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::*;
77 use middle::check_const;
80 use middle::ty::{self, Ty};
82 use syntax::ast::{MutImmutable, MutMutable};
84 use syntax::codemap::Span;
89 #[derive(Clone, PartialEq)]
90 pub enum categorization<'tcx> {
91 cat_rvalue(ty::Region), // temporary val, argument is its scope
93 cat_upvar(Upvar), // upvar referenced by closure env
94 cat_local(ast::NodeId), // local variable
95 cat_deref(cmt<'tcx>, usize, PointerKind), // deref of a ptr
96 cat_interior(cmt<'tcx>, InteriorKind), // something interior: field, tuple, etc
97 cat_downcast(cmt<'tcx>, ast::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 {
116 BorrowedPtr(ty::BorrowKind, ty::Region),
119 UnsafePtr(ast::Mutability),
121 /// Implicit deref of the `&T` that results from an overloaded index `[]`.
122 Implicit(ty::BorrowKind, ty::Region),
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, ElementKind),
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 ElementKind {
151 #[derive(Clone, Copy, PartialEq, Eq, Hash, Debug)]
152 pub enum MutabilityCategory {
153 McImmutable, // Immutable.
154 McDeclared, // Directly declared as mutable.
155 McInherited, // Inherited from the fact that owner is mutable.
158 // A note about the provenance of a `cmt`. This is used for
159 // special-case handling of upvars such as mutability inference.
160 // Upvar categorization can generate a variable number of nested
161 // derefs. The note allows detecting them without deep pattern
162 // matching on the categorization.
163 #[derive(Clone, Copy, PartialEq, Debug)]
165 NoteClosureEnv(ty::UpvarId), // Deref through closure env
166 NoteUpvarRef(ty::UpvarId), // Deref through by-ref upvar
167 NoteNone // Nothing special
170 // `cmt`: "Category, Mutability, and Type".
172 // a complete categorization of a value indicating where it originated
173 // and how it is located, as well as the mutability of the memory in
174 // which the value is stored.
176 // *WARNING* The field `cmt.type` is NOT necessarily the same as the
177 // result of `node_id_to_type(cmt.id)`. This is because the `id` is
178 // always the `id` of the node producing the type; in an expression
179 // like `*x`, the type of this deref node is the deref'd type (`T`),
180 // but in a pattern like `@x`, the `@x` pattern is again a
181 // dereference, but its type is the type *before* the dereference
182 // (`@T`). So use `cmt.ty` to find the type of the value in a consistent
183 // fashion. For more details, see the method `cat_pattern`
184 #[derive(Clone, PartialEq)]
185 pub struct cmt_<'tcx> {
186 pub id: ast::NodeId, // id of expr/pat producing this value
187 pub span: Span, // span of same expr/pat
188 pub cat: categorization<'tcx>, // categorization of expr
189 pub mutbl: MutabilityCategory, // mutability of expr as lvalue
190 pub ty: Ty<'tcx>, // type of the expr (*see WARNING above*)
191 pub note: Note, // Note about the provenance of this cmt
194 pub type cmt<'tcx> = Rc<cmt_<'tcx>>;
196 // We pun on *T to mean both actual deref of a ptr as well
197 // as accessing of components:
198 #[derive(Copy, Clone)]
199 pub enum deref_kind {
200 deref_ptr(PointerKind),
201 deref_interior(InteriorKind),
204 type DerefKindContext = Option<InteriorOffsetKind>;
206 // Categorizes a derefable type. Note that we include vectors and strings as
207 // derefable (we model an index as the combination of a deref and then a
208 // pointer adjustment).
209 fn deref_kind(t: Ty, context: DerefKindContext) -> McResult<deref_kind> {
212 Ok(deref_ptr(Unique))
215 ty::TyRef(r, mt) => {
216 let kind = ty::BorrowKind::from_mutbl(mt.mutbl);
217 Ok(deref_ptr(BorrowedPtr(kind, *r)))
220 ty::TyRawPtr(ref mt) => {
221 Ok(deref_ptr(UnsafePtr(mt.mutbl)))
225 ty::TyStruct(..) => { // newtype
226 Ok(deref_interior(InteriorField(PositionalField(0))))
229 ty::TyArray(_, _) | ty::TySlice(_) | ty::TyStr => {
230 // no deref of indexed content without supplying InteriorOffsetKind
231 if let Some(context) = context {
232 Ok(deref_interior(InteriorElement(context, element_kind(t))))
243 fn id(&self) -> ast::NodeId;
244 fn span(&self) -> Span;
247 impl ast_node for ast::Expr {
248 fn id(&self) -> ast::NodeId { self.id }
249 fn span(&self) -> Span { self.span }
252 impl ast_node for ast::Pat {
253 fn id(&self) -> ast::NodeId { self.id }
254 fn span(&self) -> Span { self.span }
257 #[derive(Copy, Clone)]
258 pub struct MemCategorizationContext<'t, 'a: 't, 'tcx : 'a> {
259 pub typer: &'t infer::InferCtxt<'a, 'tcx>,
262 pub type McResult<T> = Result<T, ()>;
264 impl MutabilityCategory {
265 pub fn from_mutbl(m: ast::Mutability) -> MutabilityCategory {
267 MutImmutable => McImmutable,
268 MutMutable => McDeclared
270 debug!("MutabilityCategory::{}({:?}) => {:?}",
271 "from_mutbl", m, ret);
275 pub fn from_borrow_kind(borrow_kind: ty::BorrowKind) -> MutabilityCategory {
276 let ret = match borrow_kind {
277 ty::ImmBorrow => McImmutable,
278 ty::UniqueImmBorrow => McImmutable,
279 ty::MutBorrow => McDeclared,
281 debug!("MutabilityCategory::{}({:?}) => {:?}",
282 "from_borrow_kind", borrow_kind, ret);
286 fn from_pointer_kind(base_mutbl: MutabilityCategory,
287 ptr: PointerKind) -> MutabilityCategory {
288 let ret = match ptr {
292 BorrowedPtr(borrow_kind, _) | Implicit(borrow_kind, _) => {
293 MutabilityCategory::from_borrow_kind(borrow_kind)
296 MutabilityCategory::from_mutbl(m)
299 debug!("MutabilityCategory::{}({:?}, {:?}) => {:?}",
300 "from_pointer_kind", base_mutbl, ptr, ret);
304 fn from_local(tcx: &ty::ctxt, id: ast::NodeId) -> MutabilityCategory {
305 let ret = match tcx.map.get(id) {
306 ast_map::NodeLocal(p) | ast_map::NodeArg(p) => match p.node {
307 ast::PatIdent(bind_mode, _, _) => {
308 if bind_mode == ast::BindByValue(ast::MutMutable) {
314 _ => tcx.sess.span_bug(p.span, "expected identifier pattern")
316 _ => tcx.sess.span_bug(tcx.map.span(id), "expected identifier pattern")
318 debug!("MutabilityCategory::{}(tcx, id={:?}) => {:?}",
319 "from_local", id, ret);
323 pub fn inherit(&self) -> MutabilityCategory {
324 let ret = match *self {
325 McImmutable => McImmutable,
326 McDeclared => McInherited,
327 McInherited => McInherited,
329 debug!("{:?}.inherit() => {:?}", self, ret);
333 pub fn is_mutable(&self) -> bool {
334 let ret = match *self {
335 McImmutable => false,
339 debug!("{:?}.is_mutable() => {:?}", self, ret);
343 pub fn is_immutable(&self) -> bool {
344 let ret = match *self {
346 McDeclared | McInherited => false
348 debug!("{:?}.is_immutable() => {:?}", self, ret);
352 pub fn to_user_str(&self) -> &'static str {
354 McDeclared | McInherited => "mutable",
355 McImmutable => "immutable",
360 impl<'t, 'a,'tcx> MemCategorizationContext<'t, 'a, 'tcx> {
361 pub fn new(typer: &'t infer::InferCtxt<'a, 'tcx>) -> MemCategorizationContext<'t, 'a, 'tcx> {
362 MemCategorizationContext { typer: typer }
365 fn tcx(&self) -> &'a ty::ctxt<'tcx> {
369 fn expr_ty(&self, expr: &ast::Expr) -> McResult<Ty<'tcx>> {
370 match self.typer.node_ty(expr.id) {
373 debug!("expr_ty({:?}) yielded Err", expr);
379 fn expr_ty_adjusted(&self, expr: &ast::Expr) -> McResult<Ty<'tcx>> {
380 let unadjusted_ty = try!(self.expr_ty(expr));
381 Ok(unadjusted_ty.adjust(
382 self.tcx(), expr.span, expr.id,
383 self.typer.adjustments().get(&expr.id),
384 |method_call| self.typer.node_method_ty(method_call)))
387 fn node_ty(&self, id: ast::NodeId) -> McResult<Ty<'tcx>> {
388 self.typer.node_ty(id)
391 fn pat_ty(&self, pat: &ast::Pat) -> McResult<Ty<'tcx>> {
392 let base_ty = try!(self.typer.node_ty(pat.id));
393 // FIXME (Issue #18207): This code detects whether we are
394 // looking at a `ref x`, and if so, figures out what the type
395 // *being borrowed* is. But ideally we would put in a more
396 // fundamental fix to this conflated use of the node id.
397 let ret_ty = match pat.node {
398 ast::PatIdent(ast::BindByRef(_), _, _) => {
399 // a bind-by-ref means that the base_ty will be the type of the ident itself,
400 // but what we want here is the type of the underlying value being borrowed.
401 // So peel off one-level, turning the &T into T.
402 match base_ty.builtin_deref(false) {
404 None => { return Err(()); }
409 debug!("pat_ty(pat={:?}) base_ty={:?} ret_ty={:?}",
410 pat, base_ty, ret_ty);
414 pub fn cat_expr(&self, expr: &ast::Expr) -> McResult<cmt<'tcx>> {
415 match self.typer.adjustments().get(&expr.id) {
418 self.cat_expr_unadjusted(expr)
421 Some(adjustment) => {
425 autoref: None, unsize: None, autoderefs, ..}) => {
426 // Equivalent to *expr or something similar.
427 self.cat_expr_autoderefd(expr, autoderefs)
430 ty::AdjustReifyFnPointer |
431 ty::AdjustUnsafeFnPointer |
432 ty::AdjustDerefRef(_) => {
433 debug!("cat_expr({:?}): {:?}",
436 // Result is an rvalue.
437 let expr_ty = try!(self.expr_ty_adjusted(expr));
438 Ok(self.cat_rvalue_node(expr.id(), expr.span(), expr_ty))
445 pub fn cat_expr_autoderefd(&self,
448 -> McResult<cmt<'tcx>> {
449 let mut cmt = try!(self.cat_expr_unadjusted(expr));
450 debug!("cat_expr_autoderefd: autoderefs={}, cmt={:?}",
453 for deref in 1..autoderefs + 1 {
454 cmt = try!(self.cat_deref(expr, cmt, deref, None));
459 pub fn cat_expr_unadjusted(&self, expr: &ast::Expr) -> McResult<cmt<'tcx>> {
460 debug!("cat_expr: id={} expr={:?}", expr.id, expr);
462 let expr_ty = try!(self.expr_ty(expr));
464 ast::ExprUnary(ast::UnDeref, ref e_base) => {
465 let base_cmt = try!(self.cat_expr(&**e_base));
466 self.cat_deref(expr, base_cmt, 0, None)
469 ast::ExprField(ref base, f_name) => {
470 let base_cmt = try!(self.cat_expr(&**base));
471 debug!("cat_expr(cat_field): id={} expr={:?} base={:?}",
475 Ok(self.cat_field(expr, base_cmt, f_name.node.name, expr_ty))
478 ast::ExprTupField(ref base, idx) => {
479 let base_cmt = try!(self.cat_expr(&**base));
480 Ok(self.cat_tup_field(expr, base_cmt, idx.node, expr_ty))
483 ast::ExprIndex(ref base, _) => {
484 let method_call = ty::MethodCall::expr(expr.id());
485 let context = InteriorOffsetKind::Index;
486 match self.typer.node_method_ty(method_call) {
488 // If this is an index implemented by a method call, then it
489 // will include an implicit deref of the result.
490 let ret_ty = self.overloaded_method_return_ty(method_ty);
492 // The index method always returns an `&T`, so
493 // dereference it to find the result type.
494 let elem_ty = match ret_ty.sty {
495 ty::TyRef(_, mt) => mt.ty,
497 debug!("cat_expr_unadjusted: return type of overloaded index is {:?}?",
503 // The call to index() returns a `&T` value, which
504 // is an rvalue. That is what we will be
506 let base_cmt = self.cat_rvalue_node(expr.id(), expr.span(), ret_ty);
507 self.cat_deref_common(expr, base_cmt, 1, elem_ty, Some(context), true)
510 self.cat_index(expr, try!(self.cat_expr(&**base)), context)
515 ast::ExprPath(..) => {
516 let def = self.tcx().def_map.borrow().get(&expr.id).unwrap().full_def();
517 self.cat_def(expr.id, expr.span, expr_ty, def)
520 ast::ExprParen(ref e) => {
524 ast::ExprAddrOf(..) | ast::ExprCall(..) |
525 ast::ExprAssign(..) | ast::ExprAssignOp(..) |
526 ast::ExprClosure(..) | ast::ExprRet(..) |
527 ast::ExprUnary(..) | ast::ExprRange(..) |
528 ast::ExprMethodCall(..) | ast::ExprCast(..) |
529 ast::ExprVec(..) | ast::ExprTup(..) | ast::ExprIf(..) |
530 ast::ExprBinary(..) | ast::ExprWhile(..) |
531 ast::ExprBlock(..) | ast::ExprLoop(..) | ast::ExprMatch(..) |
532 ast::ExprLit(..) | ast::ExprBreak(..) | ast::ExprMac(..) |
533 ast::ExprAgain(..) | ast::ExprStruct(..) | ast::ExprRepeat(..) |
534 ast::ExprInlineAsm(..) | ast::ExprBox(..) => {
535 Ok(self.cat_rvalue_node(expr.id(), expr.span(), expr_ty))
538 ast::ExprIfLet(..) => {
539 self.tcx().sess.span_bug(expr.span, "non-desugared ExprIfLet");
541 ast::ExprWhileLet(..) => {
542 self.tcx().sess.span_bug(expr.span, "non-desugared ExprWhileLet");
544 ast::ExprForLoop(..) => {
545 self.tcx().sess.span_bug(expr.span, "non-desugared ExprForLoop");
550 pub fn cat_def(&self,
555 -> McResult<cmt<'tcx>> {
556 debug!("cat_def: id={} expr={:?} def={:?}",
560 def::DefStruct(..) | def::DefVariant(..) | def::DefConst(..) |
561 def::DefAssociatedConst(..) | def::DefFn(..) | def::DefMethod(..) => {
562 Ok(self.cat_rvalue_node(id, span, expr_ty))
564 def::DefMod(_) | def::DefForeignMod(_) | def::DefUse(_) |
565 def::DefTrait(_) | def::DefTy(..) | def::DefPrimTy(_) |
566 def::DefTyParam(..) | def::DefRegion(_) |
567 def::DefLabel(_) | def::DefSelfTy(..) |
568 def::DefAssociatedTy(..) => {
579 def::DefStatic(_, mutbl) => {
584 mutbl: if mutbl { McDeclared } else { McImmutable},
590 def::DefUpvar(var_id, fn_node_id) => {
591 let ty = try!(self.node_ty(fn_node_id));
593 ty::TyClosure(closure_id, _) => {
594 match self.typer.closure_kind(closure_id) {
596 self.cat_upvar(id, span, var_id, fn_node_id, kind)
599 self.tcx().sess.span_bug(
601 &*format!("No closure kind for {:?}", closure_id));
606 self.tcx().sess.span_bug(
608 &format!("Upvar of non-closure {} - {:?}",
615 def::DefLocal(vid) => {
620 mutbl: MutabilityCategory::from_local(self.tcx(), vid),
628 // Categorize an upvar, complete with invisible derefs of closure
629 // environment and upvar reference as appropriate.
634 fn_node_id: ast::NodeId,
635 kind: ty::ClosureKind)
636 -> McResult<cmt<'tcx>>
638 // An upvar can have up to 3 components. We translate first to a
639 // `cat_upvar`, which is itself a fiction -- it represents the reference to the
640 // field from the environment.
642 // `cat_upvar`. Next, we add a deref through the implicit
643 // environment pointer with an anonymous free region 'env and
644 // appropriate borrow kind for closure kinds that take self by
645 // reference. Finally, if the upvar was captured
646 // by-reference, we add a deref through that reference. The
647 // region of this reference is an inference variable 'up that
648 // was previously generated and recorded in the upvar borrow
649 // map. The borrow kind bk is inferred by based on how the
652 // This results in the following table for concrete closure
656 // ---------------+----------------------+-------------------------------
657 // Fn | copied -> &'env | upvar -> &'env -> &'up bk
658 // FnMut | copied -> &'env mut | upvar -> &'env mut -> &'up bk
659 // FnOnce | copied | upvar -> &'up bk
661 let upvar_id = ty::UpvarId { var_id: var_id,
662 closure_expr_id: fn_node_id };
663 let var_ty = try!(self.node_ty(var_id));
665 // Mutability of original variable itself
666 let var_mutbl = MutabilityCategory::from_local(self.tcx(), var_id);
668 // Construct the upvar. This represents access to the field
669 // from the environment (perhaps we should eventually desugar
670 // this field further, but it will do for now).
671 let cmt_result = cmt_ {
674 cat: cat_upvar(Upvar {id: upvar_id, kind: kind}),
680 // If this is a `FnMut` or `Fn` closure, then the above is
681 // conceptually a `&mut` or `&` reference, so we have to add a
683 let cmt_result = match kind {
684 ty::FnOnceClosureKind => {
687 ty::FnMutClosureKind => {
688 self.env_deref(id, span, upvar_id, var_mutbl, ty::MutBorrow, cmt_result)
690 ty::FnClosureKind => {
691 self.env_deref(id, span, upvar_id, var_mutbl, ty::ImmBorrow, cmt_result)
695 // If this is a by-ref capture, then the upvar we loaded is
696 // actually a reference, so we have to add an implicit deref
698 let upvar_id = ty::UpvarId { var_id: var_id,
699 closure_expr_id: fn_node_id };
700 let upvar_capture = self.typer.upvar_capture(upvar_id).unwrap();
701 let cmt_result = match upvar_capture {
702 ty::UpvarCapture::ByValue => {
705 ty::UpvarCapture::ByRef(upvar_borrow) => {
706 let ptr = BorrowedPtr(upvar_borrow.kind, upvar_borrow.region);
710 cat: cat_deref(Rc::new(cmt_result), 0, ptr),
711 mutbl: MutabilityCategory::from_borrow_kind(upvar_borrow.kind),
713 note: NoteUpvarRef(upvar_id)
718 let ret = Rc::new(cmt_result);
719 debug!("cat_upvar ret={:?}", ret);
726 upvar_id: ty::UpvarId,
727 upvar_mutbl: MutabilityCategory,
728 env_borrow_kind: ty::BorrowKind,
729 cmt_result: cmt_<'tcx>)
732 // Look up the node ID of the closure body so we can construct
733 // a free region within it
735 let fn_expr = match self.tcx().map.find(upvar_id.closure_expr_id) {
736 Some(ast_map::NodeExpr(e)) => e,
741 ast::ExprClosure(_, _, ref body) => body.id,
746 // Region of environment pointer
747 let env_region = ty::ReFree(ty::FreeRegion {
748 // The environment of a closure is guaranteed to
749 // outlive any bindings introduced in the body of the
751 scope: region::DestructionScopeData::new(fn_body_id),
752 bound_region: ty::BrEnv
755 let env_ptr = BorrowedPtr(env_borrow_kind, env_region);
757 let var_ty = cmt_result.ty;
759 // We need to add the env deref. This means
760 // that the above is actually immutable and
761 // has a ref type. However, nothing should
762 // actually look at the type, so we can get
763 // away with stuffing a `TyError` in there
764 // instead of bothering to construct a proper
766 let cmt_result = cmt_ {
768 ty: self.tcx().types.err,
772 let mut deref_mutbl = MutabilityCategory::from_borrow_kind(env_borrow_kind);
774 // Issue #18335. If variable is declared as immutable, override the
775 // mutability from the environment and substitute an `&T` anyway.
777 McImmutable => { deref_mutbl = McImmutable; }
778 McDeclared | McInherited => { }
784 cat: cat_deref(Rc::new(cmt_result), 0, env_ptr),
787 note: NoteClosureEnv(upvar_id)
790 debug!("env_deref ret {:?}", ret);
795 /// Returns the lifetime of a temporary created by expr with id `id`.
796 /// This could be `'static` if `id` is part of a constant expression.
797 pub fn temporary_scope(&self, id: ast::NodeId) -> ty::Region {
798 match self.typer.temporary_scope(id) {
799 Some(scope) => ty::ReScope(scope),
804 pub fn cat_rvalue_node(&self,
809 let qualif = self.tcx().const_qualif_map.borrow().get(&id).cloned()
810 .unwrap_or(check_const::ConstQualif::NOT_CONST);
812 // Only promote `[T; 0]` before an RFC for rvalue promotions
814 let qualif = match expr_ty.sty {
815 ty::TyArray(_, 0) => qualif,
816 _ => check_const::ConstQualif::NOT_CONST
819 // Compute maximum lifetime of this rvalue. This is 'static if
820 // we can promote to a constant, otherwise equal to enclosing temp
822 let re = if qualif.intersects(check_const::ConstQualif::NON_STATIC_BORROWS) {
823 self.temporary_scope(id)
827 let ret = self.cat_rvalue(id, span, re, expr_ty);
828 debug!("cat_rvalue_node ret {:?}", ret);
832 pub fn cat_rvalue(&self,
835 temp_scope: ty::Region,
836 expr_ty: Ty<'tcx>) -> cmt<'tcx> {
837 let ret = Rc::new(cmt_ {
840 cat:cat_rvalue(temp_scope),
845 debug!("cat_rvalue ret {:?}", ret);
849 pub fn cat_field<N:ast_node>(&self,
855 let ret = Rc::new(cmt_ {
858 mutbl: base_cmt.mutbl.inherit(),
859 cat: cat_interior(base_cmt, InteriorField(NamedField(f_name))),
863 debug!("cat_field ret {:?}", ret);
867 pub fn cat_tup_field<N:ast_node>(&self,
873 let ret = Rc::new(cmt_ {
876 mutbl: base_cmt.mutbl.inherit(),
877 cat: cat_interior(base_cmt, InteriorField(PositionalField(f_idx))),
881 debug!("cat_tup_field ret {:?}", ret);
885 fn cat_deref<N:ast_node>(&self,
889 deref_context: DerefKindContext)
890 -> McResult<cmt<'tcx>> {
891 let method_call = ty::MethodCall {
893 autoderef: deref_cnt as u32
895 let method_ty = self.typer.node_method_ty(method_call);
897 debug!("cat_deref: method_call={:?} method_ty={:?}",
898 method_call, method_ty.map(|ty| ty));
900 let base_cmt = match method_ty {
903 self.tcx().no_late_bound_regions(&method_ty.fn_ret()).unwrap().unwrap();
904 self.cat_rvalue_node(node.id(), node.span(), ref_ty)
908 let base_cmt_ty = base_cmt.ty;
909 match base_cmt_ty.builtin_deref(true) {
911 let ret = self.cat_deref_common(node, base_cmt, deref_cnt,
914 /* implicit: */ false);
915 debug!("cat_deref ret {:?}", ret);
919 debug!("Explicit deref of non-derefable type: {:?}",
926 fn cat_deref_common<N:ast_node>(&self,
931 deref_context: DerefKindContext,
933 -> McResult<cmt<'tcx>>
935 let (m, cat) = match try!(deref_kind(base_cmt.ty, deref_context)) {
937 let ptr = if implicit {
939 BorrowedPtr(bk, r) => Implicit(bk, r),
940 _ => self.tcx().sess.span_bug(node.span(),
941 "Implicit deref of non-borrowed pointer")
946 // for unique ptrs, we inherit mutability from the
948 (MutabilityCategory::from_pointer_kind(base_cmt.mutbl, ptr),
949 cat_deref(base_cmt, deref_cnt, ptr))
951 deref_interior(interior) => {
952 (base_cmt.mutbl.inherit(), cat_interior(base_cmt, interior))
955 let ret = Rc::new(cmt_ {
963 debug!("cat_deref_common ret {:?}", ret);
967 pub fn cat_index<N:ast_node>(&self,
969 mut base_cmt: cmt<'tcx>,
970 context: InteriorOffsetKind)
971 -> McResult<cmt<'tcx>> {
972 //! Creates a cmt for an indexing operation (`[]`).
974 //! One subtle aspect of indexing that may not be
975 //! immediately obvious: for anything other than a fixed-length
976 //! vector, an operation like `x[y]` actually consists of two
977 //! disjoint (from the point of view of borrowck) operations.
978 //! The first is a deref of `x` to create a pointer `p` that points
979 //! at the first element in the array. The second operation is
980 //! an index which adds `y*sizeof(T)` to `p` to obtain the
981 //! pointer to `x[y]`. `cat_index` will produce a resulting
982 //! cmt containing both this deref and the indexing,
983 //! presuming that `base_cmt` is not of fixed-length type.
986 //! - `elt`: the AST node being indexed
987 //! - `base_cmt`: the cmt of `elt`
989 let method_call = ty::MethodCall::expr(elt.id());
990 let method_ty = self.typer.node_method_ty(method_call);
992 let element_ty = match method_ty {
994 let ref_ty = self.overloaded_method_return_ty(method_ty);
995 base_cmt = self.cat_rvalue_node(elt.id(), elt.span(), ref_ty);
997 // FIXME(#20649) -- why are we using the `self_ty` as the element type...?
998 let self_ty = method_ty.fn_sig().input(0);
999 self.tcx().no_late_bound_regions(&self_ty).unwrap()
1002 match base_cmt.ty.builtin_index() {
1011 let m = base_cmt.mutbl.inherit();
1012 let ret = interior(elt, base_cmt.clone(), base_cmt.ty,
1013 m, context, element_ty);
1014 debug!("cat_index ret {:?}", ret);
1017 fn interior<'tcx, N: ast_node>(elt: &N,
1020 mutbl: MutabilityCategory,
1021 context: InteriorOffsetKind,
1022 element_ty: Ty<'tcx>) -> cmt<'tcx>
1024 let interior_elem = InteriorElement(context, element_kind(vec_ty));
1028 cat:cat_interior(of_cmt, interior_elem),
1036 // Takes either a vec or a reference to a vec and returns the cmt for the
1038 fn deref_vec<N:ast_node>(&self,
1040 base_cmt: cmt<'tcx>,
1041 context: InteriorOffsetKind)
1042 -> McResult<cmt<'tcx>>
1044 let ret = match try!(deref_kind(base_cmt.ty, Some(context))) {
1046 // for unique ptrs, we inherit mutability from the
1047 // owning reference.
1048 let m = MutabilityCategory::from_pointer_kind(base_cmt.mutbl, ptr);
1050 // the deref is explicit in the resulting cmt
1054 cat:cat_deref(base_cmt.clone(), 0, ptr),
1056 ty: match base_cmt.ty.builtin_deref(false) {
1058 None => self.tcx().sess.bug("Found non-derefable type")
1064 deref_interior(_) => {
1068 debug!("deref_vec ret {:?}", ret);
1072 /// Given a pattern P like: `[_, ..Q, _]`, where `vec_cmt` is the cmt for `P`, `slice_pat` is
1073 /// the pattern `Q`, returns:
1076 /// * the mutability and region of the slice `Q`
1078 /// These last two bits of info happen to be things that borrowck needs.
1079 pub fn cat_slice_pattern(&self,
1081 slice_pat: &ast::Pat)
1082 -> McResult<(cmt<'tcx>, ast::Mutability, ty::Region)> {
1083 let slice_ty = try!(self.node_ty(slice_pat.id));
1084 let (slice_mutbl, slice_r) = vec_slice_info(self.tcx(),
1087 let context = InteriorOffsetKind::Pattern;
1088 let cmt_vec = try!(self.deref_vec(slice_pat, vec_cmt, context));
1089 let cmt_slice = try!(self.cat_index(slice_pat, cmt_vec, context));
1090 return Ok((cmt_slice, slice_mutbl, slice_r));
1092 /// In a pattern like [a, b, ..c], normally `c` has slice type, but if you have [a, b,
1093 /// ..ref c], then the type of `ref c` will be `&&[]`, so to extract the slice details we
1094 /// have to recurse through rptrs.
1095 fn vec_slice_info(tcx: &ty::ctxt,
1098 -> (ast::Mutability, ty::Region) {
1099 match slice_ty.sty {
1100 ty::TyRef(r, ref mt) => match mt.ty.sty {
1101 ty::TySlice(_) => (mt.mutbl, *r),
1102 _ => vec_slice_info(tcx, pat, mt.ty),
1106 tcx.sess.span_bug(pat.span,
1107 "type of slice pattern is not a slice");
1113 pub fn cat_imm_interior<N:ast_node>(&self,
1115 base_cmt: cmt<'tcx>,
1116 interior_ty: Ty<'tcx>,
1117 interior: InteriorKind)
1119 let ret = Rc::new(cmt_ {
1122 mutbl: base_cmt.mutbl.inherit(),
1123 cat: cat_interior(base_cmt, interior),
1127 debug!("cat_imm_interior ret={:?}", ret);
1131 pub fn cat_downcast<N:ast_node>(&self,
1133 base_cmt: cmt<'tcx>,
1134 downcast_ty: Ty<'tcx>,
1135 variant_did: ast::DefId)
1137 let ret = Rc::new(cmt_ {
1140 mutbl: base_cmt.mutbl.inherit(),
1141 cat: cat_downcast(base_cmt, variant_did),
1145 debug!("cat_downcast ret={:?}", ret);
1149 pub fn cat_pattern<F>(&self, cmt: cmt<'tcx>, pat: &ast::Pat, mut op: F) -> McResult<()>
1150 where F: FnMut(&MemCategorizationContext<'t, 'a, 'tcx>, cmt<'tcx>, &ast::Pat),
1152 self.cat_pattern_(cmt, pat, &mut op)
1155 // FIXME(#19596) This is a workaround, but there should be a better way to do this
1156 fn cat_pattern_<F>(&self, cmt: cmt<'tcx>, pat: &ast::Pat, op: &mut F)
1158 where F : FnMut(&MemCategorizationContext<'t, 'a, 'tcx>, cmt<'tcx>, &ast::Pat),
1160 // Here, `cmt` is the categorization for the value being
1161 // matched and pat is the pattern it is being matched against.
1163 // In general, the way that this works is that we walk down
1164 // the pattern, constructing a cmt that represents the path
1165 // that will be taken to reach the value being matched.
1167 // When we encounter named bindings, we take the cmt that has
1168 // been built up and pass it off to guarantee_valid() so that
1169 // we can be sure that the binding will remain valid for the
1170 // duration of the arm.
1172 // (*2) There is subtlety concerning the correspondence between
1173 // pattern ids and types as compared to *expression* ids and
1174 // types. This is explained briefly. on the definition of the
1175 // type `cmt`, so go off and read what it says there, then
1176 // come back and I'll dive into a bit more detail here. :) OK,
1179 // In general, the id of the cmt should be the node that
1180 // "produces" the value---patterns aren't executable code
1181 // exactly, but I consider them to "execute" when they match a
1182 // value, and I consider them to produce the value that was
1183 // matched. So if you have something like:
1190 // In this case, the cmt and the relevant ids would be:
1192 // CMT Id Type of Id Type of cmt
1195 // ^~~~~~~^ `x` from discr @@int @@int
1196 // ^~~~~~~~~~^ `@@y` pattern node @@int @int
1197 // ^~~~~~~~~~~~~^ `@y` pattern node @int int
1199 // You can see that the types of the id and the cmt are in
1200 // sync in the first line, because that id is actually the id
1201 // of an expression. But once we get to pattern ids, the types
1202 // step out of sync again. So you'll see below that we always
1203 // get the type of the *subpattern* and use that.
1205 debug!("cat_pattern: {:?} cmt={:?}",
1209 (*op)(self, cmt.clone(), pat);
1211 let opt_def = self.tcx().def_map.borrow().get(&pat.id).map(|d| d.full_def());
1213 // Note: This goes up here (rather than within the PatEnum arm
1214 // alone) because struct patterns can refer to struct types or
1215 // to struct variants within enums.
1216 let cmt = match opt_def {
1217 Some(def::DefVariant(enum_did, variant_did, _))
1218 // univariant enums do not need downcasts
1219 if !self.tcx().lookup_adt_def(enum_did).is_univariant() => {
1220 self.cat_downcast(pat, cmt.clone(), cmt.ty, variant_did)
1226 ast::PatWild(_) => {
1230 ast::PatEnum(_, None) => {
1233 ast::PatEnum(_, Some(ref subpats)) => {
1235 Some(def::DefVariant(..)) => {
1237 for (i, subpat) in subpats.iter().enumerate() {
1238 let subpat_ty = try!(self.pat_ty(&**subpat)); // see (*2)
1241 self.cat_imm_interior(
1242 pat, cmt.clone(), subpat_ty,
1243 InteriorField(PositionalField(i)));
1245 try!(self.cat_pattern_(subcmt, &**subpat, op));
1248 Some(def::DefStruct(..)) => {
1249 for (i, subpat) in subpats.iter().enumerate() {
1250 let subpat_ty = try!(self.pat_ty(&**subpat)); // see (*2)
1252 self.cat_imm_interior(
1253 pat, cmt.clone(), subpat_ty,
1254 InteriorField(PositionalField(i)));
1255 try!(self.cat_pattern_(cmt_field, &**subpat, op));
1258 Some(def::DefConst(..)) | Some(def::DefAssociatedConst(..)) => {
1259 for subpat in subpats {
1260 try!(self.cat_pattern_(cmt.clone(), &**subpat, op));
1264 self.tcx().sess.span_bug(
1266 "enum pattern didn't resolve to enum or struct");
1271 ast::PatQPath(..) => {
1272 // Lone constant: ignore
1275 ast::PatIdent(_, _, Some(ref subpat)) => {
1276 try!(self.cat_pattern_(cmt, &**subpat, op));
1279 ast::PatIdent(_, _, None) => {
1280 // nullary variant or identifier: ignore
1283 ast::PatStruct(_, ref field_pats, _) => {
1284 // {f1: p1, ..., fN: pN}
1285 for fp in field_pats {
1286 let field_ty = try!(self.pat_ty(&*fp.node.pat)); // see (*2)
1287 let cmt_field = self.cat_field(pat, cmt.clone(), fp.node.ident.name, field_ty);
1288 try!(self.cat_pattern_(cmt_field, &*fp.node.pat, op));
1292 ast::PatTup(ref subpats) => {
1294 for (i, subpat) in subpats.iter().enumerate() {
1295 let subpat_ty = try!(self.pat_ty(&**subpat)); // see (*2)
1297 self.cat_imm_interior(
1298 pat, cmt.clone(), subpat_ty,
1299 InteriorField(PositionalField(i)));
1300 try!(self.cat_pattern_(subcmt, &**subpat, op));
1304 ast::PatBox(ref subpat) | ast::PatRegion(ref subpat, _) => {
1305 // box p1, &p1, &mut p1. we can ignore the mutability of
1306 // PatRegion since that information is already contained
1308 let subcmt = try!(self.cat_deref(pat, cmt, 0, None));
1309 try!(self.cat_pattern_(subcmt, &**subpat, op));
1312 ast::PatVec(ref before, ref slice, ref after) => {
1313 let context = InteriorOffsetKind::Pattern;
1314 let vec_cmt = try!(self.deref_vec(pat, cmt, context));
1315 let elt_cmt = try!(self.cat_index(pat, vec_cmt, context));
1316 for before_pat in before {
1317 try!(self.cat_pattern_(elt_cmt.clone(), &**before_pat, op));
1319 if let Some(ref slice_pat) = *slice {
1320 let slice_ty = try!(self.pat_ty(&**slice_pat));
1321 let slice_cmt = self.cat_rvalue_node(pat.id(), pat.span(), slice_ty);
1322 try!(self.cat_pattern_(slice_cmt, &**slice_pat, op));
1324 for after_pat in after {
1325 try!(self.cat_pattern_(elt_cmt.clone(), &**after_pat, op));
1329 ast::PatLit(_) | ast::PatRange(_, _) => {
1334 self.tcx().sess.span_bug(pat.span, "unexpanded macro");
1341 fn overloaded_method_return_ty(&self,
1342 method_ty: Ty<'tcx>)
1345 // When we process an overloaded `*` or `[]` etc, we often
1346 // need to extract the return type of the method. These method
1347 // types are generated by method resolution and always have
1348 // all late-bound regions fully instantiated, so we just want
1349 // to skip past the binder.
1350 self.tcx().no_late_bound_regions(&method_ty.fn_ret())
1352 .unwrap() // overloaded ops do not diverge, either
1356 #[derive(Clone, Debug)]
1357 pub enum Aliasability {
1358 FreelyAliasable(AliasableReason),
1360 ImmutableUnique(Box<Aliasability>),
1363 #[derive(Copy, Clone, Debug)]
1364 pub enum AliasableReason {
1366 AliasableClosure(ast::NodeId), // Aliasable due to capture Fn closure env
1368 UnaliasableImmutable, // Created as needed upon seeing ImmutableUnique
1373 impl<'tcx> cmt_<'tcx> {
1374 pub fn guarantor(&self) -> cmt<'tcx> {
1375 //! Returns `self` after stripping away any derefs or
1376 //! interior content. The return value is basically the `cmt` which
1377 //! determines how long the value in `self` remains live.
1383 cat_deref(_, _, UnsafePtr(..)) |
1384 cat_deref(_, _, BorrowedPtr(..)) |
1385 cat_deref(_, _, Implicit(..)) |
1387 Rc::new((*self).clone())
1389 cat_downcast(ref b, _) |
1390 cat_interior(ref b, _) |
1391 cat_deref(ref b, _, Unique) => {
1397 /// Returns `FreelyAliasable(_)` if this lvalue represents a freely aliasable pointer type.
1398 pub fn freely_aliasable(&self, ctxt: &ty::ctxt<'tcx>)
1400 // Maybe non-obvious: copied upvars can only be considered
1401 // non-aliasable in once closures, since any other kind can be
1402 // aliased and eventually recused.
1405 cat_deref(ref b, _, BorrowedPtr(ty::MutBorrow, _)) |
1406 cat_deref(ref b, _, Implicit(ty::MutBorrow, _)) |
1407 cat_deref(ref b, _, BorrowedPtr(ty::UniqueImmBorrow, _)) |
1408 cat_deref(ref b, _, Implicit(ty::UniqueImmBorrow, _)) |
1409 cat_downcast(ref b, _) |
1410 cat_interior(ref b, _) => {
1411 // Aliasability depends on base cmt
1412 b.freely_aliasable(ctxt)
1415 cat_deref(ref b, _, Unique) => {
1416 let sub = b.freely_aliasable(ctxt);
1417 if b.mutbl.is_mutable() {
1418 // Aliasability depends on base cmt alone
1421 // Do not allow mutation through an immutable box.
1422 ImmutableUnique(Box::new(sub))
1429 cat_deref(_, _, UnsafePtr(..)) => { // yes, it's aliasable, but...
1433 cat_static_item(..) => {
1434 if self.mutbl.is_mutable() {
1435 FreelyAliasable(AliasableStaticMut)
1437 FreelyAliasable(AliasableStatic)
1441 cat_deref(ref base, _, BorrowedPtr(ty::ImmBorrow, _)) |
1442 cat_deref(ref base, _, Implicit(ty::ImmBorrow, _)) => {
1444 cat_upvar(Upvar{ id, .. }) =>
1445 FreelyAliasable(AliasableClosure(id.closure_expr_id)),
1446 _ => FreelyAliasable(AliasableBorrowed)
1452 // Digs down through one or two layers of deref and grabs the cmt
1453 // for the upvar if a note indicates there is one.
1454 pub fn upvar(&self) -> Option<cmt<'tcx>> {
1456 NoteClosureEnv(..) | NoteUpvarRef(..) => {
1457 Some(match self.cat {
1458 cat_deref(ref inner, _, _) => {
1460 cat_deref(ref inner, _, _) => inner.clone(),
1461 cat_upvar(..) => inner.clone(),
1473 pub fn descriptive_string(&self, tcx: &ty::ctxt) -> String {
1475 cat_static_item => {
1476 "static item".to_string()
1479 "non-lvalue".to_string()
1482 match tcx.map.find(vid) {
1483 Some(ast_map::NodeArg(_)) => {
1484 "argument".to_string()
1486 _ => "local variable".to_string()
1489 cat_deref(_, _, pk) => {
1490 let upvar = self.upvar();
1491 match upvar.as_ref().map(|i| &i.cat) {
1492 Some(&cat_upvar(ref var)) => {
1495 Some(_) => unreachable!(),
1499 format!("indexed content")
1502 format!("`Box` content")
1505 format!("dereference of raw pointer")
1507 BorrowedPtr(..) => {
1508 format!("borrowed content")
1514 cat_interior(_, InteriorField(NamedField(_))) => {
1517 cat_interior(_, InteriorField(PositionalField(_))) => {
1518 "anonymous field".to_string()
1520 cat_interior(_, InteriorElement(InteriorOffsetKind::Index,
1522 cat_interior(_, InteriorElement(InteriorOffsetKind::Index,
1524 "indexed content".to_string()
1526 cat_interior(_, InteriorElement(InteriorOffsetKind::Pattern,
1528 cat_interior(_, InteriorElement(InteriorOffsetKind::Pattern,
1530 "pattern-bound indexed content".to_string()
1532 cat_upvar(ref var) => {
1535 cat_downcast(ref cmt, _) => {
1536 cmt.descriptive_string(tcx)
1542 impl<'tcx> fmt::Debug for cmt_<'tcx> {
1543 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1544 write!(f, "{{{:?} id:{} m:{:?} ty:{:?}}}",
1552 impl<'tcx> fmt::Debug for categorization<'tcx> {
1553 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1555 cat_static_item => write!(f, "static"),
1556 cat_rvalue(r) => write!(f, "rvalue({:?})", r),
1558 let name = ty::tls::with(|tcx| tcx.local_var_name_str(id));
1559 write!(f, "local({})", name)
1561 cat_upvar(upvar) => {
1562 write!(f, "upvar({:?})", upvar)
1564 cat_deref(ref cmt, derefs, ptr) => {
1565 write!(f, "{:?}-{:?}{}->", cmt.cat, ptr, derefs)
1567 cat_interior(ref cmt, interior) => {
1568 write!(f, "{:?}.{:?}", cmt.cat, interior)
1570 cat_downcast(ref cmt, _) => {
1571 write!(f, "{:?}->(enum)", cmt.cat)
1577 pub fn ptr_sigil(ptr: PointerKind) -> &'static str {
1580 BorrowedPtr(ty::ImmBorrow, _) |
1581 Implicit(ty::ImmBorrow, _) => "&",
1582 BorrowedPtr(ty::MutBorrow, _) |
1583 Implicit(ty::MutBorrow, _) => "&mut",
1584 BorrowedPtr(ty::UniqueImmBorrow, _) |
1585 Implicit(ty::UniqueImmBorrow, _) => "&unique",
1586 UnsafePtr(_) => "*",
1590 impl fmt::Debug for PointerKind {
1591 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1593 Unique => write!(f, "Box"),
1594 BorrowedPtr(ty::ImmBorrow, ref r) |
1595 Implicit(ty::ImmBorrow, ref r) => {
1596 write!(f, "&{:?}", r)
1598 BorrowedPtr(ty::MutBorrow, ref r) |
1599 Implicit(ty::MutBorrow, ref r) => {
1600 write!(f, "&{:?} mut", r)
1602 BorrowedPtr(ty::UniqueImmBorrow, ref r) |
1603 Implicit(ty::UniqueImmBorrow, ref r) => {
1604 write!(f, "&{:?} uniq", r)
1606 UnsafePtr(_) => write!(f, "*")
1611 impl fmt::Debug for InteriorKind {
1612 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1614 InteriorField(NamedField(fld)) => write!(f, "{}", fld),
1615 InteriorField(PositionalField(i)) => write!(f, "#{}", i),
1616 InteriorElement(..) => write!(f, "[]"),
1621 fn element_kind(t: Ty) -> ElementKind {
1623 ty::TyRef(_, ty::TypeAndMut{ty, ..}) |
1624 ty::TyBox(ty) => match ty.sty {
1625 ty::TySlice(_) => VecElement,
1628 ty::TyArray(..) | ty::TySlice(_) => VecElement,
1633 impl fmt::Debug for Upvar {
1634 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1635 write!(f, "{:?}/{:?}", self.id, self.kind)
1639 impl fmt::Display for Upvar {
1640 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1641 let kind = match self.kind {
1642 ty::FnClosureKind => "Fn",
1643 ty::FnMutClosureKind => "FnMut",
1644 ty::FnOnceClosureKind => "FnOnce",
1646 write!(f, "captured outer variable in an `{}` closure", kind)