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 use syntax::feature_gate::{emit_feature_err, GateIssue};
  27
  28 use std::ops::Bound;
  29
  30 use util;
  31
  32 pub struct UnsafetyChecker<'a, 'tcx: 'a> {
  33     mir: &'a Mir<'tcx>,
  34     min_const_fn: bool,
  35     source_scope_local_data: &'a IndexVec<SourceScope, SourceScopeLocalData>,
  36     violations: Vec<UnsafetyViolation>,
  37     source_info: SourceInfo,
  38     tcx: TyCtxt<'a, 'tcx, 'tcx>,
  39     param_env: ty::ParamEnv<'tcx>,
  40     /// mark an `unsafe` block as used, so we don't lint it
  41     used_unsafe: FxHashSet<ast::NodeId>,
  42     inherited_blocks: Vec<(ast::NodeId, bool)>,
  43 }
  44
  45 impl<'a, 'gcx, 'tcx> UnsafetyChecker<'a, 'tcx> {
  46     fn new(
  47         min_const_fn: bool,
  48         mir: &'a Mir<'tcx>,
  49         source_scope_local_data: &'a IndexVec<SourceScope, SourceScopeLocalData>,
  50         tcx: TyCtxt<'a, 'tcx, 'tcx>,
  51         param_env: ty::ParamEnv<'tcx>,
  52     ) -> Self {
  53         Self {
  54             mir,
  55             min_const_fn,
  56             source_scope_local_data,
  57             violations: vec![],
  58             source_info: SourceInfo {
  59                 span: mir.span,
  60                 scope: OUTERMOST_SOURCE_SCOPE
  61             },
  62             tcx,
  63             param_env,
  64             used_unsafe: Default::default(),
  65             inherited_blocks: vec![],
  66         }
  67     }
  68 }
  69
  70 impl<'a, 'tcx> Visitor<'tcx> for UnsafetyChecker<'a, 'tcx> {
  71     fn visit_terminator(&mut self,
  72                         block: BasicBlock,
  73                         terminator: &Terminator<'tcx>,
  74                         location: Location)
  75     {
  76         self.source_info = terminator.source_info;
  77         match terminator.kind {
  78             TerminatorKind::Goto { .. } |
  79             TerminatorKind::SwitchInt { .. } |
  80             TerminatorKind::Drop { .. } |
  81             TerminatorKind::Yield { .. } |
  82             TerminatorKind::Assert { .. } |
  83             TerminatorKind::DropAndReplace { .. } |
  84             TerminatorKind::GeneratorDrop |
  85             TerminatorKind::Resume |
  86             TerminatorKind::Abort |
  87             TerminatorKind::Return |
  88             TerminatorKind::Unreachable |
  89             TerminatorKind::FalseEdges { .. } |
  90             TerminatorKind::FalseUnwind { .. } => {
  91                 // safe (at least as emitted during MIR construction)
  92             }
  93
  94             TerminatorKind::Call { ref func, .. } => {
  95                 let func_ty = func.ty(self.mir, self.tcx);
  96                 let sig = func_ty.fn_sig(self.tcx);
  97                 if let hir::Unsafety::Unsafe = sig.unsafety() {
  98                     self.require_unsafe("call to unsafe function",
  99                         "consult the function's documentation for information on how to avoid \
 100                          undefined behavior", UnsafetyViolationKind::GatedConstFnCall)
 101                 }
 102             }
 103         }
 104         self.super_terminator(block, terminator, location);
 105     }
 106
 107     fn visit_statement(&mut self,
 108                        block: BasicBlock,
 109                        statement: &Statement<'tcx>,
 110                        location: Location)
 111     {
 112         self.source_info = statement.source_info;
 113         match statement.kind {
 114             StatementKind::Assign(..) |
 115             StatementKind::FakeRead(..) |
 116             StatementKind::SetDiscriminant { .. } |
 117             StatementKind::StorageLive(..) |
 118             StatementKind::StorageDead(..) |
 119             StatementKind::Retag { .. } |
 120             StatementKind::EscapeToRaw { .. } |
 121             StatementKind::AscribeUserType(..) |
 122             StatementKind::Nop => {
 123                 // safe (at least as emitted during MIR construction)
 124             }
 125
 126             StatementKind::InlineAsm { .. } => {
 127                 self.require_unsafe("use of inline assembly",
 128                     "inline assembly is entirely unchecked and can cause undefined behavior",
 129                     UnsafetyViolationKind::General)
 130             },
 131         }
 132         self.super_statement(block, statement, location);
 133     }
 134
 135     fn visit_rvalue(&mut self,
 136                     rvalue: &Rvalue<'tcx>,
 137                     location: Location)
 138     {
 139         if let &Rvalue::Aggregate(box ref aggregate, _) = rvalue {
 140             match aggregate {
 141                 &AggregateKind::Array(..) |
 142                 &AggregateKind::Tuple => {}
 143                 &AggregateKind::Adt(ref def, ..) => {
 144                     match self.tcx.layout_scalar_valid_range(def.did) {
 145                         (Bound::Unbounded, Bound::Unbounded) => {},
 146                         _ => self.require_unsafe(
 147                             "initializing type with `rustc_layout_scalar_valid_range` attr",
 148                             "initializing a layout restricted type's field with a value outside \
 149                             the valid range is undefined behavior",
 150                             UnsafetyViolationKind::GeneralAndConstFn,
 151                         ),
 152                     }
 153                 }
 154                 &AggregateKind::Closure(def_id, _) |
 155                 &AggregateKind::Generator(def_id, _, _) => {
 156                     let UnsafetyCheckResult {
 157                         violations, unsafe_blocks
 158                     } = self.tcx.unsafety_check_result(def_id);
 159                     self.register_violations(&violations, &unsafe_blocks);
 160                 }
 161             }
 162         }
 163         self.super_rvalue(rvalue, location);
 164     }
 165
 166     fn visit_place(&mut self,
 167                     place: &Place<'tcx>,
 168                     context: PlaceContext<'tcx>,
 169                     location: Location) {
 170         match place {
 171             &Place::Projection(box Projection {
 172                 ref base, ref elem
 173             }) => {
 174                 if context.is_borrow() {
 175                     if util::is_disaligned(self.tcx, self.mir, self.param_env, place) {
 176                         let source_info = self.source_info;
 177                         let lint_root =
 178                             self.source_scope_local_data[source_info.scope].lint_root;
 179                         self.register_violations(&[UnsafetyViolation {
 180                             source_info,
 181                             description: Symbol::intern("borrow of packed field").as_interned_str(),
 182                             details:
 183                                 Symbol::intern("fields of packed structs might be misaligned: \
 184                                                 dereferencing a misaligned pointer or even just \
 185                                                 creating a misaligned reference is undefined \
 186                                                 behavior")
 187                                     .as_interned_str(),
 188                             kind: UnsafetyViolationKind::BorrowPacked(lint_root)
 189                         }], &[]);
 190                     }
 191                 }
 192                 let is_borrow_of_interior_mut = context.is_borrow() && !base
 193                     .ty(self.mir, self.tcx)
 194                     .to_ty(self.tcx)
 195                     .is_freeze(self.tcx, self.param_env, self.source_info.span);
 196                 // prevent
 197                 // * `&mut x.field`
 198                 // * `x.field = y;`
 199                 // * `&x.field` if `field`'s type has interior mutability
 200                 // because either of these would allow modifying the layout constrained field and
 201                 // insert values that violate the layout constraints.
 202                 if context.is_mutating_use() || is_borrow_of_interior_mut {
 203                     self.check_mut_borrowing_layout_constrained_field(
 204                         place, context.is_mutating_use(),
 205                     );
 206                 }
 207                 let old_source_info = self.source_info;
 208                 if let &Place::Local(local) = base {
 209                     if self.mir.local_decls[local].internal {
 210                         // Internal locals are used in the `move_val_init` desugaring.
 211                         // We want to check unsafety against the source info of the
 212                         // desugaring, rather than the source info of the RHS.
 213                         self.source_info = self.mir.local_decls[local].source_info;
 214                     }
 215                 }
 216                 let base_ty = base.ty(self.mir, self.tcx).to_ty(self.tcx);
 217                 match base_ty.sty {
 218                     ty::RawPtr(..) => {
 219                         self.require_unsafe("dereference of raw pointer",
 220                             "raw pointers may be NULL, dangling or unaligned; they can violate \
 221                              aliasing rules and cause data races: all of these are undefined \
 222                              behavior", UnsafetyViolationKind::General)
 223                     }
 224                     ty::Adt(adt, _) => {
 225                         if adt.is_union() {
 226                             if context == PlaceContext::MutatingUse(MutatingUseContext::Store) ||
 227                                 context == PlaceContext::MutatingUse(MutatingUseContext::Drop) ||
 228                                 context == PlaceContext::MutatingUse(
 229                                     MutatingUseContext::AsmOutput
 230                                 )
 231                             {
 232                                 let elem_ty = match elem {
 233                                     &ProjectionElem::Field(_, ty) => ty,
 234                                     _ => span_bug!(
 235                                         self.source_info.span,
 236                                         "non-field projection {:?} from union?",
 237                                         place)
 238                                 };
 239                                 if elem_ty.moves_by_default(self.tcx, self.param_env,
 240                                                             self.source_info.span) {
 241                                     self.require_unsafe(
 242                                         "assignment to non-`Copy` union field",
 243                                         "the previous content of the field will be dropped, which \
 244                                          causes undefined behavior if the field was not properly \
 245                                          initialized", UnsafetyViolationKind::General)
 246                                 } else {
 247                                     // write to non-move union, safe
 248                                 }
 249                             } else {
 250                                 self.require_unsafe("access to union field",
 251                                     "the field may not be properly initialized: using \
 252                                      uninitialized data will cause undefined behavior",
 253                                      UnsafetyViolationKind::General)
 254                             }
 255                         }
 256                     }
 257                     _ => {}
 258                 }
 259                 self.source_info = old_source_info;
 260             }
 261             &Place::Local(..) => {
 262                 // locals are safe
 263             }
 264             &Place::Promoted(_) => {
 265                 bug!("unsafety checking should happen before promotion")
 266             }
 267             &Place::Static(box Static { def_id, ty: _ }) => {
 268                 if self.tcx.is_static(def_id) == Some(hir::Mutability::MutMutable) {
 269                     self.require_unsafe("use of mutable static",
 270                         "mutable statics can be mutated by multiple threads: aliasing violations \
 271                          or data races will cause undefined behavior",
 272                          UnsafetyViolationKind::General);
 273                 } else if self.tcx.is_foreign_item(def_id) {
 274                     let source_info = self.source_info;
 275                     let lint_root =
 276                         self.source_scope_local_data[source_info.scope].lint_root;
 277                     self.register_violations(&[UnsafetyViolation {
 278                         source_info,
 279                         description: Symbol::intern("use of extern static").as_interned_str(),
 280                         details:
 281                             Symbol::intern("extern statics are not controlled by the Rust type \
 282                                             system: invalid data, aliasing violations or data \
 283                                             races will cause undefined behavior")
 284                                 .as_interned_str(),
 285                         kind: UnsafetyViolationKind::ExternStatic(lint_root)
 286                     }], &[]);
 287                 }
 288             }
 289         };
 290         self.super_place(place, context, location);
 291     }
 292 }
 293
 294 impl<'a, 'tcx> UnsafetyChecker<'a, 'tcx> {
 295     fn require_unsafe(
 296         &mut self,
 297         description: &'static str,
 298         details: &'static str,
 299         kind: UnsafetyViolationKind,
 300     ) {
 301         let source_info = self.source_info;
 302         self.register_violations(&[UnsafetyViolation {
 303             source_info,
 304             description: Symbol::intern(description).as_interned_str(),
 305             details: Symbol::intern(details).as_interned_str(),
 306             kind,
 307         }], &[]);
 308     }
 309
 310     fn register_violations(&mut self,
 311                            violations: &[UnsafetyViolation],
 312                            unsafe_blocks: &[(ast::NodeId, bool)]) {
 313         let safety = self.source_scope_local_data[self.source_info.scope].safety;
 314         let within_unsafe = match (safety, self.min_const_fn) {
 315             // Erring on the safe side, pun intended
 316             (Safety::BuiltinUnsafe, true) |
 317             // mir building encodes const fn bodies as safe, even for `const unsafe fn`
 318             (Safety::FnUnsafe, true) => bug!("const unsafe fn body treated as inherently unsafe"),
 319             // `unsafe` blocks are required in safe code
 320             (Safety::Safe, _) => {
 321                 for violation in violations {
 322                     let mut violation = violation.clone();
 323                     match violation.kind {
 324                         UnsafetyViolationKind::GeneralAndConstFn |
 325                         UnsafetyViolationKind::General => {},
 326                         UnsafetyViolationKind::BorrowPacked(_) |
 327                         UnsafetyViolationKind::ExternStatic(_) => if self.min_const_fn {
 328                             // const fns don't need to be backwards compatible and can
 329                             // emit these violations as a hard error instead of a backwards
 330                             // compat lint
 331                             violation.kind = UnsafetyViolationKind::General;
 332                         },
 333                         UnsafetyViolationKind::GatedConstFnCall => {
 334                             // safe code can't call unsafe const fns, this `UnsafetyViolationKind`
 335                             // is only relevant for `Safety::ExplicitUnsafe` in `unsafe const fn`s
 336                             violation.kind = UnsafetyViolationKind::General;
 337                         }
 338                     }
 339                     if !self.violations.contains(&violation) {
 340                         self.violations.push(violation)
 341                     }
 342                 }
 343                 false
 344             }
 345             // regular `unsafe` function bodies allow unsafe without additional unsafe blocks
 346             (Safety::BuiltinUnsafe, false) | (Safety::FnUnsafe, false) => true,
 347             (Safety::ExplicitUnsafe(node_id), _) => {
 348                 // mark unsafe block as used if there are any unsafe operations inside
 349                 if !violations.is_empty() {
 350                     self.used_unsafe.insert(node_id);
 351                 }
 352                 // only some unsafety is allowed in const fn
 353                 if self.min_const_fn {
 354                     let min_const_unsafe_fn = self.tcx.features().min_const_unsafe_fn;
 355                     for violation in violations {
 356                         match violation.kind {
 357                             UnsafetyViolationKind::GatedConstFnCall if min_const_unsafe_fn => {
 358                                 // these function calls to unsafe functions are allowed
 359                                 // if `#![feature(min_const_unsafe_fn)]` is active
 360                             },
 361                             UnsafetyViolationKind::GatedConstFnCall => {
 362                                 // without the feature gate, we report errors
 363                                 if !self.violations.contains(&violation) {
 364                                     self.violations.push(violation.clone())
 365                                 }
 366                             }
 367                             // these unsafe things are stable in const fn
 368                             UnsafetyViolationKind::GeneralAndConstFn => {},
 369                             // these things are forbidden in const fns
 370                             UnsafetyViolationKind::General |
 371                             UnsafetyViolationKind::BorrowPacked(_) |
 372                             UnsafetyViolationKind::ExternStatic(_) => {
 373                                 let mut violation = violation.clone();
 374                                 // const fns don't need to be backwards compatible and can
 375                                 // emit these violations as a hard error instead of a backwards
 376                                 // compat lint
 377                                 violation.kind = UnsafetyViolationKind::General;
 378                                 if !self.violations.contains(&violation) {
 379                                     self.violations.push(violation)
 380                                 }
 381                             },
 382                         }
 383                     }
 384                 }
 385                 true
 386             }
 387         };
 388         self.inherited_blocks.extend(unsafe_blocks.iter().map(|&(node_id, is_used)| {
 389             (node_id, is_used && !within_unsafe)
 390         }));
 391     }
 392     fn check_mut_borrowing_layout_constrained_field(
 393         &mut self,
 394         mut place: &Place<'tcx>,
 395         is_mut_use: bool,
 396     ) {
 397         while let &Place::Projection(box Projection {
 398             ref base, ref elem
 399         }) = place {
 400             match *elem {
 401                 ProjectionElem::Field(..) => {
 402                     let ty = base.ty(&self.mir.local_decls, self.tcx).to_ty(self.tcx);
 403                     match ty.sty {
 404                         ty::Adt(def, _) => match self.tcx.layout_scalar_valid_range(def.did) {
 405                             (Bound::Unbounded, Bound::Unbounded) => {},
 406                             _ => {
 407                                 let (description, details) = if is_mut_use {
 408                                     (
 409                                         "mutation of layout constrained field",
 410                                         "mutating layout constrained fields cannot statically be \
 411                                         checked for valid values",
 412                                     )
 413                                 } else {
 414                                     (
 415                                         "borrow of layout constrained field with interior \
 416                                         mutability",
 417                                         "references to fields of layout constrained fields \
 418                                         lose the constraints. Coupled with interior mutability, \
 419                                         the field can be changed to invalid values",
 420                                     )
 421                                 };
 422                                 let source_info = self.source_info;
 423                                 self.register_violations(&[UnsafetyViolation {
 424                                     source_info,
 425                                     description: Symbol::intern(description).as_interned_str(),
 426                                     details: Symbol::intern(details).as_interned_str(),
 427                                     kind: UnsafetyViolationKind::GeneralAndConstFn,
 428                                 }], &[]);
 429                             }
 430                         },
 431                         _ => {}
 432                     }
 433                 }
 434                 _ => {}
 435             }
 436             place = base;
 437         }
 438     }
 439 }
 440
 441 pub(crate) fn provide(providers: &mut Providers) {
 442     *providers = Providers {
 443         unsafety_check_result,
 444         unsafe_derive_on_repr_packed,
 445         ..*providers
 446     };
 447 }
 448
 449 struct UnusedUnsafeVisitor<'a> {
 450     used_unsafe: &'a FxHashSet<ast::NodeId>,
 451     unsafe_blocks: &'a mut Vec<(ast::NodeId, bool)>,
 452 }
 453
 454 impl<'a, 'tcx> hir::intravisit::Visitor<'tcx> for UnusedUnsafeVisitor<'a> {
 455     fn nested_visit_map<'this>(&'this mut self) ->
 456         hir::intravisit::NestedVisitorMap<'this, 'tcx>
 457     {
 458         hir::intravisit::NestedVisitorMap::None
 459     }
 460
 461     fn visit_block(&mut self, block: &'tcx hir::Block) {
 462         hir::intravisit::walk_block(self, block);
 463
 464         if let hir::UnsafeBlock(hir::UserProvided) = block.rules {
 465             self.unsafe_blocks.push((block.id, self.used_unsafe.contains(&block.id)));
 466         }
 467     }
 468 }
 469
 470 fn check_unused_unsafe<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
 471                                  def_id: DefId,
 472                                  used_unsafe: &FxHashSet<ast::NodeId>,
 473                                  unsafe_blocks: &'a mut Vec<(ast::NodeId, bool)>)
 474 {
 475     let body_id =
 476         tcx.hir().as_local_node_id(def_id).and_then(|node_id| {
 477             tcx.hir().maybe_body_owned_by(node_id)
 478         });
 479
 480     let body_id = match body_id {
 481         Some(body) => body,
 482         None => {
 483             debug!("check_unused_unsafe({:?}) - no body found", def_id);
 484             return
 485         }
 486     };
 487     let body = tcx.hir().body(body_id);
 488     debug!("check_unused_unsafe({:?}, body={:?}, used_unsafe={:?})",
 489            def_id, body, used_unsafe);
 490
 491     let mut visitor =  UnusedUnsafeVisitor { used_unsafe, unsafe_blocks };
 492     hir::intravisit::Visitor::visit_body(&mut visitor, body);
 493 }
 494
 495 fn unsafety_check_result<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, def_id: DefId)
 496                                    -> UnsafetyCheckResult
 497 {
 498     debug!("unsafety_violations({:?})", def_id);
 499
 500     // NB: this borrow is valid because all the consumers of
 501     // `mir_built` force this.
 502     let mir = &tcx.mir_built(def_id).borrow();
 503
 504     let source_scope_local_data = match mir.source_scope_local_data {
 505         ClearCrossCrate::Set(ref data) => data,
 506         ClearCrossCrate::Clear => {
 507             debug!("unsafety_violations: {:?} - remote, skipping", def_id);
 508             return UnsafetyCheckResult {
 509                 violations: Lrc::new([]),
 510                 unsafe_blocks: Lrc::new([])
 511             }
 512         }
 513     };
 514
 515     let param_env = tcx.param_env(def_id);
 516     let mut checker = UnsafetyChecker::new(
 517         tcx.is_min_const_fn(def_id),
 518         mir, source_scope_local_data, tcx, param_env);
 519     checker.visit_mir(mir);
 520
 521     check_unused_unsafe(tcx, def_id, &checker.used_unsafe, &mut checker.inherited_blocks);
 522     UnsafetyCheckResult {
 523         violations: checker.violations.into(),
 524         unsafe_blocks: checker.inherited_blocks.into()
 525     }
 526 }
 527
 528 fn unsafe_derive_on_repr_packed<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, def_id: DefId) {
 529     let lint_node_id = match tcx.hir().as_local_node_id(def_id) {
 530         Some(node_id) => node_id,
 531         None => bug!("checking unsafety for non-local def id {:?}", def_id)
 532     };
 533
 534     // FIXME: when we make this a hard error, this should have its
 535     // own error code.
 536     let message = if tcx.generics_of(def_id).own_counts().types != 0 {
 537         "#[derive] can't be used on a #[repr(packed)] struct with \
 538          type parameters (error E0133)".to_string()
 539     } else {
 540         "#[derive] can't be used on a #[repr(packed)] struct that \
 541          does not derive Copy (error E0133)".to_string()
 542     };
 543     tcx.lint_node(SAFE_PACKED_BORROWS,
 544                   lint_node_id,
 545                   tcx.def_span(def_id),
 546                   &message);
 547 }
 548
 549 /// Return the NodeId for an enclosing scope that is also `unsafe`
 550 fn is_enclosed(tcx: TyCtxt,
 551                used_unsafe: &FxHashSet<ast::NodeId>,
 552                id: ast::NodeId) -> Option<(String, ast::NodeId)> {
 553     let parent_id = tcx.hir().get_parent_node(id);
 554     if parent_id != id {
 555         if used_unsafe.contains(&parent_id) {
 556             Some(("block".to_string(), parent_id))
 557         } else if let Some(Node::Item(&hir::Item {
 558             node: hir::ItemKind::Fn(_, header, _, _),
 559             ..
 560         })) = tcx.hir().find(parent_id) {
 561             match header.unsafety {
 562                 hir::Unsafety::Unsafe => Some(("fn".to_string(), parent_id)),
 563                 hir::Unsafety::Normal => None,
 564             }
 565         } else {
 566             is_enclosed(tcx, used_unsafe, parent_id)
 567         }
 568     } else {
 569         None
 570     }
 571 }
 572
 573 fn report_unused_unsafe(tcx: TyCtxt, used_unsafe: &FxHashSet<ast::NodeId>, id: ast::NodeId) {
 574     let span = tcx.sess.source_map().def_span(tcx.hir().span(id));
 575     let msg = "unnecessary `unsafe` block";
 576     let mut db = tcx.struct_span_lint_node(UNUSED_UNSAFE, id, span, msg);
 577     db.span_label(span, msg);
 578     if let Some((kind, id)) = is_enclosed(tcx, used_unsafe, id) {
 579         db.span_label(tcx.sess.source_map().def_span(tcx.hir().span(id)),
 580                       format!("because it's nested under this `unsafe` {}", kind));
 581     }
 582     db.emit();
 583 }
 584
 585 fn builtin_derive_def_id<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, def_id: DefId) -> Option<DefId> {
 586     debug!("builtin_derive_def_id({:?})", def_id);
 587     if let Some(impl_def_id) = tcx.impl_of_method(def_id) {
 588         if tcx.has_attr(impl_def_id, "automatically_derived") {
 589             debug!("builtin_derive_def_id({:?}) - is {:?}", def_id, impl_def_id);
 590             Some(impl_def_id)
 591         } else {
 592             debug!("builtin_derive_def_id({:?}) - not automatically derived", def_id);
 593             None
 594         }
 595     } else {
 596         debug!("builtin_derive_def_id({:?}) - not a method", def_id);
 597         None
 598     }
 599 }
 600
 601 pub fn check_unsafety<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, def_id: DefId) {
 602     debug!("check_unsafety({:?})", def_id);
 603
 604     // closures are handled by their parent fn.
 605     if tcx.is_closure(def_id) {
 606         return;
 607     }
 608
 609     let UnsafetyCheckResult {
 610         violations,
 611         unsafe_blocks
 612     } = tcx.unsafety_check_result(def_id);
 613
 614     for &UnsafetyViolation {
 615         source_info, description, details, kind
 616     } in violations.iter() {
 617         // Report an error.
 618         match kind {
 619             UnsafetyViolationKind::General if tcx.is_min_const_fn(def_id) => {
 620                 let mut err = tcx.sess.struct_span_err(
 621                     source_info.span,
 622                     &format!("{} is unsafe and unsafe operations \
 623                             are not allowed in const fn", description));
 624                 err.span_label(source_info.span, &description.as_str()[..])
 625                     .note(&details.as_str()[..]);
 626                 if tcx.fn_sig(def_id).unsafety() == hir::Unsafety::Unsafe {
 627                     err.note(
 628                         "unsafe action within a `const unsafe fn` still require an `unsafe` \
 629                         block in contrast to regular `unsafe fn`."
 630                     );
 631                 }
 632                 err.emit();
 633             }
 634             UnsafetyViolationKind::GeneralAndConstFn |
 635             UnsafetyViolationKind::General => {
 636                 struct_span_err!(
 637                     tcx.sess, source_info.span, E0133,
 638                     "{} is unsafe and requires unsafe function or block", description)
 639                     .span_label(source_info.span, &description.as_str()[..])
 640                     .note(&details.as_str()[..])
 641                     .emit();
 642             }
 643             UnsafetyViolationKind::GatedConstFnCall => {
 644                 emit_feature_err(
 645                     &tcx.sess.parse_sess,
 646                     "min_const_unsafe_fn",
 647                     source_info.span,
 648                     GateIssue::Language,
 649                     "calls to `const unsafe fn` in const fns are unstable",
 650                 );
 651
 652             }
 653             UnsafetyViolationKind::ExternStatic(lint_node_id) => {
 654                 tcx.lint_node_note(SAFE_EXTERN_STATICS,
 655                               lint_node_id,
 656                               source_info.span,
 657                               &format!("{} is unsafe and requires unsafe function or block \
 658                                         (error E0133)", &description.as_str()[..]),
 659                               &details.as_str()[..]);
 660             }
 661             UnsafetyViolationKind::BorrowPacked(lint_node_id) => {
 662                 if let Some(impl_def_id) = builtin_derive_def_id(tcx, def_id) {
 663                     tcx.unsafe_derive_on_repr_packed(impl_def_id);
 664                 } else {
 665                     tcx.lint_node_note(SAFE_PACKED_BORROWS,
 666                                   lint_node_id,
 667                                   source_info.span,
 668                                   &format!("{} is unsafe and requires unsafe function or block \
 669                                             (error E0133)", &description.as_str()[..]),
 670                                   &details.as_str()[..]);
 671                 }
 672             }
 673         }
 674     }
 675
 676     let mut unsafe_blocks: Vec<_> = unsafe_blocks.into_iter().collect();
 677     unsafe_blocks.sort();
 678     let used_unsafe: FxHashSet<_> = unsafe_blocks.iter()
 679         .flat_map(|&&(id, used)| if used { Some(id) } else { None })
 680         .collect();
 681     for &(block_id, is_used) in unsafe_blocks {
 682         if !is_used {
 683             report_unused_unsafe(tcx, &used_unsafe, block_id);
 684         }
 685     }
 686 }