src/librustc_mir/transform/check_unsafety.rs

   1 use rustc::hir::map::Map;
   2 use rustc::lint::builtin::{SAFE_PACKED_BORROWS, UNUSED_UNSAFE};
   3 use rustc::mir::visit::{MutatingUseContext, PlaceContext, Visitor};
   4 use rustc::mir::*;
   5 use rustc::ty::cast::CastTy;
   6 use rustc::ty::query::Providers;
   7 use rustc::ty::{self, TyCtxt};
   8 use rustc_data_structures::fx::FxHashSet;
   9 use rustc_errors::struct_span_err;
  10 use rustc_hir as hir;
  11 use rustc_hir::def_id::DefId;
  12 use rustc_hir::intravisit;
  13 use rustc_hir::Node;
  14 use rustc_span::symbol::{sym, Symbol};
  15
  16 use std::ops::Bound;
  17
  18 use crate::const_eval::{is_const_fn, is_min_const_fn};
  19 use crate::util;
  20
  21 use rustc_error_codes::*;
  22
  23 pub struct UnsafetyChecker<'a, 'tcx> {
  24     body: &'a Body<'tcx>,
  25     const_context: bool,
  26     min_const_fn: bool,
  27     violations: Vec<UnsafetyViolation>,
  28     source_info: SourceInfo,
  29     tcx: TyCtxt<'tcx>,
  30     param_env: ty::ParamEnv<'tcx>,
  31     /// Mark an `unsafe` block as used, so we don't lint it.
  32     used_unsafe: FxHashSet<hir::HirId>,
  33     inherited_blocks: Vec<(hir::HirId, bool)>,
  34 }
  35
  36 impl<'a, 'tcx> UnsafetyChecker<'a, 'tcx> {
  37     fn new(
  38         const_context: bool,
  39         min_const_fn: bool,
  40         body: &'a Body<'tcx>,
  41         tcx: TyCtxt<'tcx>,
  42         param_env: ty::ParamEnv<'tcx>,
  43     ) -> Self {
  44         // sanity check
  45         if min_const_fn {
  46             assert!(const_context);
  47         }
  48         Self {
  49             body,
  50             const_context,
  51             min_const_fn,
  52             violations: vec![],
  53             source_info: SourceInfo { span: body.span, scope: OUTERMOST_SOURCE_SCOPE },
  54             tcx,
  55             param_env,
  56             used_unsafe: Default::default(),
  57             inherited_blocks: vec![],
  58         }
  59     }
  60 }
  61
  62 impl<'a, 'tcx> Visitor<'tcx> for UnsafetyChecker<'a, 'tcx> {
  63     fn visit_terminator(&mut self, terminator: &Terminator<'tcx>, location: Location) {
  64         self.source_info = terminator.source_info;
  65         match terminator.kind {
  66             TerminatorKind::Goto { .. }
  67             | TerminatorKind::SwitchInt { .. }
  68             | TerminatorKind::Drop { .. }
  69             | TerminatorKind::Yield { .. }
  70             | TerminatorKind::Assert { .. }
  71             | TerminatorKind::DropAndReplace { .. }
  72             | TerminatorKind::GeneratorDrop
  73             | TerminatorKind::Resume
  74             | TerminatorKind::Abort
  75             | TerminatorKind::Return
  76             | TerminatorKind::Unreachable
  77             | TerminatorKind::FalseEdges { .. }
  78             | TerminatorKind::FalseUnwind { .. } => {
  79                 // safe (at least as emitted during MIR construction)
  80             }
  81
  82             TerminatorKind::Call { ref func, .. } => {
  83                 let func_ty = func.ty(self.body, self.tcx);
  84                 let sig = func_ty.fn_sig(self.tcx);
  85                 if let hir::Unsafety::Unsafe = sig.unsafety() {
  86                     self.require_unsafe(
  87                         "call to unsafe function",
  88                         "consult the function's documentation for information on how to avoid \
  89                          undefined behavior",
  90                         UnsafetyViolationKind::GeneralAndConstFn,
  91                     )
  92                 }
  93             }
  94         }
  95         self.super_terminator(terminator, location);
  96     }
  97
  98     fn visit_statement(&mut self, statement: &Statement<'tcx>, location: Location) {
  99         self.source_info = statement.source_info;
 100         match statement.kind {
 101             StatementKind::Assign(..)
 102             | StatementKind::FakeRead(..)
 103             | StatementKind::SetDiscriminant { .. }
 104             | StatementKind::StorageLive(..)
 105             | StatementKind::StorageDead(..)
 106             | StatementKind::Retag { .. }
 107             | StatementKind::AscribeUserType(..)
 108             | StatementKind::Nop => {
 109                 // safe (at least as emitted during MIR construction)
 110             }
 111
 112             StatementKind::InlineAsm { .. } => self.require_unsafe(
 113                 "use of inline assembly",
 114                 "inline assembly is entirely unchecked and can cause undefined behavior",
 115                 UnsafetyViolationKind::General,
 116             ),
 117         }
 118         self.super_statement(statement, location);
 119     }
 120
 121     fn visit_rvalue(&mut self, rvalue: &Rvalue<'tcx>, location: Location) {
 122         match rvalue {
 123             Rvalue::Aggregate(box ref aggregate, _) => match aggregate {
 124                 &AggregateKind::Array(..) | &AggregateKind::Tuple => {}
 125                 &AggregateKind::Adt(ref def, ..) => {
 126                     match self.tcx.layout_scalar_valid_range(def.did) {
 127                         (Bound::Unbounded, Bound::Unbounded) => {}
 128                         _ => self.require_unsafe(
 129                             "initializing type with `rustc_layout_scalar_valid_range` attr",
 130                             "initializing a layout restricted type's field with a value \
 131                                 outside the valid range is undefined behavior",
 132                             UnsafetyViolationKind::GeneralAndConstFn,
 133                         ),
 134                     }
 135                 }
 136                 &AggregateKind::Closure(def_id, _) | &AggregateKind::Generator(def_id, _, _) => {
 137                     let UnsafetyCheckResult { violations, unsafe_blocks } =
 138                         self.tcx.unsafety_check_result(def_id);
 139                     self.register_violations(&violations, &unsafe_blocks);
 140                 }
 141             },
 142             // casting pointers to ints is unsafe in const fn because the const evaluator cannot
 143             // possibly know what the result of various operations like `address / 2` would be
 144             // pointers during const evaluation have no integral address, only an abstract one
 145             Rvalue::Cast(CastKind::Misc, ref operand, cast_ty)
 146                 if self.const_context && self.tcx.features().const_raw_ptr_to_usize_cast =>
 147             {
 148                 let operand_ty = operand.ty(self.body, self.tcx);
 149                 let cast_in = CastTy::from_ty(operand_ty).expect("bad input type for cast");
 150                 let cast_out = CastTy::from_ty(cast_ty).expect("bad output type for cast");
 151                 match (cast_in, cast_out) {
 152                     (CastTy::Ptr(_), CastTy::Int(_)) | (CastTy::FnPtr, CastTy::Int(_)) => {
 153                         self.register_violations(
 154                             &[UnsafetyViolation {
 155                                 source_info: self.source_info,
 156                                 description: Symbol::intern("cast of pointer to int"),
 157                                 details: Symbol::intern(
 158                                     "casting pointers to integers in constants",
 159                                 ),
 160                                 kind: UnsafetyViolationKind::General,
 161                             }],
 162                             &[],
 163                         );
 164                     }
 165                     _ => {}
 166                 }
 167             }
 168             // raw pointer and fn pointer operations are unsafe as it is not clear whether one
 169             // pointer would be "less" or "equal" to another, because we cannot know where llvm
 170             // or the linker will place various statics in memory. Without this information the
 171             // result of a comparison of addresses would differ between runtime and compile-time.
 172             Rvalue::BinaryOp(_, ref lhs, _)
 173                 if self.const_context && self.tcx.features().const_compare_raw_pointers =>
 174             {
 175                 if let ty::RawPtr(_) | ty::FnPtr(..) = lhs.ty(self.body, self.tcx).kind {
 176                     self.register_violations(
 177                         &[UnsafetyViolation {
 178                             source_info: self.source_info,
 179                             description: Symbol::intern("pointer operation"),
 180                             details: Symbol::intern("operations on pointers in constants"),
 181                             kind: UnsafetyViolationKind::General,
 182                         }],
 183                         &[],
 184                     );
 185                 }
 186             }
 187             _ => {}
 188         }
 189         self.super_rvalue(rvalue, location);
 190     }
 191
 192     fn visit_place(&mut self, place: &Place<'tcx>, context: PlaceContext, _location: Location) {
 193         match place.base {
 194             PlaceBase::Local(..) => {
 195                 // Locals are safe.
 196             }
 197             PlaceBase::Static(box Static { kind: StaticKind::Static, .. }) => {
 198                 bug!("StaticKind::Static should not exist");
 199             }
 200         }
 201
 202         for (i, elem) in place.projection.iter().enumerate() {
 203             let proj_base = &place.projection[..i];
 204
 205             if context.is_borrow() {
 206                 if util::is_disaligned(self.tcx, self.body, self.param_env, place) {
 207                     let source_info = self.source_info;
 208                     let lint_root = self.body.source_scopes[source_info.scope]
 209                         .local_data
 210                         .as_ref()
 211                         .assert_crate_local()
 212                         .lint_root;
 213                     self.register_violations(
 214                         &[UnsafetyViolation {
 215                             source_info,
 216                             description: Symbol::intern("borrow of packed field"),
 217                             details: Symbol::intern(
 218                                 "fields of packed structs might be misaligned: dereferencing a \
 219                             misaligned pointer or even just creating a misaligned reference \
 220                             is undefined behavior",
 221                             ),
 222                             kind: UnsafetyViolationKind::BorrowPacked(lint_root),
 223                         }],
 224                         &[],
 225                     );
 226                 }
 227             }
 228             let is_borrow_of_interior_mut = context.is_borrow()
 229                 && !Place::ty_from(&place.base, proj_base, self.body, self.tcx).ty.is_freeze(
 230                     self.tcx,
 231                     self.param_env,
 232                     self.source_info.span,
 233                 );
 234             // prevent
 235             // * `&mut x.field`
 236             // * `x.field = y;`
 237             // * `&x.field` if `field`'s type has interior mutability
 238             // because either of these would allow modifying the layout constrained field and
 239             // insert values that violate the layout constraints.
 240             if context.is_mutating_use() || is_borrow_of_interior_mut {
 241                 self.check_mut_borrowing_layout_constrained_field(place, context.is_mutating_use());
 242             }
 243             let old_source_info = self.source_info;
 244             if let (PlaceBase::Local(local), []) = (&place.base, proj_base) {
 245                 let decl = &self.body.local_decls[*local];
 246                 if decl.internal {
 247                     // Internal locals are used in the `move_val_init` desugaring.
 248                     // We want to check unsafety against the source info of the
 249                     // desugaring, rather than the source info of the RHS.
 250                     self.source_info = self.body.local_decls[*local].source_info;
 251                 } else if let LocalInfo::StaticRef { def_id, .. } = decl.local_info {
 252                     if self.tcx.is_mutable_static(def_id) {
 253                         self.require_unsafe(
 254                             "use of mutable static",
 255                             "mutable statics can be mutated by multiple threads: aliasing \
 256                         violations or data races will cause undefined behavior",
 257                             UnsafetyViolationKind::General,
 258                         );
 259                         return;
 260                     } else if self.tcx.is_foreign_item(def_id) {
 261                         self.require_unsafe(
 262                             "use of extern static",
 263                             "extern statics are not controlled by the Rust type system: \
 264                         invalid data, aliasing violations or data races will cause \
 265                         undefined behavior",
 266                             UnsafetyViolationKind::General,
 267                         );
 268                         return;
 269                     }
 270                 }
 271             }
 272             let base_ty = Place::ty_from(&place.base, proj_base, self.body, self.tcx).ty;
 273             match base_ty.kind {
 274                 ty::RawPtr(..) => self.require_unsafe(
 275                     "dereference of raw pointer",
 276                     "raw pointers may be NULL, dangling or unaligned; they can violate \
 277                          aliasing rules and cause data races: all of these are undefined \
 278                          behavior",
 279                     UnsafetyViolationKind::General,
 280                 ),
 281                 ty::Adt(adt, _) => {
 282                     if adt.is_union() {
 283                         if context == PlaceContext::MutatingUse(MutatingUseContext::Store)
 284                             || context == PlaceContext::MutatingUse(MutatingUseContext::Drop)
 285                             || context == PlaceContext::MutatingUse(MutatingUseContext::AsmOutput)
 286                         {
 287                             let elem_ty = match elem {
 288                                 ProjectionElem::Field(_, ty) => ty,
 289                                 _ => span_bug!(
 290                                     self.source_info.span,
 291                                     "non-field projection {:?} from union?",
 292                                     place
 293                                 ),
 294                             };
 295                             if !elem_ty.is_copy_modulo_regions(
 296                                 self.tcx,
 297                                 self.param_env,
 298                                 self.source_info.span,
 299                             ) {
 300                                 self.require_unsafe(
 301                                     "assignment to non-`Copy` union field",
 302                                     "the previous content of the field will be dropped, which \
 303                                      causes undefined behavior if the field was not properly \
 304                                      initialized",
 305                                     UnsafetyViolationKind::GeneralAndConstFn,
 306                                 )
 307                             } else {
 308                                 // write to non-move union, safe
 309                             }
 310                         } else {
 311                             self.require_unsafe(
 312                                 "access to union field",
 313                                 "the field may not be properly initialized: using \
 314                                  uninitialized data will cause undefined behavior",
 315                                 UnsafetyViolationKind::GeneralAndConstFn,
 316                             )
 317                         }
 318                     }
 319                 }
 320                 _ => {}
 321             }
 322             self.source_info = old_source_info;
 323         }
 324     }
 325 }
 326
 327 impl<'a, 'tcx> UnsafetyChecker<'a, 'tcx> {
 328     fn require_unsafe(
 329         &mut self,
 330         description: &'static str,
 331         details: &'static str,
 332         kind: UnsafetyViolationKind,
 333     ) {
 334         let source_info = self.source_info;
 335         self.register_violations(
 336             &[UnsafetyViolation {
 337                 source_info,
 338                 description: Symbol::intern(description),
 339                 details: Symbol::intern(details),
 340                 kind,
 341             }],
 342             &[],
 343         );
 344     }
 345
 346     fn register_violations(
 347         &mut self,
 348         violations: &[UnsafetyViolation],
 349         unsafe_blocks: &[(hir::HirId, bool)],
 350     ) {
 351         let safety = self.body.source_scopes[self.source_info.scope]
 352             .local_data
 353             .as_ref()
 354             .assert_crate_local()
 355             .safety;
 356         let within_unsafe = match safety {
 357             // `unsafe` blocks are required in safe code
 358             Safety::Safe => {
 359                 for violation in violations {
 360                     let mut violation = violation.clone();
 361                     match violation.kind {
 362                         UnsafetyViolationKind::GeneralAndConstFn
 363                         | UnsafetyViolationKind::General => {}
 364                         UnsafetyViolationKind::BorrowPacked(_) => {
 365                             if self.min_const_fn {
 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                             }
 371                         }
 372                     }
 373                     if !self.violations.contains(&violation) {
 374                         self.violations.push(violation)
 375                     }
 376                 }
 377                 false
 378             }
 379             // `unsafe` function bodies allow unsafe without additional unsafe blocks
 380             Safety::BuiltinUnsafe | Safety::FnUnsafe => true,
 381             Safety::ExplicitUnsafe(hir_id) => {
 382                 // mark unsafe block as used if there are any unsafe operations inside
 383                 if !violations.is_empty() {
 384                     self.used_unsafe.insert(hir_id);
 385                 }
 386                 // only some unsafety is allowed in const fn
 387                 if self.min_const_fn {
 388                     for violation in violations {
 389                         match violation.kind {
 390                             // these unsafe things are stable in const fn
 391                             UnsafetyViolationKind::GeneralAndConstFn => {}
 392                             // these things are forbidden in const fns
 393                             UnsafetyViolationKind::General
 394                             | UnsafetyViolationKind::BorrowPacked(_) => {
 395                                 let mut violation = violation.clone();
 396                                 // const fns don't need to be backwards compatible and can
 397                                 // emit these violations as a hard error instead of a backwards
 398                                 // compat lint
 399                                 violation.kind = UnsafetyViolationKind::General;
 400                                 if !self.violations.contains(&violation) {
 401                                     self.violations.push(violation)
 402                                 }
 403                             }
 404                         }
 405                     }
 406                 }
 407                 true
 408             }
 409         };
 410         self.inherited_blocks.extend(
 411             unsafe_blocks.iter().map(|&(hir_id, is_used)| (hir_id, is_used && !within_unsafe)),
 412         );
 413     }
 414     fn check_mut_borrowing_layout_constrained_field(
 415         &mut self,
 416         place: &Place<'tcx>,
 417         is_mut_use: bool,
 418     ) {
 419         let mut cursor = place.projection.as_ref();
 420         while let &[ref proj_base @ .., elem] = cursor {
 421             cursor = proj_base;
 422
 423             match elem {
 424                 ProjectionElem::Field(..) => {
 425                     let ty =
 426                         Place::ty_from(&place.base, proj_base, &self.body.local_decls, self.tcx).ty;
 427                     match ty.kind {
 428                         ty::Adt(def, _) => match self.tcx.layout_scalar_valid_range(def.did) {
 429                             (Bound::Unbounded, Bound::Unbounded) => {}
 430                             _ => {
 431                                 let (description, details) = if is_mut_use {
 432                                     (
 433                                         "mutation of layout constrained field",
 434                                         "mutating layout constrained fields cannot statically be \
 435                                         checked for valid values",
 436                                     )
 437                                 } else {
 438                                     (
 439                                         "borrow of layout constrained field with interior \
 440                                         mutability",
 441                                         "references to fields of layout constrained fields \
 442                                         lose the constraints. Coupled with interior mutability, \
 443                                         the field can be changed to invalid values",
 444                                     )
 445                                 };
 446                                 let source_info = self.source_info;
 447                                 self.register_violations(
 448                                     &[UnsafetyViolation {
 449                                         source_info,
 450                                         description: Symbol::intern(description),
 451                                         details: Symbol::intern(details),
 452                                         kind: UnsafetyViolationKind::GeneralAndConstFn,
 453                                     }],
 454                                     &[],
 455                                 );
 456                             }
 457                         },
 458                         _ => {}
 459                     }
 460                 }
 461                 _ => {}
 462             }
 463         }
 464     }
 465 }
 466
 467 pub(crate) fn provide(providers: &mut Providers<'_>) {
 468     *providers = Providers { unsafety_check_result, unsafe_derive_on_repr_packed, ..*providers };
 469 }
 470
 471 struct UnusedUnsafeVisitor<'a> {
 472     used_unsafe: &'a FxHashSet<hir::HirId>,
 473     unsafe_blocks: &'a mut Vec<(hir::HirId, bool)>,
 474 }
 475
 476 impl<'a, 'tcx> intravisit::Visitor<'tcx> for UnusedUnsafeVisitor<'a> {
 477     type Map = Map<'tcx>;
 478
 479     fn nested_visit_map<'this>(&'this mut self) -> intravisit::NestedVisitorMap<'this, Self::Map> {
 480         intravisit::NestedVisitorMap::None
 481     }
 482
 483     fn visit_block(&mut self, block: &'tcx hir::Block<'tcx>) {
 484         intravisit::walk_block(self, block);
 485
 486         if let hir::BlockCheckMode::UnsafeBlock(hir::UnsafeSource::UserProvided) = block.rules {
 487             self.unsafe_blocks.push((block.hir_id, self.used_unsafe.contains(&block.hir_id)));
 488         }
 489     }
 490 }
 491
 492 fn check_unused_unsafe(
 493     tcx: TyCtxt<'_>,
 494     def_id: DefId,
 495     used_unsafe: &FxHashSet<hir::HirId>,
 496     unsafe_blocks: &mut Vec<(hir::HirId, bool)>,
 497 ) {
 498     let body_id =
 499         tcx.hir().as_local_hir_id(def_id).and_then(|hir_id| tcx.hir().maybe_body_owned_by(hir_id));
 500
 501     let body_id = match body_id {
 502         Some(body) => body,
 503         None => {
 504             debug!("check_unused_unsafe({:?}) - no body found", def_id);
 505             return;
 506         }
 507     };
 508     let body = tcx.hir().body(body_id);
 509     debug!("check_unused_unsafe({:?}, body={:?}, used_unsafe={:?})", def_id, body, used_unsafe);
 510
 511     let mut visitor = UnusedUnsafeVisitor { used_unsafe, unsafe_blocks };
 512     intravisit::Visitor::visit_body(&mut visitor, body);
 513 }
 514
 515 fn unsafety_check_result(tcx: TyCtxt<'_>, def_id: DefId) -> UnsafetyCheckResult {
 516     debug!("unsafety_violations({:?})", def_id);
 517
 518     // N.B., this borrow is valid because all the consumers of
 519     // `mir_built` force this.
 520     let body = &tcx.mir_built(def_id).borrow();
 521
 522     let param_env = tcx.param_env(def_id);
 523
 524     let id = tcx.hir().as_local_hir_id(def_id).unwrap();
 525     let (const_context, min_const_fn) = match tcx.hir().body_owner_kind(id) {
 526         hir::BodyOwnerKind::Closure => (false, false),
 527         hir::BodyOwnerKind::Fn => (is_const_fn(tcx, def_id), is_min_const_fn(tcx, def_id)),
 528         hir::BodyOwnerKind::Const | hir::BodyOwnerKind::Static(_) => (true, false),
 529     };
 530     let mut checker = UnsafetyChecker::new(const_context, min_const_fn, body, tcx, param_env);
 531     // mir_built ensures that body has a computed cache, so we don't (and can't) attempt to
 532     // recompute it here.
 533     let body = body.unwrap_read_only();
 534     checker.visit_body(body);
 535
 536     check_unused_unsafe(tcx, def_id, &checker.used_unsafe, &mut checker.inherited_blocks);
 537     UnsafetyCheckResult {
 538         violations: checker.violations.into(),
 539         unsafe_blocks: checker.inherited_blocks.into(),
 540     }
 541 }
 542
 543 fn unsafe_derive_on_repr_packed(tcx: TyCtxt<'_>, def_id: DefId) {
 544     let lint_hir_id = tcx
 545         .hir()
 546         .as_local_hir_id(def_id)
 547         .unwrap_or_else(|| bug!("checking unsafety for non-local def id {:?}", def_id));
 548
 549     // FIXME: when we make this a hard error, this should have its
 550     // own error code.
 551     let message = if tcx.generics_of(def_id).own_requires_monomorphization() {
 552         "`#[derive]` can't be used on a `#[repr(packed)]` struct with \
 553          type or const parameters (error E0133)"
 554             .to_string()
 555     } else {
 556         "`#[derive]` can't be used on a `#[repr(packed)]` struct that \
 557          does not derive Copy (error E0133)"
 558             .to_string()
 559     };
 560     tcx.lint_hir(SAFE_PACKED_BORROWS, lint_hir_id, tcx.def_span(def_id), &message);
 561 }
 562
 563 /// Returns the `HirId` for an enclosing scope that is also `unsafe`.
 564 fn is_enclosed(
 565     tcx: TyCtxt<'_>,
 566     used_unsafe: &FxHashSet<hir::HirId>,
 567     id: hir::HirId,
 568 ) -> Option<(String, hir::HirId)> {
 569     let parent_id = tcx.hir().get_parent_node(id);
 570     if parent_id != id {
 571         if used_unsafe.contains(&parent_id) {
 572             Some(("block".to_string(), parent_id))
 573         } else if let Some(Node::Item(&hir::Item {
 574             kind: hir::ItemKind::Fn(ref sig, _, _), ..
 575         })) = tcx.hir().find(parent_id)
 576         {
 577             match sig.header.unsafety {
 578                 hir::Unsafety::Unsafe => Some(("fn".to_string(), parent_id)),
 579                 hir::Unsafety::Normal => None,
 580             }
 581         } else {
 582             is_enclosed(tcx, used_unsafe, parent_id)
 583         }
 584     } else {
 585         None
 586     }
 587 }
 588
 589 fn report_unused_unsafe(tcx: TyCtxt<'_>, used_unsafe: &FxHashSet<hir::HirId>, id: hir::HirId) {
 590     let span = tcx.sess.source_map().def_span(tcx.hir().span(id));
 591     let msg = "unnecessary `unsafe` block";
 592     let mut db = tcx.struct_span_lint_hir(UNUSED_UNSAFE, id, span, msg);
 593     db.span_label(span, msg);
 594     if let Some((kind, id)) = is_enclosed(tcx, used_unsafe, id) {
 595         db.span_label(
 596             tcx.sess.source_map().def_span(tcx.hir().span(id)),
 597             format!("because it's nested under this `unsafe` {}", kind),
 598         );
 599     }
 600     db.emit();
 601 }
 602
 603 fn builtin_derive_def_id(tcx: TyCtxt<'_>, def_id: DefId) -> Option<DefId> {
 604     debug!("builtin_derive_def_id({:?})", def_id);
 605     if let Some(impl_def_id) = tcx.impl_of_method(def_id) {
 606         if tcx.has_attr(impl_def_id, sym::automatically_derived) {
 607             debug!("builtin_derive_def_id({:?}) - is {:?}", def_id, impl_def_id);
 608             Some(impl_def_id)
 609         } else {
 610             debug!("builtin_derive_def_id({:?}) - not automatically derived", def_id);
 611             None
 612         }
 613     } else {
 614         debug!("builtin_derive_def_id({:?}) - not a method", def_id);
 615         None
 616     }
 617 }
 618
 619 pub fn check_unsafety(tcx: TyCtxt<'_>, def_id: DefId) {
 620     debug!("check_unsafety({:?})", def_id);
 621
 622     // closures are handled by their parent fn.
 623     if tcx.is_closure(def_id) {
 624         return;
 625     }
 626
 627     let UnsafetyCheckResult { violations, unsafe_blocks } = tcx.unsafety_check_result(def_id);
 628
 629     for &UnsafetyViolation { source_info, description, details, kind } in violations.iter() {
 630         // Report an error.
 631         match kind {
 632             UnsafetyViolationKind::GeneralAndConstFn | UnsafetyViolationKind::General => {
 633                 struct_span_err!(
 634                     tcx.sess,
 635                     source_info.span,
 636                     E0133,
 637                     "{} is unsafe and requires unsafe function or block",
 638                     description
 639                 )
 640                 .span_label(source_info.span, &*description.as_str())
 641                 .note(&details.as_str())
 642                 .emit();
 643             }
 644             UnsafetyViolationKind::BorrowPacked(lint_hir_id) => {
 645                 if let Some(impl_def_id) = builtin_derive_def_id(tcx, def_id) {
 646                     tcx.unsafe_derive_on_repr_packed(impl_def_id);
 647                 } else {
 648                     tcx.lint_node_note(
 649                         SAFE_PACKED_BORROWS,
 650                         lint_hir_id,
 651                         source_info.span,
 652                         &format!(
 653                             "{} is unsafe and requires unsafe function or block \
 654                                             (error E0133)",
 655                             description
 656                         ),
 657                         &details.as_str(),
 658                     );
 659                 }
 660             }
 661         }
 662     }
 663
 664     let mut unsafe_blocks: Vec<_> = unsafe_blocks.into_iter().collect();
 665     unsafe_blocks.sort_by_cached_key(|(hir_id, _)| tcx.hir().hir_to_node_id(*hir_id));
 666     let used_unsafe: FxHashSet<_> =
 667         unsafe_blocks.iter().flat_map(|&&(id, used)| used.then_some(id)).collect();
 668     for &(block_id, is_used) in unsafe_blocks {
 669         if !is_used {
 670             report_unused_unsafe(tcx, &used_unsafe, block_id);
 671         }
 672     }
 673 }