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};
43 use self::Promotability::*;
44 use std::ops::{BitAnd, BitAndAssign, BitOr};
46 pub fn provide(providers: &mut Providers) {
47 *providers = Providers {
48 rvalue_promotable_map,
49 const_is_rvalue_promotable_to_static,
54 pub fn check_crate<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>) {
55 for &body_id in &tcx.hir.krate().body_ids {
56 let def_id = tcx.hir.body_owner_def_id(body_id);
57 tcx.const_is_rvalue_promotable_to_static(def_id);
59 tcx.sess.abort_if_errors();
62 fn const_is_rvalue_promotable_to_static<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
66 assert!(def_id.is_local());
68 let node_id = tcx.hir.as_local_node_id(def_id)
69 .expect("rvalue_promotable_map invoked with non-local def-id");
70 let body_id = tcx.hir.body_owned_by(node_id);
71 let body_hir_id = tcx.hir.node_to_hir_id(body_id.node_id);
72 tcx.rvalue_promotable_map(def_id).contains(&body_hir_id.local_id)
75 fn rvalue_promotable_map<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
79 let outer_def_id = tcx.closure_base_def_id(def_id);
80 if outer_def_id != def_id {
81 return tcx.rvalue_promotable_map(outer_def_id);
84 let mut visitor = CheckCrateVisitor {
86 tables: &ty::TypeckTables::empty(None),
89 mut_rvalue_borrows: NodeSet(),
90 param_env: ty::ParamEnv::empty(),
91 identity_substs: Substs::empty(),
92 result: ItemLocalSet(),
95 // `def_id` should be a `Body` owner
96 let node_id = tcx.hir.as_local_node_id(def_id)
97 .expect("rvalue_promotable_map invoked with non-local def-id");
98 let body_id = tcx.hir.body_owned_by(node_id);
99 let _ = visitor.check_nested_body(body_id);
101 Lrc::new(visitor.result)
104 struct CheckCrateVisitor<'a, 'tcx: 'a> {
105 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,
116 #[derive(Debug, Clone, Copy, PartialEq)]
122 impl BitAnd for Promotability {
125 fn bitand(self, rhs: Self) -> Self {
127 (Promotable, Promotable) => Promotable,
133 impl BitAndAssign for Promotability {
134 fn bitand_assign(&mut self, rhs: Self) {
139 impl BitOr for Promotability {
142 fn bitor(self, rhs: Self) -> Self {
144 (NotPromotable, NotPromotable) => NotPromotable,
150 impl<'a, 'gcx> CheckCrateVisitor<'a, 'gcx> {
151 // Returns true iff all the values of the type are promotable.
152 fn type_promotability(&mut self, ty: Ty<'gcx>) -> Promotability {
153 debug!("type_promotability({})", ty);
155 if ty.is_freeze(self.tcx, self.param_env, DUMMY_SP) &&
156 !ty.needs_drop(self.tcx, self.param_env) {
163 fn handle_const_fn_call(&mut self, def_id: DefId,
164 ret_ty: Ty<'gcx>, span: Span) -> Promotability {
165 if self.type_promotability(ret_ty) == NotPromotable {
166 return NotPromotable;
169 let node_check = if let Some(fn_id) = self.tcx.hir.as_local_node_id(def_id) {
170 FnLikeNode::from_node(self.tcx.hir.get(fn_id)).map_or(false, |fn_like| {
171 fn_like.constness() == hir::Constness::Const
174 self.tcx.is_const_fn(def_id)
181 if let Some(&attr::Stability {
182 const_stability: Some(ref feature_name),
183 .. }) = self.tcx.lookup_stability(def_id) {
185 // feature-gate is enabled,
187 .declared_lib_features
189 .any(|&(ref sym, _)| sym == feature_name) ||
191 // this comes from a macro that has #[allow_internal_unstable]
192 span.allows_unstable();
200 /// While the `ExprUseVisitor` walks, we will identify which
201 /// expressions are borrowed, and insert their ids into this
202 /// table. Actually, we insert the "borrow-id", which is normally
203 /// the id of the expession being borrowed: but in the case of
204 /// `ref mut` borrows, the `id` of the pattern is
205 /// inserted. Therefore later we remove that entry from the table
206 /// and transfer it over to the value being matched. This will
207 /// then prevent said value from being promoted.
208 fn remove_mut_rvalue_borrow(&mut self, pat: &hir::Pat) -> bool {
209 let mut any_removed = false;
211 any_removed |= self.mut_rvalue_borrows.remove(&p.id);
218 impl<'a, 'tcx> CheckCrateVisitor<'a, 'tcx> {
219 fn check_nested_body(&mut self, body_id: hir::BodyId) -> Promotability {
220 let item_id = self.tcx.hir.body_owner(body_id);
221 let item_def_id = self.tcx.hir.local_def_id(item_id);
223 let outer_in_fn = self.in_fn;
224 let outer_tables = self.tables;
225 let outer_param_env = self.param_env;
226 let outer_identity_substs = self.identity_substs;
229 self.in_static = false;
231 match self.tcx.hir.body_owner_kind(item_id) {
232 hir::BodyOwnerKind::Fn => self.in_fn = true,
233 hir::BodyOwnerKind::Static(_) => self.in_static = true,
238 self.tables = self.tcx.typeck_tables_of(item_def_id);
239 self.param_env = self.tcx.param_env(item_def_id);
240 self.identity_substs = Substs::identity_for_item(self.tcx, item_def_id);
242 let body = self.tcx.hir.body(body_id);
245 let param_env = self.param_env;
246 let region_scope_tree = self.tcx.region_scope_tree(item_def_id);
247 let tables = self.tables;
248 euv::ExprUseVisitor::new(self, tcx, param_env, ®ion_scope_tree, tables, None)
251 let body_promotable = self.check_expr(&body.value);
252 self.in_fn = outer_in_fn;
253 self.tables = outer_tables;
254 self.param_env = outer_param_env;
255 self.identity_substs = outer_identity_substs;
259 fn check_stmt(&mut self, stmt: &'tcx hir::Stmt) -> Promotability {
261 hir::StmtKind::Decl(ref decl, _node_id) => {
263 hir::DeclKind::Local(local) => {
264 if self.remove_mut_rvalue_borrow(&local.pat) {
265 if let Some(init) = &local.init {
266 self.mut_rvalue_borrows.insert(init.id);
270 if let Some(ref expr) = local.init {
271 let _ = self.check_expr(&expr);
275 // Item statements are allowed
276 hir::DeclKind::Item(_) => Promotable
279 hir::StmtKind::Expr(ref box_expr, _node_id) |
280 hir::StmtKind::Semi(ref box_expr, _node_id) => {
281 let _ = self.check_expr(box_expr);
287 fn check_expr(&mut self, ex: &'tcx hir::Expr) -> Promotability {
288 let node_ty = self.tables.node_id_to_type(ex.hir_id);
289 let mut outer = check_expr_kind(self, ex, node_ty);
290 outer &= check_adjustments(self, ex);
292 // Handle borrows on (or inside the autorefs of) this expression.
293 if self.mut_rvalue_borrows.remove(&ex.id) {
294 outer = NotPromotable
297 if outer == Promotable {
298 self.result.insert(ex.hir_id.local_id);
303 fn check_block(&mut self, block: &'tcx hir::Block) -> Promotability {
304 let mut iter_result = Promotable;
305 for index in block.stmts.iter() {
306 iter_result &= self.check_stmt(index);
309 Some(ref box_expr) => iter_result & self.check_expr(&*box_expr),
315 /// This function is used to enforce the constraints on
316 /// const/static items. It walks through the *value*
317 /// of the item walking down the expression and evaluating
318 /// every nested expression. If the expression is not part
319 /// of a const/static item, it is qualified for promotion
320 /// instead of producing errors.
321 fn check_expr_kind<'a, 'tcx>(
322 v: &mut CheckCrateVisitor<'a, 'tcx>,
323 e: &'tcx hir::Expr, node_ty: Ty<'tcx>) -> Promotability {
325 let ty_result = match node_ty.sty {
326 ty::Adt(def, _) if def.has_dtor(v.tcx) => {
332 let node_result = match e.node {
333 hir::ExprKind::Box(ref expr) => {
334 let _ = v.check_expr(&expr);
337 hir::ExprKind::Unary(op, ref expr) => {
338 let expr_promotability = v.check_expr(expr);
339 if v.tables.is_method_call(e) || op == hir::UnDeref {
340 return NotPromotable;
344 hir::ExprKind::Binary(op, ref lhs, ref rhs) => {
345 let lefty = v.check_expr(lhs);
346 let righty = v.check_expr(rhs);
347 if v.tables.is_method_call(e) {
348 return NotPromotable;
350 match v.tables.node_id_to_type(lhs.hir_id).sty {
352 assert!(op.node == hir::BinOpKind::Eq || op.node == hir::BinOpKind::Ne ||
353 op.node == hir::BinOpKind::Le || op.node == hir::BinOpKind::Lt ||
354 op.node == hir::BinOpKind::Ge || op.node == hir::BinOpKind::Gt);
361 hir::ExprKind::Cast(ref from, _) => {
362 let expr_promotability = v.check_expr(from);
363 debug!("Checking const cast(id={})", from.id);
364 match v.tables.cast_kinds().get(from.hir_id) {
366 v.tcx.sess.delay_span_bug(e.span, "no kind for cast");
369 Some(&CastKind::PtrAddrCast) | Some(&CastKind::FnPtrAddrCast) => {
372 _ => expr_promotability
375 hir::ExprKind::Path(ref qpath) => {
376 let def = v.tables.qpath_def(qpath, e.hir_id);
378 Def::VariantCtor(..) | Def::StructCtor(..) |
379 Def::Fn(..) | Def::Method(..) | Def::SelfCtor(..) => Promotable,
381 // References to a static that are themselves within a static
382 // are inherently promotable with the exception
383 // of "#[thread_local]" statics, which may not
384 // outlive the current function
385 Def::Static(did, _) => {
388 for attr in &v.tcx.get_attrs(did)[..] {
389 if attr.check_name("thread_local") {
390 debug!("Reference to Static(id={:?}) is unpromotable \
391 due to a #[thread_local] attribute", did);
392 return NotPromotable;
397 debug!("Reference to Static(id={:?}) is unpromotable as it is not \
398 referenced from a static", did);
404 Def::AssociatedConst(did) => {
405 let promotable = if v.tcx.trait_of_item(did).is_some() {
406 // Don't peek inside trait associated constants.
408 } else if v.tcx.at(e.span).const_is_rvalue_promotable_to_static(did) {
413 // Just in case the type is more specific than the definition,
414 // e.g. impl associated const with type parameters, check it.
415 // Also, trait associated consts are relaxed by this.
416 promotable | v.type_promotability(node_ty)
421 hir::ExprKind::Call(ref callee, ref hirvec) => {
422 let mut call_result = v.check_expr(callee);
423 for index in hirvec.iter() {
424 call_result &= v.check_expr(index);
426 let mut callee = &**callee;
428 callee = match callee.node {
429 hir::ExprKind::Block(ref block, _) => match block.expr {
430 Some(ref tail) => &tail,
436 // The callee is an arbitrary expression, it doesn't necessarily have a definition.
437 let def = if let hir::ExprKind::Path(ref qpath) = callee.node {
438 v.tables.qpath_def(qpath, callee.hir_id)
442 let def_result = match def {
443 Def::StructCtor(_, CtorKind::Fn) |
444 Def::VariantCtor(_, CtorKind::Fn) |
445 Def::SelfCtor(..) => Promotable,
447 v.handle_const_fn_call(did, node_ty, e.span)
449 Def::Method(did) => {
450 match v.tcx.associated_item(did).container {
451 ty::ImplContainer(_) => {
452 v.handle_const_fn_call(did, node_ty, e.span)
454 ty::TraitContainer(_) => NotPromotable,
459 def_result & call_result
461 hir::ExprKind::MethodCall(ref _pathsegment, ref _span, ref hirvec) => {
462 let mut method_call_result = Promotable;
463 for index in hirvec.iter() {
464 method_call_result &= v.check_expr(index);
466 if let Some(def) = v.tables.type_dependent_defs().get(e.hir_id) {
467 let def_id = def.def_id();
468 match v.tcx.associated_item(def_id).container {
469 ty::ImplContainer(_) => {
470 method_call_result = method_call_result
471 & v.handle_const_fn_call(def_id, node_ty, e.span);
473 ty::TraitContainer(_) => return NotPromotable,
476 v.tcx.sess.delay_span_bug(e.span, "no type-dependent def for method call");
480 hir::ExprKind::Struct(ref _qpath, ref hirvec, ref option_expr) => {
481 let mut struct_result = Promotable;
482 for index in hirvec.iter() {
483 struct_result &= v.check_expr(&index.expr);
485 if let Some(ref expr) = *option_expr {
486 struct_result &= v.check_expr(&expr);
488 if let ty::Adt(adt, ..) = v.tables.expr_ty(e).sty {
489 // unsafe_cell_type doesn't necessarily exist with no_core
490 if Some(adt.did) == v.tcx.lang_items().unsafe_cell_type() {
491 return NotPromotable;
497 hir::ExprKind::Lit(_) => Promotable,
499 hir::ExprKind::AddrOf(_, ref expr) |
500 hir::ExprKind::Repeat(ref expr, _) => {
504 hir::ExprKind::Closure(_capture_clause, ref _box_fn_decl,
505 body_id, _span, _option_generator_movability) => {
506 let nested_body_promotable = v.check_nested_body(body_id);
507 // Paths in constant contexts cannot refer to local variables,
508 // as there are none, and thus closures can't have upvars there.
509 if v.tcx.with_freevars(e.id, |fv| !fv.is_empty()) {
512 nested_body_promotable
516 hir::ExprKind::Field(ref expr, _ident) => {
517 let expr_promotability = v.check_expr(&expr);
518 if let Some(def) = v.tables.expr_ty(expr).ty_adt_def() {
520 return NotPromotable;
526 hir::ExprKind::Block(ref box_block, ref _option_label) => {
527 v.check_block(box_block)
530 hir::ExprKind::Index(ref lhs, ref rhs) => {
531 let lefty = v.check_expr(lhs);
532 let righty = v.check_expr(rhs);
533 if v.tables.is_method_call(e) {
534 return NotPromotable;
539 hir::ExprKind::Array(ref hirvec) => {
540 let mut array_result = Promotable;
541 for index in hirvec.iter() {
542 array_result &= v.check_expr(index);
547 hir::ExprKind::Type(ref expr, ref _ty) => {
551 hir::ExprKind::Tup(ref hirvec) => {
552 let mut tup_result = Promotable;
553 for index in hirvec.iter() {
554 tup_result &= v.check_expr(index);
560 // Conditional control flow (possible to implement).
561 hir::ExprKind::Match(ref expr, ref hirvec_arm, ref _match_source) => {
562 // Compute the most demanding borrow from all the arms'
563 // patterns and set that on the discriminator.
564 let mut mut_borrow = false;
565 for pat in hirvec_arm.iter().flat_map(|arm| &arm.pats) {
566 mut_borrow = v.remove_mut_rvalue_borrow(pat);
569 v.mut_rvalue_borrows.insert(expr.id);
572 let _ = v.check_expr(expr);
573 for index in hirvec_arm.iter() {
574 let _ = v.check_expr(&*index.body);
575 if let Some(hir::Guard::If(ref expr)) = index.guard {
576 let _ = v.check_expr(&expr);
582 hir::ExprKind::If(ref lhs, ref rhs, ref option_expr) => {
583 let _ = v.check_expr(lhs);
584 let _ = v.check_expr(rhs);
585 if let Some(ref expr) = option_expr {
586 let _ = v.check_expr(&expr);
591 // Loops (not very meaningful in constants).
592 hir::ExprKind::While(ref expr, ref box_block, ref _option_label) => {
593 let _ = v.check_expr(expr);
594 let _ = v.check_block(box_block);
598 hir::ExprKind::Loop(ref box_block, ref _option_label, ref _loop_source) => {
599 let _ = v.check_block(box_block);
603 // More control flow (also not very meaningful).
604 hir::ExprKind::Break(_, ref option_expr) | hir::ExprKind::Ret(ref option_expr) => {
605 if let Some(ref expr) = *option_expr {
606 let _ = v.check_expr(&expr);
611 hir::ExprKind::Continue(_) => {
615 // Generator expressions
616 hir::ExprKind::Yield(ref expr) => {
617 let _ = v.check_expr(&expr);
621 // Expressions with side-effects.
622 hir::ExprKind::AssignOp(_, ref lhs, ref rhs) | hir::ExprKind::Assign(ref lhs, ref rhs) => {
623 let _ = v.check_expr(lhs);
624 let _ = v.check_expr(rhs);
628 hir::ExprKind::InlineAsm(ref _inline_asm, ref hirvec_lhs, ref hirvec_rhs) => {
629 for index in hirvec_lhs.iter().chain(hirvec_rhs.iter()) {
630 let _ = v.check_expr(index);
635 ty_result & node_result
638 /// Check the adjustments of an expression
639 fn check_adjustments<'a, 'tcx>(
640 v: &mut CheckCrateVisitor<'a, 'tcx>,
641 e: &hir::Expr) -> Promotability {
642 use rustc::ty::adjustment::*;
644 let mut adjustments = v.tables.expr_adjustments(e).iter().peekable();
645 while let Some(adjustment) = adjustments.next() {
646 match adjustment.kind {
648 Adjust::ReifyFnPointer |
649 Adjust::UnsafeFnPointer |
650 Adjust::ClosureFnPointer |
651 Adjust::MutToConstPointer |
655 Adjust::Deref(_) => {
656 if let Some(next_adjustment) = adjustments.peek() {
657 if let Adjust::Borrow(_) = next_adjustment.kind {
661 return NotPromotable;
668 impl<'a, 'gcx, 'tcx> euv::Delegate<'tcx> for CheckCrateVisitor<'a, 'gcx> {
669 fn consume(&mut self,
670 _consume_id: ast::NodeId,
673 _mode: euv::ConsumeMode) {}
676 borrow_id: ast::NodeId,
678 cmt: &mc::cmt_<'tcx>,
679 _loan_region: ty::Region<'tcx>,
681 loan_cause: euv::LoanCause) {
683 "borrow(borrow_id={:?}, cmt={:?}, bk={:?}, loan_cause={:?})",
690 // Kind of hacky, but we allow Unsafe coercions in constants.
691 // These occur when we convert a &T or *T to a *U, as well as
692 // when making a thin pointer (e.g., `*T`) into a fat pointer
694 if let euv::LoanCause::AutoUnsafe = loan_cause {
701 Categorization::Rvalue(..) => {
702 if loan_cause == euv::MatchDiscriminant {
703 // Ignore the dummy immutable borrow created by EUV.
706 if bk.to_mutbl_lossy() == hir::MutMutable {
707 self.mut_rvalue_borrows.insert(borrow_id);
711 Categorization::StaticItem => {
714 Categorization::Deref(ref cmt, _) |
715 Categorization::Downcast(ref cmt, _) |
716 Categorization::Interior(ref cmt, _) => {
720 Categorization::Upvar(..) |
721 Categorization::Local(..) => break,
726 fn decl_without_init(&mut self, _id: ast::NodeId, _span: Span) {}
728 _assignment_id: ast::NodeId,
729 _assignment_span: Span,
730 _assignee_cmt: &mc::cmt_,
731 _mode: euv::MutateMode) {
734 fn matched_pat(&mut self, _: &hir::Pat, _: &mc::cmt_, _: euv::MatchMode) {}
736 fn consume_pat(&mut self, _consume_pat: &hir::Pat, _cmt: &mc::cmt_, _mode: euv::ConsumeMode) {}