                         self.source_info = self.body.local_decls[place.local].source_info;
 238                     }
 239                 }
 240             }
 241             let base_ty = Place::ty_from(place.local, proj_base, self.body, self.tcx).ty;
 242             match base_ty.kind {
 243                 ty::RawPtr(..) => self.require_unsafe(
 244                     "dereference of raw pointer",
 245                     "raw pointers may be NULL, dangling or unaligned; they can violate \
 246                          aliasing rules and cause data races: all of these are undefined \
 247                          behavior",
 248                     UnsafetyViolationKind::General,
 249                 ),
 250                 ty::Adt(adt, _) => {
 251                     if adt.is_union() {
 252                         if context == PlaceContext::MutatingUse(MutatingUseContext::Store)
 253                             || context == PlaceContext::MutatingUse(MutatingUseContext::Drop)
 254                             || context == PlaceContext::MutatingUse(MutatingUseContext::AsmOutput)
 255                         {
 256                             let elem_ty = match elem {
 257                                 ProjectionElem::Field(_, ty) => ty,
 258                                 _ => span_bug!(
 259                                     self.source_info.span,
 260                                     "non-field projection {:?} from union?",
 261                                     place
 262                                 ),
 263                             };
 264                             if !elem_ty.is_copy_modulo_regions(
 265                                 self.tcx,
 266                                 self.param_env,
 267                                 self.source_info.span,
 268                             ) {
 269                                 self.require_unsafe(
 270                                     "assignment to non-`Copy` union field",
 271                                     "the previous content of the field will be dropped, which \
 272                                      causes undefined behavior if the field was not properly \
 273                                      initialized",
 274                                     UnsafetyViolationKind::GeneralAndConstFn,
 275                                 )
 276                             } else {
 277                                 // write to non-move union, safe
 278                             }
 279                         } else {
 280                             self.require_unsafe(
 281                                 "access to union field",
 282                                 "the field may not be properly initialized: using \
 283                                  uninitialized data will cause undefined behavior",
 284                                 UnsafetyViolationKind::GeneralAndConstFn,
 285                             )
 286                         }
 287                     }
 288                 }
 289                 _ => {}
 290             }
 291             self.source_info = old_source_info;
 292         }
 293     }
 294 }
 295
 296 impl<'a, 'tcx> UnsafetyChecker<'a, 'tcx> {
 297     fn require_unsafe(
 298         &mut self,
 299         description: &'static str,
 300         details: &'static str,
 301         kind: UnsafetyViolationKind,
 302     ) {
 303         let source_info = self.source_info;
 304         self.register_violations(
 305             &[UnsafetyViolation {
 306                 source_info,
 307                 description: Symbol::intern(description),
 308                 details: Symbol::intern(details),
 309                 kind,
 310             }],
 311             &[],
 312         );
 313     }
 314
 315     fn register_violations(
 316         &mut self,
 317         violations: &[UnsafetyViolation],
 318         unsafe_blocks: &[(hir::HirId, bool)],
 319     ) {
 320         let safety = self.body.source_scopes[self.source_info.scope]
 321             .local_data
 322             .as_ref()
 323             .assert_crate_local()
 324             .safety;
 325         let within_unsafe = match safety {
 326             // `unsafe` blocks are required in safe code
 327             Safety::Safe => {
 328                 for violation in violations {
 329                     let mut violation = *violation;
 330                     match violation.kind {
 331                         UnsafetyViolationKind::GeneralAndConstFn
 332                         | UnsafetyViolationKind::General => {}
 333                         UnsafetyViolationKind::BorrowPacked(_) => {
 334                             if self.min_const_fn {
 335                                 // const fns don't need to be backwards compatible and can
 336                                 // emit these violations as a hard error instead of a backwards
 337                                 // compat lint
 338                                 violation.kind = UnsafetyViolationKind::General;
 339                             }
 340                         }
 341                     }
 342                     if !self.violations.contains(&violation) {
 343                         self.violations.push(violation)
 344                     }
 345                 }
 346                 false
 347             }
 348             // `unsafe` function bodies allow unsafe without additional unsafe blocks
 349             Safety::BuiltinUnsafe | Safety::FnUnsafe => true,
 350             Safety::ExplicitUnsafe(hir_id) => {
 351                 // mark unsafe block as used if there are any unsafe operations inside
 352                 if !violations.is_empty() {
 353                     self.used_unsafe.insert(hir_id);
 354                 }
 355                 // only some unsafety is allowed in const fn
 356                 if self.min_const_fn {
 357                     for violation in violations {
 358                         match violation.kind {
 359                             // these unsafe things are stable in const fn
 360                             UnsafetyViolationKind::GeneralAndConstFn => {}
 361                             // these things are forbidden in const fns
 362                             UnsafetyViolationKind::General
 363                             | UnsafetyViolationKind::BorrowPacked(_) => {
 364                                 let mut violation = *violation;
 365                                 // const fns don't need to be backwards compatible and can
 366                                 // emit these violations as a hard error instead of a backwards
 367                                 // compat lint
 368                                 violation.kind = UnsafetyViolationKind::General;
 369                                 if !self.violations.contains(&violation) {
 370                                     self.violations.push(violation)
 371                                 }
 372                             }
 373                         }
 374                     }
 375                 }
 376                 true
 377             }
 378         };
 379         self.inherited_blocks.extend(
 380             unsafe_blocks.iter().map(|&(hir_id, is_used)| (hir_id, is_used && !within_unsafe)),
 381         );
 382     }
 383     fn check_mut_borrowing_layout_constrained_field(
 384         &mut self,
 385         place: &Place<'tcx>,
 386         is_mut_use: bool,
 387     ) {
 388         let mut cursor = place.projection.as_ref();
 389         while let &[ref proj_base @ .., elem] = cursor {
 390             cursor = proj_base;
 391
 392             match elem {
 393                 // Modifications behind a dereference don't affect the value of
 394                 // the pointer.
 395                 ProjectionElem::Deref => return,
 396                 ProjectionElem::Field(..) => {
 397                     let ty =
 398                         Place::ty_from(place.local, proj_base, &self.body.local_decls, self.tcx).ty;
 399                     match ty.kind {
 400                         ty::Adt(def, _) => match self.tcx.layout_scalar_valid_range(def.did) {
 401                             (Bound::Unbounded, Bound::Unbounded) => {}
 402                             _ => {
 403                                 let (description, details) = if is_mut_use {
 404                                     (
 405                                         "mutation of layout constrained field",
 406                                         "mutating layout constrained fields cannot statically be \
 407                                         checked for valid values",
 408                                     )
 409
 410                                 // Check `is_freeze` as late as possible to avoid cycle errors
 411                                 // with opaque types.
 412                                 } else if !place.ty(self.body, self.tcx).ty.is_freeze(
 413                                     self.tcx,
 414                                     self.param_env,
 415                                     self.source_info.span,
 416                                 ) {
 417                                     (
 418                                         "borrow of layout constrained field with interior \
 419                                         mutability",
 420                                         "references to fields of layout constrained fields \
 421                                         lose the constraints. Coupled with interior mutability, \
 422                                         the field can be changed to invalid values",
 423                                     )
 424                                 } else {
 425                                     continue;
 426                                 };
 427                                 self.require_unsafe(
 428                                     description,
 429                                     details,
 430                                     UnsafetyViolationKind::GeneralAndConstFn,
 431                                 );
 432                             }
 433                         },
 434                         _ => {}
 435                     }
 436                 }
 437                 _ => {}
 438             }
 439         }
 440     }
 441 }
 442
 443 pub(crate) fn provide(providers: &mut Providers<'_>) {
 444     *providers = Providers { unsafety_check_result, unsafe_derive_on_repr_packed, ..*providers };
 445 }
 446
 447 struct UnusedUnsafeVisitor<'a> {
 448     used_unsafe: &'a FxHashSet<hir::HirId>,
 449     unsafe_blocks: &'a mut Vec<(hir::HirId, bool)>,
 450 }
 451
 452 impl<'a, 'tcx> intravisit::Visitor<'tcx> for UnusedUnsafeVisitor<'a> {
 453     type Map = intravisit::ErasedMap<'tcx>;
 454
 455     fn nested_visit_map(&mut self) -> intravisit::NestedVisitorMap<Self::Map> {
 456         intravisit::NestedVisitorMap::None
 457     }
 458
 459     fn visit_block(&mut self, block: &'tcx hir::Block<'tcx>) {
 460         intravisit::walk_block(self, block);
 461
 462         if let hir::BlockCheckMode::UnsafeBlock(hir::UnsafeSource::UserProvided) = block.rules {
 463             self.unsafe_blocks.push((block.hir_id, self.used_unsafe.contains(&block.hir_id)));
 464         }
 465     }
 466 }
 467
 468 fn check_unused_unsafe(
 469     tcx: TyCtxt<'_>,
 470     def_id: DefId,
 471     used_unsafe: &FxHashSet<hir::HirId>,
 472     unsafe_blocks: &mut Vec<(hir::HirId, bool)>,
 473 ) {
 474     let body_id =
 475         tcx.hir().as_local_hir_id(def_id).and_then(|hir_id| tcx.hir().maybe_body_owned_by(hir_id));
 476
 477     let body_id = match body_id {
 478         Some(body) => body,
 479         None => {
 480             debug!("check_unused_unsafe({:?}) - no body found", def_id);
 481             return;
 482         }
 483     };
 484     let body = tcx.hir().body(body_id);
 485     debug!("check_unused_unsafe({:?}, body={:?}, used_unsafe={:?})", def_id, body, used_unsafe);
 486
 487     let mut visitor = UnusedUnsafeVisitor { used_unsafe, unsafe_blocks };
 488     intravisit::Visitor::visit_body(&mut visitor, body);
 489 }
 490
 491 fn unsafety_check_result(tcx: TyCtxt<'_>, def_id: DefId) -> UnsafetyCheckResult {
 492     debug!("unsafety_violations({:?})", def_id);
 493
 494     // N.B., this borrow is valid because all the consumers of
 495     // `mir_built` force this.
 496     let body = &tcx.mir_built(def_id).borrow();
 497
 498     let param_env = tcx.param_env(def_id);
 499
 500     let id = tcx.hir().as_local_hir_id(def_id).unwrap();
 501     let (const_context, min_const_fn) = match tcx.hir().body_owner_kind(id) {
 502         hir::BodyOwnerKind::Closure => (false, false),
 503         hir::BodyOwnerKind::Fn => (is_const_fn(tcx, def_id), is_min_const_fn(tcx, def_id)),
 504         hir::BodyOwnerKind::Const | hir::BodyOwnerKind::Static(_) => (true, false),
 505     };
 506     let mut checker = UnsafetyChecker::new(const_context, min_const_fn, body, tcx, param_env);
 507     // mir_built ensures that body has a computed cache, so we don't (and can't) attempt to
 508     // recompute it here.
 509     let body = body.unwrap_read_only();
 510     checker.visit_body(body);
 511
 512     check_unused_unsafe(tcx, def_id, &checker.used_unsafe, &mut checker.inherited_blocks);
 513     UnsafetyCheckResult {
 514         violations: checker.violations.into(),
 515         unsafe_blocks: checker.inherited_blocks.into(),
 516     }
 517 }
 518
 519 fn unsafe_derive_on_repr_packed(tcx: TyCtxt<'_>, def_id: DefId) {
 520     let lint_hir_id = tcx
 521         .hir()
 522         .as_local_hir_id(def_id)
 523         .unwrap_or_else(|| bug!("checking unsafety for non-local def id {:?}", def_id));
 524
 525     tcx.struct_span_lint_hir(SAFE_PACKED_BORROWS, lint_hir_id, tcx.def_span(def_id), |lint| {
 526         // FIXME: when we make this a hard error, this should have its
 527         // own error code.
 528         let message = if tcx.generics_of(def_id).own_requires_monomorphization() {
 529             "`#[derive]` can't be used on a `#[repr(packed)]` struct with \
 530              type or const parameters (error E0133)"
 531                 .to_string()
 532         } else {
 533             "`#[derive]` can't be used on a `#[repr(packed)]` struct that \
 534              does not derive Copy (error E0133)"
 535                 .to_string()
 536         };
 537         lint.build(&message).emit()
 538     });
 539 }
 540
 541 /// Returns the `HirId` for an enclosing scope that is also `unsafe`.
 542 fn is_enclosed(
 543     tcx: TyCtxt<'_>,
 544     used_unsafe: &FxHashSet<hir::HirId>,
 545     id: hir::HirId,
 546 ) -> Option<(String, hir::HirId)> {
 547     let parent_id = tcx.hir().get_parent_node(id);
 548     if parent_id != id {
 549         if used_unsafe.contains(&parent_id) {
 550             Some(("block".to_string(), parent_id))
 551         } else if let Some(Node::Item(&hir::Item {
 552             kind: hir::ItemKind::Fn(ref sig, _, _), ..
 553         })) = tcx.hir().find(parent_id)
 554         {
 555             match sig.header.unsafety {
 556                 hir::Unsafety::Unsafe => Some(("fn".to_string(), parent_id)),
 557                 hir::Unsafety::Normal => None,
 558             }
 559         } else {
 560             is_enclosed(tcx, used_unsafe, parent_id)
 561         }
 562     } else {
 563         None
 564     }
 565 }
 566
 567 fn report_unused_unsafe(tcx: TyCtxt<'_>, used_unsafe: &FxHashSet<hir::HirId>, id: hir::HirId) {
 568     let span = tcx.sess.source_map().def_span(tcx.hir().span(id));
 569     tcx.struct_span_lint_hir(UNUSED_UNSAFE, id, span, |lint| {
 570         let msg = "unnecessary `unsafe` block";
 571         let mut db = lint.build(msg);
 572         db.span_label(span, msg);
 573         if let Some((kind, id)) = is_enclosed(tcx, used_unsafe, id) {
 574             db.span_label(
 575                 tcx.sess.source_map().def_span(tcx.hir().span(id)),
 576                 format!("because it's nested under this `unsafe` {}", kind),
 577             );
 578         }
 579         db.emit();
 580     });
 581 }
 582
 583 fn builtin_derive_def_id(tcx: TyCtxt<'_>, def_id: DefId) -> Option<DefId> {
 584     debug!("builtin_derive_def_id({:?})", def_id);
 585     if let Some(impl_def_id) = tcx.impl_of_method(def_id) {
 586         if tcx.has_attr(impl_def_id, sym::automatically_derived) {
 587             debug!("builtin_derive_def_id({:?}) - is {:?}", def_id, impl_def_id);
 588             Some(impl_def_id)
 589         } else {
 590             debug!("builtin_derive_def_id({:?}) - not automatically derived", def_id);
 591             None
 592         }
 593     } else {
 594         debug!("builtin_derive_def_id({:?}) - not a method", def_id);
 595         None
 596     }
 597 }
 598
 599 pub fn check_unsafety(tcx: TyCtxt<'_>, def_id: DefId) {
 600     debug!("check_unsafety({:?})", def_id);
 601
 602     // closures are handled by their parent fn.
 603     if tcx.is_closure(def_id) {
 604         return;
 605     }
 606
 607     let UnsafetyCheckResult { violations, unsafe_blocks } = tcx.unsafety_check_result(def_id);
 608
 609     for &UnsafetyViolation { source_info, description, details, kind } in violations.iter() {
 610         // Report an error.
 611         match kind {
 612             UnsafetyViolationKind::GeneralAndConstFn | UnsafetyViolationKind::General => {
 613                 struct_span_err!(
 614                     tcx.sess,
 615                     source_info.span,
 616                     E0133,
 617                     "{} is unsafe and requires unsafe function or block",
 618                     description
 619                 )
 620                 .span_label(source_info.span, &*description.as_str())
 621                 .note(&details.as_str())
 622                 .emit();
 623             }
 624             UnsafetyViolationKind::BorrowPacked(lint_hir_id) => {
 625                 if let Some(impl_def_id) = builtin_derive_def_id(tcx, def_id) {
 626                     tcx.unsafe_derive_on_repr_packed(impl_def_id);
 627                 } else {
 628                     tcx.struct_span_lint_hir(
 629                         SAFE_PACKED_BORROWS,
 630                         lint_hir_id,
 631                         source_info.span,
 632                         |lint| {
 633                             lint.build(&format!(
 634                                 "{} is unsafe and requires unsafe function or block (error E0133)",
 635                                 description
 636                             ))
 637                             .note(&details.as_str())
 638                             .emit()
 639                         },
 640                     )
 641                 }
 642             }
 643         }
 644     }
 645
 646     let mut unsafe_blocks: Vec<_> = unsafe_blocks.iter().collect();
 647     unsafe_blocks.sort_by_cached_key(|(hir_id, _)| tcx.hir().hir_to_node_id(*hir_id));
 648     let used_unsafe: FxHashSet<_> =
 649         unsafe_blocks.iter().flat_map(|&&(id, used)| used.then_some(id)).collect();
 650     for &(block_id, is_used) in unsafe_blocks {
 651         if !is_used {
 652             report_unused_unsafe(tcx, &used_unsafe, block_id);
 653         }
 654     }
 655 }