1 use rustc_data_structures::fx::FxHashSet;
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::mir::*;
9 use rustc_middle::ty::query::Providers;
10 use rustc_middle::ty::{self, TyCtxt};
11 use rustc_session::lint::builtin::{UNSAFE_OP_IN_UNSAFE_FN, UNUSED_UNSAFE};
12 use rustc_session::lint::Level;
16 pub struct UnsafetyChecker<'a, 'tcx> {
19 violations: Vec<UnsafetyViolation>,
20 source_info: SourceInfo,
22 param_env: ty::ParamEnv<'tcx>,
24 /// Used `unsafe` blocks in this function. This is used for the "unused_unsafe" lint.
25 used_unsafe_blocks: FxHashSet<HirId>,
28 impl<'a, 'tcx> UnsafetyChecker<'a, 'tcx> {
33 param_env: ty::ParamEnv<'tcx>,
39 source_info: SourceInfo::outermost(body.span),
42 used_unsafe_blocks: Default::default(),
47 impl<'tcx> Visitor<'tcx> for UnsafetyChecker<'_, 'tcx> {
48 fn visit_terminator(&mut self, terminator: &Terminator<'tcx>, location: Location) {
49 self.source_info = terminator.source_info;
50 match terminator.kind {
51 TerminatorKind::Goto { .. }
52 | TerminatorKind::SwitchInt { .. }
53 | TerminatorKind::Drop { .. }
54 | TerminatorKind::Yield { .. }
55 | TerminatorKind::Assert { .. }
56 | TerminatorKind::DropAndReplace { .. }
57 | TerminatorKind::GeneratorDrop
58 | TerminatorKind::Resume
59 | TerminatorKind::Abort
60 | TerminatorKind::Return
61 | TerminatorKind::Unreachable
62 | TerminatorKind::FalseEdge { .. }
63 | TerminatorKind::FalseUnwind { .. } => {
64 // safe (at least as emitted during MIR construction)
67 TerminatorKind::Call { ref func, .. } => {
68 let func_ty = func.ty(self.body, self.tcx);
70 if let ty::FnDef(func_id, _) = func_ty.kind() { Some(func_id) } else { None };
71 let sig = func_ty.fn_sig(self.tcx);
72 if let hir::Unsafety::Unsafe = sig.unsafety() {
74 UnsafetyViolationKind::General,
75 UnsafetyViolationDetails::CallToUnsafeFunction,
79 if let Some(func_id) = func_id {
80 self.check_target_features(*func_id);
84 TerminatorKind::InlineAsm { .. } => self.require_unsafe(
85 UnsafetyViolationKind::General,
86 UnsafetyViolationDetails::UseOfInlineAssembly,
89 self.super_terminator(terminator, location);
92 fn visit_statement(&mut self, statement: &Statement<'tcx>, location: Location) {
93 self.source_info = statement.source_info;
94 match statement.kind {
95 StatementKind::Assign(..)
96 | StatementKind::FakeRead(..)
97 | StatementKind::SetDiscriminant { .. }
98 | StatementKind::Deinit(..)
99 | StatementKind::StorageLive(..)
100 | StatementKind::StorageDead(..)
101 | StatementKind::Retag { .. }
102 | StatementKind::AscribeUserType(..)
103 | StatementKind::Coverage(..)
104 | StatementKind::Nop => {
105 // safe (at least as emitted during MIR construction)
108 // Move to above list once mir construction uses it.
109 StatementKind::Intrinsic(..) => unreachable!(),
111 self.super_statement(statement, location);
114 fn visit_rvalue(&mut self, rvalue: &Rvalue<'tcx>, location: Location) {
116 Rvalue::Aggregate(box ref aggregate, _) => match aggregate {
117 &AggregateKind::Array(..) | &AggregateKind::Tuple => {}
118 &AggregateKind::Adt(adt_did, ..) => {
119 match self.tcx.layout_scalar_valid_range(adt_did) {
120 (Bound::Unbounded, Bound::Unbounded) => {}
121 _ => self.require_unsafe(
122 UnsafetyViolationKind::General,
123 UnsafetyViolationDetails::InitializingTypeWith,
127 &AggregateKind::Closure(def_id, _) | &AggregateKind::Generator(def_id, _, _) => {
128 let UnsafetyCheckResult { violations, used_unsafe_blocks, .. } =
129 self.tcx.unsafety_check_result(def_id);
130 self.register_violations(violations, used_unsafe_blocks.iter().copied());
135 self.super_rvalue(rvalue, location);
138 fn visit_place(&mut self, place: &Place<'tcx>, context: PlaceContext, _location: Location) {
139 // On types with `scalar_valid_range`, prevent
142 // * `&x.field` if `field`'s type has interior mutability
143 // because either of these would allow modifying the layout constrained field and
144 // insert values that violate the layout constraints.
145 if context.is_mutating_use() || context.is_borrow() {
146 self.check_mut_borrowing_layout_constrained_field(*place, context.is_mutating_use());
149 // Some checks below need the extra meta info of the local declaration.
150 let decl = &self.body.local_decls[place.local];
152 // Check the base local: it might be an unsafe-to-access static. We only check derefs of the
153 // temporary holding the static pointer to avoid duplicate errors
154 // <https://github.com/rust-lang/rust/pull/78068#issuecomment-731753506>.
155 if decl.internal && place.projection.first() == Some(&ProjectionElem::Deref) {
156 // If the projection root is an artificial local that we introduced when
157 // desugaring `static`, give a more specific error message
158 // (avoid the general "raw pointer" clause below, that would only be confusing).
159 if let Some(box LocalInfo::StaticRef { def_id, .. }) = decl.local_info {
160 if self.tcx.is_mutable_static(def_id) {
162 UnsafetyViolationKind::General,
163 UnsafetyViolationDetails::UseOfMutableStatic,
166 } else if self.tcx.is_foreign_item(def_id) {
168 UnsafetyViolationKind::General,
169 UnsafetyViolationDetails::UseOfExternStatic,
176 // Check for raw pointer `Deref`.
177 for (base, proj) in place.iter_projections() {
178 if proj == ProjectionElem::Deref {
179 let base_ty = base.ty(self.body, self.tcx).ty;
180 if base_ty.is_unsafe_ptr() {
182 UnsafetyViolationKind::General,
183 UnsafetyViolationDetails::DerefOfRawPointer,
189 // Check for union fields. For this we traverse right-to-left, as the last `Deref` changes
190 // whether we *read* the union field or potentially *write* to it (if this place is being assigned to).
191 let mut saw_deref = false;
192 for (base, proj) in place.iter_projections().rev() {
193 if proj == ProjectionElem::Deref {
198 let base_ty = base.ty(self.body, self.tcx).ty;
199 if base_ty.is_union() {
200 // If we did not hit a `Deref` yet and the overall place use is an assignment, the
201 // rules are different.
202 let assign_to_field = !saw_deref
205 PlaceContext::MutatingUse(
206 MutatingUseContext::Store
207 | MutatingUseContext::Drop
208 | MutatingUseContext::AsmOutput
211 // If this is just an assignment, determine if the assigned type needs dropping.
213 // We have to check the actual type of the assignment, as that determines if the
214 // old value is being dropped.
215 let assigned_ty = place.ty(&self.body.local_decls, self.tcx).ty;
216 if assigned_ty.needs_drop(self.tcx, self.param_env) {
217 // This would be unsafe, but should be outright impossible since we reject such unions.
218 self.tcx.sess.delay_span_bug(
219 self.source_info.span,
220 format!("union fields that need dropping should be impossible: {assigned_ty}")
225 UnsafetyViolationKind::General,
226 UnsafetyViolationDetails::AccessToUnionField,
234 impl<'tcx> UnsafetyChecker<'_, 'tcx> {
235 fn require_unsafe(&mut self, kind: UnsafetyViolationKind, details: UnsafetyViolationDetails) {
236 // Violations can turn out to be `UnsafeFn` during analysis, but they should not start out as such.
237 assert_ne!(kind, UnsafetyViolationKind::UnsafeFn);
239 let source_info = self.source_info;
240 let lint_root = self.body.source_scopes[self.source_info.scope]
243 .assert_crate_local()
245 self.register_violations(
246 [&UnsafetyViolation { source_info, lint_root, kind, details }],
251 fn register_violations<'a>(
253 violations: impl IntoIterator<Item = &'a UnsafetyViolation>,
254 new_used_unsafe_blocks: impl IntoIterator<Item = HirId>,
256 let safety = self.body.source_scopes[self.source_info.scope]
259 .assert_crate_local()
262 // `unsafe` blocks are required in safe code
263 Safety::Safe => violations.into_iter().for_each(|&violation| {
264 match violation.kind {
265 UnsafetyViolationKind::General => {}
266 UnsafetyViolationKind::UnsafeFn => {
267 bug!("`UnsafetyViolationKind::UnsafeFn` in an `Safe` context")
270 if !self.violations.contains(&violation) {
271 self.violations.push(violation)
274 // With the RFC 2585, no longer allow `unsafe` operations in `unsafe fn`s
275 Safety::FnUnsafe => violations.into_iter().for_each(|&(mut violation)| {
276 violation.kind = UnsafetyViolationKind::UnsafeFn;
277 if !self.violations.contains(&violation) {
278 self.violations.push(violation)
281 Safety::BuiltinUnsafe => {}
282 Safety::ExplicitUnsafe(hir_id) => violations.into_iter().for_each(|_violation| {
283 self.used_unsafe_blocks.insert(hir_id);
287 new_used_unsafe_blocks.into_iter().for_each(|hir_id| {
288 self.used_unsafe_blocks.insert(hir_id);
291 fn check_mut_borrowing_layout_constrained_field(
296 for (place_base, elem) in place.iter_projections().rev() {
298 // Modifications behind a dereference don't affect the value of
300 ProjectionElem::Deref => return,
301 ProjectionElem::Field(..) => {
302 let ty = place_base.ty(&self.body.local_decls, self.tcx).ty;
303 if let ty::Adt(def, _) = ty.kind() {
304 if self.tcx.layout_scalar_valid_range(def.did())
305 != (Bound::Unbounded, Bound::Unbounded)
307 let details = if is_mut_use {
308 UnsafetyViolationDetails::MutationOfLayoutConstrainedField
310 // Check `is_freeze` as late as possible to avoid cycle errors
311 // with opaque types.
313 .ty(self.body, self.tcx)
315 .is_freeze(self.tcx.at(self.source_info.span), self.param_env)
317 UnsafetyViolationDetails::BorrowOfLayoutConstrainedField
321 self.require_unsafe(UnsafetyViolationKind::General, details);
330 /// Checks whether calling `func_did` needs an `unsafe` context or not, i.e. whether
331 /// the called function has target features the calling function hasn't.
332 fn check_target_features(&mut self, func_did: DefId) {
333 // Unsafety isn't required on wasm targets. For more information see
334 // the corresponding check in typeck/src/collect.rs
335 if self.tcx.sess.target.options.is_like_wasm {
339 let callee_features = &self.tcx.codegen_fn_attrs(func_did).target_features;
340 // The body might be a constant, so it doesn't have codegen attributes.
341 let self_features = &self.tcx.body_codegen_attrs(self.body_did.to_def_id()).target_features;
343 // Is `callee_features` a subset of `calling_features`?
344 if !callee_features.iter().all(|feature| self_features.contains(feature)) {
346 UnsafetyViolationKind::General,
347 UnsafetyViolationDetails::CallToFunctionWith,
353 pub(crate) fn provide(providers: &mut Providers) {
354 *providers = Providers {
355 unsafety_check_result: |tcx, def_id| {
356 if let Some(def) = ty::WithOptConstParam::try_lookup(def_id, tcx) {
357 tcx.unsafety_check_result_for_const_arg(def)
359 unsafety_check_result(tcx, ty::WithOptConstParam::unknown(def_id))
362 unsafety_check_result_for_const_arg: |tcx, (did, param_did)| {
363 unsafety_check_result(
365 ty::WithOptConstParam { did, const_param_did: Some(param_did) },
372 /// Context information for [`UnusedUnsafeVisitor`] traversal,
373 /// saves (innermost) relevant context
374 #[derive(Copy, Clone, Debug)]
377 /// in an `unsafe fn`
379 /// in a *used* `unsafe` block
380 /// (i.e. a block without unused-unsafe warning)
384 struct UnusedUnsafeVisitor<'a, 'tcx> {
386 used_unsafe_blocks: &'a FxHashSet<HirId>,
388 unused_unsafes: &'a mut Vec<(HirId, UnusedUnsafe)>,
391 impl<'tcx> intravisit::Visitor<'tcx> for UnusedUnsafeVisitor<'_, 'tcx> {
392 fn visit_block(&mut self, block: &'tcx hir::Block<'tcx>) {
393 if let hir::BlockCheckMode::UnsafeBlock(hir::UnsafeSource::UserProvided) = block.rules {
394 let used = match self.tcx.lint_level_at_node(UNUSED_UNSAFE, block.hir_id) {
395 (Level::Allow, _) => true,
396 _ => self.used_unsafe_blocks.contains(&block.hir_id),
398 let unused_unsafe = match (self.context, used) {
399 (_, false) => UnusedUnsafe::Unused,
400 (Context::Safe, true) | (Context::UnsafeFn(_), true) => {
401 let previous_context = self.context;
402 self.context = Context::UnsafeBlock(block.hir_id);
403 intravisit::walk_block(self, block);
404 self.context = previous_context;
407 (Context::UnsafeBlock(hir_id), true) => UnusedUnsafe::InUnsafeBlock(hir_id),
409 self.unused_unsafes.push((block.hir_id, unused_unsafe));
411 intravisit::walk_block(self, block);
416 fk: intravisit::FnKind<'tcx>,
417 _fd: &'tcx hir::FnDecl<'tcx>,
419 _s: rustc_span::Span,
422 if matches!(fk, intravisit::FnKind::Closure) {
423 self.visit_body(self.tcx.hir().body(b))
428 fn check_unused_unsafe(
431 used_unsafe_blocks: &FxHashSet<HirId>,
432 ) -> Vec<(HirId, UnusedUnsafe)> {
433 let body_id = tcx.hir().maybe_body_owned_by(def_id);
435 let Some(body_id) = body_id else {
436 debug!("check_unused_unsafe({:?}) - no body found", def_id);
440 let body = tcx.hir().body(body_id);
441 let hir_id = tcx.hir().local_def_id_to_hir_id(def_id);
442 let context = match tcx.hir().fn_sig_by_hir_id(hir_id) {
443 Some(sig) if sig.header.unsafety == hir::Unsafety::Unsafe => Context::UnsafeFn(hir_id),
448 "check_unused_unsafe({:?}, context={:?}, body={:?}, used_unsafe_blocks={:?})",
449 def_id, body, context, used_unsafe_blocks
452 let mut unused_unsafes = vec![];
454 let mut visitor = UnusedUnsafeVisitor {
458 unused_unsafes: &mut unused_unsafes,
460 intravisit::Visitor::visit_body(&mut visitor, body);
465 fn unsafety_check_result<'tcx>(
467 def: ty::WithOptConstParam<LocalDefId>,
468 ) -> &'tcx UnsafetyCheckResult {
469 debug!("unsafety_violations({:?})", def);
471 // N.B., this borrow is valid because all the consumers of
472 // `mir_built` force this.
473 let body = &tcx.mir_built(def).borrow();
475 let param_env = tcx.param_env(def.did);
477 let mut checker = UnsafetyChecker::new(body, def.did, tcx, param_env);
478 checker.visit_body(&body);
480 let unused_unsafes = (!tcx.is_closure(def.did.to_def_id()))
481 .then(|| check_unused_unsafe(tcx, def.did, &checker.used_unsafe_blocks));
483 tcx.arena.alloc(UnsafetyCheckResult {
484 violations: checker.violations,
485 used_unsafe_blocks: checker.used_unsafe_blocks,
490 fn report_unused_unsafe(tcx: TyCtxt<'_>, kind: UnusedUnsafe, id: HirId) {
491 let span = tcx.sess.source_map().guess_head_span(tcx.hir().span(id));
492 tcx.struct_span_lint_hir(UNUSED_UNSAFE, id, span, |lint| {
493 let msg = "unnecessary `unsafe` block";
494 let mut db = lint.build(msg);
495 db.span_label(span, msg);
497 UnusedUnsafe::Unused => {}
498 UnusedUnsafe::InUnsafeBlock(id) => {
500 tcx.sess.source_map().guess_head_span(tcx.hir().span(id)),
501 "because it's nested under this `unsafe` block",
510 pub fn check_unsafety(tcx: TyCtxt<'_>, def_id: LocalDefId) {
511 debug!("check_unsafety({:?})", def_id);
513 // closures are handled by their parent fn.
514 if tcx.is_closure(def_id.to_def_id()) {
518 let UnsafetyCheckResult { violations, unused_unsafes, .. } = tcx.unsafety_check_result(def_id);
520 for &UnsafetyViolation { source_info, lint_root, kind, details } in violations.iter() {
521 let (description, note) = details.description_and_note();
525 if unsafe_op_in_unsafe_fn_allowed(tcx, lint_root) { " function or" } else { "" };
528 UnsafetyViolationKind::General => {
534 "{} is unsafe and requires unsafe{} block",
538 .span_label(source_info.span, description)
542 UnsafetyViolationKind::UnsafeFn => tcx.struct_span_lint_hir(
543 UNSAFE_OP_IN_UNSAFE_FN,
548 "{} is unsafe and requires unsafe block (error E0133)",
551 .span_label(source_info.span, description)
559 for &(block_id, kind) in unused_unsafes.as_ref().unwrap() {
560 report_unused_unsafe(tcx, kind, block_id);
564 fn unsafe_op_in_unsafe_fn_allowed(tcx: TyCtxt<'_>, id: HirId) -> bool {
565 tcx.lint_level_at_node(UNSAFE_OP_IN_UNSAFE_FN, id).0 == Level::Allow