src/librustc_mir/transform/check_unsafety.rs

   1 use rustc::hir::intravisit;
   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_hir as hir;
  10 use rustc_hir::def_id::DefId;
  11 use rustc_hir::Node;
  12 use rustc_span::symbol::{sym, Symbol};
  13
  14 use std::ops::Bound;
  15
  16 use crate::util;
  17
  18 use rustc_error_codes::*;
  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.register_violations(
 151                             &[UnsafetyViolation {
 152                                 source_info: self.source_info,
 153                                 description: Symbol::intern("cast of pointer to int"),
 154                                 details: Symbol::intern(
 155                                     "casting pointers to integers in constants",
 156                                 ),
 157                                 kind: UnsafetyViolationKind::General,
 158                             }],
 159                             &[],
 160                         );
 161                     }
 162                     _ => {}
 163                 }
 164             }
 165             // raw pointer and fn pointer operations are unsafe as it is not clear whether one
 166             // pointer would be "less" or "equal" to another, because we cannot know where llvm
 167             // or the linker will place various statics in memory. Without this information the
 168             // result of a comparison of addresses would differ between runtime and compile-time.
 169             Rvalue::BinaryOp(_, ref lhs, _)
 170                 if self.const_context && self.tcx.features().const_compare_raw_pointers =>
 171             {
 172                 if let ty::RawPtr(_) | ty::FnPtr(..) = lhs.ty(self.body, self.tcx).kind {
 173                     self.register_violations(
 174                         &[UnsafetyViolation {
 175                             source_info: self.source_info,
 176                             description: Symbol::intern("pointer operation"),
 177                             details: Symbol::intern("operations on pointers in constants"),
 178                             kind: UnsafetyViolationKind::General,
 179                         }],
 180                         &[],
 181                     );
 182                 }
 183             }
 184             _ => {}
 185         }
 186         self.super_rvalue(rvalue, location);
 187     }
 188
 189     fn visit_place(&mut self, place: &Place<'tcx>, context: PlaceContext, _location: Location) {
 190         match place.base {
 191             PlaceBase::Local(..) => {
 192                 // Locals are safe.
 193             }
 194             PlaceBase::Static(box Static { kind: StaticKind::Promoted(_, _), .. }) => {
 195                 bug!("unsafety checking should happen before promotion");
 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     fn nested_visit_map<'this>(&'this mut self) -> intravisit::NestedVisitorMap<'this, 'tcx> {
 478         intravisit::NestedVisitorMap::None
 479     }
 480
 481     fn visit_block(&mut self, block: &'tcx hir::Block<'tcx>) {
 482         intravisit::walk_block(self, block);
 483
 484         if let hir::BlockCheckMode::UnsafeBlock(hir::UnsafeSource::UserProvided) = block.rules {
 485             self.unsafe_blocks.push((block.hir_id, self.used_unsafe.contains(&block.hir_id)));
 486         }
 487     }
 488 }
 489
 490 fn check_unused_unsafe(
 491     tcx: TyCtxt<'_>,
 492     def_id: DefId,
 493     used_unsafe: &FxHashSet<hir::HirId>,
 494     unsafe_blocks: &mut Vec<(hir::HirId, bool)>,
 495 ) {
 496     let body_id =
 497         tcx.hir().as_local_hir_id(def_id).and_then(|hir_id| tcx.hir().maybe_body_owned_by(hir_id));
 498
 499     let body_id = match body_id {
 500         Some(body) => body,
 501         None => {
 502             debug!("check_unused_unsafe({:?}) - no body found", def_id);
 503             return;
 504         }
 505     };
 506     let body = tcx.hir().body(body_id);
 507     debug!("check_unused_unsafe({:?}, body={:?}, used_unsafe={:?})", def_id, body, used_unsafe);
 508
 509     let mut visitor = UnusedUnsafeVisitor { used_unsafe, unsafe_blocks };
 510     intravisit::Visitor::visit_body(&mut visitor, body);
 511 }
 512
 513 fn unsafety_check_result(tcx: TyCtxt<'_>, def_id: DefId) -> UnsafetyCheckResult {
 514     debug!("unsafety_violations({:?})", def_id);
 515
 516     // N.B., this borrow is valid because all the consumers of
 517     // `mir_built` force this.
 518     let body = &tcx.mir_built(def_id).borrow();
 519
 520     let param_env = tcx.param_env(def_id);
 521
 522     let id = tcx.hir().as_local_hir_id(def_id).unwrap();
 523     let (const_context, min_const_fn) = match tcx.hir().body_owner_kind(id) {
 524         hir::BodyOwnerKind::Closure => (false, false),
 525         hir::BodyOwnerKind::Fn => (tcx.is_const_fn(def_id), tcx.is_min_const_fn(def_id)),
 526         hir::BodyOwnerKind::Const | hir::BodyOwnerKind::Static(_) => (true, false),
 527     };
 528     let mut checker = UnsafetyChecker::new(const_context, min_const_fn, body, tcx, param_env);
 529     // mir_built ensures that body has a computed cache, so we don't (and can't) attempt to
 530     // recompute it here.
 531     let body = body.unwrap_read_only();
 532     checker.visit_body(body);
 533
 534     check_unused_unsafe(tcx, def_id, &checker.used_unsafe, &mut checker.inherited_blocks);
 535     UnsafetyCheckResult {
 536         violations: checker.violations.into(),
 537         unsafe_blocks: checker.inherited_blocks.into(),
 538     }
 539 }
 540
 541 fn unsafe_derive_on_repr_packed(tcx: TyCtxt<'_>, def_id: DefId) {
 542     let lint_hir_id = tcx
 543         .hir()
 544         .as_local_hir_id(def_id)
 545         .unwrap_or_else(|| bug!("checking unsafety for non-local def id {:?}", def_id));
 546
 547     // FIXME: when we make this a hard error, this should have its
 548     // own error code.
 549     let message = if tcx.generics_of(def_id).own_requires_monomorphization() {
 550         "`#[derive]` can't be used on a `#[repr(packed)]` struct with \
 551          type or const parameters (error E0133)"
 552             .to_string()
 553     } else {
 554         "`#[derive]` can't be used on a `#[repr(packed)]` struct that \
 555          does not derive Copy (error E0133)"
 556             .to_string()
 557     };
 558     tcx.lint_hir(SAFE_PACKED_BORROWS, lint_hir_id, tcx.def_span(def_id), &message);
 559 }
 560
 561 /// Returns the `HirId` for an enclosing scope that is also `unsafe`.
 562 fn is_enclosed(
 563     tcx: TyCtxt<'_>,
 564     used_unsafe: &FxHashSet<hir::HirId>,
 565     id: hir::HirId,
 566 ) -> Option<(String, hir::HirId)> {
 567     let parent_id = tcx.hir().get_parent_node(id);
 568     if parent_id != id {
 569         if used_unsafe.contains(&parent_id) {
 570             Some(("block".to_string(), parent_id))
 571         } else if let Some(Node::Item(&hir::Item {
 572             kind: hir::ItemKind::Fn(ref sig, _, _), ..
 573         })) = tcx.hir().find(parent_id)
 574         {
 575             match sig.header.unsafety {
 576                 hir::Unsafety::Unsafe => Some(("fn".to_string(), parent_id)),
 577                 hir::Unsafety::Normal => None,
 578             }
 579         } else {
 580             is_enclosed(tcx, used_unsafe, parent_id)
 581         }
 582     } else {
 583         None
 584     }
 585 }
 586
 587 fn report_unused_unsafe(tcx: TyCtxt<'_>, used_unsafe: &FxHashSet<hir::HirId>, id: hir::HirId) {
 588     let span = tcx.sess.source_map().def_span(tcx.hir().span(id));
 589     let msg = "unnecessary `unsafe` block";
 590     let mut db = tcx.struct_span_lint_hir(UNUSED_UNSAFE, id, span, msg);
 591     db.span_label(span, msg);
 592     if let Some((kind, id)) = is_enclosed(tcx, used_unsafe, id) {
 593         db.span_label(
 594             tcx.sess.source_map().def_span(tcx.hir().span(id)),
 595             format!("because it's nested under this `unsafe` {}", kind),
 596         );
 597     }
 598     db.emit();
 599 }
 600
 601 fn builtin_derive_def_id(tcx: TyCtxt<'_>, def_id: DefId) -> Option<DefId> {
 602     debug!("builtin_derive_def_id({:?})", def_id);
 603     if let Some(impl_def_id) = tcx.impl_of_method(def_id) {
 604         if tcx.has_attr(impl_def_id, sym::automatically_derived) {
 605             debug!("builtin_derive_def_id({:?}) - is {:?}", def_id, impl_def_id);
 606             Some(impl_def_id)
 607         } else {
 608             debug!("builtin_derive_def_id({:?}) - not automatically derived", def_id);
 609             None
 610         }
 611     } else {
 612         debug!("builtin_derive_def_id({:?}) - not a method", def_id);
 613         None
 614     }
 615 }
 616
 617 pub fn check_unsafety(tcx: TyCtxt<'_>, def_id: DefId) {
 618     debug!("check_unsafety({:?})", def_id);
 619
 620     // closures are handled by their parent fn.
 621     if tcx.is_closure(def_id) {
 622         return;
 623     }
 624
 625     let UnsafetyCheckResult { violations, unsafe_blocks } = tcx.unsafety_check_result(def_id);
 626
 627     for &UnsafetyViolation { source_info, description, details, kind } in violations.iter() {
 628         // Report an error.
 629         match kind {
 630             UnsafetyViolationKind::GeneralAndConstFn | UnsafetyViolationKind::General => {
 631                 struct_span_err!(
 632                     tcx.sess,
 633                     source_info.span,
 634                     E0133,
 635                     "{} is unsafe and requires unsafe function or block",
 636                     description
 637                 )
 638                 .span_label(source_info.span, &*description.as_str())
 639                 .note(&details.as_str())
 640                 .emit();
 641             }
 642             UnsafetyViolationKind::BorrowPacked(lint_hir_id) => {
 643                 if let Some(impl_def_id) = builtin_derive_def_id(tcx, def_id) {
 644                     tcx.unsafe_derive_on_repr_packed(impl_def_id);
 645                 } else {
 646                     tcx.lint_node_note(
 647                         SAFE_PACKED_BORROWS,
 648                         lint_hir_id,
 649                         source_info.span,
 650                         &format!(
 651                             "{} is unsafe and requires unsafe function or block \
 652                                             (error E0133)",
 653                             description
 654                         ),
 655                         &details.as_str(),
 656                     );
 657                 }
 658             }
 659         }
 660     }
 661
 662     let mut unsafe_blocks: Vec<_> = unsafe_blocks.into_iter().collect();
 663     unsafe_blocks.sort_by_cached_key(|(hir_id, _)| tcx.hir().hir_to_node_id(*hir_id));
 664     let used_unsafe: FxHashSet<_> =
 665         unsafe_blocks.iter().flat_map(|&&(id, used)| used.then_some(id)).collect();
 666     for &(block_id, is_used) in unsafe_blocks {
 667         if !is_used {
 668             report_unused_unsafe(tcx, &used_unsafe, block_id);
 669         }
 670     }
 671 }