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::MutabilityCategory::*;
67 pub use self::AliasableReason::*;
68 pub use self::Note::*;
70 use self::Aliasability::*;
72 use middle::region::RegionMaps;
73 use hir::def_id::DefId;
74 use hir::map as hir_map;
76 use hir::def::{Def, CtorKind};
78 use ty::{self, Ty, TyCtxt};
80 use hir::{MutImmutable, MutMutable, PatKind};
81 use hir::pat_util::EnumerateAndAdjustIterator;
89 #[derive(Clone, PartialEq)]
90 pub enum Categorization<'tcx> {
91 Rvalue(ty::Region<'tcx>), // temporary val, argument is its scope
93 Upvar(Upvar), // upvar referenced by closure env
94 Local(ast::NodeId), // local variable
95 Deref(cmt<'tcx>, PointerKind<'tcx>), // deref of a ptr
96 Interior(cmt<'tcx>, InteriorKind), // something interior: field, tuple, etc
97 Downcast(cmt<'tcx>, DefId), // selects a particular enum variant (*1)
99 // (*1) downcast is only required if the enum has more than one variant
102 // Represents any kind of upvar
103 #[derive(Clone, Copy, PartialEq)]
106 pub kind: ty::ClosureKind
109 // different kinds of pointers:
110 #[derive(Clone, Copy, PartialEq, Eq, Hash)]
111 pub enum PointerKind<'tcx> {
116 BorrowedPtr(ty::BorrowKind, ty::Region<'tcx>),
119 UnsafePtr(hir::Mutability),
121 /// Implicit deref of the `&T` that results from an overloaded index `[]`.
122 Implicit(ty::BorrowKind, ty::Region<'tcx>),
125 // We use the term "interior" to mean "something reachable from the
126 // base without a pointer dereference", e.g. a field
127 #[derive(Clone, Copy, PartialEq, Eq, Hash)]
128 pub enum InteriorKind {
129 InteriorField(FieldName),
130 InteriorElement(InteriorOffsetKind),
133 #[derive(Clone, Copy, PartialEq, Eq, Hash, Debug)]
135 NamedField(ast::Name),
136 PositionalField(usize)
139 #[derive(Clone, Copy, PartialEq, Eq, Hash, Debug)]
140 pub enum InteriorOffsetKind {
141 Index, // e.g. `array_expr[index_expr]`
142 Pattern, // e.g. `fn foo([_, a, _, _]: [A; 4]) { ... }`
145 #[derive(Clone, Copy, PartialEq, Eq, Hash, Debug)]
146 pub enum MutabilityCategory {
147 McImmutable, // Immutable.
148 McDeclared, // Directly declared as mutable.
149 McInherited, // Inherited from the fact that owner is mutable.
152 // A note about the provenance of a `cmt`. This is used for
153 // special-case handling of upvars such as mutability inference.
154 // Upvar categorization can generate a variable number of nested
155 // derefs. The note allows detecting them without deep pattern
156 // matching on the categorization.
157 #[derive(Clone, Copy, PartialEq, Debug)]
159 NoteClosureEnv(ty::UpvarId), // Deref through closure env
160 NoteUpvarRef(ty::UpvarId), // Deref through by-ref upvar
161 NoteNone // Nothing special
164 // `cmt`: "Category, Mutability, and Type".
166 // a complete categorization of a value indicating where it originated
167 // and how it is located, as well as the mutability of the memory in
168 // which the value is stored.
170 // *WARNING* The field `cmt.type` is NOT necessarily the same as the
171 // result of `node_id_to_type(cmt.id)`. This is because the `id` is
172 // always the `id` of the node producing the type; in an expression
173 // like `*x`, the type of this deref node is the deref'd type (`T`),
174 // but in a pattern like `@x`, the `@x` pattern is again a
175 // dereference, but its type is the type *before* the dereference
176 // (`@T`). So use `cmt.ty` to find the type of the value in a consistent
177 // fashion. For more details, see the method `cat_pattern`
178 #[derive(Clone, PartialEq)]
179 pub struct cmt_<'tcx> {
180 pub id: ast::NodeId, // id of expr/pat producing this value
181 pub span: Span, // span of same expr/pat
182 pub cat: Categorization<'tcx>, // categorization of expr
183 pub mutbl: MutabilityCategory, // mutability of expr as lvalue
184 pub ty: Ty<'tcx>, // type of the expr (*see WARNING above*)
185 pub note: Note, // Note about the provenance of this cmt
188 pub type cmt<'tcx> = Rc<cmt_<'tcx>>;
190 pub enum ImmutabilityBlame<'tcx> {
191 ImmLocal(ast::NodeId),
192 ClosureEnv(ast::NodeId),
193 LocalDeref(ast::NodeId),
194 AdtFieldDeref(&'tcx ty::AdtDef, &'tcx ty::FieldDef)
197 impl<'tcx> cmt_<'tcx> {
198 fn resolve_field(&self, field_name: FieldName) -> Option<(&'tcx ty::AdtDef, &'tcx ty::FieldDef)>
200 let adt_def = match self.ty.sty {
201 ty::TyAdt(def, _) => def,
202 ty::TyTuple(..) => return None,
203 // closures get `Categorization::Upvar` rather than `Categorization::Interior`
204 _ => bug!("interior cmt {:?} is not an ADT", self)
206 let variant_def = match self.cat {
207 Categorization::Downcast(_, variant_did) => {
208 adt_def.variant_with_id(variant_did)
211 assert!(adt_def.is_univariant());
215 let field_def = match field_name {
216 NamedField(name) => variant_def.field_named(name),
217 PositionalField(idx) => &variant_def.fields[idx]
219 Some((adt_def, field_def))
222 pub fn immutability_blame(&self) -> Option<ImmutabilityBlame<'tcx>> {
224 Categorization::Deref(ref base_cmt, BorrowedPtr(ty::ImmBorrow, _)) |
225 Categorization::Deref(ref base_cmt, Implicit(ty::ImmBorrow, _)) => {
226 // try to figure out where the immutable reference came from
228 Categorization::Local(node_id) =>
229 Some(ImmutabilityBlame::LocalDeref(node_id)),
230 Categorization::Interior(ref base_cmt, InteriorField(field_name)) => {
231 base_cmt.resolve_field(field_name).map(|(adt_def, field_def)| {
232 ImmutabilityBlame::AdtFieldDeref(adt_def, field_def)
235 Categorization::Upvar(Upvar { id, .. }) => {
236 if let NoteClosureEnv(..) = self.note {
237 Some(ImmutabilityBlame::ClosureEnv(id.closure_expr_id))
245 Categorization::Local(node_id) => {
246 Some(ImmutabilityBlame::ImmLocal(node_id))
248 Categorization::Rvalue(..) |
249 Categorization::Upvar(..) |
250 Categorization::Deref(_, UnsafePtr(..)) => {
251 // This should not be reachable up to inference limitations.
254 Categorization::Interior(ref base_cmt, _) |
255 Categorization::Downcast(ref base_cmt, _) |
256 Categorization::Deref(ref base_cmt, _) => {
257 base_cmt.immutability_blame()
259 Categorization::StaticItem => {
260 // Do we want to do something here?
268 fn id(&self) -> ast::NodeId;
269 fn span(&self) -> Span;
272 impl ast_node for hir::Expr {
273 fn id(&self) -> ast::NodeId { self.id }
274 fn span(&self) -> Span { self.span }
277 impl ast_node for hir::Pat {
278 fn id(&self) -> ast::NodeId { self.id }
279 fn span(&self) -> Span { self.span }
283 pub struct MemCategorizationContext<'a, 'gcx: 'a+'tcx, 'tcx: 'a> {
284 pub infcx: &'a InferCtxt<'a, 'gcx, 'tcx>,
285 pub region_maps: &'a RegionMaps,
288 pub type McResult<T> = Result<T, ()>;
290 impl MutabilityCategory {
291 pub fn from_mutbl(m: hir::Mutability) -> MutabilityCategory {
293 MutImmutable => McImmutable,
294 MutMutable => McDeclared
296 debug!("MutabilityCategory::{}({:?}) => {:?}",
297 "from_mutbl", m, ret);
301 pub fn from_borrow_kind(borrow_kind: ty::BorrowKind) -> MutabilityCategory {
302 let ret = match borrow_kind {
303 ty::ImmBorrow => McImmutable,
304 ty::UniqueImmBorrow => McImmutable,
305 ty::MutBorrow => McDeclared,
307 debug!("MutabilityCategory::{}({:?}) => {:?}",
308 "from_borrow_kind", borrow_kind, ret);
312 fn from_pointer_kind(base_mutbl: MutabilityCategory,
313 ptr: PointerKind) -> MutabilityCategory {
314 let ret = match ptr {
318 BorrowedPtr(borrow_kind, _) | Implicit(borrow_kind, _) => {
319 MutabilityCategory::from_borrow_kind(borrow_kind)
322 MutabilityCategory::from_mutbl(m)
325 debug!("MutabilityCategory::{}({:?}, {:?}) => {:?}",
326 "from_pointer_kind", base_mutbl, ptr, ret);
330 fn from_local(tcx: TyCtxt, id: ast::NodeId) -> MutabilityCategory {
331 let ret = match tcx.hir.get(id) {
332 hir_map::NodeLocal(p) => match p.node {
333 PatKind::Binding(bind_mode, ..) => {
334 if bind_mode == hir::BindByValue(hir::MutMutable) {
340 _ => span_bug!(p.span, "expected identifier pattern")
342 _ => span_bug!(tcx.hir.span(id), "expected identifier pattern")
344 debug!("MutabilityCategory::{}(tcx, id={:?}) => {:?}",
345 "from_local", id, ret);
349 pub fn inherit(&self) -> MutabilityCategory {
350 let ret = match *self {
351 McImmutable => McImmutable,
352 McDeclared => McInherited,
353 McInherited => McInherited,
355 debug!("{:?}.inherit() => {:?}", self, ret);
359 pub fn is_mutable(&self) -> bool {
360 let ret = match *self {
361 McImmutable => false,
365 debug!("{:?}.is_mutable() => {:?}", self, ret);
369 pub fn is_immutable(&self) -> bool {
370 let ret = match *self {
372 McDeclared | McInherited => false
374 debug!("{:?}.is_immutable() => {:?}", self, ret);
378 pub fn to_user_str(&self) -> &'static str {
380 McDeclared | McInherited => "mutable",
381 McImmutable => "immutable",
386 impl<'a, 'gcx, 'tcx> MemCategorizationContext<'a, 'gcx, 'tcx> {
387 /// Context should be the `DefId` we use to fetch region-maps.
388 pub fn new(infcx: &'a InferCtxt<'a, 'gcx, 'tcx>,
389 region_maps: &'a RegionMaps)
390 -> MemCategorizationContext<'a, 'gcx, 'tcx> {
391 MemCategorizationContext { infcx, region_maps }
394 fn tcx(&self) -> TyCtxt<'a, 'gcx, 'tcx> {
398 fn expr_ty(&self, expr: &hir::Expr) -> McResult<Ty<'tcx>> {
399 match self.infcx.node_ty(expr.id) {
402 debug!("expr_ty({:?}) yielded Err", expr);
408 fn expr_ty_adjusted(&self, expr: &hir::Expr) -> McResult<Ty<'tcx>> {
409 self.infcx.expr_ty_adjusted(expr)
412 fn node_ty(&self, id: ast::NodeId) -> McResult<Ty<'tcx>> {
413 self.infcx.node_ty(id)
416 fn pat_ty(&self, pat: &hir::Pat) -> McResult<Ty<'tcx>> {
417 let base_ty = self.infcx.node_ty(pat.id)?;
418 // FIXME (Issue #18207): This code detects whether we are
419 // looking at a `ref x`, and if so, figures out what the type
420 // *being borrowed* is. But ideally we would put in a more
421 // fundamental fix to this conflated use of the node id.
422 let ret_ty = match pat.node {
423 PatKind::Binding(hir::BindByRef(_), ..) => {
424 // a bind-by-ref means that the base_ty will be the type of the ident itself,
425 // but what we want here is the type of the underlying value being borrowed.
426 // So peel off one-level, turning the &T into T.
427 match base_ty.builtin_deref(false, ty::NoPreference) {
430 debug!("By-ref binding of non-derefable type {:?}", base_ty);
437 debug!("pat_ty(pat={:?}) base_ty={:?} ret_ty={:?}",
438 pat, base_ty, ret_ty);
442 pub fn cat_expr(&self, expr: &hir::Expr) -> McResult<cmt<'tcx>> {
443 // This recursion helper avoids going through *too many*
444 // adjustments, since *only* non-overloaded deref recurses.
445 fn helper<'a, 'gcx, 'tcx>(mc: &MemCategorizationContext<'a, 'gcx, 'tcx>,
447 adjustments: &[adjustment::Adjustment<'tcx>])
448 -> McResult<cmt<'tcx>> {
449 match adjustments.split_last() {
450 None => mc.cat_expr_unadjusted(expr),
451 Some((adjustment, previous)) => {
452 mc.cat_expr_adjusted_with(expr, || helper(mc, expr, previous), adjustment)
457 helper(self, expr, self.infcx.tables.borrow().expr_adjustments(expr))
460 pub fn cat_expr_adjusted(&self, expr: &hir::Expr,
462 adjustment: &adjustment::Adjustment<'tcx>)
463 -> McResult<cmt<'tcx>> {
464 self.cat_expr_adjusted_with(expr, || Ok(previous), adjustment)
467 fn cat_expr_adjusted_with<F>(&self, expr: &hir::Expr,
469 adjustment: &adjustment::Adjustment<'tcx>)
470 -> McResult<cmt<'tcx>>
471 where F: FnOnce() -> McResult<cmt<'tcx>>
473 debug!("cat_expr_adjusted_with({:?}): {:?}", adjustment, expr);
474 let target = self.infcx.resolve_type_vars_if_possible(&adjustment.target);
475 match adjustment.kind {
476 adjustment::Adjust::Deref(overloaded) => {
477 // Equivalent to *expr or something similar.
478 let base = if let Some(deref) = overloaded {
479 let ref_ty = self.tcx().mk_ref(deref.region, ty::TypeAndMut {
483 self.cat_rvalue_node(expr.id, expr.span, ref_ty)
487 self.cat_deref(expr, base, false)
490 adjustment::Adjust::NeverToAny |
491 adjustment::Adjust::ReifyFnPointer |
492 adjustment::Adjust::UnsafeFnPointer |
493 adjustment::Adjust::ClosureFnPointer |
494 adjustment::Adjust::MutToConstPointer |
495 adjustment::Adjust::Borrow(_) |
496 adjustment::Adjust::Unsize => {
497 // Result is an rvalue.
498 Ok(self.cat_rvalue_node(expr.id, expr.span, target))
503 pub fn cat_expr_unadjusted(&self, expr: &hir::Expr) -> McResult<cmt<'tcx>> {
504 debug!("cat_expr: id={} expr={:?}", expr.id, expr);
506 let expr_ty = self.expr_ty(expr)?;
508 hir::ExprUnary(hir::UnDeref, ref e_base) => {
509 if self.infcx.tables.borrow().is_method_call(expr) {
510 self.cat_overloaded_lvalue(expr, e_base, false)
512 let base_cmt = self.cat_expr(&e_base)?;
513 self.cat_deref(expr, base_cmt, false)
517 hir::ExprField(ref base, f_name) => {
518 let base_cmt = self.cat_expr(&base)?;
519 debug!("cat_expr(cat_field): id={} expr={:?} base={:?}",
523 Ok(self.cat_field(expr, base_cmt, f_name.node, expr_ty))
526 hir::ExprTupField(ref base, idx) => {
527 let base_cmt = self.cat_expr(&base)?;
528 Ok(self.cat_tup_field(expr, base_cmt, idx.node, expr_ty))
531 hir::ExprIndex(ref base, _) => {
532 if self.infcx.tables.borrow().is_method_call(expr) {
533 // If this is an index implemented by a method call, then it
534 // will include an implicit deref of the result.
535 // The call to index() returns a `&T` value, which
536 // is an rvalue. That is what we will be
538 self.cat_overloaded_lvalue(expr, base, true)
540 let base_cmt = self.cat_expr(&base)?;
541 self.cat_index(expr, base_cmt, expr_ty, InteriorOffsetKind::Index)
545 hir::ExprPath(ref qpath) => {
546 let def = self.infcx.tables.borrow().qpath_def(qpath, expr.id);
547 self.cat_def(expr.id, expr.span, expr_ty, def)
550 hir::ExprType(ref e, _) => {
554 hir::ExprAddrOf(..) | hir::ExprCall(..) |
555 hir::ExprAssign(..) | hir::ExprAssignOp(..) |
556 hir::ExprClosure(..) | hir::ExprRet(..) |
558 hir::ExprMethodCall(..) | hir::ExprCast(..) |
559 hir::ExprArray(..) | hir::ExprTup(..) | hir::ExprIf(..) |
560 hir::ExprBinary(..) | hir::ExprWhile(..) |
561 hir::ExprBlock(..) | hir::ExprLoop(..) | hir::ExprMatch(..) |
562 hir::ExprLit(..) | hir::ExprBreak(..) |
563 hir::ExprAgain(..) | hir::ExprStruct(..) | hir::ExprRepeat(..) |
564 hir::ExprInlineAsm(..) | hir::ExprBox(..) => {
565 Ok(self.cat_rvalue_node(expr.id(), expr.span(), expr_ty))
570 pub fn cat_def(&self,
575 -> McResult<cmt<'tcx>> {
576 debug!("cat_def: id={} expr={:?} def={:?}",
580 Def::StructCtor(..) | Def::VariantCtor(..) | Def::Const(..) |
581 Def::AssociatedConst(..) | Def::Fn(..) | Def::Method(..) => {
582 Ok(self.cat_rvalue_node(id, span, expr_ty))
585 Def::Static(_, mutbl) => {
589 cat:Categorization::StaticItem,
590 mutbl: if mutbl { McDeclared } else { McImmutable},
596 Def::Upvar(def_id, _, fn_node_id) => {
597 let var_id = self.tcx().hir.as_local_node_id(def_id).unwrap();
598 let closure_id = self.tcx().hir.local_def_id(fn_node_id);
599 match self.infcx.closure_kind(closure_id) {
601 self.cat_upvar(id, span, var_id, fn_node_id, kind)
604 span_bug!(span, "No closure kind for {:?}", closure_id);
609 Def::Local(def_id) => {
610 let vid = self.tcx().hir.as_local_node_id(def_id).unwrap();
614 cat: Categorization::Local(vid),
615 mutbl: MutabilityCategory::from_local(self.tcx(), vid),
621 def => span_bug!(span, "unexpected definition in memory categorization: {:?}", def)
625 // Categorize an upvar, complete with invisible derefs of closure
626 // environment and upvar reference as appropriate.
631 fn_node_id: ast::NodeId,
632 kind: ty::ClosureKind)
633 -> McResult<cmt<'tcx>>
635 // An upvar can have up to 3 components. We translate first to a
636 // `Categorization::Upvar`, which is itself a fiction -- it represents the reference to the
637 // field from the environment.
639 // `Categorization::Upvar`. Next, we add a deref through the implicit
640 // environment pointer with an anonymous free region 'env and
641 // appropriate borrow kind for closure kinds that take self by
642 // reference. Finally, if the upvar was captured
643 // by-reference, we add a deref through that reference. The
644 // region of this reference is an inference variable 'up that
645 // was previously generated and recorded in the upvar borrow
646 // map. The borrow kind bk is inferred by based on how the
649 // This results in the following table for concrete closure
653 // ---------------+----------------------+-------------------------------
654 // Fn | copied -> &'env | upvar -> &'env -> &'up bk
655 // FnMut | copied -> &'env mut | upvar -> &'env mut -> &'up bk
656 // FnOnce | copied | upvar -> &'up bk
658 let upvar_id = ty::UpvarId { var_id: var_id,
659 closure_expr_id: fn_node_id };
660 let var_ty = self.node_ty(var_id)?;
662 // Mutability of original variable itself
663 let var_mutbl = MutabilityCategory::from_local(self.tcx(), var_id);
665 // Construct the upvar. This represents access to the field
666 // from the environment (perhaps we should eventually desugar
667 // this field further, but it will do for now).
668 let cmt_result = cmt_ {
671 cat: Categorization::Upvar(Upvar {id: upvar_id, kind: kind}),
677 // If this is a `FnMut` or `Fn` closure, then the above is
678 // conceptually a `&mut` or `&` reference, so we have to add a
680 let cmt_result = match kind {
681 ty::ClosureKind::FnOnce => {
684 ty::ClosureKind::FnMut => {
685 self.env_deref(id, span, upvar_id, var_mutbl, ty::MutBorrow, cmt_result)
687 ty::ClosureKind::Fn => {
688 self.env_deref(id, span, upvar_id, var_mutbl, ty::ImmBorrow, cmt_result)
692 // If this is a by-ref capture, then the upvar we loaded is
693 // actually a reference, so we have to add an implicit deref
695 let upvar_id = ty::UpvarId { var_id: var_id,
696 closure_expr_id: fn_node_id };
697 let upvar_capture = self.infcx.tables.borrow().upvar_capture(upvar_id);
698 let cmt_result = match upvar_capture {
699 ty::UpvarCapture::ByValue => {
702 ty::UpvarCapture::ByRef(upvar_borrow) => {
703 let ptr = BorrowedPtr(upvar_borrow.kind, upvar_borrow.region);
707 cat: Categorization::Deref(Rc::new(cmt_result), ptr),
708 mutbl: MutabilityCategory::from_borrow_kind(upvar_borrow.kind),
710 note: NoteUpvarRef(upvar_id)
715 let ret = Rc::new(cmt_result);
716 debug!("cat_upvar ret={:?}", ret);
723 upvar_id: ty::UpvarId,
724 upvar_mutbl: MutabilityCategory,
725 env_borrow_kind: ty::BorrowKind,
726 cmt_result: cmt_<'tcx>)
729 // Region of environment pointer
730 let env_region = self.tcx().mk_region(ty::ReFree(ty::FreeRegion {
731 // The environment of a closure is guaranteed to
732 // outlive any bindings introduced in the body of the
734 scope: self.tcx().hir.local_def_id(upvar_id.closure_expr_id),
735 bound_region: ty::BrEnv
738 let env_ptr = BorrowedPtr(env_borrow_kind, env_region);
740 let var_ty = cmt_result.ty;
742 // We need to add the env deref. This means
743 // that the above is actually immutable and
744 // has a ref type. However, nothing should
745 // actually look at the type, so we can get
746 // away with stuffing a `TyError` in there
747 // instead of bothering to construct a proper
749 let cmt_result = cmt_ {
751 ty: self.tcx().types.err,
755 let mut deref_mutbl = MutabilityCategory::from_borrow_kind(env_borrow_kind);
757 // Issue #18335. If variable is declared as immutable, override the
758 // mutability from the environment and substitute an `&T` anyway.
760 McImmutable => { deref_mutbl = McImmutable; }
761 McDeclared | McInherited => { }
767 cat: Categorization::Deref(Rc::new(cmt_result), env_ptr),
770 note: NoteClosureEnv(upvar_id)
773 debug!("env_deref ret {:?}", ret);
778 /// Returns the lifetime of a temporary created by expr with id `id`.
779 /// This could be `'static` if `id` is part of a constant expression.
780 pub fn temporary_scope(&self, id: ast::NodeId) -> ty::Region<'tcx>
782 let scope = self.region_maps.temporary_scope(id);
783 self.tcx().mk_region(match scope {
784 Some(scope) => ty::ReScope(scope),
789 pub fn cat_rvalue_node(&self,
794 let promotable = self.tcx().rvalue_promotable_to_static.borrow().get(&id).cloned()
797 // When the corresponding feature isn't toggled, only promote `[T; 0]`.
798 let promotable = match expr_ty.sty {
799 ty::TyArray(_, 0) => true,
800 _ => promotable && self.tcx().sess.features.borrow().rvalue_static_promotion,
803 // Compute maximum lifetime of this rvalue. This is 'static if
804 // we can promote to a constant, otherwise equal to enclosing temp
806 let re = if promotable {
807 self.tcx().types.re_static
809 self.temporary_scope(id)
811 let ret = self.cat_rvalue(id, span, re, expr_ty);
812 debug!("cat_rvalue_node ret {:?}", ret);
816 pub fn cat_rvalue(&self,
819 temp_scope: ty::Region<'tcx>,
820 expr_ty: Ty<'tcx>) -> cmt<'tcx> {
821 let ret = Rc::new(cmt_ {
824 cat:Categorization::Rvalue(temp_scope),
829 debug!("cat_rvalue ret {:?}", ret);
833 pub fn cat_field<N:ast_node>(&self,
839 let ret = Rc::new(cmt_ {
842 mutbl: base_cmt.mutbl.inherit(),
843 cat: Categorization::Interior(base_cmt, InteriorField(NamedField(f_name))),
847 debug!("cat_field ret {:?}", ret);
851 pub fn cat_tup_field<N:ast_node>(&self,
857 let ret = Rc::new(cmt_ {
860 mutbl: base_cmt.mutbl.inherit(),
861 cat: Categorization::Interior(base_cmt, InteriorField(PositionalField(f_idx))),
865 debug!("cat_tup_field ret {:?}", ret);
869 fn cat_overloaded_lvalue(&self,
873 -> McResult<cmt<'tcx>> {
874 debug!("cat_overloaded_lvalue: implicit={}", implicit);
876 // Reconstruct the output assuming it's a reference with the
877 // same region and mutability as the receiver. This holds for
878 // `Deref(Mut)::Deref(_mut)` and `Index(Mut)::index(_mut)`.
879 let lvalue_ty = self.expr_ty(expr)?;
880 let base_ty = self.expr_ty_adjusted(base)?;
882 let (region, mutbl) = match base_ty.sty {
883 ty::TyRef(region, mt) => (region, mt.mutbl),
885 span_bug!(expr.span, "cat_overloaded_lvalue: base is not a reference")
888 let ref_ty = self.tcx().mk_ref(region, ty::TypeAndMut {
893 let base_cmt = self.cat_rvalue_node(expr.id, expr.span, ref_ty);
894 self.cat_deref(expr, base_cmt, implicit)
897 pub fn cat_deref<N:ast_node>(&self,
901 -> McResult<cmt<'tcx>> {
902 debug!("cat_deref: base_cmt={:?}", base_cmt);
904 let base_cmt_ty = base_cmt.ty;
905 let deref_ty = match base_cmt_ty.builtin_deref(true, ty::NoPreference) {
908 debug!("Explicit deref of non-derefable type: {:?}",
914 let ptr = match base_cmt.ty.sty {
915 ty::TyAdt(def, ..) if def.is_box() => Unique,
916 ty::TyRawPtr(ref mt) => UnsafePtr(mt.mutbl),
917 ty::TyRef(r, mt) => {
918 let bk = ty::BorrowKind::from_mutbl(mt.mutbl);
919 if implicit { Implicit(bk, r) } else { BorrowedPtr(bk, r) }
921 ref ty => bug!("unexpected type in cat_deref: {:?}", ty)
923 let ret = Rc::new(cmt_ {
926 // For unique ptrs, we inherit mutability from the owning reference.
927 mutbl: MutabilityCategory::from_pointer_kind(base_cmt.mutbl, ptr),
928 cat: Categorization::Deref(base_cmt, ptr),
932 debug!("cat_deref ret {:?}", ret);
936 fn cat_index<N:ast_node>(&self,
939 element_ty: Ty<'tcx>,
940 context: InteriorOffsetKind)
941 -> McResult<cmt<'tcx>> {
942 //! Creates a cmt for an indexing operation (`[]`).
944 //! One subtle aspect of indexing that may not be
945 //! immediately obvious: for anything other than a fixed-length
946 //! vector, an operation like `x[y]` actually consists of two
947 //! disjoint (from the point of view of borrowck) operations.
948 //! The first is a deref of `x` to create a pointer `p` that points
949 //! at the first element in the array. The second operation is
950 //! an index which adds `y*sizeof(T)` to `p` to obtain the
951 //! pointer to `x[y]`. `cat_index` will produce a resulting
952 //! cmt containing both this deref and the indexing,
953 //! presuming that `base_cmt` is not of fixed-length type.
956 //! - `elt`: the AST node being indexed
957 //! - `base_cmt`: the cmt of `elt`
959 let interior_elem = InteriorElement(context);
961 self.cat_imm_interior(elt, base_cmt, element_ty, interior_elem);
962 debug!("cat_index ret {:?}", ret);
966 pub fn cat_imm_interior<N:ast_node>(&self,
969 interior_ty: Ty<'tcx>,
970 interior: InteriorKind)
972 let ret = Rc::new(cmt_ {
975 mutbl: base_cmt.mutbl.inherit(),
976 cat: Categorization::Interior(base_cmt, interior),
980 debug!("cat_imm_interior ret={:?}", ret);
984 pub fn cat_downcast<N:ast_node>(&self,
987 downcast_ty: Ty<'tcx>,
990 let ret = Rc::new(cmt_ {
993 mutbl: base_cmt.mutbl.inherit(),
994 cat: Categorization::Downcast(base_cmt, variant_did),
998 debug!("cat_downcast ret={:?}", ret);
1002 pub fn cat_pattern<F>(&self, cmt: cmt<'tcx>, pat: &hir::Pat, mut op: F) -> McResult<()>
1003 where F: FnMut(&MemCategorizationContext<'a, 'gcx, 'tcx>, cmt<'tcx>, &hir::Pat),
1005 self.cat_pattern_(cmt, pat, &mut op)
1008 // FIXME(#19596) This is a workaround, but there should be a better way to do this
1009 fn cat_pattern_<F>(&self, cmt: cmt<'tcx>, pat: &hir::Pat, op: &mut F) -> McResult<()>
1010 where F : FnMut(&MemCategorizationContext<'a, 'gcx, 'tcx>, cmt<'tcx>, &hir::Pat)
1012 // Here, `cmt` is the categorization for the value being
1013 // matched and pat is the pattern it is being matched against.
1015 // In general, the way that this works is that we walk down
1016 // the pattern, constructing a cmt that represents the path
1017 // that will be taken to reach the value being matched.
1019 // When we encounter named bindings, we take the cmt that has
1020 // been built up and pass it off to guarantee_valid() so that
1021 // we can be sure that the binding will remain valid for the
1022 // duration of the arm.
1024 // (*2) There is subtlety concerning the correspondence between
1025 // pattern ids and types as compared to *expression* ids and
1026 // types. This is explained briefly. on the definition of the
1027 // type `cmt`, so go off and read what it says there, then
1028 // come back and I'll dive into a bit more detail here. :) OK,
1031 // In general, the id of the cmt should be the node that
1032 // "produces" the value---patterns aren't executable code
1033 // exactly, but I consider them to "execute" when they match a
1034 // value, and I consider them to produce the value that was
1035 // matched. So if you have something like:
1042 // In this case, the cmt and the relevant ids would be:
1044 // CMT Id Type of Id Type of cmt
1047 // ^~~~~~~^ `x` from discr @@int @@int
1048 // ^~~~~~~~~~^ `@@y` pattern node @@int @int
1049 // ^~~~~~~~~~~~~^ `@y` pattern node @int int
1051 // You can see that the types of the id and the cmt are in
1052 // sync in the first line, because that id is actually the id
1053 // of an expression. But once we get to pattern ids, the types
1054 // step out of sync again. So you'll see below that we always
1055 // get the type of the *subpattern* and use that.
1057 debug!("cat_pattern: {:?} cmt={:?}", pat, cmt);
1059 op(self, cmt.clone(), pat);
1061 // Note: This goes up here (rather than within the PatKind::TupleStruct arm
1062 // alone) because PatKind::Struct can also refer to variants.
1063 let cmt = match pat.node {
1064 PatKind::Path(hir::QPath::Resolved(_, ref path)) |
1065 PatKind::TupleStruct(hir::QPath::Resolved(_, ref path), ..) |
1066 PatKind::Struct(hir::QPath::Resolved(_, ref path), ..) => {
1069 debug!("access to unresolvable pattern {:?}", pat);
1072 Def::Variant(variant_did) |
1073 Def::VariantCtor(variant_did, ..) => {
1074 // univariant enums do not need downcasts
1075 let enum_did = self.tcx().parent_def_id(variant_did).unwrap();
1076 if !self.tcx().adt_def(enum_did).is_univariant() {
1077 self.cat_downcast(pat, cmt.clone(), cmt.ty, variant_did)
1089 PatKind::TupleStruct(ref qpath, ref subpats, ddpos) => {
1090 let def = self.infcx.tables.borrow().qpath_def(qpath, pat.id);
1091 let expected_len = match def {
1092 Def::VariantCtor(def_id, CtorKind::Fn) => {
1093 let enum_def = self.tcx().parent_def_id(def_id).unwrap();
1094 self.tcx().adt_def(enum_def).variant_with_id(def_id).fields.len()
1096 Def::StructCtor(_, CtorKind::Fn) => {
1097 match self.pat_ty(&pat)?.sty {
1098 ty::TyAdt(adt_def, _) => {
1099 adt_def.struct_variant().fields.len()
1102 span_bug!(pat.span, "tuple struct pattern unexpected type {:?}", ty);
1107 span_bug!(pat.span, "tuple struct pattern didn't resolve \
1108 to variant or struct {:?}", def);
1112 for (i, subpat) in subpats.iter().enumerate_and_adjust(expected_len, ddpos) {
1113 let subpat_ty = self.pat_ty(&subpat)?; // see (*2)
1114 let subcmt = self.cat_imm_interior(pat, cmt.clone(), subpat_ty,
1115 InteriorField(PositionalField(i)));
1116 self.cat_pattern_(subcmt, &subpat, op)?;
1120 PatKind::Struct(_, ref field_pats, _) => {
1121 // {f1: p1, ..., fN: pN}
1122 for fp in field_pats {
1123 let field_ty = self.pat_ty(&fp.node.pat)?; // see (*2)
1124 let cmt_field = self.cat_field(pat, cmt.clone(), fp.node.name, field_ty);
1125 self.cat_pattern_(cmt_field, &fp.node.pat, op)?;
1129 PatKind::Binding(.., Some(ref subpat)) => {
1130 self.cat_pattern_(cmt, &subpat, op)?;
1133 PatKind::Tuple(ref subpats, ddpos) => {
1135 let expected_len = match self.pat_ty(&pat)?.sty {
1136 ty::TyTuple(ref tys, _) => tys.len(),
1137 ref ty => span_bug!(pat.span, "tuple pattern unexpected type {:?}", ty),
1139 for (i, subpat) in subpats.iter().enumerate_and_adjust(expected_len, ddpos) {
1140 let subpat_ty = self.pat_ty(&subpat)?; // see (*2)
1141 let subcmt = self.cat_imm_interior(pat, cmt.clone(), subpat_ty,
1142 InteriorField(PositionalField(i)));
1143 self.cat_pattern_(subcmt, &subpat, op)?;
1147 PatKind::Box(ref subpat) | PatKind::Ref(ref subpat, _) => {
1148 // box p1, &p1, &mut p1. we can ignore the mutability of
1149 // PatKind::Ref since that information is already contained
1151 let subcmt = self.cat_deref(pat, cmt, false)?;
1152 self.cat_pattern_(subcmt, &subpat, op)?;
1155 PatKind::Slice(ref before, ref slice, ref after) => {
1156 let element_ty = match cmt.ty.builtin_index() {
1159 debug!("Explicit index of non-indexable type {:?}", cmt);
1163 let context = InteriorOffsetKind::Pattern;
1164 let elt_cmt = self.cat_index(pat, cmt, element_ty, context)?;
1165 for before_pat in before {
1166 self.cat_pattern_(elt_cmt.clone(), &before_pat, op)?;
1168 if let Some(ref slice_pat) = *slice {
1169 self.cat_pattern_(elt_cmt.clone(), &slice_pat, op)?;
1171 for after_pat in after {
1172 self.cat_pattern_(elt_cmt.clone(), &after_pat, op)?;
1176 PatKind::Path(_) | PatKind::Binding(.., None) |
1177 PatKind::Lit(..) | PatKind::Range(..) | PatKind::Wild => {
1186 #[derive(Clone, Debug)]
1187 pub enum Aliasability {
1188 FreelyAliasable(AliasableReason),
1190 ImmutableUnique(Box<Aliasability>),
1193 #[derive(Copy, Clone, Debug)]
1194 pub enum AliasableReason {
1200 impl<'tcx> cmt_<'tcx> {
1201 pub fn guarantor(&self) -> cmt<'tcx> {
1202 //! Returns `self` after stripping away any derefs or
1203 //! interior content. The return value is basically the `cmt` which
1204 //! determines how long the value in `self` remains live.
1207 Categorization::Rvalue(..) |
1208 Categorization::StaticItem |
1209 Categorization::Local(..) |
1210 Categorization::Deref(_, UnsafePtr(..)) |
1211 Categorization::Deref(_, BorrowedPtr(..)) |
1212 Categorization::Deref(_, Implicit(..)) |
1213 Categorization::Upvar(..) => {
1214 Rc::new((*self).clone())
1216 Categorization::Downcast(ref b, _) |
1217 Categorization::Interior(ref b, _) |
1218 Categorization::Deref(ref b, Unique) => {
1224 /// Returns `FreelyAliasable(_)` if this lvalue represents a freely aliasable pointer type.
1225 pub fn freely_aliasable(&self) -> Aliasability {
1226 // Maybe non-obvious: copied upvars can only be considered
1227 // non-aliasable in once closures, since any other kind can be
1228 // aliased and eventually recused.
1231 Categorization::Deref(ref b, BorrowedPtr(ty::MutBorrow, _)) |
1232 Categorization::Deref(ref b, Implicit(ty::MutBorrow, _)) |
1233 Categorization::Deref(ref b, BorrowedPtr(ty::UniqueImmBorrow, _)) |
1234 Categorization::Deref(ref b, Implicit(ty::UniqueImmBorrow, _)) |
1235 Categorization::Deref(ref b, Unique) |
1236 Categorization::Downcast(ref b, _) |
1237 Categorization::Interior(ref b, _) => {
1238 // Aliasability depends on base cmt
1239 b.freely_aliasable()
1242 Categorization::Rvalue(..) |
1243 Categorization::Local(..) |
1244 Categorization::Upvar(..) |
1245 Categorization::Deref(_, UnsafePtr(..)) => { // yes, it's aliasable, but...
1249 Categorization::StaticItem => {
1250 if self.mutbl.is_mutable() {
1251 FreelyAliasable(AliasableStaticMut)
1253 FreelyAliasable(AliasableStatic)
1257 Categorization::Deref(_, BorrowedPtr(ty::ImmBorrow, _)) |
1258 Categorization::Deref(_, Implicit(ty::ImmBorrow, _)) => {
1259 FreelyAliasable(AliasableBorrowed)
1264 // Digs down through one or two layers of deref and grabs the cmt
1265 // for the upvar if a note indicates there is one.
1266 pub fn upvar(&self) -> Option<cmt<'tcx>> {
1268 NoteClosureEnv(..) | NoteUpvarRef(..) => {
1269 Some(match self.cat {
1270 Categorization::Deref(ref inner, _) => {
1272 Categorization::Deref(ref inner, _) => inner.clone(),
1273 Categorization::Upvar(..) => inner.clone(),
1285 pub fn descriptive_string(&self, tcx: TyCtxt) -> String {
1287 Categorization::StaticItem => {
1288 "static item".to_string()
1290 Categorization::Rvalue(..) => {
1291 "non-lvalue".to_string()
1293 Categorization::Local(vid) => {
1294 if tcx.hir.is_argument(vid) {
1295 "argument".to_string()
1297 "local variable".to_string()
1300 Categorization::Deref(_, pk) => {
1301 let upvar = self.upvar();
1302 match upvar.as_ref().map(|i| &i.cat) {
1303 Some(&Categorization::Upvar(ref var)) => {
1310 format!("indexed content")
1313 format!("`Box` content")
1316 format!("dereference of raw pointer")
1318 BorrowedPtr(..) => {
1319 format!("borrowed content")
1325 Categorization::Interior(_, InteriorField(NamedField(_))) => {
1328 Categorization::Interior(_, InteriorField(PositionalField(_))) => {
1329 "anonymous field".to_string()
1331 Categorization::Interior(_, InteriorElement(InteriorOffsetKind::Index)) => {
1332 "indexed content".to_string()
1334 Categorization::Interior(_, InteriorElement(InteriorOffsetKind::Pattern)) => {
1335 "pattern-bound indexed content".to_string()
1337 Categorization::Upvar(ref var) => {
1340 Categorization::Downcast(ref cmt, _) => {
1341 cmt.descriptive_string(tcx)
1347 impl<'tcx> fmt::Debug for cmt_<'tcx> {
1348 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1349 write!(f, "{{{:?} id:{} m:{:?} ty:{:?}}}",
1357 impl<'tcx> fmt::Debug for Categorization<'tcx> {
1358 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1360 Categorization::StaticItem => write!(f, "static"),
1361 Categorization::Rvalue(r) => { write!(f, "rvalue({:?})", r) }
1362 Categorization::Local(id) => {
1363 let name = ty::tls::with(|tcx| tcx.local_var_name_str(id));
1364 write!(f, "local({})", name)
1366 Categorization::Upvar(upvar) => {
1367 write!(f, "upvar({:?})", upvar)
1369 Categorization::Deref(ref cmt, ptr) => {
1370 write!(f, "{:?}-{:?}->", cmt.cat, ptr)
1372 Categorization::Interior(ref cmt, interior) => {
1373 write!(f, "{:?}.{:?}", cmt.cat, interior)
1375 Categorization::Downcast(ref cmt, _) => {
1376 write!(f, "{:?}->(enum)", cmt.cat)
1382 pub fn ptr_sigil(ptr: PointerKind) -> &'static str {
1385 BorrowedPtr(ty::ImmBorrow, _) |
1386 Implicit(ty::ImmBorrow, _) => "&",
1387 BorrowedPtr(ty::MutBorrow, _) |
1388 Implicit(ty::MutBorrow, _) => "&mut",
1389 BorrowedPtr(ty::UniqueImmBorrow, _) |
1390 Implicit(ty::UniqueImmBorrow, _) => "&unique",
1391 UnsafePtr(_) => "*",
1395 impl<'tcx> fmt::Debug for PointerKind<'tcx> {
1396 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1398 Unique => write!(f, "Box"),
1399 BorrowedPtr(ty::ImmBorrow, ref r) |
1400 Implicit(ty::ImmBorrow, ref r) => {
1401 write!(f, "&{:?}", r)
1403 BorrowedPtr(ty::MutBorrow, ref r) |
1404 Implicit(ty::MutBorrow, ref r) => {
1405 write!(f, "&{:?} mut", r)
1407 BorrowedPtr(ty::UniqueImmBorrow, ref r) |
1408 Implicit(ty::UniqueImmBorrow, ref r) => {
1409 write!(f, "&{:?} uniq", r)
1411 UnsafePtr(_) => write!(f, "*")
1416 impl fmt::Debug for InteriorKind {
1417 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1419 InteriorField(NamedField(fld)) => write!(f, "{}", fld),
1420 InteriorField(PositionalField(i)) => write!(f, "#{}", i),
1421 InteriorElement(..) => write!(f, "[]"),
1426 impl fmt::Debug for Upvar {
1427 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1428 write!(f, "{:?}/{:?}", self.id, self.kind)
1432 impl fmt::Display for Upvar {
1433 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1434 let kind = match self.kind {
1435 ty::ClosureKind::Fn => "Fn",
1436 ty::ClosureKind::FnMut => "FnMut",
1437 ty::ClosureKind::FnOnce => "FnOnce",
1439 write!(f, "captured outer variable in an `{}` closure", kind)