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.register_violations(
 152                             &[UnsafetyViolation {
 153                                 source_info: self.source_info,
 154                                 description: Symbol::intern("cast of pointer to int"),
 155                                 details: Symbol::intern(
 156                                     "casting pointers to integers in constants",
 157                                 ),
 158                                 kind: UnsafetyViolationKind::General,
 159                             }],
 160                             &[],
 161                         );
 162                     }
 163                     _ => {}
 164                 }
 165             }
 166             // raw pointer and fn pointer operations are unsafe as it is not clear whether one
 167             // pointer would be "less" or "equal" to another, because we cannot know where llvm
 168             // or the linker will place various statics in memory. Without this information the
 169             // result of a comparison of addresses would differ between runtime and compile-time.
 170             Rvalue::BinaryOp(_, ref lhs, _)
 171                 if self.const_context && self.tcx.features().const_compare_raw_pointers =>
 172             {
 173                 if let ty::RawPtr(_) | ty::FnPtr(..) = lhs.ty(self.body, self.tcx).kind {
 174                     self.register_violations(
 175                         &[UnsafetyViolation {
 176                             source_info: self.source_info,
 177                             description: Symbol::intern("pointer operation"),
 178                             details: Symbol::intern("operations on pointers in constants"),
 179                             kind: UnsafetyViolationKind::General,
 180                         }],
 181                         &[],
 182                     );
 183                 }
 184             }
 185             _ => {}
 186         }
 187         self.super_rvalue(rvalue, location);
 188     }
 189
 190     fn visit_place(&mut self, place: &Place<'tcx>, context: PlaceContext, _location: Location) {
 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.register_violations(
 203                         &[UnsafetyViolation {
 204                             source_info,
 205                             description: Symbol::intern("borrow of packed field"),
 206                             details: Symbol::intern(
 207                                 "fields of packed structs might be misaligned: dereferencing a \
 208                             misaligned pointer or even just creating a misaligned reference \
 209                             is undefined behavior",
 210                             ),
 211                             kind: UnsafetyViolationKind::BorrowPacked(lint_root),
 212                         }],
 213                         &[],
 214                     );
 215                 }
 216             }
 217             let is_borrow_of_interior_mut = context.is_borrow()
 218                 && !Place::ty_from(&place.local, proj_base, self.body, self.tcx).ty.is_freeze(
 219                     self.tcx,
 220                     self.param_env,
 221                     self.source_info.span,
 222                 );
 223             // prevent
 224             // * `&mut x.field`
 225             // * `x.field = y;`
 226             // * `&x.field` if `field`'s type has interior mutability
 227             // because either of these would allow modifying the layout constrained field and
 228             // insert values that violate the layout constraints.
 229             if context.is_mutating_use() || is_borrow_of_interior_mut {
 230                 self.check_mut_borrowing_layout_constrained_field(place, context.is_mutating_use());
 231             }
 232             let old_source_info = self.source_info;
 233             if let (local, []) = (&place.local, proj_base) {
 234                 let decl = &self.body.local_decls[*local];
 235                 if decl.internal {
 236                     // Internal locals are used in the `move_val_init` desugaring.
 237                     // We want to check unsafety against the source info of the
 238                     // desugaring, rather than the source info of the RHS.
 239                     self.source_info = self.body.local_decls[*local].source_info;
 240                 } else if let LocalInfo::StaticRef { def_id, .. } = decl.local_info {
 241                     if self.tcx.is_mutable_static(def_id) {
 242                         self.require_unsafe(
 243                             "use of mutable static",
 244                             "mutable statics can be mutated by multiple threads: aliasing \
 245                         violations or data races will cause undefined behavior",
 246                             UnsafetyViolationKind::General,
 247                         );
 248                         return;
 249                     } else if self.tcx.is_foreign_item(def_id) {
 250                         self.require_unsafe(
 251                             "use of extern static",
 252                             "extern statics are not controlled by the Rust type system: \
 253                         invalid data, aliasing violations or data races will cause \
 254                         undefined behavior",
 255                             UnsafetyViolationKind::General,
 256                         );
 257                         return;
 258                     }
 259                 }
 260             }
 261             let base_ty = Place::ty_from(&place.local, proj_base, self.body, self.tcx).ty;
 262             match base_ty.kind {
 263                 ty::RawPtr(..) => self.require_unsafe(
 264                     "dereference of raw pointer",
 265                     "raw pointers may be NULL, dangling or unaligned; they can violate \
 266                          aliasing rules and cause data races: all of these are undefined \
 267                          behavior",
 268                     UnsafetyViolationKind::General,
 269                 ),
 270                 ty::Adt(adt, _) => {
 271                     if adt.is_union() {
 272                         if context == PlaceContext::MutatingUse(MutatingUseContext::Store)
 273                             || context == PlaceContext::MutatingUse(MutatingUseContext::Drop)
 274                             || context == PlaceContext::MutatingUse(MutatingUseContext::AsmOutput)
 275                         {
 276                             let elem_ty = match elem {
 277                                 ProjectionElem::Field(_, ty) => ty,
 278                                 _ => span_bug!(
 279                                     self.source_info.span,
 280                                     "non-field projection {:?} from union?",
 281                                     place
 282                                 ),
 283                             };
 284                             if !elem_ty.is_copy_modulo_regions(
 285                                 self.tcx,
 286                                 self.param_env,
 287                                 self.source_info.span,
 288                             ) {
 289                                 self.require_unsafe(
 290                                     "assignment to non-`Copy` union field",
 291                                     "the previous content of the field will be dropped, which \
 292                                      causes undefined behavior if the field was not properly \
 293                                      initialized",
 294                                     UnsafetyViolationKind::GeneralAndConstFn,
 295                                 )
 296                             } else {
 297                                 // write to non-move union, safe
 298                             }
 299                         } else {
 300                             self.require_unsafe(
 301                                 "access to union field",
 302                                 "the field may not be properly initialized: using \
 303                                  uninitialized data will cause undefined behavior",
 304                                 UnsafetyViolationKind::GeneralAndConstFn,
 305                             )
 306                         }
 307                     }
 308                 }
 309                 _ => {}
 310             }
 311             self.source_info = old_source_info;
 312         }
 313     }
 314 }
 315
 316 impl<'a, 'tcx> UnsafetyChecker<'a, 'tcx> {
 317     fn require_unsafe(
 318         &mut self,
 319         description: &'static str,
 320         details: &'static str,
 321         kind: UnsafetyViolationKind,
 322     ) {
 323         let source_info = self.source_info;
 324         self.register_violations(
 325             &[UnsafetyViolation {
 326                 source_info,
 327                 description: Symbol::intern(description),
 328                 details: Symbol::intern(details),
 329                 kind,
 330             }],
 331             &[],
 332         );
 333     }
 334
 335     fn register_violations(
 336         &mut self,
 337         violations: &[UnsafetyViolation],
 338         unsafe_blocks: &[(hir::HirId, bool)],
 339     ) {
 340         let safety = self.body.source_scopes[self.source_info.scope]
 341             .local_data
 342             .as_ref()
 343             .assert_crate_local()
 344             .safety;
 345         let within_unsafe = match safety {
 346             // `unsafe` blocks are required in safe code
 347             Safety::Safe => {
 348                 for violation in violations {
 349                     let mut violation = violation.clone();
 350                     match violation.kind {
 351                         UnsafetyViolationKind::GeneralAndConstFn
 352                         | UnsafetyViolationKind::General => {}
 353                         UnsafetyViolationKind::BorrowPacked(_) => {
 354                             if self.min_const_fn {
 355                                 // const fns don't need to be backwards compatible and can
 356                                 // emit these violations as a hard error instead of a backwards
 357                                 // compat lint
 358                                 violation.kind = UnsafetyViolationKind::General;
 359                             }
 360                         }
 361                     }
 362                     if !self.violations.contains(&violation) {
 363                         self.violations.push(violation)
 364                     }
 365                 }
 366                 false
 367             }
 368             // `unsafe` function bodies allow unsafe without additional unsafe blocks
 369             Safety::BuiltinUnsafe | Safety::FnUnsafe => true,
 370             Safety::ExplicitUnsafe(hir_id) => {
 371                 // mark unsafe block as used if there are any unsafe operations inside
 372                 if !violations.is_empty() {
 373                     self.used_unsafe.insert(hir_id);
 374                 }
 375                 // only some unsafety is allowed in const fn
 376                 if self.min_const_fn {
 377                     for violation in violations {
 378                         match violation.kind {
 379                             // these unsafe things are stable in const fn
 380                             UnsafetyViolationKind::GeneralAndConstFn => {}
 381                             // these things are forbidden in const fns
 382                             UnsafetyViolationKind::General
 383                             | UnsafetyViolationKind::BorrowPacked(_) => {
 384                                 let mut violation = violation.clone();
 385                                 // const fns don't need to be backwards compatible and can
 386                                 // emit these violations as a hard error instead of a backwards
 387                                 // compat lint
 388                                 violation.kind = UnsafetyViolationKind::General;
 389                                 if !self.violations.contains(&violation) {
 390                                     self.violations.push(violation)
 391                                 }
 392                             }
 393                         }
 394                     }
 395                 }
 396                 true
 397             }
 398         };
 399         self.inherited_blocks.extend(
 400             unsafe_blocks.iter().map(|&(hir_id, is_used)| (hir_id, is_used && !within_unsafe)),
 401         );
 402     }
 403     fn check_mut_borrowing_layout_constrained_field(
 404         &mut self,
 405         place: &Place<'tcx>,
 406         is_mut_use: bool,
 407     ) {
 408         let mut cursor = place.projection.as_ref();
 409         while let &[ref proj_base @ .., elem] = cursor {
 410             cursor = proj_base;
 411
 412             match elem {
 413                 ProjectionElem::Field(..) => {
 414                     let ty =
 415                         Place::ty_from(&place.local, proj_base, &self.body.local_decls, self.tcx)
 416                             .ty;
 417                     match ty.kind {
 418                         ty::Adt(def, _) => match self.tcx.layout_scalar_valid_range(def.did) {
 419                             (Bound::Unbounded, Bound::Unbounded) => {}
 420                             _ => {
 421                                 let (description, details) = if is_mut_use {
 422                                     (
 423                                         "mutation of layout constrained field",
 424                                         "mutating layout constrained fields cannot statically be \
 425                                         checked for valid values",
 426                                     )
 427                                 } else {
 428                                     (
 429                                         "borrow of layout constrained field with interior \
 430                                         mutability",
 431                                         "references to fields of layout constrained fields \
 432                                         lose the constraints. Coupled with interior mutability, \
 433                                         the field can be changed to invalid values",
 434                                     )
 435                                 };
 436                                 let source_info = self.source_info;
 437                                 self.register_violations(
 438                                     &[UnsafetyViolation {
 439                                         source_info,
 440                                         description: Symbol::intern(description),
 441                                         details: Symbol::intern(details),
 442                                         kind: UnsafetyViolationKind::GeneralAndConstFn,
 443                                     }],
 444                                     &[],
 445                                 );
 446                             }
 447                         },
 448                         _ => {}
 449                     }
 450                 }
 451                 _ => {}
 452             }
 453         }
 454     }
 455 }
 456
 457 pub(crate) fn provide(providers: &mut Providers<'_>) {
 458     *providers = Providers { unsafety_check_result, unsafe_derive_on_repr_packed, ..*providers };
 459 }
 460
 461 struct UnusedUnsafeVisitor<'a> {
 462     used_unsafe: &'a FxHashSet<hir::HirId>,
 463     unsafe_blocks: &'a mut Vec<(hir::HirId, bool)>,
 464 }
 465
 466 impl<'a, 'tcx> intravisit::Visitor<'tcx> for UnusedUnsafeVisitor<'a> {
 467     type Map = Map<'tcx>;
 468
 469     fn nested_visit_map<'this>(&'this mut self) -> intravisit::NestedVisitorMap<'this, Self::Map> {
 470         intravisit::NestedVisitorMap::None
 471     }
 472
 473     fn visit_block(&mut self, block: &'tcx hir::Block<'tcx>) {
 474         intravisit::walk_block(self, block);
 475
 476         if let hir::BlockCheckMode::UnsafeBlock(hir::UnsafeSource::UserProvided) = block.rules {
 477             self.unsafe_blocks.push((block.hir_id, self.used_unsafe.contains(&block.hir_id)));
 478         }
 479     }
 480 }
 481
 482 fn check_unused_unsafe(
 483     tcx: TyCtxt<'_>,
 484     def_id: DefId,
 485     used_unsafe: &FxHashSet<hir::HirId>,
 486     unsafe_blocks: &mut Vec<(hir::HirId, bool)>,
 487 ) {
 488     let body_id =
 489         tcx.hir().as_local_hir_id(def_id).and_then(|hir_id| tcx.hir().maybe_body_owned_by(hir_id));
 490
 491     let body_id = match body_id {
 492         Some(body) => body,
 493         None => {
 494             debug!("check_unused_unsafe({:?}) - no body found", def_id);
 495             return;
 496         }
 497     };
 498     let body = tcx.hir().body(body_id);
 499     debug!("check_unused_unsafe({:?}, body={:?}, used_unsafe={:?})", def_id, body, used_unsafe);
 500
 501     let mut visitor = UnusedUnsafeVisitor { used_unsafe, unsafe_blocks };
 502     intravisit::Visitor::visit_body(&mut visitor, body);
 503 }
 504
 505 fn unsafety_check_result(tcx: TyCtxt<'_>, def_id: DefId) -> UnsafetyCheckResult {
 506     debug!("unsafety_violations({:?})", def_id);
 507
 508     // N.B., this borrow is valid because all the consumers of
 509     // `mir_built` force this.
 510     let body = &tcx.mir_built(def_id).borrow();
 511
 512     let param_env = tcx.param_env(def_id);
 513
 514     let id = tcx.hir().as_local_hir_id(def_id).unwrap();
 515     let (const_context, min_const_fn) = match tcx.hir().body_owner_kind(id) {
 516         hir::BodyOwnerKind::Closure => (false, false),
 517         hir::BodyOwnerKind::Fn => (is_const_fn(tcx, def_id), is_min_const_fn(tcx, def_id)),
 518         hir::BodyOwnerKind::Const | hir::BodyOwnerKind::Static(_) => (true, false),
 519     };
 520     let mut checker = UnsafetyChecker::new(const_context, min_const_fn, body, tcx, param_env);
 521     // mir_built ensures that body has a computed cache, so we don't (and can't) attempt to
 522     // recompute it here.
 523     let body = body.unwrap_read_only();
 524     checker.visit_body(body);
 525
 526     check_unused_unsafe(tcx, def_id, &checker.used_unsafe, &mut checker.inherited_blocks);
 527     UnsafetyCheckResult {
 528         violations: checker.violations.into(),
 529         unsafe_blocks: checker.inherited_blocks.into(),
 530     }
 531 }
 532
 533 fn unsafe_derive_on_repr_packed(tcx: TyCtxt<'_>, def_id: DefId) {
 534     let lint_hir_id = tcx
 535         .hir()
 536         .as_local_hir_id(def_id)
 537         .unwrap_or_else(|| bug!("checking unsafety for non-local def id {:?}", def_id));
 538
 539     // FIXME: when we make this a hard error, this should have its
 540     // own error code.
 541     let message = if tcx.generics_of(def_id).own_requires_monomorphization() {
 542         "`#[derive]` can't be used on a `#[repr(packed)]` struct with \
 543          type or const parameters (error E0133)"
 544             .to_string()
 545     } else {
 546         "`#[derive]` can't be used on a `#[repr(packed)]` struct that \
 547          does not derive Copy (error E0133)"
 548             .to_string()
 549     };
 550     tcx.lint_hir(SAFE_PACKED_BORROWS, lint_hir_id, tcx.def_span(def_id), &message);
 551 }
 552
 553 /// Returns the `HirId` for an enclosing scope that is also `unsafe`.
 554 fn is_enclosed(
 555     tcx: TyCtxt<'_>,
 556     used_unsafe: &FxHashSet<hir::HirId>,
 557     id: hir::HirId,
 558 ) -> Option<(String, hir::HirId)> {
 559     let parent_id = tcx.hir().get_parent_node(id);
 560     if parent_id != id {
 561         if used_unsafe.contains(&parent_id) {
 562             Some(("block".to_string(), parent_id))
 563         } else if let Some(Node::Item(&hir::Item {
 564             kind: hir::ItemKind::Fn(ref sig, _, _), ..
 565         })) = tcx.hir().find(parent_id)
 566         {
 567             match sig.header.unsafety {
 568                 hir::Unsafety::Unsafe => Some(("fn".to_string(), parent_id)),
 569                 hir::Unsafety::Normal => None,
 570             }
 571         } else {
 572             is_enclosed(tcx, used_unsafe, parent_id)
 573         }
 574     } else {
 575         None
 576     }
 577 }
 578
 579 fn report_unused_unsafe(tcx: TyCtxt<'_>, used_unsafe: &FxHashSet<hir::HirId>, id: hir::HirId) {
 580     let span = tcx.sess.source_map().def_span(tcx.hir().span(id));
 581     let msg = "unnecessary `unsafe` block";
 582     let mut db = tcx.struct_span_lint_hir(UNUSED_UNSAFE, id, span, msg);
 583     db.span_label(span, msg);
 584     if let Some((kind, id)) = is_enclosed(tcx, used_unsafe, id) {
 585         db.span_label(
 586             tcx.sess.source_map().def_span(tcx.hir().span(id)),
 587             format!("because it's nested under this `unsafe` {}", kind),
 588         );
 589     }
 590     db.emit();
 591 }
 592
 593 fn builtin_derive_def_id(tcx: TyCtxt<'_>, def_id: DefId) -> Option<DefId> {
 594     debug!("builtin_derive_def_id({:?})", def_id);
 595     if let Some(impl_def_id) = tcx.impl_of_method(def_id) {
 596         if tcx.has_attr(impl_def_id, sym::automatically_derived) {
 597             debug!("builtin_derive_def_id({:?}) - is {:?}", def_id, impl_def_id);
 598             Some(impl_def_id)
 599         } else {
 600             debug!("builtin_derive_def_id({:?}) - not automatically derived", def_id);
 601             None
 602         }
 603     } else {
 604         debug!("builtin_derive_def_id({:?}) - not a method", def_id);
 605         None
 606     }
 607 }
 608
 609 pub fn check_unsafety(tcx: TyCtxt<'_>, def_id: DefId) {
 610     debug!("check_unsafety({:?})", def_id);
 611
 612     // closures are handled by their parent fn.
 613     if tcx.is_closure(def_id) {
 614         return;
 615     }
 616
 617     let UnsafetyCheckResult { violations, unsafe_blocks } = tcx.unsafety_check_result(def_id);
 618
 619     for &UnsafetyViolation { source_info, description, details, kind } in violations.iter() {
 620         // Report an error.
 621         match kind {
 622             UnsafetyViolationKind::GeneralAndConstFn | UnsafetyViolationKind::General => {
 623                 struct_span_err!(
 624                     tcx.sess,
 625                     source_info.span,
 626                     E0133,
 627                     "{} is unsafe and requires unsafe function or block",
 628                     description
 629                 )
 630                 .span_label(source_info.span, &*description.as_str())
 631                 .note(&details.as_str())
 632                 .emit();
 633             }
 634             UnsafetyViolationKind::BorrowPacked(lint_hir_id) => {
 635                 if let Some(impl_def_id) = builtin_derive_def_id(tcx, def_id) {
 636                     tcx.unsafe_derive_on_repr_packed(impl_def_id);
 637                 } else {
 638                     tcx.struct_span_lint_hir(
 639                         SAFE_PACKED_BORROWS,
 640                         lint_hir_id,
 641                         source_info.span,
 642                         &format!(
 643                             "{} is unsafe and requires unsafe function or block (error E0133)",
 644                             description
 645                         ),
 646                     )
 647                     .note(&details.as_str())
 648                     .emit();
 649                 }
 650             }
 651         }
 652     }
 653
 654     let mut unsafe_blocks: Vec<_> = unsafe_blocks.into_iter().collect();
 655     unsafe_blocks.sort_by_cached_key(|(hir_id, _)| tcx.hir().hir_to_node_id(*hir_id));
 656     let used_unsafe: FxHashSet<_> =
 657         unsafe_blocks.iter().flat_map(|&&(id, used)| used.then_some(id)).collect();
 658     for &(block_id, is_used) in unsafe_blocks {
 659         if !is_used {
 660             report_unused_unsafe(tcx, &used_unsafe, block_id);
 661         }
 662     }
 663 }