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::*;
75 use middle::def_id::DefId;
76 use front::map as ast_map;
78 use middle::check_const;
80 use middle::ty::adjustment;
81 use middle::ty::{self, Ty};
83 use rustc_front::hir::{MutImmutable, MutMutable};
86 use syntax::codemap::Span;
91 #[derive(Clone, PartialEq)]
92 pub enum categorization<'tcx> {
93 cat_rvalue(ty::Region), // temporary val, argument is its scope
95 cat_upvar(Upvar), // upvar referenced by closure env
96 cat_local(ast::NodeId), // local variable
97 cat_deref(cmt<'tcx>, usize, PointerKind), // deref of a ptr
98 cat_interior(cmt<'tcx>, InteriorKind), // something interior: field, tuple, etc
99 cat_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(_) | ty::TyStr => {
232 // no deref of indexed content without supplying InteriorOffsetKind
233 if let Some(context) = context {
234 Ok(deref_interior(InteriorElement(context, element_kind(t))))
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<'t, 'a: 't, 'tcx : 'a> {
261 pub typer: &'t infer::InferCtxt<'a, 'tcx>,
264 pub type McResult<T> = Result<T, ()>;
266 impl MutabilityCategory {
267 pub fn from_mutbl(m: hir::Mutability) -> MutabilityCategory {
269 MutImmutable => McImmutable,
270 MutMutable => McDeclared
272 debug!("MutabilityCategory::{}({:?}) => {:?}",
273 "from_mutbl", m, ret);
277 pub fn from_borrow_kind(borrow_kind: ty::BorrowKind) -> MutabilityCategory {
278 let ret = match borrow_kind {
279 ty::ImmBorrow => McImmutable,
280 ty::UniqueImmBorrow => McImmutable,
281 ty::MutBorrow => McDeclared,
283 debug!("MutabilityCategory::{}({:?}) => {:?}",
284 "from_borrow_kind", borrow_kind, ret);
288 fn from_pointer_kind(base_mutbl: MutabilityCategory,
289 ptr: PointerKind) -> MutabilityCategory {
290 let ret = match ptr {
294 BorrowedPtr(borrow_kind, _) | Implicit(borrow_kind, _) => {
295 MutabilityCategory::from_borrow_kind(borrow_kind)
298 MutabilityCategory::from_mutbl(m)
301 debug!("MutabilityCategory::{}({:?}, {:?}) => {:?}",
302 "from_pointer_kind", base_mutbl, ptr, ret);
306 fn from_local(tcx: &ty::ctxt, id: ast::NodeId) -> MutabilityCategory {
307 let ret = match tcx.map.get(id) {
308 ast_map::NodeLocal(p) | ast_map::NodeArg(p) => match p.node {
309 hir::PatIdent(bind_mode, _, _) => {
310 if bind_mode == hir::BindByValue(hir::MutMutable) {
316 _ => tcx.sess.span_bug(p.span, "expected identifier pattern")
318 _ => tcx.sess.span_bug(tcx.map.span(id), "expected identifier pattern")
320 debug!("MutabilityCategory::{}(tcx, id={:?}) => {:?}",
321 "from_local", id, ret);
325 pub fn inherit(&self) -> MutabilityCategory {
326 let ret = match *self {
327 McImmutable => McImmutable,
328 McDeclared => McInherited,
329 McInherited => McInherited,
331 debug!("{:?}.inherit() => {:?}", self, ret);
335 pub fn is_mutable(&self) -> bool {
336 let ret = match *self {
337 McImmutable => false,
341 debug!("{:?}.is_mutable() => {:?}", self, ret);
345 pub fn is_immutable(&self) -> bool {
346 let ret = match *self {
348 McDeclared | McInherited => false
350 debug!("{:?}.is_immutable() => {:?}", self, ret);
354 pub fn to_user_str(&self) -> &'static str {
356 McDeclared | McInherited => "mutable",
357 McImmutable => "immutable",
362 impl<'t, 'a,'tcx> MemCategorizationContext<'t, 'a, 'tcx> {
363 pub fn new(typer: &'t infer::InferCtxt<'a, 'tcx>) -> MemCategorizationContext<'t, 'a, 'tcx> {
364 MemCategorizationContext { typer: typer }
367 fn tcx(&self) -> &'a ty::ctxt<'tcx> {
371 fn expr_ty(&self, expr: &hir::Expr) -> McResult<Ty<'tcx>> {
372 match self.typer.node_ty(expr.id) {
375 debug!("expr_ty({:?}) yielded Err", expr);
381 fn expr_ty_adjusted(&self, expr: &hir::Expr) -> McResult<Ty<'tcx>> {
382 let unadjusted_ty = try!(self.expr_ty(expr));
383 Ok(unadjusted_ty.adjust(
384 self.tcx(), expr.span, expr.id,
385 self.typer.adjustments().get(&expr.id),
386 |method_call| self.typer.node_method_ty(method_call)))
389 fn node_ty(&self, id: ast::NodeId) -> McResult<Ty<'tcx>> {
390 self.typer.node_ty(id)
393 fn pat_ty(&self, pat: &hir::Pat) -> McResult<Ty<'tcx>> {
394 let base_ty = try!(self.typer.node_ty(pat.id));
395 // FIXME (Issue #18207): This code detects whether we are
396 // looking at a `ref x`, and if so, figures out what the type
397 // *being borrowed* is. But ideally we would put in a more
398 // fundamental fix to this conflated use of the node id.
399 let ret_ty = match pat.node {
400 hir::PatIdent(hir::BindByRef(_), _, _) => {
401 // a bind-by-ref means that the base_ty will be the type of the ident itself,
402 // but what we want here is the type of the underlying value being borrowed.
403 // So peel off one-level, turning the &T into T.
404 match base_ty.builtin_deref(false, ty::NoPreference) {
406 None => { return Err(()); }
411 debug!("pat_ty(pat={:?}) base_ty={:?} ret_ty={:?}",
412 pat, base_ty, ret_ty);
416 pub fn cat_expr(&self, expr: &hir::Expr) -> McResult<cmt<'tcx>> {
417 match self.typer.adjustments().get(&expr.id) {
420 self.cat_expr_unadjusted(expr)
423 Some(adjustment) => {
425 adjustment::AdjustDerefRef(
426 adjustment::AutoDerefRef {
427 autoref: None, unsize: None, autoderefs, ..}) => {
428 // Equivalent to *expr or something similar.
429 self.cat_expr_autoderefd(expr, autoderefs)
432 adjustment::AdjustReifyFnPointer |
433 adjustment::AdjustUnsafeFnPointer |
434 adjustment::AdjustDerefRef(_) => {
435 debug!("cat_expr({:?}): {:?}",
438 // Result is an rvalue.
439 let expr_ty = try!(self.expr_ty_adjusted(expr));
440 Ok(self.cat_rvalue_node(expr.id(), expr.span(), expr_ty))
447 pub fn cat_expr_autoderefd(&self,
450 -> McResult<cmt<'tcx>> {
451 let mut cmt = try!(self.cat_expr_unadjusted(expr));
452 debug!("cat_expr_autoderefd: autoderefs={}, cmt={:?}",
455 for deref in 1..autoderefs + 1 {
456 cmt = try!(self.cat_deref(expr, cmt, deref, None));
461 pub fn cat_expr_unadjusted(&self, expr: &hir::Expr) -> McResult<cmt<'tcx>> {
462 debug!("cat_expr: id={} expr={:?}", expr.id, expr);
464 let expr_ty = try!(self.expr_ty(expr));
466 hir::ExprUnary(hir::UnDeref, ref e_base) => {
467 let base_cmt = try!(self.cat_expr(&**e_base));
468 self.cat_deref(expr, base_cmt, 0, None)
471 hir::ExprField(ref base, f_name) => {
472 let base_cmt = try!(self.cat_expr(&**base));
473 debug!("cat_expr(cat_field): id={} expr={:?} base={:?}",
477 Ok(self.cat_field(expr, base_cmt, f_name.node.name, expr_ty))
480 hir::ExprTupField(ref base, idx) => {
481 let base_cmt = try!(self.cat_expr(&**base));
482 Ok(self.cat_tup_field(expr, base_cmt, idx.node, expr_ty))
485 hir::ExprIndex(ref base, _) => {
486 let method_call = ty::MethodCall::expr(expr.id());
487 let context = InteriorOffsetKind::Index;
488 match self.typer.node_method_ty(method_call) {
490 // If this is an index implemented by a method call, then it
491 // will include an implicit deref of the result.
492 let ret_ty = self.overloaded_method_return_ty(method_ty);
494 // The index method always returns an `&T`, so
495 // dereference it to find the result type.
496 let elem_ty = match ret_ty.sty {
497 ty::TyRef(_, mt) => mt.ty,
499 debug!("cat_expr_unadjusted: return type of overloaded index is {:?}?",
505 // The call to index() returns a `&T` value, which
506 // is an rvalue. That is what we will be
508 let base_cmt = self.cat_rvalue_node(expr.id(), expr.span(), ret_ty);
509 self.cat_deref_common(expr, base_cmt, 1, elem_ty, Some(context), true)
512 self.cat_index(expr, try!(self.cat_expr(&**base)), context)
517 hir::ExprPath(..) => {
518 let def = self.tcx().def_map.borrow().get(&expr.id).unwrap().full_def();
519 self.cat_def(expr.id, expr.span, expr_ty, def)
522 hir::ExprAddrOf(..) | hir::ExprCall(..) |
523 hir::ExprAssign(..) | hir::ExprAssignOp(..) |
524 hir::ExprClosure(..) | hir::ExprRet(..) |
525 hir::ExprUnary(..) | hir::ExprRange(..) |
526 hir::ExprMethodCall(..) | hir::ExprCast(..) |
527 hir::ExprVec(..) | hir::ExprTup(..) | hir::ExprIf(..) |
528 hir::ExprBinary(..) | hir::ExprWhile(..) |
529 hir::ExprBlock(..) | hir::ExprLoop(..) | hir::ExprMatch(..) |
530 hir::ExprLit(..) | hir::ExprBreak(..) |
531 hir::ExprAgain(..) | hir::ExprStruct(..) | hir::ExprRepeat(..) |
532 hir::ExprInlineAsm(..) | hir::ExprBox(..) => {
533 Ok(self.cat_rvalue_node(expr.id(), expr.span(), expr_ty))
538 pub fn cat_def(&self,
543 -> McResult<cmt<'tcx>> {
544 debug!("cat_def: id={} expr={:?} def={:?}",
548 def::DefStruct(..) | def::DefVariant(..) | def::DefConst(..) |
549 def::DefAssociatedConst(..) | def::DefFn(..) | def::DefMethod(..) => {
550 Ok(self.cat_rvalue_node(id, span, expr_ty))
552 def::DefMod(_) | def::DefForeignMod(_) | def::DefUse(_) |
553 def::DefTrait(_) | def::DefTy(..) | def::DefPrimTy(_) |
554 def::DefTyParam(..) | def::DefRegion(_) |
555 def::DefLabel(_) | def::DefSelfTy(..) |
556 def::DefAssociatedTy(..) => {
567 def::DefStatic(_, mutbl) => {
572 mutbl: if mutbl { McDeclared } else { McImmutable},
578 def::DefUpvar(var_id, _, fn_node_id) => {
579 let ty = try!(self.node_ty(fn_node_id));
581 ty::TyClosure(closure_id, _) => {
582 match self.typer.closure_kind(closure_id) {
584 self.cat_upvar(id, span, var_id, fn_node_id, kind)
587 self.tcx().sess.span_bug(
589 &*format!("No closure kind for {:?}", closure_id));
594 self.tcx().sess.span_bug(
596 &format!("Upvar of non-closure {} - {:?}",
603 def::DefLocal(vid) => {
608 mutbl: MutabilityCategory::from_local(self.tcx(), vid),
616 // Categorize an upvar, complete with invisible derefs of closure
617 // environment and upvar reference as appropriate.
622 fn_node_id: ast::NodeId,
623 kind: ty::ClosureKind)
624 -> McResult<cmt<'tcx>>
626 // An upvar can have up to 3 components. We translate first to a
627 // `cat_upvar`, which is itself a fiction -- it represents the reference to the
628 // field from the environment.
630 // `cat_upvar`. Next, we add a deref through the implicit
631 // environment pointer with an anonymous free region 'env and
632 // appropriate borrow kind for closure kinds that take self by
633 // reference. Finally, if the upvar was captured
634 // by-reference, we add a deref through that reference. The
635 // region of this reference is an inference variable 'up that
636 // was previously generated and recorded in the upvar borrow
637 // map. The borrow kind bk is inferred by based on how the
640 // This results in the following table for concrete closure
644 // ---------------+----------------------+-------------------------------
645 // Fn | copied -> &'env | upvar -> &'env -> &'up bk
646 // FnMut | copied -> &'env mut | upvar -> &'env mut -> &'up bk
647 // FnOnce | copied | upvar -> &'up bk
649 let upvar_id = ty::UpvarId { var_id: var_id,
650 closure_expr_id: fn_node_id };
651 let var_ty = try!(self.node_ty(var_id));
653 // Mutability of original variable itself
654 let var_mutbl = MutabilityCategory::from_local(self.tcx(), var_id);
656 // Construct the upvar. This represents access to the field
657 // from the environment (perhaps we should eventually desugar
658 // this field further, but it will do for now).
659 let cmt_result = cmt_ {
662 cat: cat_upvar(Upvar {id: upvar_id, kind: kind}),
668 // If this is a `FnMut` or `Fn` closure, then the above is
669 // conceptually a `&mut` or `&` reference, so we have to add a
671 let cmt_result = match kind {
672 ty::FnOnceClosureKind => {
675 ty::FnMutClosureKind => {
676 self.env_deref(id, span, upvar_id, var_mutbl, ty::MutBorrow, cmt_result)
678 ty::FnClosureKind => {
679 self.env_deref(id, span, upvar_id, var_mutbl, ty::ImmBorrow, cmt_result)
683 // If this is a by-ref capture, then the upvar we loaded is
684 // actually a reference, so we have to add an implicit deref
686 let upvar_id = ty::UpvarId { var_id: var_id,
687 closure_expr_id: fn_node_id };
688 let upvar_capture = self.typer.upvar_capture(upvar_id).unwrap();
689 let cmt_result = match upvar_capture {
690 ty::UpvarCapture::ByValue => {
693 ty::UpvarCapture::ByRef(upvar_borrow) => {
694 let ptr = BorrowedPtr(upvar_borrow.kind, upvar_borrow.region);
698 cat: cat_deref(Rc::new(cmt_result), 0, ptr),
699 mutbl: MutabilityCategory::from_borrow_kind(upvar_borrow.kind),
701 note: NoteUpvarRef(upvar_id)
706 let ret = Rc::new(cmt_result);
707 debug!("cat_upvar ret={:?}", ret);
714 upvar_id: ty::UpvarId,
715 upvar_mutbl: MutabilityCategory,
716 env_borrow_kind: ty::BorrowKind,
717 cmt_result: cmt_<'tcx>)
720 // Look up the node ID of the closure body so we can construct
721 // a free region within it
723 let fn_expr = match self.tcx().map.find(upvar_id.closure_expr_id) {
724 Some(ast_map::NodeExpr(e)) => e,
729 hir::ExprClosure(_, _, ref body) => body.id,
734 // Region of environment pointer
735 let env_region = ty::ReFree(ty::FreeRegion {
736 // The environment of a closure is guaranteed to
737 // outlive any bindings introduced in the body of the
739 scope: self.tcx().region_maps.item_extent(fn_body_id),
740 bound_region: ty::BrEnv
743 let env_ptr = BorrowedPtr(env_borrow_kind, env_region);
745 let var_ty = cmt_result.ty;
747 // We need to add the env deref. This means
748 // that the above is actually immutable and
749 // has a ref type. However, nothing should
750 // actually look at the type, so we can get
751 // away with stuffing a `TyError` in there
752 // instead of bothering to construct a proper
754 let cmt_result = cmt_ {
756 ty: self.tcx().types.err,
760 let mut deref_mutbl = MutabilityCategory::from_borrow_kind(env_borrow_kind);
762 // Issue #18335. If variable is declared as immutable, override the
763 // mutability from the environment and substitute an `&T` anyway.
765 McImmutable => { deref_mutbl = McImmutable; }
766 McDeclared | McInherited => { }
772 cat: cat_deref(Rc::new(cmt_result), 0, env_ptr),
775 note: NoteClosureEnv(upvar_id)
778 debug!("env_deref ret {:?}", ret);
783 /// Returns the lifetime of a temporary created by expr with id `id`.
784 /// This could be `'static` if `id` is part of a constant expression.
785 pub fn temporary_scope(&self, id: ast::NodeId) -> ty::Region {
786 match self.typer.temporary_scope(id) {
787 Some(scope) => ty::ReScope(scope),
792 pub fn cat_rvalue_node(&self,
797 let qualif = self.tcx().const_qualif_map.borrow().get(&id).cloned()
798 .unwrap_or(check_const::ConstQualif::NOT_CONST);
800 // Only promote `[T; 0]` before an RFC for rvalue promotions
802 let qualif = match expr_ty.sty {
803 ty::TyArray(_, 0) => qualif,
804 _ => check_const::ConstQualif::NOT_CONST
807 // Compute maximum lifetime of this rvalue. This is 'static if
808 // we can promote to a constant, otherwise equal to enclosing temp
810 let re = if qualif.intersects(check_const::ConstQualif::NON_STATIC_BORROWS) {
811 self.temporary_scope(id)
815 let ret = self.cat_rvalue(id, span, re, expr_ty);
816 debug!("cat_rvalue_node ret {:?}", ret);
820 pub fn cat_rvalue(&self,
823 temp_scope: ty::Region,
824 expr_ty: Ty<'tcx>) -> cmt<'tcx> {
825 let ret = Rc::new(cmt_ {
828 cat:cat_rvalue(temp_scope),
833 debug!("cat_rvalue ret {:?}", ret);
837 pub fn cat_field<N:ast_node>(&self,
843 let ret = Rc::new(cmt_ {
846 mutbl: base_cmt.mutbl.inherit(),
847 cat: cat_interior(base_cmt, InteriorField(NamedField(f_name))),
851 debug!("cat_field ret {:?}", ret);
855 pub fn cat_tup_field<N:ast_node>(&self,
861 let ret = Rc::new(cmt_ {
864 mutbl: base_cmt.mutbl.inherit(),
865 cat: cat_interior(base_cmt, InteriorField(PositionalField(f_idx))),
869 debug!("cat_tup_field ret {:?}", ret);
873 fn cat_deref<N:ast_node>(&self,
877 deref_context: DerefKindContext)
878 -> McResult<cmt<'tcx>> {
879 let method_call = ty::MethodCall {
881 autoderef: deref_cnt as u32
883 let method_ty = self.typer.node_method_ty(method_call);
885 debug!("cat_deref: method_call={:?} method_ty={:?}",
886 method_call, method_ty.map(|ty| ty));
888 let base_cmt = match method_ty {
891 self.tcx().no_late_bound_regions(&method_ty.fn_ret()).unwrap().unwrap();
892 self.cat_rvalue_node(node.id(), node.span(), ref_ty)
896 let base_cmt_ty = base_cmt.ty;
897 match base_cmt_ty.builtin_deref(true, ty::NoPreference) {
899 let ret = self.cat_deref_common(node, base_cmt, deref_cnt,
902 /* implicit: */ false);
903 debug!("cat_deref ret {:?}", ret);
907 debug!("Explicit deref of non-derefable type: {:?}",
914 fn cat_deref_common<N:ast_node>(&self,
919 deref_context: DerefKindContext,
921 -> McResult<cmt<'tcx>>
923 let (m, cat) = match try!(deref_kind(base_cmt.ty, deref_context)) {
925 let ptr = if implicit {
927 BorrowedPtr(bk, r) => Implicit(bk, r),
928 _ => self.tcx().sess.span_bug(node.span(),
929 "Implicit deref of non-borrowed pointer")
934 // for unique ptrs, we inherit mutability from the
936 (MutabilityCategory::from_pointer_kind(base_cmt.mutbl, ptr),
937 cat_deref(base_cmt, deref_cnt, ptr))
939 deref_interior(interior) => {
940 (base_cmt.mutbl.inherit(), cat_interior(base_cmt, interior))
943 let ret = Rc::new(cmt_ {
951 debug!("cat_deref_common ret {:?}", ret);
955 pub fn cat_index<N:ast_node>(&self,
957 mut base_cmt: cmt<'tcx>,
958 context: InteriorOffsetKind)
959 -> McResult<cmt<'tcx>> {
960 //! Creates a cmt for an indexing operation (`[]`).
962 //! One subtle aspect of indexing that may not be
963 //! immediately obvious: for anything other than a fixed-length
964 //! vector, an operation like `x[y]` actually consists of two
965 //! disjoint (from the point of view of borrowck) operations.
966 //! The first is a deref of `x` to create a pointer `p` that points
967 //! at the first element in the array. The second operation is
968 //! an index which adds `y*sizeof(T)` to `p` to obtain the
969 //! pointer to `x[y]`. `cat_index` will produce a resulting
970 //! cmt containing both this deref and the indexing,
971 //! presuming that `base_cmt` is not of fixed-length type.
974 //! - `elt`: the AST node being indexed
975 //! - `base_cmt`: the cmt of `elt`
977 let method_call = ty::MethodCall::expr(elt.id());
978 let method_ty = self.typer.node_method_ty(method_call);
980 let element_ty = match method_ty {
982 let ref_ty = self.overloaded_method_return_ty(method_ty);
983 base_cmt = self.cat_rvalue_node(elt.id(), elt.span(), ref_ty);
985 // FIXME(#20649) -- why are we using the `self_ty` as the element type...?
986 let self_ty = method_ty.fn_sig().input(0);
987 self.tcx().no_late_bound_regions(&self_ty).unwrap()
990 match base_cmt.ty.builtin_index() {
999 let m = base_cmt.mutbl.inherit();
1000 let ret = interior(elt, base_cmt.clone(), base_cmt.ty,
1001 m, context, element_ty);
1002 debug!("cat_index ret {:?}", ret);
1005 fn interior<'tcx, N: ast_node>(elt: &N,
1008 mutbl: MutabilityCategory,
1009 context: InteriorOffsetKind,
1010 element_ty: Ty<'tcx>) -> cmt<'tcx>
1012 let interior_elem = InteriorElement(context, element_kind(vec_ty));
1016 cat:cat_interior(of_cmt, interior_elem),
1024 // Takes either a vec or a reference to a vec and returns the cmt for the
1026 fn deref_vec<N:ast_node>(&self,
1028 base_cmt: cmt<'tcx>,
1029 context: InteriorOffsetKind)
1030 -> McResult<cmt<'tcx>>
1032 let ret = match try!(deref_kind(base_cmt.ty, Some(context))) {
1034 // for unique ptrs, we inherit mutability from the
1035 // owning reference.
1036 let m = MutabilityCategory::from_pointer_kind(base_cmt.mutbl, ptr);
1038 // the deref is explicit in the resulting cmt
1042 cat:cat_deref(base_cmt.clone(), 0, ptr),
1044 ty: match base_cmt.ty.builtin_deref(false, ty::NoPreference) {
1046 None => self.tcx().sess.bug("Found non-derefable type")
1052 deref_interior(_) => {
1056 debug!("deref_vec ret {:?}", ret);
1060 /// Given a pattern P like: `[_, ..Q, _]`, where `vec_cmt` is the cmt for `P`, `slice_pat` is
1061 /// the pattern `Q`, returns:
1064 /// * the mutability and region of the slice `Q`
1066 /// These last two bits of info happen to be things that borrowck needs.
1067 pub fn cat_slice_pattern(&self,
1069 slice_pat: &hir::Pat)
1070 -> McResult<(cmt<'tcx>, hir::Mutability, ty::Region)> {
1071 let slice_ty = try!(self.node_ty(slice_pat.id));
1072 let (slice_mutbl, slice_r) = vec_slice_info(self.tcx(),
1075 let context = InteriorOffsetKind::Pattern;
1076 let cmt_vec = try!(self.deref_vec(slice_pat, vec_cmt, context));
1077 let cmt_slice = try!(self.cat_index(slice_pat, cmt_vec, context));
1078 return Ok((cmt_slice, slice_mutbl, slice_r));
1080 /// In a pattern like [a, b, ..c], normally `c` has slice type, but if you have [a, b,
1081 /// ..ref c], then the type of `ref c` will be `&&[]`, so to extract the slice details we
1082 /// have to recurse through rptrs.
1083 fn vec_slice_info(tcx: &ty::ctxt,
1086 -> (hir::Mutability, ty::Region) {
1087 match slice_ty.sty {
1088 ty::TyRef(r, ref mt) => match mt.ty.sty {
1089 ty::TySlice(_) => (mt.mutbl, *r),
1090 _ => vec_slice_info(tcx, pat, mt.ty),
1094 tcx.sess.span_bug(pat.span,
1095 "type of slice pattern is not a slice");
1101 pub fn cat_imm_interior<N:ast_node>(&self,
1103 base_cmt: cmt<'tcx>,
1104 interior_ty: Ty<'tcx>,
1105 interior: InteriorKind)
1107 let ret = Rc::new(cmt_ {
1110 mutbl: base_cmt.mutbl.inherit(),
1111 cat: cat_interior(base_cmt, interior),
1115 debug!("cat_imm_interior ret={:?}", ret);
1119 pub fn cat_downcast<N:ast_node>(&self,
1121 base_cmt: cmt<'tcx>,
1122 downcast_ty: Ty<'tcx>,
1125 let ret = Rc::new(cmt_ {
1128 mutbl: base_cmt.mutbl.inherit(),
1129 cat: cat_downcast(base_cmt, variant_did),
1133 debug!("cat_downcast ret={:?}", ret);
1137 pub fn cat_pattern<F>(&self, cmt: cmt<'tcx>, pat: &hir::Pat, mut op: F) -> McResult<()>
1138 where F: FnMut(&MemCategorizationContext<'t, 'a, 'tcx>, cmt<'tcx>, &hir::Pat),
1140 self.cat_pattern_(cmt, pat, &mut op)
1143 // FIXME(#19596) This is a workaround, but there should be a better way to do this
1144 fn cat_pattern_<F>(&self, cmt: cmt<'tcx>, pat: &hir::Pat, op: &mut F)
1146 where F : FnMut(&MemCategorizationContext<'t, 'a, 'tcx>, cmt<'tcx>, &hir::Pat),
1148 // Here, `cmt` is the categorization for the value being
1149 // matched and pat is the pattern it is being matched against.
1151 // In general, the way that this works is that we walk down
1152 // the pattern, constructing a cmt that represents the path
1153 // that will be taken to reach the value being matched.
1155 // When we encounter named bindings, we take the cmt that has
1156 // been built up and pass it off to guarantee_valid() so that
1157 // we can be sure that the binding will remain valid for the
1158 // duration of the arm.
1160 // (*2) There is subtlety concerning the correspondence between
1161 // pattern ids and types as compared to *expression* ids and
1162 // types. This is explained briefly. on the definition of the
1163 // type `cmt`, so go off and read what it says there, then
1164 // come back and I'll dive into a bit more detail here. :) OK,
1167 // In general, the id of the cmt should be the node that
1168 // "produces" the value---patterns aren't executable code
1169 // exactly, but I consider them to "execute" when they match a
1170 // value, and I consider them to produce the value that was
1171 // matched. So if you have something like:
1178 // In this case, the cmt and the relevant ids would be:
1180 // CMT Id Type of Id Type of cmt
1183 // ^~~~~~~^ `x` from discr @@int @@int
1184 // ^~~~~~~~~~^ `@@y` pattern node @@int @int
1185 // ^~~~~~~~~~~~~^ `@y` pattern node @int int
1187 // You can see that the types of the id and the cmt are in
1188 // sync in the first line, because that id is actually the id
1189 // of an expression. But once we get to pattern ids, the types
1190 // step out of sync again. So you'll see below that we always
1191 // get the type of the *subpattern* and use that.
1193 debug!("cat_pattern: {:?} cmt={:?}",
1197 (*op)(self, cmt.clone(), pat);
1199 let opt_def = self.tcx().def_map.borrow().get(&pat.id).map(|d| d.full_def());
1201 // Note: This goes up here (rather than within the PatEnum arm
1202 // alone) because struct patterns can refer to struct types or
1203 // to struct variants within enums.
1204 let cmt = match opt_def {
1205 Some(def::DefVariant(enum_did, variant_did, _))
1206 // univariant enums do not need downcasts
1207 if !self.tcx().lookup_adt_def(enum_did).is_univariant() => {
1208 self.cat_downcast(pat, cmt.clone(), cmt.ty, variant_did)
1214 hir::PatWild(_) => {
1218 hir::PatEnum(_, None) => {
1221 hir::PatEnum(_, Some(ref subpats)) => {
1223 Some(def::DefVariant(..)) => {
1225 for (i, subpat) in subpats.iter().enumerate() {
1226 let subpat_ty = try!(self.pat_ty(&**subpat)); // see (*2)
1229 self.cat_imm_interior(
1230 pat, cmt.clone(), subpat_ty,
1231 InteriorField(PositionalField(i)));
1233 try!(self.cat_pattern_(subcmt, &**subpat, op));
1236 Some(def::DefStruct(..)) => {
1237 for (i, subpat) in subpats.iter().enumerate() {
1238 let subpat_ty = try!(self.pat_ty(&**subpat)); // see (*2)
1240 self.cat_imm_interior(
1241 pat, cmt.clone(), subpat_ty,
1242 InteriorField(PositionalField(i)));
1243 try!(self.cat_pattern_(cmt_field, &**subpat, op));
1246 Some(def::DefConst(..)) | Some(def::DefAssociatedConst(..)) => {
1247 for subpat in subpats {
1248 try!(self.cat_pattern_(cmt.clone(), &**subpat, op));
1252 self.tcx().sess.span_bug(
1254 "enum pattern didn't resolve to enum or struct");
1259 hir::PatQPath(..) => {
1260 // Lone constant: ignore
1263 hir::PatIdent(_, _, Some(ref subpat)) => {
1264 try!(self.cat_pattern_(cmt, &**subpat, op));
1267 hir::PatIdent(_, _, None) => {
1268 // nullary variant or identifier: ignore
1271 hir::PatStruct(_, ref field_pats, _) => {
1272 // {f1: p1, ..., fN: pN}
1273 for fp in field_pats {
1274 let field_ty = try!(self.pat_ty(&*fp.node.pat)); // see (*2)
1275 let cmt_field = self.cat_field(pat, cmt.clone(), fp.node.ident.name, field_ty);
1276 try!(self.cat_pattern_(cmt_field, &*fp.node.pat, op));
1280 hir::PatTup(ref subpats) => {
1282 for (i, subpat) in subpats.iter().enumerate() {
1283 let subpat_ty = try!(self.pat_ty(&**subpat)); // see (*2)
1285 self.cat_imm_interior(
1286 pat, cmt.clone(), subpat_ty,
1287 InteriorField(PositionalField(i)));
1288 try!(self.cat_pattern_(subcmt, &**subpat, op));
1292 hir::PatBox(ref subpat) | hir::PatRegion(ref subpat, _) => {
1293 // box p1, &p1, &mut p1. we can ignore the mutability of
1294 // PatRegion since that information is already contained
1296 let subcmt = try!(self.cat_deref(pat, cmt, 0, None));
1297 try!(self.cat_pattern_(subcmt, &**subpat, op));
1300 hir::PatVec(ref before, ref slice, ref after) => {
1301 let context = InteriorOffsetKind::Pattern;
1302 let vec_cmt = try!(self.deref_vec(pat, cmt, context));
1303 let elt_cmt = try!(self.cat_index(pat, vec_cmt, context));
1304 for before_pat in before {
1305 try!(self.cat_pattern_(elt_cmt.clone(), &**before_pat, op));
1307 if let Some(ref slice_pat) = *slice {
1308 let slice_ty = try!(self.pat_ty(&**slice_pat));
1309 let slice_cmt = self.cat_rvalue_node(pat.id(), pat.span(), slice_ty);
1310 try!(self.cat_pattern_(slice_cmt, &**slice_pat, op));
1312 for after_pat in after {
1313 try!(self.cat_pattern_(elt_cmt.clone(), &**after_pat, op));
1317 hir::PatLit(_) | hir::PatRange(_, _) => {
1325 fn overloaded_method_return_ty(&self,
1326 method_ty: Ty<'tcx>)
1329 // When we process an overloaded `*` or `[]` etc, we often
1330 // need to extract the return type of the method. These method
1331 // types are generated by method resolution and always have
1332 // all late-bound regions fully instantiated, so we just want
1333 // to skip past the binder.
1334 self.tcx().no_late_bound_regions(&method_ty.fn_ret())
1336 .unwrap() // overloaded ops do not diverge, either
1340 #[derive(Clone, Debug)]
1341 pub enum Aliasability {
1342 FreelyAliasable(AliasableReason),
1344 ImmutableUnique(Box<Aliasability>),
1347 #[derive(Copy, Clone, Debug)]
1348 pub enum AliasableReason {
1350 AliasableClosure(ast::NodeId), // Aliasable due to capture Fn closure env
1352 UnaliasableImmutable, // Created as needed upon seeing ImmutableUnique
1357 impl<'tcx> cmt_<'tcx> {
1358 pub fn guarantor(&self) -> cmt<'tcx> {
1359 //! Returns `self` after stripping away any derefs or
1360 //! interior content. The return value is basically the `cmt` which
1361 //! determines how long the value in `self` remains live.
1367 cat_deref(_, _, UnsafePtr(..)) |
1368 cat_deref(_, _, BorrowedPtr(..)) |
1369 cat_deref(_, _, Implicit(..)) |
1371 Rc::new((*self).clone())
1373 cat_downcast(ref b, _) |
1374 cat_interior(ref b, _) |
1375 cat_deref(ref b, _, Unique) => {
1381 /// Returns `FreelyAliasable(_)` if this lvalue represents a freely aliasable pointer type.
1382 pub fn freely_aliasable(&self, ctxt: &ty::ctxt<'tcx>)
1384 // Maybe non-obvious: copied upvars can only be considered
1385 // non-aliasable in once closures, since any other kind can be
1386 // aliased and eventually recused.
1389 cat_deref(ref b, _, BorrowedPtr(ty::MutBorrow, _)) |
1390 cat_deref(ref b, _, Implicit(ty::MutBorrow, _)) |
1391 cat_deref(ref b, _, BorrowedPtr(ty::UniqueImmBorrow, _)) |
1392 cat_deref(ref b, _, Implicit(ty::UniqueImmBorrow, _)) |
1393 cat_downcast(ref b, _) |
1394 cat_interior(ref b, _) => {
1395 // Aliasability depends on base cmt
1396 b.freely_aliasable(ctxt)
1399 cat_deref(ref b, _, Unique) => {
1400 let sub = b.freely_aliasable(ctxt);
1401 if b.mutbl.is_mutable() {
1402 // Aliasability depends on base cmt alone
1405 // Do not allow mutation through an immutable box.
1406 ImmutableUnique(Box::new(sub))
1413 cat_deref(_, _, UnsafePtr(..)) => { // yes, it's aliasable, but...
1417 cat_static_item(..) => {
1418 if self.mutbl.is_mutable() {
1419 FreelyAliasable(AliasableStaticMut)
1421 FreelyAliasable(AliasableStatic)
1425 cat_deref(ref base, _, BorrowedPtr(ty::ImmBorrow, _)) |
1426 cat_deref(ref base, _, Implicit(ty::ImmBorrow, _)) => {
1428 cat_upvar(Upvar{ id, .. }) =>
1429 FreelyAliasable(AliasableClosure(id.closure_expr_id)),
1430 _ => FreelyAliasable(AliasableBorrowed)
1436 // Digs down through one or two layers of deref and grabs the cmt
1437 // for the upvar if a note indicates there is one.
1438 pub fn upvar(&self) -> Option<cmt<'tcx>> {
1440 NoteClosureEnv(..) | NoteUpvarRef(..) => {
1441 Some(match self.cat {
1442 cat_deref(ref inner, _, _) => {
1444 cat_deref(ref inner, _, _) => inner.clone(),
1445 cat_upvar(..) => inner.clone(),
1457 pub fn descriptive_string(&self, tcx: &ty::ctxt) -> String {
1459 cat_static_item => {
1460 "static item".to_string()
1463 "non-lvalue".to_string()
1466 match tcx.map.find(vid) {
1467 Some(ast_map::NodeArg(_)) => {
1468 "argument".to_string()
1470 _ => "local variable".to_string()
1473 cat_deref(_, _, pk) => {
1474 let upvar = self.upvar();
1475 match upvar.as_ref().map(|i| &i.cat) {
1476 Some(&cat_upvar(ref var)) => {
1479 Some(_) => unreachable!(),
1483 format!("indexed content")
1486 format!("`Box` content")
1489 format!("dereference of raw pointer")
1491 BorrowedPtr(..) => {
1492 format!("borrowed content")
1498 cat_interior(_, InteriorField(NamedField(_))) => {
1501 cat_interior(_, InteriorField(PositionalField(_))) => {
1502 "anonymous field".to_string()
1504 cat_interior(_, InteriorElement(InteriorOffsetKind::Index,
1506 cat_interior(_, InteriorElement(InteriorOffsetKind::Index,
1508 "indexed content".to_string()
1510 cat_interior(_, InteriorElement(InteriorOffsetKind::Pattern,
1512 cat_interior(_, InteriorElement(InteriorOffsetKind::Pattern,
1514 "pattern-bound indexed content".to_string()
1516 cat_upvar(ref var) => {
1519 cat_downcast(ref cmt, _) => {
1520 cmt.descriptive_string(tcx)
1526 impl<'tcx> fmt::Debug for cmt_<'tcx> {
1527 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1528 write!(f, "{{{:?} id:{} m:{:?} ty:{:?}}}",
1536 impl<'tcx> fmt::Debug for categorization<'tcx> {
1537 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1539 cat_static_item => write!(f, "static"),
1540 cat_rvalue(r) => write!(f, "rvalue({:?})", r),
1542 let name = ty::tls::with(|tcx| tcx.local_var_name_str(id));
1543 write!(f, "local({})", name)
1545 cat_upvar(upvar) => {
1546 write!(f, "upvar({:?})", upvar)
1548 cat_deref(ref cmt, derefs, ptr) => {
1549 write!(f, "{:?}-{:?}{}->", cmt.cat, ptr, derefs)
1551 cat_interior(ref cmt, interior) => {
1552 write!(f, "{:?}.{:?}", cmt.cat, interior)
1554 cat_downcast(ref cmt, _) => {
1555 write!(f, "{:?}->(enum)", cmt.cat)
1561 pub fn ptr_sigil(ptr: PointerKind) -> &'static str {
1564 BorrowedPtr(ty::ImmBorrow, _) |
1565 Implicit(ty::ImmBorrow, _) => "&",
1566 BorrowedPtr(ty::MutBorrow, _) |
1567 Implicit(ty::MutBorrow, _) => "&mut",
1568 BorrowedPtr(ty::UniqueImmBorrow, _) |
1569 Implicit(ty::UniqueImmBorrow, _) => "&unique",
1570 UnsafePtr(_) => "*",
1574 impl fmt::Debug for PointerKind {
1575 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1577 Unique => write!(f, "Box"),
1578 BorrowedPtr(ty::ImmBorrow, ref r) |
1579 Implicit(ty::ImmBorrow, ref r) => {
1580 write!(f, "&{:?}", r)
1582 BorrowedPtr(ty::MutBorrow, ref r) |
1583 Implicit(ty::MutBorrow, ref r) => {
1584 write!(f, "&{:?} mut", r)
1586 BorrowedPtr(ty::UniqueImmBorrow, ref r) |
1587 Implicit(ty::UniqueImmBorrow, ref r) => {
1588 write!(f, "&{:?} uniq", r)
1590 UnsafePtr(_) => write!(f, "*")
1595 impl fmt::Debug for InteriorKind {
1596 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1598 InteriorField(NamedField(fld)) => write!(f, "{}", fld),
1599 InteriorField(PositionalField(i)) => write!(f, "#{}", i),
1600 InteriorElement(..) => write!(f, "[]"),
1605 fn element_kind(t: Ty) -> ElementKind {
1607 ty::TyRef(_, ty::TypeAndMut{ty, ..}) |
1608 ty::TyBox(ty) => match ty.sty {
1609 ty::TySlice(_) => VecElement,
1612 ty::TyArray(..) | ty::TySlice(_) => VecElement,
1617 impl fmt::Debug for Upvar {
1618 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1619 write!(f, "{:?}/{:?}", self.id, self.kind)
1623 impl fmt::Display for Upvar {
1624 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1625 let kind = match self.kind {
1626 ty::FnClosureKind => "Fn",
1627 ty::FnMutClosureKind => "FnMut",
1628 ty::FnOnceClosureKind => "FnOnce",
1630 write!(f, "captured outer variable in an `{}` closure", kind)