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::{Def, 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 rustc_data_structures::sync::Lrc;
29 use syntax_pos::{Span, DUMMY_SP};
32 use std::ops::{BitAnd, BitAndAssign, BitOr};
34 pub fn provide(providers: &mut Providers<'_>) {
35 *providers = Providers {
36 rvalue_promotable_map,
37 const_is_rvalue_promotable_to_static,
42 fn const_is_rvalue_promotable_to_static<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
46 assert!(def_id.is_local());
48 let hir_id = tcx.hir().as_local_hir_id(def_id)
49 .expect("rvalue_promotable_map invoked with non-local def-id");
50 let body_id = tcx.hir().body_owned_by(hir_id);
51 tcx.rvalue_promotable_map(def_id).contains(&body_id.hir_id.local_id)
54 fn rvalue_promotable_map<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
58 let outer_def_id = tcx.closure_base_def_id(def_id);
59 if outer_def_id != def_id {
60 return tcx.rvalue_promotable_map(outer_def_id);
63 let mut visitor = CheckCrateVisitor {
65 tables: &ty::TypeckTables::empty(None),
68 mut_rvalue_borrows: Default::default(),
69 param_env: ty::ParamEnv::empty(),
70 identity_substs: InternalSubsts::empty(),
71 result: ItemLocalSet::default(),
74 // `def_id` should be a `Body` owner
75 let hir_id = tcx.hir().as_local_hir_id(def_id)
76 .expect("rvalue_promotable_map invoked with non-local def-id");
77 let body_id = tcx.hir().body_owned_by(hir_id);
78 let _ = visitor.check_nested_body(body_id);
80 Lrc::new(visitor.result)
83 struct CheckCrateVisitor<'a, 'tcx: 'a> {
84 tcx: TyCtxt<'a, 'tcx, 'tcx>,
87 mut_rvalue_borrows: HirIdSet,
88 param_env: ty::ParamEnv<'tcx>,
89 identity_substs: SubstsRef<'tcx>,
90 tables: &'a ty::TypeckTables<'tcx>,
95 #[derive(Debug, Clone, Copy, PartialEq)]
101 impl BitAnd for Promotability {
104 fn bitand(self, rhs: Self) -> Self {
106 (Promotable, Promotable) => Promotable,
112 impl BitAndAssign for Promotability {
113 fn bitand_assign(&mut self, rhs: Self) {
118 impl BitOr for Promotability {
121 fn bitor(self, rhs: Self) -> Self {
123 (NotPromotable, NotPromotable) => NotPromotable,
129 impl<'a, 'gcx> CheckCrateVisitor<'a, 'gcx> {
130 // Returns true iff all the values of the type are promotable.
131 fn type_promotability(&mut self, ty: Ty<'gcx>) -> Promotability {
132 debug!("type_promotability({})", ty);
134 if ty.is_freeze(self.tcx, self.param_env, DUMMY_SP) &&
135 !ty.needs_drop(self.tcx, self.param_env) {
142 fn handle_const_fn_call(
146 if self.tcx.is_promotable_const_fn(def_id) {
153 /// While the `ExprUseVisitor` walks, we will identify which
154 /// expressions are borrowed, and insert their IDs into this
155 /// table. Actually, we insert the "borrow-id", which is normally
156 /// the ID of the expression being borrowed: but in the case of
157 /// `ref mut` borrows, the `id` of the pattern is
158 /// inserted. Therefore, later we remove that entry from the table
159 /// and transfer it over to the value being matched. This will
160 /// then prevent said value from being promoted.
161 fn remove_mut_rvalue_borrow(&mut self, pat: &hir::Pat) -> bool {
162 let mut any_removed = false;
164 any_removed |= self.mut_rvalue_borrows.remove(&p.hir_id);
171 impl<'a, 'tcx> CheckCrateVisitor<'a, 'tcx> {
172 fn check_nested_body(&mut self, body_id: hir::BodyId) -> Promotability {
173 let item_id = self.tcx.hir().body_owner(body_id);
174 let item_def_id = self.tcx.hir().local_def_id(item_id);
176 let outer_in_fn = self.in_fn;
177 let outer_tables = self.tables;
178 let outer_param_env = self.param_env;
179 let outer_identity_substs = self.identity_substs;
182 self.in_static = false;
184 match self.tcx.hir().body_owner_kind(item_id) {
185 hir::BodyOwnerKind::Closure |
186 hir::BodyOwnerKind::Fn => self.in_fn = true,
187 hir::BodyOwnerKind::Static(_) => self.in_static = true,
192 self.tables = self.tcx.typeck_tables_of(item_def_id);
193 self.param_env = self.tcx.param_env(item_def_id);
194 self.identity_substs = InternalSubsts::identity_for_item(self.tcx, item_def_id);
196 let body = self.tcx.hir().body(body_id);
199 let param_env = self.param_env;
200 let region_scope_tree = self.tcx.region_scope_tree(item_def_id);
201 let tables = self.tables;
202 euv::ExprUseVisitor::new(self, tcx, param_env, ®ion_scope_tree, tables, None)
205 let body_promotable = self.check_expr(&body.value);
206 self.in_fn = outer_in_fn;
207 self.tables = outer_tables;
208 self.param_env = outer_param_env;
209 self.identity_substs = outer_identity_substs;
213 fn check_stmt(&mut self, stmt: &'tcx hir::Stmt) -> Promotability {
215 hir::StmtKind::Local(ref local) => {
216 if self.remove_mut_rvalue_borrow(&local.pat) {
217 if let Some(init) = &local.init {
218 self.mut_rvalue_borrows.insert(init.hir_id);
222 if let Some(ref expr) = local.init {
223 let _ = self.check_expr(&expr);
227 // Item statements are allowed
228 hir::StmtKind::Item(..) => Promotable,
229 hir::StmtKind::Expr(ref box_expr) |
230 hir::StmtKind::Semi(ref box_expr) => {
231 let _ = self.check_expr(box_expr);
237 fn check_expr(&mut self, ex: &'tcx hir::Expr) -> Promotability {
238 let node_ty = self.tables.node_type(ex.hir_id);
239 let mut outer = check_expr_kind(self, ex, node_ty);
240 outer &= check_adjustments(self, ex);
242 // Handle borrows on (or inside the autorefs of) this expression.
243 if self.mut_rvalue_borrows.remove(&ex.hir_id) {
244 outer = NotPromotable
247 if outer == Promotable {
248 self.result.insert(ex.hir_id.local_id);
253 fn check_block(&mut self, block: &'tcx hir::Block) -> Promotability {
254 let mut iter_result = Promotable;
255 for index in block.stmts.iter() {
256 iter_result &= self.check_stmt(index);
259 Some(ref box_expr) => iter_result & self.check_expr(&*box_expr),
265 /// This function is used to enforce the constraints on
266 /// const/static items. It walks through the *value*
267 /// of the item walking down the expression and evaluating
268 /// every nested expression. If the expression is not part
269 /// of a const/static item, it is qualified for promotion
270 /// instead of producing errors.
271 fn check_expr_kind<'a, 'tcx>(
272 v: &mut CheckCrateVisitor<'a, 'tcx>,
273 e: &'tcx hir::Expr, node_ty: Ty<'tcx>) -> Promotability {
275 let ty_result = match node_ty.sty {
276 ty::Adt(def, _) if def.has_dtor(v.tcx) => {
282 let node_result = match e.node {
283 hir::ExprKind::Box(ref expr) => {
284 let _ = v.check_expr(&expr);
287 hir::ExprKind::Unary(op, ref expr) => {
288 let expr_promotability = v.check_expr(expr);
289 if v.tables.is_method_call(e) || op == hir::UnDeref {
290 return NotPromotable;
294 hir::ExprKind::Binary(op, ref lhs, ref rhs) => {
295 let lefty = v.check_expr(lhs);
296 let righty = v.check_expr(rhs);
297 if v.tables.is_method_call(e) {
298 return NotPromotable;
300 match v.tables.node_type(lhs.hir_id).sty {
301 ty::RawPtr(_) | ty::FnPtr(..) => {
302 assert!(op.node == hir::BinOpKind::Eq || op.node == hir::BinOpKind::Ne ||
303 op.node == hir::BinOpKind::Le || op.node == hir::BinOpKind::Lt ||
304 op.node == hir::BinOpKind::Ge || op.node == hir::BinOpKind::Gt);
311 hir::ExprKind::Cast(ref from, _) => {
312 let expr_promotability = v.check_expr(from);
313 debug!("Checking const cast(id={})", from.hir_id);
314 let cast_in = CastTy::from_ty(v.tables.expr_ty(from));
315 let cast_out = CastTy::from_ty(v.tables.expr_ty(e));
316 match (cast_in, cast_out) {
317 (Some(CastTy::FnPtr), Some(CastTy::Int(_))) |
318 (Some(CastTy::Ptr(_)), Some(CastTy::Int(_))) => NotPromotable,
319 (_, _) => expr_promotability
322 hir::ExprKind::Path(ref qpath) => {
323 let def = v.tables.qpath_def(qpath, e.hir_id);
325 Def::Ctor(..) | Def::Fn(..) | Def::Method(..) | Def::SelfCtor(..) =>
328 // References to a static that are themselves within a static
329 // are inherently promotable with the exception
330 // of "#[thread_local]" statics, which may not
331 // outlive the current function
332 Def::Static(did, _) => {
335 for attr in &v.tcx.get_attrs(did)[..] {
336 if attr.check_name("thread_local") {
337 debug!("Reference to Static(id={:?}) is unpromotable \
338 due to a #[thread_local] attribute", did);
339 return NotPromotable;
344 debug!("Reference to Static(id={:?}) is unpromotable as it is not \
345 referenced from a static", did);
351 Def::AssociatedConst(did) => {
352 let promotable = if v.tcx.trait_of_item(did).is_some() {
353 // Don't peek inside trait associated constants.
355 } else if v.tcx.at(e.span).const_is_rvalue_promotable_to_static(did) {
360 // Just in case the type is more specific than the definition,
361 // e.g., impl associated const with type parameters, check it.
362 // Also, trait associated consts are relaxed by this.
363 promotable | v.type_promotability(node_ty)
368 hir::ExprKind::Call(ref callee, ref hirvec) => {
369 let mut call_result = v.check_expr(callee);
370 for index in hirvec.iter() {
371 call_result &= v.check_expr(index);
373 let mut callee = &**callee;
375 callee = match callee.node {
376 hir::ExprKind::Block(ref block, _) => match block.expr {
377 Some(ref tail) => &tail,
383 // The callee is an arbitrary expression, it doesn't necessarily have a definition.
384 let def = if let hir::ExprKind::Path(ref qpath) = callee.node {
385 v.tables.qpath_def(qpath, callee.hir_id)
389 let def_result = match def {
390 Def::Ctor(_, _, CtorKind::Fn) |
391 Def::SelfCtor(..) => Promotable,
392 Def::Fn(did) => v.handle_const_fn_call(did),
393 Def::Method(did) => {
394 match v.tcx.associated_item(did).container {
395 ty::ImplContainer(_) => v.handle_const_fn_call(did),
396 ty::TraitContainer(_) => NotPromotable,
401 def_result & call_result
403 hir::ExprKind::MethodCall(ref _pathsegment, ref _span, ref hirvec) => {
404 let mut method_call_result = Promotable;
405 for index in hirvec.iter() {
406 method_call_result &= v.check_expr(index);
408 if let Some(def) = v.tables.type_dependent_defs().get(e.hir_id) {
409 let def_id = def.def_id();
410 match v.tcx.associated_item(def_id).container {
411 ty::ImplContainer(_) => method_call_result & v.handle_const_fn_call(def_id),
412 ty::TraitContainer(_) => NotPromotable,
415 v.tcx.sess.delay_span_bug(e.span, "no type-dependent def for method call");
419 hir::ExprKind::Struct(ref _qpath, ref hirvec, ref option_expr) => {
420 let mut struct_result = Promotable;
421 for index in hirvec.iter() {
422 struct_result &= v.check_expr(&index.expr);
424 if let Some(ref expr) = *option_expr {
425 struct_result &= v.check_expr(&expr);
427 if let ty::Adt(adt, ..) = v.tables.expr_ty(e).sty {
428 // unsafe_cell_type doesn't necessarily exist with no_core
429 if Some(adt.did) == v.tcx.lang_items().unsafe_cell_type() {
430 return NotPromotable;
436 hir::ExprKind::Lit(_) |
437 hir::ExprKind::Err => Promotable,
439 hir::ExprKind::AddrOf(_, ref expr) |
440 hir::ExprKind::Repeat(ref expr, _) => {
444 hir::ExprKind::Closure(_capture_clause, ref _box_fn_decl,
445 body_id, _span, _option_generator_movability) => {
446 let nested_body_promotable = v.check_nested_body(body_id);
447 // Paths in constant contexts cannot refer to local variables,
448 // as there are none, and thus closures can't have upvars there.
449 if v.tcx.with_freevars(e.hir_id, |fv| !fv.is_empty()) {
452 nested_body_promotable
456 hir::ExprKind::Field(ref expr, _ident) => {
457 let expr_promotability = v.check_expr(&expr);
458 if let Some(def) = v.tables.expr_ty(expr).ty_adt_def() {
460 return NotPromotable;
466 hir::ExprKind::Block(ref box_block, ref _option_label) => {
467 v.check_block(box_block)
470 hir::ExprKind::Index(ref lhs, ref rhs) => {
471 let lefty = v.check_expr(lhs);
472 let righty = v.check_expr(rhs);
473 if v.tables.is_method_call(e) {
474 return NotPromotable;
479 hir::ExprKind::Array(ref hirvec) => {
480 let mut array_result = Promotable;
481 for index in hirvec.iter() {
482 array_result &= v.check_expr(index);
487 hir::ExprKind::Type(ref expr, ref _ty) => {
491 hir::ExprKind::Tup(ref hirvec) => {
492 let mut tup_result = Promotable;
493 for index in hirvec.iter() {
494 tup_result &= v.check_expr(index);
500 // Conditional control flow (possible to implement).
501 hir::ExprKind::Match(ref expr, ref hirvec_arm, ref _match_source) => {
502 // Compute the most demanding borrow from all the arms'
503 // patterns and set that on the discriminator.
504 let mut mut_borrow = false;
505 for pat in hirvec_arm.iter().flat_map(|arm| &arm.pats) {
506 mut_borrow = v.remove_mut_rvalue_borrow(pat);
509 v.mut_rvalue_borrows.insert(expr.hir_id);
512 let _ = v.check_expr(expr);
513 for index in hirvec_arm.iter() {
514 let _ = v.check_expr(&*index.body);
515 if let Some(hir::Guard::If(ref expr)) = index.guard {
516 let _ = v.check_expr(&expr);
522 hir::ExprKind::If(ref lhs, ref rhs, ref option_expr) => {
523 let _ = v.check_expr(lhs);
524 let _ = v.check_expr(rhs);
525 if let Some(ref expr) = option_expr {
526 let _ = v.check_expr(&expr);
531 // Loops (not very meaningful in constants).
532 hir::ExprKind::While(ref expr, ref box_block, ref _option_label) => {
533 let _ = v.check_expr(expr);
534 let _ = v.check_block(box_block);
538 hir::ExprKind::Loop(ref box_block, ref _option_label, ref _loop_source) => {
539 let _ = v.check_block(box_block);
543 // More control flow (also not very meaningful).
544 hir::ExprKind::Break(_, ref option_expr) | hir::ExprKind::Ret(ref option_expr) => {
545 if let Some(ref expr) = *option_expr {
546 let _ = v.check_expr(&expr);
551 hir::ExprKind::Continue(_) => {
555 // Generator expressions
556 hir::ExprKind::Yield(ref expr) => {
557 let _ = v.check_expr(&expr);
561 // Expressions with side-effects.
562 hir::ExprKind::AssignOp(_, ref lhs, ref rhs) | hir::ExprKind::Assign(ref lhs, ref rhs) => {
563 let _ = v.check_expr(lhs);
564 let _ = v.check_expr(rhs);
568 hir::ExprKind::InlineAsm(ref _inline_asm, ref hirvec_lhs, ref hirvec_rhs) => {
569 for index in hirvec_lhs.iter().chain(hirvec_rhs.iter()) {
570 let _ = v.check_expr(index);
575 ty_result & node_result
578 /// Checks the adjustments of an expression.
579 fn check_adjustments<'a, 'tcx>(
580 v: &mut CheckCrateVisitor<'a, 'tcx>,
581 e: &hir::Expr) -> Promotability {
582 use rustc::ty::adjustment::*;
584 let mut adjustments = v.tables.expr_adjustments(e).iter().peekable();
585 while let Some(adjustment) = adjustments.next() {
586 match adjustment.kind {
588 Adjust::ReifyFnPointer |
589 Adjust::UnsafeFnPointer |
590 Adjust::ClosureFnPointer |
591 Adjust::MutToConstPointer |
595 Adjust::Deref(_) => {
596 if let Some(next_adjustment) = adjustments.peek() {
597 if let Adjust::Borrow(_) = next_adjustment.kind {
601 return NotPromotable;
608 impl<'a, 'gcx, 'tcx> euv::Delegate<'tcx> for CheckCrateVisitor<'a, 'gcx> {
609 fn consume(&mut self,
610 _consume_id: hir::HirId,
613 _mode: euv::ConsumeMode) {}
616 borrow_id: hir::HirId,
618 cmt: &mc::cmt_<'tcx>,
619 _loan_region: ty::Region<'tcx>,
621 loan_cause: euv::LoanCause) {
623 "borrow(borrow_id={:?}, cmt={:?}, bk={:?}, loan_cause={:?})",
630 // Kind of hacky, but we allow Unsafe coercions in constants.
631 // These occur when we convert a &T or *T to a *U, as well as
632 // when making a thin pointer (e.g., `*T`) into a fat pointer
634 if let euv::LoanCause::AutoUnsafe = loan_cause {
641 Categorization::ThreadLocal(..) |
642 Categorization::Rvalue(..) => {
643 if loan_cause == euv::MatchDiscriminant {
644 // Ignore the dummy immutable borrow created by EUV.
647 if bk.to_mutbl_lossy() == hir::MutMutable {
648 self.mut_rvalue_borrows.insert(borrow_id);
652 Categorization::StaticItem => {
655 Categorization::Deref(ref cmt, _) |
656 Categorization::Downcast(ref cmt, _) |
657 Categorization::Interior(ref cmt, _) => {
661 Categorization::Upvar(..) |
662 Categorization::Local(..) => break,
667 fn decl_without_init(&mut self, _id: hir::HirId, _span: Span) {}
669 _assignment_id: hir::HirId,
670 _assignment_span: Span,
671 _assignee_cmt: &mc::cmt_<'_>,
672 _mode: euv::MutateMode) {
675 fn matched_pat(&mut self, _: &hir::Pat, _: &mc::cmt_<'_>, _: euv::MatchMode) {}
677 fn consume_pat(&mut self,
678 _consume_pat: &hir::Pat,
680 _mode: euv::ConsumeMode) {}