rustc_mir_build/
check_unsafety.rs

Help
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::def::DefKind;
9use rustc_hir::{self as hir, BindingMode, ByRef, HirId, Mutability};
10use rustc_middle::middle::codegen_fn_attrs::TargetFeature;
11use rustc_middle::mir::BorrowKind;
12use rustc_middle::span_bug;
13use rustc_middle::thir::visit::Visitor;
14use rustc_middle::thir::*;
15use rustc_middle::ty::print::with_no_trimmed_paths;
16use rustc_middle::ty::{self, Ty, TyCtxt};
17use rustc_session::lint::Level;
18use rustc_session::lint::builtin::{DEPRECATED_SAFE_2024, UNSAFE_OP_IN_UNSAFE_FN, UNUSED_UNSAFE};
19use rustc_span::def_id::{DefId, LocalDefId};
20use rustc_span::{Span, Symbol, sym};
21
22use crate::builder::ExprCategory;
23use crate::errors::*;
24
25struct UnsafetyVisitor<'a, 'tcx> {
26    tcx: TyCtxt<'tcx>,
27    thir: &'a Thir<'tcx>,
28    /// The `HirId` of the current scope, which would be the `HirId`
29    /// of the current HIR node, modulo adjustments. Used for lint levels.
30    hir_context: HirId,
31    /// The current "safety context". This notably tracks whether we are in an
32    /// `unsafe` block, and whether it has been used.
33    safety_context: SafetyContext,
34    /// The `#[target_feature]` attributes of the body. Used for checking
35    /// calls to functions with `#[target_feature]` (RFC 2396).
36    body_target_features: &'tcx [TargetFeature],
37    /// When inside the LHS of an assignment to a field, this is the type
38    /// of the LHS and the span of the assignment expression.
39    assignment_info: Option<Ty<'tcx>>,
40    in_union_destructure: bool,
41    typing_env: ty::TypingEnv<'tcx>,
42    inside_adt: bool,
43    warnings: &'a mut Vec<UnusedUnsafeWarning>,
44
45    /// Flag to ensure that we only suggest wrapping the entire function body in
46    /// an unsafe block once.
47    suggest_unsafe_block: bool,
48}
49
50impl<'tcx> UnsafetyVisitor<'_, 'tcx> {
51    fn in_safety_context(&mut self, safety_context: SafetyContext, f: impl FnOnce(&mut Self)) {
52        let prev_context = mem::replace(&mut self.safety_context, safety_context);
53
54        f(self);
55
56        let safety_context = mem::replace(&mut self.safety_context, prev_context);
57        if let SafetyContext::UnsafeBlock { used, span, hir_id, nested_used_blocks } =
58            safety_context
59        {
60            if !used {
61                self.warn_unused_unsafe(hir_id, span, None);
62
63                if let SafetyContext::UnsafeBlock {
64                    nested_used_blocks: ref mut prev_nested_used_blocks,
65                    ..
66                } = self.safety_context
67                {
68                    prev_nested_used_blocks.extend(nested_used_blocks);
69                }
70            } else {
71                for block in nested_used_blocks {
72                    self.warn_unused_unsafe(
73                        block.hir_id,
74                        block.span,
75                        Some(UnusedUnsafeEnclosing::Block {
76                            span: self.tcx.sess.source_map().guess_head_span(span),
77                        }),
78                    );
79                }
80
81                match self.safety_context {
82                    SafetyContext::UnsafeBlock {
83                        nested_used_blocks: ref mut prev_nested_used_blocks,
84                        ..
85                    } => {
86                        prev_nested_used_blocks.push(NestedUsedBlock { hir_id, span });
87                    }
88                    _ => (),
89                }
90            }
91        }
92    }
93
94    fn emit_deprecated_safe_fn_call(&self, span: Span, kind: &UnsafeOpKind) -> bool {
95        match kind {
96            // Allow calls to deprecated-safe unsafe functions if the caller is
97            // from an edition before 2024.
98            &UnsafeOpKind::CallToUnsafeFunction(Some(id))
99                if !span.at_least_rust_2024()
100                    && let Some(attr) = self.tcx.get_attr(id, sym::rustc_deprecated_safe_2024) =>
101            {
102                let suggestion = attr
103                    .meta_item_list()
104                    .unwrap_or_default()
105                    .into_iter()
106                    .find(|item| item.has_name(sym::audit_that))
107                    .map(|item| {
108                        item.value_str().expect(
109                            "`#[rustc_deprecated_safe_2024(audit_that)]` must have a string value",
110                        )
111                    });
112
113                let sm = self.tcx.sess.source_map();
114                let guarantee = suggestion
115                    .as_ref()
116                    .map(|suggestion| format!("that {}", suggestion))
117                    .unwrap_or_else(|| String::from("its unsafe preconditions"));
118                let suggestion = suggestion
119                    .and_then(|suggestion| {
120                        sm.indentation_before(span).map(|indent| {
121                            format!("{}// TODO: Audit that {}.\n", indent, suggestion) // ignore-tidy-todo
122                        })
123                    })
124                    .unwrap_or_default();
125
126                self.tcx.emit_node_span_lint(
127                    DEPRECATED_SAFE_2024,
128                    self.hir_context,
129                    span,
130                    CallToDeprecatedSafeFnRequiresUnsafe {
131                        span,
132                        function: with_no_trimmed_paths!(self.tcx.def_path_str(id)),
133                        guarantee,
134                        sub: CallToDeprecatedSafeFnRequiresUnsafeSub {
135                            start_of_line_suggestion: suggestion,
136                            start_of_line: sm.span_extend_to_line(span).shrink_to_lo(),
137                            left: span.shrink_to_lo(),
138                            right: span.shrink_to_hi(),
139                        },
140                    },
141                );
142                true
143            }
144            _ => false,
145        }
146    }
147
148    fn requires_unsafe(&mut self, span: Span, kind: UnsafeOpKind) {
149        let unsafe_op_in_unsafe_fn_allowed = self.unsafe_op_in_unsafe_fn_allowed();
150        match self.safety_context {
151            SafetyContext::BuiltinUnsafeBlock => {}
152            SafetyContext::UnsafeBlock { ref mut used, .. } => {
153                // Mark this block as useful (even inside `unsafe fn`, where it is technically
154                // redundant -- but we want to eventually enable `unsafe_op_in_unsafe_fn` by
155                // default which will require those blocks:
156                // https://github.com/rust-lang/rust/issues/71668#issuecomment-1203075594).
157                *used = true;
158            }
159            SafetyContext::UnsafeFn if unsafe_op_in_unsafe_fn_allowed => {}
160            SafetyContext::UnsafeFn => {
161                let deprecated_safe_fn = self.emit_deprecated_safe_fn_call(span, &kind);
162                if !deprecated_safe_fn {
163                    // unsafe_op_in_unsafe_fn is disallowed
164                    kind.emit_unsafe_op_in_unsafe_fn_lint(
165                        self.tcx,
166                        self.hir_context,
167                        span,
168                        self.suggest_unsafe_block,
169                    );
170                    self.suggest_unsafe_block = false;
171                }
172            }
173            SafetyContext::Safe => {
174                let deprecated_safe_fn = self.emit_deprecated_safe_fn_call(span, &kind);
175                if !deprecated_safe_fn {
176                    kind.emit_requires_unsafe_err(
177                        self.tcx,
178                        span,
179                        self.hir_context,
180                        unsafe_op_in_unsafe_fn_allowed,
181                    );
182                }
183            }
184        }
185    }
186
187    fn warn_unused_unsafe(
188        &mut self,
189        hir_id: HirId,
190        block_span: Span,
191        enclosing_unsafe: Option<UnusedUnsafeEnclosing>,
192    ) {
193        self.warnings.push(UnusedUnsafeWarning { hir_id, block_span, enclosing_unsafe });
194    }
195
196    /// Whether the `unsafe_op_in_unsafe_fn` lint is `allow`ed at the current HIR node.
197    fn unsafe_op_in_unsafe_fn_allowed(&self) -> bool {
198        self.tcx.lint_level_at_node(UNSAFE_OP_IN_UNSAFE_FN, self.hir_context).0 == Level::Allow
199    }
200
201    /// Handle closures/coroutines/inline-consts, which is unsafecked with their parent body.
202    fn visit_inner_body(&mut self, def: LocalDefId) {
203        if let Ok((inner_thir, expr)) = self.tcx.thir_body(def) {
204            // Runs all other queries that depend on THIR.
205            self.tcx.ensure_done().mir_built(def);
206            let inner_thir = &inner_thir.steal();
207            let hir_context = self.tcx.local_def_id_to_hir_id(def);
208            let safety_context = mem::replace(&mut self.safety_context, SafetyContext::Safe);
209            let mut inner_visitor = UnsafetyVisitor {
210                tcx: self.tcx,
211                thir: inner_thir,
212                hir_context,
213                safety_context,
214                body_target_features: self.body_target_features,
215                assignment_info: self.assignment_info,
216                in_union_destructure: false,
217                typing_env: self.typing_env,
218                inside_adt: false,
219                warnings: self.warnings,
220                suggest_unsafe_block: self.suggest_unsafe_block,
221            };
222            // params in THIR may be unsafe, e.g. a union pattern.
223            for param in &inner_thir.params {
224                if let Some(param_pat) = param.pat.as_deref() {
225                    inner_visitor.visit_pat(param_pat);
226                }
227            }
228            // Visit the body.
229            inner_visitor.visit_expr(&inner_thir[expr]);
230            // Unsafe blocks can be used in the inner body, make sure to take it into account
231            self.safety_context = inner_visitor.safety_context;
232        }
233    }
234}
235
236// Searches for accesses to layout constrained fields.
237struct LayoutConstrainedPlaceVisitor<'a, 'tcx> {
238    found: bool,
239    thir: &'a Thir<'tcx>,
240    tcx: TyCtxt<'tcx>,
241}
242
243impl<'a, 'tcx> LayoutConstrainedPlaceVisitor<'a, 'tcx> {
244    fn new(thir: &'a Thir<'tcx>, tcx: TyCtxt<'tcx>) -> Self {
245        Self { found: false, thir, tcx }
246    }
247}
248
249impl<'a, 'tcx> Visitor<'a, 'tcx> for LayoutConstrainedPlaceVisitor<'a, 'tcx> {
250    fn thir(&self) -> &'a Thir<'tcx> {
251        self.thir
252    }
253
254    fn visit_expr(&mut self, expr: &'a Expr<'tcx>) {
255        match expr.kind {
256            ExprKind::Field { lhs, .. } => {
257                if let ty::Adt(adt_def, _) = self.thir[lhs].ty.kind() {
258                    if (Bound::Unbounded, Bound::Unbounded)
259                        != self.tcx.layout_scalar_valid_range(adt_def.did())
260                    {
261                        self.found = true;
262                    }
263                }
264                visit::walk_expr(self, expr);
265            }
266
267            // Keep walking through the expression as long as we stay in the same
268            // place, i.e. the expression is a place expression and not a dereference
269            // (since dereferencing something leads us to a different place).
270            ExprKind::Deref { .. } => {}
271            ref kind if ExprCategory::of(kind).is_none_or(|cat| cat == ExprCategory::Place) => {
272                visit::walk_expr(self, expr);
273            }
274
275            _ => {}
276        }
277    }
278}
279
280impl<'a, 'tcx> Visitor<'a, 'tcx> for UnsafetyVisitor<'a, 'tcx> {
281    fn thir(&self) -> &'a Thir<'tcx> {
282        self.thir
283    }
284
285    fn visit_block(&mut self, block: &'a Block) {
286        match block.safety_mode {
287            // compiler-generated unsafe code should not count towards the usefulness of
288            // an outer unsafe block
289            BlockSafety::BuiltinUnsafe => {
290                self.in_safety_context(SafetyContext::BuiltinUnsafeBlock, |this| {
291                    visit::walk_block(this, block)
292                });
293            }
294            BlockSafety::ExplicitUnsafe(hir_id) => {
295                let used =
296                    matches!(self.tcx.lint_level_at_node(UNUSED_UNSAFE, hir_id), (Level::Allow, _));
297                self.in_safety_context(
298                    SafetyContext::UnsafeBlock {
299                        span: block.span,
300                        hir_id,
301                        used,
302                        nested_used_blocks: Vec::new(),
303                    },
304                    |this| visit::walk_block(this, block),
305                );
306            }
307            BlockSafety::Safe => {
308                visit::walk_block(self, block);
309            }
310        }
311    }
312
313    fn visit_pat(&mut self, pat: &'a Pat<'tcx>) {
314        if self.in_union_destructure {
315            match pat.kind {
316                // binding to a variable allows getting stuff out of variable
317                PatKind::Binding { .. }
318                // match is conditional on having this value
319                | PatKind::Constant { .. }
320                | PatKind::Variant { .. }
321                | PatKind::Leaf { .. }
322                | PatKind::Deref { .. }
323                | PatKind::DerefPattern { .. }
324                | PatKind::Range { .. }
325                | PatKind::Slice { .. }
326                | PatKind::Array { .. }
327                // Never constitutes a witness of uninhabitedness.
328                | PatKind::Never => {
329                    self.requires_unsafe(pat.span, AccessToUnionField);
330                    return; // we can return here since this already requires unsafe
331                }
332                // wildcard doesn't read anything.
333                PatKind::Wild |
334                // these just wrap other patterns, which we recurse on below.
335                PatKind::Or { .. } |
336                PatKind::ExpandedConstant { .. } |
337                PatKind::AscribeUserType { .. } |
338                PatKind::Error(_) => {}
339            }
340        };
341
342        match &pat.kind {
343            PatKind::Leaf { subpatterns, .. } => {
344                if let ty::Adt(adt_def, ..) = pat.ty.kind() {
345                    for pat in subpatterns {
346                        if adt_def.non_enum_variant().fields[pat.field].safety.is_unsafe() {
347                            self.requires_unsafe(pat.pattern.span, UseOfUnsafeField);
348                        }
349                    }
350                    if adt_def.is_union() {
351                        let old_in_union_destructure =
352                            std::mem::replace(&mut self.in_union_destructure, true);
353                        visit::walk_pat(self, pat);
354                        self.in_union_destructure = old_in_union_destructure;
355                    } else if (Bound::Unbounded, Bound::Unbounded)
356                        != self.tcx.layout_scalar_valid_range(adt_def.did())
357                    {
358                        let old_inside_adt = std::mem::replace(&mut self.inside_adt, true);
359                        visit::walk_pat(self, pat);
360                        self.inside_adt = old_inside_adt;
361                    } else {
362                        visit::walk_pat(self, pat);
363                    }
364                } else {
365                    visit::walk_pat(self, pat);
366                }
367            }
368            PatKind::Variant { adt_def, args: _, variant_index, subpatterns } => {
369                for pat in subpatterns {
370                    let field = &pat.field;
371                    if adt_def.variant(*variant_index).fields[*field].safety.is_unsafe() {
372                        self.requires_unsafe(pat.pattern.span, UseOfUnsafeField);
373                    }
374                }
375                visit::walk_pat(self, pat);
376            }
377            PatKind::Binding { mode: BindingMode(ByRef::Yes(rm), _), ty, .. } => {
378                if self.inside_adt {
379                    let ty::Ref(_, ty, _) = ty.kind() else {
380                        span_bug!(
381                            pat.span,
382                            "ByRef::Yes in pattern, but found non-reference type {}",
383                            ty
384                        );
385                    };
386                    match rm {
387                        Mutability::Not => {
388                            if !ty.is_freeze(self.tcx, self.typing_env) {
389                                self.requires_unsafe(pat.span, BorrowOfLayoutConstrainedField);
390                            }
391                        }
392                        Mutability::Mut { .. } => {
393                            self.requires_unsafe(pat.span, MutationOfLayoutConstrainedField);
394                        }
395                    }
396                }
397                visit::walk_pat(self, pat);
398            }
399            PatKind::Deref { .. } | PatKind::DerefPattern { .. } => {
400                let old_inside_adt = std::mem::replace(&mut self.inside_adt, false);
401                visit::walk_pat(self, pat);
402                self.inside_adt = old_inside_adt;
403            }
404            PatKind::ExpandedConstant { def_id, is_inline, .. } => {
405                if let Some(def) = def_id.as_local()
406                    && *is_inline
407                {
408                    self.visit_inner_body(def);
409                }
410                visit::walk_pat(self, pat);
411            }
412            _ => {
413                visit::walk_pat(self, pat);
414            }
415        }
416    }
417
418    fn visit_expr(&mut self, expr: &'a Expr<'tcx>) {
419        // could we be in the LHS of an assignment to a field?
420        match expr.kind {
421            ExprKind::Field { .. }
422            | ExprKind::VarRef { .. }
423            | ExprKind::UpvarRef { .. }
424            | ExprKind::Scope { .. }
425            | ExprKind::Cast { .. } => {}
426
427            ExprKind::RawBorrow { .. }
428            | ExprKind::Adt { .. }
429            | ExprKind::Array { .. }
430            | ExprKind::Binary { .. }
431            | ExprKind::Block { .. }
432            | ExprKind::Borrow { .. }
433            | ExprKind::Literal { .. }
434            | ExprKind::NamedConst { .. }
435            | ExprKind::NonHirLiteral { .. }
436            | ExprKind::ZstLiteral { .. }
437            | ExprKind::ConstParam { .. }
438            | ExprKind::ConstBlock { .. }
439            | ExprKind::Deref { .. }
440            | ExprKind::Index { .. }
441            | ExprKind::NeverToAny { .. }
442            | ExprKind::PlaceTypeAscription { .. }
443            | ExprKind::ValueTypeAscription { .. }
444            | ExprKind::PlaceUnwrapUnsafeBinder { .. }
445            | ExprKind::ValueUnwrapUnsafeBinder { .. }
446            | ExprKind::WrapUnsafeBinder { .. }
447            | ExprKind::PointerCoercion { .. }
448            | ExprKind::Repeat { .. }
449            | ExprKind::StaticRef { .. }
450            | ExprKind::ThreadLocalRef { .. }
451            | ExprKind::Tuple { .. }
452            | ExprKind::Unary { .. }
453            | ExprKind::Call { .. }
454            | ExprKind::ByUse { .. }
455            | ExprKind::Assign { .. }
456            | ExprKind::AssignOp { .. }
457            | ExprKind::Break { .. }
458            | ExprKind::Closure { .. }
459            | ExprKind::Continue { .. }
460            | ExprKind::Return { .. }
461            | ExprKind::Become { .. }
462            | ExprKind::Yield { .. }
463            | ExprKind::Loop { .. }
464            | ExprKind::Let { .. }
465            | ExprKind::Match { .. }
466            | ExprKind::Box { .. }
467            | ExprKind::If { .. }
468            | ExprKind::InlineAsm { .. }
469            | ExprKind::OffsetOf { .. }
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.implied
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            ExprKind::Deref { arg } => {
548                if let ExprKind::StaticRef { def_id, .. } | ExprKind::ThreadLocalRef(def_id) =
549                    self.thir[arg].kind
550                {
551                    if self.tcx.is_mutable_static(def_id) {
552                        self.requires_unsafe(expr.span, UseOfMutableStatic);
553                    } else if self.tcx.is_foreign_item(def_id) {
554                        match self.tcx.def_kind(def_id) {
555                            DefKind::Static { safety: hir::Safety::Safe, .. } => {}
556                            _ => self.requires_unsafe(expr.span, UseOfExternStatic),
557                        }
558                    }
559                } else if self.thir[arg].ty.is_raw_ptr() {
560                    self.requires_unsafe(expr.span, DerefOfRawPointer);
561                }
562            }
563            ExprKind::InlineAsm(box InlineAsmExpr {
564                asm_macro: AsmMacro::Asm | AsmMacro::NakedAsm,
565                ref operands,
566                template: _,
567                options: _,
568                line_spans: _,
569            }) => {
570                self.requires_unsafe(expr.span, UseOfInlineAssembly);
571
572                // For inline asm, do not use `walk_expr`, since we want to handle the label block
573                // specially.
574                for op in &**operands {
575                    use rustc_middle::thir::InlineAsmOperand::*;
576                    match op {
577                        In { expr, reg: _ }
578                        | Out { expr: Some(expr), reg: _, late: _ }
579                        | InOut { expr, reg: _, late: _ } => self.visit_expr(&self.thir()[*expr]),
580                        SplitInOut { in_expr, out_expr, reg: _, late: _ } => {
581                            self.visit_expr(&self.thir()[*in_expr]);
582                            if let Some(out_expr) = out_expr {
583                                self.visit_expr(&self.thir()[*out_expr]);
584                            }
585                        }
586                        Out { expr: None, reg: _, late: _ }
587                        | Const { value: _, span: _ }
588                        | SymFn { value: _ }
589                        | SymStatic { def_id: _ } => {}
590                        Label { block } => {
591                            // Label blocks are safe context.
592                            // `asm!()` is forced to be wrapped inside unsafe. If there's no special
593                            // treatment, the label blocks would also always be unsafe with no way
594                            // of opting out.
595                            self.in_safety_context(SafetyContext::Safe, |this| {
596                                visit::walk_block(this, &this.thir()[*block])
597                            });
598                        }
599                    }
600                }
601                return;
602            }
603            ExprKind::Adt(box AdtExpr {
604                adt_def,
605                variant_index,
606                args: _,
607                user_ty: _,
608                fields: _,
609                base: _,
610            }) => {
611                if adt_def.variant(variant_index).has_unsafe_fields() {
612                    self.requires_unsafe(expr.span, InitializingTypeWithUnsafeField)
613                }
614                match self.tcx.layout_scalar_valid_range(adt_def.did()) {
615                    (Bound::Unbounded, Bound::Unbounded) => {}
616                    _ => self.requires_unsafe(expr.span, InitializingTypeWith),
617                }
618            }
619            ExprKind::Closure(box ClosureExpr {
620                closure_id,
621                args: _,
622                upvars: _,
623                movability: _,
624                fake_reads: _,
625            }) => {
626                self.visit_inner_body(closure_id);
627            }
628            ExprKind::ConstBlock { did, args: _ } => {
629                let def_id = did.expect_local();
630                self.visit_inner_body(def_id);
631            }
632            ExprKind::Field { lhs, variant_index, name } => {
633                let lhs = &self.thir[lhs];
634                if let ty::Adt(adt_def, _) = lhs.ty.kind() {
635                    if adt_def.variant(variant_index).fields[name].safety.is_unsafe() {
636                        self.requires_unsafe(expr.span, UseOfUnsafeField);
637                    } else if adt_def.is_union() {
638                        if let Some(assigned_ty) = self.assignment_info {
639                            if assigned_ty.needs_drop(self.tcx, self.typing_env) {
640                                // This would be unsafe, but should be outright impossible since we
641                                // reject such unions.
642                                assert!(
643                                    self.tcx.dcx().has_errors().is_some(),
644                                    "union fields that need dropping should be impossible: {assigned_ty}"
645                                );
646                            }
647                        } else {
648                            self.requires_unsafe(expr.span, AccessToUnionField);
649                        }
650                    }
651                }
652            }
653            ExprKind::Assign { lhs, rhs } | ExprKind::AssignOp { lhs, rhs, .. } => {
654                let lhs = &self.thir[lhs];
655                // First, check whether we are mutating a layout constrained field
656                let mut visitor = LayoutConstrainedPlaceVisitor::new(self.thir, self.tcx);
657                visit::walk_expr(&mut visitor, lhs);
658                if visitor.found {
659                    self.requires_unsafe(expr.span, MutationOfLayoutConstrainedField);
660                }
661
662                // Second, check for accesses to union fields. Don't have any
663                // special handling for AssignOp since it causes a read *and*
664                // write to lhs.
665                if matches!(expr.kind, ExprKind::Assign { .. }) {
666                    self.assignment_info = Some(lhs.ty);
667                    visit::walk_expr(self, lhs);
668                    self.assignment_info = None;
669                    visit::walk_expr(self, &self.thir()[rhs]);
670                    return; // We have already visited everything by now.
671                }
672            }
673            ExprKind::Borrow { borrow_kind, arg } => {
674                let mut visitor = LayoutConstrainedPlaceVisitor::new(self.thir, self.tcx);
675                visit::walk_expr(&mut visitor, expr);
676                if visitor.found {
677                    match borrow_kind {
678                        BorrowKind::Fake(_) | BorrowKind::Shared
679                            if !self.thir[arg].ty.is_freeze(self.tcx, self.typing_env) =>
680                        {
681                            self.requires_unsafe(expr.span, BorrowOfLayoutConstrainedField)
682                        }
683                        BorrowKind::Mut { .. } => {
684                            self.requires_unsafe(expr.span, MutationOfLayoutConstrainedField)
685                        }
686                        BorrowKind::Fake(_) | BorrowKind::Shared => {}
687                    }
688                }
689            }
690            ExprKind::PlaceUnwrapUnsafeBinder { .. }
691            | ExprKind::ValueUnwrapUnsafeBinder { .. }
692            | ExprKind::WrapUnsafeBinder { .. } => {
693                self.requires_unsafe(expr.span, UnsafeBinderCast);
694            }
695            _ => {}
696        }
697        visit::walk_expr(self, expr);
698    }
699}
700
701#[derive(Clone)]
702enum SafetyContext {
703    Safe,
704    BuiltinUnsafeBlock,
705    UnsafeFn,
706    UnsafeBlock { span: Span, hir_id: HirId, used: bool, nested_used_blocks: Vec<NestedUsedBlock> },
707}
708
709#[derive(Clone, Copy)]
710struct NestedUsedBlock {
711    hir_id: HirId,
712    span: Span,
713}
714
715struct UnusedUnsafeWarning {
716    hir_id: HirId,
717    block_span: Span,
718    enclosing_unsafe: Option<UnusedUnsafeEnclosing>,
719}
720
721#[derive(Clone, PartialEq)]
722enum UnsafeOpKind {
723    CallToUnsafeFunction(Option<DefId>),
724    UseOfInlineAssembly,
725    InitializingTypeWith,
726    InitializingTypeWithUnsafeField,
727    UseOfMutableStatic,
728    UseOfExternStatic,
729    UseOfUnsafeField,
730    DerefOfRawPointer,
731    AccessToUnionField,
732    MutationOfLayoutConstrainedField,
733    BorrowOfLayoutConstrainedField,
734    CallToFunctionWith {
735        function: DefId,
736        /// Target features enabled in callee's `#[target_feature]` but missing in
737        /// caller's `#[target_feature]`.
738        missing: Vec<Symbol>,
739        /// Target features in `missing` that are enabled at compile time
740        /// (e.g., with `-C target-feature`).
741        build_enabled: Vec<Symbol>,
742    },
743    UnsafeBinderCast,
744}
745
746use UnsafeOpKind::*;
747
748impl UnsafeOpKind {
749    fn emit_unsafe_op_in_unsafe_fn_lint(
750        &self,
751        tcx: TyCtxt<'_>,
752        hir_id: HirId,
753        span: Span,
754        suggest_unsafe_block: bool,
755    ) {
756        if tcx.hir_opt_delegation_sig_id(hir_id.owner.def_id).is_some() {
757            // The body of the delegation item is synthesized, so it makes no sense
758            // to emit this lint.
759            return;
760        }
761        let parent_id = tcx.hir_get_parent_item(hir_id);
762        let parent_owner = tcx.hir_owner_node(parent_id);
763        let should_suggest = parent_owner.fn_sig().is_some_and(|sig| {
764            // Do not suggest for safe target_feature functions
765            matches!(sig.header.safety, hir::HeaderSafety::Normal(hir::Safety::Unsafe))
766        });
767        let unsafe_not_inherited_note = if should_suggest {
768            suggest_unsafe_block.then(|| {
769                let body_span = tcx.hir_body(parent_owner.body_id().unwrap()).value.span;
770                UnsafeNotInheritedLintNote {
771                    signature_span: tcx.def_span(parent_id.def_id),
772                    body_span,
773                }
774            })
775        } else {
776            None
777        };
778        // FIXME: ideally we would want to trim the def paths, but this is not
779        // feasible with the current lint emission API (see issue #106126).
780        match self {
781            CallToUnsafeFunction(Some(did)) => tcx.emit_node_span_lint(
782                UNSAFE_OP_IN_UNSAFE_FN,
783                hir_id,
784                span,
785                UnsafeOpInUnsafeFnCallToUnsafeFunctionRequiresUnsafe {
786                    span,
787                    function: with_no_trimmed_paths!(tcx.def_path_str(*did)),
788                    unsafe_not_inherited_note,
789                },
790            ),
791            CallToUnsafeFunction(None) => tcx.emit_node_span_lint(
792                UNSAFE_OP_IN_UNSAFE_FN,
793                hir_id,
794                span,
795                UnsafeOpInUnsafeFnCallToUnsafeFunctionRequiresUnsafeNameless {
796                    span,
797                    unsafe_not_inherited_note,
798                },
799            ),
800            UseOfInlineAssembly => tcx.emit_node_span_lint(
801                UNSAFE_OP_IN_UNSAFE_FN,
802                hir_id,
803                span,
804                UnsafeOpInUnsafeFnUseOfInlineAssemblyRequiresUnsafe {
805                    span,
806                    unsafe_not_inherited_note,
807                },
808            ),
809            InitializingTypeWith => tcx.emit_node_span_lint(
810                UNSAFE_OP_IN_UNSAFE_FN,
811                hir_id,
812                span,
813                UnsafeOpInUnsafeFnInitializingTypeWithRequiresUnsafe {
814                    span,
815                    unsafe_not_inherited_note,
816                },
817            ),
818            InitializingTypeWithUnsafeField => tcx.emit_node_span_lint(
819                UNSAFE_OP_IN_UNSAFE_FN,
820                hir_id,
821                span,
822                UnsafeOpInUnsafeFnInitializingTypeWithUnsafeFieldRequiresUnsafe {
823                    span,
824                    unsafe_not_inherited_note,
825                },
826            ),
827            UseOfMutableStatic => tcx.emit_node_span_lint(
828                UNSAFE_OP_IN_UNSAFE_FN,
829                hir_id,
830                span,
831                UnsafeOpInUnsafeFnUseOfMutableStaticRequiresUnsafe {
832                    span,
833                    unsafe_not_inherited_note,
834                },
835            ),
836            UseOfExternStatic => tcx.emit_node_span_lint(
837                UNSAFE_OP_IN_UNSAFE_FN,
838                hir_id,
839                span,
840                UnsafeOpInUnsafeFnUseOfExternStaticRequiresUnsafe {
841                    span,
842                    unsafe_not_inherited_note,
843                },
844            ),
845            UseOfUnsafeField => tcx.emit_node_span_lint(
846                UNSAFE_OP_IN_UNSAFE_FN,
847                hir_id,
848                span,
849                UnsafeOpInUnsafeFnUseOfUnsafeFieldRequiresUnsafe {
850                    span,
851                    unsafe_not_inherited_note,
852                },
853            ),
854            DerefOfRawPointer => tcx.emit_node_span_lint(
855                UNSAFE_OP_IN_UNSAFE_FN,
856                hir_id,
857                span,
858                UnsafeOpInUnsafeFnDerefOfRawPointerRequiresUnsafe {
859                    span,
860                    unsafe_not_inherited_note,
861                },
862            ),
863            AccessToUnionField => tcx.emit_node_span_lint(
864                UNSAFE_OP_IN_UNSAFE_FN,
865                hir_id,
866                span,
867                UnsafeOpInUnsafeFnAccessToUnionFieldRequiresUnsafe {
868                    span,
869                    unsafe_not_inherited_note,
870                },
871            ),
872            MutationOfLayoutConstrainedField => tcx.emit_node_span_lint(
873                UNSAFE_OP_IN_UNSAFE_FN,
874                hir_id,
875                span,
876                UnsafeOpInUnsafeFnMutationOfLayoutConstrainedFieldRequiresUnsafe {
877                    span,
878                    unsafe_not_inherited_note,
879                },
880            ),
881            BorrowOfLayoutConstrainedField => tcx.emit_node_span_lint(
882                UNSAFE_OP_IN_UNSAFE_FN,
883                hir_id,
884                span,
885                UnsafeOpInUnsafeFnBorrowOfLayoutConstrainedFieldRequiresUnsafe {
886                    span,
887                    unsafe_not_inherited_note,
888                },
889            ),
890            CallToFunctionWith { function, missing, build_enabled } => tcx.emit_node_span_lint(
891                UNSAFE_OP_IN_UNSAFE_FN,
892                hir_id,
893                span,
894                UnsafeOpInUnsafeFnCallToFunctionWithRequiresUnsafe {
895                    span,
896                    function: with_no_trimmed_paths!(tcx.def_path_str(*function)),
897                    missing_target_features: DiagArgValue::StrListSepByAnd(
898                        missing.iter().map(|feature| Cow::from(feature.to_string())).collect(),
899                    ),
900                    missing_target_features_count: missing.len(),
901                    note: !build_enabled.is_empty(),
902                    build_target_features: DiagArgValue::StrListSepByAnd(
903                        build_enabled
904                            .iter()
905                            .map(|feature| Cow::from(feature.to_string()))
906                            .collect(),
907                    ),
908                    build_target_features_count: build_enabled.len(),
909                    unsafe_not_inherited_note,
910                },
911            ),
912            UnsafeBinderCast => tcx.emit_node_span_lint(
913                UNSAFE_OP_IN_UNSAFE_FN,
914                hir_id,
915                span,
916                UnsafeOpInUnsafeFnUnsafeBinderCastRequiresUnsafe {
917                    span,
918                    unsafe_not_inherited_note,
919                },
920            ),
921        }
922    }
923
924    fn emit_requires_unsafe_err(
925        &self,
926        tcx: TyCtxt<'_>,
927        span: Span,
928        hir_context: HirId,
929        unsafe_op_in_unsafe_fn_allowed: bool,
930    ) {
931        let note_non_inherited = tcx.hir_parent_iter(hir_context).find(|(id, node)| {
932            if let hir::Node::Expr(block) = node
933                && let hir::ExprKind::Block(block, _) = block.kind
934                && let hir::BlockCheckMode::UnsafeBlock(_) = block.rules
935            {
936                true
937            } else if let Some(sig) = tcx.hir_fn_sig_by_hir_id(*id)
938                && matches!(sig.header.safety, hir::HeaderSafety::Normal(hir::Safety::Unsafe))
939            {
940                true
941            } else {
942                false
943            }
944        });
945        let unsafe_not_inherited_note = if let Some((id, _)) = note_non_inherited {
946            let span = tcx.hir().span(id);
947            let span = tcx.sess.source_map().guess_head_span(span);
948            Some(UnsafeNotInheritedNote { span })
949        } else {
950            None
951        };
952
953        let dcx = tcx.dcx();
954        match self {
955            CallToUnsafeFunction(Some(did)) if unsafe_op_in_unsafe_fn_allowed => {
956                dcx.emit_err(CallToUnsafeFunctionRequiresUnsafeUnsafeOpInUnsafeFnAllowed {
957                    span,
958                    unsafe_not_inherited_note,
959                    function: tcx.def_path_str(*did),
960                });
961            }
962            CallToUnsafeFunction(Some(did)) => {
963                dcx.emit_err(CallToUnsafeFunctionRequiresUnsafe {
964                    span,
965                    unsafe_not_inherited_note,
966                    function: tcx.def_path_str(*did),
967                });
968            }
969            CallToUnsafeFunction(None) if unsafe_op_in_unsafe_fn_allowed => {
970                dcx.emit_err(CallToUnsafeFunctionRequiresUnsafeNamelessUnsafeOpInUnsafeFnAllowed {
971                    span,
972                    unsafe_not_inherited_note,
973                });
974            }
975            CallToUnsafeFunction(None) => {
976                dcx.emit_err(CallToUnsafeFunctionRequiresUnsafeNameless {
977                    span,
978                    unsafe_not_inherited_note,
979                });
980            }
981            UseOfInlineAssembly if unsafe_op_in_unsafe_fn_allowed => {
982                dcx.emit_err(UseOfInlineAssemblyRequiresUnsafeUnsafeOpInUnsafeFnAllowed {
983                    span,
984                    unsafe_not_inherited_note,
985                });
986            }
987            UseOfInlineAssembly => {
988                dcx.emit_err(UseOfInlineAssemblyRequiresUnsafe { span, unsafe_not_inherited_note });
989            }
990            InitializingTypeWith if unsafe_op_in_unsafe_fn_allowed => {
991                dcx.emit_err(InitializingTypeWithRequiresUnsafeUnsafeOpInUnsafeFnAllowed {
992                    span,
993                    unsafe_not_inherited_note,
994                });
995            }
996            InitializingTypeWith => {
997                dcx.emit_err(InitializingTypeWithRequiresUnsafe {
998                    span,
999                    unsafe_not_inherited_note,
1000                });
1001            }
1002            InitializingTypeWithUnsafeField if unsafe_op_in_unsafe_fn_allowed => {
1003                dcx.emit_err(
1004                    InitializingTypeWithUnsafeFieldRequiresUnsafeUnsafeOpInUnsafeFnAllowed {
1005                        span,
1006                        unsafe_not_inherited_note,
1007                    },
1008                );
1009            }
1010            InitializingTypeWithUnsafeField => {
1011                dcx.emit_err(InitializingTypeWithUnsafeFieldRequiresUnsafe {
1012                    span,
1013                    unsafe_not_inherited_note,
1014                });
1015            }
1016            UseOfMutableStatic if unsafe_op_in_unsafe_fn_allowed => {
1017                dcx.emit_err(UseOfMutableStaticRequiresUnsafeUnsafeOpInUnsafeFnAllowed {
1018                    span,
1019                    unsafe_not_inherited_note,
1020                });
1021            }
1022            UseOfMutableStatic => {
1023                dcx.emit_err(UseOfMutableStaticRequiresUnsafe { span, unsafe_not_inherited_note });
1024            }
1025            UseOfExternStatic if unsafe_op_in_unsafe_fn_allowed => {
1026                dcx.emit_err(UseOfExternStaticRequiresUnsafeUnsafeOpInUnsafeFnAllowed {
1027                    span,
1028                    unsafe_not_inherited_note,
1029                });
1030            }
1031            UseOfExternStatic => {
1032                dcx.emit_err(UseOfExternStaticRequiresUnsafe { span, unsafe_not_inherited_note });
1033            }
1034            UseOfUnsafeField if unsafe_op_in_unsafe_fn_allowed => {
1035                dcx.emit_err(UseOfUnsafeFieldRequiresUnsafeUnsafeOpInUnsafeFnAllowed {
1036                    span,
1037                    unsafe_not_inherited_note,
1038                });
1039            }
1040            UseOfUnsafeField => {
1041                dcx.emit_err(UseOfUnsafeFieldRequiresUnsafe { span, unsafe_not_inherited_note });
1042            }
1043            DerefOfRawPointer if unsafe_op_in_unsafe_fn_allowed => {
1044                dcx.emit_err(DerefOfRawPointerRequiresUnsafeUnsafeOpInUnsafeFnAllowed {
1045                    span,
1046                    unsafe_not_inherited_note,
1047                });
1048            }
1049            DerefOfRawPointer => {
1050                dcx.emit_err(DerefOfRawPointerRequiresUnsafe { span, unsafe_not_inherited_note });
1051            }
1052            AccessToUnionField if unsafe_op_in_unsafe_fn_allowed => {
1053                dcx.emit_err(AccessToUnionFieldRequiresUnsafeUnsafeOpInUnsafeFnAllowed {
1054                    span,
1055                    unsafe_not_inherited_note,
1056                });
1057            }
1058            AccessToUnionField => {
1059                dcx.emit_err(AccessToUnionFieldRequiresUnsafe { span, unsafe_not_inherited_note });
1060            }
1061            MutationOfLayoutConstrainedField if unsafe_op_in_unsafe_fn_allowed => {
1062                dcx.emit_err(
1063                    MutationOfLayoutConstrainedFieldRequiresUnsafeUnsafeOpInUnsafeFnAllowed {
1064                        span,
1065                        unsafe_not_inherited_note,
1066                    },
1067                );
1068            }
1069            MutationOfLayoutConstrainedField => {
1070                dcx.emit_err(MutationOfLayoutConstrainedFieldRequiresUnsafe {
1071                    span,
1072                    unsafe_not_inherited_note,
1073                });
1074            }
1075            BorrowOfLayoutConstrainedField if unsafe_op_in_unsafe_fn_allowed => {
1076                dcx.emit_err(
1077                    BorrowOfLayoutConstrainedFieldRequiresUnsafeUnsafeOpInUnsafeFnAllowed {
1078                        span,
1079                        unsafe_not_inherited_note,
1080                    },
1081                );
1082            }
1083            BorrowOfLayoutConstrainedField => {
1084                dcx.emit_err(BorrowOfLayoutConstrainedFieldRequiresUnsafe {
1085                    span,
1086                    unsafe_not_inherited_note,
1087                });
1088            }
1089            CallToFunctionWith { function, missing, build_enabled }
1090                if unsafe_op_in_unsafe_fn_allowed =>
1091            {
1092                dcx.emit_err(CallToFunctionWithRequiresUnsafeUnsafeOpInUnsafeFnAllowed {
1093                    span,
1094                    missing_target_features: DiagArgValue::StrListSepByAnd(
1095                        missing.iter().map(|feature| Cow::from(feature.to_string())).collect(),
1096                    ),
1097                    missing_target_features_count: missing.len(),
1098                    note: !build_enabled.is_empty(),
1099                    build_target_features: DiagArgValue::StrListSepByAnd(
1100                        build_enabled
1101                            .iter()
1102                            .map(|feature| Cow::from(feature.to_string()))
1103                            .collect(),
1104                    ),
1105                    build_target_features_count: build_enabled.len(),
1106                    unsafe_not_inherited_note,
1107                    function: tcx.def_path_str(*function),
1108                });
1109            }
1110            CallToFunctionWith { function, missing, build_enabled } => {
1111                dcx.emit_err(CallToFunctionWithRequiresUnsafe {
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            UnsafeBinderCast if unsafe_op_in_unsafe_fn_allowed => {
1130                dcx.emit_err(UnsafeBinderCastRequiresUnsafeUnsafeOpInUnsafeFnAllowed {
1131                    span,
1132                    unsafe_not_inherited_note,
1133                });
1134            }
1135            UnsafeBinderCast => {
1136                dcx.emit_err(UnsafeBinderCastRequiresUnsafe { span, unsafe_not_inherited_note });
1137            }
1138        }
1139    }
1140}
1141
1142pub(crate) fn check_unsafety(tcx: TyCtxt<'_>, def: LocalDefId) {
1143    // Closures and inline consts are handled by their owner, if it has a body
1144    // Also, don't safety check custom MIR
1145    if tcx.is_typeck_child(def.to_def_id()) || tcx.has_attr(def, sym::custom_mir) {
1146        return;
1147    }
1148
1149    let Ok((thir, expr)) = tcx.thir_body(def) else { return };
1150    // Runs all other queries that depend on THIR.
1151    tcx.ensure_done().mir_built(def);
1152    let thir = &thir.steal();
1153
1154    let hir_id = tcx.local_def_id_to_hir_id(def);
1155    let safety_context = tcx.hir_fn_sig_by_hir_id(hir_id).map_or(SafetyContext::Safe, |fn_sig| {
1156        match fn_sig.header.safety {
1157            // We typeck the body as safe, but otherwise treat it as unsafe everywhere else.
1158            // Call sites to other SafeTargetFeatures functions are checked explicitly and don't need
1159            // to care about safety of the body.
1160            hir::HeaderSafety::SafeTargetFeatures => SafetyContext::Safe,
1161            hir::HeaderSafety::Normal(safety) => match safety {
1162                hir::Safety::Unsafe => SafetyContext::UnsafeFn,
1163                hir::Safety::Safe => SafetyContext::Safe,
1164            },
1165        }
1166    });
1167    let body_target_features = &tcx.body_codegen_attrs(def.to_def_id()).target_features;
1168    let mut warnings = Vec::new();
1169    let mut visitor = UnsafetyVisitor {
1170        tcx,
1171        thir,
1172        safety_context,
1173        hir_context: hir_id,
1174        body_target_features,
1175        assignment_info: None,
1176        in_union_destructure: false,
1177        // FIXME(#132279): we're clearly in a body here.
1178        typing_env: ty::TypingEnv::non_body_analysis(tcx, def),
1179        inside_adt: false,
1180        warnings: &mut warnings,
1181        suggest_unsafe_block: true,
1182    };
1183    // params in THIR may be unsafe, e.g. a union pattern.
1184    for param in &thir.params {
1185        if let Some(param_pat) = param.pat.as_deref() {
1186            visitor.visit_pat(param_pat);
1187        }
1188    }
1189    // Visit the body.
1190    visitor.visit_expr(&thir[expr]);
1191
1192    warnings.sort_by_key(|w| w.block_span);
1193    for UnusedUnsafeWarning { hir_id, block_span, enclosing_unsafe } in warnings {
1194        let block_span = tcx.sess.source_map().guess_head_span(block_span);
1195        tcx.emit_node_span_lint(
1196            UNUSED_UNSAFE,
1197            hir_id,
1198            block_span,
1199            UnusedUnsafe { span: block_span, enclosing: enclosing_unsafe },
1200        );
1201    }
1202}
rustc_mir_build/check_unsafety.rs

rustc_mir_build/
check_unsafety.rs
