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                     |lint| {
  93                         lint.build(&format!(
  94                             "{} is unsafe and requires unsafe block (error E0133)",
  95                             description,
  96                         ))
  97                         .span_label(span, kind.simple_description())
  98                         .note(note)
  99                         .emit();
 100                     },
 101                 )
 102             }
 103             SafetyContext::Safe => {
 104                 let (description, note) = kind.description_and_note(self.tcx);
 105                 let fn_sugg = if unsafe_op_in_unsafe_fn_allowed { " function or" } else { "" };
 106                 struct_span_err!(
 107                     self.tcx.sess,
 108                     span,
 109                     E0133,
 110                     "{} is unsafe and requires unsafe{} block",
 111                     description,
 112                     fn_sugg,
 113                 )
 114                 .span_label(span, kind.simple_description())
 115                 .note(note)
 116                 .emit();
 117             }
 118         }
 119     }
 120
 121     fn warn_unused_unsafe(
 122         &self,
 123         hir_id: hir::HirId,
 124         block_span: Span,
 125         enclosing_unsafe: Option<(Span, &'static str)>,
 126     ) {
 127         let block_span = self.tcx.sess.source_map().guess_head_span(block_span);
 128         self.tcx.struct_span_lint_hir(UNUSED_UNSAFE, hir_id, block_span, |lint| {
 129             let msg = "unnecessary `unsafe` block";
 130             let mut db = lint.build(msg);
 131             db.span_label(block_span, msg);
 132             if let Some((span, kind)) = enclosing_unsafe {
 133                 db.span_label(span, format!("because it's nested under this `unsafe` {}", kind));
 134             }
 135             db.emit();
 136         });
 137     }
 138
 139     /// Whether the `unsafe_op_in_unsafe_fn` lint is `allow`ed at the current HIR node.
 140     fn unsafe_op_in_unsafe_fn_allowed(&self) -> bool {
 141         self.tcx.lint_level_at_node(UNSAFE_OP_IN_UNSAFE_FN, self.hir_context).0 == Level::Allow
 142     }
 143 }
 144
 145 // Searches for accesses to layout constrained fields.
 146 struct LayoutConstrainedPlaceVisitor<'a, 'tcx> {
 147     found: bool,
 148     thir: &'a Thir<'tcx>,
 149     tcx: TyCtxt<'tcx>,
 150 }
 151
 152 impl<'a, 'tcx> LayoutConstrainedPlaceVisitor<'a, 'tcx> {
 153     fn new(thir: &'a Thir<'tcx>, tcx: TyCtxt<'tcx>) -> Self {
 154         Self { found: false, thir, tcx }
 155     }
 156 }
 157
 158 impl<'a, 'tcx> Visitor<'a, 'tcx> for LayoutConstrainedPlaceVisitor<'a, 'tcx> {
 159     fn thir(&self) -> &'a Thir<'tcx> {
 160         self.thir
 161     }
 162
 163     fn visit_expr(&mut self, expr: &Expr<'tcx>) {
 164         match expr.kind {
 165             ExprKind::Field { lhs, .. } => {
 166                 if let ty::Adt(adt_def, _) = self.thir[lhs].ty.kind() {
 167                     if (Bound::Unbounded, Bound::Unbounded)
 168                         != self.tcx.layout_scalar_valid_range(adt_def.did())
 169                     {
 170                         self.found = true;
 171                     }
 172                 }
 173                 visit::walk_expr(self, expr);
 174             }
 175
 176             // Keep walking through the expression as long as we stay in the same
 177             // place, i.e. the expression is a place expression and not a dereference
 178             // (since dereferencing something leads us to a different place).
 179             ExprKind::Deref { .. } => {}
 180             ref kind if ExprCategory::of(kind).map_or(true, |cat| cat == ExprCategory::Place) => {
 181                 visit::walk_expr(self, expr);
 182             }
 183
 184             _ => {}
 185         }
 186     }
 187 }
 188
 189 impl<'a, 'tcx> Visitor<'a, 'tcx> for UnsafetyVisitor<'a, 'tcx> {
 190     fn thir(&self) -> &'a Thir<'tcx> {
 191         &self.thir
 192     }
 193
 194     fn visit_block(&mut self, block: &Block) {
 195         match block.safety_mode {
 196             // compiler-generated unsafe code should not count towards the usefulness of
 197             // an outer unsafe block
 198             BlockSafety::BuiltinUnsafe => {
 199                 self.in_safety_context(SafetyContext::BuiltinUnsafeBlock, |this| {
 200                     visit::walk_block(this, block)
 201                 });
 202             }
 203             BlockSafety::ExplicitUnsafe(hir_id) => {
 204                 self.in_safety_context(
 205                     SafetyContext::UnsafeBlock { span: block.span, hir_id, used: false },
 206                     |this| visit::walk_block(this, block),
 207                 );
 208             }
 209             BlockSafety::Safe => {
 210                 visit::walk_block(self, block);
 211             }
 212         }
 213     }
 214
 215     fn visit_pat(&mut self, pat: &Pat<'tcx>) {
 216         if self.in_union_destructure {
 217             match pat.kind {
 218                 // binding to a variable allows getting stuff out of variable
 219                 PatKind::Binding { .. }
 220                 // match is conditional on having this value
 221                 | PatKind::Constant { .. }
 222                 | PatKind::Variant { .. }
 223                 | PatKind::Leaf { .. }
 224                 | PatKind::Deref { .. }
 225                 | PatKind::Range { .. }
 226                 | PatKind::Slice { .. }
 227                 | PatKind::Array { .. } => {
 228                     self.requires_unsafe(pat.span, AccessToUnionField);
 229                     return; // we can return here since this already requires unsafe
 230                 }
 231                 // wildcard doesn't take anything
 232                 PatKind::Wild |
 233                 // these just wrap other patterns
 234                 PatKind::Or { .. } |
 235                 PatKind::AscribeUserType { .. } => {}
 236             }
 237         };
 238
 239         match &pat.kind {
 240             PatKind::Leaf { .. } => {
 241                 if let ty::Adt(adt_def, ..) = pat.ty.kind() {
 242                     if adt_def.is_union() {
 243                         let old_in_union_destructure =
 244                             std::mem::replace(&mut self.in_union_destructure, true);
 245                         visit::walk_pat(self, pat);
 246                         self.in_union_destructure = old_in_union_destructure;
 247                     } else if (Bound::Unbounded, Bound::Unbounded)
 248                         != self.tcx.layout_scalar_valid_range(adt_def.did())
 249                     {
 250                         let old_inside_adt = std::mem::replace(&mut self.inside_adt, true);
 251                         visit::walk_pat(self, pat);
 252                         self.inside_adt = old_inside_adt;
 253                     } else {
 254                         visit::walk_pat(self, pat);
 255                     }
 256                 } else {
 257                     visit::walk_pat(self, pat);
 258                 }
 259             }
 260             PatKind::Binding { mode: BindingMode::ByRef(borrow_kind), ty, .. } => {
 261                 if self.inside_adt {
 262                     let ty::Ref(_, ty, _) = ty.kind() else {
 263                         span_bug!(
 264                             pat.span,
 265                             "BindingMode::ByRef in pattern, but found non-reference type {}",
 266                             ty
 267                         );
 268                     };
 269                     match borrow_kind {
 270                         BorrowKind::Shallow | BorrowKind::Shared | BorrowKind::Unique => {
 271                             if !ty.is_freeze(self.tcx.at(pat.span), self.param_env) {
 272                                 self.requires_unsafe(pat.span, BorrowOfLayoutConstrainedField);
 273                             }
 274                         }
 275                         BorrowKind::Mut { .. } => {
 276                             self.requires_unsafe(pat.span, MutationOfLayoutConstrainedField);
 277                         }
 278                     }
 279                 }
 280                 visit::walk_pat(self, pat);
 281             }
 282             PatKind::Deref { .. } => {
 283                 let old_inside_adt = std::mem::replace(&mut self.inside_adt, false);
 284                 visit::walk_pat(self, pat);
 285                 self.inside_adt = old_inside_adt;
 286             }
 287             _ => {
 288                 visit::walk_pat(self, pat);
 289             }
 290         }
 291     }
 292
 293     fn visit_expr(&mut self, expr: &Expr<'tcx>) {
 294         // could we be in the LHS of an assignment to a field?
 295         match expr.kind {
 296             ExprKind::Field { .. }
 297             | ExprKind::VarRef { .. }
 298             | ExprKind::UpvarRef { .. }
 299             | ExprKind::Scope { .. }
 300             | ExprKind::Cast { .. } => {}
 301
 302             ExprKind::AddressOf { .. }
 303             | ExprKind::Adt { .. }
 304             | ExprKind::Array { .. }
 305             | ExprKind::Binary { .. }
 306             | ExprKind::Block { .. }
 307             | ExprKind::Borrow { .. }
 308             | ExprKind::Literal { .. }
 309             | ExprKind::NamedConst { .. }
 310             | ExprKind::NonHirLiteral { .. }
 311             | ExprKind::ZstLiteral { .. }
 312             | ExprKind::ConstParam { .. }
 313             | ExprKind::ConstBlock { .. }
 314             | ExprKind::Deref { .. }
 315             | ExprKind::Index { .. }
 316             | ExprKind::NeverToAny { .. }
 317             | ExprKind::PlaceTypeAscription { .. }
 318             | ExprKind::ValueTypeAscription { .. }
 319             | ExprKind::Pointer { .. }
 320             | ExprKind::Repeat { .. }
 321             | ExprKind::StaticRef { .. }
 322             | ExprKind::ThreadLocalRef { .. }
 323             | ExprKind::Tuple { .. }
 324             | ExprKind::Unary { .. }
 325             | ExprKind::Call { .. }
 326             | ExprKind::Assign { .. }
 327             | ExprKind::AssignOp { .. }
 328             | ExprKind::Break { .. }
 329             | ExprKind::Closure { .. }
 330             | ExprKind::Continue { .. }
 331             | ExprKind::Return { .. }
 332             | ExprKind::Yield { .. }
 333             | ExprKind::Loop { .. }
 334             | ExprKind::Let { .. }
 335             | ExprKind::Match { .. }
 336             | ExprKind::Box { .. }
 337             | ExprKind::If { .. }
 338             | ExprKind::InlineAsm { .. }
 339             | ExprKind::LogicalOp { .. }
 340             | ExprKind::Use { .. } => {
 341                 // We don't need to save the old value and restore it
 342                 // because all the place expressions can't have more
 343                 // than one child.
 344                 self.assignment_info = None;
 345             }
 346         };
 347         match expr.kind {
 348             ExprKind::Scope { value, lint_level: LintLevel::Explicit(hir_id), region_scope: _ } => {
 349                 let prev_id = self.hir_context;
 350                 self.hir_context = hir_id;
 351                 self.visit_expr(&self.thir[value]);
 352                 self.hir_context = prev_id;
 353                 return; // don't visit the whole expression
 354             }
 355             ExprKind::Call { fun, ty: _, args: _, from_hir_call: _, fn_span: _ } => {
 356                 if self.thir[fun].ty.fn_sig(self.tcx).unsafety() == hir::Unsafety::Unsafe {
 357                     let func_id = if let ty::FnDef(func_id, _) = self.thir[fun].ty.kind() {
 358                         Some(*func_id)
 359                     } else {
 360                         None
 361                     };
 362                     self.requires_unsafe(expr.span, CallToUnsafeFunction(func_id));
 363                 } else if let &ty::FnDef(func_did, _) = self.thir[fun].ty.kind() {
 364                     // If the called function has target features the calling function hasn't,
 365                     // the call requires `unsafe`. Don't check this on wasm
 366                     // targets, though. For more information on wasm see the
 367                     // is_like_wasm check in hir_analysis/src/collect.rs
 368                     if !self.tcx.sess.target.options.is_like_wasm
 369                         && !self
 370                             .tcx
 371                             .codegen_fn_attrs(func_did)
 372                             .target_features
 373                             .iter()
 374                             .all(|feature| self.body_target_features.contains(feature))
 375                     {
 376                         self.requires_unsafe(expr.span, CallToFunctionWith(func_did));
 377                     }
 378                 }
 379             }
 380             ExprKind::Deref { arg } => {
 381                 if let ExprKind::StaticRef { def_id, .. } = self.thir[arg].kind {
 382                     if self.tcx.is_mutable_static(def_id) {
 383                         self.requires_unsafe(expr.span, UseOfMutableStatic);
 384                     } else if self.tcx.is_foreign_item(def_id) {
 385                         self.requires_unsafe(expr.span, UseOfExternStatic);
 386                     }
 387                 } else if self.thir[arg].ty.is_unsafe_ptr() {
 388                     self.requires_unsafe(expr.span, DerefOfRawPointer);
 389                 }
 390             }
 391             ExprKind::InlineAsm { .. } => {
 392                 self.requires_unsafe(expr.span, UseOfInlineAssembly);
 393             }
 394             ExprKind::Adt(box AdtExpr {
 395                 adt_def,
 396                 variant_index: _,
 397                 substs: _,
 398                 user_ty: _,
 399                 fields: _,
 400                 base: _,
 401             }) => match self.tcx.layout_scalar_valid_range(adt_def.did()) {
 402                 (Bound::Unbounded, Bound::Unbounded) => {}
 403                 _ => self.requires_unsafe(expr.span, InitializingTypeWith),
 404             },
 405             ExprKind::Closure(box ClosureExpr {
 406                 closure_id,
 407                 substs: _,
 408                 upvars: _,
 409                 movability: _,
 410                 fake_reads: _,
 411             }) => {
 412                 let closure_def = if let Some((did, const_param_id)) =
 413                     ty::WithOptConstParam::try_lookup(closure_id, self.tcx)
 414                 {
 415                     ty::WithOptConstParam { did, const_param_did: Some(const_param_id) }
 416                 } else {
 417                     ty::WithOptConstParam::unknown(closure_id)
 418                 };
 419                 let (closure_thir, expr) = self.tcx.thir_body(closure_def).unwrap_or_else(|_| {
 420                     (self.tcx.alloc_steal_thir(Thir::new()), ExprId::from_u32(0))
 421                 });
 422                 let closure_thir = &closure_thir.borrow();
 423                 let hir_context = self.tcx.hir().local_def_id_to_hir_id(closure_id);
 424                 let mut closure_visitor =
 425                     UnsafetyVisitor { thir: closure_thir, hir_context, ..*self };
 426                 closure_visitor.visit_expr(&closure_thir[expr]);
 427                 // Unsafe blocks can be used in closures, make sure to take it into account
 428                 self.safety_context = closure_visitor.safety_context;
 429             }
 430             ExprKind::Field { lhs, .. } => {
 431                 let lhs = &self.thir[lhs];
 432                 if let ty::Adt(adt_def, _) = lhs.ty.kind() && adt_def.is_union() {
 433                     if let Some((assigned_ty, assignment_span)) = self.assignment_info {
 434                         if assigned_ty.needs_drop(self.tcx, self.param_env) {
 435                             // This would be unsafe, but should be outright impossible since we reject such unions.
 436                             self.tcx.sess.delay_span_bug(assignment_span, format!("union fields that need dropping should be impossible: {assigned_ty}"));
 437                         }
 438                     } else {
 439                         self.requires_unsafe(expr.span, AccessToUnionField);
 440                     }
 441                 }
 442             }
 443             ExprKind::Assign { lhs, rhs } | ExprKind::AssignOp { lhs, rhs, .. } => {
 444                 let lhs = &self.thir[lhs];
 445                 // First, check whether we are mutating a layout constrained field
 446                 let mut visitor = LayoutConstrainedPlaceVisitor::new(self.thir, self.tcx);
 447                 visit::walk_expr(&mut visitor, lhs);
 448                 if visitor.found {
 449                     self.requires_unsafe(expr.span, MutationOfLayoutConstrainedField);
 450                 }
 451
 452                 // Second, check for accesses to union fields
 453                 // don't have any special handling for AssignOp since it causes a read *and* write to lhs
 454                 if matches!(expr.kind, ExprKind::Assign { .. }) {
 455                     self.assignment_info = Some((lhs.ty, expr.span));
 456                     visit::walk_expr(self, lhs);
 457                     self.assignment_info = None;
 458                     visit::walk_expr(self, &self.thir()[rhs]);
 459                     return; // we have already visited everything by now
 460                 }
 461             }
 462             ExprKind::Borrow { borrow_kind, arg } => {
 463                 let mut visitor = LayoutConstrainedPlaceVisitor::new(self.thir, self.tcx);
 464                 visit::walk_expr(&mut visitor, expr);
 465                 if visitor.found {
 466                     match borrow_kind {
 467                         BorrowKind::Shallow | BorrowKind::Shared | BorrowKind::Unique
 468                             if !self.thir[arg]
 469                                 .ty
 470                                 .is_freeze(self.tcx.at(self.thir[arg].span), self.param_env) =>
 471                         {
 472                             self.requires_unsafe(expr.span, BorrowOfLayoutConstrainedField)
 473                         }
 474                         BorrowKind::Mut { .. } => {
 475                             self.requires_unsafe(expr.span, MutationOfLayoutConstrainedField)
 476                         }
 477                         BorrowKind::Shallow | BorrowKind::Shared | BorrowKind::Unique => {}
 478                     }
 479                 }
 480             }
 481             ExprKind::Let { expr: expr_id, .. } => {
 482                 let let_expr = &self.thir[expr_id];
 483                 if let ty::Adt(adt_def, _) = let_expr.ty.kind() && adt_def.is_union() {
 484                     self.requires_unsafe(expr.span, AccessToUnionField);
 485                 }
 486             }
 487             _ => {}
 488         }
 489         visit::walk_expr(self, expr);
 490     }
 491 }
 492
 493 #[derive(Clone, Copy)]
 494 enum SafetyContext {
 495     Safe,
 496     BuiltinUnsafeBlock,
 497     UnsafeFn,
 498     UnsafeBlock { span: Span, hir_id: hir::HirId, used: bool },
 499 }
 500
 501 #[derive(Clone, Copy)]
 502 enum BodyUnsafety {
 503     /// The body is not unsafe.
 504     Safe,
 505     /// The body is an unsafe function. The span points to
 506     /// the signature of the function.
 507     Unsafe(Span),
 508 }
 509
 510 impl BodyUnsafety {
 511     /// Returns whether the body is unsafe.
 512     fn is_unsafe(&self) -> bool {
 513         matches!(self, BodyUnsafety::Unsafe(_))
 514     }
 515
 516     /// If the body is unsafe, returns the `Span` of its signature.
 517     fn unsafe_fn_sig_span(self) -> Option<Span> {
 518         match self {
 519             BodyUnsafety::Unsafe(span) => Some(span),
 520             BodyUnsafety::Safe => None,
 521         }
 522     }
 523 }
 524
 525 #[derive(Clone, Copy, PartialEq)]
 526 enum UnsafeOpKind {
 527     CallToUnsafeFunction(Option<DefId>),
 528     UseOfInlineAssembly,
 529     InitializingTypeWith,
 530     UseOfMutableStatic,
 531     UseOfExternStatic,
 532     DerefOfRawPointer,
 533     AccessToUnionField,
 534     MutationOfLayoutConstrainedField,
 535     BorrowOfLayoutConstrainedField,
 536     CallToFunctionWith(DefId),
 537 }
 538
 539 use UnsafeOpKind::*;
 540
 541 impl UnsafeOpKind {
 542     pub fn simple_description(&self) -> &'static str {
 543         match self {
 544             CallToUnsafeFunction(..) => "call to unsafe function",
 545             UseOfInlineAssembly => "use of inline assembly",
 546             InitializingTypeWith => "initializing type with `rustc_layout_scalar_valid_range` attr",
 547             UseOfMutableStatic => "use of mutable static",
 548             UseOfExternStatic => "use of extern static",
 549             DerefOfRawPointer => "dereference of raw pointer",
 550             AccessToUnionField => "access to union field",
 551             MutationOfLayoutConstrainedField => "mutation of layout constrained field",
 552             BorrowOfLayoutConstrainedField => {
 553                 "borrow of layout constrained field with interior mutability"
 554             }
 555             CallToFunctionWith(..) => "call to function with `#[target_feature]`",
 556         }
 557     }
 558
 559     pub fn description_and_note(&self, tcx: TyCtxt<'_>) -> (Cow<'static, str>, &'static str) {
 560         match self {
 561             CallToUnsafeFunction(did) => (
 562                 if let Some(did) = did {
 563                     Cow::from(format!("call to unsafe function `{}`", tcx.def_path_str(*did)))
 564                 } else {
 565                     Cow::Borrowed(self.simple_description())
 566                 },
 567                 "consult the function's documentation for information on how to avoid undefined \
 568                  behavior",
 569             ),
 570             UseOfInlineAssembly => (
 571                 Cow::Borrowed(self.simple_description()),
 572                 "inline assembly is entirely unchecked and can cause undefined behavior",
 573             ),
 574             InitializingTypeWith => (
 575                 Cow::Borrowed(self.simple_description()),
 576                 "initializing a layout restricted type's field with a value outside the valid \
 577                  range is undefined behavior",
 578             ),
 579             UseOfMutableStatic => (
 580                 Cow::Borrowed(self.simple_description()),
 581                 "mutable statics can be mutated by multiple threads: aliasing violations or data \
 582                  races will cause undefined behavior",
 583             ),
 584             UseOfExternStatic => (
 585                 Cow::Borrowed(self.simple_description()),
 586                 "extern statics are not controlled by the Rust type system: invalid data, \
 587                  aliasing violations or data races will cause undefined behavior",
 588             ),
 589             DerefOfRawPointer => (
 590                 Cow::Borrowed(self.simple_description()),
 591                 "raw pointers may be null, dangling or unaligned; they can violate aliasing rules \
 592                  and cause data races: all of these are undefined behavior",
 593             ),
 594             AccessToUnionField => (
 595                 Cow::Borrowed(self.simple_description()),
 596                 "the field may not be properly initialized: using uninitialized data will cause \
 597                  undefined behavior",
 598             ),
 599             MutationOfLayoutConstrainedField => (
 600                 Cow::Borrowed(self.simple_description()),
 601                 "mutating layout constrained fields cannot statically be checked for valid values",
 602             ),
 603             BorrowOfLayoutConstrainedField => (
 604                 Cow::Borrowed(self.simple_description()),
 605                 "references to fields of layout constrained fields lose the constraints. Coupled \
 606                  with interior mutability, the field can be changed to invalid values",
 607             ),
 608             CallToFunctionWith(did) => (
 609                 Cow::from(format!(
 610                     "call to function `{}` with `#[target_feature]`",
 611                     tcx.def_path_str(*did)
 612                 )),
 613                 "can only be called if the required target features are available",
 614             ),
 615         }
 616     }
 617 }
 618
 619 pub fn check_unsafety<'tcx>(tcx: TyCtxt<'tcx>, def: ty::WithOptConstParam<LocalDefId>) {
 620     // THIR unsafeck is gated under `-Z thir-unsafeck`
 621     if !tcx.sess.opts.unstable_opts.thir_unsafeck {
 622         return;
 623     }
 624
 625     // Closures are handled by their owner, if it has a body
 626     if tcx.is_closure(def.did.to_def_id()) {
 627         let hir = tcx.hir();
 628         let owner = hir.enclosing_body_owner(hir.local_def_id_to_hir_id(def.did));
 629         tcx.ensure().thir_check_unsafety(owner);
 630         return;
 631     }
 632
 633     let Ok((thir, expr)) = tcx.thir_body(def) else {
 634         return
 635     };
 636     let thir = &thir.borrow();
 637     // If `thir` is empty, a type error occurred, skip this body.
 638     if thir.exprs.is_empty() {
 639         return;
 640     }
 641
 642     let hir_id = tcx.hir().local_def_id_to_hir_id(def.did);
 643     let body_unsafety = tcx.hir().fn_sig_by_hir_id(hir_id).map_or(BodyUnsafety::Safe, |fn_sig| {
 644         if fn_sig.header.unsafety == hir::Unsafety::Unsafe {
 645             BodyUnsafety::Unsafe(fn_sig.span)
 646         } else {
 647             BodyUnsafety::Safe
 648         }
 649     });
 650     let body_target_features = &tcx.body_codegen_attrs(def.did.to_def_id()).target_features;
 651     let safety_context =
 652         if body_unsafety.is_unsafe() { SafetyContext::UnsafeFn } else { SafetyContext::Safe };
 653     let mut visitor = UnsafetyVisitor {
 654         tcx,
 655         thir,
 656         safety_context,
 657         hir_context: hir_id,
 658         body_unsafety,
 659         body_target_features,
 660         assignment_info: None,
 661         in_union_destructure: false,
 662         param_env: tcx.param_env(def.did),
 663         inside_adt: false,
 664     };
 665     visitor.visit_expr(&thir[expr]);
 666 }
 667
 668 pub(crate) fn thir_check_unsafety<'tcx>(tcx: TyCtxt<'tcx>, def_id: LocalDefId) {
 669     if let Some(def) = ty::WithOptConstParam::try_lookup(def_id, tcx) {
 670         tcx.thir_check_unsafety_for_const_arg(def)
 671     } else {
 672         check_unsafety(tcx, ty::WithOptConstParam::unknown(def_id))
 673     }
 674 }
 675
 676 pub(crate) fn thir_check_unsafety_for_const_arg<'tcx>(
 677     tcx: TyCtxt<'tcx>,
 678     (did, param_did): (LocalDefId, DefId),
 679 ) {
 680     check_unsafety(tcx, ty::WithOptConstParam { did, const_param_did: Some(param_did) })
 681 }