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 `Categorization::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::*;
72 use self::Aliasability::*;
74 use hir::def_id::DefId;
75 use hir::map as ast_map;
77 use middle::const_qualif::ConstQualif;
80 use ty::{self, Ty, TyCtxt};
82 use hir::{MutImmutable, MutMutable, PatKind};
83 use hir::pat_util::EnumerateAndAdjustIterator;
91 #[derive(Clone, PartialEq)]
92 pub enum Categorization<'tcx> {
93 Rvalue(ty::Region), // temporary val, argument is its scope
95 Upvar(Upvar), // upvar referenced by closure env
96 Local(ast::NodeId), // local variable
97 Deref(cmt<'tcx>, usize, PointerKind), // deref of a ptr
98 Interior(cmt<'tcx>, InteriorKind), // something interior: field, tuple, etc
99 Downcast(cmt<'tcx>, DefId), // selects a particular enum variant (*1)
101 // (*1) downcast is only required if the enum has more than one variant
104 // Represents any kind of upvar
105 #[derive(Clone, Copy, PartialEq)]
108 pub kind: ty::ClosureKind
111 // different kinds of pointers:
112 #[derive(Clone, Copy, PartialEq, Eq, Hash)]
113 pub enum PointerKind {
118 BorrowedPtr(ty::BorrowKind, ty::Region),
121 UnsafePtr(hir::Mutability),
123 /// Implicit deref of the `&T` that results from an overloaded index `[]`.
124 Implicit(ty::BorrowKind, ty::Region),
127 // We use the term "interior" to mean "something reachable from the
128 // base without a pointer dereference", e.g. a field
129 #[derive(Clone, Copy, PartialEq, Eq, Hash)]
130 pub enum InteriorKind {
131 InteriorField(FieldName),
132 InteriorElement(InteriorOffsetKind, ElementKind),
135 #[derive(Clone, Copy, PartialEq, Eq, Hash, Debug)]
137 NamedField(ast::Name),
138 PositionalField(usize)
141 #[derive(Clone, Copy, PartialEq, Eq, Hash, Debug)]
142 pub enum InteriorOffsetKind {
143 Index, // e.g. `array_expr[index_expr]`
144 Pattern, // e.g. `fn foo([_, a, _, _]: [A; 4]) { ... }`
147 #[derive(Clone, Copy, PartialEq, Eq, Hash, Debug)]
148 pub enum ElementKind {
153 #[derive(Clone, Copy, PartialEq, Eq, Hash, Debug)]
154 pub enum MutabilityCategory {
155 McImmutable, // Immutable.
156 McDeclared, // Directly declared as mutable.
157 McInherited, // Inherited from the fact that owner is mutable.
160 // A note about the provenance of a `cmt`. This is used for
161 // special-case handling of upvars such as mutability inference.
162 // Upvar categorization can generate a variable number of nested
163 // derefs. The note allows detecting them without deep pattern
164 // matching on the categorization.
165 #[derive(Clone, Copy, PartialEq, Debug)]
167 NoteClosureEnv(ty::UpvarId), // Deref through closure env
168 NoteUpvarRef(ty::UpvarId), // Deref through by-ref upvar
169 NoteNone // Nothing special
172 // `cmt`: "Category, Mutability, and Type".
174 // a complete categorization of a value indicating where it originated
175 // and how it is located, as well as the mutability of the memory in
176 // which the value is stored.
178 // *WARNING* The field `cmt.type` is NOT necessarily the same as the
179 // result of `node_id_to_type(cmt.id)`. This is because the `id` is
180 // always the `id` of the node producing the type; in an expression
181 // like `*x`, the type of this deref node is the deref'd type (`T`),
182 // but in a pattern like `@x`, the `@x` pattern is again a
183 // dereference, but its type is the type *before* the dereference
184 // (`@T`). So use `cmt.ty` to find the type of the value in a consistent
185 // fashion. For more details, see the method `cat_pattern`
186 #[derive(Clone, PartialEq)]
187 pub struct cmt_<'tcx> {
188 pub id: ast::NodeId, // id of expr/pat producing this value
189 pub span: Span, // span of same expr/pat
190 pub cat: Categorization<'tcx>, // categorization of expr
191 pub mutbl: MutabilityCategory, // mutability of expr as lvalue
192 pub ty: Ty<'tcx>, // type of the expr (*see WARNING above*)
193 pub note: Note, // Note about the provenance of this cmt
196 pub type cmt<'tcx> = Rc<cmt_<'tcx>>;
198 // We pun on *T to mean both actual deref of a ptr as well
199 // as accessing of components:
200 #[derive(Copy, Clone)]
201 pub enum deref_kind {
202 deref_ptr(PointerKind),
203 deref_interior(InteriorKind),
206 type DerefKindContext = Option<InteriorOffsetKind>;
208 // Categorizes a derefable type. Note that we include vectors and strings as
209 // derefable (we model an index as the combination of a deref and then a
210 // pointer adjustment).
211 fn deref_kind(t: Ty, context: DerefKindContext) -> McResult<deref_kind> {
214 Ok(deref_ptr(Unique))
217 ty::TyRef(r, mt) => {
218 let kind = ty::BorrowKind::from_mutbl(mt.mutbl);
219 Ok(deref_ptr(BorrowedPtr(kind, *r)))
222 ty::TyRawPtr(ref mt) => {
223 Ok(deref_ptr(UnsafePtr(mt.mutbl)))
227 ty::TyStruct(..) => { // newtype
228 Ok(deref_interior(InteriorField(PositionalField(0))))
231 ty::TyArray(_, _) | ty::TySlice(_) => {
232 // no deref of indexed content without supplying InteriorOffsetKind
233 if let Some(context) = context {
234 Ok(deref_interior(InteriorElement(context, ElementKind::VecElement)))
245 fn id(&self) -> ast::NodeId;
246 fn span(&self) -> Span;
249 impl ast_node for hir::Expr {
250 fn id(&self) -> ast::NodeId { self.id }
251 fn span(&self) -> Span { self.span }
254 impl ast_node for hir::Pat {
255 fn id(&self) -> ast::NodeId { self.id }
256 fn span(&self) -> Span { self.span }
259 #[derive(Copy, Clone)]
260 pub struct MemCategorizationContext<'a, 'gcx: 'a+'tcx, 'tcx: 'a> {
261 pub infcx: &'a InferCtxt<'a, 'gcx, 'tcx>,
262 options: MemCategorizationOptions,
265 #[derive(Copy, Clone, Default)]
266 pub struct MemCategorizationOptions {
267 // If true, then when analyzing a closure upvar, if the closure
268 // has a missing kind, we treat it like a Fn closure. When false,
269 // we ICE if the closure has a missing kind. Should be false
270 // except during closure kind inference. It is used by the
271 // mem-categorization code to be able to have stricter assertions
272 // (which are always true except during upvar inference).
273 pub during_closure_kind_inference: bool,
276 pub type McResult<T> = Result<T, ()>;
278 impl MutabilityCategory {
279 pub fn from_mutbl(m: hir::Mutability) -> MutabilityCategory {
281 MutImmutable => McImmutable,
282 MutMutable => McDeclared
284 debug!("MutabilityCategory::{}({:?}) => {:?}",
285 "from_mutbl", m, ret);
289 pub fn from_borrow_kind(borrow_kind: ty::BorrowKind) -> MutabilityCategory {
290 let ret = match borrow_kind {
291 ty::ImmBorrow => McImmutable,
292 ty::UniqueImmBorrow => McImmutable,
293 ty::MutBorrow => McDeclared,
295 debug!("MutabilityCategory::{}({:?}) => {:?}",
296 "from_borrow_kind", borrow_kind, ret);
300 fn from_pointer_kind(base_mutbl: MutabilityCategory,
301 ptr: PointerKind) -> MutabilityCategory {
302 let ret = match ptr {
306 BorrowedPtr(borrow_kind, _) | Implicit(borrow_kind, _) => {
307 MutabilityCategory::from_borrow_kind(borrow_kind)
310 MutabilityCategory::from_mutbl(m)
313 debug!("MutabilityCategory::{}({:?}, {:?}) => {:?}",
314 "from_pointer_kind", base_mutbl, ptr, ret);
318 fn from_local(tcx: TyCtxt, id: ast::NodeId) -> MutabilityCategory {
319 let ret = match tcx.map.get(id) {
320 ast_map::NodeLocal(p) => match p.node {
321 PatKind::Binding(bind_mode, _, _) => {
322 if bind_mode == hir::BindByValue(hir::MutMutable) {
328 _ => span_bug!(p.span, "expected identifier pattern")
330 _ => span_bug!(tcx.map.span(id), "expected identifier pattern")
332 debug!("MutabilityCategory::{}(tcx, id={:?}) => {:?}",
333 "from_local", id, ret);
337 pub fn inherit(&self) -> MutabilityCategory {
338 let ret = match *self {
339 McImmutable => McImmutable,
340 McDeclared => McInherited,
341 McInherited => McInherited,
343 debug!("{:?}.inherit() => {:?}", self, ret);
347 pub fn is_mutable(&self) -> bool {
348 let ret = match *self {
349 McImmutable => false,
353 debug!("{:?}.is_mutable() => {:?}", self, ret);
357 pub fn is_immutable(&self) -> bool {
358 let ret = match *self {
360 McDeclared | McInherited => false
362 debug!("{:?}.is_immutable() => {:?}", self, ret);
366 pub fn to_user_str(&self) -> &'static str {
368 McDeclared | McInherited => "mutable",
369 McImmutable => "immutable",
374 impl<'a, 'gcx, 'tcx> MemCategorizationContext<'a, 'gcx, 'tcx> {
375 pub fn new(infcx: &'a InferCtxt<'a, 'gcx, 'tcx>)
376 -> MemCategorizationContext<'a, 'gcx, 'tcx> {
377 MemCategorizationContext::with_options(infcx, MemCategorizationOptions::default())
380 pub fn with_options(infcx: &'a InferCtxt<'a, 'gcx, 'tcx>,
381 options: MemCategorizationOptions)
382 -> MemCategorizationContext<'a, 'gcx, 'tcx> {
383 MemCategorizationContext {
389 fn tcx(&self) -> TyCtxt<'a, 'gcx, 'tcx> {
393 fn expr_ty(&self, expr: &hir::Expr) -> McResult<Ty<'tcx>> {
394 match self.infcx.node_ty(expr.id) {
397 debug!("expr_ty({:?}) yielded Err", expr);
403 fn expr_ty_adjusted(&self, expr: &hir::Expr) -> McResult<Ty<'tcx>> {
404 let unadjusted_ty = self.expr_ty(expr)?;
405 Ok(unadjusted_ty.adjust(
406 self.tcx(), expr.span, expr.id,
407 self.infcx.adjustments().get(&expr.id),
408 |method_call| self.infcx.node_method_ty(method_call)))
411 fn node_ty(&self, id: ast::NodeId) -> McResult<Ty<'tcx>> {
412 self.infcx.node_ty(id)
415 fn pat_ty(&self, pat: &hir::Pat) -> McResult<Ty<'tcx>> {
416 let base_ty = self.infcx.node_ty(pat.id)?;
417 // FIXME (Issue #18207): This code detects whether we are
418 // looking at a `ref x`, and if so, figures out what the type
419 // *being borrowed* is. But ideally we would put in a more
420 // fundamental fix to this conflated use of the node id.
421 let ret_ty = match pat.node {
422 PatKind::Binding(hir::BindByRef(_), _, _) => {
423 // a bind-by-ref means that the base_ty will be the type of the ident itself,
424 // but what we want here is the type of the underlying value being borrowed.
425 // So peel off one-level, turning the &T into T.
426 match base_ty.builtin_deref(false, ty::NoPreference) {
428 None => { return Err(()); }
433 debug!("pat_ty(pat={:?}) base_ty={:?} ret_ty={:?}",
434 pat, base_ty, ret_ty);
438 pub fn cat_expr(&self, expr: &hir::Expr) -> McResult<cmt<'tcx>> {
439 match self.infcx.adjustments().get(&expr.id) {
442 self.cat_expr_unadjusted(expr)
445 Some(adjustment) => {
447 adjustment::AdjustDerefRef(
448 adjustment::AutoDerefRef {
449 autoref: None, unsize: None, autoderefs, ..}) => {
450 // Equivalent to *expr or something similar.
451 self.cat_expr_autoderefd(expr, autoderefs)
454 adjustment::AdjustNeverToAny(..) |
455 adjustment::AdjustReifyFnPointer |
456 adjustment::AdjustUnsafeFnPointer |
457 adjustment::AdjustMutToConstPointer |
458 adjustment::AdjustDerefRef(_) => {
459 debug!("cat_expr({:?}): {:?}",
462 // Result is an rvalue.
463 let expr_ty = self.expr_ty_adjusted(expr)?;
464 Ok(self.cat_rvalue_node(expr.id(), expr.span(), expr_ty))
471 pub fn cat_expr_autoderefd(&self,
474 -> McResult<cmt<'tcx>> {
475 let mut cmt = self.cat_expr_unadjusted(expr)?;
476 debug!("cat_expr_autoderefd: autoderefs={}, cmt={:?}",
479 for deref in 1..autoderefs + 1 {
480 cmt = self.cat_deref(expr, cmt, deref, None)?;
485 pub fn cat_expr_unadjusted(&self, expr: &hir::Expr) -> McResult<cmt<'tcx>> {
486 debug!("cat_expr: id={} expr={:?}", expr.id, expr);
488 let expr_ty = self.expr_ty(expr)?;
490 hir::ExprUnary(hir::UnDeref, ref e_base) => {
491 let base_cmt = self.cat_expr(&e_base)?;
492 self.cat_deref(expr, base_cmt, 0, None)
495 hir::ExprField(ref base, f_name) => {
496 let base_cmt = self.cat_expr(&base)?;
497 debug!("cat_expr(cat_field): id={} expr={:?} base={:?}",
501 Ok(self.cat_field(expr, base_cmt, f_name.node, expr_ty))
504 hir::ExprTupField(ref base, idx) => {
505 let base_cmt = self.cat_expr(&base)?;
506 Ok(self.cat_tup_field(expr, base_cmt, idx.node, expr_ty))
509 hir::ExprIndex(ref base, _) => {
510 let method_call = ty::MethodCall::expr(expr.id());
511 let context = InteriorOffsetKind::Index;
512 match self.infcx.node_method_ty(method_call) {
514 // If this is an index implemented by a method call, then it
515 // will include an implicit deref of the result.
516 let ret_ty = self.overloaded_method_return_ty(method_ty);
518 // The index method always returns an `&T`, so
519 // dereference it to find the result type.
520 let elem_ty = match ret_ty.sty {
521 ty::TyRef(_, mt) => mt.ty,
523 debug!("cat_expr_unadjusted: return type of overloaded index is {:?}?",
529 // The call to index() returns a `&T` value, which
530 // is an rvalue. That is what we will be
532 let base_cmt = self.cat_rvalue_node(expr.id(), expr.span(), ret_ty);
533 self.cat_deref_common(expr, base_cmt, 1, elem_ty, Some(context), true)
536 self.cat_index(expr, self.cat_expr(&base)?, context)
541 hir::ExprPath(..) => {
542 self.cat_def(expr.id, expr.span, expr_ty, self.tcx().expect_def(expr.id))
545 hir::ExprType(ref e, _) => {
549 hir::ExprAddrOf(..) | hir::ExprCall(..) |
550 hir::ExprAssign(..) | hir::ExprAssignOp(..) |
551 hir::ExprClosure(..) | hir::ExprRet(..) |
553 hir::ExprMethodCall(..) | hir::ExprCast(..) |
554 hir::ExprVec(..) | hir::ExprTup(..) | hir::ExprIf(..) |
555 hir::ExprBinary(..) | hir::ExprWhile(..) |
556 hir::ExprBlock(..) | hir::ExprLoop(..) | hir::ExprMatch(..) |
557 hir::ExprLit(..) | hir::ExprBreak(..) |
558 hir::ExprAgain(..) | hir::ExprStruct(..) | hir::ExprRepeat(..) |
559 hir::ExprInlineAsm(..) | hir::ExprBox(..) => {
560 Ok(self.cat_rvalue_node(expr.id(), expr.span(), expr_ty))
565 pub fn cat_def(&self,
570 -> McResult<cmt<'tcx>> {
571 debug!("cat_def: id={} expr={:?} def={:?}",
575 Def::Struct(..) | Def::Variant(..) | Def::Const(..) |
576 Def::AssociatedConst(..) | Def::Fn(..) | Def::Method(..) => {
577 Ok(self.cat_rvalue_node(id, span, expr_ty))
580 Def::Mod(_) | Def::ForeignMod(_) |
581 Def::Trait(_) | Def::Enum(..) | Def::TyAlias(..) | Def::PrimTy(_) |
583 Def::Label(_) | Def::SelfTy(..) |
584 Def::AssociatedTy(..) => {
585 span_bug!(span, "Unexpected definition in \
586 memory categorization: {:?}", def);
589 Def::Static(_, mutbl) => {
593 cat:Categorization::StaticItem,
594 mutbl: if mutbl { McDeclared } else { McImmutable},
600 Def::Upvar(_, var_id, _, fn_node_id) => {
601 let ty = self.node_ty(fn_node_id)?;
603 ty::TyClosure(closure_id, _) => {
604 match self.infcx.closure_kind(closure_id) {
606 self.cat_upvar(id, span, var_id, fn_node_id, kind)
609 if !self.options.during_closure_kind_inference {
612 "No closure kind for {:?}",
616 // during closure kind inference, we
617 // don't know the closure kind yet, but
618 // it's ok because we detect that we are
619 // accessing an upvar and handle that
620 // case specially anyhow. Use Fn
622 self.cat_upvar(id, span, var_id, fn_node_id, ty::ClosureKind::Fn)
629 "Upvar of non-closure {} - {:?}",
636 Def::Local(_, vid) => {
640 cat: Categorization::Local(vid),
641 mutbl: MutabilityCategory::from_local(self.tcx(), vid),
647 Def::Err => bug!("Def::Err in memory categorization")
651 // Categorize an upvar, complete with invisible derefs of closure
652 // environment and upvar reference as appropriate.
657 fn_node_id: ast::NodeId,
658 kind: ty::ClosureKind)
659 -> McResult<cmt<'tcx>>
661 // An upvar can have up to 3 components. We translate first to a
662 // `Categorization::Upvar`, which is itself a fiction -- it represents the reference to the
663 // field from the environment.
665 // `Categorization::Upvar`. Next, we add a deref through the implicit
666 // environment pointer with an anonymous free region 'env and
667 // appropriate borrow kind for closure kinds that take self by
668 // reference. Finally, if the upvar was captured
669 // by-reference, we add a deref through that reference. The
670 // region of this reference is an inference variable 'up that
671 // was previously generated and recorded in the upvar borrow
672 // map. The borrow kind bk is inferred by based on how the
675 // This results in the following table for concrete closure
679 // ---------------+----------------------+-------------------------------
680 // Fn | copied -> &'env | upvar -> &'env -> &'up bk
681 // FnMut | copied -> &'env mut | upvar -> &'env mut -> &'up bk
682 // FnOnce | copied | upvar -> &'up bk
684 let upvar_id = ty::UpvarId { var_id: var_id,
685 closure_expr_id: fn_node_id };
686 let var_ty = self.node_ty(var_id)?;
688 // Mutability of original variable itself
689 let var_mutbl = MutabilityCategory::from_local(self.tcx(), var_id);
691 // Construct the upvar. This represents access to the field
692 // from the environment (perhaps we should eventually desugar
693 // this field further, but it will do for now).
694 let cmt_result = cmt_ {
697 cat: Categorization::Upvar(Upvar {id: upvar_id, kind: kind}),
703 // If this is a `FnMut` or `Fn` closure, then the above is
704 // conceptually a `&mut` or `&` reference, so we have to add a
706 let cmt_result = match kind {
707 ty::ClosureKind::FnOnce => {
710 ty::ClosureKind::FnMut => {
711 self.env_deref(id, span, upvar_id, var_mutbl, ty::MutBorrow, cmt_result)
713 ty::ClosureKind::Fn => {
714 self.env_deref(id, span, upvar_id, var_mutbl, ty::ImmBorrow, cmt_result)
718 // If this is a by-ref capture, then the upvar we loaded is
719 // actually a reference, so we have to add an implicit deref
721 let upvar_id = ty::UpvarId { var_id: var_id,
722 closure_expr_id: fn_node_id };
723 let upvar_capture = self.infcx.upvar_capture(upvar_id).unwrap();
724 let cmt_result = match upvar_capture {
725 ty::UpvarCapture::ByValue => {
728 ty::UpvarCapture::ByRef(upvar_borrow) => {
729 let ptr = BorrowedPtr(upvar_borrow.kind, upvar_borrow.region);
733 cat: Categorization::Deref(Rc::new(cmt_result), 0, ptr),
734 mutbl: MutabilityCategory::from_borrow_kind(upvar_borrow.kind),
736 note: NoteUpvarRef(upvar_id)
741 let ret = Rc::new(cmt_result);
742 debug!("cat_upvar ret={:?}", ret);
749 upvar_id: ty::UpvarId,
750 upvar_mutbl: MutabilityCategory,
751 env_borrow_kind: ty::BorrowKind,
752 cmt_result: cmt_<'tcx>)
755 // Look up the node ID of the closure body so we can construct
756 // a free region within it
758 let fn_expr = match self.tcx().map.find(upvar_id.closure_expr_id) {
759 Some(ast_map::NodeExpr(e)) => e,
764 hir::ExprClosure(_, _, ref body, _) => body.id,
769 // Region of environment pointer
770 let env_region = ty::ReFree(ty::FreeRegion {
771 // The environment of a closure is guaranteed to
772 // outlive any bindings introduced in the body of the
774 scope: self.tcx().region_maps.item_extent(fn_body_id),
775 bound_region: ty::BrEnv
778 let env_ptr = BorrowedPtr(env_borrow_kind, env_region);
780 let var_ty = cmt_result.ty;
782 // We need to add the env deref. This means
783 // that the above is actually immutable and
784 // has a ref type. However, nothing should
785 // actually look at the type, so we can get
786 // away with stuffing a `TyError` in there
787 // instead of bothering to construct a proper
789 let cmt_result = cmt_ {
791 ty: self.tcx().types.err,
795 let mut deref_mutbl = MutabilityCategory::from_borrow_kind(env_borrow_kind);
797 // Issue #18335. If variable is declared as immutable, override the
798 // mutability from the environment and substitute an `&T` anyway.
800 McImmutable => { deref_mutbl = McImmutable; }
801 McDeclared | McInherited => { }
807 cat: Categorization::Deref(Rc::new(cmt_result), 0, env_ptr),
810 note: NoteClosureEnv(upvar_id)
813 debug!("env_deref ret {:?}", ret);
818 /// Returns the lifetime of a temporary created by expr with id `id`.
819 /// This could be `'static` if `id` is part of a constant expression.
820 pub fn temporary_scope(&self, id: ast::NodeId) -> ty::Region {
821 match self.infcx.temporary_scope(id) {
822 Some(scope) => ty::ReScope(scope),
827 pub fn cat_rvalue_node(&self,
832 let qualif = self.tcx().const_qualif_map.borrow().get(&id).cloned()
833 .unwrap_or(ConstQualif::NOT_CONST);
835 // Only promote `[T; 0]` before an RFC for rvalue promotions
837 let qualif = match expr_ty.sty {
838 ty::TyArray(_, 0) => qualif,
839 _ => ConstQualif::NOT_CONST
842 // Compute maximum lifetime of this rvalue. This is 'static if
843 // we can promote to a constant, otherwise equal to enclosing temp
845 let re = if qualif.intersects(ConstQualif::NON_STATIC_BORROWS) {
846 self.temporary_scope(id)
850 let ret = self.cat_rvalue(id, span, re, expr_ty);
851 debug!("cat_rvalue_node ret {:?}", ret);
855 pub fn cat_rvalue(&self,
858 temp_scope: ty::Region,
859 expr_ty: Ty<'tcx>) -> cmt<'tcx> {
860 let ret = Rc::new(cmt_ {
863 cat:Categorization::Rvalue(temp_scope),
868 debug!("cat_rvalue ret {:?}", ret);
872 pub fn cat_field<N:ast_node>(&self,
878 let ret = Rc::new(cmt_ {
881 mutbl: base_cmt.mutbl.inherit(),
882 cat: Categorization::Interior(base_cmt, InteriorField(NamedField(f_name))),
886 debug!("cat_field ret {:?}", ret);
890 pub fn cat_tup_field<N:ast_node>(&self,
896 let ret = Rc::new(cmt_ {
899 mutbl: base_cmt.mutbl.inherit(),
900 cat: Categorization::Interior(base_cmt, InteriorField(PositionalField(f_idx))),
904 debug!("cat_tup_field ret {:?}", ret);
908 fn cat_deref<N:ast_node>(&self,
912 deref_context: DerefKindContext)
913 -> McResult<cmt<'tcx>> {
914 let method_call = ty::MethodCall {
916 autoderef: deref_cnt as u32
918 let method_ty = self.infcx.node_method_ty(method_call);
920 debug!("cat_deref: method_call={:?} method_ty={:?}",
921 method_call, method_ty.map(|ty| ty));
923 let base_cmt = match method_ty {
926 self.tcx().no_late_bound_regions(&method_ty.fn_ret()).unwrap();
927 self.cat_rvalue_node(node.id(), node.span(), ref_ty)
931 let base_cmt_ty = base_cmt.ty;
932 match base_cmt_ty.builtin_deref(true, ty::NoPreference) {
934 let ret = self.cat_deref_common(node, base_cmt, deref_cnt,
937 /* implicit: */ false);
938 debug!("cat_deref ret {:?}", ret);
942 debug!("Explicit deref of non-derefable type: {:?}",
949 fn cat_deref_common<N:ast_node>(&self,
954 deref_context: DerefKindContext,
956 -> McResult<cmt<'tcx>>
958 let (m, cat) = match deref_kind(base_cmt.ty, deref_context)? {
960 let ptr = if implicit {
962 BorrowedPtr(bk, r) => Implicit(bk, r),
963 _ => span_bug!(node.span(),
964 "Implicit deref of non-borrowed pointer")
969 // for unique ptrs, we inherit mutability from the
971 (MutabilityCategory::from_pointer_kind(base_cmt.mutbl, ptr),
972 Categorization::Deref(base_cmt, deref_cnt, ptr))
974 deref_interior(interior) => {
975 (base_cmt.mutbl.inherit(), Categorization::Interior(base_cmt, interior))
978 let ret = Rc::new(cmt_ {
986 debug!("cat_deref_common ret {:?}", ret);
990 pub fn cat_index<N:ast_node>(&self,
992 mut base_cmt: cmt<'tcx>,
993 context: InteriorOffsetKind)
994 -> McResult<cmt<'tcx>> {
995 //! Creates a cmt for an indexing operation (`[]`).
997 //! One subtle aspect of indexing that may not be
998 //! immediately obvious: for anything other than a fixed-length
999 //! vector, an operation like `x[y]` actually consists of two
1000 //! disjoint (from the point of view of borrowck) operations.
1001 //! The first is a deref of `x` to create a pointer `p` that points
1002 //! at the first element in the array. The second operation is
1003 //! an index which adds `y*sizeof(T)` to `p` to obtain the
1004 //! pointer to `x[y]`. `cat_index` will produce a resulting
1005 //! cmt containing both this deref and the indexing,
1006 //! presuming that `base_cmt` is not of fixed-length type.
1009 //! - `elt`: the AST node being indexed
1010 //! - `base_cmt`: the cmt of `elt`
1012 let method_call = ty::MethodCall::expr(elt.id());
1013 let method_ty = self.infcx.node_method_ty(method_call);
1015 let (element_ty, element_kind) = match method_ty {
1016 Some(method_ty) => {
1017 let ref_ty = self.overloaded_method_return_ty(method_ty);
1018 base_cmt = self.cat_rvalue_node(elt.id(), elt.span(), ref_ty);
1020 // FIXME(#20649) -- why are we using the `self_ty` as the element type...?
1021 let self_ty = method_ty.fn_sig().input(0);
1022 (self.tcx().no_late_bound_regions(&self_ty).unwrap(),
1023 ElementKind::OtherElement)
1026 match base_cmt.ty.builtin_index() {
1027 Some(ty) => (ty, ElementKind::VecElement),
1035 let interior_elem = InteriorElement(context, element_kind);
1037 self.cat_imm_interior(elt, base_cmt.clone(), element_ty, interior_elem);
1038 debug!("cat_index ret {:?}", ret);
1042 pub fn cat_imm_interior<N:ast_node>(&self,
1044 base_cmt: cmt<'tcx>,
1045 interior_ty: Ty<'tcx>,
1046 interior: InteriorKind)
1048 let ret = Rc::new(cmt_ {
1051 mutbl: base_cmt.mutbl.inherit(),
1052 cat: Categorization::Interior(base_cmt, interior),
1056 debug!("cat_imm_interior ret={:?}", ret);
1060 pub fn cat_downcast<N:ast_node>(&self,
1062 base_cmt: cmt<'tcx>,
1063 downcast_ty: Ty<'tcx>,
1066 let ret = Rc::new(cmt_ {
1069 mutbl: base_cmt.mutbl.inherit(),
1070 cat: Categorization::Downcast(base_cmt, variant_did),
1074 debug!("cat_downcast ret={:?}", ret);
1078 pub fn cat_pattern<F>(&self, cmt: cmt<'tcx>, pat: &hir::Pat, mut op: F) -> McResult<()>
1079 where F: FnMut(&MemCategorizationContext<'a, 'gcx, 'tcx>, cmt<'tcx>, &hir::Pat),
1081 self.cat_pattern_(cmt, pat, &mut op)
1084 // FIXME(#19596) This is a workaround, but there should be a better way to do this
1085 fn cat_pattern_<F>(&self, cmt: cmt<'tcx>, pat: &hir::Pat, op: &mut F) -> McResult<()>
1086 where F : FnMut(&MemCategorizationContext<'a, 'gcx, 'tcx>, cmt<'tcx>, &hir::Pat)
1088 // Here, `cmt` is the categorization for the value being
1089 // matched and pat is the pattern it is being matched against.
1091 // In general, the way that this works is that we walk down
1092 // the pattern, constructing a cmt that represents the path
1093 // that will be taken to reach the value being matched.
1095 // When we encounter named bindings, we take the cmt that has
1096 // been built up and pass it off to guarantee_valid() so that
1097 // we can be sure that the binding will remain valid for the
1098 // duration of the arm.
1100 // (*2) There is subtlety concerning the correspondence between
1101 // pattern ids and types as compared to *expression* ids and
1102 // types. This is explained briefly. on the definition of the
1103 // type `cmt`, so go off and read what it says there, then
1104 // come back and I'll dive into a bit more detail here. :) OK,
1107 // In general, the id of the cmt should be the node that
1108 // "produces" the value---patterns aren't executable code
1109 // exactly, but I consider them to "execute" when they match a
1110 // value, and I consider them to produce the value that was
1111 // matched. So if you have something like:
1118 // In this case, the cmt and the relevant ids would be:
1120 // CMT Id Type of Id Type of cmt
1123 // ^~~~~~~^ `x` from discr @@int @@int
1124 // ^~~~~~~~~~^ `@@y` pattern node @@int @int
1125 // ^~~~~~~~~~~~~^ `@y` pattern node @int int
1127 // You can see that the types of the id and the cmt are in
1128 // sync in the first line, because that id is actually the id
1129 // of an expression. But once we get to pattern ids, the types
1130 // step out of sync again. So you'll see below that we always
1131 // get the type of the *subpattern* and use that.
1133 debug!("cat_pattern: {:?} cmt={:?}", pat, cmt);
1135 op(self, cmt.clone(), pat);
1137 // Note: This goes up here (rather than within the PatKind::TupleStruct arm
1138 // alone) because PatKind::Struct can also refer to variants.
1139 let cmt = match self.tcx().expect_def_or_none(pat.id) {
1140 Some(Def::Err) => return Err(()),
1141 Some(Def::Variant(enum_did, variant_did))
1142 // univariant enums do not need downcasts
1143 if !self.tcx().lookup_adt_def(enum_did).is_univariant() => {
1144 self.cat_downcast(pat, cmt.clone(), cmt.ty, variant_did)
1150 PatKind::TupleStruct(_, ref subpats, ddpos) => {
1151 let expected_len = match self.tcx().expect_def(pat.id) {
1152 Def::Variant(enum_def, def_id) => {
1153 self.tcx().lookup_adt_def(enum_def).variant_with_id(def_id).fields.len()
1155 Def::Struct(..) => {
1156 match self.pat_ty(&pat)?.sty {
1157 ty::TyStruct(adt_def, _) => {
1158 adt_def.struct_variant().fields.len()
1161 span_bug!(pat.span, "tuple struct pattern unexpected type {:?}", ty);
1166 span_bug!(pat.span, "tuple struct pattern didn't resolve \
1167 to variant or struct {:?}", def);
1171 for (i, subpat) in subpats.iter().enumerate_and_adjust(expected_len, ddpos) {
1172 let subpat_ty = self.pat_ty(&subpat)?; // see (*2)
1173 let subcmt = self.cat_imm_interior(pat, cmt.clone(), subpat_ty,
1174 InteriorField(PositionalField(i)));
1175 self.cat_pattern_(subcmt, &subpat, op)?;
1179 PatKind::Struct(_, ref field_pats, _) => {
1180 // {f1: p1, ..., fN: pN}
1181 for fp in field_pats {
1182 let field_ty = self.pat_ty(&fp.node.pat)?; // see (*2)
1183 let cmt_field = self.cat_field(pat, cmt.clone(), fp.node.name, field_ty);
1184 self.cat_pattern_(cmt_field, &fp.node.pat, op)?;
1188 PatKind::Binding(_, _, Some(ref subpat)) => {
1189 self.cat_pattern_(cmt, &subpat, op)?;
1192 PatKind::Tuple(ref subpats, ddpos) => {
1194 let expected_len = match self.pat_ty(&pat)?.sty {
1195 ty::TyTuple(ref tys) => tys.len(),
1196 ref ty => span_bug!(pat.span, "tuple pattern unexpected type {:?}", ty),
1198 for (i, subpat) in subpats.iter().enumerate_and_adjust(expected_len, ddpos) {
1199 let subpat_ty = self.pat_ty(&subpat)?; // see (*2)
1200 let subcmt = self.cat_imm_interior(pat, cmt.clone(), subpat_ty,
1201 InteriorField(PositionalField(i)));
1202 self.cat_pattern_(subcmt, &subpat, op)?;
1206 PatKind::Box(ref subpat) | PatKind::Ref(ref subpat, _) => {
1207 // box p1, &p1, &mut p1. we can ignore the mutability of
1208 // PatKind::Ref since that information is already contained
1210 let subcmt = self.cat_deref(pat, cmt, 0, None)?;
1211 self.cat_pattern_(subcmt, &subpat, op)?;
1214 PatKind::Vec(ref before, ref slice, ref after) => {
1215 let context = InteriorOffsetKind::Pattern;
1216 let elt_cmt = self.cat_index(pat, cmt, context)?;
1217 for before_pat in before {
1218 self.cat_pattern_(elt_cmt.clone(), &before_pat, op)?;
1220 if let Some(ref slice_pat) = *slice {
1221 self.cat_pattern_(elt_cmt.clone(), &slice_pat, op)?;
1223 for after_pat in after {
1224 self.cat_pattern_(elt_cmt.clone(), &after_pat, op)?;
1228 PatKind::Path(..) | PatKind::Binding(_, _, None) |
1229 PatKind::Lit(..) | PatKind::Range(..) | PatKind::Wild => {
1237 fn overloaded_method_return_ty(&self,
1238 method_ty: Ty<'tcx>)
1241 // When we process an overloaded `*` or `[]` etc, we often
1242 // need to extract the return type of the method. These method
1243 // types are generated by method resolution and always have
1244 // all late-bound regions fully instantiated, so we just want
1245 // to skip past the binder.
1246 self.tcx().no_late_bound_regions(&method_ty.fn_ret())
1251 #[derive(Clone, Debug)]
1252 pub enum Aliasability {
1253 FreelyAliasable(AliasableReason),
1255 ImmutableUnique(Box<Aliasability>),
1258 #[derive(Copy, Clone, Debug)]
1259 pub enum AliasableReason {
1261 AliasableClosure(ast::NodeId), // Aliasable due to capture Fn closure env
1263 UnaliasableImmutable, // Created as needed upon seeing ImmutableUnique
1268 impl<'tcx> cmt_<'tcx> {
1269 pub fn guarantor(&self) -> cmt<'tcx> {
1270 //! Returns `self` after stripping away any derefs or
1271 //! interior content. The return value is basically the `cmt` which
1272 //! determines how long the value in `self` remains live.
1275 Categorization::Rvalue(..) |
1276 Categorization::StaticItem |
1277 Categorization::Local(..) |
1278 Categorization::Deref(_, _, UnsafePtr(..)) |
1279 Categorization::Deref(_, _, BorrowedPtr(..)) |
1280 Categorization::Deref(_, _, Implicit(..)) |
1281 Categorization::Upvar(..) => {
1282 Rc::new((*self).clone())
1284 Categorization::Downcast(ref b, _) |
1285 Categorization::Interior(ref b, _) |
1286 Categorization::Deref(ref b, _, Unique) => {
1292 /// Returns `FreelyAliasable(_)` if this lvalue represents a freely aliasable pointer type.
1293 pub fn freely_aliasable(&self) -> Aliasability {
1294 // Maybe non-obvious: copied upvars can only be considered
1295 // non-aliasable in once closures, since any other kind can be
1296 // aliased and eventually recused.
1299 Categorization::Deref(ref b, _, BorrowedPtr(ty::MutBorrow, _)) |
1300 Categorization::Deref(ref b, _, Implicit(ty::MutBorrow, _)) |
1301 Categorization::Deref(ref b, _, BorrowedPtr(ty::UniqueImmBorrow, _)) |
1302 Categorization::Deref(ref b, _, Implicit(ty::UniqueImmBorrow, _)) |
1303 Categorization::Downcast(ref b, _) |
1304 Categorization::Interior(ref b, _) => {
1305 // Aliasability depends on base cmt
1306 b.freely_aliasable()
1309 Categorization::Deref(ref b, _, Unique) => {
1310 let sub = b.freely_aliasable();
1311 if b.mutbl.is_mutable() {
1312 // Aliasability depends on base cmt alone
1315 // Do not allow mutation through an immutable box.
1316 ImmutableUnique(Box::new(sub))
1320 Categorization::Rvalue(..) |
1321 Categorization::Local(..) |
1322 Categorization::Upvar(..) |
1323 Categorization::Deref(_, _, UnsafePtr(..)) => { // yes, it's aliasable, but...
1327 Categorization::StaticItem => {
1328 if self.mutbl.is_mutable() {
1329 FreelyAliasable(AliasableStaticMut)
1331 FreelyAliasable(AliasableStatic)
1335 Categorization::Deref(ref base, _, BorrowedPtr(ty::ImmBorrow, _)) |
1336 Categorization::Deref(ref base, _, Implicit(ty::ImmBorrow, _)) => {
1338 Categorization::Upvar(Upvar{ id, .. }) =>
1339 FreelyAliasable(AliasableClosure(id.closure_expr_id)),
1340 _ => FreelyAliasable(AliasableBorrowed)
1346 // Digs down through one or two layers of deref and grabs the cmt
1347 // for the upvar if a note indicates there is one.
1348 pub fn upvar(&self) -> Option<cmt<'tcx>> {
1350 NoteClosureEnv(..) | NoteUpvarRef(..) => {
1351 Some(match self.cat {
1352 Categorization::Deref(ref inner, _, _) => {
1354 Categorization::Deref(ref inner, _, _) => inner.clone(),
1355 Categorization::Upvar(..) => inner.clone(),
1367 pub fn descriptive_string(&self, tcx: TyCtxt) -> String {
1369 Categorization::StaticItem => {
1370 "static item".to_string()
1372 Categorization::Rvalue(..) => {
1373 "non-lvalue".to_string()
1375 Categorization::Local(vid) => {
1376 if tcx.map.is_argument(vid) {
1377 "argument".to_string()
1379 "local variable".to_string()
1382 Categorization::Deref(_, _, pk) => {
1383 let upvar = self.upvar();
1384 match upvar.as_ref().map(|i| &i.cat) {
1385 Some(&Categorization::Upvar(ref var)) => {
1392 format!("indexed content")
1395 format!("`Box` content")
1398 format!("dereference of raw pointer")
1400 BorrowedPtr(..) => {
1401 format!("borrowed content")
1407 Categorization::Interior(_, InteriorField(NamedField(_))) => {
1410 Categorization::Interior(_, InteriorField(PositionalField(_))) => {
1411 "anonymous field".to_string()
1413 Categorization::Interior(_, InteriorElement(InteriorOffsetKind::Index,
1415 Categorization::Interior(_, InteriorElement(InteriorOffsetKind::Index,
1417 "indexed content".to_string()
1419 Categorization::Interior(_, InteriorElement(InteriorOffsetKind::Pattern,
1421 Categorization::Interior(_, InteriorElement(InteriorOffsetKind::Pattern,
1423 "pattern-bound indexed content".to_string()
1425 Categorization::Upvar(ref var) => {
1428 Categorization::Downcast(ref cmt, _) => {
1429 cmt.descriptive_string(tcx)
1435 impl<'tcx> fmt::Debug for cmt_<'tcx> {
1436 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1437 write!(f, "{{{:?} id:{} m:{:?} ty:{:?}}}",
1445 impl<'tcx> fmt::Debug for Categorization<'tcx> {
1446 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1448 Categorization::StaticItem => write!(f, "static"),
1449 Categorization::Rvalue(r) => write!(f, "rvalue({:?})", r),
1450 Categorization::Local(id) => {
1451 let name = ty::tls::with(|tcx| tcx.local_var_name_str(id));
1452 write!(f, "local({})", name)
1454 Categorization::Upvar(upvar) => {
1455 write!(f, "upvar({:?})", upvar)
1457 Categorization::Deref(ref cmt, derefs, ptr) => {
1458 write!(f, "{:?}-{:?}{}->", cmt.cat, ptr, derefs)
1460 Categorization::Interior(ref cmt, interior) => {
1461 write!(f, "{:?}.{:?}", cmt.cat, interior)
1463 Categorization::Downcast(ref cmt, _) => {
1464 write!(f, "{:?}->(enum)", cmt.cat)
1470 pub fn ptr_sigil(ptr: PointerKind) -> &'static str {
1473 BorrowedPtr(ty::ImmBorrow, _) |
1474 Implicit(ty::ImmBorrow, _) => "&",
1475 BorrowedPtr(ty::MutBorrow, _) |
1476 Implicit(ty::MutBorrow, _) => "&mut",
1477 BorrowedPtr(ty::UniqueImmBorrow, _) |
1478 Implicit(ty::UniqueImmBorrow, _) => "&unique",
1479 UnsafePtr(_) => "*",
1483 impl fmt::Debug for PointerKind {
1484 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1486 Unique => write!(f, "Box"),
1487 BorrowedPtr(ty::ImmBorrow, ref r) |
1488 Implicit(ty::ImmBorrow, ref r) => {
1489 write!(f, "&{:?}", r)
1491 BorrowedPtr(ty::MutBorrow, ref r) |
1492 Implicit(ty::MutBorrow, ref r) => {
1493 write!(f, "&{:?} mut", r)
1495 BorrowedPtr(ty::UniqueImmBorrow, ref r) |
1496 Implicit(ty::UniqueImmBorrow, ref r) => {
1497 write!(f, "&{:?} uniq", r)
1499 UnsafePtr(_) => write!(f, "*")
1504 impl fmt::Debug for InteriorKind {
1505 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1507 InteriorField(NamedField(fld)) => write!(f, "{}", fld),
1508 InteriorField(PositionalField(i)) => write!(f, "#{}", i),
1509 InteriorElement(..) => write!(f, "[]"),
1514 impl fmt::Debug for Upvar {
1515 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1516 write!(f, "{:?}/{:?}", self.id, self.kind)
1520 impl fmt::Display for Upvar {
1521 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1522 let kind = match self.kind {
1523 ty::ClosureKind::Fn => "Fn",
1524 ty::ClosureKind::FnMut => "FnMut",
1525 ty::ClosureKind::FnOnce => "FnOnce",
1527 write!(f, "captured outer variable in an `{}` closure", kind)