// Copyright 2012-2014 The Rust Project Developers. See the COPYRIGHT // file at the top-level directory of this distribution and at // http://rust-lang.org/COPYRIGHT. // // Licensed under the Apache License, Version 2.0 or the MIT license // , at your // option. This file may not be copied, modified, or distributed // except according to those terms. //! # Categorization //! //! The job of the categorization module is to analyze an expression to //! determine what kind of memory is used in evaluating it (for example, //! where dereferences occur and what kind of pointer is dereferenced; //! whether the memory is mutable; etc) //! //! Categorization effectively transforms all of our expressions into //! expressions of the following forms (the actual enum has many more //! possibilities, naturally, but they are all variants of these base //! forms): //! //! E = rvalue // some computed rvalue //! | x // address of a local variable or argument //! | *E // deref of a ptr //! | E.comp // access to an interior component //! //! Imagine a routine ToAddr(Expr) that evaluates an expression and returns an //! address where the result is to be found. If Expr is an lvalue, then this //! is the address of the lvalue. If Expr is an rvalue, this is the address of //! some temporary spot in memory where the result is stored. //! //! Now, cat_expr() classifies the expression Expr and the address A=ToAddr(Expr) //! as follows: //! //! - cat: what kind of expression was this? This is a subset of the //! full expression forms which only includes those that we care about //! for the purpose of the analysis. //! - mutbl: mutability of the address A //! - ty: the type of data found at the address A //! //! The resulting categorization tree differs somewhat from the expressions //! themselves. For example, auto-derefs are explicit. Also, an index a[b] is //! decomposed into two operations: a dereference to reach the array data and //! then an index to jump forward to the relevant item. //! //! ## By-reference upvars //! //! One part of the translation which may be non-obvious is that we translate //! closure upvars into the dereference of a borrowed pointer; this more closely //! resembles the runtime translation. So, for example, if we had: //! //! let mut x = 3; //! let y = 5; //! let inc = || x += y; //! //! Then when we categorize `x` (*within* the closure) we would yield a //! result of `*x'`, effectively, where `x'` is a `Categorization::Upvar` reference //! tied to `x`. The type of `x'` will be a borrowed pointer. #![allow(non_camel_case_types)] pub use self::PointerKind::*; pub use self::InteriorKind::*; pub use self::FieldName::*; pub use self::ElementKind::*; pub use self::MutabilityCategory::*; pub use self::AliasableReason::*; pub use self::Note::*; pub use self::deref_kind::*; use self::Aliasability::*; use middle::def_id::DefId; use front::map as ast_map; use middle::infer; use middle::const_qualif::ConstQualif; use middle::def::Def; use middle::ty::adjustment; use middle::ty::{self, Ty, TyCtxt}; use rustc_front::hir::{MutImmutable, MutMutable, PatKind}; use rustc_front::hir; use syntax::ast; use syntax::codemap::Span; use std::fmt; use std::rc::Rc; #[derive(Clone, PartialEq)] pub enum Categorization<'tcx> { Rvalue(ty::Region), // temporary val, argument is its scope StaticItem, Upvar(Upvar), // upvar referenced by closure env Local(ast::NodeId), // local variable Deref(cmt<'tcx>, usize, PointerKind), // deref of a ptr Interior(cmt<'tcx>, InteriorKind), // something interior: field, tuple, etc Downcast(cmt<'tcx>, DefId), // selects a particular enum variant (*1) // (*1) downcast is only required if the enum has more than one variant } // Represents any kind of upvar #[derive(Clone, Copy, PartialEq)] pub struct Upvar { pub id: ty::UpvarId, pub kind: ty::ClosureKind } // different kinds of pointers: #[derive(Clone, Copy, PartialEq, Eq, Hash)] pub enum PointerKind { /// `Box` Unique, /// `&T` BorrowedPtr(ty::BorrowKind, ty::Region), /// `*T` UnsafePtr(hir::Mutability), /// Implicit deref of the `&T` that results from an overloaded index `[]`. Implicit(ty::BorrowKind, ty::Region), } // We use the term "interior" to mean "something reachable from the // base without a pointer dereference", e.g. a field #[derive(Clone, Copy, PartialEq, Eq, Hash)] pub enum InteriorKind { InteriorField(FieldName), InteriorElement(InteriorOffsetKind, ElementKind), } #[derive(Clone, Copy, PartialEq, Eq, Hash, Debug)] pub enum FieldName { NamedField(ast::Name), PositionalField(usize) } #[derive(Clone, Copy, PartialEq, Eq, Hash, Debug)] pub enum InteriorOffsetKind { Index, // e.g. `array_expr[index_expr]` Pattern, // e.g. `fn foo([_, a, _, _]: [A; 4]) { ... }` } #[derive(Clone, Copy, PartialEq, Eq, Hash, Debug)] pub enum ElementKind { VecElement, OtherElement, } #[derive(Clone, Copy, PartialEq, Eq, Hash, Debug)] pub enum MutabilityCategory { McImmutable, // Immutable. McDeclared, // Directly declared as mutable. McInherited, // Inherited from the fact that owner is mutable. } // A note about the provenance of a `cmt`. This is used for // special-case handling of upvars such as mutability inference. // Upvar categorization can generate a variable number of nested // derefs. The note allows detecting them without deep pattern // matching on the categorization. #[derive(Clone, Copy, PartialEq, Debug)] pub enum Note { NoteClosureEnv(ty::UpvarId), // Deref through closure env NoteUpvarRef(ty::UpvarId), // Deref through by-ref upvar NoteNone // Nothing special } // `cmt`: "Category, Mutability, and Type". // // a complete categorization of a value indicating where it originated // and how it is located, as well as the mutability of the memory in // which the value is stored. // // *WARNING* The field `cmt.type` is NOT necessarily the same as the // result of `node_id_to_type(cmt.id)`. This is because the `id` is // always the `id` of the node producing the type; in an expression // like `*x`, the type of this deref node is the deref'd type (`T`), // but in a pattern like `@x`, the `@x` pattern is again a // dereference, but its type is the type *before* the dereference // (`@T`). So use `cmt.ty` to find the type of the value in a consistent // fashion. For more details, see the method `cat_pattern` #[derive(Clone, PartialEq)] pub struct cmt_<'tcx> { pub id: ast::NodeId, // id of expr/pat producing this value pub span: Span, // span of same expr/pat pub cat: Categorization<'tcx>, // categorization of expr pub mutbl: MutabilityCategory, // mutability of expr as lvalue pub ty: Ty<'tcx>, // type of the expr (*see WARNING above*) pub note: Note, // Note about the provenance of this cmt } pub type cmt<'tcx> = Rc>; // We pun on *T to mean both actual deref of a ptr as well // as accessing of components: #[derive(Copy, Clone)] pub enum deref_kind { deref_ptr(PointerKind), deref_interior(InteriorKind), } type DerefKindContext = Option; // Categorizes a derefable type. Note that we include vectors and strings as // derefable (we model an index as the combination of a deref and then a // pointer adjustment). fn deref_kind(t: Ty, context: DerefKindContext) -> McResult { match t.sty { ty::TyBox(_) => { Ok(deref_ptr(Unique)) } ty::TyRef(r, mt) => { let kind = ty::BorrowKind::from_mutbl(mt.mutbl); Ok(deref_ptr(BorrowedPtr(kind, *r))) } ty::TyRawPtr(ref mt) => { Ok(deref_ptr(UnsafePtr(mt.mutbl))) } ty::TyEnum(..) | ty::TyStruct(..) => { // newtype Ok(deref_interior(InteriorField(PositionalField(0)))) } ty::TyArray(_, _) | ty::TySlice(_) | ty::TyStr => { // no deref of indexed content without supplying InteriorOffsetKind if let Some(context) = context { Ok(deref_interior(InteriorElement(context, element_kind(t)))) } else { Err(()) } } _ => Err(()), } } pub trait ast_node { fn id(&self) -> ast::NodeId; fn span(&self) -> Span; } impl ast_node for hir::Expr { fn id(&self) -> ast::NodeId { self.id } fn span(&self) -> Span { self.span } } impl ast_node for hir::Pat { fn id(&self) -> ast::NodeId { self.id } fn span(&self) -> Span { self.span } } #[derive(Copy, Clone)] pub struct MemCategorizationContext<'t, 'a: 't, 'tcx : 'a> { pub typer: &'t infer::InferCtxt<'a, 'tcx>, } pub type McResult = Result; impl MutabilityCategory { pub fn from_mutbl(m: hir::Mutability) -> MutabilityCategory { let ret = match m { MutImmutable => McImmutable, MutMutable => McDeclared }; debug!("MutabilityCategory::{}({:?}) => {:?}", "from_mutbl", m, ret); ret } pub fn from_borrow_kind(borrow_kind: ty::BorrowKind) -> MutabilityCategory { let ret = match borrow_kind { ty::ImmBorrow => McImmutable, ty::UniqueImmBorrow => McImmutable, ty::MutBorrow => McDeclared, }; debug!("MutabilityCategory::{}({:?}) => {:?}", "from_borrow_kind", borrow_kind, ret); ret } fn from_pointer_kind(base_mutbl: MutabilityCategory, ptr: PointerKind) -> MutabilityCategory { let ret = match ptr { Unique => { base_mutbl.inherit() } BorrowedPtr(borrow_kind, _) | Implicit(borrow_kind, _) => { MutabilityCategory::from_borrow_kind(borrow_kind) } UnsafePtr(m) => { MutabilityCategory::from_mutbl(m) } }; debug!("MutabilityCategory::{}({:?}, {:?}) => {:?}", "from_pointer_kind", base_mutbl, ptr, ret); ret } fn from_local(tcx: &TyCtxt, id: ast::NodeId) -> MutabilityCategory { let ret = match tcx.map.get(id) { ast_map::NodeLocal(p) => match p.node { PatKind::Ident(bind_mode, _, _) => { if bind_mode == hir::BindByValue(hir::MutMutable) { McDeclared } else { McImmutable } } _ => tcx.sess.span_bug(p.span, "expected identifier pattern") }, _ => tcx.sess.span_bug(tcx.map.span(id), "expected identifier pattern") }; debug!("MutabilityCategory::{}(tcx, id={:?}) => {:?}", "from_local", id, ret); ret } pub fn inherit(&self) -> MutabilityCategory { let ret = match *self { McImmutable => McImmutable, McDeclared => McInherited, McInherited => McInherited, }; debug!("{:?}.inherit() => {:?}", self, ret); ret } pub fn is_mutable(&self) -> bool { let ret = match *self { McImmutable => false, McInherited => true, McDeclared => true, }; debug!("{:?}.is_mutable() => {:?}", self, ret); ret } pub fn is_immutable(&self) -> bool { let ret = match *self { McImmutable => true, McDeclared | McInherited => false }; debug!("{:?}.is_immutable() => {:?}", self, ret); ret } pub fn to_user_str(&self) -> &'static str { match *self { McDeclared | McInherited => "mutable", McImmutable => "immutable", } } } impl<'t, 'a,'tcx> MemCategorizationContext<'t, 'a, 'tcx> { pub fn new(typer: &'t infer::InferCtxt<'a, 'tcx>) -> MemCategorizationContext<'t, 'a, 'tcx> { MemCategorizationContext { typer: typer } } fn tcx(&self) -> &'a TyCtxt<'tcx> { self.typer.tcx } fn expr_ty(&self, expr: &hir::Expr) -> McResult> { match self.typer.node_ty(expr.id) { Ok(t) => Ok(t), Err(()) => { debug!("expr_ty({:?}) yielded Err", expr); Err(()) } } } fn expr_ty_adjusted(&self, expr: &hir::Expr) -> McResult> { let unadjusted_ty = try!(self.expr_ty(expr)); Ok(unadjusted_ty.adjust( self.tcx(), expr.span, expr.id, self.typer.adjustments().get(&expr.id), |method_call| self.typer.node_method_ty(method_call))) } fn node_ty(&self, id: ast::NodeId) -> McResult> { self.typer.node_ty(id) } fn pat_ty(&self, pat: &hir::Pat) -> McResult> { let base_ty = try!(self.typer.node_ty(pat.id)); // FIXME (Issue #18207): This code detects whether we are // looking at a `ref x`, and if so, figures out what the type // *being borrowed* is. But ideally we would put in a more // fundamental fix to this conflated use of the node id. let ret_ty = match pat.node { PatKind::Ident(hir::BindByRef(_), _, _) => { // a bind-by-ref means that the base_ty will be the type of the ident itself, // but what we want here is the type of the underlying value being borrowed. // So peel off one-level, turning the &T into T. match base_ty.builtin_deref(false, ty::NoPreference) { Some(t) => t.ty, None => { return Err(()); } } } _ => base_ty, }; debug!("pat_ty(pat={:?}) base_ty={:?} ret_ty={:?}", pat, base_ty, ret_ty); Ok(ret_ty) } pub fn cat_expr(&self, expr: &hir::Expr) -> McResult> { match self.typer.adjustments().get(&expr.id) { None => { // No adjustments. self.cat_expr_unadjusted(expr) } Some(adjustment) => { match *adjustment { adjustment::AdjustDerefRef( adjustment::AutoDerefRef { autoref: None, unsize: None, autoderefs, ..}) => { // Equivalent to *expr or something similar. self.cat_expr_autoderefd(expr, autoderefs) } adjustment::AdjustReifyFnPointer | adjustment::AdjustUnsafeFnPointer | adjustment::AdjustMutToConstPointer | adjustment::AdjustDerefRef(_) => { debug!("cat_expr({:?}): {:?}", adjustment, expr); // Result is an rvalue. let expr_ty = try!(self.expr_ty_adjusted(expr)); Ok(self.cat_rvalue_node(expr.id(), expr.span(), expr_ty)) } } } } } pub fn cat_expr_autoderefd(&self, expr: &hir::Expr, autoderefs: usize) -> McResult> { let mut cmt = try!(self.cat_expr_unadjusted(expr)); debug!("cat_expr_autoderefd: autoderefs={}, cmt={:?}", autoderefs, cmt); for deref in 1..autoderefs + 1 { cmt = try!(self.cat_deref(expr, cmt, deref, None)); } return Ok(cmt); } pub fn cat_expr_unadjusted(&self, expr: &hir::Expr) -> McResult> { debug!("cat_expr: id={} expr={:?}", expr.id, expr); let expr_ty = try!(self.expr_ty(expr)); match expr.node { hir::ExprUnary(hir::UnDeref, ref e_base) => { let base_cmt = try!(self.cat_expr(&e_base)); self.cat_deref(expr, base_cmt, 0, None) } hir::ExprField(ref base, f_name) => { let base_cmt = try!(self.cat_expr(&base)); debug!("cat_expr(cat_field): id={} expr={:?} base={:?}", expr.id, expr, base_cmt); Ok(self.cat_field(expr, base_cmt, f_name.node, expr_ty)) } hir::ExprTupField(ref base, idx) => { let base_cmt = try!(self.cat_expr(&base)); Ok(self.cat_tup_field(expr, base_cmt, idx.node, expr_ty)) } hir::ExprIndex(ref base, _) => { let method_call = ty::MethodCall::expr(expr.id()); let context = InteriorOffsetKind::Index; match self.typer.node_method_ty(method_call) { Some(method_ty) => { // If this is an index implemented by a method call, then it // will include an implicit deref of the result. let ret_ty = self.overloaded_method_return_ty(method_ty); // The index method always returns an `&T`, so // dereference it to find the result type. let elem_ty = match ret_ty.sty { ty::TyRef(_, mt) => mt.ty, _ => { debug!("cat_expr_unadjusted: return type of overloaded index is {:?}?", ret_ty); return Err(()); } }; // The call to index() returns a `&T` value, which // is an rvalue. That is what we will be // dereferencing. let base_cmt = self.cat_rvalue_node(expr.id(), expr.span(), ret_ty); self.cat_deref_common(expr, base_cmt, 1, elem_ty, Some(context), true) } None => { self.cat_index(expr, try!(self.cat_expr(&base)), context) } } } hir::ExprPath(..) => { let def = self.tcx().def_map.borrow().get(&expr.id).unwrap().full_def(); self.cat_def(expr.id, expr.span, expr_ty, def) } hir::ExprType(ref e, _) => { self.cat_expr(&e) } hir::ExprAddrOf(..) | hir::ExprCall(..) | hir::ExprAssign(..) | hir::ExprAssignOp(..) | hir::ExprClosure(..) | hir::ExprRet(..) | hir::ExprUnary(..) | hir::ExprMethodCall(..) | hir::ExprCast(..) | hir::ExprVec(..) | hir::ExprTup(..) | hir::ExprIf(..) | hir::ExprBinary(..) | hir::ExprWhile(..) | hir::ExprBlock(..) | hir::ExprLoop(..) | hir::ExprMatch(..) | hir::ExprLit(..) | hir::ExprBreak(..) | hir::ExprAgain(..) | hir::ExprStruct(..) | hir::ExprRepeat(..) | hir::ExprInlineAsm(..) | hir::ExprBox(..) => { Ok(self.cat_rvalue_node(expr.id(), expr.span(), expr_ty)) } } } pub fn cat_def(&self, id: ast::NodeId, span: Span, expr_ty: Ty<'tcx>, def: Def) -> McResult> { debug!("cat_def: id={} expr={:?} def={:?}", id, expr_ty, def); match def { Def::Struct(..) | Def::Variant(..) | Def::Const(..) | Def::AssociatedConst(..) | Def::Fn(..) | Def::Method(..) => { Ok(self.cat_rvalue_node(id, span, expr_ty)) } Def::Mod(_) | Def::ForeignMod(_) | Def::Trait(_) | Def::Enum(..) | Def::TyAlias(..) | Def::PrimTy(_) | Def::TyParam(..) | Def::Label(_) | Def::SelfTy(..) | Def::AssociatedTy(..) => { self.tcx().sess.span_bug(span, &format!("Unexpected definition in \ memory categorization: {:?}", def)); } Def::Static(_, mutbl) => { Ok(Rc::new(cmt_ { id:id, span:span, cat:Categorization::StaticItem, mutbl: if mutbl { McDeclared } else { McImmutable}, ty:expr_ty, note: NoteNone })) } Def::Upvar(_, var_id, _, fn_node_id) => { let ty = try!(self.node_ty(fn_node_id)); match ty.sty { ty::TyClosure(closure_id, _) => { match self.typer.closure_kind(closure_id) { Some(kind) => { self.cat_upvar(id, span, var_id, fn_node_id, kind) } None => { self.tcx().sess.span_bug( span, &format!("No closure kind for {:?}", closure_id)); } } } _ => { self.tcx().sess.span_bug( span, &format!("Upvar of non-closure {} - {:?}", fn_node_id, ty)); } } } Def::Local(_, vid) => { Ok(Rc::new(cmt_ { id: id, span: span, cat: Categorization::Local(vid), mutbl: MutabilityCategory::from_local(self.tcx(), vid), ty: expr_ty, note: NoteNone })) } Def::Err => panic!("Def::Err in memory categorization") } } // Categorize an upvar, complete with invisible derefs of closure // environment and upvar reference as appropriate. fn cat_upvar(&self, id: ast::NodeId, span: Span, var_id: ast::NodeId, fn_node_id: ast::NodeId, kind: ty::ClosureKind) -> McResult> { // An upvar can have up to 3 components. We translate first to a // `Categorization::Upvar`, which is itself a fiction -- it represents the reference to the // field from the environment. // // `Categorization::Upvar`. Next, we add a deref through the implicit // environment pointer with an anonymous free region 'env and // appropriate borrow kind for closure kinds that take self by // reference. Finally, if the upvar was captured // by-reference, we add a deref through that reference. The // region of this reference is an inference variable 'up that // was previously generated and recorded in the upvar borrow // map. The borrow kind bk is inferred by based on how the // upvar is used. // // This results in the following table for concrete closure // types: // // | move | ref // ---------------+----------------------+------------------------------- // Fn | copied -> &'env | upvar -> &'env -> &'up bk // FnMut | copied -> &'env mut | upvar -> &'env mut -> &'up bk // FnOnce | copied | upvar -> &'up bk let upvar_id = ty::UpvarId { var_id: var_id, closure_expr_id: fn_node_id }; let var_ty = try!(self.node_ty(var_id)); // Mutability of original variable itself let var_mutbl = MutabilityCategory::from_local(self.tcx(), var_id); // Construct the upvar. This represents access to the field // from the environment (perhaps we should eventually desugar // this field further, but it will do for now). let cmt_result = cmt_ { id: id, span: span, cat: Categorization::Upvar(Upvar {id: upvar_id, kind: kind}), mutbl: var_mutbl, ty: var_ty, note: NoteNone }; // If this is a `FnMut` or `Fn` closure, then the above is // conceptually a `&mut` or `&` reference, so we have to add a // deref. let cmt_result = match kind { ty::ClosureKind::FnOnce => { cmt_result } ty::ClosureKind::FnMut => { self.env_deref(id, span, upvar_id, var_mutbl, ty::MutBorrow, cmt_result) } ty::ClosureKind::Fn => { self.env_deref(id, span, upvar_id, var_mutbl, ty::ImmBorrow, cmt_result) } }; // If this is a by-ref capture, then the upvar we loaded is // actually a reference, so we have to add an implicit deref // for that. let upvar_id = ty::UpvarId { var_id: var_id, closure_expr_id: fn_node_id }; let upvar_capture = self.typer.upvar_capture(upvar_id).unwrap(); let cmt_result = match upvar_capture { ty::UpvarCapture::ByValue => { cmt_result } ty::UpvarCapture::ByRef(upvar_borrow) => { let ptr = BorrowedPtr(upvar_borrow.kind, upvar_borrow.region); cmt_ { id: id, span: span, cat: Categorization::Deref(Rc::new(cmt_result), 0, ptr), mutbl: MutabilityCategory::from_borrow_kind(upvar_borrow.kind), ty: var_ty, note: NoteUpvarRef(upvar_id) } } }; let ret = Rc::new(cmt_result); debug!("cat_upvar ret={:?}", ret); Ok(ret) } fn env_deref(&self, id: ast::NodeId, span: Span, upvar_id: ty::UpvarId, upvar_mutbl: MutabilityCategory, env_borrow_kind: ty::BorrowKind, cmt_result: cmt_<'tcx>) -> cmt_<'tcx> { // Look up the node ID of the closure body so we can construct // a free region within it let fn_body_id = { let fn_expr = match self.tcx().map.find(upvar_id.closure_expr_id) { Some(ast_map::NodeExpr(e)) => e, _ => unreachable!() }; match fn_expr.node { hir::ExprClosure(_, _, ref body) => body.id, _ => unreachable!() } }; // Region of environment pointer let env_region = ty::ReFree(ty::FreeRegion { // The environment of a closure is guaranteed to // outlive any bindings introduced in the body of the // closure itself. scope: self.tcx().region_maps.item_extent(fn_body_id), bound_region: ty::BrEnv }); let env_ptr = BorrowedPtr(env_borrow_kind, env_region); let var_ty = cmt_result.ty; // We need to add the env deref. This means // that the above is actually immutable and // has a ref type. However, nothing should // actually look at the type, so we can get // away with stuffing a `TyError` in there // instead of bothering to construct a proper // one. let cmt_result = cmt_ { mutbl: McImmutable, ty: self.tcx().types.err, ..cmt_result }; let mut deref_mutbl = MutabilityCategory::from_borrow_kind(env_borrow_kind); // Issue #18335. If variable is declared as immutable, override the // mutability from the environment and substitute an `&T` anyway. match upvar_mutbl { McImmutable => { deref_mutbl = McImmutable; } McDeclared | McInherited => { } } let ret = cmt_ { id: id, span: span, cat: Categorization::Deref(Rc::new(cmt_result), 0, env_ptr), mutbl: deref_mutbl, ty: var_ty, note: NoteClosureEnv(upvar_id) }; debug!("env_deref ret {:?}", ret); ret } /// Returns the lifetime of a temporary created by expr with id `id`. /// This could be `'static` if `id` is part of a constant expression. pub fn temporary_scope(&self, id: ast::NodeId) -> ty::Region { match self.typer.temporary_scope(id) { Some(scope) => ty::ReScope(scope), None => ty::ReStatic } } pub fn cat_rvalue_node(&self, id: ast::NodeId, span: Span, expr_ty: Ty<'tcx>) -> cmt<'tcx> { let qualif = self.tcx().const_qualif_map.borrow().get(&id).cloned() .unwrap_or(ConstQualif::NOT_CONST); // Only promote `[T; 0]` before an RFC for rvalue promotions // is accepted. let qualif = match expr_ty.sty { ty::TyArray(_, 0) => qualif, _ => ConstQualif::NOT_CONST }; // Compute maximum lifetime of this rvalue. This is 'static if // we can promote to a constant, otherwise equal to enclosing temp // lifetime. let re = if qualif.intersects(ConstQualif::NON_STATIC_BORROWS) { self.temporary_scope(id) } else { ty::ReStatic }; let ret = self.cat_rvalue(id, span, re, expr_ty); debug!("cat_rvalue_node ret {:?}", ret); ret } pub fn cat_rvalue(&self, cmt_id: ast::NodeId, span: Span, temp_scope: ty::Region, expr_ty: Ty<'tcx>) -> cmt<'tcx> { let ret = Rc::new(cmt_ { id:cmt_id, span:span, cat:Categorization::Rvalue(temp_scope), mutbl:McDeclared, ty:expr_ty, note: NoteNone }); debug!("cat_rvalue ret {:?}", ret); ret } pub fn cat_field(&self, node: &N, base_cmt: cmt<'tcx>, f_name: ast::Name, f_ty: Ty<'tcx>) -> cmt<'tcx> { let ret = Rc::new(cmt_ { id: node.id(), span: node.span(), mutbl: base_cmt.mutbl.inherit(), cat: Categorization::Interior(base_cmt, InteriorField(NamedField(f_name))), ty: f_ty, note: NoteNone }); debug!("cat_field ret {:?}", ret); ret } pub fn cat_tup_field(&self, node: &N, base_cmt: cmt<'tcx>, f_idx: usize, f_ty: Ty<'tcx>) -> cmt<'tcx> { let ret = Rc::new(cmt_ { id: node.id(), span: node.span(), mutbl: base_cmt.mutbl.inherit(), cat: Categorization::Interior(base_cmt, InteriorField(PositionalField(f_idx))), ty: f_ty, note: NoteNone }); debug!("cat_tup_field ret {:?}", ret); ret } fn cat_deref(&self, node: &N, base_cmt: cmt<'tcx>, deref_cnt: usize, deref_context: DerefKindContext) -> McResult> { let method_call = ty::MethodCall { expr_id: node.id(), autoderef: deref_cnt as u32 }; let method_ty = self.typer.node_method_ty(method_call); debug!("cat_deref: method_call={:?} method_ty={:?}", method_call, method_ty.map(|ty| ty)); let base_cmt = match method_ty { Some(method_ty) => { let ref_ty = self.tcx().no_late_bound_regions(&method_ty.fn_ret()).unwrap().unwrap(); self.cat_rvalue_node(node.id(), node.span(), ref_ty) } None => base_cmt }; let base_cmt_ty = base_cmt.ty; match base_cmt_ty.builtin_deref(true, ty::NoPreference) { Some(mt) => { let ret = self.cat_deref_common(node, base_cmt, deref_cnt, mt.ty, deref_context, /* implicit: */ false); debug!("cat_deref ret {:?}", ret); ret } None => { debug!("Explicit deref of non-derefable type: {:?}", base_cmt_ty); return Err(()); } } } fn cat_deref_common(&self, node: &N, base_cmt: cmt<'tcx>, deref_cnt: usize, deref_ty: Ty<'tcx>, deref_context: DerefKindContext, implicit: bool) -> McResult> { let (m, cat) = match try!(deref_kind(base_cmt.ty, deref_context)) { deref_ptr(ptr) => { let ptr = if implicit { match ptr { BorrowedPtr(bk, r) => Implicit(bk, r), _ => self.tcx().sess.span_bug(node.span(), "Implicit deref of non-borrowed pointer") } } else { ptr }; // for unique ptrs, we inherit mutability from the // owning reference. (MutabilityCategory::from_pointer_kind(base_cmt.mutbl, ptr), Categorization::Deref(base_cmt, deref_cnt, ptr)) } deref_interior(interior) => { (base_cmt.mutbl.inherit(), Categorization::Interior(base_cmt, interior)) } }; let ret = Rc::new(cmt_ { id: node.id(), span: node.span(), cat: cat, mutbl: m, ty: deref_ty, note: NoteNone }); debug!("cat_deref_common ret {:?}", ret); Ok(ret) } pub fn cat_index(&self, elt: &N, mut base_cmt: cmt<'tcx>, context: InteriorOffsetKind) -> McResult> { //! Creates a cmt for an indexing operation (`[]`). //! //! One subtle aspect of indexing that may not be //! immediately obvious: for anything other than a fixed-length //! vector, an operation like `x[y]` actually consists of two //! disjoint (from the point of view of borrowck) operations. //! The first is a deref of `x` to create a pointer `p` that points //! at the first element in the array. The second operation is //! an index which adds `y*sizeof(T)` to `p` to obtain the //! pointer to `x[y]`. `cat_index` will produce a resulting //! cmt containing both this deref and the indexing, //! presuming that `base_cmt` is not of fixed-length type. //! //! # Parameters //! - `elt`: the AST node being indexed //! - `base_cmt`: the cmt of `elt` let method_call = ty::MethodCall::expr(elt.id()); let method_ty = self.typer.node_method_ty(method_call); let element_ty = match method_ty { Some(method_ty) => { let ref_ty = self.overloaded_method_return_ty(method_ty); base_cmt = self.cat_rvalue_node(elt.id(), elt.span(), ref_ty); // FIXME(#20649) -- why are we using the `self_ty` as the element type...? let self_ty = method_ty.fn_sig().input(0); self.tcx().no_late_bound_regions(&self_ty).unwrap() } None => { match base_cmt.ty.builtin_index() { Some(ty) => ty, None => { return Err(()); } } } }; let m = base_cmt.mutbl.inherit(); let ret = interior(elt, base_cmt.clone(), base_cmt.ty, m, context, element_ty); debug!("cat_index ret {:?}", ret); return Ok(ret); fn interior<'tcx, N: ast_node>(elt: &N, of_cmt: cmt<'tcx>, vec_ty: Ty<'tcx>, mutbl: MutabilityCategory, context: InteriorOffsetKind, element_ty: Ty<'tcx>) -> cmt<'tcx> { let interior_elem = InteriorElement(context, element_kind(vec_ty)); Rc::new(cmt_ { id:elt.id(), span:elt.span(), cat:Categorization::Interior(of_cmt, interior_elem), mutbl:mutbl, ty:element_ty, note: NoteNone }) } } // Takes either a vec or a reference to a vec and returns the cmt for the // underlying vec. fn deref_vec(&self, elt: &N, base_cmt: cmt<'tcx>, context: InteriorOffsetKind) -> McResult> { let ret = match try!(deref_kind(base_cmt.ty, Some(context))) { deref_ptr(ptr) => { // for unique ptrs, we inherit mutability from the // owning reference. let m = MutabilityCategory::from_pointer_kind(base_cmt.mutbl, ptr); // the deref is explicit in the resulting cmt Rc::new(cmt_ { id:elt.id(), span:elt.span(), cat:Categorization::Deref(base_cmt.clone(), 0, ptr), mutbl:m, ty: match base_cmt.ty.builtin_deref(false, ty::NoPreference) { Some(mt) => mt.ty, None => self.tcx().sess.bug("Found non-derefable type") }, note: NoteNone }) } deref_interior(_) => { base_cmt } }; debug!("deref_vec ret {:?}", ret); Ok(ret) } /// Given a pattern P like: `[_, ..Q, _]`, where `vec_cmt` is the cmt for `P`, `slice_pat` is /// the pattern `Q`, returns: /// /// * a cmt for `Q` /// * the mutability and region of the slice `Q` /// /// These last two bits of info happen to be things that borrowck needs. pub fn cat_slice_pattern(&self, vec_cmt: cmt<'tcx>, slice_pat: &hir::Pat) -> McResult<(cmt<'tcx>, hir::Mutability, ty::Region)> { let slice_ty = try!(self.node_ty(slice_pat.id)); let (slice_mutbl, slice_r) = vec_slice_info(self.tcx(), slice_pat, slice_ty); let context = InteriorOffsetKind::Pattern; let cmt_vec = try!(self.deref_vec(slice_pat, vec_cmt, context)); let cmt_slice = try!(self.cat_index(slice_pat, cmt_vec, context)); return Ok((cmt_slice, slice_mutbl, slice_r)); /// In a pattern like [a, b, ..c], normally `c` has slice type, but if you have [a, b, /// ..ref c], then the type of `ref c` will be `&&[]`, so to extract the slice details we /// have to recurse through rptrs. fn vec_slice_info(tcx: &TyCtxt, pat: &hir::Pat, slice_ty: Ty) -> (hir::Mutability, ty::Region) { match slice_ty.sty { ty::TyRef(r, ref mt) => match mt.ty.sty { ty::TySlice(_) => (mt.mutbl, *r), _ => vec_slice_info(tcx, pat, mt.ty), }, _ => { tcx.sess.span_bug(pat.span, "type of slice pattern is not a slice"); } } } } pub fn cat_imm_interior(&self, node: &N, base_cmt: cmt<'tcx>, interior_ty: Ty<'tcx>, interior: InteriorKind) -> cmt<'tcx> { let ret = Rc::new(cmt_ { id: node.id(), span: node.span(), mutbl: base_cmt.mutbl.inherit(), cat: Categorization::Interior(base_cmt, interior), ty: interior_ty, note: NoteNone }); debug!("cat_imm_interior ret={:?}", ret); ret } pub fn cat_downcast(&self, node: &N, base_cmt: cmt<'tcx>, downcast_ty: Ty<'tcx>, variant_did: DefId) -> cmt<'tcx> { let ret = Rc::new(cmt_ { id: node.id(), span: node.span(), mutbl: base_cmt.mutbl.inherit(), cat: Categorization::Downcast(base_cmt, variant_did), ty: downcast_ty, note: NoteNone }); debug!("cat_downcast ret={:?}", ret); ret } pub fn cat_pattern(&self, cmt: cmt<'tcx>, pat: &hir::Pat, mut op: F) -> McResult<()> where F: FnMut(&MemCategorizationContext<'t, 'a, 'tcx>, cmt<'tcx>, &hir::Pat), { self.cat_pattern_(cmt, pat, &mut op) } // FIXME(#19596) This is a workaround, but there should be a better way to do this fn cat_pattern_(&self, cmt: cmt<'tcx>, pat: &hir::Pat, op: &mut F) -> McResult<()> where F : FnMut(&MemCategorizationContext<'t, 'a, 'tcx>, cmt<'tcx>, &hir::Pat), { // Here, `cmt` is the categorization for the value being // matched and pat is the pattern it is being matched against. // // In general, the way that this works is that we walk down // the pattern, constructing a cmt that represents the path // that will be taken to reach the value being matched. // // When we encounter named bindings, we take the cmt that has // been built up and pass it off to guarantee_valid() so that // we can be sure that the binding will remain valid for the // duration of the arm. // // (*2) There is subtlety concerning the correspondence between // pattern ids and types as compared to *expression* ids and // types. This is explained briefly. on the definition of the // type `cmt`, so go off and read what it says there, then // come back and I'll dive into a bit more detail here. :) OK, // back? // // In general, the id of the cmt should be the node that // "produces" the value---patterns aren't executable code // exactly, but I consider them to "execute" when they match a // value, and I consider them to produce the value that was // matched. So if you have something like: // // let x = @@3; // match x { // @@y { ... } // } // // In this case, the cmt and the relevant ids would be: // // CMT Id Type of Id Type of cmt // // local(x)->@->@ // ^~~~~~~^ `x` from discr @@int @@int // ^~~~~~~~~~^ `@@y` pattern node @@int @int // ^~~~~~~~~~~~~^ `@y` pattern node @int int // // You can see that the types of the id and the cmt are in // sync in the first line, because that id is actually the id // of an expression. But once we get to pattern ids, the types // step out of sync again. So you'll see below that we always // get the type of the *subpattern* and use that. debug!("cat_pattern: {:?} cmt={:?}", pat, cmt); (*op)(self, cmt.clone(), pat); let opt_def = if let Some(path_res) = self.tcx().def_map.borrow().get(&pat.id) { if path_res.depth != 0 || path_res.base_def == Def::Err { // Since patterns can be associated constants // which are resolved during typeck, we might have // some unresolved patterns reaching this stage // without aborting return Err(()); } Some(path_res.full_def()) } else { None }; // Note: This goes up here (rather than within the PatKind::TupleStruct arm // alone) because struct patterns can refer to struct types or // to struct variants within enums. let cmt = match opt_def { Some(Def::Variant(enum_did, variant_did)) // univariant enums do not need downcasts if !self.tcx().lookup_adt_def(enum_did).is_univariant() => { self.cat_downcast(pat, cmt.clone(), cmt.ty, variant_did) } _ => cmt }; match pat.node { PatKind::Wild => { // _ } PatKind::TupleStruct(_, None) => { // variant(..) } PatKind::TupleStruct(_, Some(ref subpats)) => { match opt_def { Some(Def::Variant(..)) => { // variant(x, y, z) for (i, subpat) in subpats.iter().enumerate() { let subpat_ty = try!(self.pat_ty(&subpat)); // see (*2) let subcmt = self.cat_imm_interior( pat, cmt.clone(), subpat_ty, InteriorField(PositionalField(i))); try!(self.cat_pattern_(subcmt, &subpat, op)); } } Some(Def::Struct(..)) => { for (i, subpat) in subpats.iter().enumerate() { let subpat_ty = try!(self.pat_ty(&subpat)); // see (*2) let cmt_field = self.cat_imm_interior( pat, cmt.clone(), subpat_ty, InteriorField(PositionalField(i))); try!(self.cat_pattern_(cmt_field, &subpat, op)); } } Some(Def::Const(..)) | Some(Def::AssociatedConst(..)) => { for subpat in subpats { try!(self.cat_pattern_(cmt.clone(), &subpat, op)); } } _ => { self.tcx().sess.span_bug( pat.span, &format!("enum pattern didn't resolve to enum or struct {:?}", opt_def)); } } } PatKind::Path(..) | PatKind::QPath(..) | PatKind::Ident(_, _, None) => { // Lone constant, or unit variant or identifier: ignore } PatKind::Ident(_, _, Some(ref subpat)) => { try!(self.cat_pattern_(cmt, &subpat, op)); } PatKind::Struct(_, ref field_pats, _) => { // {f1: p1, ..., fN: pN} for fp in field_pats { let field_ty = try!(self.pat_ty(&fp.node.pat)); // see (*2) let cmt_field = self.cat_field(pat, cmt.clone(), fp.node.name, field_ty); try!(self.cat_pattern_(cmt_field, &fp.node.pat, op)); } } PatKind::Tup(ref subpats) => { // (p1, ..., pN) for (i, subpat) in subpats.iter().enumerate() { let subpat_ty = try!(self.pat_ty(&subpat)); // see (*2) let subcmt = self.cat_imm_interior( pat, cmt.clone(), subpat_ty, InteriorField(PositionalField(i))); try!(self.cat_pattern_(subcmt, &subpat, op)); } } PatKind::Box(ref subpat) | PatKind::Ref(ref subpat, _) => { // box p1, &p1, &mut p1. we can ignore the mutability of // PatKind::Ref since that information is already contained // in the type. let subcmt = try!(self.cat_deref(pat, cmt, 0, None)); try!(self.cat_pattern_(subcmt, &subpat, op)); } PatKind::Vec(ref before, ref slice, ref after) => { let context = InteriorOffsetKind::Pattern; let vec_cmt = try!(self.deref_vec(pat, cmt, context)); let elt_cmt = try!(self.cat_index(pat, vec_cmt, context)); for before_pat in before { try!(self.cat_pattern_(elt_cmt.clone(), &before_pat, op)); } if let Some(ref slice_pat) = *slice { let slice_ty = try!(self.pat_ty(&slice_pat)); let slice_cmt = self.cat_rvalue_node(pat.id(), pat.span(), slice_ty); try!(self.cat_pattern_(slice_cmt, &slice_pat, op)); } for after_pat in after { try!(self.cat_pattern_(elt_cmt.clone(), &after_pat, op)); } } PatKind::Lit(_) | PatKind::Range(_, _) => { /*always ok*/ } } Ok(()) } fn overloaded_method_return_ty(&self, method_ty: Ty<'tcx>) -> Ty<'tcx> { // When we process an overloaded `*` or `[]` etc, we often // need to extract the return type of the method. These method // types are generated by method resolution and always have // all late-bound regions fully instantiated, so we just want // to skip past the binder. self.tcx().no_late_bound_regions(&method_ty.fn_ret()) .unwrap() .unwrap() // overloaded ops do not diverge, either } } #[derive(Clone, Debug)] pub enum Aliasability { FreelyAliasable(AliasableReason), NonAliasable, ImmutableUnique(Box), } #[derive(Copy, Clone, Debug)] pub enum AliasableReason { AliasableBorrowed, AliasableClosure(ast::NodeId), // Aliasable due to capture Fn closure env AliasableOther, UnaliasableImmutable, // Created as needed upon seeing ImmutableUnique AliasableStatic, AliasableStaticMut, } impl<'tcx> cmt_<'tcx> { pub fn guarantor(&self) -> cmt<'tcx> { //! Returns `self` after stripping away any derefs or //! interior content. The return value is basically the `cmt` which //! determines how long the value in `self` remains live. match self.cat { Categorization::Rvalue(..) | Categorization::StaticItem | Categorization::Local(..) | Categorization::Deref(_, _, UnsafePtr(..)) | Categorization::Deref(_, _, BorrowedPtr(..)) | Categorization::Deref(_, _, Implicit(..)) | Categorization::Upvar(..) => { Rc::new((*self).clone()) } Categorization::Downcast(ref b, _) | Categorization::Interior(ref b, _) | Categorization::Deref(ref b, _, Unique) => { b.guarantor() } } } /// Returns `FreelyAliasable(_)` if this lvalue represents a freely aliasable pointer type. pub fn freely_aliasable(&self, ctxt: &TyCtxt<'tcx>) -> Aliasability { // Maybe non-obvious: copied upvars can only be considered // non-aliasable in once closures, since any other kind can be // aliased and eventually recused. match self.cat { Categorization::Deref(ref b, _, BorrowedPtr(ty::MutBorrow, _)) | Categorization::Deref(ref b, _, Implicit(ty::MutBorrow, _)) | Categorization::Deref(ref b, _, BorrowedPtr(ty::UniqueImmBorrow, _)) | Categorization::Deref(ref b, _, Implicit(ty::UniqueImmBorrow, _)) | Categorization::Downcast(ref b, _) | Categorization::Interior(ref b, _) => { // Aliasability depends on base cmt b.freely_aliasable(ctxt) } Categorization::Deref(ref b, _, Unique) => { let sub = b.freely_aliasable(ctxt); if b.mutbl.is_mutable() { // Aliasability depends on base cmt alone sub } else { // Do not allow mutation through an immutable box. ImmutableUnique(Box::new(sub)) } } Categorization::Rvalue(..) | Categorization::Local(..) | Categorization::Upvar(..) | Categorization::Deref(_, _, UnsafePtr(..)) => { // yes, it's aliasable, but... NonAliasable } Categorization::StaticItem => { if self.mutbl.is_mutable() { FreelyAliasable(AliasableStaticMut) } else { FreelyAliasable(AliasableStatic) } } Categorization::Deref(ref base, _, BorrowedPtr(ty::ImmBorrow, _)) | Categorization::Deref(ref base, _, Implicit(ty::ImmBorrow, _)) => { match base.cat { Categorization::Upvar(Upvar{ id, .. }) => FreelyAliasable(AliasableClosure(id.closure_expr_id)), _ => FreelyAliasable(AliasableBorrowed) } } } } // Digs down through one or two layers of deref and grabs the cmt // for the upvar if a note indicates there is one. pub fn upvar(&self) -> Option> { match self.note { NoteClosureEnv(..) | NoteUpvarRef(..) => { Some(match self.cat { Categorization::Deref(ref inner, _, _) => { match inner.cat { Categorization::Deref(ref inner, _, _) => inner.clone(), Categorization::Upvar(..) => inner.clone(), _ => unreachable!() } } _ => unreachable!() }) } NoteNone => None } } pub fn descriptive_string(&self, tcx: &TyCtxt) -> String { match self.cat { Categorization::StaticItem => { "static item".to_string() } Categorization::Rvalue(..) => { "non-lvalue".to_string() } Categorization::Local(vid) => { if tcx.map.is_argument(vid) { "argument".to_string() } else { "local variable".to_string() } } Categorization::Deref(_, _, pk) => { let upvar = self.upvar(); match upvar.as_ref().map(|i| &i.cat) { Some(&Categorization::Upvar(ref var)) => { var.to_string() } Some(_) => unreachable!(), None => { match pk { Implicit(..) => { format!("indexed content") } Unique => { format!("`Box` content") } UnsafePtr(..) => { format!("dereference of raw pointer") } BorrowedPtr(..) => { format!("borrowed content") } } } } } Categorization::Interior(_, InteriorField(NamedField(_))) => { "field".to_string() } Categorization::Interior(_, InteriorField(PositionalField(_))) => { "anonymous field".to_string() } Categorization::Interior(_, InteriorElement(InteriorOffsetKind::Index, VecElement)) | Categorization::Interior(_, InteriorElement(InteriorOffsetKind::Index, OtherElement)) => { "indexed content".to_string() } Categorization::Interior(_, InteriorElement(InteriorOffsetKind::Pattern, VecElement)) | Categorization::Interior(_, InteriorElement(InteriorOffsetKind::Pattern, OtherElement)) => { "pattern-bound indexed content".to_string() } Categorization::Upvar(ref var) => { var.to_string() } Categorization::Downcast(ref cmt, _) => { cmt.descriptive_string(tcx) } } } } impl<'tcx> fmt::Debug for cmt_<'tcx> { fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { write!(f, "{{{:?} id:{} m:{:?} ty:{:?}}}", self.cat, self.id, self.mutbl, self.ty) } } impl<'tcx> fmt::Debug for Categorization<'tcx> { fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { match *self { Categorization::StaticItem => write!(f, "static"), Categorization::Rvalue(r) => write!(f, "rvalue({:?})", r), Categorization::Local(id) => { let name = ty::tls::with(|tcx| tcx.local_var_name_str(id)); write!(f, "local({})", name) } Categorization::Upvar(upvar) => { write!(f, "upvar({:?})", upvar) } Categorization::Deref(ref cmt, derefs, ptr) => { write!(f, "{:?}-{:?}{}->", cmt.cat, ptr, derefs) } Categorization::Interior(ref cmt, interior) => { write!(f, "{:?}.{:?}", cmt.cat, interior) } Categorization::Downcast(ref cmt, _) => { write!(f, "{:?}->(enum)", cmt.cat) } } } } pub fn ptr_sigil(ptr: PointerKind) -> &'static str { match ptr { Unique => "Box", BorrowedPtr(ty::ImmBorrow, _) | Implicit(ty::ImmBorrow, _) => "&", BorrowedPtr(ty::MutBorrow, _) | Implicit(ty::MutBorrow, _) => "&mut", BorrowedPtr(ty::UniqueImmBorrow, _) | Implicit(ty::UniqueImmBorrow, _) => "&unique", UnsafePtr(_) => "*", } } impl fmt::Debug for PointerKind { fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { match *self { Unique => write!(f, "Box"), BorrowedPtr(ty::ImmBorrow, ref r) | Implicit(ty::ImmBorrow, ref r) => { write!(f, "&{:?}", r) } BorrowedPtr(ty::MutBorrow, ref r) | Implicit(ty::MutBorrow, ref r) => { write!(f, "&{:?} mut", r) } BorrowedPtr(ty::UniqueImmBorrow, ref r) | Implicit(ty::UniqueImmBorrow, ref r) => { write!(f, "&{:?} uniq", r) } UnsafePtr(_) => write!(f, "*") } } } impl fmt::Debug for InteriorKind { fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { match *self { InteriorField(NamedField(fld)) => write!(f, "{}", fld), InteriorField(PositionalField(i)) => write!(f, "#{}", i), InteriorElement(..) => write!(f, "[]"), } } } fn element_kind(t: Ty) -> ElementKind { match t.sty { ty::TyRef(_, ty::TypeAndMut{ty, ..}) | ty::TyBox(ty) => match ty.sty { ty::TySlice(_) => VecElement, _ => OtherElement }, ty::TyArray(..) | ty::TySlice(_) => VecElement, _ => OtherElement } } impl fmt::Debug for Upvar { fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { write!(f, "{:?}/{:?}", self.id, self.kind) } } impl fmt::Display for Upvar { fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { let kind = match self.kind { ty::ClosureKind::Fn => "Fn", ty::ClosureKind::FnMut => "FnMut", ty::ClosureKind::FnOnce => "FnOnce", }; write!(f, "captured outer variable in an `{}` closure", kind) } }