rustc_mir_build/
check_unsafety.rs

1use std::borrow::Cow;
2use std::mem;
3use std::ops::Bound;
4
5use rustc_ast::AsmMacro;
6use rustc_data_structures::stack::ensure_sufficient_stack;
7use rustc_errors::DiagArgValue;
8use rustc_hir::attrs::AttributeKind;
9use rustc_hir::def::DefKind;
10use rustc_hir::{self as hir, BindingMode, ByRef, HirId, Mutability, find_attr};
11use rustc_middle::middle::codegen_fn_attrs::{TargetFeature, TargetFeatureKind};
12use rustc_middle::mir::BorrowKind;
13use rustc_middle::span_bug;
14use rustc_middle::thir::visit::Visitor;
15use rustc_middle::thir::*;
16use rustc_middle::ty::print::with_no_trimmed_paths;
17use rustc_middle::ty::{self, Ty, TyCtxt};
18use rustc_session::lint::Level;
19use rustc_session::lint::builtin::{DEPRECATED_SAFE_2024, UNSAFE_OP_IN_UNSAFE_FN, UNUSED_UNSAFE};
20use rustc_span::def_id::{DefId, LocalDefId};
21use rustc_span::{Span, Symbol, sym};
22
23use crate::builder::ExprCategory;
24use crate::errors::*;
25
26struct UnsafetyVisitor<'a, 'tcx> {
27    tcx: TyCtxt<'tcx>,
28    thir: &'a Thir<'tcx>,
29    /// The `HirId` of the current scope, which would be the `HirId`
30    /// of the current HIR node, modulo adjustments. Used for lint levels.
31    hir_context: HirId,
32    /// The current "safety context". This notably tracks whether we are in an
33    /// `unsafe` block, and whether it has been used.
34    safety_context: SafetyContext,
35    /// The `#[target_feature]` attributes of the body. Used for checking
36    /// calls to functions with `#[target_feature]` (RFC 2396).
37    body_target_features: &'tcx [TargetFeature],
38    /// When inside the LHS of an assignment to a field, this is the type
39    /// of the LHS and the span of the assignment expression.
40    assignment_info: Option<Ty<'tcx>>,
41    in_union_destructure: bool,
42    typing_env: ty::TypingEnv<'tcx>,
43    inside_adt: bool,
44    warnings: &'a mut Vec<UnusedUnsafeWarning>,
45
46    /// Flag to ensure that we only suggest wrapping the entire function body in
47    /// an unsafe block once.
48    suggest_unsafe_block: bool,
49}
50
51impl<'tcx> UnsafetyVisitor<'_, 'tcx> {
52    fn in_safety_context(&mut self, safety_context: SafetyContext, f: impl FnOnce(&mut Self)) {
53        let prev_context = mem::replace(&mut self.safety_context, safety_context);
54
55        f(self);
56
57        let safety_context = mem::replace(&mut self.safety_context, prev_context);
58        if let SafetyContext::UnsafeBlock { used, span, hir_id, nested_used_blocks } =
59            safety_context
60        {
61            if !used {
62                self.warn_unused_unsafe(hir_id, span, None);
63
64                if let SafetyContext::UnsafeBlock {
65                    nested_used_blocks: ref mut prev_nested_used_blocks,
66                    ..
67                } = self.safety_context
68                {
69                    prev_nested_used_blocks.extend(nested_used_blocks);
70                }
71            } else {
72                for block in nested_used_blocks {
73                    self.warn_unused_unsafe(
74                        block.hir_id,
75                        block.span,
76                        Some(UnusedUnsafeEnclosing::Block {
77                            span: self.tcx.sess.source_map().guess_head_span(span),
78                        }),
79                    );
80                }
81
82                match self.safety_context {
83                    SafetyContext::UnsafeBlock {
84                        nested_used_blocks: ref mut prev_nested_used_blocks,
85                        ..
86                    } => {
87                        prev_nested_used_blocks.push(NestedUsedBlock { hir_id, span });
88                    }
89                    _ => (),
90                }
91            }
92        }
93    }
94
95    fn emit_deprecated_safe_fn_call(&self, span: Span, kind: &UnsafeOpKind) -> bool {
96        match kind {
97            // Allow calls to deprecated-safe unsafe functions if the caller is
98            // from an edition before 2024.
99            &UnsafeOpKind::CallToUnsafeFunction(Some(id))
100                if !span.at_least_rust_2024()
101                    && let Some(attr) = self.tcx.get_attr(id, sym::rustc_deprecated_safe_2024) =>
102            {
103                let suggestion = attr
104                    .meta_item_list()
105                    .unwrap_or_default()
106                    .into_iter()
107                    .find(|item| item.has_name(sym::audit_that))
108                    .map(|item| {
109                        item.value_str().expect(
110                            "`#[rustc_deprecated_safe_2024(audit_that)]` must have a string value",
111                        )
112                    });
113
114                let sm = self.tcx.sess.source_map();
115                let guarantee = suggestion
116                    .as_ref()
117                    .map(|suggestion| format!("that {}", suggestion))
118                    .unwrap_or_else(|| String::from("its unsafe preconditions"));
119                let suggestion = suggestion
120                    .and_then(|suggestion| {
121                        sm.indentation_before(span).map(|indent| {
122                            format!("{}// TODO: Audit that {}.\n", indent, suggestion) // ignore-tidy-todo
123                        })
124                    })
125                    .unwrap_or_default();
126
127                self.tcx.emit_node_span_lint(
128                    DEPRECATED_SAFE_2024,
129                    self.hir_context,
130                    span,
131                    CallToDeprecatedSafeFnRequiresUnsafe {
132                        span,
133                        function: with_no_trimmed_paths!(self.tcx.def_path_str(id)),
134                        guarantee,
135                        sub: CallToDeprecatedSafeFnRequiresUnsafeSub {
136                            start_of_line_suggestion: suggestion,
137                            start_of_line: sm.span_extend_to_line(span).shrink_to_lo(),
138                            left: span.shrink_to_lo(),
139                            right: span.shrink_to_hi(),
140                        },
141                    },
142                );
143                true
144            }
145            _ => false,
146        }
147    }
148
149    fn requires_unsafe(&mut self, span: Span, kind: UnsafeOpKind) {
150        let unsafe_op_in_unsafe_fn_allowed = self.unsafe_op_in_unsafe_fn_allowed();
151        match self.safety_context {
152            SafetyContext::BuiltinUnsafeBlock => {}
153            SafetyContext::UnsafeBlock { ref mut used, .. } => {
154                // Mark this block as useful (even inside `unsafe fn`, where it is technically
155                // redundant -- but we want to eventually enable `unsafe_op_in_unsafe_fn` by
156                // default which will require those blocks:
157                // https://github.com/rust-lang/rust/issues/71668#issuecomment-1203075594).
158                *used = true;
159            }
160            SafetyContext::UnsafeFn if unsafe_op_in_unsafe_fn_allowed => {}
161            SafetyContext::UnsafeFn => {
162                let deprecated_safe_fn = self.emit_deprecated_safe_fn_call(span, &kind);
163                if !deprecated_safe_fn {
164                    // unsafe_op_in_unsafe_fn is disallowed
165                    kind.emit_unsafe_op_in_unsafe_fn_lint(
166                        self.tcx,
167                        self.hir_context,
168                        span,
169                        self.suggest_unsafe_block,
170                    );
171                    self.suggest_unsafe_block = false;
172                }
173            }
174            SafetyContext::Safe => {
175                let deprecated_safe_fn = self.emit_deprecated_safe_fn_call(span, &kind);
176                if !deprecated_safe_fn {
177                    kind.emit_requires_unsafe_err(
178                        self.tcx,
179                        span,
180                        self.hir_context,
181                        unsafe_op_in_unsafe_fn_allowed,
182                    );
183                }
184            }
185        }
186    }
187
188    fn warn_unused_unsafe(
189        &mut self,
190        hir_id: HirId,
191        block_span: Span,
192        enclosing_unsafe: Option<UnusedUnsafeEnclosing>,
193    ) {
194        self.warnings.push(UnusedUnsafeWarning { hir_id, block_span, enclosing_unsafe });
195    }
196
197    /// Whether the `unsafe_op_in_unsafe_fn` lint is `allow`ed at the current HIR node.
198    fn unsafe_op_in_unsafe_fn_allowed(&self) -> bool {
199        self.tcx.lint_level_at_node(UNSAFE_OP_IN_UNSAFE_FN, self.hir_context).level == Level::Allow
200    }
201
202    /// Handle closures/coroutines/inline-consts, which is unsafecked with their parent body.
203    fn visit_inner_body(&mut self, def: LocalDefId) {
204        if let Ok((inner_thir, expr)) = self.tcx.thir_body(def) {
205            // Run all other queries that depend on THIR.
206            self.tcx.ensure_done().mir_built(def);
207            let inner_thir = if self.tcx.sess.opts.unstable_opts.no_steal_thir {
208                &inner_thir.borrow()
209            } else {
210                // We don't have other use for the THIR. Steal it to reduce memory usage.
211                &inner_thir.steal()
212            };
213            let hir_context = self.tcx.local_def_id_to_hir_id(def);
214            let safety_context = mem::replace(&mut self.safety_context, SafetyContext::Safe);
215            let mut inner_visitor = UnsafetyVisitor {
216                tcx: self.tcx,
217                thir: inner_thir,
218                hir_context,
219                safety_context,
220                body_target_features: self.body_target_features,
221                assignment_info: self.assignment_info,
222                in_union_destructure: false,
223                typing_env: self.typing_env,
224                inside_adt: false,
225                warnings: self.warnings,
226                suggest_unsafe_block: self.suggest_unsafe_block,
227            };
228            // params in THIR may be unsafe, e.g. a union pattern.
229            for param in &inner_thir.params {
230                if let Some(param_pat) = param.pat.as_deref() {
231                    inner_visitor.visit_pat(param_pat);
232                }
233            }
234            // Visit the body.
235            inner_visitor.visit_expr(&inner_thir[expr]);
236            // Unsafe blocks can be used in the inner body, make sure to take it into account
237            self.safety_context = inner_visitor.safety_context;
238        }
239    }
240}
241
242// Searches for accesses to layout constrained fields.
243struct LayoutConstrainedPlaceVisitor<'a, 'tcx> {
244    found: bool,
245    thir: &'a Thir<'tcx>,
246    tcx: TyCtxt<'tcx>,
247}
248
249impl<'a, 'tcx> LayoutConstrainedPlaceVisitor<'a, 'tcx> {
250    fn new(thir: &'a Thir<'tcx>, tcx: TyCtxt<'tcx>) -> Self {
251        Self { found: false, thir, tcx }
252    }
253}
254
255impl<'a, 'tcx> Visitor<'a, 'tcx> for LayoutConstrainedPlaceVisitor<'a, 'tcx> {
256    fn thir(&self) -> &'a Thir<'tcx> {
257        self.thir
258    }
259
260    fn visit_expr(&mut self, expr: &'a Expr<'tcx>) {
261        match expr.kind {
262            ExprKind::Field { lhs, .. } => {
263                if let ty::Adt(adt_def, _) = self.thir[lhs].ty.kind() {
264                    if (Bound::Unbounded, Bound::Unbounded)
265                        != self.tcx.layout_scalar_valid_range(adt_def.did())
266                    {
267                        self.found = true;
268                    }
269                }
270                visit::walk_expr(self, expr);
271            }
272
273            // Keep walking through the expression as long as we stay in the same
274            // place, i.e. the expression is a place expression and not a dereference
275            // (since dereferencing something leads us to a different place).
276            ExprKind::Deref { .. } => {}
277            ref kind if ExprCategory::of(kind).is_none_or(|cat| cat == ExprCategory::Place) => {
278                visit::walk_expr(self, expr);
279            }
280
281            _ => {}
282        }
283    }
284}
285
286impl<'a, 'tcx> Visitor<'a, 'tcx> for UnsafetyVisitor<'a, 'tcx> {
287    fn thir(&self) -> &'a Thir<'tcx> {
288        self.thir
289    }
290
291    fn visit_block(&mut self, block: &'a Block) {
292        match block.safety_mode {
293            // compiler-generated unsafe code should not count towards the usefulness of
294            // an outer unsafe block
295            BlockSafety::BuiltinUnsafe => {
296                self.in_safety_context(SafetyContext::BuiltinUnsafeBlock, |this| {
297                    visit::walk_block(this, block)
298                });
299            }
300            BlockSafety::ExplicitUnsafe(hir_id) => {
301                let used = matches!(
302                    self.tcx.lint_level_at_node(UNUSED_UNSAFE, hir_id).level,
303                    Level::Allow
304                );
305                self.in_safety_context(
306                    SafetyContext::UnsafeBlock {
307                        span: block.span,
308                        hir_id,
309                        used,
310                        nested_used_blocks: Vec::new(),
311                    },
312                    |this| visit::walk_block(this, block),
313                );
314            }
315            BlockSafety::Safe => {
316                visit::walk_block(self, block);
317            }
318        }
319    }
320
321    fn visit_pat(&mut self, pat: &'a Pat<'tcx>) {
322        if self.in_union_destructure {
323            match pat.kind {
324                PatKind::Missing => unreachable!(),
325                // binding to a variable allows getting stuff out of variable
326                PatKind::Binding { .. }
327                // match is conditional on having this value
328                | PatKind::Constant { .. }
329                | PatKind::Variant { .. }
330                | PatKind::Leaf { .. }
331                | PatKind::Deref { .. }
332                | PatKind::DerefPattern { .. }
333                | PatKind::Range { .. }
334                | PatKind::Slice { .. }
335                | PatKind::Array { .. }
336                // Never constitutes a witness of uninhabitedness.
337                | PatKind::Never => {
338                    self.requires_unsafe(pat.span, AccessToUnionField);
339                    return; // we can return here since this already requires unsafe
340                }
341                // wildcard doesn't read anything.
342                PatKind::Wild |
343                // these just wrap other patterns, which we recurse on below.
344                PatKind::Or { .. } |
345                PatKind::Error(_) => {}
346            }
347        };
348
349        match &pat.kind {
350            PatKind::Leaf { subpatterns, .. } => {
351                if let ty::Adt(adt_def, ..) = pat.ty.kind() {
352                    for pat in subpatterns {
353                        if adt_def.non_enum_variant().fields[pat.field].safety.is_unsafe() {
354                            self.requires_unsafe(pat.pattern.span, UseOfUnsafeField);
355                        }
356                    }
357                    if adt_def.is_union() {
358                        let old_in_union_destructure =
359                            std::mem::replace(&mut self.in_union_destructure, true);
360                        visit::walk_pat(self, pat);
361                        self.in_union_destructure = old_in_union_destructure;
362                    } else if (Bound::Unbounded, Bound::Unbounded)
363                        != self.tcx.layout_scalar_valid_range(adt_def.did())
364                    {
365                        let old_inside_adt = std::mem::replace(&mut self.inside_adt, true);
366                        visit::walk_pat(self, pat);
367                        self.inside_adt = old_inside_adt;
368                    } else {
369                        visit::walk_pat(self, pat);
370                    }
371                } else {
372                    visit::walk_pat(self, pat);
373                }
374            }
375            PatKind::Variant { adt_def, args: _, variant_index, subpatterns } => {
376                for pat in subpatterns {
377                    let field = &pat.field;
378                    if adt_def.variant(*variant_index).fields[*field].safety.is_unsafe() {
379                        self.requires_unsafe(pat.pattern.span, UseOfUnsafeField);
380                    }
381                }
382                visit::walk_pat(self, pat);
383            }
384            PatKind::Binding { mode: BindingMode(ByRef::Yes(_, rm), _), ty, .. } => {
385                if self.inside_adt {
386                    let ty::Ref(_, ty, _) = ty.kind() else {
387                        span_bug!(
388                            pat.span,
389                            "ByRef::Yes in pattern, but found non-reference type {}",
390                            ty
391                        );
392                    };
393                    match rm {
394                        Mutability::Not => {
395                            if !ty.is_freeze(self.tcx, self.typing_env) {
396                                self.requires_unsafe(pat.span, BorrowOfLayoutConstrainedField);
397                            }
398                        }
399                        Mutability::Mut { .. } => {
400                            self.requires_unsafe(pat.span, MutationOfLayoutConstrainedField);
401                        }
402                    }
403                }
404                visit::walk_pat(self, pat);
405            }
406            PatKind::Deref { .. } | PatKind::DerefPattern { .. } => {
407                let old_inside_adt = std::mem::replace(&mut self.inside_adt, false);
408                visit::walk_pat(self, pat);
409                self.inside_adt = old_inside_adt;
410            }
411            _ => {
412                visit::walk_pat(self, pat);
413            }
414        }
415    }
416
417    fn visit_expr(&mut self, expr: &'a Expr<'tcx>) {
418        // could we be in the LHS of an assignment to a field?
419        match expr.kind {
420            ExprKind::Field { .. }
421            | ExprKind::VarRef { .. }
422            | ExprKind::UpvarRef { .. }
423            | ExprKind::Scope { .. }
424            | ExprKind::Cast { .. } => {}
425
426            ExprKind::RawBorrow { .. }
427            | ExprKind::Adt { .. }
428            | ExprKind::Array { .. }
429            | ExprKind::Binary { .. }
430            | ExprKind::Block { .. }
431            | ExprKind::Borrow { .. }
432            | ExprKind::Literal { .. }
433            | ExprKind::NamedConst { .. }
434            | ExprKind::NonHirLiteral { .. }
435            | ExprKind::ZstLiteral { .. }
436            | ExprKind::ConstParam { .. }
437            | ExprKind::ConstBlock { .. }
438            | ExprKind::Deref { .. }
439            | ExprKind::Index { .. }
440            | ExprKind::NeverToAny { .. }
441            | ExprKind::PlaceTypeAscription { .. }
442            | ExprKind::ValueTypeAscription { .. }
443            | ExprKind::PlaceUnwrapUnsafeBinder { .. }
444            | ExprKind::ValueUnwrapUnsafeBinder { .. }
445            | ExprKind::WrapUnsafeBinder { .. }
446            | ExprKind::PointerCoercion { .. }
447            | ExprKind::Repeat { .. }
448            | ExprKind::StaticRef { .. }
449            | ExprKind::ThreadLocalRef { .. }
450            | ExprKind::Tuple { .. }
451            | ExprKind::Unary { .. }
452            | ExprKind::Call { .. }
453            | ExprKind::ByUse { .. }
454            | ExprKind::Assign { .. }
455            | ExprKind::AssignOp { .. }
456            | ExprKind::Break { .. }
457            | ExprKind::Closure { .. }
458            | ExprKind::Continue { .. }
459            | ExprKind::ConstContinue { .. }
460            | ExprKind::Return { .. }
461            | ExprKind::Become { .. }
462            | ExprKind::Yield { .. }
463            | ExprKind::Loop { .. }
464            | ExprKind::LoopMatch { .. }
465            | ExprKind::Let { .. }
466            | ExprKind::Match { .. }
467            | ExprKind::Box { .. }
468            | ExprKind::If { .. }
469            | ExprKind::InlineAsm { .. }
470            | ExprKind::LogicalOp { .. }
471            | ExprKind::Use { .. } => {
472                // We don't need to save the old value and restore it
473                // because all the place expressions can't have more
474                // than one child.
475                self.assignment_info = None;
476            }
477        };
478        match expr.kind {
479            ExprKind::Scope { value, lint_level: LintLevel::Explicit(hir_id), region_scope: _ } => {
480                let prev_id = self.hir_context;
481                self.hir_context = hir_id;
482                ensure_sufficient_stack(|| {
483                    self.visit_expr(&self.thir[value]);
484                });
485                self.hir_context = prev_id;
486                return; // don't visit the whole expression
487            }
488            ExprKind::Call { fun, ty: _, args: _, from_hir_call: _, fn_span: _ } => {
489                let fn_ty = self.thir[fun].ty;
490                let sig = fn_ty.fn_sig(self.tcx);
491                let (callee_features, safe_target_features): (&[_], _) = match fn_ty.kind() {
492                    ty::FnDef(func_id, ..) => {
493                        let cg_attrs = self.tcx.codegen_fn_attrs(func_id);
494                        (&cg_attrs.target_features, cg_attrs.safe_target_features)
495                    }
496                    _ => (&[], false),
497                };
498                if sig.safety().is_unsafe() && !safe_target_features {
499                    let func_id = if let ty::FnDef(func_id, _) = fn_ty.kind() {
500                        Some(*func_id)
501                    } else {
502                        None
503                    };
504                    self.requires_unsafe(expr.span, CallToUnsafeFunction(func_id));
505                } else if let &ty::FnDef(func_did, _) = fn_ty.kind() {
506                    if !self
507                        .tcx
508                        .is_target_feature_call_safe(callee_features, self.body_target_features)
509                    {
510                        let missing: Vec<_> = callee_features
511                            .iter()
512                            .copied()
513                            .filter(|feature| {
514                                feature.kind == TargetFeatureKind::Enabled
515                                    && !self
516                                        .body_target_features
517                                        .iter()
518                                        .any(|body_feature| body_feature.name == feature.name)
519                            })
520                            .map(|feature| feature.name)
521                            .collect();
522                        let build_enabled = self
523                            .tcx
524                            .sess
525                            .target_features
526                            .iter()
527                            .copied()
528                            .filter(|feature| missing.contains(feature))
529                            .collect();
530                        self.requires_unsafe(
531                            expr.span,
532                            CallToFunctionWith { function: func_did, missing, build_enabled },
533                        );
534                    }
535                }
536            }
537            ExprKind::RawBorrow { arg, .. } => {
538                if let ExprKind::Scope { value: arg, .. } = self.thir[arg].kind
539                    && let ExprKind::Deref { arg } = self.thir[arg].kind
540                {
541                    // Taking a raw ref to a deref place expr is always safe.
542                    // Make sure the expression we're deref'ing is safe, though.
543                    visit::walk_expr(self, &self.thir[arg]);
544                    return;
545                }
546
547                // Secondly, we allow raw borrows of union field accesses. Peel
548                // any of those off, and recurse normally on the LHS, which should
549                // reject any unsafe operations within.
550                let mut peeled = arg;
551                while let ExprKind::Scope { value: arg, .. } = self.thir[peeled].kind
552                    && let ExprKind::Field { lhs, name: _, variant_index: _ } = self.thir[arg].kind
553                    && let ty::Adt(def, _) = &self.thir[lhs].ty.kind()
554                    && def.is_union()
555                {
556                    peeled = lhs;
557                }
558                visit::walk_expr(self, &self.thir[peeled]);
559                // And return so we don't recurse directly onto the union field access(es).
560                return;
561            }
562            ExprKind::Deref { arg } => {
563                if let ExprKind::StaticRef { def_id, .. } | ExprKind::ThreadLocalRef(def_id) =
564                    self.thir[arg].kind
565                {
566                    if self.tcx.is_mutable_static(def_id) {
567                        self.requires_unsafe(expr.span, UseOfMutableStatic);
568                    } else if self.tcx.is_foreign_item(def_id) {
569                        match self.tcx.def_kind(def_id) {
570                            DefKind::Static { safety: hir::Safety::Safe, .. } => {}
571                            _ => self.requires_unsafe(expr.span, UseOfExternStatic),
572                        }
573                    }
574                } else if self.thir[arg].ty.is_raw_ptr() {
575                    self.requires_unsafe(expr.span, DerefOfRawPointer);
576                }
577            }
578            ExprKind::InlineAsm(box InlineAsmExpr {
579                asm_macro: asm_macro @ (AsmMacro::Asm | AsmMacro::NakedAsm),
580                ref operands,
581                template: _,
582                options: _,
583                line_spans: _,
584            }) => {
585                // The `naked` attribute and the `naked_asm!` block form one atomic unit of
586                // unsafety, and `naked_asm!` does not itself need to be wrapped in an unsafe block.
587                if let AsmMacro::Asm = asm_macro {
588                    self.requires_unsafe(expr.span, UseOfInlineAssembly);
589                }
590
591                // For inline asm, do not use `walk_expr`, since we want to handle the label block
592                // specially.
593                for op in &**operands {
594                    use rustc_middle::thir::InlineAsmOperand::*;
595                    match op {
596                        In { expr, reg: _ }
597                        | Out { expr: Some(expr), reg: _, late: _ }
598                        | InOut { expr, reg: _, late: _ } => self.visit_expr(&self.thir()[*expr]),
599                        SplitInOut { in_expr, out_expr, reg: _, late: _ } => {
600                            self.visit_expr(&self.thir()[*in_expr]);
601                            if let Some(out_expr) = out_expr {
602                                self.visit_expr(&self.thir()[*out_expr]);
603                            }
604                        }
605                        Out { expr: None, reg: _, late: _ }
606                        | Const { value: _, span: _ }
607                        | SymFn { value: _ }
608                        | SymStatic { def_id: _ } => {}
609                        Label { block } => {
610                            // Label blocks are safe context.
611                            // `asm!()` is forced to be wrapped inside unsafe. If there's no special
612                            // treatment, the label blocks would also always be unsafe with no way
613                            // of opting out.
614                            self.in_safety_context(SafetyContext::Safe, |this| {
615                                visit::walk_block(this, &this.thir()[*block])
616                            });
617                        }
618                    }
619                }
620                return;
621            }
622            ExprKind::Adt(box AdtExpr {
623                adt_def,
624                variant_index,
625                args: _,
626                user_ty: _,
627                fields: _,
628                base: _,
629            }) => {
630                if adt_def.variant(variant_index).has_unsafe_fields() {
631                    self.requires_unsafe(expr.span, InitializingTypeWithUnsafeField)
632                }
633                match self.tcx.layout_scalar_valid_range(adt_def.did()) {
634                    (Bound::Unbounded, Bound::Unbounded) => {}
635                    _ => self.requires_unsafe(expr.span, InitializingTypeWith),
636                }
637            }
638            ExprKind::Closure(box ClosureExpr {
639                closure_id,
640                args: _,
641                upvars: _,
642                movability: _,
643                fake_reads: _,
644            }) => {
645                self.visit_inner_body(closure_id);
646            }
647            ExprKind::ConstBlock { did, args: _ } => {
648                let def_id = did.expect_local();
649                self.visit_inner_body(def_id);
650            }
651            ExprKind::Field { lhs, variant_index, name } => {
652                let lhs = &self.thir[lhs];
653                if let ty::Adt(adt_def, _) = lhs.ty.kind() {
654                    if adt_def.variant(variant_index).fields[name].safety.is_unsafe() {
655                        self.requires_unsafe(expr.span, UseOfUnsafeField);
656                    } else if adt_def.is_union() {
657                        if let Some(assigned_ty) = self.assignment_info {
658                            if assigned_ty.needs_drop(self.tcx, self.typing_env) {
659                                // This would be unsafe, but should be outright impossible since we
660                                // reject such unions.
661                                assert!(
662                                    self.tcx.dcx().has_errors().is_some(),
663                                    "union fields that need dropping should be impossible: {assigned_ty}"
664                                );
665                            }
666                        } else {
667                            self.requires_unsafe(expr.span, AccessToUnionField);
668                        }
669                    }
670                }
671            }
672            ExprKind::Assign { lhs, rhs } | ExprKind::AssignOp { lhs, rhs, .. } => {
673                let lhs = &self.thir[lhs];
674                // First, check whether we are mutating a layout constrained field
675                let mut visitor = LayoutConstrainedPlaceVisitor::new(self.thir, self.tcx);
676                visit::walk_expr(&mut visitor, lhs);
677                if visitor.found {
678                    self.requires_unsafe(expr.span, MutationOfLayoutConstrainedField);
679                }
680
681                // Second, check for accesses to union fields. Don't have any
682                // special handling for AssignOp since it causes a read *and*
683                // write to lhs.
684                if matches!(expr.kind, ExprKind::Assign { .. }) {
685                    self.assignment_info = Some(lhs.ty);
686                    visit::walk_expr(self, lhs);
687                    self.assignment_info = None;
688                    visit::walk_expr(self, &self.thir()[rhs]);
689                    return; // We have already visited everything by now.
690                }
691            }
692            ExprKind::Borrow { borrow_kind, arg } => {
693                let mut visitor = LayoutConstrainedPlaceVisitor::new(self.thir, self.tcx);
694                visit::walk_expr(&mut visitor, expr);
695                if visitor.found {
696                    match borrow_kind {
697                        BorrowKind::Fake(_) | BorrowKind::Shared
698                            if !self.thir[arg].ty.is_freeze(self.tcx, self.typing_env) =>
699                        {
700                            self.requires_unsafe(expr.span, BorrowOfLayoutConstrainedField)
701                        }
702                        BorrowKind::Mut { .. } => {
703                            self.requires_unsafe(expr.span, MutationOfLayoutConstrainedField)
704                        }
705                        BorrowKind::Fake(_) | BorrowKind::Shared => {}
706                    }
707                }
708            }
709            ExprKind::PlaceUnwrapUnsafeBinder { .. }
710            | ExprKind::ValueUnwrapUnsafeBinder { .. }
711            | ExprKind::WrapUnsafeBinder { .. } => {
712                self.requires_unsafe(expr.span, UnsafeBinderCast);
713            }
714            _ => {}
715        }
716        visit::walk_expr(self, expr);
717    }
718}
719
720#[derive(Clone)]
721enum SafetyContext {
722    Safe,
723    BuiltinUnsafeBlock,
724    UnsafeFn,
725    UnsafeBlock { span: Span, hir_id: HirId, used: bool, nested_used_blocks: Vec<NestedUsedBlock> },
726}
727
728#[derive(Clone, Copy)]
729struct NestedUsedBlock {
730    hir_id: HirId,
731    span: Span,
732}
733
734struct UnusedUnsafeWarning {
735    hir_id: HirId,
736    block_span: Span,
737    enclosing_unsafe: Option<UnusedUnsafeEnclosing>,
738}
739
740#[derive(Clone, PartialEq)]
741enum UnsafeOpKind {
742    CallToUnsafeFunction(Option<DefId>),
743    UseOfInlineAssembly,
744    InitializingTypeWith,
745    InitializingTypeWithUnsafeField,
746    UseOfMutableStatic,
747    UseOfExternStatic,
748    UseOfUnsafeField,
749    DerefOfRawPointer,
750    AccessToUnionField,
751    MutationOfLayoutConstrainedField,
752    BorrowOfLayoutConstrainedField,
753    CallToFunctionWith {
754        function: DefId,
755        /// Target features enabled in callee's `#[target_feature]` but missing in
756        /// caller's `#[target_feature]`.
757        missing: Vec<Symbol>,
758        /// Target features in `missing` that are enabled at compile time
759        /// (e.g., with `-C target-feature`).
760        build_enabled: Vec<Symbol>,
761    },
762    UnsafeBinderCast,
763}
764
765use UnsafeOpKind::*;
766
767impl UnsafeOpKind {
768    fn emit_unsafe_op_in_unsafe_fn_lint(
769        &self,
770        tcx: TyCtxt<'_>,
771        hir_id: HirId,
772        span: Span,
773        suggest_unsafe_block: bool,
774    ) {
775        if tcx.hir_opt_delegation_sig_id(hir_id.owner.def_id).is_some() {
776            // The body of the delegation item is synthesized, so it makes no sense
777            // to emit this lint.
778            return;
779        }
780        let parent_id = tcx.hir_get_parent_item(hir_id);
781        let parent_owner = tcx.hir_owner_node(parent_id);
782        let should_suggest = parent_owner.fn_sig().is_some_and(|sig| {
783            // Do not suggest for safe target_feature functions
784            matches!(sig.header.safety, hir::HeaderSafety::Normal(hir::Safety::Unsafe))
785        });
786        let unsafe_not_inherited_note = if should_suggest {
787            suggest_unsafe_block.then(|| {
788                let body_span = tcx.hir_body(parent_owner.body_id().unwrap()).value.span;
789                UnsafeNotInheritedLintNote {
790                    signature_span: tcx.def_span(parent_id.def_id),
791                    body_span,
792                }
793            })
794        } else {
795            None
796        };
797        // FIXME: ideally we would want to trim the def paths, but this is not
798        // feasible with the current lint emission API (see issue #106126).
799        match self {
800            CallToUnsafeFunction(Some(did)) => tcx.emit_node_span_lint(
801                UNSAFE_OP_IN_UNSAFE_FN,
802                hir_id,
803                span,
804                UnsafeOpInUnsafeFnCallToUnsafeFunctionRequiresUnsafe {
805                    span,
806                    function: with_no_trimmed_paths!(tcx.def_path_str(*did)),
807                    unsafe_not_inherited_note,
808                },
809            ),
810            CallToUnsafeFunction(None) => tcx.emit_node_span_lint(
811                UNSAFE_OP_IN_UNSAFE_FN,
812                hir_id,
813                span,
814                UnsafeOpInUnsafeFnCallToUnsafeFunctionRequiresUnsafeNameless {
815                    span,
816                    unsafe_not_inherited_note,
817                },
818            ),
819            UseOfInlineAssembly => tcx.emit_node_span_lint(
820                UNSAFE_OP_IN_UNSAFE_FN,
821                hir_id,
822                span,
823                UnsafeOpInUnsafeFnUseOfInlineAssemblyRequiresUnsafe {
824                    span,
825                    unsafe_not_inherited_note,
826                },
827            ),
828            InitializingTypeWith => tcx.emit_node_span_lint(
829                UNSAFE_OP_IN_UNSAFE_FN,
830                hir_id,
831                span,
832                UnsafeOpInUnsafeFnInitializingTypeWithRequiresUnsafe {
833                    span,
834                    unsafe_not_inherited_note,
835                },
836            ),
837            InitializingTypeWithUnsafeField => tcx.emit_node_span_lint(
838                UNSAFE_OP_IN_UNSAFE_FN,
839                hir_id,
840                span,
841                UnsafeOpInUnsafeFnInitializingTypeWithUnsafeFieldRequiresUnsafe {
842                    span,
843                    unsafe_not_inherited_note,
844                },
845            ),
846            UseOfMutableStatic => tcx.emit_node_span_lint(
847                UNSAFE_OP_IN_UNSAFE_FN,
848                hir_id,
849                span,
850                UnsafeOpInUnsafeFnUseOfMutableStaticRequiresUnsafe {
851                    span,
852                    unsafe_not_inherited_note,
853                },
854            ),
855            UseOfExternStatic => tcx.emit_node_span_lint(
856                UNSAFE_OP_IN_UNSAFE_FN,
857                hir_id,
858                span,
859                UnsafeOpInUnsafeFnUseOfExternStaticRequiresUnsafe {
860                    span,
861                    unsafe_not_inherited_note,
862                },
863            ),
864            UseOfUnsafeField => tcx.emit_node_span_lint(
865                UNSAFE_OP_IN_UNSAFE_FN,
866                hir_id,
867                span,
868                UnsafeOpInUnsafeFnUseOfUnsafeFieldRequiresUnsafe {
869                    span,
870                    unsafe_not_inherited_note,
871                },
872            ),
873            DerefOfRawPointer => tcx.emit_node_span_lint(
874                UNSAFE_OP_IN_UNSAFE_FN,
875                hir_id,
876                span,
877                UnsafeOpInUnsafeFnDerefOfRawPointerRequiresUnsafe {
878                    span,
879                    unsafe_not_inherited_note,
880                },
881            ),
882            AccessToUnionField => tcx.emit_node_span_lint(
883                UNSAFE_OP_IN_UNSAFE_FN,
884                hir_id,
885                span,
886                UnsafeOpInUnsafeFnAccessToUnionFieldRequiresUnsafe {
887                    span,
888                    unsafe_not_inherited_note,
889                },
890            ),
891            MutationOfLayoutConstrainedField => tcx.emit_node_span_lint(
892                UNSAFE_OP_IN_UNSAFE_FN,
893                hir_id,
894                span,
895                UnsafeOpInUnsafeFnMutationOfLayoutConstrainedFieldRequiresUnsafe {
896                    span,
897                    unsafe_not_inherited_note,
898                },
899            ),
900            BorrowOfLayoutConstrainedField => tcx.emit_node_span_lint(
901                UNSAFE_OP_IN_UNSAFE_FN,
902                hir_id,
903                span,
904                UnsafeOpInUnsafeFnBorrowOfLayoutConstrainedFieldRequiresUnsafe {
905                    span,
906                    unsafe_not_inherited_note,
907                },
908            ),
909            CallToFunctionWith { function, missing, build_enabled } => tcx.emit_node_span_lint(
910                UNSAFE_OP_IN_UNSAFE_FN,
911                hir_id,
912                span,
913                UnsafeOpInUnsafeFnCallToFunctionWithRequiresUnsafe {
914                    span,
915                    function: with_no_trimmed_paths!(tcx.def_path_str(*function)),
916                    missing_target_features: DiagArgValue::StrListSepByAnd(
917                        missing.iter().map(|feature| Cow::from(feature.to_string())).collect(),
918                    ),
919                    missing_target_features_count: missing.len(),
920                    note: !build_enabled.is_empty(),
921                    build_target_features: DiagArgValue::StrListSepByAnd(
922                        build_enabled
923                            .iter()
924                            .map(|feature| Cow::from(feature.to_string()))
925                            .collect(),
926                    ),
927                    build_target_features_count: build_enabled.len(),
928                    unsafe_not_inherited_note,
929                },
930            ),
931            UnsafeBinderCast => tcx.emit_node_span_lint(
932                UNSAFE_OP_IN_UNSAFE_FN,
933                hir_id,
934                span,
935                UnsafeOpInUnsafeFnUnsafeBinderCastRequiresUnsafe {
936                    span,
937                    unsafe_not_inherited_note,
938                },
939            ),
940        }
941    }
942
943    fn emit_requires_unsafe_err(
944        &self,
945        tcx: TyCtxt<'_>,
946        span: Span,
947        hir_context: HirId,
948        unsafe_op_in_unsafe_fn_allowed: bool,
949    ) {
950        let note_non_inherited = tcx.hir_parent_iter(hir_context).find(|(id, node)| {
951            if let hir::Node::Expr(block) = node
952                && let hir::ExprKind::Block(block, _) = block.kind
953                && let hir::BlockCheckMode::UnsafeBlock(_) = block.rules
954            {
955                true
956            } else if let Some(sig) = tcx.hir_fn_sig_by_hir_id(*id)
957                && matches!(sig.header.safety, hir::HeaderSafety::Normal(hir::Safety::Unsafe))
958            {
959                true
960            } else {
961                false
962            }
963        });
964        let unsafe_not_inherited_note = if let Some((id, _)) = note_non_inherited {
965            let span = tcx.hir_span(id);
966            let span = tcx.sess.source_map().guess_head_span(span);
967            Some(UnsafeNotInheritedNote { span })
968        } else {
969            None
970        };
971
972        let dcx = tcx.dcx();
973        match self {
974            CallToUnsafeFunction(Some(did)) if unsafe_op_in_unsafe_fn_allowed => {
975                dcx.emit_err(CallToUnsafeFunctionRequiresUnsafeUnsafeOpInUnsafeFnAllowed {
976                    span,
977                    unsafe_not_inherited_note,
978                    function: tcx.def_path_str(*did),
979                });
980            }
981            CallToUnsafeFunction(Some(did)) => {
982                dcx.emit_err(CallToUnsafeFunctionRequiresUnsafe {
983                    span,
984                    unsafe_not_inherited_note,
985                    function: tcx.def_path_str(*did),
986                });
987            }
988            CallToUnsafeFunction(None) if unsafe_op_in_unsafe_fn_allowed => {
989                dcx.emit_err(CallToUnsafeFunctionRequiresUnsafeNamelessUnsafeOpInUnsafeFnAllowed {
990                    span,
991                    unsafe_not_inherited_note,
992                });
993            }
994            CallToUnsafeFunction(None) => {
995                dcx.emit_err(CallToUnsafeFunctionRequiresUnsafeNameless {
996                    span,
997                    unsafe_not_inherited_note,
998                });
999            }
1000            UseOfInlineAssembly if unsafe_op_in_unsafe_fn_allowed => {
1001                dcx.emit_err(UseOfInlineAssemblyRequiresUnsafeUnsafeOpInUnsafeFnAllowed {
1002                    span,
1003                    unsafe_not_inherited_note,
1004                });
1005            }
1006            UseOfInlineAssembly => {
1007                dcx.emit_err(UseOfInlineAssemblyRequiresUnsafe { span, unsafe_not_inherited_note });
1008            }
1009            InitializingTypeWith if unsafe_op_in_unsafe_fn_allowed => {
1010                dcx.emit_err(InitializingTypeWithRequiresUnsafeUnsafeOpInUnsafeFnAllowed {
1011                    span,
1012                    unsafe_not_inherited_note,
1013                });
1014            }
1015            InitializingTypeWith => {
1016                dcx.emit_err(InitializingTypeWithRequiresUnsafe {
1017                    span,
1018                    unsafe_not_inherited_note,
1019                });
1020            }
1021            InitializingTypeWithUnsafeField if unsafe_op_in_unsafe_fn_allowed => {
1022                dcx.emit_err(
1023                    InitializingTypeWithUnsafeFieldRequiresUnsafeUnsafeOpInUnsafeFnAllowed {
1024                        span,
1025                        unsafe_not_inherited_note,
1026                    },
1027                );
1028            }
1029            InitializingTypeWithUnsafeField => {
1030                dcx.emit_err(InitializingTypeWithUnsafeFieldRequiresUnsafe {
1031                    span,
1032                    unsafe_not_inherited_note,
1033                });
1034            }
1035            UseOfMutableStatic if unsafe_op_in_unsafe_fn_allowed => {
1036                dcx.emit_err(UseOfMutableStaticRequiresUnsafeUnsafeOpInUnsafeFnAllowed {
1037                    span,
1038                    unsafe_not_inherited_note,
1039                });
1040            }
1041            UseOfMutableStatic => {
1042                dcx.emit_err(UseOfMutableStaticRequiresUnsafe { span, unsafe_not_inherited_note });
1043            }
1044            UseOfExternStatic if unsafe_op_in_unsafe_fn_allowed => {
1045                dcx.emit_err(UseOfExternStaticRequiresUnsafeUnsafeOpInUnsafeFnAllowed {
1046                    span,
1047                    unsafe_not_inherited_note,
1048                });
1049            }
1050            UseOfExternStatic => {
1051                dcx.emit_err(UseOfExternStaticRequiresUnsafe { span, unsafe_not_inherited_note });
1052            }
1053            UseOfUnsafeField if unsafe_op_in_unsafe_fn_allowed => {
1054                dcx.emit_err(UseOfUnsafeFieldRequiresUnsafeUnsafeOpInUnsafeFnAllowed {
1055                    span,
1056                    unsafe_not_inherited_note,
1057                });
1058            }
1059            UseOfUnsafeField => {
1060                dcx.emit_err(UseOfUnsafeFieldRequiresUnsafe { span, unsafe_not_inherited_note });
1061            }
1062            DerefOfRawPointer if unsafe_op_in_unsafe_fn_allowed => {
1063                dcx.emit_err(DerefOfRawPointerRequiresUnsafeUnsafeOpInUnsafeFnAllowed {
1064                    span,
1065                    unsafe_not_inherited_note,
1066                });
1067            }
1068            DerefOfRawPointer => {
1069                dcx.emit_err(DerefOfRawPointerRequiresUnsafe { span, unsafe_not_inherited_note });
1070            }
1071            AccessToUnionField if unsafe_op_in_unsafe_fn_allowed => {
1072                dcx.emit_err(AccessToUnionFieldRequiresUnsafeUnsafeOpInUnsafeFnAllowed {
1073                    span,
1074                    unsafe_not_inherited_note,
1075                });
1076            }
1077            AccessToUnionField => {
1078                dcx.emit_err(AccessToUnionFieldRequiresUnsafe { span, unsafe_not_inherited_note });
1079            }
1080            MutationOfLayoutConstrainedField if unsafe_op_in_unsafe_fn_allowed => {
1081                dcx.emit_err(
1082                    MutationOfLayoutConstrainedFieldRequiresUnsafeUnsafeOpInUnsafeFnAllowed {
1083                        span,
1084                        unsafe_not_inherited_note,
1085                    },
1086                );
1087            }
1088            MutationOfLayoutConstrainedField => {
1089                dcx.emit_err(MutationOfLayoutConstrainedFieldRequiresUnsafe {
1090                    span,
1091                    unsafe_not_inherited_note,
1092                });
1093            }
1094            BorrowOfLayoutConstrainedField if unsafe_op_in_unsafe_fn_allowed => {
1095                dcx.emit_err(
1096                    BorrowOfLayoutConstrainedFieldRequiresUnsafeUnsafeOpInUnsafeFnAllowed {
1097                        span,
1098                        unsafe_not_inherited_note,
1099                    },
1100                );
1101            }
1102            BorrowOfLayoutConstrainedField => {
1103                dcx.emit_err(BorrowOfLayoutConstrainedFieldRequiresUnsafe {
1104                    span,
1105                    unsafe_not_inherited_note,
1106                });
1107            }
1108            CallToFunctionWith { function, missing, build_enabled }
1109                if unsafe_op_in_unsafe_fn_allowed =>
1110            {
1111                dcx.emit_err(CallToFunctionWithRequiresUnsafeUnsafeOpInUnsafeFnAllowed {
1112                    span,
1113                    missing_target_features: DiagArgValue::StrListSepByAnd(
1114                        missing.iter().map(|feature| Cow::from(feature.to_string())).collect(),
1115                    ),
1116                    missing_target_features_count: missing.len(),
1117                    note: !build_enabled.is_empty(),
1118                    build_target_features: DiagArgValue::StrListSepByAnd(
1119                        build_enabled
1120                            .iter()
1121                            .map(|feature| Cow::from(feature.to_string()))
1122                            .collect(),
1123                    ),
1124                    build_target_features_count: build_enabled.len(),
1125                    unsafe_not_inherited_note,
1126                    function: tcx.def_path_str(*function),
1127                });
1128            }
1129            CallToFunctionWith { function, missing, build_enabled } => {
1130                dcx.emit_err(CallToFunctionWithRequiresUnsafe {
1131                    span,
1132                    missing_target_features: DiagArgValue::StrListSepByAnd(
1133                        missing.iter().map(|feature| Cow::from(feature.to_string())).collect(),
1134                    ),
1135                    missing_target_features_count: missing.len(),
1136                    note: !build_enabled.is_empty(),
1137                    build_target_features: DiagArgValue::StrListSepByAnd(
1138                        build_enabled
1139                            .iter()
1140                            .map(|feature| Cow::from(feature.to_string()))
1141                            .collect(),
1142                    ),
1143                    build_target_features_count: build_enabled.len(),
1144                    unsafe_not_inherited_note,
1145                    function: tcx.def_path_str(*function),
1146                });
1147            }
1148            UnsafeBinderCast if unsafe_op_in_unsafe_fn_allowed => {
1149                dcx.emit_err(UnsafeBinderCastRequiresUnsafeUnsafeOpInUnsafeFnAllowed {
1150                    span,
1151                    unsafe_not_inherited_note,
1152                });
1153            }
1154            UnsafeBinderCast => {
1155                dcx.emit_err(UnsafeBinderCastRequiresUnsafe { span, unsafe_not_inherited_note });
1156            }
1157        }
1158    }
1159}
1160
1161pub(crate) fn check_unsafety(tcx: TyCtxt<'_>, def: LocalDefId) {
1162    // Closures and inline consts are handled by their owner, if it has a body
1163    assert!(!tcx.is_typeck_child(def.to_def_id()));
1164    // Also, don't safety check custom MIR
1165    if find_attr!(tcx.get_all_attrs(def), AttributeKind::CustomMir(..) => ()).is_some() {
1166        return;
1167    }
1168
1169    let Ok((thir, expr)) = tcx.thir_body(def) else { return };
1170    // Runs all other queries that depend on THIR.
1171    tcx.ensure_done().mir_built(def);
1172    let thir = if tcx.sess.opts.unstable_opts.no_steal_thir {
1173        &thir.borrow()
1174    } else {
1175        // We don't have other use for the THIR. Steal it to reduce memory usage.
1176        &thir.steal()
1177    };
1178
1179    let hir_id = tcx.local_def_id_to_hir_id(def);
1180    let safety_context = tcx.hir_fn_sig_by_hir_id(hir_id).map_or(SafetyContext::Safe, |fn_sig| {
1181        match fn_sig.header.safety {
1182            // We typeck the body as safe, but otherwise treat it as unsafe everywhere else.
1183            // Call sites to other SafeTargetFeatures functions are checked explicitly and don't need
1184            // to care about safety of the body.
1185            hir::HeaderSafety::SafeTargetFeatures => SafetyContext::Safe,
1186            hir::HeaderSafety::Normal(safety) => match safety {
1187                hir::Safety::Unsafe => SafetyContext::UnsafeFn,
1188                hir::Safety::Safe => SafetyContext::Safe,
1189            },
1190        }
1191    });
1192    let body_target_features = &tcx.body_codegen_attrs(def.to_def_id()).target_features;
1193    let mut warnings = Vec::new();
1194    let mut visitor = UnsafetyVisitor {
1195        tcx,
1196        thir,
1197        safety_context,
1198        hir_context: hir_id,
1199        body_target_features,
1200        assignment_info: None,
1201        in_union_destructure: false,
1202        // FIXME(#132279): we're clearly in a body here.
1203        typing_env: ty::TypingEnv::non_body_analysis(tcx, def),
1204        inside_adt: false,
1205        warnings: &mut warnings,
1206        suggest_unsafe_block: true,
1207    };
1208    // params in THIR may be unsafe, e.g. a union pattern.
1209    for param in &thir.params {
1210        if let Some(param_pat) = param.pat.as_deref() {
1211            visitor.visit_pat(param_pat);
1212        }
1213    }
1214    // Visit the body.
1215    visitor.visit_expr(&thir[expr]);
1216
1217    warnings.sort_by_key(|w| w.block_span);
1218    for UnusedUnsafeWarning { hir_id, block_span, enclosing_unsafe } in warnings {
1219        let block_span = tcx.sess.source_map().guess_head_span(block_span);
1220        tcx.emit_node_span_lint(
1221            UNUSED_UNSAFE,
1222            hir_id,
1223            block_span,
1224            UnusedUnsafe { span: block_span, enclosing: enclosing_unsafe },
1225        );
1226    }
1227}
rustc_mir_build/check_unsafety.rs

rustc_mir_build/
check_unsafety.rs
