src/librustc_mir/transform/check_unsafety.rs

   1 // Copyright 2017 The Rust Project Developers. See the COPYRIGHT
   2 // file at the top-level directory of this distribution and at
   3 // http://rust-lang.org/COPYRIGHT.
   4 //
   5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
   8 // option. This file may not be copied, modified, or distributed
   9 // except according to those terms.
  10
  11 use rustc_data_structures::fx::FxHashSet;
  12 use rustc_data_structures::indexed_vec::IndexVec;
  13 use rustc_data_structures::sync::Lrc;
  14
  15 use rustc::ty::query::Providers;
  16 use rustc::ty::{self, TyCtxt};
  17 use rustc::hir;
  18 use rustc::hir::Node;
  19 use rustc::hir::def_id::DefId;
  20 use rustc::lint::builtin::{SAFE_EXTERN_STATICS, SAFE_PACKED_BORROWS, UNUSED_UNSAFE};
  21 use rustc::mir::*;
  22 use rustc::mir::visit::{PlaceContext, Visitor, MutatingUseContext};
  23
  24 use syntax::ast;
  25 use syntax::symbol::Symbol;
  26
  27 use std::ops::Bound;
  28
  29 use util;
  30
  31 pub struct UnsafetyChecker<'a, 'tcx: 'a> {
  32     mir: &'a Mir<'tcx>,
  33     min_const_fn: bool,
  34     source_scope_local_data: &'a IndexVec<SourceScope, SourceScopeLocalData>,
  35     violations: Vec<UnsafetyViolation>,
  36     source_info: SourceInfo,
  37     tcx: TyCtxt<'a, 'tcx, 'tcx>,
  38     param_env: ty::ParamEnv<'tcx>,
  39     /// mark an `unsafe` block as used, so we don't lint it
  40     used_unsafe: FxHashSet<ast::NodeId>,
  41     inherited_blocks: Vec<(ast::NodeId, bool)>,
  42 }
  43
  44 impl<'a, 'gcx, 'tcx> UnsafetyChecker<'a, 'tcx> {
  45     fn new(
  46         min_const_fn: bool,
  47         mir: &'a Mir<'tcx>,
  48         source_scope_local_data: &'a IndexVec<SourceScope, SourceScopeLocalData>,
  49         tcx: TyCtxt<'a, 'tcx, 'tcx>,
  50         param_env: ty::ParamEnv<'tcx>,
  51     ) -> Self {
  52         Self {
  53             mir,
  54             min_const_fn,
  55             source_scope_local_data,
  56             violations: vec![],
  57             source_info: SourceInfo {
  58                 span: mir.span,
  59                 scope: OUTERMOST_SOURCE_SCOPE
  60             },
  61             tcx,
  62             param_env,
  63             used_unsafe: Default::default(),
  64             inherited_blocks: vec![],
  65         }
  66     }
  67 }
  68
  69 impl<'a, 'tcx> Visitor<'tcx> for UnsafetyChecker<'a, 'tcx> {
  70     fn visit_terminator(&mut self,
  71                         block: BasicBlock,
  72                         terminator: &Terminator<'tcx>,
  73                         location: Location)
  74     {
  75         self.source_info = terminator.source_info;
  76         match terminator.kind {
  77             TerminatorKind::Goto { .. } |
  78             TerminatorKind::SwitchInt { .. } |
  79             TerminatorKind::Drop { .. } |
  80             TerminatorKind::Yield { .. } |
  81             TerminatorKind::Assert { .. } |
  82             TerminatorKind::DropAndReplace { .. } |
  83             TerminatorKind::GeneratorDrop |
  84             TerminatorKind::Resume |
  85             TerminatorKind::Abort |
  86             TerminatorKind::Return |
  87             TerminatorKind::Unreachable |
  88             TerminatorKind::FalseEdges { .. } |
  89             TerminatorKind::FalseUnwind { .. } => {
  90                 // safe (at least as emitted during MIR construction)
  91             }
  92
  93             TerminatorKind::Call { ref func, .. } => {
  94                 let func_ty = func.ty(self.mir, self.tcx);
  95                 let sig = func_ty.fn_sig(self.tcx);
  96                 if let hir::Unsafety::Unsafe = sig.unsafety() {
  97                     self.require_unsafe("call to unsafe function",
  98                         "consult the function's documentation for information on how to avoid \
  99                          undefined behavior", UnsafetyViolationKind::MinConstFn)
 100                 }
 101             }
 102         }
 103         self.super_terminator(block, terminator, location);
 104     }
 105
 106     fn visit_statement(&mut self,
 107                        block: BasicBlock,
 108                        statement: &Statement<'tcx>,
 109                        location: Location)
 110     {
 111         self.source_info = statement.source_info;
 112         match statement.kind {
 113             StatementKind::Assign(..) |
 114             StatementKind::FakeRead(..) |
 115             StatementKind::SetDiscriminant { .. } |
 116             StatementKind::StorageLive(..) |
 117             StatementKind::StorageDead(..) |
 118             StatementKind::Retag { .. } |
 119             StatementKind::EscapeToRaw { .. } |
 120             StatementKind::AscribeUserType(..) |
 121             StatementKind::Nop => {
 122                 // safe (at least as emitted during MIR construction)
 123             }
 124
 125             StatementKind::InlineAsm { .. } => {
 126                 self.require_unsafe("use of inline assembly",
 127                     "inline assembly is entirely unchecked and can cause undefined behavior",
 128                     UnsafetyViolationKind::General)
 129             },
 130         }
 131         self.super_statement(block, statement, location);
 132     }
 133
 134     fn visit_rvalue(&mut self,
 135                     rvalue: &Rvalue<'tcx>,
 136                     location: Location)
 137     {
 138         if let &Rvalue::Aggregate(box ref aggregate, _) = rvalue {
 139             match aggregate {
 140                 &AggregateKind::Array(..) |
 141                 &AggregateKind::Tuple => {}
 142                 &AggregateKind::Adt(ref def, ..) => {
 143                     match self.tcx.layout_scalar_valid_range(def.did) {
 144                         (Bound::Unbounded, Bound::Unbounded) => {},
 145                         _ => self.require_unsafe(
 146                             "initializing type with `rustc_layout_scalar_valid_range` attr",
 147                             "initializing `NonZero` with a `0` violates layout constraints \
 148                             and is undefined behavior",
 149                             UnsafetyViolationKind::MinConstFn,
 150                         ),
 151                     }
 152                 }
 153                 &AggregateKind::Closure(def_id, _) |
 154                 &AggregateKind::Generator(def_id, _, _) => {
 155                     let UnsafetyCheckResult {
 156                         violations, unsafe_blocks
 157                     } = self.tcx.unsafety_check_result(def_id);
 158                     self.register_violations(&violations, &unsafe_blocks);
 159                 }
 160             }
 161         }
 162         self.super_rvalue(rvalue, location);
 163     }
 164
 165     fn visit_place(&mut self,
 166                     place: &Place<'tcx>,
 167                     context: PlaceContext<'tcx>,
 168                     location: Location) {
 169         if context.is_borrow() {
 170             if util::is_disaligned(self.tcx, self.mir, self.param_env, place) {
 171                 let source_info = self.source_info;
 172                 let lint_root =
 173                     self.source_scope_local_data[source_info.scope].lint_root;
 174                 self.register_violations(&[UnsafetyViolation {
 175                     source_info,
 176                     description: Symbol::intern("borrow of packed field").as_interned_str(),
 177                     details:
 178                         Symbol::intern("fields of packed structs might be misaligned: \
 179                                         dereferencing a misaligned pointer or even just creating a \
 180                                         misaligned reference is undefined behavior")
 181                             .as_interned_str(),
 182                     kind: UnsafetyViolationKind::BorrowPacked(lint_root)
 183                 }], &[]);
 184             }
 185         }
 186
 187         match place {
 188             &Place::Projection(box Projection {
 189                 ref base, ref elem
 190             }) => {
 191                 let old_source_info = self.source_info;
 192                 if let &Place::Local(local) = base {
 193                     if self.mir.local_decls[local].internal {
 194                         // Internal locals are used in the `move_val_init` desugaring.
 195                         // We want to check unsafety against the source info of the
 196                         // desugaring, rather than the source info of the RHS.
 197                         self.source_info = self.mir.local_decls[local].source_info;
 198                     }
 199                 }
 200                 let base_ty = base.ty(self.mir, self.tcx).to_ty(self.tcx);
 201                 match base_ty.sty {
 202                     ty::RawPtr(..) => {
 203                         self.require_unsafe("dereference of raw pointer",
 204                             "raw pointers may be NULL, dangling or unaligned; they can violate \
 205                              aliasing rules and cause data races: all of these are undefined \
 206                              behavior", UnsafetyViolationKind::General)
 207                     }
 208                     ty::Adt(adt, _) => {
 209                         if adt.is_union() {
 210                             if context == PlaceContext::MutatingUse(MutatingUseContext::Store) ||
 211                                 context == PlaceContext::MutatingUse(MutatingUseContext::Drop) ||
 212                                 context == PlaceContext::MutatingUse(
 213                                     MutatingUseContext::AsmOutput
 214                                 )
 215                             {
 216                                 let elem_ty = match elem {
 217                                     &ProjectionElem::Field(_, ty) => ty,
 218                                     _ => span_bug!(
 219                                         self.source_info.span,
 220                                         "non-field projection {:?} from union?",
 221                                         place)
 222                                 };
 223                                 if elem_ty.moves_by_default(self.tcx, self.param_env,
 224                                                             self.source_info.span) {
 225                                     self.require_unsafe(
 226                                         "assignment to non-`Copy` union field",
 227                                         "the previous content of the field will be dropped, which \
 228                                          causes undefined behavior if the field was not properly \
 229                                          initialized", UnsafetyViolationKind::General)
 230                                 } else {
 231                                     // write to non-move union, safe
 232                                 }
 233                             } else {
 234                                 self.require_unsafe("access to union field",
 235                                     "the field may not be properly initialized: using \
 236                                      uninitialized data will cause undefined behavior",
 237                                      UnsafetyViolationKind::General)
 238                             }
 239                         }
 240                     }
 241                     _ => {}
 242                 }
 243                 self.source_info = old_source_info;
 244             }
 245             &Place::Local(..) => {
 246                 // locals are safe
 247             }
 248             &Place::Promoted(_) => {
 249                 bug!("unsafety checking should happen before promotion")
 250             }
 251             &Place::Static(box Static { def_id, ty: _ }) => {
 252                 if self.tcx.is_static(def_id) == Some(hir::Mutability::MutMutable) {
 253                     self.require_unsafe("use of mutable static",
 254                         "mutable statics can be mutated by multiple threads: aliasing violations \
 255                          or data races will cause undefined behavior",
 256                          UnsafetyViolationKind::General);
 257                 } else if self.tcx.is_foreign_item(def_id) {
 258                     let source_info = self.source_info;
 259                     let lint_root =
 260                         self.source_scope_local_data[source_info.scope].lint_root;
 261                     self.register_violations(&[UnsafetyViolation {
 262                         source_info,
 263                         description: Symbol::intern("use of extern static").as_interned_str(),
 264                         details:
 265                             Symbol::intern("extern statics are not controlled by the Rust type \
 266                                             system: invalid data, aliasing violations or data \
 267                                             races will cause undefined behavior")
 268                                 .as_interned_str(),
 269                         kind: UnsafetyViolationKind::ExternStatic(lint_root)
 270                     }], &[]);
 271                 }
 272             }
 273         };
 274         self.super_place(place, context, location);
 275     }
 276 }
 277
 278 impl<'a, 'tcx> UnsafetyChecker<'a, 'tcx> {
 279     fn require_unsafe(
 280         &mut self,
 281         description: &'static str,
 282         details: &'static str,
 283         kind: UnsafetyViolationKind,
 284     ) {
 285         let source_info = self.source_info;
 286         self.register_violations(&[UnsafetyViolation {
 287             source_info,
 288             description: Symbol::intern(description).as_interned_str(),
 289             details: Symbol::intern(details).as_interned_str(),
 290             kind,
 291         }], &[]);
 292     }
 293
 294     fn register_violations(&mut self,
 295                            violations: &[UnsafetyViolation],
 296                            unsafe_blocks: &[(ast::NodeId, bool)]) {
 297         let safety = self.source_scope_local_data[self.source_info.scope].safety;
 298         let within_unsafe = match (safety, self.min_const_fn) {
 299             // Erring on the safe side, pun intended
 300             (Safety::BuiltinUnsafe, true) |
 301             // mir building encodes const fn bodies as safe, even for `const unsafe fn`
 302             (Safety::FnUnsafe, true) => bug!("const unsafe fn body treated as inherently unsafe"),
 303             // `unsafe` blocks are required in safe code
 304             (Safety::Safe, _) => {
 305                 for violation in violations {
 306                     let mut violation = violation.clone();
 307                     if self.min_const_fn {
 308                         // overwrite unsafety violation in const fn with a single hard error kind
 309                         violation.kind = UnsafetyViolationKind::MinConstFn;
 310                     } else if let UnsafetyViolationKind::MinConstFn = violation.kind {
 311                         // outside of const fns we treat `MinConstFn` and `General` the same
 312                         violation.kind = UnsafetyViolationKind::General;
 313                     }
 314                     if !self.violations.contains(&violation) {
 315                         self.violations.push(violation)
 316                     }
 317                 }
 318                 false
 319             }
 320             // regular `unsafe` function bodies allow unsafe without additional unsafe blocks
 321             (Safety::BuiltinUnsafe, false) | (Safety::FnUnsafe, false) => true,
 322             (Safety::ExplicitUnsafe(node_id), _) => {
 323                 // mark unsafe block as used if there are any unsafe operations inside
 324                 if !violations.is_empty() {
 325                     self.used_unsafe.insert(node_id);
 326                 }
 327                 // only some unsafety is allowed in const fn
 328                 if self.min_const_fn {
 329                     for violation in violations {
 330                         match violation.kind {
 331                             // these are allowed
 332                             UnsafetyViolationKind::MinConstFn
 333                                 // if `#![feature(min_const_unsafe_fn)]` is active
 334                                 if self.tcx.sess.features_untracked().min_const_unsafe_fn => {},
 335                             _ => {
 336                                 let mut violation = violation.clone();
 337                                 // overwrite unsafety violation in const fn with a hard error
 338                                 violation.kind = UnsafetyViolationKind::MinConstFn;
 339                                 if !self.violations.contains(&violation) {
 340                                     self.violations.push(violation)
 341                                 }
 342                             },
 343                         }
 344                     }
 345                 }
 346                 true
 347             }
 348         };
 349         self.inherited_blocks.extend(unsafe_blocks.iter().map(|&(node_id, is_used)| {
 350             (node_id, is_used && !within_unsafe)
 351         }));
 352     }
 353 }
 354
 355 pub(crate) fn provide(providers: &mut Providers) {
 356     *providers = Providers {
 357         unsafety_check_result,
 358         unsafe_derive_on_repr_packed,
 359         ..*providers
 360     };
 361 }
 362
 363 struct UnusedUnsafeVisitor<'a> {
 364     used_unsafe: &'a FxHashSet<ast::NodeId>,
 365     unsafe_blocks: &'a mut Vec<(ast::NodeId, bool)>,
 366 }
 367
 368 impl<'a, 'tcx> hir::intravisit::Visitor<'tcx> for UnusedUnsafeVisitor<'a> {
 369     fn nested_visit_map<'this>(&'this mut self) ->
 370         hir::intravisit::NestedVisitorMap<'this, 'tcx>
 371     {
 372         hir::intravisit::NestedVisitorMap::None
 373     }
 374
 375     fn visit_block(&mut self, block: &'tcx hir::Block) {
 376         hir::intravisit::walk_block(self, block);
 377
 378         if let hir::UnsafeBlock(hir::UserProvided) = block.rules {
 379             self.unsafe_blocks.push((block.id, self.used_unsafe.contains(&block.id)));
 380         }
 381     }
 382 }
 383
 384 fn check_unused_unsafe<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
 385                                  def_id: DefId,
 386                                  used_unsafe: &FxHashSet<ast::NodeId>,
 387                                  unsafe_blocks: &'a mut Vec<(ast::NodeId, bool)>)
 388 {
 389     let body_id =
 390         tcx.hir.as_local_node_id(def_id).and_then(|node_id| {
 391             tcx.hir.maybe_body_owned_by(node_id)
 392         });
 393
 394     let body_id = match body_id {
 395         Some(body) => body,
 396         None => {
 397             debug!("check_unused_unsafe({:?}) - no body found", def_id);
 398             return
 399         }
 400     };
 401     let body = tcx.hir.body(body_id);
 402     debug!("check_unused_unsafe({:?}, body={:?}, used_unsafe={:?})",
 403            def_id, body, used_unsafe);
 404
 405     let mut visitor =  UnusedUnsafeVisitor { used_unsafe, unsafe_blocks };
 406     hir::intravisit::Visitor::visit_body(&mut visitor, body);
 407 }
 408
 409 fn unsafety_check_result<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, def_id: DefId)
 410                                    -> UnsafetyCheckResult
 411 {
 412     debug!("unsafety_violations({:?})", def_id);
 413
 414     // NB: this borrow is valid because all the consumers of
 415     // `mir_built` force this.
 416     let mir = &tcx.mir_built(def_id).borrow();
 417
 418     let source_scope_local_data = match mir.source_scope_local_data {
 419         ClearCrossCrate::Set(ref data) => data,
 420         ClearCrossCrate::Clear => {
 421             debug!("unsafety_violations: {:?} - remote, skipping", def_id);
 422             return UnsafetyCheckResult {
 423                 violations: Lrc::new([]),
 424                 unsafe_blocks: Lrc::new([])
 425             }
 426         }
 427     };
 428
 429     let param_env = tcx.param_env(def_id);
 430     let mut checker = UnsafetyChecker::new(
 431         tcx.is_const_fn(def_id) && tcx.is_min_const_fn(def_id),
 432         mir, source_scope_local_data, tcx, param_env);
 433     checker.visit_mir(mir);
 434
 435     check_unused_unsafe(tcx, def_id, &checker.used_unsafe, &mut checker.inherited_blocks);
 436     UnsafetyCheckResult {
 437         violations: checker.violations.into(),
 438         unsafe_blocks: checker.inherited_blocks.into()
 439     }
 440 }
 441
 442 fn unsafe_derive_on_repr_packed<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, def_id: DefId) {
 443     let lint_node_id = match tcx.hir.as_local_node_id(def_id) {
 444         Some(node_id) => node_id,
 445         None => bug!("checking unsafety for non-local def id {:?}", def_id)
 446     };
 447
 448     // FIXME: when we make this a hard error, this should have its
 449     // own error code.
 450     let message = if tcx.generics_of(def_id).own_counts().types != 0 {
 451         "#[derive] can't be used on a #[repr(packed)] struct with \
 452          type parameters (error E0133)".to_string()
 453     } else {
 454         "#[derive] can't be used on a #[repr(packed)] struct that \
 455          does not derive Copy (error E0133)".to_string()
 456     };
 457     tcx.lint_node(SAFE_PACKED_BORROWS,
 458                   lint_node_id,
 459                   tcx.def_span(def_id),
 460                   &message);
 461 }
 462
 463 /// Return the NodeId for an enclosing scope that is also `unsafe`
 464 fn is_enclosed(tcx: TyCtxt,
 465                used_unsafe: &FxHashSet<ast::NodeId>,
 466                id: ast::NodeId) -> Option<(String, ast::NodeId)> {
 467     let parent_id = tcx.hir.get_parent_node(id);
 468     if parent_id != id {
 469         if used_unsafe.contains(&parent_id) {
 470             Some(("block".to_string(), parent_id))
 471         } else if let Some(Node::Item(&hir::Item {
 472             node: hir::ItemKind::Fn(_, header, _, _),
 473             ..
 474         })) = tcx.hir.find(parent_id) {
 475             match header.unsafety {
 476                 hir::Unsafety::Unsafe => Some(("fn".to_string(), parent_id)),
 477                 hir::Unsafety::Normal => None,
 478             }
 479         } else {
 480             is_enclosed(tcx, used_unsafe, parent_id)
 481         }
 482     } else {
 483         None
 484     }
 485 }
 486
 487 fn report_unused_unsafe(tcx: TyCtxt, used_unsafe: &FxHashSet<ast::NodeId>, id: ast::NodeId) {
 488     let span = tcx.sess.source_map().def_span(tcx.hir.span(id));
 489     let msg = "unnecessary `unsafe` block";
 490     let mut db = tcx.struct_span_lint_node(UNUSED_UNSAFE, id, span, msg);
 491     db.span_label(span, msg);
 492     if let Some((kind, id)) = is_enclosed(tcx, used_unsafe, id) {
 493         db.span_label(tcx.sess.source_map().def_span(tcx.hir.span(id)),
 494                       format!("because it's nested under this `unsafe` {}", kind));
 495     }
 496     db.emit();
 497 }
 498
 499 fn builtin_derive_def_id<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, def_id: DefId) -> Option<DefId> {
 500     debug!("builtin_derive_def_id({:?})", def_id);
 501     if let Some(impl_def_id) = tcx.impl_of_method(def_id) {
 502         if tcx.has_attr(impl_def_id, "automatically_derived") {
 503             debug!("builtin_derive_def_id({:?}) - is {:?}", def_id, impl_def_id);
 504             Some(impl_def_id)
 505         } else {
 506             debug!("builtin_derive_def_id({:?}) - not automatically derived", def_id);
 507             None
 508         }
 509     } else {
 510         debug!("builtin_derive_def_id({:?}) - not a method", def_id);
 511         None
 512     }
 513 }
 514
 515 pub fn check_unsafety<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, def_id: DefId) {
 516     debug!("check_unsafety({:?})", def_id);
 517
 518     // closures are handled by their parent fn.
 519     if tcx.is_closure(def_id) {
 520         return;
 521     }
 522
 523     let UnsafetyCheckResult {
 524         violations,
 525         unsafe_blocks
 526     } = tcx.unsafety_check_result(def_id);
 527
 528     for &UnsafetyViolation {
 529         source_info, description, details, kind
 530     } in violations.iter() {
 531         // Report an error.
 532         match kind {
 533             UnsafetyViolationKind::General => {
 534                 struct_span_err!(
 535                     tcx.sess, source_info.span, E0133,
 536                     "{} is unsafe and requires unsafe function or block", description)
 537                     .span_label(source_info.span, &description.as_str()[..])
 538                     .note(&details.as_str()[..])
 539                     .emit();
 540             }
 541             UnsafetyViolationKind::MinConstFn => {
 542                 tcx.sess.struct_span_err(
 543                     source_info.span,
 544                     &format!("{} is unsafe and unsafe operations \
 545                             are not allowed in const fn", description))
 546                     .span_label(source_info.span, &description.as_str()[..])
 547                     .note(&details.as_str()[..])
 548                     .emit();
 549             }
 550             UnsafetyViolationKind::ExternStatic(lint_node_id) => {
 551                 tcx.lint_node_note(SAFE_EXTERN_STATICS,
 552                               lint_node_id,
 553                               source_info.span,
 554                               &format!("{} is unsafe and requires unsafe function or block \
 555                                         (error E0133)", &description.as_str()[..]),
 556                               &details.as_str()[..]);
 557             }
 558             UnsafetyViolationKind::BorrowPacked(lint_node_id) => {
 559                 if let Some(impl_def_id) = builtin_derive_def_id(tcx, def_id) {
 560                     tcx.unsafe_derive_on_repr_packed(impl_def_id);
 561                 } else {
 562                     tcx.lint_node_note(SAFE_PACKED_BORROWS,
 563                                   lint_node_id,
 564                                   source_info.span,
 565                                   &format!("{} is unsafe and requires unsafe function or block \
 566                                             (error E0133)", &description.as_str()[..]),
 567                                   &details.as_str()[..]);
 568                 }
 569             }
 570         }
 571     }
 572
 573     let mut unsafe_blocks: Vec<_> = unsafe_blocks.into_iter().collect();
 574     unsafe_blocks.sort();
 575     let used_unsafe: FxHashSet<_> = unsafe_blocks.iter()
 576         .flat_map(|&&(id, used)| if used { Some(id) } else { None })
 577         .collect();
 578     for &(block_id, is_used) in unsafe_blocks {
 579         if !is_used {
 580             report_unused_unsafe(tcx, &used_unsafe, block_id);
 581         }
 582     }
 583 }