compiler/rustc_mir_build/src/check_unsafety.rs

   1 use crate::build::ExprCategory;
   2 use rustc_middle::thir::visit::{self, Visitor};
   3
   4 use rustc_errors::struct_span_err;
   5 use rustc_hir as hir;
   6 use rustc_middle::mir::BorrowKind;
   7 use rustc_middle::thir::*;
   8 use rustc_middle::ty::{self, ParamEnv, Ty, TyCtxt};
   9 use rustc_session::lint::builtin::{UNSAFE_OP_IN_UNSAFE_FN, UNUSED_UNSAFE};
  10 use rustc_session::lint::Level;
  11 use rustc_span::def_id::{DefId, LocalDefId};
  12 use rustc_span::symbol::Symbol;
  13 use rustc_span::Span;
  14
  15 use std::borrow::Cow;
  16 use std::ops::Bound;
  17
  18 struct UnsafetyVisitor<'a, 'tcx> {
  19     tcx: TyCtxt<'tcx>,
  20     thir: &'a Thir<'tcx>,
  21     /// The `HirId` of the current scope, which would be the `HirId`
  22     /// of the current HIR node, modulo adjustments. Used for lint levels.
  23     hir_context: hir::HirId,
  24     /// The current "safety context". This notably tracks whether we are in an
  25     /// `unsafe` block, and whether it has been used.
  26     safety_context: SafetyContext,
  27     body_unsafety: BodyUnsafety,
  28     /// The `#[target_feature]` attributes of the body. Used for checking
  29     /// calls to functions with `#[target_feature]` (RFC 2396).
  30     body_target_features: &'tcx [Symbol],
  31     /// When inside the LHS of an assignment to a field, this is the type
  32     /// of the LHS and the span of the assignment expression.
  33     assignment_info: Option<(Ty<'tcx>, Span)>,
  34     in_union_destructure: bool,
  35     param_env: ParamEnv<'tcx>,
  36     inside_adt: bool,
  37 }
  38
  39 impl<'tcx> UnsafetyVisitor<'_, 'tcx> {
  40     fn in_safety_context(&mut self, safety_context: SafetyContext, f: impl FnOnce(&mut Self)) {
  41         if let (
  42             SafetyContext::UnsafeBlock { span: enclosing_span, .. },
  43             SafetyContext::UnsafeBlock { span: block_span, hir_id, .. },
  44         ) = (self.safety_context, safety_context)
  45         {
  46             self.warn_unused_unsafe(
  47                 hir_id,
  48                 block_span,
  49                 Some((self.tcx.sess.source_map().guess_head_span(enclosing_span), "block")),
  50             );
  51             f(self);
  52         } else {
  53             let prev_context = self.safety_context;
  54             self.safety_context = safety_context;
  55
  56             f(self);
  57
  58             if let SafetyContext::UnsafeBlock { used: false, span, hir_id } = self.safety_context {
  59                 self.warn_unused_unsafe(
  60                     hir_id,
  61                     span,
  62                     if self.unsafe_op_in_unsafe_fn_allowed() {
  63                         self.body_unsafety.unsafe_fn_sig_span().map(|span| (span, "fn"))
  64                     } else {
  65                         None
  66                     },
  67                 );
  68             }
  69             self.safety_context = prev_context;
  70         }
  71     }
  72
  73     fn requires_unsafe(&mut self, span: Span, kind: UnsafeOpKind) {
  74         let unsafe_op_in_unsafe_fn_allowed = self.unsafe_op_in_unsafe_fn_allowed();
  75         match self.safety_context {
  76             SafetyContext::BuiltinUnsafeBlock => {}
  77             SafetyContext::UnsafeBlock { ref mut used, .. } => {
  78                 // Mark this block as useful (even inside `unsafe fn`, where it is technically
  79                 // redundant -- but we want to eventually enable `unsafe_op_in_unsafe_fn` by
  80                 // default which will require those blocks:
  81                 // https://github.com/rust-lang/rust/issues/71668#issuecomment-1203075594).
  82                 *used = true;
  83             }
  84             SafetyContext::UnsafeFn if unsafe_op_in_unsafe_fn_allowed => {}
  85             SafetyContext::UnsafeFn => {
  86                 let (description, note) = kind.description_and_note(self.tcx);
  87                 // unsafe_op_in_unsafe_fn is disallowed
  88                 self.tcx.struct_span_lint_hir(
  89                     UNSAFE_OP_IN_UNSAFE_FN,
  90                     self.hir_context,
  91                     span,
  92                     format!("{} is unsafe and requires unsafe block (error E0133)", description,),
  93                     |lint| lint.span_label(span, kind.simple_description()).note(note),
  94                 )
  95             }
  96             SafetyContext::Safe => {
  97                 let (description, note) = kind.description_and_note(self.tcx);
  98                 let fn_sugg = if unsafe_op_in_unsafe_fn_allowed { " function or" } else { "" };
  99                 struct_span_err!(
 100                     self.tcx.sess,
 101                     span,
 102                     E0133,
 103                     "{} is unsafe and requires unsafe{} block",
 104                     description,
 105                     fn_sugg,
 106                 )
 107                 .span_label(span, kind.simple_description())
 108                 .note(note)
 109                 .emit();
 110             }
 111         }
 112     }
 113
 114     fn warn_unused_unsafe(
 115         &self,
 116         hir_id: hir::HirId,
 117         block_span: Span,
 118         enclosing_unsafe: Option<(Span, &'static str)>,
 119     ) {
 120         let block_span = self.tcx.sess.source_map().guess_head_span(block_span);
 121         let msg = "unnecessary `unsafe` block";
 122         self.tcx.struct_span_lint_hir(UNUSED_UNSAFE, hir_id, block_span, msg, |lint| {
 123             lint.span_label(block_span, msg);
 124             if let Some((span, kind)) = enclosing_unsafe {
 125                 lint.span_label(span, format!("because it's nested under this `unsafe` {}", kind));
 126             }
 127             lint
 128         });
 129     }
 130
 131     /// Whether the `unsafe_op_in_unsafe_fn` lint is `allow`ed at the current HIR node.
 132     fn unsafe_op_in_unsafe_fn_allowed(&self) -> bool {
 133         self.tcx.lint_level_at_node(UNSAFE_OP_IN_UNSAFE_FN, self.hir_context).0 == Level::Allow
 134     }
 135 }
 136
 137 // Searches for accesses to layout constrained fields.
 138 struct LayoutConstrainedPlaceVisitor<'a, 'tcx> {
 139     found: bool,
 140     thir: &'a Thir<'tcx>,
 141     tcx: TyCtxt<'tcx>,
 142 }
 143
 144 impl<'a, 'tcx> LayoutConstrainedPlaceVisitor<'a, 'tcx> {
 145     fn new(thir: &'a Thir<'tcx>, tcx: TyCtxt<'tcx>) -> Self {
 146         Self { found: false, thir, tcx }
 147     }
 148 }
 149
 150 impl<'a, 'tcx> Visitor<'a, 'tcx> for LayoutConstrainedPlaceVisitor<'a, 'tcx> {
 151     fn thir(&self) -> &'a Thir<'tcx> {
 152         self.thir
 153     }
 154
 155     fn visit_expr(&mut self, expr: &Expr<'tcx>) {
 156         match expr.kind {
 157             ExprKind::Field { lhs, .. } => {
 158                 if let ty::Adt(adt_def, _) = self.thir[lhs].ty.kind() {
 159                     if (Bound::Unbounded, Bound::Unbounded)
 160                         != self.tcx.layout_scalar_valid_range(adt_def.did())
 161                     {
 162                         self.found = true;
 163                     }
 164                 }
 165                 visit::walk_expr(self, expr);
 166             }
 167
 168             // Keep walking through the expression as long as we stay in the same
 169             // place, i.e. the expression is a place expression and not a dereference
 170             // (since dereferencing something leads us to a different place).
 171             ExprKind::Deref { .. } => {}
 172             ref kind if ExprCategory::of(kind).map_or(true, |cat| cat == ExprCategory::Place) => {
 173                 visit::walk_expr(self, expr);
 174             }
 175
 176             _ => {}
 177         }
 178     }
 179 }
 180
 181 impl<'a, 'tcx> Visitor<'a, 'tcx> for UnsafetyVisitor<'a, 'tcx> {
 182     fn thir(&self) -> &'a Thir<'tcx> {
 183         &self.thir
 184     }
 185
 186     fn visit_block(&mut self, block: &Block) {
 187         match block.safety_mode {
 188             // compiler-generated unsafe code should not count towards the usefulness of
 189             // an outer unsafe block
 190             BlockSafety::BuiltinUnsafe => {
 191                 self.in_safety_context(SafetyContext::BuiltinUnsafeBlock, |this| {
 192                     visit::walk_block(this, block)
 193                 });
 194             }
 195             BlockSafety::ExplicitUnsafe(hir_id) => {
 196                 self.in_safety_context(
 197                     SafetyContext::UnsafeBlock { span: block.span, hir_id, used: false },
 198                     |this| visit::walk_block(this, block),
 199                 );
 200             }
 201             BlockSafety::Safe => {
 202                 visit::walk_block(self, block);
 203             }
 204         }
 205     }
 206
 207     fn visit_pat(&mut self, pat: &Pat<'tcx>) {
 208         if self.in_union_destructure {
 209             match pat.kind {
 210                 // binding to a variable allows getting stuff out of variable
 211                 PatKind::Binding { .. }
 212                 // match is conditional on having this value
 213                 | PatKind::Constant { .. }
 214                 | PatKind::Variant { .. }
 215                 | PatKind::Leaf { .. }
 216                 | PatKind::Deref { .. }
 217                 | PatKind::Range { .. }
 218                 | PatKind::Slice { .. }
 219                 | PatKind::Array { .. } => {
 220                     self.requires_unsafe(pat.span, AccessToUnionField);
 221                     return; // we can return here since this already requires unsafe
 222                 }
 223                 // wildcard doesn't take anything
 224                 PatKind::Wild |
 225                 // these just wrap other patterns
 226                 PatKind::Or { .. } |
 227                 PatKind::AscribeUserType { .. } => {}
 228             }
 229         };
 230
 231         match &pat.kind {
 232             PatKind::Leaf { .. } => {
 233                 if let ty::Adt(adt_def, ..) = pat.ty.kind() {
 234                     if adt_def.is_union() {
 235                         let old_in_union_destructure =
 236                             std::mem::replace(&mut self.in_union_destructure, true);
 237                         visit::walk_pat(self, pat);
 238                         self.in_union_destructure = old_in_union_destructure;
 239                     } else if (Bound::Unbounded, Bound::Unbounded)
 240                         != self.tcx.layout_scalar_valid_range(adt_def.did())
 241                     {
 242                         let old_inside_adt = std::mem::replace(&mut self.inside_adt, true);
 243                         visit::walk_pat(self, pat);
 244                         self.inside_adt = old_inside_adt;
 245                     } else {
 246                         visit::walk_pat(self, pat);
 247                     }
 248                 } else {
 249                     visit::walk_pat(self, pat);
 250                 }
 251             }
 252             PatKind::Binding { mode: BindingMode::ByRef(borrow_kind), ty, .. } => {
 253                 if self.inside_adt {
 254                     let ty::Ref(_, ty, _) = ty.kind() else {
 255                         span_bug!(
 256                             pat.span,
 257                             "BindingMode::ByRef in pattern, but found non-reference type {}",
 258                             ty
 259                         );
 260                     };
 261                     match borrow_kind {
 262                         BorrowKind::Shallow | BorrowKind::Shared | BorrowKind::Unique => {
 263                             if !ty.is_freeze(self.tcx, self.param_env) {
 264                                 self.requires_unsafe(pat.span, BorrowOfLayoutConstrainedField);
 265                             }
 266                         }
 267                         BorrowKind::Mut { .. } => {
 268                             self.requires_unsafe(pat.span, MutationOfLayoutConstrainedField);
 269                         }
 270                     }
 271                 }
 272                 visit::walk_pat(self, pat);
 273             }
 274             PatKind::Deref { .. } => {
 275                 let old_inside_adt = std::mem::replace(&mut self.inside_adt, false);
 276                 visit::walk_pat(self, pat);
 277                 self.inside_adt = old_inside_adt;
 278             }
 279             _ => {
 280                 visit::walk_pat(self, pat);
 281             }
 282         }
 283     }
 284
 285     fn visit_expr(&mut self, expr: &Expr<'tcx>) {
 286         // could we be in the LHS of an assignment to a field?
 287         match expr.kind {
 288             ExprKind::Field { .. }
 289             | ExprKind::VarRef { .. }
 290             | ExprKind::UpvarRef { .. }
 291             | ExprKind::Scope { .. }
 292             | ExprKind::Cast { .. } => {}
 293
 294             ExprKind::AddressOf { .. }
 295             | ExprKind::Adt { .. }
 296             | ExprKind::Array { .. }
 297             | ExprKind::Binary { .. }
 298             | ExprKind::Block { .. }
 299             | ExprKind::Borrow { .. }
 300             | ExprKind::Literal { .. }
 301             | ExprKind::NamedConst { .. }
 302             | ExprKind::NonHirLiteral { .. }
 303             | ExprKind::ZstLiteral { .. }
 304             | ExprKind::ConstParam { .. }
 305             | ExprKind::ConstBlock { .. }
 306             | ExprKind::Deref { .. }
 307             | ExprKind::Index { .. }
 308             | ExprKind::NeverToAny { .. }
 309             | ExprKind::PlaceTypeAscription { .. }
 310             | ExprKind::ValueTypeAscription { .. }
 311             | ExprKind::Pointer { .. }
 312             | ExprKind::Repeat { .. }
 313             | ExprKind::StaticRef { .. }
 314             | ExprKind::ThreadLocalRef { .. }
 315             | ExprKind::Tuple { .. }
 316             | ExprKind::Unary { .. }
 317             | ExprKind::Call { .. }
 318             | ExprKind::Assign { .. }
 319             | ExprKind::AssignOp { .. }
 320             | ExprKind::Break { .. }
 321             | ExprKind::Closure { .. }
 322             | ExprKind::Continue { .. }
 323             | ExprKind::Return { .. }
 324             | ExprKind::Yield { .. }
 325             | ExprKind::Loop { .. }
 326             | ExprKind::Let { .. }
 327             | ExprKind::Match { .. }
 328             | ExprKind::Box { .. }
 329             | ExprKind::If { .. }
 330             | ExprKind::InlineAsm { .. }
 331             | ExprKind::LogicalOp { .. }
 332             | ExprKind::Use { .. } => {
 333                 // We don't need to save the old value and restore it
 334                 // because all the place expressions can't have more
 335                 // than one child.
 336                 self.assignment_info = None;
 337             }
 338         };
 339         match expr.kind {
 340             ExprKind::Scope { value, lint_level: LintLevel::Explicit(hir_id), region_scope: _ } => {
 341                 let prev_id = self.hir_context;
 342                 self.hir_context = hir_id;
 343                 self.visit_expr(&self.thir[value]);
 344                 self.hir_context = prev_id;
 345                 return; // don't visit the whole expression
 346             }
 347             ExprKind::Call { fun, ty: _, args: _, from_hir_call: _, fn_span: _ } => {
 348                 if self.thir[fun].ty.fn_sig(self.tcx).unsafety() == hir::Unsafety::Unsafe {
 349                     let func_id = if let ty::FnDef(func_id, _) = self.thir[fun].ty.kind() {
 350                         Some(*func_id)
 351                     } else {
 352                         None
 353                     };
 354                     self.requires_unsafe(expr.span, CallToUnsafeFunction(func_id));
 355                 } else if let &ty::FnDef(func_did, _) = self.thir[fun].ty.kind() {
 356                     // If the called function has target features the calling function hasn't,
 357                     // the call requires `unsafe`. Don't check this on wasm
 358                     // targets, though. For more information on wasm see the
 359                     // is_like_wasm check in hir_analysis/src/collect.rs
 360                     if !self.tcx.sess.target.options.is_like_wasm
 361                         && !self
 362                             .tcx
 363                             .codegen_fn_attrs(func_did)
 364                             .target_features
 365                             .iter()
 366                             .all(|feature| self.body_target_features.contains(feature))
 367                     {
 368                         self.requires_unsafe(expr.span, CallToFunctionWith(func_did));
 369                     }
 370                 }
 371             }
 372             ExprKind::Deref { arg } => {
 373                 if let ExprKind::StaticRef { def_id, .. } = self.thir[arg].kind {
 374                     if self.tcx.is_mutable_static(def_id) {
 375                         self.requires_unsafe(expr.span, UseOfMutableStatic);
 376                     } else if self.tcx.is_foreign_item(def_id) {
 377                         self.requires_unsafe(expr.span, UseOfExternStatic);
 378                     }
 379                 } else if self.thir[arg].ty.is_unsafe_ptr() {
 380                     self.requires_unsafe(expr.span, DerefOfRawPointer);
 381                 }
 382             }
 383             ExprKind::InlineAsm { .. } => {
 384                 self.requires_unsafe(expr.span, UseOfInlineAssembly);
 385             }
 386             ExprKind::Adt(box AdtExpr {
 387                 adt_def,
 388                 variant_index: _,
 389                 substs: _,
 390                 user_ty: _,
 391                 fields: _,
 392                 base: _,
 393             }) => match self.tcx.layout_scalar_valid_range(adt_def.did()) {
 394                 (Bound::Unbounded, Bound::Unbounded) => {}
 395                 _ => self.requires_unsafe(expr.span, InitializingTypeWith),
 396             },
 397             ExprKind::Closure(box ClosureExpr {
 398                 closure_id,
 399                 substs: _,
 400                 upvars: _,
 401                 movability: _,
 402                 fake_reads: _,
 403             }) => {
 404                 let closure_def = if let Some((did, const_param_id)) =
 405                     ty::WithOptConstParam::try_lookup(closure_id, self.tcx)
 406                 {
 407                     ty::WithOptConstParam { did, const_param_did: Some(const_param_id) }
 408                 } else {
 409                     ty::WithOptConstParam::unknown(closure_id)
 410                 };
 411                 let (closure_thir, expr) = self.tcx.thir_body(closure_def).unwrap_or_else(|_| {
 412                     (self.tcx.alloc_steal_thir(Thir::new()), ExprId::from_u32(0))
 413                 });
 414                 let closure_thir = &closure_thir.borrow();
 415                 let hir_context = self.tcx.hir().local_def_id_to_hir_id(closure_id);
 416                 let mut closure_visitor =
 417                     UnsafetyVisitor { thir: closure_thir, hir_context, ..*self };
 418                 closure_visitor.visit_expr(&closure_thir[expr]);
 419                 // Unsafe blocks can be used in closures, make sure to take it into account
 420                 self.safety_context = closure_visitor.safety_context;
 421             }
 422             ExprKind::Field { lhs, .. } => {
 423                 let lhs = &self.thir[lhs];
 424                 if let ty::Adt(adt_def, _) = lhs.ty.kind() && adt_def.is_union() {
 425                     if let Some((assigned_ty, assignment_span)) = self.assignment_info {
 426                         if assigned_ty.needs_drop(self.tcx, self.param_env) {
 427                             // This would be unsafe, but should be outright impossible since we reject such unions.
 428                             self.tcx.sess.delay_span_bug(assignment_span, format!("union fields that need dropping should be impossible: {assigned_ty}"));
 429                         }
 430                     } else {
 431                         self.requires_unsafe(expr.span, AccessToUnionField);
 432                     }
 433                 }
 434             }
 435             ExprKind::Assign { lhs, rhs } | ExprKind::AssignOp { lhs, rhs, .. } => {
 436                 let lhs = &self.thir[lhs];
 437                 // First, check whether we are mutating a layout constrained field
 438                 let mut visitor = LayoutConstrainedPlaceVisitor::new(self.thir, self.tcx);
 439                 visit::walk_expr(&mut visitor, lhs);
 440                 if visitor.found {
 441                     self.requires_unsafe(expr.span, MutationOfLayoutConstrainedField);
 442                 }
 443
 444                 // Second, check for accesses to union fields
 445                 // don't have any special handling for AssignOp since it causes a read *and* write to lhs
 446                 if matches!(expr.kind, ExprKind::Assign { .. }) {
 447                     self.assignment_info = Some((lhs.ty, expr.span));
 448                     visit::walk_expr(self, lhs);
 449                     self.assignment_info = None;
 450                     visit::walk_expr(self, &self.thir()[rhs]);
 451                     return; // we have already visited everything by now
 452                 }
 453             }
 454             ExprKind::Borrow { borrow_kind, arg } => {
 455                 let mut visitor = LayoutConstrainedPlaceVisitor::new(self.thir, self.tcx);
 456                 visit::walk_expr(&mut visitor, expr);
 457                 if visitor.found {
 458                     match borrow_kind {
 459                         BorrowKind::Shallow | BorrowKind::Shared | BorrowKind::Unique
 460                             if !self.thir[arg].ty.is_freeze(self.tcx, self.param_env) =>
 461                         {
 462                             self.requires_unsafe(expr.span, BorrowOfLayoutConstrainedField)
 463                         }
 464                         BorrowKind::Mut { .. } => {
 465                             self.requires_unsafe(expr.span, MutationOfLayoutConstrainedField)
 466                         }
 467                         BorrowKind::Shallow | BorrowKind::Shared | BorrowKind::Unique => {}
 468                     }
 469                 }
 470             }
 471             ExprKind::Let { expr: expr_id, .. } => {
 472                 let let_expr = &self.thir[expr_id];
 473                 if let ty::Adt(adt_def, _) = let_expr.ty.kind() && adt_def.is_union() {
 474                     self.requires_unsafe(expr.span, AccessToUnionField);
 475                 }
 476             }
 477             _ => {}
 478         }
 479         visit::walk_expr(self, expr);
 480     }
 481 }
 482
 483 #[derive(Clone, Copy)]
 484 enum SafetyContext {
 485     Safe,
 486     BuiltinUnsafeBlock,
 487     UnsafeFn,
 488     UnsafeBlock { span: Span, hir_id: hir::HirId, used: bool },
 489 }
 490
 491 #[derive(Clone, Copy)]
 492 enum BodyUnsafety {
 493     /// The body is not unsafe.
 494     Safe,
 495     /// The body is an unsafe function. The span points to
 496     /// the signature of the function.
 497     Unsafe(Span),
 498 }
 499
 500 impl BodyUnsafety {
 501     /// Returns whether the body is unsafe.
 502     fn is_unsafe(&self) -> bool {
 503         matches!(self, BodyUnsafety::Unsafe(_))
 504     }
 505
 506     /// If the body is unsafe, returns the `Span` of its signature.
 507     fn unsafe_fn_sig_span(self) -> Option<Span> {
 508         match self {
 509             BodyUnsafety::Unsafe(span) => Some(span),
 510             BodyUnsafety::Safe => None,
 511         }
 512     }
 513 }
 514
 515 #[derive(Clone, Copy, PartialEq)]
 516 enum UnsafeOpKind {
 517     CallToUnsafeFunction(Option<DefId>),
 518     UseOfInlineAssembly,
 519     InitializingTypeWith,
 520     UseOfMutableStatic,
 521     UseOfExternStatic,
 522     DerefOfRawPointer,
 523     AccessToUnionField,
 524     MutationOfLayoutConstrainedField,
 525     BorrowOfLayoutConstrainedField,
 526     CallToFunctionWith(DefId),
 527 }
 528
 529 use UnsafeOpKind::*;
 530
 531 impl UnsafeOpKind {
 532     pub fn simple_description(&self) -> &'static str {
 533         match self {
 534             CallToUnsafeFunction(..) => "call to unsafe function",
 535             UseOfInlineAssembly => "use of inline assembly",
 536             InitializingTypeWith => "initializing type with `rustc_layout_scalar_valid_range` attr",
 537             UseOfMutableStatic => "use of mutable static",
 538             UseOfExternStatic => "use of extern static",
 539             DerefOfRawPointer => "dereference of raw pointer",
 540             AccessToUnionField => "access to union field",
 541             MutationOfLayoutConstrainedField => "mutation of layout constrained field",
 542             BorrowOfLayoutConstrainedField => {
 543                 "borrow of layout constrained field with interior mutability"
 544             }
 545             CallToFunctionWith(..) => "call to function with `#[target_feature]`",
 546         }
 547     }
 548
 549     pub fn description_and_note(&self, tcx: TyCtxt<'_>) -> (Cow<'static, str>, &'static str) {
 550         match self {
 551             CallToUnsafeFunction(did) => (
 552                 if let Some(did) = did {
 553                     Cow::from(format!("call to unsafe function `{}`", tcx.def_path_str(*did)))
 554                 } else {
 555                     Cow::Borrowed(self.simple_description())
 556                 },
 557                 "consult the function's documentation for information on how to avoid undefined \
 558                  behavior",
 559             ),
 560             UseOfInlineAssembly => (
 561                 Cow::Borrowed(self.simple_description()),
 562                 "inline assembly is entirely unchecked and can cause undefined behavior",
 563             ),
 564             InitializingTypeWith => (
 565                 Cow::Borrowed(self.simple_description()),
 566                 "initializing a layout restricted type's field with a value outside the valid \
 567                  range is undefined behavior",
 568             ),
 569             UseOfMutableStatic => (
 570                 Cow::Borrowed(self.simple_description()),
 571                 "mutable statics can be mutated by multiple threads: aliasing violations or data \
 572                  races will cause undefined behavior",
 573             ),
 574             UseOfExternStatic => (
 575                 Cow::Borrowed(self.simple_description()),
 576                 "extern statics are not controlled by the Rust type system: invalid data, \
 577                  aliasing violations or data races will cause undefined behavior",
 578             ),
 579             DerefOfRawPointer => (
 580                 Cow::Borrowed(self.simple_description()),
 581                 "raw pointers may be null, dangling or unaligned; they can violate aliasing rules \
 582                  and cause data races: all of these are undefined behavior",
 583             ),
 584             AccessToUnionField => (
 585                 Cow::Borrowed(self.simple_description()),
 586                 "the field may not be properly initialized: using uninitialized data will cause \
 587                  undefined behavior",
 588             ),
 589             MutationOfLayoutConstrainedField => (
 590                 Cow::Borrowed(self.simple_description()),
 591                 "mutating layout constrained fields cannot statically be checked for valid values",
 592             ),
 593             BorrowOfLayoutConstrainedField => (
 594                 Cow::Borrowed(self.simple_description()),
 595                 "references to fields of layout constrained fields lose the constraints. Coupled \
 596                  with interior mutability, the field can be changed to invalid values",
 597             ),
 598             CallToFunctionWith(did) => (
 599                 Cow::from(format!(
 600                     "call to function `{}` with `#[target_feature]`",
 601                     tcx.def_path_str(*did)
 602                 )),
 603                 "can only be called if the required target features are available",
 604             ),
 605         }
 606     }
 607 }
 608
 609 pub fn check_unsafety<'tcx>(tcx: TyCtxt<'tcx>, def: ty::WithOptConstParam<LocalDefId>) {
 610     // THIR unsafeck is gated under `-Z thir-unsafeck`
 611     if !tcx.sess.opts.unstable_opts.thir_unsafeck {
 612         return;
 613     }
 614
 615     // Closures are handled by their owner, if it has a body
 616     if tcx.is_closure(def.did.to_def_id()) {
 617         let hir = tcx.hir();
 618         let owner = hir.enclosing_body_owner(hir.local_def_id_to_hir_id(def.did));
 619         tcx.ensure().thir_check_unsafety(owner);
 620         return;
 621     }
 622
 623     let Ok((thir, expr)) = tcx.thir_body(def) else {
 624         return
 625     };
 626     let thir = &thir.borrow();
 627     // If `thir` is empty, a type error occurred, skip this body.
 628     if thir.exprs.is_empty() {
 629         return;
 630     }
 631
 632     let hir_id = tcx.hir().local_def_id_to_hir_id(def.did);
 633     let body_unsafety = tcx.hir().fn_sig_by_hir_id(hir_id).map_or(BodyUnsafety::Safe, |fn_sig| {
 634         if fn_sig.header.unsafety == hir::Unsafety::Unsafe {
 635             BodyUnsafety::Unsafe(fn_sig.span)
 636         } else {
 637             BodyUnsafety::Safe
 638         }
 639     });
 640     let body_target_features = &tcx.body_codegen_attrs(def.did.to_def_id()).target_features;
 641     let safety_context =
 642         if body_unsafety.is_unsafe() { SafetyContext::UnsafeFn } else { SafetyContext::Safe };
 643     let mut visitor = UnsafetyVisitor {
 644         tcx,
 645         thir,
 646         safety_context,
 647         hir_context: hir_id,
 648         body_unsafety,
 649         body_target_features,
 650         assignment_info: None,
 651         in_union_destructure: false,
 652         param_env: tcx.param_env(def.did),
 653         inside_adt: false,
 654     };
 655     visitor.visit_expr(&thir[expr]);
 656 }
 657
 658 pub(crate) fn thir_check_unsafety<'tcx>(tcx: TyCtxt<'tcx>, def_id: LocalDefId) {
 659     if let Some(def) = ty::WithOptConstParam::try_lookup(def_id, tcx) {
 660         tcx.thir_check_unsafety_for_const_arg(def)
 661     } else {
 662         check_unsafety(tcx, ty::WithOptConstParam::unknown(def_id))
 663     }
 664 }
 665
 666 pub(crate) fn thir_check_unsafety_for_const_arg<'tcx>(
 667     tcx: TyCtxt<'tcx>,
 668     (did, param_did): (LocalDefId, DefId),
 669 ) {
 670     check_unsafety(tcx, ty::WithOptConstParam { did, const_param_did: Some(param_did) })
 671 }