1 // Copyright 2012-2014 The Rust Project Developers. See the COPYRIGHT
2 // file at the top-level directory of this distribution and at
3 // http://rust-lang.org/COPYRIGHT.
5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
8 // option. This file may not be copied, modified, or distributed
9 // except according to those terms.
11 // Verifies that the types and values of const and static items
12 // are safe. The rules enforced by this module are:
14 // - For each *mutable* static item, it checks that its **type**:
15 // - doesn't have a destructor
16 // - doesn't own a box
18 // - For each *immutable* static item, it checks that its **value**:
19 // - doesn't own a box
20 // - doesn't contain a struct literal or a call to an enum variant / struct constructor where
21 // - the type of the struct/enum has a dtor
23 // Rules Enforced Elsewhere:
24 // - It's not possible to take the address of a static item with unsafe interior. This is enforced
25 // by borrowck::gather_loans
27 use rustc::ty::cast::CastKind;
28 use rustc::hir::def::{Def, CtorKind};
29 use rustc::hir::def_id::DefId;
30 use rustc::hir::map::blocks::FnLikeNode;
31 use rustc::middle::expr_use_visitor as euv;
32 use rustc::middle::mem_categorization as mc;
33 use rustc::middle::mem_categorization::Categorization;
34 use rustc::ty::{self, Ty, TyCtxt};
35 use rustc::ty::query::Providers;
36 use rustc::ty::subst::Substs;
37 use rustc::util::nodemap::{ItemLocalSet, NodeSet};
39 use rustc_data_structures::sync::Lrc;
42 use syntax_pos::{Span, DUMMY_SP};
44 pub fn provide(providers: &mut Providers) {
45 *providers = Providers {
46 rvalue_promotable_map,
47 const_is_rvalue_promotable_to_static,
52 pub fn check_crate<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>) {
53 for &body_id in &tcx.hir.krate().body_ids {
54 let def_id = tcx.hir.body_owner_def_id(body_id);
55 tcx.const_is_rvalue_promotable_to_static(def_id);
57 tcx.sess.abort_if_errors();
60 fn const_is_rvalue_promotable_to_static<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
64 assert!(def_id.is_local());
66 let node_id = tcx.hir.as_local_node_id(def_id)
67 .expect("rvalue_promotable_map invoked with non-local def-id");
68 let body_id = tcx.hir.body_owned_by(node_id);
69 let body_hir_id = tcx.hir.node_to_hir_id(body_id.node_id);
70 tcx.rvalue_promotable_map(def_id).contains(&body_hir_id.local_id)
73 fn rvalue_promotable_map<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
77 let outer_def_id = tcx.closure_base_def_id(def_id);
78 if outer_def_id != def_id {
79 return tcx.rvalue_promotable_map(outer_def_id);
82 let mut visitor = CheckCrateVisitor {
84 tables: &ty::TypeckTables::empty(None),
88 mut_rvalue_borrows: NodeSet(),
89 param_env: ty::ParamEnv::empty(),
90 identity_substs: Substs::empty(),
91 result: ItemLocalSet(),
94 // `def_id` should be a `Body` owner
95 let node_id = tcx.hir.as_local_node_id(def_id)
96 .expect("rvalue_promotable_map invoked with non-local def-id");
97 let body_id = tcx.hir.body_owned_by(node_id);
98 visitor.visit_nested_body(body_id);
100 Lrc::new(visitor.result)
103 struct CheckCrateVisitor<'a, 'tcx: 'a> {
104 tcx: TyCtxt<'a, 'tcx, 'tcx>,
108 mut_rvalue_borrows: NodeSet,
109 param_env: ty::ParamEnv<'tcx>,
110 identity_substs: &'tcx Substs<'tcx>,
111 tables: &'a ty::TypeckTables<'tcx>,
112 result: ItemLocalSet,
115 impl<'a, 'gcx> CheckCrateVisitor<'a, 'gcx> {
116 // Returns true iff all the values of the type are promotable.
117 fn type_has_only_promotable_values(&mut self, ty: Ty<'gcx>) -> bool {
118 ty.is_freeze(self.tcx, self.param_env, DUMMY_SP) &&
119 !ty.needs_drop(self.tcx, self.param_env)
122 fn handle_const_fn_call(&mut self, def_id: DefId, ret_ty: Ty<'gcx>, span: Span) {
123 self.promotable &= self.type_has_only_promotable_values(ret_ty);
125 self.promotable &= if let Some(fn_id) = self.tcx.hir.as_local_node_id(def_id) {
126 FnLikeNode::from_node(self.tcx.hir.get(fn_id)).map_or(false, |fn_like| {
127 fn_like.constness() == hir::Constness::Const
130 self.tcx.is_const_fn(def_id)
133 if let Some(&attr::Stability {
134 rustc_const_unstable: Some(attr::RustcConstUnstable {
135 feature: ref feature_name
137 .. }) = self.tcx.lookup_stability(def_id) {
139 // feature-gate is enabled,
141 .declared_lib_features
143 .any(|&(ref sym, _)| sym == feature_name) ||
145 // this comes from a crate with the feature-gate enabled,
146 !def_id.is_local() ||
148 // this comes from a macro that has #[allow_internal_unstable]
149 span.allows_unstable();
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 expession 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.id);
171 impl<'a, 'tcx> CheckCrateVisitor<'a, 'tcx> {
172 fn visit_nested_body(&mut self, body_id: hir::BodyId) {
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::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 = Substs::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 euv::ExprUseVisitor::new(self, tcx, param_env, ®ion_scope_tree, self.tables, None)
203 self.visit_expr(&body.value);
204 self.in_fn = outer_in_fn;
205 self.tables = outer_tables;
206 self.param_env = outer_param_env;
207 self.identity_substs = outer_identity_substs;
210 fn visit_stmt(&mut self, stmt: &'tcx hir::Stmt) {
212 hir::StmtDecl(ref decl, _node_id) => {
214 hir::DeclLocal(local) => {
215 self.promotable = false;
216 if self.remove_mut_rvalue_borrow(&local.pat) {
217 if let Some(init) = &local.init {
218 self.mut_rvalue_borrows.insert(init.id);
223 Some(ref expr) => self.visit_expr(&expr),
227 // Item statements are allowed
228 hir::DeclItem(_) => {}
231 hir::StmtExpr(ref box_expr, _node_id) |
232 hir::StmtSemi(ref box_expr, _node_id) => {
233 self.visit_expr(box_expr);
234 self.promotable = false;
239 fn visit_expr(&mut self, ex: &'tcx hir::Expr) {
240 let outer = self.promotable;
241 self.promotable = true;
243 let node_ty = self.tables.node_id_to_type(ex.hir_id);
244 check_expr(self, ex, node_ty);
245 check_adjustments(self, ex);
247 // Handle borrows on (or inside the autorefs of) this expression.
248 if self.mut_rvalue_borrows.remove(&ex.id) {
249 self.promotable = false;
253 self.result.insert(ex.hir_id.local_id);
255 self.promotable &= outer;
258 fn visit_block(&mut self, block: &'tcx hir::Block) {
259 for index in block.stmts.iter() {
260 self.visit_stmt(index)
263 Some(ref box_expr) => { self.visit_expr(&*box_expr) },
269 /// This function is used to enforce the constraints on
270 /// const/static items. It walks through the *value*
271 /// of the item walking down the expression and evaluating
272 /// every nested expression. If the expression is not part
273 /// of a const/static item, it is qualified for promotion
274 /// instead of producing errors.
275 fn check_expr<'a, 'tcx>(
276 v: &mut CheckCrateVisitor<'a, 'tcx>,
277 e: &'tcx hir::Expr, node_ty: Ty<'tcx>) {
279 ty::TyAdt(def, _) if def.has_dtor(v.tcx) => {
280 v.promotable = false;
286 hir::ExprBox(ref expr) => {
288 v.promotable = false;
290 hir::ExprUnary(op, ref expr) => {
291 if v.tables.is_method_call(e) {
292 v.promotable = false;
294 if op == hir::UnDeref {
295 v.promotable = false;
299 hir::ExprBinary(op, ref lhs, ref rhs) => {
300 if v.tables.is_method_call(e) {
301 v.promotable = false;
305 match v.tables.node_id_to_type(lhs.hir_id).sty {
307 assert!(op.node == hir::BiEq || op.node == hir::BiNe ||
308 op.node == hir::BiLe || op.node == hir::BiLt ||
309 op.node == hir::BiGe || op.node == hir::BiGt);
311 v.promotable = false;
316 hir::ExprCast(ref from, _) => {
318 debug!("Checking const cast(id={})", from.id);
319 match v.tables.cast_kinds().get(from.hir_id) {
320 None => v.tcx.sess.delay_span_bug(e.span, "no kind for cast"),
321 Some(&CastKind::PtrAddrCast) | Some(&CastKind::FnPtrAddrCast) => {
322 v.promotable = false;
327 hir::ExprPath(ref qpath) => {
328 let def = v.tables.qpath_def(qpath, e.hir_id);
330 Def::VariantCtor(..) | Def::StructCtor(..) |
331 Def::Fn(..) | Def::Method(..) => {}
333 // References to a static that are themselves within a static
334 // are inherently promotable with the exception
335 // of "#[thread_local]" statics, which may not
336 // outlive the current function
337 Def::Static(did, _) => {
340 let mut thread_local = false;
342 for attr in &v.tcx.get_attrs(did)[..] {
343 if attr.check_name("thread_local") {
344 debug!("Reference to Static(id={:?}) is unpromotable \
345 due to a #[thread_local] attribute", did);
346 v.promotable = false;
353 debug!("Allowing promotion of reference to Static(id={:?})", did);
356 debug!("Reference to Static(id={:?}) is unpromotable as it is not \
357 referenced from a static", did);
358 v.promotable = false;
364 Def::AssociatedConst(did) => {
365 let promotable = if v.tcx.trait_of_item(did).is_some() {
366 // Don't peek inside trait associated constants.
369 v.tcx.at(e.span).const_is_rvalue_promotable_to_static(did)
372 // Just in case the type is more specific than the definition,
373 // e.g. impl associated const with type parameters, check it.
374 // Also, trait associated consts are relaxed by this.
375 v.promotable &= promotable || v.type_has_only_promotable_values(node_ty);
379 v.promotable = false;
383 hir::ExprCall(ref callee, ref hirvec) => {
384 v.visit_expr(callee);
385 for index in hirvec.iter() {
388 let mut callee = &**callee;
390 callee = match callee.node {
391 hir::ExprBlock(ref block, _) => match block.expr {
392 Some(ref tail) => &tail,
398 // The callee is an arbitrary expression, it doesn't necessarily have a definition.
399 let def = if let hir::ExprPath(ref qpath) = callee.node {
400 v.tables.qpath_def(qpath, callee.hir_id)
405 Def::StructCtor(_, CtorKind::Fn) |
406 Def::VariantCtor(_, CtorKind::Fn) => {}
408 v.handle_const_fn_call(did, node_ty, e.span)
410 Def::Method(did) => {
411 match v.tcx.associated_item(did).container {
412 ty::ImplContainer(_) => {
413 v.handle_const_fn_call(did, node_ty, e.span)
415 ty::TraitContainer(_) => v.promotable = false
418 _ => v.promotable = false
421 hir::ExprMethodCall(ref _pathsegment, ref _span, ref hirvec) => {
422 for index in hirvec.iter() {
425 if let Some(def) = v.tables.type_dependent_defs().get(e.hir_id) {
426 let def_id = def.def_id();
427 match v.tcx.associated_item(def_id).container {
428 ty::ImplContainer(_) => v.handle_const_fn_call(def_id, node_ty, e.span),
429 ty::TraitContainer(_) => v.promotable = false
432 v.tcx.sess.delay_span_bug(e.span, "no type-dependent def for method call");
435 hir::ExprStruct(ref _qpath, ref hirvec, ref option_expr) => {
436 for index in hirvec.iter() {
437 v.visit_expr(&index.expr);
440 Some(ref expr) => { v.visit_expr(&expr) },
443 if let ty::TyAdt(adt, ..) = v.tables.expr_ty(e).sty {
444 // unsafe_cell_type doesn't necessarily exist with no_core
445 if Some(adt.did) == v.tcx.lang_items().unsafe_cell_type() {
446 v.promotable = false;
451 hir::ExprLit(_) => {}
453 hir::ExprAddrOf(_, ref expr) |
454 hir::ExprRepeat(ref expr, _) => {
458 hir::ExprClosure(_capture_clause, ref _box_fn_decl,
459 body_id, _span, _option_generator_movability) => {
460 v.visit_nested_body(body_id);
461 // Paths in constant contexts cannot refer to local variables,
462 // as there are none, and thus closures can't have upvars there.
463 if v.tcx.with_freevars(e.id, |fv| !fv.is_empty()) {
464 v.promotable = false;
468 hir::ExprField(ref expr, _ident) => {
470 if let Some(def) = v.tables.expr_ty(expr).ty_adt_def() {
477 hir::ExprBlock(ref box_block, ref _option_label) => {
478 v.visit_block(box_block);
481 hir::ExprIndex(ref lhs, ref rhs) => {
482 if v.tables.is_method_call(e) {
483 v.promotable = false;
489 hir::ExprArray(ref hirvec) => {
490 for index in hirvec.iter() {
495 hir::ExprType(ref expr, ref _ty) => {
499 hir::ExprTup(ref hirvec) => {
500 for index in hirvec.iter() {
506 // Conditional control flow (possible to implement).
507 hir::ExprMatch(ref expr, ref hirvec_arm, ref _match_source) => {
508 // Compute the most demanding borrow from all the arms'
509 // patterns and set that on the discriminator.
510 let mut mut_borrow = false;
511 for pat in hirvec_arm.iter().flat_map(|arm| &arm.pats) {
512 mut_borrow = v.remove_mut_rvalue_borrow(pat);
515 v.mut_rvalue_borrows.insert(expr.id);
519 for index in hirvec_arm.iter() {
520 v.visit_expr(&*index.body);
522 Some(ref expr) => v.visit_expr(&expr),
526 v.promotable = false;
529 hir::ExprIf(ref lhs, ref rhs, ref option_expr) => {
533 Some(ref expr) => v.visit_expr(&expr),
536 v.promotable = false;
539 // Loops (not very meaningful in constants).
540 hir::ExprWhile(ref expr, ref box_block, ref _option_label) => {
542 v.visit_block(box_block);
543 v.promotable = false;
546 hir::ExprLoop(ref box_block, ref _option_label, ref _loop_source) => {
547 v.visit_block(box_block);
548 v.promotable = false;
551 // More control flow (also not very meaningful).
552 hir::ExprBreak(_, ref option_expr) | hir::ExprRet(ref option_expr) => {
554 Some(ref expr) => { v.visit_expr(&expr) },
557 v.promotable = false;
560 hir::ExprContinue(_) => {
561 v.promotable = false;
564 // Generator expressions
565 hir::ExprYield(ref expr) => {
567 v.promotable = false;
570 // Expressions with side-effects.
571 hir::ExprAssignOp(_, ref lhs, ref rhs) | hir::ExprAssign(ref lhs, ref rhs) => {
574 v.promotable = false;
577 hir::ExprInlineAsm(ref _inline_asm, ref hirvec_lhs, ref hirvec_rhs) => {
578 for index in hirvec_lhs.iter() {
581 for index in hirvec_rhs.iter() {
584 v.promotable = false;
589 /// Check the adjustments of an expression
590 fn check_adjustments<'a, 'tcx>(v: &mut CheckCrateVisitor<'a, 'tcx>, e: &hir::Expr) {
591 use rustc::ty::adjustment::*;
593 let mut adjustments = v.tables.expr_adjustments(e).iter().peekable();
594 while let Some(adjustment) = adjustments.next() {
595 match adjustment.kind {
597 Adjust::ReifyFnPointer |
598 Adjust::UnsafeFnPointer |
599 Adjust::ClosureFnPointer |
600 Adjust::MutToConstPointer |
604 Adjust::Deref(_) => {
605 if let Some(next_adjustment) = adjustments.peek() {
606 if let Adjust::Borrow(_) = next_adjustment.kind {
610 v.promotable = false;
617 impl<'a, 'gcx, 'tcx> euv::Delegate<'tcx> for CheckCrateVisitor<'a, 'gcx> {
618 fn consume(&mut self,
619 _consume_id: ast::NodeId,
622 _mode: euv::ConsumeMode) {}
625 borrow_id: ast::NodeId,
627 cmt: &mc::cmt_<'tcx>,
628 _loan_region: ty::Region<'tcx>,
630 loan_cause: euv::LoanCause) {
632 "borrow(borrow_id={:?}, cmt={:?}, bk={:?}, loan_cause={:?})",
639 // Kind of hacky, but we allow Unsafe coercions in constants.
640 // These occur when we convert a &T or *T to a *U, as well as
641 // when making a thin pointer (e.g., `*T`) into a fat pointer
644 euv::LoanCause::AutoUnsafe => {
653 Categorization::Rvalue(..) => {
654 if loan_cause == euv::MatchDiscriminant {
655 // Ignore the dummy immutable borrow created by EUV.
658 if bk.to_mutbl_lossy() == hir::MutMutable {
659 self.mut_rvalue_borrows.insert(borrow_id);
663 Categorization::StaticItem => {
666 Categorization::Deref(ref cmt, _) |
667 Categorization::Downcast(ref cmt, _) |
668 Categorization::Interior(ref cmt, _) => {
672 Categorization::Upvar(..) |
673 Categorization::Local(..) => break,
678 fn decl_without_init(&mut self, _id: ast::NodeId, _span: Span) {}
680 _assignment_id: ast::NodeId,
681 _assignment_span: Span,
682 _assignee_cmt: &mc::cmt_,
683 _mode: euv::MutateMode) {
686 fn matched_pat(&mut self, _: &hir::Pat, _: &mc::cmt_, _: euv::MatchMode) {}
688 fn consume_pat(&mut self, _consume_pat: &hir::Pat, _cmt: &mc::cmt_, _mode: euv::ConsumeMode) {}