src/librustc_mir/transform/check_unsafety.rs

   1 use rustc_data_structures::fx::FxHashSet;
   2
   3 use rustc::hir;
   4 use rustc::hir::def_id::DefId;
   5 use rustc::hir::Node;
   6 use rustc::lint::builtin::{SAFE_PACKED_BORROWS, UNUSED_UNSAFE};
   7 use rustc::mir::visit::{MutatingUseContext, PlaceContext, Visitor};
   8 use rustc::mir::*;
   9 use rustc::ty::cast::CastTy;
  10 use rustc::ty::query::Providers;
  11 use rustc::ty::{self, TyCtxt};
  12
  13 use rustc_span::symbol::{sym, Symbol};
  14
  15 use std::ops::Bound;
  16
  17 use crate::util;
  18
  19 use rustc_error_codes::*;
  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         match place.base {
 192             PlaceBase::Local(..) => {
 193                 // Locals are safe.
 194             }
 195             PlaceBase::Static(box Static { kind: StaticKind::Promoted(_, _), .. }) => {
 196                 bug!("unsafety checking should happen before promotion");
 197             }
 198             PlaceBase::Static(box Static { kind: StaticKind::Static, .. }) => {
 199                 bug!("StaticKind::Static should not exist");
 200             }
 201         }
 202
 203         for (i, elem) in place.projection.iter().enumerate() {
 204             let proj_base = &place.projection[..i];
 205
 206             if context.is_borrow() {
 207                 if util::is_disaligned(self.tcx, self.body, self.param_env, place) {
 208                     let source_info = self.source_info;
 209                     let lint_root = self.body.source_scopes[source_info.scope]
 210                         .local_data
 211                         .as_ref()
 212                         .assert_crate_local()
 213                         .lint_root;
 214                     self.register_violations(
 215                         &[UnsafetyViolation {
 216                             source_info,
 217                             description: Symbol::intern("borrow of packed field"),
 218                             details: Symbol::intern(
 219                                 "fields of packed structs might be misaligned: dereferencing a \
 220                             misaligned pointer or even just creating a misaligned reference \
 221                             is undefined behavior",
 222                             ),
 223                             kind: UnsafetyViolationKind::BorrowPacked(lint_root),
 224                         }],
 225                         &[],
 226                     );
 227                 }
 228             }
 229             let is_borrow_of_interior_mut = context.is_borrow()
 230                 && !Place::ty_from(&place.base, proj_base, self.body, self.tcx).ty.is_freeze(
 231                     self.tcx,
 232                     self.param_env,
 233                     self.source_info.span,
 234                 );
 235             // prevent
 236             // * `&mut x.field`
 237             // * `x.field = y;`
 238             // * `&x.field` if `field`'s type has interior mutability
 239             // because either of these would allow modifying the layout constrained field and
 240             // insert values that violate the layout constraints.
 241             if context.is_mutating_use() || is_borrow_of_interior_mut {
 242                 self.check_mut_borrowing_layout_constrained_field(place, context.is_mutating_use());
 243             }
 244             let old_source_info = self.source_info;
 245             if let (PlaceBase::Local(local), []) = (&place.base, proj_base) {
 246                 let decl = &self.body.local_decls[*local];
 247                 if decl.internal {
 248                     // Internal locals are used in the `move_val_init` desugaring.
 249                     // We want to check unsafety against the source info of the
 250                     // desugaring, rather than the source info of the RHS.
 251                     self.source_info = self.body.local_decls[*local].source_info;
 252                 } else if let LocalInfo::StaticRef { def_id, .. } = decl.local_info {
 253                     if self.tcx.is_mutable_static(def_id) {
 254                         self.require_unsafe(
 255                             "use of mutable static",
 256                             "mutable statics can be mutated by multiple threads: aliasing \
 257                         violations or data races will cause undefined behavior",
 258                             UnsafetyViolationKind::General,
 259                         );
 260                         return;
 261                     } else if self.tcx.is_foreign_item(def_id) {
 262                         self.require_unsafe(
 263                             "use of extern static",
 264                             "extern statics are not controlled by the Rust type system: \
 265                         invalid data, aliasing violations or data races will cause \
 266                         undefined behavior",
 267                             UnsafetyViolationKind::General,
 268                         );
 269                         return;
 270                     }
 271                 }
 272             }
 273             let base_ty = Place::ty_from(&place.base, proj_base, self.body, self.tcx).ty;
 274             match base_ty.kind {
 275                 ty::RawPtr(..) => self.require_unsafe(
 276                     "dereference of raw pointer",
 277                     "raw pointers may be NULL, dangling or unaligned; they can violate \
 278                          aliasing rules and cause data races: all of these are undefined \
 279                          behavior",
 280                     UnsafetyViolationKind::General,
 281                 ),
 282                 ty::Adt(adt, _) => {
 283                     if adt.is_union() {
 284                         if context == PlaceContext::MutatingUse(MutatingUseContext::Store)
 285                             || context == PlaceContext::MutatingUse(MutatingUseContext::Drop)
 286                             || context == PlaceContext::MutatingUse(MutatingUseContext::AsmOutput)
 287                         {
 288                             let elem_ty = match elem {
 289                                 ProjectionElem::Field(_, ty) => ty,
 290                                 _ => span_bug!(
 291                                     self.source_info.span,
 292                                     "non-field projection {:?} from union?",
 293                                     place
 294                                 ),
 295                             };
 296                             if !elem_ty.is_copy_modulo_regions(
 297                                 self.tcx,
 298                                 self.param_env,
 299                                 self.source_info.span,
 300                             ) {
 301                                 self.require_unsafe(
 302                                     "assignment to non-`Copy` union field",
 303                                     "the previous content of the field will be dropped, which \
 304                                      causes undefined behavior if the field was not properly \
 305                                      initialized",
 306                                     UnsafetyViolationKind::GeneralAndConstFn,
 307                                 )
 308                             } else {
 309                                 // write to non-move union, safe
 310                             }
 311                         } else {
 312                             self.require_unsafe(
 313                                 "access to union field",
 314                                 "the field may not be properly initialized: using \
 315                                  uninitialized data will cause undefined behavior",
 316                                 UnsafetyViolationKind::GeneralAndConstFn,
 317                             )
 318                         }
 319                     }
 320                 }
 321                 _ => {}
 322             }
 323             self.source_info = old_source_info;
 324         }
 325     }
 326 }
 327
 328 impl<'a, 'tcx> UnsafetyChecker<'a, 'tcx> {
 329     fn require_unsafe(
 330         &mut self,
 331         description: &'static str,
 332         details: &'static str,
 333         kind: UnsafetyViolationKind,
 334     ) {
 335         let source_info = self.source_info;
 336         self.register_violations(
 337             &[UnsafetyViolation {
 338                 source_info,
 339                 description: Symbol::intern(description),
 340                 details: Symbol::intern(details),
 341                 kind,
 342             }],
 343             &[],
 344         );
 345     }
 346
 347     fn register_violations(
 348         &mut self,
 349         violations: &[UnsafetyViolation],
 350         unsafe_blocks: &[(hir::HirId, bool)],
 351     ) {
 352         let safety = self.body.source_scopes[self.source_info.scope]
 353             .local_data
 354             .as_ref()
 355             .assert_crate_local()
 356             .safety;
 357         let within_unsafe = match safety {
 358             // `unsafe` blocks are required in safe code
 359             Safety::Safe => {
 360                 for violation in violations {
 361                     let mut violation = violation.clone();
 362                     match violation.kind {
 363                         UnsafetyViolationKind::GeneralAndConstFn
 364                         | UnsafetyViolationKind::General => {}
 365                         UnsafetyViolationKind::BorrowPacked(_) => {
 366                             if self.min_const_fn {
 367                                 // const fns don't need to be backwards compatible and can
 368                                 // emit these violations as a hard error instead of a backwards
 369                                 // compat lint
 370                                 violation.kind = UnsafetyViolationKind::General;
 371                             }
 372                         }
 373                     }
 374                     if !self.violations.contains(&violation) {
 375                         self.violations.push(violation)
 376                     }
 377                 }
 378                 false
 379             }
 380             // `unsafe` function bodies allow unsafe without additional unsafe blocks
 381             Safety::BuiltinUnsafe | Safety::FnUnsafe => true,
 382             Safety::ExplicitUnsafe(hir_id) => {
 383                 // mark unsafe block as used if there are any unsafe operations inside
 384                 if !violations.is_empty() {
 385                     self.used_unsafe.insert(hir_id);
 386                 }
 387                 // only some unsafety is allowed in const fn
 388                 if self.min_const_fn {
 389                     for violation in violations {
 390                         match violation.kind {
 391                             // these unsafe things are stable in const fn
 392                             UnsafetyViolationKind::GeneralAndConstFn => {}
 393                             // these things are forbidden in const fns
 394                             UnsafetyViolationKind::General
 395                             | UnsafetyViolationKind::BorrowPacked(_) => {
 396                                 let mut violation = violation.clone();
 397                                 // const fns don't need to be backwards compatible and can
 398                                 // emit these violations as a hard error instead of a backwards
 399                                 // compat lint
 400                                 violation.kind = UnsafetyViolationKind::General;
 401                                 if !self.violations.contains(&violation) {
 402                                     self.violations.push(violation)
 403                                 }
 404                             }
 405                         }
 406                     }
 407                 }
 408                 true
 409             }
 410         };
 411         self.inherited_blocks.extend(
 412             unsafe_blocks.iter().map(|&(hir_id, is_used)| (hir_id, is_used && !within_unsafe)),
 413         );
 414     }
 415     fn check_mut_borrowing_layout_constrained_field(
 416         &mut self,
 417         place: &Place<'tcx>,
 418         is_mut_use: bool,
 419     ) {
 420         let mut cursor = place.projection.as_ref();
 421         while let &[ref proj_base @ .., elem] = cursor {
 422             cursor = proj_base;
 423
 424             match elem {
 425                 ProjectionElem::Field(..) => {
 426                     let ty =
 427                         Place::ty_from(&place.base, proj_base, &self.body.local_decls, self.tcx).ty;
 428                     match ty.kind {
 429                         ty::Adt(def, _) => match self.tcx.layout_scalar_valid_range(def.did) {
 430                             (Bound::Unbounded, Bound::Unbounded) => {}
 431                             _ => {
 432                                 let (description, details) = if is_mut_use {
 433                                     (
 434                                         "mutation of layout constrained field",
 435                                         "mutating layout constrained fields cannot statically be \
 436                                         checked for valid values",
 437                                     )
 438                                 } else {
 439                                     (
 440                                         "borrow of layout constrained field with interior \
 441                                         mutability",
 442                                         "references to fields of layout constrained fields \
 443                                         lose the constraints. Coupled with interior mutability, \
 444                                         the field can be changed to invalid values",
 445                                     )
 446                                 };
 447                                 let source_info = self.source_info;
 448                                 self.register_violations(
 449                                     &[UnsafetyViolation {
 450                                         source_info,
 451                                         description: Symbol::intern(description),
 452                                         details: Symbol::intern(details),
 453                                         kind: UnsafetyViolationKind::GeneralAndConstFn,
 454                                     }],
 455                                     &[],
 456                                 );
 457                             }
 458                         },
 459                         _ => {}
 460                     }
 461                 }
 462                 _ => {}
 463             }
 464         }
 465     }
 466 }
 467
 468 pub(crate) fn provide(providers: &mut Providers<'_>) {
 469     *providers = Providers { unsafety_check_result, unsafe_derive_on_repr_packed, ..*providers };
 470 }
 471
 472 struct UnusedUnsafeVisitor<'a> {
 473     used_unsafe: &'a FxHashSet<hir::HirId>,
 474     unsafe_blocks: &'a mut Vec<(hir::HirId, bool)>,
 475 }
 476
 477 impl<'a, 'tcx> hir::intravisit::Visitor<'tcx> for UnusedUnsafeVisitor<'a> {
 478     fn nested_visit_map<'this>(&'this mut self) -> hir::intravisit::NestedVisitorMap<'this, 'tcx> {
 479         hir::intravisit::NestedVisitorMap::None
 480     }
 481
 482     fn visit_block(&mut self, block: &'tcx hir::Block<'tcx>) {
 483         hir::intravisit::walk_block(self, block);
 484
 485         if let hir::UnsafeBlock(hir::UserProvided) = block.rules {
 486             self.unsafe_blocks.push((block.hir_id, self.used_unsafe.contains(&block.hir_id)));
 487         }
 488     }
 489 }
 490
 491 fn check_unused_unsafe(
 492     tcx: TyCtxt<'_>,
 493     def_id: DefId,
 494     used_unsafe: &FxHashSet<hir::HirId>,
 495     unsafe_blocks: &mut Vec<(hir::HirId, bool)>,
 496 ) {
 497     let body_id =
 498         tcx.hir().as_local_hir_id(def_id).and_then(|hir_id| tcx.hir().maybe_body_owned_by(hir_id));
 499
 500     let body_id = match body_id {
 501         Some(body) => body,
 502         None => {
 503             debug!("check_unused_unsafe({:?}) - no body found", def_id);
 504             return;
 505         }
 506     };
 507     let body = tcx.hir().body(body_id);
 508     debug!("check_unused_unsafe({:?}, body={:?}, used_unsafe={:?})", def_id, body, used_unsafe);
 509
 510     let mut visitor = UnusedUnsafeVisitor { used_unsafe, unsafe_blocks };
 511     hir::intravisit::Visitor::visit_body(&mut visitor, body);
 512 }
 513
 514 fn unsafety_check_result(tcx: TyCtxt<'_>, def_id: DefId) -> UnsafetyCheckResult {
 515     debug!("unsafety_violations({:?})", def_id);
 516
 517     // N.B., this borrow is valid because all the consumers of
 518     // `mir_built` force this.
 519     let body = &tcx.mir_built(def_id).borrow();
 520
 521     let param_env = tcx.param_env(def_id);
 522
 523     let id = tcx.hir().as_local_hir_id(def_id).unwrap();
 524     let (const_context, min_const_fn) = match tcx.hir().body_owner_kind(id) {
 525         hir::BodyOwnerKind::Closure => (false, false),
 526         hir::BodyOwnerKind::Fn => (tcx.is_const_fn(def_id), tcx.is_min_const_fn(def_id)),
 527         hir::BodyOwnerKind::Const | hir::BodyOwnerKind::Static(_) => (true, false),
 528     };
 529     let mut checker = UnsafetyChecker::new(const_context, min_const_fn, body, tcx, param_env);
 530     // mir_built ensures that body has a computed cache, so we don't (and can't) attempt to
 531     // recompute it here.
 532     let body = body.unwrap_read_only();
 533     checker.visit_body(body);
 534
 535     check_unused_unsafe(tcx, def_id, &checker.used_unsafe, &mut checker.inherited_blocks);
 536     UnsafetyCheckResult {
 537         violations: checker.violations.into(),
 538         unsafe_blocks: checker.inherited_blocks.into(),
 539     }
 540 }
 541
 542 fn unsafe_derive_on_repr_packed(tcx: TyCtxt<'_>, def_id: DefId) {
 543     let lint_hir_id = tcx
 544         .hir()
 545         .as_local_hir_id(def_id)
 546         .unwrap_or_else(|| bug!("checking unsafety for non-local def id {:?}", def_id));
 547
 548     // FIXME: when we make this a hard error, this should have its
 549     // own error code.
 550     let message = if tcx.generics_of(def_id).own_requires_monomorphization() {
 551         "`#[derive]` can't be used on a `#[repr(packed)]` struct with \
 552          type or const parameters (error E0133)"
 553             .to_string()
 554     } else {
 555         "`#[derive]` can't be used on a `#[repr(packed)]` struct that \
 556          does not derive Copy (error E0133)"
 557             .to_string()
 558     };
 559     tcx.lint_hir(SAFE_PACKED_BORROWS, lint_hir_id, tcx.def_span(def_id), &message);
 560 }
 561
 562 /// Returns the `HirId` for an enclosing scope that is also `unsafe`.
 563 fn is_enclosed(
 564     tcx: TyCtxt<'_>,
 565     used_unsafe: &FxHashSet<hir::HirId>,
 566     id: hir::HirId,
 567 ) -> Option<(String, hir::HirId)> {
 568     let parent_id = tcx.hir().get_parent_node(id);
 569     if parent_id != id {
 570         if used_unsafe.contains(&parent_id) {
 571             Some(("block".to_string(), parent_id))
 572         } else if let Some(Node::Item(&hir::Item {
 573             kind: hir::ItemKind::Fn(ref sig, _, _), ..
 574         })) = tcx.hir().find(parent_id)
 575         {
 576             match sig.header.unsafety {
 577                 hir::Unsafety::Unsafe => Some(("fn".to_string(), parent_id)),
 578                 hir::Unsafety::Normal => None,
 579             }
 580         } else {
 581             is_enclosed(tcx, used_unsafe, parent_id)
 582         }
 583     } else {
 584         None
 585     }
 586 }
 587
 588 fn report_unused_unsafe(tcx: TyCtxt<'_>, used_unsafe: &FxHashSet<hir::HirId>, id: hir::HirId) {
 589     let span = tcx.sess.source_map().def_span(tcx.hir().span(id));
 590     let msg = "unnecessary `unsafe` block";
 591     let mut db = tcx.struct_span_lint_hir(UNUSED_UNSAFE, id, span, msg);
 592     db.span_label(span, msg);
 593     if let Some((kind, id)) = is_enclosed(tcx, used_unsafe, id) {
 594         db.span_label(
 595             tcx.sess.source_map().def_span(tcx.hir().span(id)),
 596             format!("because it's nested under this `unsafe` {}", kind),
 597         );
 598     }
 599     db.emit();
 600 }
 601
 602 fn builtin_derive_def_id(tcx: TyCtxt<'_>, def_id: DefId) -> Option<DefId> {
 603     debug!("builtin_derive_def_id({:?})", def_id);
 604     if let Some(impl_def_id) = tcx.impl_of_method(def_id) {
 605         if tcx.has_attr(impl_def_id, sym::automatically_derived) {
 606             debug!("builtin_derive_def_id({:?}) - is {:?}", def_id, impl_def_id);
 607             Some(impl_def_id)
 608         } else {
 609             debug!("builtin_derive_def_id({:?}) - not automatically derived", def_id);
 610             None
 611         }
 612     } else {
 613         debug!("builtin_derive_def_id({:?}) - not a method", def_id);
 614         None
 615     }
 616 }
 617
 618 pub fn check_unsafety(tcx: TyCtxt<'_>, def_id: DefId) {
 619     debug!("check_unsafety({:?})", def_id);
 620
 621     // closures are handled by their parent fn.
 622     if tcx.is_closure(def_id) {
 623         return;
 624     }
 625
 626     let UnsafetyCheckResult { violations, unsafe_blocks } = tcx.unsafety_check_result(def_id);
 627
 628     for &UnsafetyViolation { source_info, description, details, kind } in violations.iter() {
 629         // Report an error.
 630         match kind {
 631             UnsafetyViolationKind::GeneralAndConstFn | UnsafetyViolationKind::General => {
 632                 struct_span_err!(
 633                     tcx.sess,
 634                     source_info.span,
 635                     E0133,
 636                     "{} is unsafe and requires unsafe function or block",
 637                     description
 638                 )
 639                 .span_label(source_info.span, &*description.as_str())
 640                 .note(&details.as_str())
 641                 .emit();
 642             }
 643             UnsafetyViolationKind::BorrowPacked(lint_hir_id) => {
 644                 if let Some(impl_def_id) = builtin_derive_def_id(tcx, def_id) {
 645                     tcx.unsafe_derive_on_repr_packed(impl_def_id);
 646                 } else {
 647                     tcx.lint_node_note(
 648                         SAFE_PACKED_BORROWS,
 649                         lint_hir_id,
 650                         source_info.span,
 651                         &format!(
 652                             "{} is unsafe and requires unsafe function or block \
 653                                             (error E0133)",
 654                             description
 655                         ),
 656                         &details.as_str(),
 657                     );
 658                 }
 659             }
 660         }
 661     }
 662
 663     let mut unsafe_blocks: Vec<_> = unsafe_blocks.into_iter().collect();
 664     unsafe_blocks.sort_by_cached_key(|(hir_id, _)| tcx.hir().hir_to_node_id(*hir_id));
 665     let used_unsafe: FxHashSet<_> =
 666         unsafe_blocks.iter().flat_map(|&&(id, used)| used.then_some(id)).collect();
 667     for &(block_id, is_used) in unsafe_blocks {
 668         if !is_used {
 669             report_unused_unsafe(tcx, &used_unsafe, block_id);
 670         }
 671     }
 672 }