1 // Copyright 2012-2014 The Rust Project Developers. See the COPYRIGHT
2 // file at the top-level directory of this distribution and at
3 // http://rust-lang.org/COPYRIGHT.
5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
8 // option. This file may not be copied, modified, or distributed
9 // except according to those terms.
13 //! The job of the categorization module is to analyze an expression to
14 //! determine what kind of memory is used in evaluating it (for example,
15 //! where dereferences occur and what kind of pointer is dereferenced;
16 //! whether the memory is mutable; etc)
18 //! Categorization effectively transforms all of our expressions into
19 //! expressions of the following forms (the actual enum has many more
20 //! possibilities, naturally, but they are all variants of these base
23 //! E = rvalue // some computed rvalue
24 //! | x // address of a local variable or argument
25 //! | *E // deref of a ptr
26 //! | E.comp // access to an interior component
28 //! Imagine a routine ToAddr(Expr) that evaluates an expression and returns an
29 //! address where the result is to be found. If Expr is an lvalue, then this
30 //! is the address of the lvalue. If Expr is an rvalue, this is the address of
31 //! some temporary spot in memory where the result is stored.
33 //! Now, cat_expr() classifies the expression Expr and the address A=ToAddr(Expr)
36 //! - cat: what kind of expression was this? This is a subset of the
37 //! full expression forms which only includes those that we care about
38 //! for the purpose of the analysis.
39 //! - mutbl: mutability of the address A
40 //! - ty: the type of data found at the address A
42 //! The resulting categorization tree differs somewhat from the expressions
43 //! themselves. For example, auto-derefs are explicit. Also, an index a[b] is
44 //! decomposed into two operations: a dereference to reach the array data and
45 //! then an index to jump forward to the relevant item.
47 //! ## By-reference upvars
49 //! One part of the translation which may be non-obvious is that we translate
50 //! closure upvars into the dereference of a borrowed pointer; this more closely
51 //! resembles the runtime translation. So, for example, if we had:
55 //! let inc = || x += y;
57 //! Then when we categorize `x` (*within* the closure) we would yield a
58 //! result of `*x'`, effectively, where `x'` is a `Categorization::Upvar` reference
59 //! tied to `x`. The type of `x'` will be a borrowed pointer.
61 #![allow(non_camel_case_types)]
63 pub use self::PointerKind::*;
64 pub use self::InteriorKind::*;
65 pub use self::FieldName::*;
66 pub use self::ElementKind::*;
67 pub use self::MutabilityCategory::*;
68 pub use self::AliasableReason::*;
69 pub use self::Note::*;
70 pub use self::deref_kind::*;
72 use self::Aliasability::*;
74 use middle::def_id::DefId;
75 use front::map as ast_map;
77 use middle::check_const;
79 use middle::ty::adjustment;
80 use middle::ty::{self, Ty};
82 use rustc_front::hir::{MutImmutable, MutMutable};
85 use syntax::codemap::Span;
90 #[derive(Clone, PartialEq)]
91 pub enum Categorization<'tcx> {
92 Rvalue(ty::Region), // temporary val, argument is its scope
94 Upvar(Upvar), // upvar referenced by closure env
95 Local(ast::NodeId), // local variable
96 Deref(cmt<'tcx>, usize, PointerKind), // deref of a ptr
97 Interior(cmt<'tcx>, InteriorKind), // something interior: field, tuple, etc
98 Downcast(cmt<'tcx>, DefId), // selects a particular enum variant (*1)
100 // (*1) downcast is only required if the enum has more than one variant
103 // Represents any kind of upvar
104 #[derive(Clone, Copy, PartialEq)]
107 pub kind: ty::ClosureKind
110 // different kinds of pointers:
111 #[derive(Clone, Copy, PartialEq, Eq, Hash)]
112 pub enum PointerKind {
117 BorrowedPtr(ty::BorrowKind, ty::Region),
120 UnsafePtr(hir::Mutability),
122 /// Implicit deref of the `&T` that results from an overloaded index `[]`.
123 Implicit(ty::BorrowKind, ty::Region),
126 // We use the term "interior" to mean "something reachable from the
127 // base without a pointer dereference", e.g. a field
128 #[derive(Clone, Copy, PartialEq, Eq, Hash)]
129 pub enum InteriorKind {
130 InteriorField(FieldName),
131 InteriorElement(InteriorOffsetKind, ElementKind),
134 #[derive(Clone, Copy, PartialEq, Eq, Hash, Debug)]
136 NamedField(ast::Name),
137 PositionalField(usize)
140 #[derive(Clone, Copy, PartialEq, Eq, Hash, Debug)]
141 pub enum InteriorOffsetKind {
142 Index, // e.g. `array_expr[index_expr]`
143 Pattern, // e.g. `fn foo([_, a, _, _]: [A; 4]) { ... }`
146 #[derive(Clone, Copy, PartialEq, Eq, Hash, Debug)]
147 pub enum ElementKind {
152 #[derive(Clone, Copy, PartialEq, Eq, Hash, Debug)]
153 pub enum MutabilityCategory {
154 McImmutable, // Immutable.
155 McDeclared, // Directly declared as mutable.
156 McInherited, // Inherited from the fact that owner is mutable.
159 // A note about the provenance of a `cmt`. This is used for
160 // special-case handling of upvars such as mutability inference.
161 // Upvar categorization can generate a variable number of nested
162 // derefs. The note allows detecting them without deep pattern
163 // matching on the categorization.
164 #[derive(Clone, Copy, PartialEq, Debug)]
166 NoteClosureEnv(ty::UpvarId), // Deref through closure env
167 NoteUpvarRef(ty::UpvarId), // Deref through by-ref upvar
168 NoteNone // Nothing special
171 // `cmt`: "Category, Mutability, and Type".
173 // a complete categorization of a value indicating where it originated
174 // and how it is located, as well as the mutability of the memory in
175 // which the value is stored.
177 // *WARNING* The field `cmt.type` is NOT necessarily the same as the
178 // result of `node_id_to_type(cmt.id)`. This is because the `id` is
179 // always the `id` of the node producing the type; in an expression
180 // like `*x`, the type of this deref node is the deref'd type (`T`),
181 // but in a pattern like `@x`, the `@x` pattern is again a
182 // dereference, but its type is the type *before* the dereference
183 // (`@T`). So use `cmt.ty` to find the type of the value in a consistent
184 // fashion. For more details, see the method `cat_pattern`
185 #[derive(Clone, PartialEq)]
186 pub struct cmt_<'tcx> {
187 pub id: ast::NodeId, // id of expr/pat producing this value
188 pub span: Span, // span of same expr/pat
189 pub cat: Categorization<'tcx>, // categorization of expr
190 pub mutbl: MutabilityCategory, // mutability of expr as lvalue
191 pub ty: Ty<'tcx>, // type of the expr (*see WARNING above*)
192 pub note: Note, // Note about the provenance of this cmt
195 pub type cmt<'tcx> = Rc<cmt_<'tcx>>;
197 // We pun on *T to mean both actual deref of a ptr as well
198 // as accessing of components:
199 #[derive(Copy, Clone)]
200 pub enum deref_kind {
201 deref_ptr(PointerKind),
202 deref_interior(InteriorKind),
205 type DerefKindContext = Option<InteriorOffsetKind>;
207 // Categorizes a derefable type. Note that we include vectors and strings as
208 // derefable (we model an index as the combination of a deref and then a
209 // pointer adjustment).
210 fn deref_kind(t: Ty, context: DerefKindContext) -> McResult<deref_kind> {
213 Ok(deref_ptr(Unique))
216 ty::TyRef(r, mt) => {
217 let kind = ty::BorrowKind::from_mutbl(mt.mutbl);
218 Ok(deref_ptr(BorrowedPtr(kind, *r)))
221 ty::TyRawPtr(ref mt) => {
222 Ok(deref_ptr(UnsafePtr(mt.mutbl)))
226 ty::TyStruct(..) => { // newtype
227 Ok(deref_interior(InteriorField(PositionalField(0))))
230 ty::TyArray(_, _) | ty::TySlice(_) | ty::TyStr => {
231 // no deref of indexed content without supplying InteriorOffsetKind
232 if let Some(context) = context {
233 Ok(deref_interior(InteriorElement(context, element_kind(t))))
244 fn id(&self) -> ast::NodeId;
245 fn span(&self) -> Span;
248 impl ast_node for hir::Expr {
249 fn id(&self) -> ast::NodeId { self.id }
250 fn span(&self) -> Span { self.span }
253 impl ast_node for hir::Pat {
254 fn id(&self) -> ast::NodeId { self.id }
255 fn span(&self) -> Span { self.span }
258 #[derive(Copy, Clone)]
259 pub struct MemCategorizationContext<'t, 'a: 't, 'tcx : 'a> {
260 pub typer: &'t infer::InferCtxt<'a, 'tcx>,
263 pub type McResult<T> = Result<T, ()>;
265 impl MutabilityCategory {
266 pub fn from_mutbl(m: hir::Mutability) -> MutabilityCategory {
268 MutImmutable => McImmutable,
269 MutMutable => McDeclared
271 debug!("MutabilityCategory::{}({:?}) => {:?}",
272 "from_mutbl", m, ret);
276 pub fn from_borrow_kind(borrow_kind: ty::BorrowKind) -> MutabilityCategory {
277 let ret = match borrow_kind {
278 ty::ImmBorrow => McImmutable,
279 ty::UniqueImmBorrow => McImmutable,
280 ty::MutBorrow => McDeclared,
282 debug!("MutabilityCategory::{}({:?}) => {:?}",
283 "from_borrow_kind", borrow_kind, ret);
287 fn from_pointer_kind(base_mutbl: MutabilityCategory,
288 ptr: PointerKind) -> MutabilityCategory {
289 let ret = match ptr {
293 BorrowedPtr(borrow_kind, _) | Implicit(borrow_kind, _) => {
294 MutabilityCategory::from_borrow_kind(borrow_kind)
297 MutabilityCategory::from_mutbl(m)
300 debug!("MutabilityCategory::{}({:?}, {:?}) => {:?}",
301 "from_pointer_kind", base_mutbl, ptr, ret);
305 fn from_local(tcx: &ty::ctxt, id: ast::NodeId) -> MutabilityCategory {
306 let ret = match tcx.map.get(id) {
307 ast_map::NodeLocal(p) => match p.node {
308 hir::PatIdent(bind_mode, _, _) => {
309 if bind_mode == hir::BindByValue(hir::MutMutable) {
315 _ => tcx.sess.span_bug(p.span, "expected identifier pattern")
317 _ => tcx.sess.span_bug(tcx.map.span(id), "expected identifier pattern")
319 debug!("MutabilityCategory::{}(tcx, id={:?}) => {:?}",
320 "from_local", id, ret);
324 pub fn inherit(&self) -> MutabilityCategory {
325 let ret = match *self {
326 McImmutable => McImmutable,
327 McDeclared => McInherited,
328 McInherited => McInherited,
330 debug!("{:?}.inherit() => {:?}", self, ret);
334 pub fn is_mutable(&self) -> bool {
335 let ret = match *self {
336 McImmutable => false,
340 debug!("{:?}.is_mutable() => {:?}", self, ret);
344 pub fn is_immutable(&self) -> bool {
345 let ret = match *self {
347 McDeclared | McInherited => false
349 debug!("{:?}.is_immutable() => {:?}", self, ret);
353 pub fn to_user_str(&self) -> &'static str {
355 McDeclared | McInherited => "mutable",
356 McImmutable => "immutable",
361 impl<'t, 'a,'tcx> MemCategorizationContext<'t, 'a, 'tcx> {
362 pub fn new(typer: &'t infer::InferCtxt<'a, 'tcx>) -> MemCategorizationContext<'t, 'a, 'tcx> {
363 MemCategorizationContext { typer: typer }
366 fn tcx(&self) -> &'a ty::ctxt<'tcx> {
370 fn expr_ty(&self, expr: &hir::Expr) -> McResult<Ty<'tcx>> {
371 match self.typer.node_ty(expr.id) {
374 debug!("expr_ty({:?}) yielded Err", expr);
380 fn expr_ty_adjusted(&self, expr: &hir::Expr) -> McResult<Ty<'tcx>> {
381 let unadjusted_ty = try!(self.expr_ty(expr));
382 Ok(unadjusted_ty.adjust(
383 self.tcx(), expr.span, expr.id,
384 self.typer.adjustments().get(&expr.id),
385 |method_call| self.typer.node_method_ty(method_call)))
388 fn node_ty(&self, id: ast::NodeId) -> McResult<Ty<'tcx>> {
389 self.typer.node_ty(id)
392 fn pat_ty(&self, pat: &hir::Pat) -> McResult<Ty<'tcx>> {
393 let base_ty = try!(self.typer.node_ty(pat.id));
394 // FIXME (Issue #18207): This code detects whether we are
395 // looking at a `ref x`, and if so, figures out what the type
396 // *being borrowed* is. But ideally we would put in a more
397 // fundamental fix to this conflated use of the node id.
398 let ret_ty = match pat.node {
399 hir::PatIdent(hir::BindByRef(_), _, _) => {
400 // a bind-by-ref means that the base_ty will be the type of the ident itself,
401 // but what we want here is the type of the underlying value being borrowed.
402 // So peel off one-level, turning the &T into T.
403 match base_ty.builtin_deref(false, ty::NoPreference) {
405 None => { return Err(()); }
410 debug!("pat_ty(pat={:?}) base_ty={:?} ret_ty={:?}",
411 pat, base_ty, ret_ty);
415 pub fn cat_expr(&self, expr: &hir::Expr) -> McResult<cmt<'tcx>> {
416 match self.typer.adjustments().get(&expr.id) {
419 self.cat_expr_unadjusted(expr)
422 Some(adjustment) => {
424 adjustment::AdjustDerefRef(
425 adjustment::AutoDerefRef {
426 autoref: None, unsize: None, autoderefs, ..}) => {
427 // Equivalent to *expr or something similar.
428 self.cat_expr_autoderefd(expr, autoderefs)
431 adjustment::AdjustReifyFnPointer |
432 adjustment::AdjustUnsafeFnPointer |
433 adjustment::AdjustDerefRef(_) => {
434 debug!("cat_expr({:?}): {:?}",
437 // Result is an rvalue.
438 let expr_ty = try!(self.expr_ty_adjusted(expr));
439 Ok(self.cat_rvalue_node(expr.id(), expr.span(), expr_ty))
446 pub fn cat_expr_autoderefd(&self,
449 -> McResult<cmt<'tcx>> {
450 let mut cmt = try!(self.cat_expr_unadjusted(expr));
451 debug!("cat_expr_autoderefd: autoderefs={}, cmt={:?}",
454 for deref in 1..autoderefs + 1 {
455 cmt = try!(self.cat_deref(expr, cmt, deref, None));
460 pub fn cat_expr_unadjusted(&self, expr: &hir::Expr) -> McResult<cmt<'tcx>> {
461 debug!("cat_expr: id={} expr={:?}", expr.id, expr);
463 let expr_ty = try!(self.expr_ty(expr));
465 hir::ExprUnary(hir::UnDeref, ref e_base) => {
466 let base_cmt = try!(self.cat_expr(&**e_base));
467 self.cat_deref(expr, base_cmt, 0, None)
470 hir::ExprField(ref base, f_name) => {
471 let base_cmt = try!(self.cat_expr(&**base));
472 debug!("cat_expr(cat_field): id={} expr={:?} base={:?}",
476 Ok(self.cat_field(expr, base_cmt, f_name.node, expr_ty))
479 hir::ExprTupField(ref base, idx) => {
480 let base_cmt = try!(self.cat_expr(&**base));
481 Ok(self.cat_tup_field(expr, base_cmt, idx.node, expr_ty))
484 hir::ExprIndex(ref base, _) => {
485 let method_call = ty::MethodCall::expr(expr.id());
486 let context = InteriorOffsetKind::Index;
487 match self.typer.node_method_ty(method_call) {
489 // If this is an index implemented by a method call, then it
490 // will include an implicit deref of the result.
491 let ret_ty = self.overloaded_method_return_ty(method_ty);
493 // The index method always returns an `&T`, so
494 // dereference it to find the result type.
495 let elem_ty = match ret_ty.sty {
496 ty::TyRef(_, mt) => mt.ty,
498 debug!("cat_expr_unadjusted: return type of overloaded index is {:?}?",
504 // The call to index() returns a `&T` value, which
505 // is an rvalue. That is what we will be
507 let base_cmt = self.cat_rvalue_node(expr.id(), expr.span(), ret_ty);
508 self.cat_deref_common(expr, base_cmt, 1, elem_ty, Some(context), true)
511 self.cat_index(expr, try!(self.cat_expr(&**base)), context)
516 hir::ExprPath(..) => {
517 let def = self.tcx().def_map.borrow().get(&expr.id).unwrap().full_def();
518 self.cat_def(expr.id, expr.span, expr_ty, def)
521 hir::ExprAddrOf(..) | hir::ExprCall(..) |
522 hir::ExprAssign(..) | hir::ExprAssignOp(..) |
523 hir::ExprClosure(..) | hir::ExprRet(..) |
524 hir::ExprUnary(..) | hir::ExprRange(..) |
525 hir::ExprMethodCall(..) | hir::ExprCast(..) |
526 hir::ExprVec(..) | hir::ExprTup(..) | hir::ExprIf(..) |
527 hir::ExprBinary(..) | hir::ExprWhile(..) |
528 hir::ExprBlock(..) | hir::ExprLoop(..) | hir::ExprMatch(..) |
529 hir::ExprLit(..) | hir::ExprBreak(..) |
530 hir::ExprAgain(..) | hir::ExprStruct(..) | hir::ExprRepeat(..) |
531 hir::ExprInlineAsm(..) | hir::ExprBox(..) => {
532 Ok(self.cat_rvalue_node(expr.id(), expr.span(), expr_ty))
537 pub fn cat_def(&self,
542 -> McResult<cmt<'tcx>> {
543 debug!("cat_def: id={} expr={:?} def={:?}",
547 def::DefStruct(..) | def::DefVariant(..) | def::DefConst(..) |
548 def::DefAssociatedConst(..) | def::DefFn(..) | def::DefMethod(..) => {
549 Ok(self.cat_rvalue_node(id, span, expr_ty))
551 def::DefMod(_) | def::DefForeignMod(_) | def::DefUse(_) |
552 def::DefTrait(_) | def::DefTy(..) | def::DefPrimTy(_) |
553 def::DefTyParam(..) |
554 def::DefLabel(_) | def::DefSelfTy(..) |
555 def::DefAssociatedTy(..) => {
559 cat:Categorization::StaticItem,
566 def::DefStatic(_, mutbl) => {
570 cat:Categorization::StaticItem,
571 mutbl: if mutbl { McDeclared } else { McImmutable},
577 def::DefUpvar(_, var_id, _, fn_node_id) => {
578 let ty = try!(self.node_ty(fn_node_id));
580 ty::TyClosure(closure_id, _) => {
581 match self.typer.closure_kind(closure_id) {
583 self.cat_upvar(id, span, var_id, fn_node_id, kind)
586 self.tcx().sess.span_bug(
588 &*format!("No closure kind for {:?}", closure_id));
593 self.tcx().sess.span_bug(
595 &format!("Upvar of non-closure {} - {:?}",
602 def::DefLocal(_, vid) => {
606 cat: Categorization::Local(vid),
607 mutbl: MutabilityCategory::from_local(self.tcx(), vid),
615 // Categorize an upvar, complete with invisible derefs of closure
616 // environment and upvar reference as appropriate.
621 fn_node_id: ast::NodeId,
622 kind: ty::ClosureKind)
623 -> McResult<cmt<'tcx>>
625 // An upvar can have up to 3 components. We translate first to a
626 // `Categorization::Upvar`, which is itself a fiction -- it represents the reference to the
627 // field from the environment.
629 // `Categorization::Upvar`. Next, we add a deref through the implicit
630 // environment pointer with an anonymous free region 'env and
631 // appropriate borrow kind for closure kinds that take self by
632 // reference. Finally, if the upvar was captured
633 // by-reference, we add a deref through that reference. The
634 // region of this reference is an inference variable 'up that
635 // was previously generated and recorded in the upvar borrow
636 // map. The borrow kind bk is inferred by based on how the
639 // This results in the following table for concrete closure
643 // ---------------+----------------------+-------------------------------
644 // Fn | copied -> &'env | upvar -> &'env -> &'up bk
645 // FnMut | copied -> &'env mut | upvar -> &'env mut -> &'up bk
646 // FnOnce | copied | upvar -> &'up bk
648 let upvar_id = ty::UpvarId { var_id: var_id,
649 closure_expr_id: fn_node_id };
650 let var_ty = try!(self.node_ty(var_id));
652 // Mutability of original variable itself
653 let var_mutbl = MutabilityCategory::from_local(self.tcx(), var_id);
655 // Construct the upvar. This represents access to the field
656 // from the environment (perhaps we should eventually desugar
657 // this field further, but it will do for now).
658 let cmt_result = cmt_ {
661 cat: Categorization::Upvar(Upvar {id: upvar_id, kind: kind}),
667 // If this is a `FnMut` or `Fn` closure, then the above is
668 // conceptually a `&mut` or `&` reference, so we have to add a
670 let cmt_result = match kind {
671 ty::FnOnceClosureKind => {
674 ty::FnMutClosureKind => {
675 self.env_deref(id, span, upvar_id, var_mutbl, ty::MutBorrow, cmt_result)
677 ty::FnClosureKind => {
678 self.env_deref(id, span, upvar_id, var_mutbl, ty::ImmBorrow, cmt_result)
682 // If this is a by-ref capture, then the upvar we loaded is
683 // actually a reference, so we have to add an implicit deref
685 let upvar_id = ty::UpvarId { var_id: var_id,
686 closure_expr_id: fn_node_id };
687 let upvar_capture = self.typer.upvar_capture(upvar_id).unwrap();
688 let cmt_result = match upvar_capture {
689 ty::UpvarCapture::ByValue => {
692 ty::UpvarCapture::ByRef(upvar_borrow) => {
693 let ptr = BorrowedPtr(upvar_borrow.kind, upvar_borrow.region);
697 cat: Categorization::Deref(Rc::new(cmt_result), 0, ptr),
698 mutbl: MutabilityCategory::from_borrow_kind(upvar_borrow.kind),
700 note: NoteUpvarRef(upvar_id)
705 let ret = Rc::new(cmt_result);
706 debug!("cat_upvar ret={:?}", ret);
713 upvar_id: ty::UpvarId,
714 upvar_mutbl: MutabilityCategory,
715 env_borrow_kind: ty::BorrowKind,
716 cmt_result: cmt_<'tcx>)
719 // Look up the node ID of the closure body so we can construct
720 // a free region within it
722 let fn_expr = match self.tcx().map.find(upvar_id.closure_expr_id) {
723 Some(ast_map::NodeExpr(e)) => e,
728 hir::ExprClosure(_, _, ref body) => body.id,
733 // Region of environment pointer
734 let env_region = ty::ReFree(ty::FreeRegion {
735 // The environment of a closure is guaranteed to
736 // outlive any bindings introduced in the body of the
738 scope: self.tcx().region_maps.item_extent(fn_body_id),
739 bound_region: ty::BrEnv
742 let env_ptr = BorrowedPtr(env_borrow_kind, env_region);
744 let var_ty = cmt_result.ty;
746 // We need to add the env deref. This means
747 // that the above is actually immutable and
748 // has a ref type. However, nothing should
749 // actually look at the type, so we can get
750 // away with stuffing a `TyError` in there
751 // instead of bothering to construct a proper
753 let cmt_result = cmt_ {
755 ty: self.tcx().types.err,
759 let mut deref_mutbl = MutabilityCategory::from_borrow_kind(env_borrow_kind);
761 // Issue #18335. If variable is declared as immutable, override the
762 // mutability from the environment and substitute an `&T` anyway.
764 McImmutable => { deref_mutbl = McImmutable; }
765 McDeclared | McInherited => { }
771 cat: Categorization::Deref(Rc::new(cmt_result), 0, env_ptr),
774 note: NoteClosureEnv(upvar_id)
777 debug!("env_deref ret {:?}", ret);
782 /// Returns the lifetime of a temporary created by expr with id `id`.
783 /// This could be `'static` if `id` is part of a constant expression.
784 pub fn temporary_scope(&self, id: ast::NodeId) -> ty::Region {
785 match self.typer.temporary_scope(id) {
786 Some(scope) => ty::ReScope(scope),
791 pub fn cat_rvalue_node(&self,
796 let qualif = self.tcx().const_qualif_map.borrow().get(&id).cloned()
797 .unwrap_or(check_const::ConstQualif::NOT_CONST);
799 // Only promote `[T; 0]` before an RFC for rvalue promotions
801 let qualif = match expr_ty.sty {
802 ty::TyArray(_, 0) => qualif,
803 _ => check_const::ConstQualif::NOT_CONST
806 // Compute maximum lifetime of this rvalue. This is 'static if
807 // we can promote to a constant, otherwise equal to enclosing temp
809 let re = if qualif.intersects(check_const::ConstQualif::NON_STATIC_BORROWS) {
810 self.temporary_scope(id)
814 let ret = self.cat_rvalue(id, span, re, expr_ty);
815 debug!("cat_rvalue_node ret {:?}", ret);
819 pub fn cat_rvalue(&self,
822 temp_scope: ty::Region,
823 expr_ty: Ty<'tcx>) -> cmt<'tcx> {
824 let ret = Rc::new(cmt_ {
827 cat:Categorization::Rvalue(temp_scope),
832 debug!("cat_rvalue ret {:?}", ret);
836 pub fn cat_field<N:ast_node>(&self,
842 let ret = Rc::new(cmt_ {
845 mutbl: base_cmt.mutbl.inherit(),
846 cat: Categorization::Interior(base_cmt, InteriorField(NamedField(f_name))),
850 debug!("cat_field ret {:?}", ret);
854 pub fn cat_tup_field<N:ast_node>(&self,
860 let ret = Rc::new(cmt_ {
863 mutbl: base_cmt.mutbl.inherit(),
864 cat: Categorization::Interior(base_cmt, InteriorField(PositionalField(f_idx))),
868 debug!("cat_tup_field ret {:?}", ret);
872 fn cat_deref<N:ast_node>(&self,
876 deref_context: DerefKindContext)
877 -> McResult<cmt<'tcx>> {
878 let method_call = ty::MethodCall {
880 autoderef: deref_cnt as u32
882 let method_ty = self.typer.node_method_ty(method_call);
884 debug!("cat_deref: method_call={:?} method_ty={:?}",
885 method_call, method_ty.map(|ty| ty));
887 let base_cmt = match method_ty {
890 self.tcx().no_late_bound_regions(&method_ty.fn_ret()).unwrap().unwrap();
891 self.cat_rvalue_node(node.id(), node.span(), ref_ty)
895 let base_cmt_ty = base_cmt.ty;
896 match base_cmt_ty.builtin_deref(true, ty::NoPreference) {
898 let ret = self.cat_deref_common(node, base_cmt, deref_cnt,
901 /* implicit: */ false);
902 debug!("cat_deref ret {:?}", ret);
906 debug!("Explicit deref of non-derefable type: {:?}",
913 fn cat_deref_common<N:ast_node>(&self,
918 deref_context: DerefKindContext,
920 -> McResult<cmt<'tcx>>
922 let (m, cat) = match try!(deref_kind(base_cmt.ty, deref_context)) {
924 let ptr = if implicit {
926 BorrowedPtr(bk, r) => Implicit(bk, r),
927 _ => self.tcx().sess.span_bug(node.span(),
928 "Implicit deref of non-borrowed pointer")
933 // for unique ptrs, we inherit mutability from the
935 (MutabilityCategory::from_pointer_kind(base_cmt.mutbl, ptr),
936 Categorization::Deref(base_cmt, deref_cnt, ptr))
938 deref_interior(interior) => {
939 (base_cmt.mutbl.inherit(), Categorization::Interior(base_cmt, interior))
942 let ret = Rc::new(cmt_ {
950 debug!("cat_deref_common ret {:?}", ret);
954 pub fn cat_index<N:ast_node>(&self,
956 mut base_cmt: cmt<'tcx>,
957 context: InteriorOffsetKind)
958 -> McResult<cmt<'tcx>> {
959 //! Creates a cmt for an indexing operation (`[]`).
961 //! One subtle aspect of indexing that may not be
962 //! immediately obvious: for anything other than a fixed-length
963 //! vector, an operation like `x[y]` actually consists of two
964 //! disjoint (from the point of view of borrowck) operations.
965 //! The first is a deref of `x` to create a pointer `p` that points
966 //! at the first element in the array. The second operation is
967 //! an index which adds `y*sizeof(T)` to `p` to obtain the
968 //! pointer to `x[y]`. `cat_index` will produce a resulting
969 //! cmt containing both this deref and the indexing,
970 //! presuming that `base_cmt` is not of fixed-length type.
973 //! - `elt`: the AST node being indexed
974 //! - `base_cmt`: the cmt of `elt`
976 let method_call = ty::MethodCall::expr(elt.id());
977 let method_ty = self.typer.node_method_ty(method_call);
979 let element_ty = match method_ty {
981 let ref_ty = self.overloaded_method_return_ty(method_ty);
982 base_cmt = self.cat_rvalue_node(elt.id(), elt.span(), ref_ty);
984 // FIXME(#20649) -- why are we using the `self_ty` as the element type...?
985 let self_ty = method_ty.fn_sig().input(0);
986 self.tcx().no_late_bound_regions(&self_ty).unwrap()
989 match base_cmt.ty.builtin_index() {
998 let m = base_cmt.mutbl.inherit();
999 let ret = interior(elt, base_cmt.clone(), base_cmt.ty,
1000 m, context, element_ty);
1001 debug!("cat_index ret {:?}", ret);
1004 fn interior<'tcx, N: ast_node>(elt: &N,
1007 mutbl: MutabilityCategory,
1008 context: InteriorOffsetKind,
1009 element_ty: Ty<'tcx>) -> cmt<'tcx>
1011 let interior_elem = InteriorElement(context, element_kind(vec_ty));
1015 cat:Categorization::Interior(of_cmt, interior_elem),
1023 // Takes either a vec or a reference to a vec and returns the cmt for the
1025 fn deref_vec<N:ast_node>(&self,
1027 base_cmt: cmt<'tcx>,
1028 context: InteriorOffsetKind)
1029 -> McResult<cmt<'tcx>>
1031 let ret = match try!(deref_kind(base_cmt.ty, Some(context))) {
1033 // for unique ptrs, we inherit mutability from the
1034 // owning reference.
1035 let m = MutabilityCategory::from_pointer_kind(base_cmt.mutbl, ptr);
1037 // the deref is explicit in the resulting cmt
1041 cat:Categorization::Deref(base_cmt.clone(), 0, ptr),
1043 ty: match base_cmt.ty.builtin_deref(false, ty::NoPreference) {
1045 None => self.tcx().sess.bug("Found non-derefable type")
1051 deref_interior(_) => {
1055 debug!("deref_vec ret {:?}", ret);
1059 /// Given a pattern P like: `[_, ..Q, _]`, where `vec_cmt` is the cmt for `P`, `slice_pat` is
1060 /// the pattern `Q`, returns:
1063 /// * the mutability and region of the slice `Q`
1065 /// These last two bits of info happen to be things that borrowck needs.
1066 pub fn cat_slice_pattern(&self,
1068 slice_pat: &hir::Pat)
1069 -> McResult<(cmt<'tcx>, hir::Mutability, ty::Region)> {
1070 let slice_ty = try!(self.node_ty(slice_pat.id));
1071 let (slice_mutbl, slice_r) = vec_slice_info(self.tcx(),
1074 let context = InteriorOffsetKind::Pattern;
1075 let cmt_vec = try!(self.deref_vec(slice_pat, vec_cmt, context));
1076 let cmt_slice = try!(self.cat_index(slice_pat, cmt_vec, context));
1077 return Ok((cmt_slice, slice_mutbl, slice_r));
1079 /// In a pattern like [a, b, ..c], normally `c` has slice type, but if you have [a, b,
1080 /// ..ref c], then the type of `ref c` will be `&&[]`, so to extract the slice details we
1081 /// have to recurse through rptrs.
1082 fn vec_slice_info(tcx: &ty::ctxt,
1085 -> (hir::Mutability, ty::Region) {
1086 match slice_ty.sty {
1087 ty::TyRef(r, ref mt) => match mt.ty.sty {
1088 ty::TySlice(_) => (mt.mutbl, *r),
1089 _ => vec_slice_info(tcx, pat, mt.ty),
1093 tcx.sess.span_bug(pat.span,
1094 "type of slice pattern is not a slice");
1100 pub fn cat_imm_interior<N:ast_node>(&self,
1102 base_cmt: cmt<'tcx>,
1103 interior_ty: Ty<'tcx>,
1104 interior: InteriorKind)
1106 let ret = Rc::new(cmt_ {
1109 mutbl: base_cmt.mutbl.inherit(),
1110 cat: Categorization::Interior(base_cmt, interior),
1114 debug!("cat_imm_interior ret={:?}", ret);
1118 pub fn cat_downcast<N:ast_node>(&self,
1120 base_cmt: cmt<'tcx>,
1121 downcast_ty: Ty<'tcx>,
1124 let ret = Rc::new(cmt_ {
1127 mutbl: base_cmt.mutbl.inherit(),
1128 cat: Categorization::Downcast(base_cmt, variant_did),
1132 debug!("cat_downcast ret={:?}", ret);
1136 pub fn cat_pattern<F>(&self, cmt: cmt<'tcx>, pat: &hir::Pat, mut op: F) -> McResult<()>
1137 where F: FnMut(&MemCategorizationContext<'t, 'a, 'tcx>, cmt<'tcx>, &hir::Pat),
1139 self.cat_pattern_(cmt, pat, &mut op)
1142 // FIXME(#19596) This is a workaround, but there should be a better way to do this
1143 fn cat_pattern_<F>(&self, cmt: cmt<'tcx>, pat: &hir::Pat, op: &mut F)
1145 where F : FnMut(&MemCategorizationContext<'t, 'a, 'tcx>, cmt<'tcx>, &hir::Pat),
1147 // Here, `cmt` is the categorization for the value being
1148 // matched and pat is the pattern it is being matched against.
1150 // In general, the way that this works is that we walk down
1151 // the pattern, constructing a cmt that represents the path
1152 // that will be taken to reach the value being matched.
1154 // When we encounter named bindings, we take the cmt that has
1155 // been built up and pass it off to guarantee_valid() so that
1156 // we can be sure that the binding will remain valid for the
1157 // duration of the arm.
1159 // (*2) There is subtlety concerning the correspondence between
1160 // pattern ids and types as compared to *expression* ids and
1161 // types. This is explained briefly. on the definition of the
1162 // type `cmt`, so go off and read what it says there, then
1163 // come back and I'll dive into a bit more detail here. :) OK,
1166 // In general, the id of the cmt should be the node that
1167 // "produces" the value---patterns aren't executable code
1168 // exactly, but I consider them to "execute" when they match a
1169 // value, and I consider them to produce the value that was
1170 // matched. So if you have something like:
1177 // In this case, the cmt and the relevant ids would be:
1179 // CMT Id Type of Id Type of cmt
1182 // ^~~~~~~^ `x` from discr @@int @@int
1183 // ^~~~~~~~~~^ `@@y` pattern node @@int @int
1184 // ^~~~~~~~~~~~~^ `@y` pattern node @int int
1186 // You can see that the types of the id and the cmt are in
1187 // sync in the first line, because that id is actually the id
1188 // of an expression. But once we get to pattern ids, the types
1189 // step out of sync again. So you'll see below that we always
1190 // get the type of the *subpattern* and use that.
1192 debug!("cat_pattern: {:?} cmt={:?}",
1196 (*op)(self, cmt.clone(), pat);
1198 let opt_def = if let Some(path_res) = self.tcx().def_map.borrow().get(&pat.id) {
1199 if path_res.depth != 0 {
1200 // Since patterns can be associated constants
1201 // which are resolved during typeck, we might have
1202 // some unresolved patterns reaching this stage
1206 Some(path_res.full_def())
1211 // Note: This goes up here (rather than within the PatEnum arm
1212 // alone) because struct patterns can refer to struct types or
1213 // to struct variants within enums.
1214 let cmt = match opt_def {
1215 Some(def::DefVariant(enum_did, variant_did, _))
1216 // univariant enums do not need downcasts
1217 if !self.tcx().lookup_adt_def(enum_did).is_univariant() => {
1218 self.cat_downcast(pat, cmt.clone(), cmt.ty, variant_did)
1228 hir::PatEnum(_, None) => {
1231 hir::PatEnum(_, Some(ref subpats)) => {
1233 Some(def::DefVariant(..)) => {
1235 for (i, subpat) in subpats.iter().enumerate() {
1236 let subpat_ty = try!(self.pat_ty(&**subpat)); // see (*2)
1239 self.cat_imm_interior(
1240 pat, cmt.clone(), subpat_ty,
1241 InteriorField(PositionalField(i)));
1243 try!(self.cat_pattern_(subcmt, &**subpat, op));
1246 Some(def::DefStruct(..)) => {
1247 for (i, subpat) in subpats.iter().enumerate() {
1248 let subpat_ty = try!(self.pat_ty(&**subpat)); // see (*2)
1250 self.cat_imm_interior(
1251 pat, cmt.clone(), subpat_ty,
1252 InteriorField(PositionalField(i)));
1253 try!(self.cat_pattern_(cmt_field, &**subpat, op));
1256 Some(def::DefConst(..)) | Some(def::DefAssociatedConst(..)) => {
1257 for subpat in subpats {
1258 try!(self.cat_pattern_(cmt.clone(), &**subpat, op));
1262 self.tcx().sess.span_bug(
1264 "enum pattern didn't resolve to enum or struct");
1269 hir::PatQPath(..) => {
1270 // Lone constant: ignore
1273 hir::PatIdent(_, _, Some(ref subpat)) => {
1274 try!(self.cat_pattern_(cmt, &**subpat, op));
1277 hir::PatIdent(_, _, None) => {
1278 // nullary variant or identifier: ignore
1281 hir::PatStruct(_, ref field_pats, _) => {
1282 // {f1: p1, ..., fN: pN}
1283 for fp in field_pats {
1284 let field_ty = try!(self.pat_ty(&*fp.node.pat)); // see (*2)
1285 let cmt_field = self.cat_field(pat, cmt.clone(), fp.node.name, field_ty);
1286 try!(self.cat_pattern_(cmt_field, &*fp.node.pat, op));
1290 hir::PatTup(ref subpats) => {
1292 for (i, subpat) in subpats.iter().enumerate() {
1293 let subpat_ty = try!(self.pat_ty(&**subpat)); // see (*2)
1295 self.cat_imm_interior(
1296 pat, cmt.clone(), subpat_ty,
1297 InteriorField(PositionalField(i)));
1298 try!(self.cat_pattern_(subcmt, &**subpat, op));
1302 hir::PatBox(ref subpat) | hir::PatRegion(ref subpat, _) => {
1303 // box p1, &p1, &mut p1. we can ignore the mutability of
1304 // PatRegion since that information is already contained
1306 let subcmt = try!(self.cat_deref(pat, cmt, 0, None));
1307 try!(self.cat_pattern_(subcmt, &**subpat, op));
1310 hir::PatVec(ref before, ref slice, ref after) => {
1311 let context = InteriorOffsetKind::Pattern;
1312 let vec_cmt = try!(self.deref_vec(pat, cmt, context));
1313 let elt_cmt = try!(self.cat_index(pat, vec_cmt, context));
1314 for before_pat in before {
1315 try!(self.cat_pattern_(elt_cmt.clone(), &**before_pat, op));
1317 if let Some(ref slice_pat) = *slice {
1318 let slice_ty = try!(self.pat_ty(&**slice_pat));
1319 let slice_cmt = self.cat_rvalue_node(pat.id(), pat.span(), slice_ty);
1320 try!(self.cat_pattern_(slice_cmt, &**slice_pat, op));
1322 for after_pat in after {
1323 try!(self.cat_pattern_(elt_cmt.clone(), &**after_pat, op));
1327 hir::PatLit(_) | hir::PatRange(_, _) => {
1335 fn overloaded_method_return_ty(&self,
1336 method_ty: Ty<'tcx>)
1339 // When we process an overloaded `*` or `[]` etc, we often
1340 // need to extract the return type of the method. These method
1341 // types are generated by method resolution and always have
1342 // all late-bound regions fully instantiated, so we just want
1343 // to skip past the binder.
1344 self.tcx().no_late_bound_regions(&method_ty.fn_ret())
1346 .unwrap() // overloaded ops do not diverge, either
1350 #[derive(Clone, Debug)]
1351 pub enum Aliasability {
1352 FreelyAliasable(AliasableReason),
1354 ImmutableUnique(Box<Aliasability>),
1357 #[derive(Copy, Clone, Debug)]
1358 pub enum AliasableReason {
1360 AliasableClosure(ast::NodeId), // Aliasable due to capture Fn closure env
1362 UnaliasableImmutable, // Created as needed upon seeing ImmutableUnique
1367 impl<'tcx> cmt_<'tcx> {
1368 pub fn guarantor(&self) -> cmt<'tcx> {
1369 //! Returns `self` after stripping away any derefs or
1370 //! interior content. The return value is basically the `cmt` which
1371 //! determines how long the value in `self` remains live.
1374 Categorization::Rvalue(..) |
1375 Categorization::StaticItem |
1376 Categorization::Local(..) |
1377 Categorization::Deref(_, _, UnsafePtr(..)) |
1378 Categorization::Deref(_, _, BorrowedPtr(..)) |
1379 Categorization::Deref(_, _, Implicit(..)) |
1380 Categorization::Upvar(..) => {
1381 Rc::new((*self).clone())
1383 Categorization::Downcast(ref b, _) |
1384 Categorization::Interior(ref b, _) |
1385 Categorization::Deref(ref b, _, Unique) => {
1391 /// Returns `FreelyAliasable(_)` if this lvalue represents a freely aliasable pointer type.
1392 pub fn freely_aliasable(&self, ctxt: &ty::ctxt<'tcx>)
1394 // Maybe non-obvious: copied upvars can only be considered
1395 // non-aliasable in once closures, since any other kind can be
1396 // aliased and eventually recused.
1399 Categorization::Deref(ref b, _, BorrowedPtr(ty::MutBorrow, _)) |
1400 Categorization::Deref(ref b, _, Implicit(ty::MutBorrow, _)) |
1401 Categorization::Deref(ref b, _, BorrowedPtr(ty::UniqueImmBorrow, _)) |
1402 Categorization::Deref(ref b, _, Implicit(ty::UniqueImmBorrow, _)) |
1403 Categorization::Downcast(ref b, _) |
1404 Categorization::Interior(ref b, _) => {
1405 // Aliasability depends on base cmt
1406 b.freely_aliasable(ctxt)
1409 Categorization::Deref(ref b, _, Unique) => {
1410 let sub = b.freely_aliasable(ctxt);
1411 if b.mutbl.is_mutable() {
1412 // Aliasability depends on base cmt alone
1415 // Do not allow mutation through an immutable box.
1416 ImmutableUnique(Box::new(sub))
1420 Categorization::Rvalue(..) |
1421 Categorization::Local(..) |
1422 Categorization::Upvar(..) |
1423 Categorization::Deref(_, _, UnsafePtr(..)) => { // yes, it's aliasable, but...
1427 Categorization::StaticItem => {
1428 if self.mutbl.is_mutable() {
1429 FreelyAliasable(AliasableStaticMut)
1431 FreelyAliasable(AliasableStatic)
1435 Categorization::Deref(ref base, _, BorrowedPtr(ty::ImmBorrow, _)) |
1436 Categorization::Deref(ref base, _, Implicit(ty::ImmBorrow, _)) => {
1438 Categorization::Upvar(Upvar{ id, .. }) =>
1439 FreelyAliasable(AliasableClosure(id.closure_expr_id)),
1440 _ => FreelyAliasable(AliasableBorrowed)
1446 // Digs down through one or two layers of deref and grabs the cmt
1447 // for the upvar if a note indicates there is one.
1448 pub fn upvar(&self) -> Option<cmt<'tcx>> {
1450 NoteClosureEnv(..) | NoteUpvarRef(..) => {
1451 Some(match self.cat {
1452 Categorization::Deref(ref inner, _, _) => {
1454 Categorization::Deref(ref inner, _, _) => inner.clone(),
1455 Categorization::Upvar(..) => inner.clone(),
1467 pub fn descriptive_string(&self, tcx: &ty::ctxt) -> String {
1469 Categorization::StaticItem => {
1470 "static item".to_string()
1472 Categorization::Rvalue(..) => {
1473 "non-lvalue".to_string()
1475 Categorization::Local(vid) => {
1476 if tcx.map.is_argument(vid) {
1477 "argument".to_string()
1479 "local variable".to_string()
1482 Categorization::Deref(_, _, pk) => {
1483 let upvar = self.upvar();
1484 match upvar.as_ref().map(|i| &i.cat) {
1485 Some(&Categorization::Upvar(ref var)) => {
1488 Some(_) => unreachable!(),
1492 format!("indexed content")
1495 format!("`Box` content")
1498 format!("dereference of raw pointer")
1500 BorrowedPtr(..) => {
1501 format!("borrowed content")
1507 Categorization::Interior(_, InteriorField(NamedField(_))) => {
1510 Categorization::Interior(_, InteriorField(PositionalField(_))) => {
1511 "anonymous field".to_string()
1513 Categorization::Interior(_, InteriorElement(InteriorOffsetKind::Index,
1515 Categorization::Interior(_, InteriorElement(InteriorOffsetKind::Index,
1517 "indexed content".to_string()
1519 Categorization::Interior(_, InteriorElement(InteriorOffsetKind::Pattern,
1521 Categorization::Interior(_, InteriorElement(InteriorOffsetKind::Pattern,
1523 "pattern-bound indexed content".to_string()
1525 Categorization::Upvar(ref var) => {
1528 Categorization::Downcast(ref cmt, _) => {
1529 cmt.descriptive_string(tcx)
1535 impl<'tcx> fmt::Debug for cmt_<'tcx> {
1536 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1537 write!(f, "{{{:?} id:{} m:{:?} ty:{:?}}}",
1545 impl<'tcx> fmt::Debug for Categorization<'tcx> {
1546 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1548 Categorization::StaticItem => write!(f, "static"),
1549 Categorization::Rvalue(r) => write!(f, "rvalue({:?})", r),
1550 Categorization::Local(id) => {
1551 let name = ty::tls::with(|tcx| tcx.local_var_name_str(id));
1552 write!(f, "local({})", name)
1554 Categorization::Upvar(upvar) => {
1555 write!(f, "upvar({:?})", upvar)
1557 Categorization::Deref(ref cmt, derefs, ptr) => {
1558 write!(f, "{:?}-{:?}{}->", cmt.cat, ptr, derefs)
1560 Categorization::Interior(ref cmt, interior) => {
1561 write!(f, "{:?}.{:?}", cmt.cat, interior)
1563 Categorization::Downcast(ref cmt, _) => {
1564 write!(f, "{:?}->(enum)", cmt.cat)
1570 pub fn ptr_sigil(ptr: PointerKind) -> &'static str {
1573 BorrowedPtr(ty::ImmBorrow, _) |
1574 Implicit(ty::ImmBorrow, _) => "&",
1575 BorrowedPtr(ty::MutBorrow, _) |
1576 Implicit(ty::MutBorrow, _) => "&mut",
1577 BorrowedPtr(ty::UniqueImmBorrow, _) |
1578 Implicit(ty::UniqueImmBorrow, _) => "&unique",
1579 UnsafePtr(_) => "*",
1583 impl fmt::Debug for PointerKind {
1584 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1586 Unique => write!(f, "Box"),
1587 BorrowedPtr(ty::ImmBorrow, ref r) |
1588 Implicit(ty::ImmBorrow, ref r) => {
1589 write!(f, "&{:?}", r)
1591 BorrowedPtr(ty::MutBorrow, ref r) |
1592 Implicit(ty::MutBorrow, ref r) => {
1593 write!(f, "&{:?} mut", r)
1595 BorrowedPtr(ty::UniqueImmBorrow, ref r) |
1596 Implicit(ty::UniqueImmBorrow, ref r) => {
1597 write!(f, "&{:?} uniq", r)
1599 UnsafePtr(_) => write!(f, "*")
1604 impl fmt::Debug for InteriorKind {
1605 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1607 InteriorField(NamedField(fld)) => write!(f, "{}", fld),
1608 InteriorField(PositionalField(i)) => write!(f, "#{}", i),
1609 InteriorElement(..) => write!(f, "[]"),
1614 fn element_kind(t: Ty) -> ElementKind {
1616 ty::TyRef(_, ty::TypeAndMut{ty, ..}) |
1617 ty::TyBox(ty) => match ty.sty {
1618 ty::TySlice(_) => VecElement,
1621 ty::TyArray(..) | ty::TySlice(_) => VecElement,
1626 impl fmt::Debug for Upvar {
1627 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1628 write!(f, "{:?}/{:?}", self.id, self.kind)
1632 impl fmt::Display for Upvar {
1633 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
1634 let kind = match self.kind {
1635 ty::FnClosureKind => "Fn",
1636 ty::FnMutClosureKind => "FnMut",
1637 ty::FnOnceClosureKind => "FnOnce",
1639 write!(f, "captured outer variable in an `{}` closure", kind)