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.
13 //! The job of the categorization module is to analyze an expression to
14 //! determine what kind of memory is used in evaluating it (for example,
15 //! where dereferences occur and what kind of pointer is dereferenced;
16 //! whether the memory is mutable; etc)
18 //! Categorization effectively transforms all of our expressions into
19 //! expressions of the following forms (the actual enum has many more
20 //! possibilities, naturally, but they are all variants of these base
23 //! E = rvalue // some computed rvalue
24 //! | x // address of a local variable or argument
25 //! | *E // deref of a ptr
26 //! | E.comp // access to an interior component
28 //! Imagine a routine ToAddr(Expr) that evaluates an expression and returns an
29 //! address where the result is to be found. If Expr is an lvalue, then this
30 //! is the address of the lvalue. If Expr is an rvalue, this is the address of
31 //! some temporary spot in memory where the result is stored.
33 //! Now, cat_expr() classifies the expression Expr and the address A=ToAddr(Expr)
36 //! - cat: what kind of expression was this? This is a subset of the
37 //! full expression forms which only includes those that we care about
38 //! for the purpose of the analysis.
39 //! - mutbl: mutability of the address A
40 //! - ty: the type of data found at the address A
42 //! The resulting categorization tree differs somewhat from the expressions
43 //! themselves. For example, auto-derefs are explicit. Also, an index a[b] is
44 //! decomposed into two operations: a dereference to reach the array data and
45 //! then an index to jump forward to the relevant item.
47 //! ## By-reference upvars
49 //! One part of the translation which may be non-obvious is that we translate
50 //! closure upvars into the dereference of a borrowed pointer; this more closely
51 //! resembles the runtime translation. So, for example, if we had:
55 //! let inc = || x += y;
57 //! Then when we categorize `x` (*within* the closure) we would yield a
58 //! result of `*x'`, effectively, where `x'` is a `cat_upvar` reference
59 //! tied to `x`. The type of `x'` will be a borrowed pointer.
61 #![allow(non_camel_case_types)]
63 pub use self::PointerKind::*;
64 pub use self::InteriorKind::*;
65 pub use self::FieldName::*;
66 pub use self::ElementKind::*;
67 pub use self::MutabilityCategory::*;
68 pub use self::AliasableReason::*;
69 pub use self::Note::*;
70 pub use self::deref_kind::*;
71 pub use self::categorization::*;
73 use self::Aliasability::*;
76 use middle::def_id::DefId;
78 use middle::check_const;
81 use middle::ty::{self, Ty};
83 use syntax::ast::{MutImmutable, MutMutable};
85 use syntax::codemap::Span;
90 #[derive(Clone, PartialEq)]
91 pub enum categorization<'tcx> {
92 cat_rvalue(ty::Region), // temporary val, argument is its scope
94 cat_upvar(Upvar), // upvar referenced by closure env
95 cat_local(ast::NodeId), // local variable
96 cat_deref(cmt<'tcx>, usize, PointerKind), // deref of a ptr
97 cat_interior(cmt<'tcx>, InteriorKind), // something interior: field, tuple, etc
98 cat_downcast(cmt<'tcx>, DefId), // selects a particular enum variant (*1)
100 // (*1) downcast is only required if the enum has more than one variant
103 // Represents any kind of upvar
104 #[derive(Clone, Copy, PartialEq)]
107 pub kind: ty::ClosureKind
110 // different kinds of pointers:
111 #[derive(Clone, Copy, PartialEq, Eq, Hash)]
112 pub enum PointerKind {
117 BorrowedPtr(ty::BorrowKind, ty::Region),
120 UnsafePtr(ast::Mutability),
122 /// Implicit deref of the `&T` that results from an overloaded index `[]`.
123 Implicit(ty::BorrowKind, ty::Region),
126 // We use the term "interior" to mean "something reachable from the
127 // base without a pointer dereference", e.g. a field
128 #[derive(Clone, Copy, PartialEq, Eq, Hash)]
129 pub enum InteriorKind {
130 InteriorField(FieldName),
131 InteriorElement(InteriorOffsetKind, ElementKind),
134 #[derive(Clone, Copy, PartialEq, Eq, Hash, Debug)]
136 NamedField(ast::Name),
137 PositionalField(usize)
140 #[derive(Clone, Copy, PartialEq, Eq, Hash, Debug)]
141 pub enum InteriorOffsetKind {
142 Index, // e.g. `array_expr[index_expr]`
143 Pattern, // e.g. `fn foo([_, a, _, _]: [A; 4]) { ... }`
146 #[derive(Clone, Copy, PartialEq, Eq, Hash, Debug)]
147 pub enum ElementKind {
152 #[derive(Clone, Copy, PartialEq, Eq, Hash, Debug)]
153 pub enum MutabilityCategory {
154 McImmutable, // Immutable.
155 McDeclared, // Directly declared as mutable.
156 McInherited, // Inherited from the fact that owner is mutable.
159 // A note about the provenance of a `cmt`. This is used for
160 // special-case handling of upvars such as mutability inference.
161 // Upvar categorization can generate a variable number of nested
162 // derefs. The note allows detecting them without deep pattern
163 // matching on the categorization.
164 #[derive(Clone, Copy, PartialEq, Debug)]
166 NoteClosureEnv(ty::UpvarId), // Deref through closure env
167 NoteUpvarRef(ty::UpvarId), // Deref through by-ref upvar
168 NoteNone // Nothing special
171 // `cmt`: "Category, Mutability, and Type".
173 // a complete categorization of a value indicating where it originated
174 // and how it is located, as well as the mutability of the memory in
175 // which the value is stored.
177 // *WARNING* The field `cmt.type` is NOT necessarily the same as the
178 // result of `node_id_to_type(cmt.id)`. This is because the `id` is
179 // always the `id` of the node producing the type; in an expression
180 // like `*x`, the type of this deref node is the deref'd type (`T`),
181 // but in a pattern like `@x`, the `@x` pattern is again a
182 // dereference, but its type is the type *before* the dereference
183 // (`@T`). So use `cmt.ty` to find the type of the value in a consistent
184 // fashion. For more details, see the method `cat_pattern`
185 #[derive(Clone, PartialEq)]
186 pub struct cmt_<'tcx> {
187 pub id: ast::NodeId, // id of expr/pat producing this value
188 pub span: Span, // span of same expr/pat
189 pub cat: categorization<'tcx>, // categorization of expr
190 pub mutbl: MutabilityCategory, // mutability of expr as lvalue
191 pub ty: Ty<'tcx>, // type of the expr (*see WARNING above*)
192 pub note: Note, // Note about the provenance of this cmt
195 pub type cmt<'tcx> = Rc<cmt_<'tcx>>;
197 // We pun on *T to mean both actual deref of a ptr as well
198 // as accessing of components:
199 #[derive(Copy, Clone)]
200 pub enum deref_kind {
201 deref_ptr(PointerKind),
202 deref_interior(InteriorKind),
205 type DerefKindContext = Option<InteriorOffsetKind>;
207 // Categorizes a derefable type. Note that we include vectors and strings as
208 // derefable (we model an index as the combination of a deref and then a
209 // pointer adjustment).
210 fn deref_kind(t: Ty, context: DerefKindContext) -> McResult<deref_kind> {
213 Ok(deref_ptr(Unique))
216 ty::TyRef(r, mt) => {
217 let kind = ty::BorrowKind::from_mutbl(mt.mutbl);
218 Ok(deref_ptr(BorrowedPtr(kind, *r)))
221 ty::TyRawPtr(ref mt) => {
222 Ok(deref_ptr(UnsafePtr(mt.mutbl)))
226 ty::TyStruct(..) => { // newtype
227 Ok(deref_interior(InteriorField(PositionalField(0))))
230 ty::TyArray(_, _) | ty::TySlice(_) | ty::TyStr => {
231 // no deref of indexed content without supplying InteriorOffsetKind
232 if let Some(context) = context {
233 Ok(deref_interior(InteriorElement(context, element_kind(t))))
244 fn id(&self) -> ast::NodeId;
245 fn span(&self) -> Span;
248 impl ast_node for ast::Expr {
249 fn id(&self) -> ast::NodeId { self.id }
250 fn span(&self) -> Span { self.span }
253 impl ast_node for ast::Pat {
254 fn id(&self) -> ast::NodeId { self.id }
255 fn span(&self) -> Span { self.span }
258 #[derive(Copy, Clone)]
259 pub struct MemCategorizationContext<'t, 'a: 't, 'tcx : 'a> {
260 pub typer: &'t infer::InferCtxt<'a, 'tcx>,
263 pub type McResult<T> = Result<T, ()>;
265 impl MutabilityCategory {
266 pub fn from_mutbl(m: ast::Mutability) -> MutabilityCategory {
268 MutImmutable => McImmutable,
269 MutMutable => McDeclared
271 debug!("MutabilityCategory::{}({:?}) => {:?}",
272 "from_mutbl", m, ret);
276 pub fn from_borrow_kind(borrow_kind: ty::BorrowKind) -> MutabilityCategory {
277 let ret = match borrow_kind {
278 ty::ImmBorrow => McImmutable,
279 ty::UniqueImmBorrow => McImmutable,
280 ty::MutBorrow => McDeclared,
282 debug!("MutabilityCategory::{}({:?}) => {:?}",
283 "from_borrow_kind", borrow_kind, ret);
287 fn from_pointer_kind(base_mutbl: MutabilityCategory,
288 ptr: PointerKind) -> MutabilityCategory {
289 let ret = match ptr {
293 BorrowedPtr(borrow_kind, _) | Implicit(borrow_kind, _) => {
294 MutabilityCategory::from_borrow_kind(borrow_kind)
297 MutabilityCategory::from_mutbl(m)
300 debug!("MutabilityCategory::{}({:?}, {:?}) => {:?}",
301 "from_pointer_kind", base_mutbl, ptr, ret);
305 fn from_local(tcx: &ty::ctxt, id: ast::NodeId) -> MutabilityCategory {
306 let ret = match tcx.map.get(id) {
307 ast_map::NodeLocal(p) | ast_map::NodeArg(p) => match p.node {
308 ast::PatIdent(bind_mode, _, _) => {
309 if bind_mode == ast::BindByValue(ast::MutMutable) {
315 _ => tcx.sess.span_bug(p.span, "expected identifier pattern")
317 _ => tcx.sess.span_bug(tcx.map.span(id), "expected identifier pattern")
319 debug!("MutabilityCategory::{}(tcx, id={:?}) => {:?}",
320 "from_local", id, ret);
324 pub fn inherit(&self) -> MutabilityCategory {
325 let ret = match *self {
326 McImmutable => McImmutable,
327 McDeclared => McInherited,
328 McInherited => McInherited,
330 debug!("{:?}.inherit() => {:?}", self, ret);
334 pub fn is_mutable(&self) -> bool {
335 let ret = match *self {
336 McImmutable => false,
340 debug!("{:?}.is_mutable() => {:?}", self, ret);
344 pub fn is_immutable(&self) -> bool {
345 let ret = match *self {
347 McDeclared | McInherited => false
349 debug!("{:?}.is_immutable() => {:?}", self, ret);
353 pub fn to_user_str(&self) -> &'static str {
355 McDeclared | McInherited => "mutable",
356 McImmutable => "immutable",
361 impl<'t, 'a,'tcx> MemCategorizationContext<'t, 'a, 'tcx> {
362 pub fn new(typer: &'t infer::InferCtxt<'a, 'tcx>) -> MemCategorizationContext<'t, 'a, 'tcx> {
363 MemCategorizationContext { typer: typer }
366 fn tcx(&self) -> &'a ty::ctxt<'tcx> {
370 fn expr_ty(&self, expr: &ast::Expr) -> McResult<Ty<'tcx>> {
371 match self.typer.node_ty(expr.id) {
374 debug!("expr_ty({:?}) yielded Err", expr);
380 fn expr_ty_adjusted(&self, expr: &ast::Expr) -> McResult<Ty<'tcx>> {
381 let unadjusted_ty = try!(self.expr_ty(expr));
382 Ok(unadjusted_ty.adjust(
383 self.tcx(), expr.span, expr.id,
384 self.typer.adjustments().get(&expr.id),
385 |method_call| self.typer.node_method_ty(method_call)))
388 fn node_ty(&self, id: ast::NodeId) -> McResult<Ty<'tcx>> {
389 self.typer.node_ty(id)
392 fn pat_ty(&self, pat: &ast::Pat) -> McResult<Ty<'tcx>> {
393 let base_ty = try!(self.typer.node_ty(pat.id));
394 // FIXME (Issue #18207): This code detects whether we are
395 // looking at a `ref x`, and if so, figures out what the type
396 // *being borrowed* is. But ideally we would put in a more
397 // fundamental fix to this conflated use of the node id.
398 let ret_ty = match pat.node {
399 ast::PatIdent(ast::BindByRef(_), _, _) => {
400 // a bind-by-ref means that the base_ty will be the type of the ident itself,
401 // but what we want here is the type of the underlying value being borrowed.
402 // So peel off one-level, turning the &T into T.
403 match base_ty.builtin_deref(false) {
405 None => { return Err(()); }
410 debug!("pat_ty(pat={:?}) base_ty={:?} ret_ty={:?}",
411 pat, base_ty, ret_ty);
415 pub fn cat_expr(&self, expr: &ast::Expr) -> McResult<cmt<'tcx>> {
416 match self.typer.adjustments().get(&expr.id) {
419 self.cat_expr_unadjusted(expr)
422 Some(adjustment) => {
426 autoref: None, unsize: None, autoderefs, ..}) => {
427 // Equivalent to *expr or something similar.
428 self.cat_expr_autoderefd(expr, autoderefs)
431 ty::AdjustReifyFnPointer |
432 ty::AdjustUnsafeFnPointer |
433 ty::AdjustDerefRef(_) => {
434 debug!("cat_expr({:?}): {:?}",
437 // Result is an rvalue.
438 let expr_ty = try!(self.expr_ty_adjusted(expr));
439 Ok(self.cat_rvalue_node(expr.id(), expr.span(), expr_ty))
446 pub fn cat_expr_autoderefd(&self,
449 -> McResult<cmt<'tcx>> {
450 let mut cmt = try!(self.cat_expr_unadjusted(expr));
451 debug!("cat_expr_autoderefd: autoderefs={}, cmt={:?}",
454 for deref in 1..autoderefs + 1 {
455 cmt = try!(self.cat_deref(expr, cmt, deref, None));
460 pub fn cat_expr_unadjusted(&self, expr: &ast::Expr) -> McResult<cmt<'tcx>> {
461 debug!("cat_expr: id={} expr={:?}", expr.id, expr);
463 let expr_ty = try!(self.expr_ty(expr));
465 ast::ExprUnary(ast::UnDeref, ref e_base) => {
466 let base_cmt = try!(self.cat_expr(&**e_base));
467 self.cat_deref(expr, base_cmt, 0, None)
470 ast::ExprField(ref base, f_name) => {
471 let base_cmt = try!(self.cat_expr(&**base));
472 debug!("cat_expr(cat_field): id={} expr={:?} base={:?}",
476 Ok(self.cat_field(expr, base_cmt, f_name.node.name, expr_ty))
479 ast::ExprTupField(ref base, idx) => {
480 let base_cmt = try!(self.cat_expr(&**base));
481 Ok(self.cat_tup_field(expr, base_cmt, idx.node, expr_ty))
484 ast::ExprIndex(ref base, _) => {
485 let method_call = ty::MethodCall::expr(expr.id());
486 let context = InteriorOffsetKind::Index;
487 match self.typer.node_method_ty(method_call) {
489 // If this is an index implemented by a method call, then it
490 // will include an implicit deref of the result.
491 let ret_ty = self.overloaded_method_return_ty(method_ty);
493 // The index method always returns an `&T`, so
494 // dereference it to find the result type.
495 let elem_ty = match ret_ty.sty {
496 ty::TyRef(_, mt) => mt.ty,
498 debug!("cat_expr_unadjusted: return type of overloaded index is {:?}?",
504 // The call to index() returns a `&T` value, which
505 // is an rvalue. That is what we will be
507 let base_cmt = self.cat_rvalue_node(expr.id(), expr.span(), ret_ty);
508 self.cat_deref_common(expr, base_cmt, 1, elem_ty, Some(context), true)
511 self.cat_index(expr, try!(self.cat_expr(&**base)), context)
516 ast::ExprPath(..) => {
517 let def = self.tcx().def_map.borrow().get(&expr.id).unwrap().full_def();
518 self.cat_def(expr.id, expr.span, expr_ty, def)
521 ast::ExprParen(ref e) => {
525 ast::ExprAddrOf(..) | ast::ExprCall(..) |
526 ast::ExprAssign(..) | ast::ExprAssignOp(..) |
527 ast::ExprClosure(..) | ast::ExprRet(..) |
528 ast::ExprUnary(..) | ast::ExprRange(..) |
529 ast::ExprMethodCall(..) | ast::ExprCast(..) |
530 ast::ExprVec(..) | ast::ExprTup(..) | ast::ExprIf(..) |
531 ast::ExprBinary(..) | ast::ExprWhile(..) |
532 ast::ExprBlock(..) | ast::ExprLoop(..) | ast::ExprMatch(..) |
533 ast::ExprLit(..) | ast::ExprBreak(..) | ast::ExprMac(..) |
534 ast::ExprAgain(..) | ast::ExprStruct(..) | ast::ExprRepeat(..) |
535 ast::ExprInlineAsm(..) | ast::ExprBox(..) => {
536 Ok(self.cat_rvalue_node(expr.id(), expr.span(), expr_ty))
539 ast::ExprIfLet(..) => {
540 self.tcx().sess.span_bug(expr.span, "non-desugared ExprIfLet");
542 ast::ExprWhileLet(..) => {
543 self.tcx().sess.span_bug(expr.span, "non-desugared ExprWhileLet");
545 ast::ExprForLoop(..) => {
546 self.tcx().sess.span_bug(expr.span, "non-desugared ExprForLoop");
551 pub fn cat_def(&self,
556 -> McResult<cmt<'tcx>> {
557 debug!("cat_def: id={} expr={:?} def={:?}",
561 def::DefStruct(..) | def::DefVariant(..) | def::DefConst(..) |
562 def::DefAssociatedConst(..) | def::DefFn(..) | def::DefMethod(..) => {
563 Ok(self.cat_rvalue_node(id, span, expr_ty))
565 def::DefMod(_) | def::DefForeignMod(_) | def::DefUse(_) |
566 def::DefTrait(_) | def::DefTy(..) | def::DefPrimTy(_) |
567 def::DefTyParam(..) | def::DefRegion(_) |
568 def::DefLabel(_) | def::DefSelfTy(..) |
569 def::DefAssociatedTy(..) => {
580 def::DefStatic(_, mutbl) => {
585 mutbl: if mutbl { McDeclared } else { McImmutable},
591 def::DefUpvar(var_id, fn_node_id) => {
592 let ty = try!(self.node_ty(fn_node_id));
594 ty::TyClosure(closure_id, _) => {
595 match self.typer.closure_kind(closure_id) {
597 self.cat_upvar(id, span, var_id, fn_node_id, kind)
600 self.tcx().sess.span_bug(
602 &*format!("No closure kind for {:?}", closure_id));
607 self.tcx().sess.span_bug(
609 &format!("Upvar of non-closure {} - {:?}",
616 def::DefLocal(vid) => {
621 mutbl: MutabilityCategory::from_local(self.tcx(), vid),
629 // Categorize an upvar, complete with invisible derefs of closure
630 // environment and upvar reference as appropriate.
635 fn_node_id: ast::NodeId,
636 kind: ty::ClosureKind)
637 -> McResult<cmt<'tcx>>
639 // An upvar can have up to 3 components. We translate first to a
640 // `cat_upvar`, which is itself a fiction -- it represents the reference to the
641 // field from the environment.
643 // `cat_upvar`. Next, we add a deref through the implicit
644 // environment pointer with an anonymous free region 'env and
645 // appropriate borrow kind for closure kinds that take self by
646 // reference. Finally, if the upvar was captured
647 // by-reference, we add a deref through that reference. The
648 // region of this reference is an inference variable 'up that
649 // was previously generated and recorded in the upvar borrow
650 // map. The borrow kind bk is inferred by based on how the
653 // This results in the following table for concrete closure
657 // ---------------+----------------------+-------------------------------
658 // Fn | copied -> &'env | upvar -> &'env -> &'up bk
659 // FnMut | copied -> &'env mut | upvar -> &'env mut -> &'up bk
660 // FnOnce | copied | upvar -> &'up bk
662 let upvar_id = ty::UpvarId { var_id: var_id,
663 closure_expr_id: fn_node_id };
664 let var_ty = try!(self.node_ty(var_id));
666 // Mutability of original variable itself
667 let var_mutbl = MutabilityCategory::from_local(self.tcx(), var_id);
669 // Construct the upvar. This represents access to the field
670 // from the environment (perhaps we should eventually desugar
671 // this field further, but it will do for now).
672 let cmt_result = cmt_ {
675 cat: cat_upvar(Upvar {id: upvar_id, kind: kind}),
681 // If this is a `FnMut` or `Fn` closure, then the above is
682 // conceptually a `&mut` or `&` reference, so we have to add a
684 let cmt_result = match kind {
685 ty::FnOnceClosureKind => {
688 ty::FnMutClosureKind => {
689 self.env_deref(id, span, upvar_id, var_mutbl, ty::MutBorrow, cmt_result)
691 ty::FnClosureKind => {
692 self.env_deref(id, span, upvar_id, var_mutbl, ty::ImmBorrow, cmt_result)
696 // If this is a by-ref capture, then the upvar we loaded is
697 // actually a reference, so we have to add an implicit deref
699 let upvar_id = ty::UpvarId { var_id: var_id,
700 closure_expr_id: fn_node_id };
701 let upvar_capture = self.typer.upvar_capture(upvar_id).unwrap();
702 let cmt_result = match upvar_capture {
703 ty::UpvarCapture::ByValue => {
706 ty::UpvarCapture::ByRef(upvar_borrow) => {
707 let ptr = BorrowedPtr(upvar_borrow.kind, upvar_borrow.region);
711 cat: cat_deref(Rc::new(cmt_result), 0, ptr),
712 mutbl: MutabilityCategory::from_borrow_kind(upvar_borrow.kind),
714 note: NoteUpvarRef(upvar_id)
719 let ret = Rc::new(cmt_result);
720 debug!("cat_upvar ret={:?}", ret);
727 upvar_id: ty::UpvarId,
728 upvar_mutbl: MutabilityCategory,
729 env_borrow_kind: ty::BorrowKind,
730 cmt_result: cmt_<'tcx>)
733 // Look up the node ID of the closure body so we can construct
734 // a free region within it
736 let fn_expr = match self.tcx().map.find(upvar_id.closure_expr_id) {
737 Some(ast_map::NodeExpr(e)) => e,
742 ast::ExprClosure(_, _, ref body) => body.id,
747 // Region of environment pointer
748 let env_region = ty::ReFree(ty::FreeRegion {
749 // The environment of a closure is guaranteed to
750 // outlive any bindings introduced in the body of the
752 scope: region::DestructionScopeData::new(fn_body_id),
753 bound_region: ty::BrEnv
756 let env_ptr = BorrowedPtr(env_borrow_kind, env_region);
758 let var_ty = cmt_result.ty;
760 // We need to add the env deref. This means
761 // that the above is actually immutable and
762 // has a ref type. However, nothing should
763 // actually look at the type, so we can get
764 // away with stuffing a `TyError` in there
765 // instead of bothering to construct a proper
767 let cmt_result = cmt_ {
769 ty: self.tcx().types.err,
773 let mut deref_mutbl = MutabilityCategory::from_borrow_kind(env_borrow_kind);
775 // Issue #18335. If variable is declared as immutable, override the
776 // mutability from the environment and substitute an `&T` anyway.
778 McImmutable => { deref_mutbl = McImmutable; }
779 McDeclared | McInherited => { }
785 cat: cat_deref(Rc::new(cmt_result), 0, env_ptr),
788 note: NoteClosureEnv(upvar_id)
791 debug!("env_deref ret {:?}", ret);
796 /// Returns the lifetime of a temporary created by expr with id `id`.
797 /// This could be `'static` if `id` is part of a constant expression.
798 pub fn temporary_scope(&self, id: ast::NodeId) -> ty::Region {
799 match self.typer.temporary_scope(id) {
800 Some(scope) => ty::ReScope(scope),
805 pub fn cat_rvalue_node(&self,
810 let qualif = self.tcx().const_qualif_map.borrow().get(&id).cloned()
811 .unwrap_or(check_const::ConstQualif::NOT_CONST);
813 // Only promote `[T; 0]` before an RFC for rvalue promotions
815 let qualif = match expr_ty.sty {
816 ty::TyArray(_, 0) => qualif,
817 _ => check_const::ConstQualif::NOT_CONST
820 // Compute maximum lifetime of this rvalue. This is 'static if
821 // we can promote to a constant, otherwise equal to enclosing temp
823 let re = if qualif.intersects(check_const::ConstQualif::NON_STATIC_BORROWS) {
824 self.temporary_scope(id)
828 let ret = self.cat_rvalue(id, span, re, expr_ty);
829 debug!("cat_rvalue_node ret {:?}", ret);
833 pub fn cat_rvalue(&self,
836 temp_scope: ty::Region,
837 expr_ty: Ty<'tcx>) -> cmt<'tcx> {
838 let ret = Rc::new(cmt_ {
841 cat:cat_rvalue(temp_scope),
846 debug!("cat_rvalue ret {:?}", ret);
850 pub fn cat_field<N:ast_node>(&self,
856 let ret = Rc::new(cmt_ {
859 mutbl: base_cmt.mutbl.inherit(),
860 cat: cat_interior(base_cmt, InteriorField(NamedField(f_name))),
864 debug!("cat_field ret {:?}", ret);
868 pub fn cat_tup_field<N:ast_node>(&self,
874 let ret = Rc::new(cmt_ {
877 mutbl: base_cmt.mutbl.inherit(),
878 cat: cat_interior(base_cmt, InteriorField(PositionalField(f_idx))),
882 debug!("cat_tup_field ret {:?}", ret);
886 fn cat_deref<N:ast_node>(&self,
890 deref_context: DerefKindContext)
891 -> McResult<cmt<'tcx>> {
892 let method_call = ty::MethodCall {
894 autoderef: deref_cnt as u32
896 let method_ty = self.typer.node_method_ty(method_call);
898 debug!("cat_deref: method_call={:?} method_ty={:?}",
899 method_call, method_ty.map(|ty| ty));
901 let base_cmt = match method_ty {
904 self.tcx().no_late_bound_regions(&method_ty.fn_ret()).unwrap().unwrap();
905 self.cat_rvalue_node(node.id(), node.span(), ref_ty)
909 let base_cmt_ty = base_cmt.ty;
910 match base_cmt_ty.builtin_deref(true) {
912 let ret = self.cat_deref_common(node, base_cmt, deref_cnt,
915 /* implicit: */ false);
916 debug!("cat_deref ret {:?}", ret);
920 debug!("Explicit deref of non-derefable type: {:?}",
927 fn cat_deref_common<N:ast_node>(&self,
932 deref_context: DerefKindContext,
934 -> McResult<cmt<'tcx>>
936 let (m, cat) = match try!(deref_kind(base_cmt.ty, deref_context)) {
938 let ptr = if implicit {
940 BorrowedPtr(bk, r) => Implicit(bk, r),
941 _ => self.tcx().sess.span_bug(node.span(),
942 "Implicit deref of non-borrowed pointer")
947 // for unique ptrs, we inherit mutability from the
949 (MutabilityCategory::from_pointer_kind(base_cmt.mutbl, ptr),
950 cat_deref(base_cmt, deref_cnt, ptr))
952 deref_interior(interior) => {
953 (base_cmt.mutbl.inherit(), cat_interior(base_cmt, interior))
956 let ret = Rc::new(cmt_ {
964 debug!("cat_deref_common ret {:?}", ret);
968 pub fn cat_index<N:ast_node>(&self,
970 mut base_cmt: cmt<'tcx>,
971 context: InteriorOffsetKind)
972 -> McResult<cmt<'tcx>> {
973 //! Creates a cmt for an indexing operation (`[]`).
975 //! One subtle aspect of indexing that may not be
976 //! immediately obvious: for anything other than a fixed-length
977 //! vector, an operation like `x[y]` actually consists of two
978 //! disjoint (from the point of view of borrowck) operations.
979 //! The first is a deref of `x` to create a pointer `p` that points
980 //! at the first element in the array. The second operation is
981 //! an index which adds `y*sizeof(T)` to `p` to obtain the
982 //! pointer to `x[y]`. `cat_index` will produce a resulting
983 //! cmt containing both this deref and the indexing,
984 //! presuming that `base_cmt` is not of fixed-length type.
987 //! - `elt`: the AST node being indexed
988 //! - `base_cmt`: the cmt of `elt`
990 let method_call = ty::MethodCall::expr(elt.id());
991 let method_ty = self.typer.node_method_ty(method_call);
993 let element_ty = match method_ty {
995 let ref_ty = self.overloaded_method_return_ty(method_ty);
996 base_cmt = self.cat_rvalue_node(elt.id(), elt.span(), ref_ty);
998 // FIXME(#20649) -- why are we using the `self_ty` as the element type...?
999 let self_ty = method_ty.fn_sig().input(0);
1000 self.tcx().no_late_bound_regions(&self_ty).unwrap()
1003 match base_cmt.ty.builtin_index() {
1012 let m = base_cmt.mutbl.inherit();
1013 let ret = interior(elt, base_cmt.clone(), base_cmt.ty,
1014 m, context, element_ty);
1015 debug!("cat_index ret {:?}", ret);
1018 fn interior<'tcx, N: ast_node>(elt: &N,
1021 mutbl: MutabilityCategory,
1022 context: InteriorOffsetKind,
1023 element_ty: Ty<'tcx>) -> cmt<'tcx>
1025 let interior_elem = InteriorElement(context, element_kind(vec_ty));
1029 cat:cat_interior(of_cmt, interior_elem),
1037 // Takes either a vec or a reference to a vec and returns the cmt for the
1039 fn deref_vec<N:ast_node>(&self,
1041 base_cmt: cmt<'tcx>,
1042 context: InteriorOffsetKind)
1043 -> McResult<cmt<'tcx>>
1045 let ret = match try!(deref_kind(base_cmt.ty, Some(context))) {
1047 // for unique ptrs, we inherit mutability from the
1048 // owning reference.
1049 let m = MutabilityCategory::from_pointer_kind(base_cmt.mutbl, ptr);
1051 // the deref is explicit in the resulting cmt
1055 cat:cat_deref(base_cmt.clone(), 0, ptr),
1057 ty: match base_cmt.ty.builtin_deref(false) {
1059 None => self.tcx().sess.bug("Found non-derefable type")
1065 deref_interior(_) => {
1069 debug!("deref_vec ret {:?}", ret);
1073 /// Given a pattern P like: `[_, ..Q, _]`, where `vec_cmt` is the cmt for `P`, `slice_pat` is
1074 /// the pattern `Q`, returns:
1077 /// * the mutability and region of the slice `Q`
1079 /// These last two bits of info happen to be things that borrowck needs.
1080 pub fn cat_slice_pattern(&self,
1082 slice_pat: &ast::Pat)
1083 -> McResult<(cmt<'tcx>, ast::Mutability, ty::Region)> {
1084 let slice_ty = try!(self.node_ty(slice_pat.id));
1085 let (slice_mutbl, slice_r) = vec_slice_info(self.tcx(),
1088 let context = InteriorOffsetKind::Pattern;
1089 let cmt_vec = try!(self.deref_vec(slice_pat, vec_cmt, context));
1090 let cmt_slice = try!(self.cat_index(slice_pat, cmt_vec, context));
1091 return Ok((cmt_slice, slice_mutbl, slice_r));
1093 /// In a pattern like [a, b, ..c], normally `c` has slice type, but if you have [a, b,
1094 /// ..ref c], then the type of `ref c` will be `&&[]`, so to extract the slice details we
1095 /// have to recurse through rptrs.
1096 fn vec_slice_info(tcx: &ty::ctxt,
1099 -> (ast::Mutability, ty::Region) {
1100 match slice_ty.sty {
1101 ty::TyRef(r, ref mt) => match mt.ty.sty {
1102 ty::TySlice(_) => (mt.mutbl, *r),
1103 _ => vec_slice_info(tcx, pat, mt.ty),
1107 tcx.sess.span_bug(pat.span,
1108 "type of slice pattern is not a slice");
1114 pub fn cat_imm_interior<N:ast_node>(&self,
1116 base_cmt: cmt<'tcx>,
1117 interior_ty: Ty<'tcx>,
1118 interior: InteriorKind)
1120 let ret = Rc::new(cmt_ {
1123 mutbl: base_cmt.mutbl.inherit(),
1124 cat: cat_interior(base_cmt, interior),
1128 debug!("cat_imm_interior ret={:?}", ret);
1132 pub fn cat_downcast<N:ast_node>(&self,
1134 base_cmt: cmt<'tcx>,
1135 downcast_ty: Ty<'tcx>,
1138 let ret = Rc::new(cmt_ {
1141 mutbl: base_cmt.mutbl.inherit(),
1142 cat: cat_downcast(base_cmt, variant_did),
1146 debug!("cat_downcast ret={:?}", ret);
1150 pub fn cat_pattern<F>(&self, cmt: cmt<'tcx>, pat: &ast::Pat, mut op: F) -> McResult<()>
1151 where F: FnMut(&MemCategorizationContext<'t, 'a, 'tcx>, cmt<'tcx>, &ast::Pat),
1153 self.cat_pattern_(cmt, pat, &mut op)
1156 // FIXME(#19596) This is a workaround, but there should be a better way to do this
1157 fn cat_pattern_<F>(&self, cmt: cmt<'tcx>, pat: &ast::Pat, op: &mut F)
1159 where F : FnMut(&MemCategorizationContext<'t, 'a, 'tcx>, cmt<'tcx>, &ast::Pat),
1161 // Here, `cmt` is the categorization for the value being
1162 // matched and pat is the pattern it is being matched against.
1164 // In general, the way that this works is that we walk down
1165 // the pattern, constructing a cmt that represents the path
1166 // that will be taken to reach the value being matched.
1168 // When we encounter named bindings, we take the cmt that has
1169 // been built up and pass it off to guarantee_valid() so that
1170 // we can be sure that the binding will remain valid for the
1171 // duration of the arm.
1173 // (*2) There is subtlety concerning the correspondence between
1174 // pattern ids and types as compared to *expression* ids and
1175 // types. This is explained briefly. on the definition of the
1176 // type `cmt`, so go off and read what it says there, then
1177 // come back and I'll dive into a bit more detail here. :) OK,
1180 // In general, the id of the cmt should be the node that
1181 // "produces" the value---patterns aren't executable code
1182 // exactly, but I consider them to "execute" when they match a
1183 // value, and I consider them to produce the value that was
1184 // matched. So if you have something like:
1191 // In this case, the cmt and the relevant ids would be:
1193 // CMT Id Type of Id Type of cmt
1196 // ^~~~~~~^ `x` from discr @@int @@int
1197 // ^~~~~~~~~~^ `@@y` pattern node @@int @int
1198 // ^~~~~~~~~~~~~^ `@y` pattern node @int int
1200 // You can see that the types of the id and the cmt are in
1201 // sync in the first line, because that id is actually the id
1202 // of an expression. But once we get to pattern ids, the types
1203 // step out of sync again. So you'll see below that we always
1204 // get the type of the *subpattern* and use that.
1206 debug!("cat_pattern: {:?} cmt={:?}",
1210 (*op)(self, cmt.clone(), pat);
1212 let opt_def = self.tcx().def_map.borrow().get(&pat.id).map(|d| d.full_def());
1214 // Note: This goes up here (rather than within the PatEnum arm
1215 // alone) because struct patterns can refer to struct types or
1216 // to struct variants within enums.
1217 let cmt = match opt_def {
1218 Some(def::DefVariant(enum_did, variant_did, _))
1219 // univariant enums do not need downcasts
1220 if !self.tcx().lookup_adt_def(enum_did).is_univariant() => {
1221 self.cat_downcast(pat, cmt.clone(), cmt.ty, variant_did)
1227 ast::PatWild(_) => {
1231 ast::PatEnum(_, None) => {
1234 ast::PatEnum(_, Some(ref subpats)) => {
1236 Some(def::DefVariant(..)) => {
1238 for (i, subpat) in subpats.iter().enumerate() {
1239 let subpat_ty = try!(self.pat_ty(&**subpat)); // see (*2)
1242 self.cat_imm_interior(
1243 pat, cmt.clone(), subpat_ty,
1244 InteriorField(PositionalField(i)));
1246 try!(self.cat_pattern_(subcmt, &**subpat, op));
1249 Some(def::DefStruct(..)) => {
1250 for (i, subpat) in subpats.iter().enumerate() {
1251 let subpat_ty = try!(self.pat_ty(&**subpat)); // see (*2)
1253 self.cat_imm_interior(
1254 pat, cmt.clone(), subpat_ty,
1255 InteriorField(PositionalField(i)));
1256 try!(self.cat_pattern_(cmt_field, &**subpat, op));
1259 Some(def::DefConst(..)) | Some(def::DefAssociatedConst(..)) => {
1260 for subpat in subpats {
1261 try!(self.cat_pattern_(cmt.clone(), &**subpat, op));
1265 self.tcx().sess.span_bug(
1267 "enum pattern didn't resolve to enum or struct");
1272 ast::PatQPath(..) => {
1273 // Lone constant: ignore
1276 ast::PatIdent(_, _, Some(ref subpat)) => {
1277 try!(self.cat_pattern_(cmt, &**subpat, op));
1280 ast::PatIdent(_, _, None) => {
1281 // nullary variant or identifier: ignore
1284 ast::PatStruct(_, ref field_pats, _) => {
1285 // {f1: p1, ..., fN: pN}
1286 for fp in field_pats {
1287 let field_ty = try!(self.pat_ty(&*fp.node.pat)); // see (*2)
1288 let cmt_field = self.cat_field(pat, cmt.clone(), fp.node.ident.name, field_ty);
1289 try!(self.cat_pattern_(cmt_field, &*fp.node.pat, op));
1293 ast::PatTup(ref subpats) => {
1295 for (i, subpat) in subpats.iter().enumerate() {
1296 let subpat_ty = try!(self.pat_ty(&**subpat)); // see (*2)
1298 self.cat_imm_interior(
1299 pat, cmt.clone(), subpat_ty,
1300 InteriorField(PositionalField(i)));
1301 try!(self.cat_pattern_(subcmt, &**subpat, op));
1305 ast::PatBox(ref subpat) | ast::PatRegion(ref subpat, _) => {
1306 // box p1, &p1, &mut p1. we can ignore the mutability of
1307 // PatRegion since that information is already contained
1309 let subcmt = try!(self.cat_deref(pat, cmt, 0, None));
1310 try!(self.cat_pattern_(subcmt, &**subpat, op));
1313 ast::PatVec(ref before, ref slice, ref after) => {
1314 let context = InteriorOffsetKind::Pattern;
1315 let vec_cmt = try!(self.deref_vec(pat, cmt, context));
1316 let elt_cmt = try!(self.cat_index(pat, vec_cmt, context));
1317 for before_pat in before {
1318 try!(self.cat_pattern_(elt_cmt.clone(), &**before_pat, op));
1320 if let Some(ref slice_pat) = *slice {
1321 let slice_ty = try!(self.pat_ty(&**slice_pat));
1322 let slice_cmt = self.cat_rvalue_node(pat.id(), pat.span(), slice_ty);
1323 try!(self.cat_pattern_(slice_cmt, &**slice_pat, op));
1325 for after_pat in after {
1326 try!(self.cat_pattern_(elt_cmt.clone(), &**after_pat, op));
1330 ast::PatLit(_) | ast::PatRange(_, _) => {
1335 self.tcx().sess.span_bug(pat.span, "unexpanded macro");
1342 fn overloaded_method_return_ty(&self,
1343 method_ty: Ty<'tcx>)
1346 // When we process an overloaded `*` or `[]` etc, we often
1347 // need to extract the return type of the method. These method
1348 // types are generated by method resolution and always have
1349 // all late-bound regions fully instantiated, so we just want
1350 // to skip past the binder.
1351 self.tcx().no_late_bound_regions(&method_ty.fn_ret())
1353 .unwrap() // overloaded ops do not diverge, either
1357 #[derive(Clone, Debug)]
1358 pub enum Aliasability {
1359 FreelyAliasable(AliasableReason),
1361 ImmutableUnique(Box<Aliasability>),
1364 #[derive(Copy, Clone, Debug)]
1365 pub enum AliasableReason {
1367 AliasableClosure(ast::NodeId), // Aliasable due to capture Fn closure env
1369 UnaliasableImmutable, // Created as needed upon seeing ImmutableUnique
1374 impl<'tcx> cmt_<'tcx> {
1375 pub fn guarantor(&self) -> cmt<'tcx> {
1376 //! Returns `self` after stripping away any derefs or
1377 //! interior content. The return value is basically the `cmt` which
1378 //! determines how long the value in `self` remains live.
1384 cat_deref(_, _, UnsafePtr(..)) |
1385 cat_deref(_, _, BorrowedPtr(..)) |
1386 cat_deref(_, _, Implicit(..)) |
1388 Rc::new((*self).clone())
1390 cat_downcast(ref b, _) |
1391 cat_interior(ref b, _) |
1392 cat_deref(ref b, _, Unique) => {
1398 /// Returns `FreelyAliasable(_)` if this lvalue represents a freely aliasable pointer type.
1399 pub fn freely_aliasable(&self, ctxt: &ty::ctxt<'tcx>)
1401 // Maybe non-obvious: copied upvars can only be considered
1402 // non-aliasable in once closures, since any other kind can be
1403 // aliased and eventually recused.
1406 cat_deref(ref b, _, BorrowedPtr(ty::MutBorrow, _)) |
1407 cat_deref(ref b, _, Implicit(ty::MutBorrow, _)) |
1408 cat_deref(ref b, _, BorrowedPtr(ty::UniqueImmBorrow, _)) |
1409 cat_deref(ref b, _, Implicit(ty::UniqueImmBorrow, _)) |
1410 cat_downcast(ref b, _) |
1411 cat_interior(ref b, _) => {
1412 // Aliasability depends on base cmt
1413 b.freely_aliasable(ctxt)
1416 cat_deref(ref b, _, Unique) => {
1417 let sub = b.freely_aliasable(ctxt);
1418 if b.mutbl.is_mutable() {
1419 // Aliasability depends on base cmt alone
1422 // Do not allow mutation through an immutable box.
1423 ImmutableUnique(Box::new(sub))
1430 cat_deref(_, _, UnsafePtr(..)) => { // yes, it's aliasable, but...
1434 cat_static_item(..) => {
1435 if self.mutbl.is_mutable() {
1436 FreelyAliasable(AliasableStaticMut)
1438 FreelyAliasable(AliasableStatic)
1442 cat_deref(ref base, _, BorrowedPtr(ty::ImmBorrow, _)) |
1443 cat_deref(ref base, _, Implicit(ty::ImmBorrow, _)) => {
1445 cat_upvar(Upvar{ id, .. }) =>
1446 FreelyAliasable(AliasableClosure(id.closure_expr_id)),
1447 _ => FreelyAliasable(AliasableBorrowed)
1453 // Digs down through one or two layers of deref and grabs the cmt
1454 // for the upvar if a note indicates there is one.
1455 pub fn upvar(&self) -> Option<cmt<'tcx>> {
1457 NoteClosureEnv(..) | NoteUpvarRef(..) => {
1458 Some(match self.cat {
1459 cat_deref(ref inner, _, _) => {
1461 cat_deref(ref inner, _, _) => inner.clone(),
1462 cat_upvar(..) => inner.clone(),
1474 pub fn descriptive_string(&self, tcx: &ty::ctxt) -> String {
1476 cat_static_item => {
1477 "static item".to_string()
1480 "non-lvalue".to_string()
1483 match tcx.map.find(vid) {
1484 Some(ast_map::NodeArg(_)) => {
1485 "argument".to_string()
1487 _ => "local variable".to_string()
1490 cat_deref(_, _, pk) => {
1491 let upvar = self.upvar();
1492 match upvar.as_ref().map(|i| &i.cat) {
1493 Some(&cat_upvar(ref var)) => {
1496 Some(_) => unreachable!(),
1500 format!("indexed content")
1503 format!("`Box` content")
1506 format!("dereference of raw pointer")
1508 BorrowedPtr(..) => {
1509 format!("borrowed content")
1515 cat_interior(_, InteriorField(NamedField(_))) => {
1518 cat_interior(_, InteriorField(PositionalField(_))) => {
1519 "anonymous field".to_string()
1521 cat_interior(_, InteriorElement(InteriorOffsetKind::Index,
1523 cat_interior(_, InteriorElement(InteriorOffsetKind::Index,
1525 "indexed content".to_string()
1527 cat_interior(_, InteriorElement(InteriorOffsetKind::Pattern,
1529 cat_interior(_, InteriorElement(InteriorOffsetKind::Pattern,
1531 "pattern-bound indexed content".to_string()
1533 cat_upvar(ref var) => {
1536 cat_downcast(ref cmt, _) => {
1537 cmt.descriptive_string(tcx)
1543 impl<'tcx> fmt::Debug for cmt_<'tcx> {
1544 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1545 write!(f, "{{{:?} id:{} m:{:?} ty:{:?}}}",
1553 impl<'tcx> fmt::Debug for categorization<'tcx> {
1554 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1556 cat_static_item => write!(f, "static"),
1557 cat_rvalue(r) => write!(f, "rvalue({:?})", r),
1559 let name = ty::tls::with(|tcx| tcx.local_var_name_str(id));
1560 write!(f, "local({})", name)
1562 cat_upvar(upvar) => {
1563 write!(f, "upvar({:?})", upvar)
1565 cat_deref(ref cmt, derefs, ptr) => {
1566 write!(f, "{:?}-{:?}{}->", cmt.cat, ptr, derefs)
1568 cat_interior(ref cmt, interior) => {
1569 write!(f, "{:?}.{:?}", cmt.cat, interior)
1571 cat_downcast(ref cmt, _) => {
1572 write!(f, "{:?}->(enum)", cmt.cat)
1578 pub fn ptr_sigil(ptr: PointerKind) -> &'static str {
1581 BorrowedPtr(ty::ImmBorrow, _) |
1582 Implicit(ty::ImmBorrow, _) => "&",
1583 BorrowedPtr(ty::MutBorrow, _) |
1584 Implicit(ty::MutBorrow, _) => "&mut",
1585 BorrowedPtr(ty::UniqueImmBorrow, _) |
1586 Implicit(ty::UniqueImmBorrow, _) => "&unique",
1587 UnsafePtr(_) => "*",
1591 impl fmt::Debug for PointerKind {
1592 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1594 Unique => write!(f, "Box"),
1595 BorrowedPtr(ty::ImmBorrow, ref r) |
1596 Implicit(ty::ImmBorrow, ref r) => {
1597 write!(f, "&{:?}", r)
1599 BorrowedPtr(ty::MutBorrow, ref r) |
1600 Implicit(ty::MutBorrow, ref r) => {
1601 write!(f, "&{:?} mut", r)
1603 BorrowedPtr(ty::UniqueImmBorrow, ref r) |
1604 Implicit(ty::UniqueImmBorrow, ref r) => {
1605 write!(f, "&{:?} uniq", r)
1607 UnsafePtr(_) => write!(f, "*")
1612 impl fmt::Debug for InteriorKind {
1613 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1615 InteriorField(NamedField(fld)) => write!(f, "{}", fld),
1616 InteriorField(PositionalField(i)) => write!(f, "#{}", i),
1617 InteriorElement(..) => write!(f, "[]"),
1622 fn element_kind(t: Ty) -> ElementKind {
1624 ty::TyRef(_, ty::TypeAndMut{ty, ..}) |
1625 ty::TyBox(ty) => match ty.sty {
1626 ty::TySlice(_) => VecElement,
1629 ty::TyArray(..) | ty::TySlice(_) => VecElement,
1634 impl fmt::Debug for Upvar {
1635 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1636 write!(f, "{:?}/{:?}", self.id, self.kind)
1640 impl fmt::Display for Upvar {
1641 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1642 let kind = match self.kind {
1643 ty::FnClosureKind => "Fn",
1644 ty::FnMutClosureKind => "FnMut",
1645 ty::FnOnceClosureKind => "FnOnce",
1647 write!(f, "captured outer variable in an `{}` closure", kind)