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 middle::cast::{CastKind};
28 use middle::const_eval;
29 use middle::const_eval::EvalHint::ExprTypeChecked;
31 use middle::expr_use_visitor as euv;
33 use middle::mem_categorization as mc;
35 use middle::ty::{self, Ty};
36 use util::nodemap::NodeMap;
39 use syntax::codemap::Span;
40 use syntax::visit::{self, Visitor};
42 use std::collections::hash_map::Entry;
43 use std::cmp::Ordering;
45 // Const qualification, from partial to completely promotable.
47 #[derive(RustcEncodable, RustcDecodable)]
48 flags ConstQualif: u8 {
49 // Inner mutability (can not be placed behind a reference) or behind
50 // &mut in a non-global expression. Can be copied from static memory.
51 const MUTABLE_MEM = 1 << 0,
52 // Constant value with a type that implements Drop. Can be copied
53 // from static memory, similar to MUTABLE_MEM.
54 const NEEDS_DROP = 1 << 1,
55 // Even if the value can be placed in static memory, copying it from
56 // there is more expensive than in-place instantiation, and/or it may
57 // be too large. This applies to [T; N] and everything containing it.
58 // N.B.: references need to clear this flag to not end up on the stack.
59 const PREFER_IN_PLACE = 1 << 2,
60 // May use more than 0 bytes of memory, doesn't impact the constness
61 // directly, but is not allowed to be borrowed mutably in a constant.
62 const NON_ZERO_SIZED = 1 << 3,
63 // Actually borrowed, has to always be in static memory. Does not
64 // propagate, and requires the expression to behave like a 'static
65 // lvalue. The set of expressions with this flag is the minimum
66 // that have to be promoted.
67 const HAS_STATIC_BORROWS = 1 << 4,
68 // Invalid const for miscellaneous reasons (e.g. not implemented).
69 const NOT_CONST = 1 << 5,
71 // Borrowing the expression won't produce &'static T if any of these
72 // bits are set, though the value could be copied from static memory
73 // if `NOT_CONST` isn't set.
74 const NON_STATIC_BORROWS = ConstQualif::MUTABLE_MEM.bits |
75 ConstQualif::NEEDS_DROP.bits |
76 ConstQualif::NOT_CONST.bits
80 #[derive(Copy, Clone, Eq, PartialEq)]
87 // An expression that occurs outside of any constant context
88 // (i.e. `const`, `static`, array lengths, etc.). The value
89 // can be variable at runtime, but will be promotable to
90 // static memory if we can prove it is actually constant.
94 struct CheckCrateVisitor<'a, 'tcx: 'a> {
95 tcx: &'a ty::ctxt<'tcx>,
98 rvalue_borrows: NodeMap<ast::Mutability>
101 impl<'a, 'tcx> CheckCrateVisitor<'a, 'tcx> {
102 fn with_mode<F, R>(&mut self, mode: Mode, f: F) -> R where
103 F: FnOnce(&mut CheckCrateVisitor<'a, 'tcx>) -> R,
105 let (old_mode, old_qualif) = (self.mode, self.qualif);
107 self.qualif = ConstQualif::empty();
109 self.mode = old_mode;
110 self.qualif = old_qualif;
114 fn with_euv<'b, F, R>(&'b mut self, item_id: Option<ast::NodeId>, f: F) -> R where
115 F: for<'t> FnOnce(&mut euv::ExprUseVisitor<'b, 't, 'b, 'tcx>) -> R,
117 let param_env = match item_id {
118 Some(item_id) => ty::ParameterEnvironment::for_item(self.tcx, item_id),
119 None => self.tcx.empty_parameter_environment()
122 let infcx = infer::new_infer_ctxt(self.tcx, &self.tcx.tables, Some(param_env), false);
124 f(&mut euv::ExprUseVisitor::new(self, &infcx))
127 fn global_expr(&mut self, mode: Mode, expr: &ast::Expr) -> ConstQualif {
128 assert!(mode != Mode::Var);
129 match self.tcx.const_qualif_map.borrow_mut().entry(expr.id) {
130 Entry::Occupied(entry) => return *entry.get(),
131 Entry::Vacant(entry) => {
132 // Prevent infinite recursion on re-entry.
133 entry.insert(ConstQualif::empty());
136 self.with_mode(mode, |this| {
137 this.with_euv(None, |euv| euv.consume_expr(expr));
138 this.visit_expr(expr);
143 fn fn_like(&mut self,
150 match self.tcx.const_qualif_map.borrow_mut().entry(fn_id) {
151 Entry::Occupied(entry) => return *entry.get(),
152 Entry::Vacant(entry) => {
153 // Prevent infinite recursion on re-entry.
154 entry.insert(ConstQualif::empty());
158 let mode = match fk {
159 visit::FkItemFn(_, _, _, ast::Constness::Const, _, _) => {
162 visit::FkMethod(_, m, _) => {
163 if m.constness == ast::Constness::Const {
172 // Ensure the arguments are simple, not mutable/by-ref or patterns.
173 if mode == Mode::ConstFn {
174 for arg in &fd.inputs {
176 ast::PatIdent(ast::BindByValue(ast::MutImmutable), _, None) => {}
178 span_err!(self.tcx.sess, arg.pat.span, E0022,
179 "arguments of constant functions can only \
180 be immutable by-value bindings");
186 let qualif = self.with_mode(mode, |this| {
187 this.with_euv(Some(fn_id), |euv| euv.walk_fn(fd, b));
188 visit::walk_fn(this, fk, fd, b, s);
192 // Keep only bits that aren't affected by function body (NON_ZERO_SIZED),
193 // and bits that don't change semantics, just optimizations (PREFER_IN_PLACE).
194 let qualif = qualif & (ConstQualif::NON_ZERO_SIZED | ConstQualif::PREFER_IN_PLACE);
196 self.tcx.const_qualif_map.borrow_mut().insert(fn_id, qualif);
200 fn add_qualif(&mut self, qualif: ConstQualif) {
201 self.qualif = self.qualif | qualif;
204 /// Returns true if the call is to a const fn or method.
205 fn handle_const_fn_call(&mut self,
210 if let Some(fn_like) = const_eval::lookup_const_fn_by_id(self.tcx, def_id) {
212 // we are in a static/const initializer
213 self.mode != Mode::Var &&
215 // feature-gate is not enabled
216 !self.tcx.sess.features.borrow().const_fn &&
218 // this doesn't come from a macro that has #[allow_internal_unstable]
219 !self.tcx.sess.codemap().span_allows_unstable(expr.span)
221 self.tcx.sess.span_err(
223 &format!("const fns are an unstable feature"));
227 "in Nightly builds, add `#![feature(const_fn)]` to the crate \
228 attributes to enable");
231 let qualif = self.fn_like(fn_like.kind(),
236 self.add_qualif(qualif);
238 if ret_ty.type_contents(self.tcx).interior_unsafe() {
239 self.add_qualif(ConstQualif::MUTABLE_MEM);
248 fn record_borrow(&mut self, id: ast::NodeId, mutbl: ast::Mutability) {
249 match self.rvalue_borrows.entry(id) {
250 Entry::Occupied(mut entry) => {
251 // Merge the two borrows, taking the most demanding
252 // one, mutability-wise.
253 if mutbl == ast::MutMutable {
257 Entry::Vacant(entry) => {
263 fn msg(&self) -> &'static str {
265 Mode::Const => "constant",
266 Mode::ConstFn => "constant function",
267 Mode::StaticMut | Mode::Static => "static",
268 Mode::Var => unreachable!(),
272 fn check_static_mut_type(&self, e: &ast::Expr) {
273 let node_ty = self.tcx.node_id_to_type(e.id);
274 let tcontents = node_ty.type_contents(self.tcx);
276 let suffix = if tcontents.has_dtor() {
278 } else if tcontents.owns_owned() {
284 span_err!(self.tcx.sess, e.span, E0397,
285 "mutable statics are not allowed to have {}", suffix);
288 fn check_static_type(&self, e: &ast::Expr) {
289 let ty = self.tcx.node_id_to_type(e.id);
290 let infcx = infer::new_infer_ctxt(self.tcx, &self.tcx.tables, None, false);
291 let cause = traits::ObligationCause::new(e.span, e.id, traits::SharedStatic);
292 let mut fulfill_cx = infcx.fulfillment_cx.borrow_mut();
293 fulfill_cx.register_builtin_bound(&infcx, ty, ty::BoundSync, cause);
294 match fulfill_cx.select_all_or_error(&infcx) {
297 traits::report_fulfillment_errors(&infcx, errors);
303 impl<'a, 'tcx, 'v> Visitor<'v> for CheckCrateVisitor<'a, 'tcx> {
304 fn visit_item(&mut self, i: &ast::Item) {
305 debug!("visit_item(item={})", self.tcx.map.node_to_string(i.id));
307 ast::ItemStatic(_, ast::MutImmutable, ref expr) => {
308 self.check_static_type(&**expr);
309 self.global_expr(Mode::Static, &**expr);
311 ast::ItemStatic(_, ast::MutMutable, ref expr) => {
312 self.check_static_mut_type(&**expr);
313 self.global_expr(Mode::StaticMut, &**expr);
315 ast::ItemConst(_, ref expr) => {
316 self.global_expr(Mode::Const, &**expr);
318 ast::ItemEnum(ref enum_definition, _) => {
319 for var in &enum_definition.variants {
320 if let Some(ref ex) = var.node.disr_expr {
321 self.global_expr(Mode::Const, &**ex);
326 self.with_mode(Mode::Var, |v| visit::walk_item(v, i));
331 fn visit_trait_item(&mut self, t: &'v ast::TraitItem) {
333 ast::ConstTraitItem(_, ref default) => {
334 if let Some(ref expr) = *default {
335 self.global_expr(Mode::Const, &*expr);
337 visit::walk_trait_item(self, t);
340 _ => self.with_mode(Mode::Var, |v| visit::walk_trait_item(v, t)),
344 fn visit_impl_item(&mut self, i: &'v ast::ImplItem) {
346 ast::ConstImplItem(_, ref expr) => {
347 self.global_expr(Mode::Const, &*expr);
349 _ => self.with_mode(Mode::Var, |v| visit::walk_impl_item(v, i)),
353 fn visit_fn(&mut self,
354 fk: visit::FnKind<'v>,
358 fn_id: ast::NodeId) {
359 self.fn_like(fk, fd, b, s, fn_id);
362 fn visit_pat(&mut self, p: &ast::Pat) {
364 ast::PatLit(ref lit) => {
365 self.global_expr(Mode::Const, &**lit);
367 ast::PatRange(ref start, ref end) => {
368 self.global_expr(Mode::Const, &**start);
369 self.global_expr(Mode::Const, &**end);
371 match const_eval::compare_lit_exprs(self.tcx, start, end) {
372 Some(Ordering::Less) |
373 Some(Ordering::Equal) => {}
374 Some(Ordering::Greater) => {
375 span_err!(self.tcx.sess, start.span, E0030,
376 "lower range bound must be less than or equal to upper");
379 self.tcx.sess.span_bug(
380 start.span, "literals of different types in range pat");
384 _ => visit::walk_pat(self, p)
388 fn visit_block(&mut self, block: &ast::Block) {
389 // Check all statements in the block
390 for stmt in &block.stmts {
391 let span = match stmt.node {
392 ast::StmtDecl(ref decl, _) => {
394 ast::DeclLocal(_) => decl.span,
396 // Item statements are allowed
397 ast::DeclItem(_) => continue
400 ast::StmtExpr(ref expr, _) => expr.span,
401 ast::StmtSemi(ref semi, _) => semi.span,
402 ast::StmtMac(..) => {
403 self.tcx.sess.span_bug(stmt.span, "unexpanded statement \
407 self.add_qualif(ConstQualif::NOT_CONST);
408 if self.mode != Mode::Var {
409 span_err!(self.tcx.sess, span, E0016,
410 "blocks in {}s are limited to items and \
411 tail expressions", self.msg());
414 visit::walk_block(self, block);
417 fn visit_expr(&mut self, ex: &ast::Expr) {
418 let mut outer = self.qualif;
419 self.qualif = ConstQualif::empty();
421 let node_ty = self.tcx.node_id_to_type(ex.id);
422 check_expr(self, ex, node_ty);
423 check_adjustments(self, ex);
425 // Special-case some expressions to avoid certain flags bubbling up.
427 ast::ExprCall(ref callee, ref args) => {
429 self.visit_expr(&**arg)
432 let inner = self.qualif;
433 self.visit_expr(&**callee);
434 // The callee's size doesn't count in the call.
435 let added = self.qualif - inner;
436 self.qualif = inner | (added - ConstQualif::NON_ZERO_SIZED);
438 ast::ExprRepeat(ref element, _) => {
439 self.visit_expr(&**element);
440 // The count is checked elsewhere (typeck).
441 let count = match node_ty.sty {
442 ty::TyArray(_, n) => n,
445 // [element; 0] is always zero-sized.
447 self.qualif.remove(ConstQualif::NON_ZERO_SIZED | ConstQualif::PREFER_IN_PLACE);
450 ast::ExprMatch(ref discr, ref arms, _) => {
451 // Compute the most demanding borrow from all the arms'
452 // patterns and set that on the discriminator.
453 let mut borrow = None;
454 for pat in arms.iter().flat_map(|arm| &arm.pats) {
455 let pat_borrow = self.rvalue_borrows.remove(&pat.id);
456 match (borrow, pat_borrow) {
457 (None, _) | (_, Some(ast::MutMutable)) => {
463 if let Some(mutbl) = borrow {
464 self.record_borrow(discr.id, mutbl);
466 visit::walk_expr(self, ex);
468 // Division by zero and overflow checking.
469 ast::ExprBinary(op, _, _) => {
470 visit::walk_expr(self, ex);
471 let div_or_rem = op.node == ast::BiDiv || op.node == ast::BiRem;
473 ty::TyUint(_) | ty::TyInt(_) if div_or_rem => {
474 if !self.qualif.intersects(ConstQualif::NOT_CONST) {
475 match const_eval::eval_const_expr_partial(
476 self.tcx, ex, ExprTypeChecked) {
479 span_err!(self.tcx.sess, msg.span, E0020,
480 "{} in a constant expression",
489 _ => visit::walk_expr(self, ex)
492 // Handle borrows on (or inside the autorefs of) this expression.
493 match self.rvalue_borrows.remove(&ex.id) {
494 Some(ast::MutImmutable) => {
495 // Constants cannot be borrowed if they contain interior mutability as
496 // it means that our "silent insertion of statics" could change
497 // initializer values (very bad).
498 // If the type doesn't have interior mutability, then `ConstQualif::MUTABLE_MEM` has
499 // propagated from another error, so erroring again would be just noise.
500 let tc = node_ty.type_contents(self.tcx);
501 if self.qualif.intersects(ConstQualif::MUTABLE_MEM) && tc.interior_unsafe() {
502 outer = outer | ConstQualif::NOT_CONST;
503 if self.mode != Mode::Var {
504 self.tcx.sess.span_err(ex.span,
505 "cannot borrow a constant which contains \
506 interior mutability, create a static instead");
509 // If the reference has to be 'static, avoid in-place initialization
510 // as that will end up pointing to the stack instead.
511 if !self.qualif.intersects(ConstQualif::NON_STATIC_BORROWS) {
512 self.qualif = self.qualif - ConstQualif::PREFER_IN_PLACE;
513 self.add_qualif(ConstQualif::HAS_STATIC_BORROWS);
516 Some(ast::MutMutable) => {
517 // `&mut expr` means expr could be mutated, unless it's zero-sized.
518 if self.qualif.intersects(ConstQualif::NON_ZERO_SIZED) {
519 if self.mode == Mode::Var {
520 outer = outer | ConstQualif::NOT_CONST;
521 self.add_qualif(ConstQualif::MUTABLE_MEM);
523 span_err!(self.tcx.sess, ex.span, E0017,
524 "references in {}s may only refer \
525 to immutable values", self.msg())
528 if !self.qualif.intersects(ConstQualif::NON_STATIC_BORROWS) {
529 self.add_qualif(ConstQualif::HAS_STATIC_BORROWS);
534 self.tcx.const_qualif_map.borrow_mut().insert(ex.id, self.qualif);
535 // Don't propagate certain flags.
536 self.qualif = outer | (self.qualif - ConstQualif::HAS_STATIC_BORROWS);
540 /// This function is used to enforce the constraints on
541 /// const/static items. It walks through the *value*
542 /// of the item walking down the expression and evaluating
543 /// every nested expression. If the expression is not part
544 /// of a const/static item, it is qualified for promotion
545 /// instead of producing errors.
546 fn check_expr<'a, 'tcx>(v: &mut CheckCrateVisitor<'a, 'tcx>,
547 e: &ast::Expr, node_ty: Ty<'tcx>) {
549 ty::TyStruct(def, _) |
550 ty::TyEnum(def, _) if def.has_dtor(v.tcx) => {
551 v.add_qualif(ConstQualif::NEEDS_DROP);
552 if v.mode != Mode::Var {
553 v.tcx.sess.span_err(e.span,
554 &format!("{}s are not allowed to have destructors",
561 let method_call = ty::MethodCall::expr(e.id);
564 ast::ExprBinary(..) |
565 ast::ExprIndex(..) if v.tcx.tables.borrow().method_map.contains_key(&method_call) => {
566 v.add_qualif(ConstQualif::NOT_CONST);
567 if v.mode != Mode::Var {
568 span_err!(v.tcx.sess, e.span, E0011,
569 "user-defined operators are not allowed in {}s", v.msg());
573 ast::ExprUnary(ast::UnUniq, _) => {
574 v.add_qualif(ConstQualif::NOT_CONST);
575 if v.mode != Mode::Var {
576 span_err!(v.tcx.sess, e.span, E0010,
577 "allocations are not allowed in {}s", v.msg());
580 ast::ExprUnary(op, ref inner) => {
581 match v.tcx.node_id_to_type(inner.id).sty {
583 assert!(op == ast::UnDeref);
585 v.add_qualif(ConstQualif::NOT_CONST);
586 if v.mode != Mode::Var {
587 span_err!(v.tcx.sess, e.span, E0396,
588 "raw pointers cannot be dereferenced in {}s", v.msg());
594 ast::ExprBinary(op, ref lhs, _) => {
595 match v.tcx.node_id_to_type(lhs.id).sty {
597 assert!(op.node == ast::BiEq || op.node == ast::BiNe ||
598 op.node == ast::BiLe || op.node == ast::BiLt ||
599 op.node == ast::BiGe || op.node == ast::BiGt);
601 v.add_qualif(ConstQualif::NOT_CONST);
602 if v.mode != Mode::Var {
603 span_err!(v.tcx.sess, e.span, E0395,
604 "raw pointers cannot be compared in {}s", v.msg());
610 ast::ExprCast(ref from, _) => {
611 debug!("Checking const cast(id={})", from.id);
612 match v.tcx.cast_kinds.borrow().get(&from.id) {
613 None => v.tcx.sess.span_bug(e.span, "no kind for cast"),
614 Some(&CastKind::PtrAddrCast) | Some(&CastKind::FnPtrAddrCast) => {
615 v.add_qualif(ConstQualif::NOT_CONST);
616 if v.mode != Mode::Var {
617 span_err!(v.tcx.sess, e.span, E0018,
618 "raw pointers cannot be cast to integers in {}s", v.msg());
624 ast::ExprPath(..) => {
625 let def = v.tcx.def_map.borrow().get(&e.id).map(|d| d.full_def());
627 Some(def::DefVariant(_, _, _)) => {
628 // Count the discriminator or function pointer.
629 v.add_qualif(ConstQualif::NON_ZERO_SIZED);
631 Some(def::DefStruct(_)) => {
632 if let ty::TyBareFn(..) = node_ty.sty {
633 // Count the function pointer.
634 v.add_qualif(ConstQualif::NON_ZERO_SIZED);
637 Some(def::DefFn(..)) | Some(def::DefMethod(..)) => {
638 // Count the function pointer.
639 v.add_qualif(ConstQualif::NON_ZERO_SIZED);
641 Some(def::DefStatic(..)) => {
643 Mode::Static | Mode::StaticMut => {}
644 Mode::Const | Mode::ConstFn => {
645 span_err!(v.tcx.sess, e.span, E0013,
646 "{}s cannot refer to other statics, insert \
647 an intermediate constant instead", v.msg());
649 Mode::Var => v.add_qualif(ConstQualif::NOT_CONST)
652 Some(def::DefConst(did)) |
653 Some(def::DefAssociatedConst(did)) => {
654 if let Some(expr) = const_eval::lookup_const_by_id(v.tcx, did,
656 let inner = v.global_expr(Mode::Const, expr);
659 v.tcx.sess.span_bug(e.span,
660 "DefConst or DefAssociatedConst \
661 doesn't point to a constant");
664 Some(def::DefLocal(_)) if v.mode == Mode::ConstFn => {
665 // Sadly, we can't determine whether the types are zero-sized.
666 v.add_qualif(ConstQualif::NOT_CONST | ConstQualif::NON_ZERO_SIZED);
669 v.add_qualif(ConstQualif::NOT_CONST);
670 if v.mode != Mode::Var {
671 debug!("(checking const) found bad def: {:?}", def);
672 span_err!(v.tcx.sess, e.span, E0014,
673 "paths in {}s may only refer to constants \
674 or functions", v.msg());
679 ast::ExprCall(ref callee, _) => {
680 let mut callee = &**callee;
682 callee = match callee.node {
683 ast::ExprParen(ref inner) => &**inner,
684 ast::ExprBlock(ref block) => match block.expr {
685 Some(ref tail) => &**tail,
691 let def = v.tcx.def_map.borrow().get(&callee.id).map(|d| d.full_def());
692 let is_const = match def {
693 Some(def::DefStruct(..)) => true,
694 Some(def::DefVariant(..)) => {
695 // Count the discriminator.
696 v.add_qualif(ConstQualif::NON_ZERO_SIZED);
699 Some(def::DefFn(did, _)) => {
700 v.handle_const_fn_call(e, did, node_ty)
702 Some(def::DefMethod(did)) => {
703 match v.tcx.impl_or_trait_item(did).container() {
704 ty::ImplContainer(_) => {
705 v.handle_const_fn_call(e, did, node_ty)
707 ty::TraitContainer(_) => false
713 v.add_qualif(ConstQualif::NOT_CONST);
714 if v.mode != Mode::Var {
715 span_err!(v.tcx.sess, e.span, E0015,
716 "function calls in {}s are limited to \
717 constant functions, \
718 struct and enum constructors", v.msg());
722 ast::ExprMethodCall(..) => {
723 let method = v.tcx.tables.borrow().method_map[&method_call];
724 let is_const = match v.tcx.impl_or_trait_item(method.def_id).container() {
725 ty::ImplContainer(_) => v.handle_const_fn_call(e, method.def_id, node_ty),
726 ty::TraitContainer(_) => false
729 v.add_qualif(ConstQualif::NOT_CONST);
730 if v.mode != Mode::Var {
731 span_err!(v.tcx.sess, e.span, E0378,
732 "method calls in {}s are limited to \
733 constant inherent methods", v.msg());
737 ast::ExprStruct(..) => {
738 let did = v.tcx.def_map.borrow().get(&e.id).map(|def| def.def_id());
739 if did == v.tcx.lang_items.unsafe_cell_type() {
740 v.add_qualif(ConstQualif::MUTABLE_MEM);
745 ast::ExprAddrOf(..) => {
746 v.add_qualif(ConstQualif::NON_ZERO_SIZED);
749 ast::ExprRepeat(..) => {
750 v.add_qualif(ConstQualif::PREFER_IN_PLACE);
753 ast::ExprClosure(..) => {
754 // Paths in constant contexts cannot refer to local variables,
755 // as there are none, and thus closures can't have upvars there.
756 if v.tcx.with_freevars(e.id, |fv| !fv.is_empty()) {
757 assert!(v.mode == Mode::Var,
758 "global closures can't capture anything");
759 v.add_qualif(ConstQualif::NOT_CONST);
766 ast::ExprTupField(..) |
769 ast::ExprTup(..) => {}
771 // Conditional control flow (possible to implement).
776 // Loops (not very meaningful in constants).
778 ast::ExprWhileLet(..) |
779 ast::ExprForLoop(..) |
782 // More control flow (also not very meaningful).
787 // Miscellaneous expressions that could be implemented.
790 // Expressions with side-effects.
791 ast::ExprAssign(..) |
792 ast::ExprAssignOp(..) |
793 ast::ExprInlineAsm(_) |
795 v.add_qualif(ConstQualif::NOT_CONST);
796 if v.mode != Mode::Var {
797 span_err!(v.tcx.sess, e.span, E0019,
798 "{} contains unimplemented expression type", v.msg());
804 /// Check the adjustments of an expression
805 fn check_adjustments<'a, 'tcx>(v: &mut CheckCrateVisitor<'a, 'tcx>, e: &ast::Expr) {
806 match v.tcx.tables.borrow().adjustments.get(&e.id) {
807 None | Some(&ty::AdjustReifyFnPointer) | Some(&ty::AdjustUnsafeFnPointer) => {}
808 Some(&ty::AdjustDerefRef(ty::AutoDerefRef { autoderefs, .. })) => {
809 if (0..autoderefs as u32).any(|autoderef| {
810 v.tcx.is_overloaded_autoderef(e.id, autoderef)
812 v.add_qualif(ConstQualif::NOT_CONST);
813 if v.mode != Mode::Var {
814 span_err!(v.tcx.sess, e.span, E0400,
815 "user-defined dereference operators are not allowed in {}s",
823 pub fn check_crate(tcx: &ty::ctxt) {
824 visit::walk_crate(&mut CheckCrateVisitor {
827 qualif: ConstQualif::NOT_CONST,
828 rvalue_borrows: NodeMap()
831 tcx.sess.abort_if_errors();
834 impl<'a, 'tcx> euv::Delegate<'tcx> for CheckCrateVisitor<'a, 'tcx> {
835 fn consume(&mut self,
836 _consume_id: ast::NodeId,
839 _mode: euv::ConsumeMode) {
843 mc::cat_static_item => {
844 if self.mode != Mode::Var {
845 // statics cannot be consumed by value at any time, that would imply
846 // that they're an initializer (what a const is for) or kept in sync
847 // over time (not feasible), so deny it outright.
848 span_err!(self.tcx.sess, consume_span, E0394,
849 "cannot refer to other statics by value, use the \
850 address-of operator or a constant instead");
854 mc::cat_deref(ref cmt, _, _) |
855 mc::cat_downcast(ref cmt, _) |
856 mc::cat_interior(ref cmt, _) => cur = cmt,
860 mc::cat_local(..) => break
865 borrow_id: ast::NodeId,
868 _loan_region: ty::Region,
870 loan_cause: euv::LoanCause)
872 // Kind of hacky, but we allow Unsafe coercions in constants.
873 // These occur when we convert a &T or *T to a *U, as well as
874 // when making a thin pointer (e.g., `*T`) into a fat pointer
877 euv::LoanCause::AutoUnsafe => {
884 let mut is_interior = false;
887 mc::cat_rvalue(..) => {
888 if loan_cause == euv::MatchDiscriminant {
889 // Ignore the dummy immutable borrow created by EUV.
892 let mutbl = bk.to_mutbl_lossy();
893 if mutbl == ast::MutMutable && self.mode == Mode::StaticMut {
894 // Mutable slices are the only `&mut` allowed in
895 // globals, but only in `static mut`, nowhere else.
896 // FIXME: This exception is really weird... there isn't
897 // any fundamental reason to restrict this based on
898 // type of the expression. `&mut [1]` has exactly the
899 // same representation as &mut 1.
901 ty::TyArray(_, _) | ty::TySlice(_) => break,
905 self.record_borrow(borrow_id, mutbl);
908 mc::cat_static_item => {
909 if is_interior && self.mode != Mode::Var {
910 // Borrowed statics can specifically *only* have their address taken,
911 // not any number of other borrows such as borrowing fields, reading
912 // elements of an array, etc.
913 self.tcx.sess.span_err(borrow_span,
914 "cannot refer to the interior of another \
915 static, use a constant instead");
919 mc::cat_deref(ref cmt, _, _) |
920 mc::cat_downcast(ref cmt, _) |
921 mc::cat_interior(ref cmt, _) => {
927 mc::cat_local(..) => break
932 fn decl_without_init(&mut self,
936 _assignment_id: ast::NodeId,
937 _assignment_span: Span,
938 _assignee_cmt: mc::cmt,
939 _mode: euv::MutateMode) {}
941 fn matched_pat(&mut self,
944 _: euv::MatchMode) {}
946 fn consume_pat(&mut self,
947 _consume_pat: &ast::Pat,
949 _mode: euv::ConsumeMode) {}