1 use rustc_data_structures::fx::FxHashMap;
2 use rustc_errors::struct_span_err;
4 use rustc_hir::def_id::{DefId, LocalDefId};
5 use rustc_hir::hir_id::HirId;
6 use rustc_hir::intravisit;
7 use rustc_middle::mir::visit::{MutatingUseContext, PlaceContext, Visitor};
8 use rustc_middle::ty::query::Providers;
9 use rustc_middle::ty::{self, TyCtxt};
10 use rustc_middle::{lint, mir::*};
11 use rustc_session::lint::builtin::{UNSAFE_OP_IN_UNSAFE_FN, UNUSED_UNSAFE};
12 use rustc_session::lint::Level;
14 use std::collections::hash_map;
17 pub struct UnsafetyChecker<'a, 'tcx> {
20 violations: Vec<UnsafetyViolation>,
21 source_info: SourceInfo,
23 param_env: ty::ParamEnv<'tcx>,
25 /// Used `unsafe` blocks in this function. This is used for the "unused_unsafe" lint.
27 /// The keys are the used `unsafe` blocks, the UnusedUnsafeKind indicates whether
28 /// or not any of the usages happen at a place that doesn't allow `unsafe_op_in_unsafe_fn`.
29 used_unsafe_blocks: FxHashMap<HirId, UsedUnsafeBlockData>,
32 impl<'a, 'tcx> UnsafetyChecker<'a, 'tcx> {
37 param_env: ty::ParamEnv<'tcx>,
43 source_info: SourceInfo::outermost(body.span),
46 used_unsafe_blocks: Default::default(),
51 impl<'tcx> Visitor<'tcx> for UnsafetyChecker<'_, 'tcx> {
52 fn visit_terminator(&mut self, terminator: &Terminator<'tcx>, location: Location) {
53 self.source_info = terminator.source_info;
54 match terminator.kind {
55 TerminatorKind::Goto { .. }
56 | TerminatorKind::SwitchInt { .. }
57 | TerminatorKind::Drop { .. }
58 | TerminatorKind::Yield { .. }
59 | TerminatorKind::Assert { .. }
60 | TerminatorKind::DropAndReplace { .. }
61 | TerminatorKind::GeneratorDrop
62 | TerminatorKind::Resume
63 | TerminatorKind::Abort
64 | TerminatorKind::Return
65 | TerminatorKind::Unreachable
66 | TerminatorKind::FalseEdge { .. }
67 | TerminatorKind::FalseUnwind { .. } => {
68 // safe (at least as emitted during MIR construction)
71 TerminatorKind::Call { ref func, .. } => {
72 let func_ty = func.ty(self.body, self.tcx);
74 if let ty::FnDef(func_id, _) = func_ty.kind() { Some(func_id) } else { None };
75 let sig = func_ty.fn_sig(self.tcx);
76 if let hir::Unsafety::Unsafe = sig.unsafety() {
78 UnsafetyViolationKind::General,
79 UnsafetyViolationDetails::CallToUnsafeFunction,
83 if let Some(func_id) = func_id {
84 self.check_target_features(*func_id);
88 TerminatorKind::InlineAsm { .. } => self.require_unsafe(
89 UnsafetyViolationKind::General,
90 UnsafetyViolationDetails::UseOfInlineAssembly,
93 self.super_terminator(terminator, location);
96 fn visit_statement(&mut self, statement: &Statement<'tcx>, location: Location) {
97 self.source_info = statement.source_info;
98 match statement.kind {
99 StatementKind::Assign(..)
100 | StatementKind::FakeRead(..)
101 | StatementKind::SetDiscriminant { .. }
102 | StatementKind::Deinit(..)
103 | StatementKind::StorageLive(..)
104 | StatementKind::StorageDead(..)
105 | StatementKind::Retag { .. }
106 | StatementKind::AscribeUserType(..)
107 | StatementKind::Coverage(..)
108 | StatementKind::Nop => {
109 // safe (at least as emitted during MIR construction)
112 StatementKind::CopyNonOverlapping(..) => unreachable!(),
114 self.super_statement(statement, location);
117 fn visit_rvalue(&mut self, rvalue: &Rvalue<'tcx>, location: Location) {
119 Rvalue::Aggregate(box ref aggregate, _) => match aggregate {
120 &AggregateKind::Array(..) | &AggregateKind::Tuple => {}
121 &AggregateKind::Adt(adt_did, ..) => {
122 match self.tcx.layout_scalar_valid_range(adt_did) {
123 (Bound::Unbounded, Bound::Unbounded) => {}
124 _ => self.require_unsafe(
125 UnsafetyViolationKind::General,
126 UnsafetyViolationDetails::InitializingTypeWith,
130 &AggregateKind::Closure(def_id, _) | &AggregateKind::Generator(def_id, _, _) => {
131 let UnsafetyCheckResult { violations, used_unsafe_blocks, .. } =
132 self.tcx.unsafety_check_result(def_id.expect_local());
133 self.register_violations(
135 used_unsafe_blocks.iter().map(|(&h, &d)| (h, d)),
141 self.super_rvalue(rvalue, location);
144 fn visit_place(&mut self, place: &Place<'tcx>, context: PlaceContext, _location: Location) {
145 // On types with `scalar_valid_range`, prevent
148 // * `&x.field` if `field`'s type has interior mutability
149 // because either of these would allow modifying the layout constrained field and
150 // insert values that violate the layout constraints.
151 if context.is_mutating_use() || context.is_borrow() {
152 self.check_mut_borrowing_layout_constrained_field(*place, context.is_mutating_use());
155 // Some checks below need the extra meta info of the local declaration.
156 let decl = &self.body.local_decls[place.local];
158 // Check the base local: it might be an unsafe-to-access static. We only check derefs of the
159 // temporary holding the static pointer to avoid duplicate errors
160 // <https://github.com/rust-lang/rust/pull/78068#issuecomment-731753506>.
161 if decl.internal && place.projection.first() == Some(&ProjectionElem::Deref) {
162 // If the projection root is an artificial local that we introduced when
163 // desugaring `static`, give a more specific error message
164 // (avoid the general "raw pointer" clause below, that would only be confusing).
165 if let Some(box LocalInfo::StaticRef { def_id, .. }) = decl.local_info {
166 if self.tcx.is_mutable_static(def_id) {
168 UnsafetyViolationKind::General,
169 UnsafetyViolationDetails::UseOfMutableStatic,
172 } else if self.tcx.is_foreign_item(def_id) {
174 UnsafetyViolationKind::General,
175 UnsafetyViolationDetails::UseOfExternStatic,
182 // Check for raw pointer `Deref`.
183 for (base, proj) in place.iter_projections() {
184 if proj == ProjectionElem::Deref {
185 let base_ty = base.ty(self.body, self.tcx).ty;
186 if base_ty.is_unsafe_ptr() {
188 UnsafetyViolationKind::General,
189 UnsafetyViolationDetails::DerefOfRawPointer,
195 // Check for union fields. For this we traverse right-to-left, as the last `Deref` changes
196 // whether we *read* the union field or potentially *write* to it (if this place is being assigned to).
197 let mut saw_deref = false;
198 for (base, proj) in place.iter_projections().rev() {
199 if proj == ProjectionElem::Deref {
204 let base_ty = base.ty(self.body, self.tcx).ty;
205 if base_ty.is_union() {
206 // If we did not hit a `Deref` yet and the overall place use is an assignment, the
207 // rules are different.
208 let assign_to_field = !saw_deref
211 PlaceContext::MutatingUse(
212 MutatingUseContext::Store
213 | MutatingUseContext::Drop
214 | MutatingUseContext::AsmOutput
217 // If this is just an assignment, determine if the assigned type needs dropping.
219 // We have to check the actual type of the assignment, as that determines if the
220 // old value is being dropped.
221 let assigned_ty = place.ty(&self.body.local_decls, self.tcx).ty;
222 if assigned_ty.needs_drop(self.tcx, self.param_env) {
223 // This would be unsafe, but should be outright impossible since we reject such unions.
224 self.tcx.sess.delay_span_bug(
225 self.source_info.span,
226 format!("union fields that need dropping should be impossible: {assigned_ty}")
231 UnsafetyViolationKind::General,
232 UnsafetyViolationDetails::AccessToUnionField,
240 impl<'tcx> UnsafetyChecker<'_, 'tcx> {
241 fn require_unsafe(&mut self, kind: UnsafetyViolationKind, details: UnsafetyViolationDetails) {
242 // Violations can turn out to be `UnsafeFn` during analysis, but they should not start out as such.
243 assert_ne!(kind, UnsafetyViolationKind::UnsafeFn);
245 let source_info = self.source_info;
246 let lint_root = self.body.source_scopes[self.source_info.scope]
249 .assert_crate_local()
251 self.register_violations(
252 [&UnsafetyViolation { source_info, lint_root, kind, details }],
257 fn register_violations<'a>(
259 violations: impl IntoIterator<Item = &'a UnsafetyViolation>,
260 new_used_unsafe_blocks: impl IntoIterator<Item = (HirId, UsedUnsafeBlockData)>,
262 use UsedUnsafeBlockData::{AllAllowedInUnsafeFn, SomeDisallowedInUnsafeFn};
264 let update_entry = |this: &mut Self, hir_id, new_usage| {
265 match this.used_unsafe_blocks.entry(hir_id) {
266 hash_map::Entry::Occupied(mut entry) => {
267 if new_usage == SomeDisallowedInUnsafeFn {
268 *entry.get_mut() = SomeDisallowedInUnsafeFn;
271 hash_map::Entry::Vacant(entry) => {
272 entry.insert(new_usage);
276 let safety = self.body.source_scopes[self.source_info.scope]
279 .assert_crate_local()
282 // `unsafe` blocks are required in safe code
283 Safety::Safe => violations.into_iter().for_each(|&violation| {
284 match violation.kind {
285 UnsafetyViolationKind::General => {}
286 UnsafetyViolationKind::UnsafeFn => {
287 bug!("`UnsafetyViolationKind::UnsafeFn` in an `Safe` context")
290 if !self.violations.contains(&violation) {
291 self.violations.push(violation)
294 // With the RFC 2585, no longer allow `unsafe` operations in `unsafe fn`s
295 Safety::FnUnsafe => violations.into_iter().for_each(|&(mut violation)| {
296 violation.kind = UnsafetyViolationKind::UnsafeFn;
297 if !self.violations.contains(&violation) {
298 self.violations.push(violation)
301 Safety::BuiltinUnsafe => {}
302 Safety::ExplicitUnsafe(hir_id) => violations.into_iter().for_each(|violation| {
306 match self.tcx.lint_level_at_node(UNSAFE_OP_IN_UNSAFE_FN, violation.lint_root).0
308 Level::Allow => AllAllowedInUnsafeFn(violation.lint_root),
309 _ => SomeDisallowedInUnsafeFn,
315 new_used_unsafe_blocks
317 .for_each(|(hir_id, usage_data)| update_entry(self, hir_id, usage_data));
319 fn check_mut_borrowing_layout_constrained_field(
324 for (place_base, elem) in place.iter_projections().rev() {
326 // Modifications behind a dereference don't affect the value of
328 ProjectionElem::Deref => return,
329 ProjectionElem::Field(..) => {
330 let ty = place_base.ty(&self.body.local_decls, self.tcx).ty;
331 if let ty::Adt(def, _) = ty.kind() {
332 if self.tcx.layout_scalar_valid_range(def.did())
333 != (Bound::Unbounded, Bound::Unbounded)
335 let details = if is_mut_use {
336 UnsafetyViolationDetails::MutationOfLayoutConstrainedField
338 // Check `is_freeze` as late as possible to avoid cycle errors
339 // with opaque types.
341 .ty(self.body, self.tcx)
343 .is_freeze(self.tcx.at(self.source_info.span), self.param_env)
345 UnsafetyViolationDetails::BorrowOfLayoutConstrainedField
349 self.require_unsafe(UnsafetyViolationKind::General, details);
358 /// Checks whether calling `func_did` needs an `unsafe` context or not, i.e. whether
359 /// the called function has target features the calling function hasn't.
360 fn check_target_features(&mut self, func_did: DefId) {
361 // Unsafety isn't required on wasm targets. For more information see
362 // the corresponding check in typeck/src/collect.rs
363 if self.tcx.sess.target.options.is_like_wasm {
367 let callee_features = &self.tcx.codegen_fn_attrs(func_did).target_features;
368 // The body might be a constant, so it doesn't have codegen attributes.
369 let self_features = &self.tcx.body_codegen_attrs(self.body_did.to_def_id()).target_features;
371 // Is `callee_features` a subset of `calling_features`?
372 if !callee_features.iter().all(|feature| self_features.contains(feature)) {
374 UnsafetyViolationKind::General,
375 UnsafetyViolationDetails::CallToFunctionWith,
381 pub(crate) fn provide(providers: &mut Providers) {
382 *providers = Providers {
383 unsafety_check_result: |tcx, def_id| {
384 if let Some(def) = ty::WithOptConstParam::try_lookup(def_id, tcx) {
385 tcx.unsafety_check_result_for_const_arg(def)
387 unsafety_check_result(tcx, ty::WithOptConstParam::unknown(def_id))
390 unsafety_check_result_for_const_arg: |tcx, (did, param_did)| {
391 unsafety_check_result(
393 ty::WithOptConstParam { did, const_param_did: Some(param_did) },
400 /// Context information for [`UnusedUnsafeVisitor`] traversal,
401 /// saves (innermost) relevant context
402 #[derive(Copy, Clone, Debug)]
405 /// in an `unsafe fn`
407 /// in a *used* `unsafe` block
408 /// (i.e. a block without unused-unsafe warning)
412 struct UnusedUnsafeVisitor<'a, 'tcx> {
414 used_unsafe_blocks: &'a FxHashMap<HirId, UsedUnsafeBlockData>,
416 unused_unsafes: &'a mut Vec<(HirId, UnusedUnsafe)>,
419 impl<'tcx> intravisit::Visitor<'tcx> for UnusedUnsafeVisitor<'_, 'tcx> {
420 fn visit_block(&mut self, block: &'tcx hir::Block<'tcx>) {
421 use UsedUnsafeBlockData::{AllAllowedInUnsafeFn, SomeDisallowedInUnsafeFn};
423 if let hir::BlockCheckMode::UnsafeBlock(hir::UnsafeSource::UserProvided) = block.rules {
424 let used = match self.tcx.lint_level_at_node(UNUSED_UNSAFE, block.hir_id) {
425 (Level::Allow, _) => Some(SomeDisallowedInUnsafeFn),
426 _ => self.used_unsafe_blocks.get(&block.hir_id).copied(),
428 let unused_unsafe = match (self.context, used) {
429 (_, None) => UnusedUnsafe::Unused,
430 (Context::Safe, Some(_))
431 | (Context::UnsafeFn(_), Some(SomeDisallowedInUnsafeFn)) => {
432 let previous_context = self.context;
433 self.context = Context::UnsafeBlock(block.hir_id);
434 intravisit::walk_block(self, block);
435 self.context = previous_context;
438 (Context::UnsafeFn(hir_id), Some(AllAllowedInUnsafeFn(lint_root))) => {
439 UnusedUnsafe::InUnsafeFn(hir_id, lint_root)
441 (Context::UnsafeBlock(hir_id), Some(_)) => UnusedUnsafe::InUnsafeBlock(hir_id),
443 self.unused_unsafes.push((block.hir_id, unused_unsafe));
445 intravisit::walk_block(self, block);
450 fk: intravisit::FnKind<'tcx>,
451 _fd: &'tcx hir::FnDecl<'tcx>,
453 _s: rustc_span::Span,
456 if matches!(fk, intravisit::FnKind::Closure) {
457 self.visit_body(self.tcx.hir().body(b))
462 fn check_unused_unsafe(
465 used_unsafe_blocks: &FxHashMap<HirId, UsedUnsafeBlockData>,
466 ) -> Vec<(HirId, UnusedUnsafe)> {
467 let hir_id = tcx.hir().local_def_id_to_hir_id(def_id);
468 let body_id = tcx.hir().maybe_body_owned_by(hir_id);
470 let Some(body_id) = body_id else {
471 debug!("check_unused_unsafe({:?}) - no body found", def_id);
474 let body = tcx.hir().body(body_id);
476 let context = match tcx.hir().fn_sig_by_hir_id(hir_id) {
477 Some(sig) if sig.header.unsafety == hir::Unsafety::Unsafe => Context::UnsafeFn(hir_id),
482 "check_unused_unsafe({:?}, context={:?}, body={:?}, used_unsafe_blocks={:?})",
483 def_id, body, context, used_unsafe_blocks
486 let mut unused_unsafes = vec![];
488 let mut visitor = UnusedUnsafeVisitor {
492 unused_unsafes: &mut unused_unsafes,
494 intravisit::Visitor::visit_body(&mut visitor, body);
499 fn unsafety_check_result<'tcx>(
501 def: ty::WithOptConstParam<LocalDefId>,
502 ) -> &'tcx UnsafetyCheckResult {
503 debug!("unsafety_violations({:?})", def);
505 // N.B., this borrow is valid because all the consumers of
506 // `mir_built` force this.
507 let body = &tcx.mir_built(def).borrow();
509 let param_env = tcx.param_env(def.did);
511 let mut checker = UnsafetyChecker::new(body, def.did, tcx, param_env);
512 checker.visit_body(&body);
514 let unused_unsafes = (!tcx.is_closure(def.did.to_def_id()))
515 .then(|| check_unused_unsafe(tcx, def.did, &checker.used_unsafe_blocks));
517 tcx.arena.alloc(UnsafetyCheckResult {
518 violations: checker.violations,
519 used_unsafe_blocks: checker.used_unsafe_blocks,
524 fn report_unused_unsafe(tcx: TyCtxt<'_>, kind: UnusedUnsafe, id: HirId) {
525 let span = tcx.sess.source_map().guess_head_span(tcx.hir().span(id));
526 tcx.struct_span_lint_hir(UNUSED_UNSAFE, id, span, |lint| {
527 let msg = "unnecessary `unsafe` block";
528 let mut db = lint.build(msg);
529 db.span_label(span, msg);
531 UnusedUnsafe::Unused => {}
532 UnusedUnsafe::InUnsafeBlock(id) => {
534 tcx.sess.source_map().guess_head_span(tcx.hir().span(id)),
535 "because it's nested under this `unsafe` block",
538 UnusedUnsafe::InUnsafeFn(id, usage_lint_root) => {
540 tcx.sess.source_map().guess_head_span(tcx.hir().span(id)),
541 "because it's nested under this `unsafe` fn",
544 "this `unsafe` block does contain unsafe operations, \
545 but those are already allowed in an `unsafe fn`",
547 let (level, source) =
548 tcx.lint_level_at_node(UNSAFE_OP_IN_UNSAFE_FN, usage_lint_root);
549 assert_eq!(level, Level::Allow);
550 lint::explain_lint_level_source(
551 UNSAFE_OP_IN_UNSAFE_FN,
563 pub fn check_unsafety(tcx: TyCtxt<'_>, def_id: LocalDefId) {
564 debug!("check_unsafety({:?})", def_id);
566 // closures are handled by their parent fn.
567 if tcx.is_closure(def_id.to_def_id()) {
571 let UnsafetyCheckResult { violations, unused_unsafes, .. } = tcx.unsafety_check_result(def_id);
573 for &UnsafetyViolation { source_info, lint_root, kind, details } in violations.iter() {
574 let (description, note) = details.description_and_note();
578 if unsafe_op_in_unsafe_fn_allowed(tcx, lint_root) { " function or" } else { "" };
581 UnsafetyViolationKind::General => {
587 "{} is unsafe and requires unsafe{} block",
591 .span_label(source_info.span, description)
595 UnsafetyViolationKind::UnsafeFn => tcx.struct_span_lint_hir(
596 UNSAFE_OP_IN_UNSAFE_FN,
601 "{} is unsafe and requires unsafe block (error E0133)",
604 .span_label(source_info.span, description)
612 for &(block_id, kind) in unused_unsafes.as_ref().unwrap() {
613 report_unused_unsafe(tcx, kind, block_id);
617 fn unsafe_op_in_unsafe_fn_allowed(tcx: TyCtxt<'_>, id: HirId) -> bool {
618 tcx.lint_level_at_node(UNSAFE_OP_IN_UNSAFE_FN, id).0 == Level::Allow