1 // Verifies that the types and values of const and static items
2 // are safe. The rules enforced by this module are:
4 // - For each *mutable* static item, it checks that its **type**:
5 // - doesn't have a destructor
8 // - For each *immutable* static item, it checks that its **value**:
10 // - doesn't contain a struct literal or a call to an enum variant / struct constructor where
11 // - the type of the struct/enum has a dtor
13 // Rules Enforced Elsewhere:
14 // - It's not possible to take the address of a static item with unsafe interior. This is enforced
15 // by borrowck::gather_loans
17 use rustc::ty::cast::CastTy;
18 use rustc::hir::def::{Res, DefKind, CtorKind};
19 use rustc::hir::def_id::DefId;
20 use rustc::middle::expr_use_visitor as euv;
21 use rustc::middle::mem_categorization as mc;
22 use rustc::middle::mem_categorization::Categorization;
23 use rustc::ty::{self, Ty, TyCtxt};
24 use rustc::ty::query::Providers;
25 use rustc::ty::subst::{InternalSubsts, SubstsRef};
26 use rustc::util::nodemap::{ItemLocalSet, HirIdSet};
28 use syntax_pos::{Span, DUMMY_SP};
31 use std::ops::{BitAnd, BitAndAssign, BitOr};
33 pub fn provide(providers: &mut Providers<'_>) {
34 *providers = Providers {
35 rvalue_promotable_map,
36 const_is_rvalue_promotable_to_static,
41 fn const_is_rvalue_promotable_to_static<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
45 assert!(def_id.is_local());
47 let hir_id = tcx.hir().as_local_hir_id(def_id)
48 .expect("rvalue_promotable_map invoked with non-local def-id");
49 let body_id = tcx.hir().body_owned_by(hir_id);
50 tcx.rvalue_promotable_map(def_id).contains(&body_id.hir_id.local_id)
53 fn rvalue_promotable_map<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
57 let outer_def_id = tcx.closure_base_def_id(def_id);
58 if outer_def_id != def_id {
59 return tcx.rvalue_promotable_map(outer_def_id);
62 let mut visitor = CheckCrateVisitor {
64 tables: &ty::TypeckTables::empty(None),
67 mut_rvalue_borrows: Default::default(),
68 param_env: ty::ParamEnv::empty(),
69 identity_substs: InternalSubsts::empty(),
70 result: ItemLocalSet::default(),
73 // `def_id` should be a `Body` owner
74 let hir_id = tcx.hir().as_local_hir_id(def_id)
75 .expect("rvalue_promotable_map invoked with non-local def-id");
76 let body_id = tcx.hir().body_owned_by(hir_id);
77 let _ = visitor.check_nested_body(body_id);
79 tcx.arena.alloc(visitor.result)
82 struct CheckCrateVisitor<'a, 'tcx: 'a> {
83 tcx: TyCtxt<'a, 'tcx, 'tcx>,
86 mut_rvalue_borrows: HirIdSet,
87 param_env: ty::ParamEnv<'tcx>,
88 identity_substs: SubstsRef<'tcx>,
89 tables: &'a ty::TypeckTables<'tcx>,
94 #[derive(Debug, Clone, Copy, PartialEq)]
100 impl BitAnd for Promotability {
103 fn bitand(self, rhs: Self) -> Self {
105 (Promotable, Promotable) => Promotable,
111 impl BitAndAssign for Promotability {
112 fn bitand_assign(&mut self, rhs: Self) {
117 impl BitOr for Promotability {
120 fn bitor(self, rhs: Self) -> Self {
122 (NotPromotable, NotPromotable) => NotPromotable,
128 impl<'a, 'gcx> CheckCrateVisitor<'a, 'gcx> {
129 // Returns true iff all the values of the type are promotable.
130 fn type_promotability(&mut self, ty: Ty<'gcx>) -> Promotability {
131 debug!("type_promotability({})", ty);
133 if ty.is_freeze(self.tcx, self.param_env, DUMMY_SP) &&
134 !ty.needs_drop(self.tcx, self.param_env) {
141 fn handle_const_fn_call(
145 if self.tcx.is_promotable_const_fn(def_id) {
152 /// While the `ExprUseVisitor` walks, we will identify which
153 /// expressions are borrowed, and insert their IDs into this
154 /// table. Actually, we insert the "borrow-id", which is normally
155 /// the ID of the expression being borrowed: but in the case of
156 /// `ref mut` borrows, the `id` of the pattern is
157 /// inserted. Therefore, later we remove that entry from the table
158 /// and transfer it over to the value being matched. This will
159 /// then prevent said value from being promoted.
160 fn remove_mut_rvalue_borrow(&mut self, pat: &hir::Pat) -> bool {
161 let mut any_removed = false;
163 any_removed |= self.mut_rvalue_borrows.remove(&p.hir_id);
170 impl<'a, 'tcx> CheckCrateVisitor<'a, 'tcx> {
171 fn check_nested_body(&mut self, body_id: hir::BodyId) -> Promotability {
172 let item_id = self.tcx.hir().body_owner(body_id);
173 let item_def_id = self.tcx.hir().local_def_id(item_id);
175 let outer_in_fn = self.in_fn;
176 let outer_tables = self.tables;
177 let outer_param_env = self.param_env;
178 let outer_identity_substs = self.identity_substs;
181 self.in_static = false;
183 match self.tcx.hir().body_owner_kind(item_id) {
184 hir::BodyOwnerKind::Closure |
185 hir::BodyOwnerKind::Fn => self.in_fn = true,
186 hir::BodyOwnerKind::Static(_) => self.in_static = true,
191 self.tables = self.tcx.typeck_tables_of(item_def_id);
192 self.param_env = self.tcx.param_env(item_def_id);
193 self.identity_substs = InternalSubsts::identity_for_item(self.tcx, item_def_id);
195 let body = self.tcx.hir().body(body_id);
198 let param_env = self.param_env;
199 let region_scope_tree = self.tcx.region_scope_tree(item_def_id);
200 let tables = self.tables;
201 euv::ExprUseVisitor::new(self, tcx, param_env, ®ion_scope_tree, tables, None)
204 let body_promotable = self.check_expr(&body.value);
205 self.in_fn = outer_in_fn;
206 self.tables = outer_tables;
207 self.param_env = outer_param_env;
208 self.identity_substs = outer_identity_substs;
212 fn check_stmt(&mut self, stmt: &'tcx hir::Stmt) -> Promotability {
214 hir::StmtKind::Local(ref local) => {
215 if self.remove_mut_rvalue_borrow(&local.pat) {
216 if let Some(init) = &local.init {
217 self.mut_rvalue_borrows.insert(init.hir_id);
221 if let Some(ref expr) = local.init {
222 let _ = self.check_expr(&expr);
226 // Item statements are allowed
227 hir::StmtKind::Item(..) => Promotable,
228 hir::StmtKind::Expr(ref box_expr) |
229 hir::StmtKind::Semi(ref box_expr) => {
230 let _ = self.check_expr(box_expr);
236 fn check_expr(&mut self, ex: &'tcx hir::Expr) -> Promotability {
237 let node_ty = self.tables.node_type(ex.hir_id);
238 let mut outer = check_expr_kind(self, ex, node_ty);
239 outer &= check_adjustments(self, ex);
241 // Handle borrows on (or inside the autorefs of) this expression.
242 if self.mut_rvalue_borrows.remove(&ex.hir_id) {
243 outer = NotPromotable
246 if outer == Promotable {
247 self.result.insert(ex.hir_id.local_id);
252 fn check_block(&mut self, block: &'tcx hir::Block) -> Promotability {
253 let mut iter_result = Promotable;
254 for index in block.stmts.iter() {
255 iter_result &= self.check_stmt(index);
258 Some(ref box_expr) => iter_result & self.check_expr(&*box_expr),
264 /// This function is used to enforce the constraints on
265 /// const/static items. It walks through the *value*
266 /// of the item walking down the expression and evaluating
267 /// every nested expression. If the expression is not part
268 /// of a const/static item, it is qualified for promotion
269 /// instead of producing errors.
270 fn check_expr_kind<'a, 'tcx>(
271 v: &mut CheckCrateVisitor<'a, 'tcx>,
272 e: &'tcx hir::Expr, node_ty: Ty<'tcx>) -> Promotability {
274 let ty_result = match node_ty.sty {
275 ty::Adt(def, _) if def.has_dtor(v.tcx) => {
281 let node_result = match e.node {
282 hir::ExprKind::Box(ref expr) => {
283 let _ = v.check_expr(&expr);
286 hir::ExprKind::Unary(op, ref expr) => {
287 let expr_promotability = v.check_expr(expr);
288 if v.tables.is_method_call(e) || op == hir::UnDeref {
289 return NotPromotable;
293 hir::ExprKind::Binary(op, ref lhs, ref rhs) => {
294 let lefty = v.check_expr(lhs);
295 let righty = v.check_expr(rhs);
296 if v.tables.is_method_call(e) {
297 return NotPromotable;
299 match v.tables.node_type(lhs.hir_id).sty {
300 ty::RawPtr(_) | ty::FnPtr(..) => {
301 assert!(op.node == hir::BinOpKind::Eq || op.node == hir::BinOpKind::Ne ||
302 op.node == hir::BinOpKind::Le || op.node == hir::BinOpKind::Lt ||
303 op.node == hir::BinOpKind::Ge || op.node == hir::BinOpKind::Gt);
310 hir::ExprKind::Cast(ref from, _) => {
311 let expr_promotability = v.check_expr(from);
312 debug!("Checking const cast(id={})", from.hir_id);
313 let cast_in = CastTy::from_ty(v.tables.expr_ty(from));
314 let cast_out = CastTy::from_ty(v.tables.expr_ty(e));
315 match (cast_in, cast_out) {
316 (Some(CastTy::FnPtr), Some(CastTy::Int(_))) |
317 (Some(CastTy::Ptr(_)), Some(CastTy::Int(_))) => NotPromotable,
318 (_, _) => expr_promotability
321 hir::ExprKind::Path(ref qpath) => {
322 let res = v.tables.qpath_res(qpath, e.hir_id);
324 Res::Def(DefKind::Ctor(..), _)
325 | Res::Def(DefKind::Fn, _)
326 | Res::Def(DefKind::Method, _)
327 | Res::SelfCtor(..) =>
330 // References to a static that are themselves within a static
331 // are inherently promotable with the exception
332 // of "#[thread_local]" statics, which may not
333 // outlive the current function
334 Res::Def(DefKind::Static, did) => {
337 for attr in &v.tcx.get_attrs(did)[..] {
338 if attr.check_name("thread_local") {
339 debug!("Reference to Static(id={:?}) is unpromotable \
340 due to a #[thread_local] attribute", did);
341 return NotPromotable;
346 debug!("Reference to Static(id={:?}) is unpromotable as it is not \
347 referenced from a static", did);
352 Res::Def(DefKind::Const, did) |
353 Res::Def(DefKind::AssociatedConst, did) => {
354 let promotable = if v.tcx.trait_of_item(did).is_some() {
355 // Don't peek inside trait associated constants.
357 } else if v.tcx.at(e.span).const_is_rvalue_promotable_to_static(did) {
362 // Just in case the type is more specific than the definition,
363 // e.g., impl associated const with type parameters, check it.
364 // Also, trait associated consts are relaxed by this.
365 promotable | v.type_promotability(node_ty)
370 hir::ExprKind::Call(ref callee, ref hirvec) => {
371 let mut call_result = v.check_expr(callee);
372 for index in hirvec.iter() {
373 call_result &= v.check_expr(index);
375 let mut callee = &**callee;
377 callee = match callee.node {
378 hir::ExprKind::Block(ref block, _) => match block.expr {
379 Some(ref tail) => &tail,
385 // The callee is an arbitrary expression, it doesn't necessarily have a definition.
386 let def = if let hir::ExprKind::Path(ref qpath) = callee.node {
387 v.tables.qpath_res(qpath, callee.hir_id)
391 let def_result = match def {
392 Res::Def(DefKind::Ctor(_, CtorKind::Fn), _) |
393 Res::SelfCtor(..) => Promotable,
394 Res::Def(DefKind::Fn, did) => v.handle_const_fn_call(did),
395 Res::Def(DefKind::Method, did) => {
396 match v.tcx.associated_item(did).container {
397 ty::ImplContainer(_) => v.handle_const_fn_call(did),
398 ty::TraitContainer(_) => NotPromotable,
403 def_result & call_result
405 hir::ExprKind::MethodCall(ref _pathsegment, ref _span, ref hirvec) => {
406 let mut method_call_result = Promotable;
407 for index in hirvec.iter() {
408 method_call_result &= v.check_expr(index);
410 if let Some(def_id) = v.tables.type_dependent_def_id(e.hir_id) {
411 match v.tcx.associated_item(def_id).container {
412 ty::ImplContainer(_) => method_call_result & v.handle_const_fn_call(def_id),
413 ty::TraitContainer(_) => NotPromotable,
416 v.tcx.sess.delay_span_bug(e.span, "no type-dependent def for method call");
420 hir::ExprKind::Struct(ref _qpath, ref hirvec, ref option_expr) => {
421 let mut struct_result = Promotable;
422 for index in hirvec.iter() {
423 struct_result &= v.check_expr(&index.expr);
425 if let Some(ref expr) = *option_expr {
426 struct_result &= v.check_expr(&expr);
428 if let ty::Adt(adt, ..) = v.tables.expr_ty(e).sty {
429 // unsafe_cell_type doesn't necessarily exist with no_core
430 if Some(adt.did) == v.tcx.lang_items().unsafe_cell_type() {
431 return NotPromotable;
437 hir::ExprKind::Lit(_) |
438 hir::ExprKind::Err => Promotable,
440 hir::ExprKind::AddrOf(_, ref expr) |
441 hir::ExprKind::Repeat(ref expr, _) |
442 hir::ExprKind::Type(ref expr, _) |
443 hir::ExprKind::DropTemps(ref expr) => {
447 hir::ExprKind::Closure(_capture_clause, ref _box_fn_decl,
448 body_id, _span, _option_generator_movability) => {
449 let nested_body_promotable = v.check_nested_body(body_id);
450 // Paths in constant contexts cannot refer to local variables,
451 // as there are none, and thus closures can't have upvars there.
452 if v.tcx.with_freevars(e.hir_id, |fv| !fv.is_empty()) {
455 nested_body_promotable
459 hir::ExprKind::Field(ref expr, _ident) => {
460 let expr_promotability = v.check_expr(&expr);
461 if let Some(def) = v.tables.expr_ty(expr).ty_adt_def() {
463 return NotPromotable;
469 hir::ExprKind::Block(ref box_block, ref _option_label) => {
470 v.check_block(box_block)
473 hir::ExprKind::Index(ref lhs, ref rhs) => {
474 let lefty = v.check_expr(lhs);
475 let righty = v.check_expr(rhs);
476 if v.tables.is_method_call(e) {
477 return NotPromotable;
482 hir::ExprKind::Array(ref hirvec) => {
483 let mut array_result = Promotable;
484 for index in hirvec.iter() {
485 array_result &= v.check_expr(index);
490 hir::ExprKind::Tup(ref hirvec) => {
491 let mut tup_result = Promotable;
492 for index in hirvec.iter() {
493 tup_result &= v.check_expr(index);
498 // Conditional control flow (possible to implement).
499 hir::ExprKind::Match(ref expr, ref hirvec_arm, ref _match_source) => {
500 // Compute the most demanding borrow from all the arms'
501 // patterns and set that on the discriminator.
502 let mut mut_borrow = false;
503 for pat in hirvec_arm.iter().flat_map(|arm| &arm.pats) {
504 mut_borrow = v.remove_mut_rvalue_borrow(pat);
507 v.mut_rvalue_borrows.insert(expr.hir_id);
510 let _ = v.check_expr(expr);
511 for index in hirvec_arm.iter() {
512 let _ = v.check_expr(&*index.body);
513 if let Some(hir::Guard::If(ref expr)) = index.guard {
514 let _ = v.check_expr(&expr);
520 hir::ExprKind::If(ref lhs, ref rhs, ref option_expr) => {
521 let _ = v.check_expr(lhs);
522 let _ = v.check_expr(rhs);
523 if let Some(ref expr) = option_expr {
524 let _ = v.check_expr(&expr);
529 // Loops (not very meaningful in constants).
530 hir::ExprKind::While(ref expr, ref box_block, ref _option_label) => {
531 let _ = v.check_expr(expr);
532 let _ = v.check_block(box_block);
536 hir::ExprKind::Loop(ref box_block, ref _option_label, ref _loop_source) => {
537 let _ = v.check_block(box_block);
541 // More control flow (also not very meaningful).
542 hir::ExprKind::Break(_, ref option_expr) | hir::ExprKind::Ret(ref option_expr) => {
543 if let Some(ref expr) = *option_expr {
544 let _ = v.check_expr(&expr);
549 hir::ExprKind::Continue(_) => {
553 // Generator expressions
554 hir::ExprKind::Yield(ref expr) => {
555 let _ = v.check_expr(&expr);
559 // Expressions with side-effects.
560 hir::ExprKind::AssignOp(_, ref lhs, ref rhs) | hir::ExprKind::Assign(ref lhs, ref rhs) => {
561 let _ = v.check_expr(lhs);
562 let _ = v.check_expr(rhs);
566 hir::ExprKind::InlineAsm(ref _inline_asm, ref hirvec_lhs, ref hirvec_rhs) => {
567 for index in hirvec_lhs.iter().chain(hirvec_rhs.iter()) {
568 let _ = v.check_expr(index);
573 ty_result & node_result
576 /// Checks the adjustments of an expression.
577 fn check_adjustments<'a, 'tcx>(
578 v: &mut CheckCrateVisitor<'a, 'tcx>,
579 e: &hir::Expr) -> Promotability {
580 use rustc::ty::adjustment::*;
582 let mut adjustments = v.tables.expr_adjustments(e).iter().peekable();
583 while let Some(adjustment) = adjustments.next() {
584 match adjustment.kind {
587 Adjust::Borrow(_) => {}
589 Adjust::Deref(_) => {
590 if let Some(next_adjustment) = adjustments.peek() {
591 if let Adjust::Borrow(_) = next_adjustment.kind {
595 return NotPromotable;
602 impl<'a, 'gcx, 'tcx> euv::Delegate<'tcx> for CheckCrateVisitor<'a, 'gcx> {
603 fn consume(&mut self,
604 _consume_id: hir::HirId,
607 _mode: euv::ConsumeMode) {}
610 borrow_id: hir::HirId,
612 cmt: &mc::cmt_<'tcx>,
613 _loan_region: ty::Region<'tcx>,
615 loan_cause: euv::LoanCause) {
617 "borrow(borrow_id={:?}, cmt={:?}, bk={:?}, loan_cause={:?})",
624 // Kind of hacky, but we allow Unsafe coercions in constants.
625 // These occur when we convert a &T or *T to a *U, as well as
626 // when making a thin pointer (e.g., `*T`) into a fat pointer
628 if let euv::LoanCause::AutoUnsafe = loan_cause {
635 Categorization::ThreadLocal(..) |
636 Categorization::Rvalue(..) => {
637 if loan_cause == euv::MatchDiscriminant {
638 // Ignore the dummy immutable borrow created by EUV.
641 if bk.to_mutbl_lossy() == hir::MutMutable {
642 self.mut_rvalue_borrows.insert(borrow_id);
646 Categorization::StaticItem => {
649 Categorization::Deref(ref cmt, _) |
650 Categorization::Downcast(ref cmt, _) |
651 Categorization::Interior(ref cmt, _) => {
655 Categorization::Upvar(..) |
656 Categorization::Local(..) => break,
661 fn decl_without_init(&mut self, _id: hir::HirId, _span: Span) {}
663 _assignment_id: hir::HirId,
664 _assignment_span: Span,
665 _assignee_cmt: &mc::cmt_<'_>,
666 _mode: euv::MutateMode) {
669 fn matched_pat(&mut self, _: &hir::Pat, _: &mc::cmt_<'_>, _: euv::MatchMode) {}
671 fn consume_pat(&mut self,
672 _consume_pat: &hir::Pat,
674 _mode: euv::ConsumeMode) {}