// 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 `cat_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::InteriorSafety::*; pub use self::AliasableReason::*; pub use self::Note::*; pub use self::deref_kind::*; pub use self::categorization::*; use middle::def; use middle::region; use middle::ty::{mod, Ty}; use util::nodemap::{DefIdMap, NodeMap}; use util::ppaux::{ty_to_string, Repr}; use syntax::ast::{MutImmutable, MutMutable}; use syntax::ast; use syntax::ast_map; use syntax::codemap::Span; use syntax::print::pprust; use syntax::parse::token; use std::cell::RefCell; use std::rc::Rc; #[deriving(Clone, PartialEq, Show)] pub enum categorization<'tcx> { cat_rvalue(ty::Region), // temporary val, argument is its scope cat_static_item, cat_upvar(Upvar), // upvar referenced by closure env cat_local(ast::NodeId), // local variable cat_deref(cmt<'tcx>, uint, PointerKind), // deref of a ptr cat_interior(cmt<'tcx>, InteriorKind), // something interior: field, tuple, etc cat_downcast(cmt<'tcx>, ast::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 #[deriving(Clone, PartialEq, Show)] pub struct Upvar { pub id: ty::UpvarId, // Unboxed closure kinds are used even for old-style closures for simplicity pub kind: ty::UnboxedClosureKind, // Is this from an unboxed closure? Used only for diagnostics. pub is_unboxed: bool } impl Copy for Upvar {} // different kinds of pointers: #[deriving(Clone, PartialEq, Eq, Hash, Show)] pub enum PointerKind { OwnedPtr, BorrowedPtr(ty::BorrowKind, ty::Region), Implicit(ty::BorrowKind, ty::Region), // Implicit deref of a borrowed ptr. UnsafePtr(ast::Mutability) } impl Copy for PointerKind {} // We use the term "interior" to mean "something reachable from the // base without a pointer dereference", e.g. a field #[deriving(Clone, PartialEq, Eq, Hash, Show)] pub enum InteriorKind { InteriorField(FieldName), InteriorElement(ElementKind), } impl Copy for InteriorKind {} #[deriving(Clone, PartialEq, Eq, Hash, Show)] pub enum FieldName { NamedField(ast::Name), PositionalField(uint) } impl Copy for FieldName {} #[deriving(Clone, PartialEq, Eq, Hash, Show)] pub enum ElementKind { VecElement, OtherElement, } impl Copy for ElementKind {} #[deriving(Clone, PartialEq, Eq, Hash, Show)] pub enum MutabilityCategory { McImmutable, // Immutable. McDeclared, // Directly declared as mutable. McInherited, // Inherited from the fact that owner is mutable. } impl Copy for MutabilityCategory {} // 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. #[deriving(Clone, PartialEq, Show)] pub enum Note { NoteClosureEnv(ty::UpvarId), // Deref through closure env NoteUpvarRef(ty::UpvarId), // Deref through by-ref upvar NoteNone // Nothing special } impl Copy for Note {} // `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` #[deriving(Clone, PartialEq, Show)] 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: pub enum deref_kind { deref_ptr(PointerKind), deref_interior(InteriorKind), } impl Copy for deref_kind {} // 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). pub fn opt_deref_kind(t: Ty) -> Option { match t.sty { ty::ty_uniq(_) | ty::ty_closure(box ty::ClosureTy {store: ty::UniqTraitStore, ..}) => { Some(deref_ptr(OwnedPtr)) } ty::ty_rptr(r, mt) => { let kind = ty::BorrowKind::from_mutbl(mt.mutbl); Some(deref_ptr(BorrowedPtr(kind, r))) } ty::ty_closure(box ty::ClosureTy { store: ty::RegionTraitStore(r, _), .. }) => { Some(deref_ptr(BorrowedPtr(ty::ImmBorrow, r))) } ty::ty_ptr(ref mt) => { Some(deref_ptr(UnsafePtr(mt.mutbl))) } ty::ty_enum(..) | ty::ty_struct(..) => { // newtype Some(deref_interior(InteriorField(PositionalField(0)))) } ty::ty_vec(_, _) | ty::ty_str => { Some(deref_interior(InteriorElement(element_kind(t)))) } _ => None } } pub fn deref_kind<'tcx>(tcx: &ty::ctxt<'tcx>, t: Ty<'tcx>) -> deref_kind { debug!("deref_kind {}", ty_to_string(tcx, t)); match opt_deref_kind(t) { Some(k) => k, None => { tcx.sess.bug( format!("deref_kind() invoked on non-derefable type {}", ty_to_string(tcx, t)).as_slice()); } } } pub trait ast_node { fn id(&self) -> ast::NodeId; fn span(&self) -> Span; } impl ast_node for ast::Expr { fn id(&self) -> ast::NodeId { self.id } fn span(&self) -> Span { self.span } } impl ast_node for ast::Pat { fn id(&self) -> ast::NodeId { self.id } fn span(&self) -> Span { self.span } } pub struct MemCategorizationContext<'t,TYPER:'t> { typer: &'t TYPER } impl<'t,TYPER:'t> Copy for MemCategorizationContext<'t,TYPER> {} pub type McResult = Result; /// The `Typer` trait provides the interface for the mem-categorization /// module to the results of the type check. It can be used to query /// the type assigned to an expression node, to inquire after adjustments, /// and so on. /// /// This interface is needed because mem-categorization is used from /// two places: `regionck` and `borrowck`. `regionck` executes before /// type inference is complete, and hence derives types and so on from /// intermediate tables. This also implies that type errors can occur, /// and hence `node_ty()` and friends return a `Result` type -- any /// error will propagate back up through the mem-categorization /// routines. /// /// In the borrow checker, in contrast, type checking is complete and we /// know that no errors have occurred, so we simply consult the tcx and we /// can be sure that only `Ok` results will occur. pub trait Typer<'tcx> { fn tcx<'a>(&'a self) -> &'a ty::ctxt<'tcx>; fn node_ty(&self, id: ast::NodeId) -> McResult>; fn node_method_ty(&self, method_call: ty::MethodCall) -> Option>; fn adjustments<'a>(&'a self) -> &'a RefCell>>; fn is_method_call(&self, id: ast::NodeId) -> bool; fn temporary_scope(&self, rvalue_id: ast::NodeId) -> Option; fn upvar_borrow(&self, upvar_id: ty::UpvarId) -> ty::UpvarBorrow; fn capture_mode(&self, closure_expr_id: ast::NodeId) -> ast::CaptureClause; fn unboxed_closures<'a>(&'a self) -> &'a RefCell>>; } impl MutabilityCategory { pub fn from_mutbl(m: ast::Mutability) -> MutabilityCategory { match m { MutImmutable => McImmutable, MutMutable => McDeclared } } pub fn from_borrow_kind(borrow_kind: ty::BorrowKind) -> MutabilityCategory { match borrow_kind { ty::ImmBorrow => McImmutable, ty::UniqueImmBorrow => McImmutable, ty::MutBorrow => McDeclared, } } pub fn from_pointer_kind(base_mutbl: MutabilityCategory, ptr: PointerKind) -> MutabilityCategory { match ptr { OwnedPtr => { base_mutbl.inherit() } BorrowedPtr(borrow_kind, _) | Implicit(borrow_kind, _) => { MutabilityCategory::from_borrow_kind(borrow_kind) } UnsafePtr(m) => { MutabilityCategory::from_mutbl(m) } } } fn from_local(tcx: &ty::ctxt, id: ast::NodeId) -> MutabilityCategory { match tcx.map.get(id) { ast_map::NodeLocal(p) | ast_map::NodeArg(p) => match p.node { ast::PatIdent(bind_mode, _, _) => { if bind_mode == ast::BindByValue(ast::MutMutable) { McDeclared } else { McImmutable } } _ => tcx.sess.span_bug(p.span, "expected identifier pattern") }, _ => tcx.sess.span_bug(tcx.map.span(id), "expected identifier pattern") } } pub fn inherit(&self) -> MutabilityCategory { match *self { McImmutable => McImmutable, McDeclared => McInherited, McInherited => McInherited, } } pub fn is_mutable(&self) -> bool { match *self { McImmutable => false, McInherited => true, McDeclared => true, } } pub fn is_immutable(&self) -> bool { match *self { McImmutable => true, McDeclared | McInherited => false } } pub fn to_user_str(&self) -> &'static str { match *self { McDeclared | McInherited => "mutable", McImmutable => "immutable", } } } macro_rules! if_ok( ($inp: expr) => ( match $inp { Ok(v) => { v } Err(e) => { return Err(e); } } ) ) impl<'t,'tcx,TYPER:Typer<'tcx>> MemCategorizationContext<'t,TYPER> { pub fn new(typer: &'t TYPER) -> MemCategorizationContext<'t,TYPER> { MemCategorizationContext { typer: typer } } fn tcx(&self) -> &'t ty::ctxt<'tcx> { self.typer.tcx() } fn expr_ty(&self, expr: &ast::Expr) -> McResult> { self.typer.node_ty(expr.id) } fn expr_ty_adjusted(&self, expr: &ast::Expr) -> McResult> { let unadjusted_ty = if_ok!(self.expr_ty(expr)); Ok(ty::adjust_ty(self.tcx(), expr.span, expr.id, unadjusted_ty, self.typer.adjustments().borrow().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: &ast::Pat) -> McResult> { let tcx = self.typer.tcx(); let base_ty = 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 { ast::PatIdent(ast::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. base_ty.map(|t| { ty::deref(t, false).unwrap_or_else(|| { panic!("encountered BindByRef with non &-type"); }).ty }) } _ => base_ty, }; debug!("pat_ty(pat={}) base_ty={} ret_ty={}", pat.repr(tcx), base_ty.repr(tcx), ret_ty.repr(tcx)); ret_ty } pub fn cat_expr(&self, expr: &ast::Expr) -> McResult> { match self.typer.adjustments().borrow().get(&expr.id) { None => { // No adjustments. self.cat_expr_unadjusted(expr) } Some(adjustment) => { match *adjustment { ty::AdjustAddEnv(..) => { debug!("cat_expr(AdjustAddEnv): {}", expr.repr(self.tcx())); // Convert a bare fn to a closure by adding NULL env. // Result is an rvalue. let expr_ty = if_ok!(self.expr_ty_adjusted(expr)); Ok(self.cat_rvalue_node(expr.id(), expr.span(), expr_ty)) } ty::AdjustDerefRef( ty::AutoDerefRef { autoref: Some(_), ..}) => { debug!("cat_expr(AdjustDerefRef): {}", expr.repr(self.tcx())); // Equivalent to &*expr or something similar. // Result is an rvalue. let expr_ty = if_ok!(self.expr_ty_adjusted(expr)); Ok(self.cat_rvalue_node(expr.id(), expr.span(), expr_ty)) } ty::AdjustDerefRef( ty::AutoDerefRef { autoref: None, autoderefs}) => { // Equivalent to *expr or something similar. self.cat_expr_autoderefd(expr, autoderefs) } } } } } pub fn cat_expr_autoderefd(&self, expr: &ast::Expr, autoderefs: uint) -> McResult> { let mut cmt = if_ok!(self.cat_expr_unadjusted(expr)); debug!("cat_expr_autoderefd: autoderefs={}, cmt={}", autoderefs, cmt.repr(self.tcx())); for deref in range(1u, autoderefs + 1) { cmt = self.cat_deref(expr, cmt, deref, false); } return Ok(cmt); } pub fn cat_expr_unadjusted(&self, expr: &ast::Expr) -> McResult> { debug!("cat_expr: id={} expr={}", expr.id, expr.repr(self.tcx())); let expr_ty = if_ok!(self.expr_ty(expr)); match expr.node { ast::ExprUnary(ast::UnDeref, ref e_base) => { let base_cmt = if_ok!(self.cat_expr(&**e_base)); Ok(self.cat_deref(expr, base_cmt, 0, false)) } ast::ExprField(ref base, f_name) => { let base_cmt = if_ok!(self.cat_expr(&**base)); debug!("cat_expr(cat_field): id={} expr={} base={}", expr.id, expr.repr(self.tcx()), base_cmt.repr(self.tcx())); Ok(self.cat_field(expr, base_cmt, f_name.node.name, expr_ty)) } ast::ExprTupField(ref base, idx) => { let base_cmt = if_ok!(self.cat_expr(&**base)); Ok(self.cat_tup_field(expr, base_cmt, idx.node, expr_ty)) } ast::ExprIndex(ref base, _) => { let method_call = ty::MethodCall::expr(expr.id()); 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 = ty::ty_fn_ret(method_ty).unwrap(); Ok(self.cat_deref(expr, self.cat_rvalue_node(expr.id(), expr.span(), ret_ty), 1, true)) } None => { let base_cmt = if_ok!(self.cat_expr(&**base)); Ok(self.cat_index(expr, base_cmt)) } } } ast::ExprPath(_) => { let def = (*self.tcx().def_map.borrow())[expr.id]; self.cat_def(expr.id, expr.span, expr_ty, def) } ast::ExprParen(ref e) => { self.cat_expr(&**e) } ast::ExprAddrOf(..) | ast::ExprCall(..) | ast::ExprAssign(..) | ast::ExprAssignOp(..) | ast::ExprClosure(..) | ast::ExprRet(..) | ast::ExprUnary(..) | ast::ExprSlice(..) | ast::ExprMethodCall(..) | ast::ExprCast(..) | ast::ExprVec(..) | ast::ExprTup(..) | ast::ExprIf(..) | ast::ExprBinary(..) | ast::ExprWhile(..) | ast::ExprBlock(..) | ast::ExprLoop(..) | ast::ExprMatch(..) | ast::ExprLit(..) | ast::ExprBreak(..) | ast::ExprMac(..) | ast::ExprAgain(..) | ast::ExprStruct(..) | ast::ExprRepeat(..) | ast::ExprInlineAsm(..) | ast::ExprBox(..) | ast::ExprForLoop(..) => { Ok(self.cat_rvalue_node(expr.id(), expr.span(), expr_ty)) } ast::ExprIfLet(..) => { self.tcx().sess.span_bug(expr.span, "non-desugared ExprIfLet"); } ast::ExprWhileLet(..) => { self.tcx().sess.span_bug(expr.span, "non-desugared ExprWhileLet"); } } } pub fn cat_def(&self, id: ast::NodeId, span: Span, expr_ty: Ty<'tcx>, def: def::Def) -> McResult> { debug!("cat_def: id={} expr={} def={}", id, expr_ty.repr(self.tcx()), def); match def { def::DefStruct(..) | def::DefVariant(..) | def::DefFn(..) | def::DefStaticMethod(..) | def::DefConst(..) => { Ok(self.cat_rvalue_node(id, span, expr_ty)) } def::DefMod(_) | def::DefForeignMod(_) | def::DefUse(_) | def::DefTrait(_) | def::DefTy(..) | def::DefPrimTy(_) | def::DefTyParam(..) | def::DefTyParamBinder(..) | def::DefRegion(_) | def::DefLabel(_) | def::DefSelfTy(..) | def::DefMethod(..) | def::DefAssociatedTy(..) => { Ok(Rc::new(cmt_ { id:id, span:span, cat:cat_static_item, mutbl: McImmutable, ty:expr_ty, note: NoteNone })) } def::DefStatic(_, mutbl) => { Ok(Rc::new(cmt_ { id:id, span:span, cat:cat_static_item, mutbl: if mutbl { McDeclared } else { McImmutable}, ty:expr_ty, note: NoteNone })) } def::DefUpvar(var_id, fn_node_id, _) => { let ty = if_ok!(self.node_ty(fn_node_id)); match ty.sty { ty::ty_closure(ref closure_ty) => { // Translate old closure type info into unboxed // closure kind/capture mode let (mode, kind) = match (closure_ty.store, closure_ty.onceness) { // stack closure (ty::RegionTraitStore(..), ast::Many) => { (ast::CaptureByRef, ty::FnMutUnboxedClosureKind) } // proc or once closure (_, ast::Once) => { (ast::CaptureByValue, ty::FnOnceUnboxedClosureKind) } // There should be no such old closure type (ty::UniqTraitStore, ast::Many) => { self.tcx().sess.span_bug(span, "Impossible closure type"); } }; self.cat_upvar(id, span, var_id, fn_node_id, kind, mode, false) } ty::ty_unboxed_closure(closure_id, _, _) => { let unboxed_closures = self.typer.unboxed_closures().borrow(); let kind = (*unboxed_closures)[closure_id].kind; let mode = self.typer.capture_mode(fn_node_id); self.cat_upvar(id, span, var_id, fn_node_id, kind, mode, true) } _ => { self.tcx().sess.span_bug( span, format!("Upvar of non-closure {} - {}", fn_node_id, ty.repr(self.tcx())).as_slice()); } } } def::DefLocal(vid) => { Ok(Rc::new(cmt_ { id: id, span: span, cat: cat_local(vid), mutbl: MutabilityCategory::from_local(self.tcx(), vid), ty: expr_ty, note: NoteNone })) } } } // 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::UnboxedClosureKind, mode: ast::CaptureClause, is_unboxed: bool) -> McResult> { // An upvar can have up to 3 components. The base is a // `cat_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 // old stack | N/A | upvar -> &'env mut -> &'up bk // old proc/once | copied | N/A let var_ty = if_ok!(self.node_ty(var_id)); let upvar_id = ty::UpvarId { var_id: var_id, closure_expr_id: fn_node_id }; // Mutability of original variable itself let var_mutbl = MutabilityCategory::from_local(self.tcx(), var_id); // Construct information about env pointer dereference, if any let mutbl = match kind { ty::FnOnceUnboxedClosureKind => None, // None, env is by-value ty::FnMutUnboxedClosureKind => match mode { // Depends on capture type ast::CaptureByValue => Some(var_mutbl), // Mutable if the original var is ast::CaptureByRef => Some(McDeclared) // Mutable regardless }, ty::FnUnboxedClosureKind => Some(McImmutable) // Never mutable }; let env_info = mutbl.map(|env_mutbl| { // 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(fn_node_id) { Some(ast_map::NodeExpr(e)) => e, _ => unreachable!() }; match fn_expr.node { ast::ExprClosure(_, _, _, ref body) => body.id, _ => unreachable!() } }; // Region of environment pointer let env_region = ty::ReFree(ty::FreeRegion { scope: region::CodeExtent::from_node_id(fn_body_id), bound_region: ty::BrEnv }); let env_ptr = BorrowedPtr(if env_mutbl.is_mutable() { ty::MutBorrow } else { ty::ImmBorrow }, env_region); (env_mutbl, env_ptr) }); // First, switch by capture mode Ok(match mode { ast::CaptureByValue => { let mut base = cmt_ { id: id, span: span, cat: cat_upvar(Upvar { id: upvar_id, kind: kind, is_unboxed: is_unboxed }), mutbl: var_mutbl, ty: var_ty, note: NoteNone }; match env_info { Some((env_mutbl, env_ptr)) => { // 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 `ty_err` in there // instead of bothering to construct a proper // one. base.mutbl = McImmutable; base.ty = ty::mk_err(); Rc::new(cmt_ { id: id, span: span, cat: cat_deref(Rc::new(base), 0, env_ptr), mutbl: env_mutbl, ty: var_ty, note: NoteClosureEnv(upvar_id) }) } None => Rc::new(base) } }, ast::CaptureByRef => { // The type here is actually a ref (or ref of a ref), // but we can again get away with not constructing one // properly since it will never be used. let mut base = cmt_ { id: id, span: span, cat: cat_upvar(Upvar { id: upvar_id, kind: kind, is_unboxed: is_unboxed }), mutbl: McImmutable, ty: ty::mk_err(), note: NoteNone }; match env_info { Some((env_mutbl, env_ptr)) => { base = cmt_ { id: id, span: span, cat: cat_deref(Rc::new(base), 0, env_ptr), mutbl: env_mutbl, ty: ty::mk_err(), note: NoteClosureEnv(upvar_id) }; } None => {} } // Look up upvar borrow so we can get its region let upvar_borrow = self.typer.upvar_borrow(upvar_id); let ptr = BorrowedPtr(upvar_borrow.kind, upvar_borrow.region); Rc::new(cmt_ { id: id, span: span, cat: cat_deref(Rc::new(base), 0, ptr), mutbl: MutabilityCategory::from_borrow_kind(upvar_borrow.kind), ty: var_ty, note: NoteUpvarRef(upvar_id) }) } }) } pub fn cat_rvalue_node(&self, id: ast::NodeId, span: Span, expr_ty: Ty<'tcx>) -> cmt<'tcx> { match self.typer.temporary_scope(id) { Some(scope) => { match expr_ty.sty { ty::ty_vec(_, Some(0)) => self.cat_rvalue(id, span, ty::ReStatic, expr_ty), _ => self.cat_rvalue(id, span, ty::ReScope(scope), expr_ty) } } None => { self.cat_rvalue(id, span, ty::ReStatic, expr_ty) } } } pub fn cat_rvalue(&self, cmt_id: ast::NodeId, span: Span, temp_scope: ty::Region, expr_ty: Ty<'tcx>) -> cmt<'tcx> { Rc::new(cmt_ { id:cmt_id, span:span, cat:cat_rvalue(temp_scope), mutbl:McDeclared, ty:expr_ty, note: NoteNone }) } pub fn cat_field(&self, node: &N, base_cmt: cmt<'tcx>, f_name: ast::Name, f_ty: Ty<'tcx>) -> cmt<'tcx> { Rc::new(cmt_ { id: node.id(), span: node.span(), mutbl: base_cmt.mutbl.inherit(), cat: cat_interior(base_cmt, InteriorField(NamedField(f_name))), ty: f_ty, note: NoteNone }) } pub fn cat_tup_field(&self, node: &N, base_cmt: cmt<'tcx>, f_idx: uint, f_ty: Ty<'tcx>) -> cmt<'tcx> { Rc::new(cmt_ { id: node.id(), span: node.span(), mutbl: base_cmt.mutbl.inherit(), cat: cat_interior(base_cmt, InteriorField(PositionalField(f_idx))), ty: f_ty, note: NoteNone }) } fn cat_deref(&self, node: &N, base_cmt: cmt<'tcx>, deref_cnt: uint, implicit: bool) -> cmt<'tcx> { let adjustment = match self.typer.adjustments().borrow().get(&node.id()) { Some(adj) if ty::adjust_is_object(adj) => ty::AutoObject, _ if deref_cnt != 0 => ty::AutoDeref(deref_cnt), _ => ty::NoAdjustment }; let method_call = ty::MethodCall { expr_id: node.id(), adjustment: adjustment }; let method_ty = self.typer.node_method_ty(method_call); debug!("cat_deref: method_call={} method_ty={}", method_call, method_ty.map(|ty| ty.repr(self.tcx()))); let base_cmt = match method_ty { Some(method_ty) => { let ref_ty = ty::ty_fn_ret(method_ty).unwrap(); self.cat_rvalue_node(node.id(), node.span(), ref_ty) } None => base_cmt }; match ty::deref(base_cmt.ty, true) { Some(mt) => self.cat_deref_common(node, base_cmt, deref_cnt, mt.ty, implicit), None => { self.tcx().sess.span_bug( node.span(), format!("Explicit deref of non-derefable type: {}", base_cmt.ty.repr(self.tcx())).as_slice()); } } } fn cat_deref_common(&self, node: &N, base_cmt: cmt<'tcx>, deref_cnt: uint, deref_ty: Ty<'tcx>, implicit: bool) -> cmt<'tcx> { let (m, cat) = match deref_kind(self.tcx(), base_cmt.ty) { 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), cat_deref(base_cmt, deref_cnt, ptr)) } deref_interior(interior) => { (base_cmt.mutbl.inherit(), cat_interior(base_cmt, interior)) } }; Rc::new(cmt_ { id: node.id(), span: node.span(), cat: cat, mutbl: m, ty: deref_ty, note: NoteNone }) } pub fn cat_index(&self, elt: &N, mut base_cmt: cmt<'tcx>) -> cmt<'tcx> { //! 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 = ty::ty_fn_ret(method_ty).unwrap(); base_cmt = self.cat_rvalue_node(elt.id(), elt.span(), ref_ty); ty::ty_fn_args(method_ty)[0] } None => { match ty::array_element_ty(base_cmt.ty) { Some(ty) => ty, None => { self.tcx().sess.span_bug( elt.span(), format!("Explicit index of non-index type `{}`", base_cmt.ty.repr(self.tcx())).as_slice()); } } } }; let m = base_cmt.mutbl.inherit(); return interior(elt, base_cmt.clone(), base_cmt.ty, m, element_ty); fn interior<'tcx, N: ast_node>(elt: &N, of_cmt: cmt<'tcx>, vec_ty: Ty<'tcx>, mutbl: MutabilityCategory, element_ty: Ty<'tcx>) -> cmt<'tcx> { Rc::new(cmt_ { id:elt.id(), span:elt.span(), cat:cat_interior(of_cmt, InteriorElement(element_kind(vec_ty))), 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>) -> cmt<'tcx> { match deref_kind(self.tcx(), base_cmt.ty) { 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:cat_deref(base_cmt.clone(), 0, ptr), mutbl:m, ty: match ty::deref(base_cmt.ty, false) { Some(mt) => mt.ty, None => self.tcx().sess.bug("Found non-derefable type") }, note: NoteNone }) } deref_interior(_) => { base_cmt } } } /// 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: &ast::Pat) -> McResult<(cmt<'tcx>, ast::Mutability, ty::Region)> { let slice_ty = if_ok!(self.node_ty(slice_pat.id)); let (slice_mutbl, slice_r) = vec_slice_info(self.tcx(), slice_pat, slice_ty); let cmt_slice = self.cat_index(slice_pat, self.deref_vec(slice_pat, vec_cmt)); 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: &ty::ctxt, pat: &ast::Pat, slice_ty: Ty) -> (ast::Mutability, ty::Region) { match slice_ty.sty { ty::ty_rptr(r, ref mt) => match mt.ty.sty { ty::ty_vec(_, None) => (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> { Rc::new(cmt_ { id: node.id(), span: node.span(), mutbl: base_cmt.mutbl.inherit(), cat: cat_interior(base_cmt, interior), ty: interior_ty, note: NoteNone }) } pub fn cat_downcast(&self, node: &N, base_cmt: cmt<'tcx>, downcast_ty: Ty<'tcx>, variant_did: ast::DefId) -> cmt<'tcx> { Rc::new(cmt_ { id: node.id(), span: node.span(), mutbl: base_cmt.mutbl.inherit(), cat: cat_downcast(base_cmt, variant_did), ty: downcast_ty, note: NoteNone }) } // FIXME(#19596) unbox `op` pub fn cat_pattern(&self, cmt: cmt<'tcx>, pat: &ast::Pat, op: |&MemCategorizationContext<'t, TYPER>, cmt<'tcx>, &ast::Pat|) -> McResult<()> { // 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: id={} pat={} cmt={}", pat.id, pprust::pat_to_string(pat), cmt.repr(self.tcx())); op(self, cmt.clone(), pat); let def_map = self.tcx().def_map.borrow(); let opt_def = def_map.get(&pat.id); // Note: This goes up here (rather than within the PatEnum arm // alone) because struct patterns can refer to struct types or // to struct variants within enums. let cmt = match opt_def { Some(&def::DefVariant(enum_did, variant_did, _)) // univariant enums do not need downcasts if !ty::enum_is_univariant(self.tcx(), enum_did) => { self.cat_downcast(pat, cmt.clone(), cmt.ty, variant_did) } _ => cmt }; match pat.node { ast::PatWild(_) => { // _ } ast::PatEnum(_, None) => { // variant(..) } ast::PatEnum(_, Some(ref subpats)) => { match opt_def { Some(&def::DefVariant(..)) => { // variant(x, y, z) for (i, subpat) in subpats.iter().enumerate() { let subpat_ty = if_ok!(self.pat_ty(&**subpat)); // see (*2) let subcmt = self.cat_imm_interior( pat, cmt.clone(), subpat_ty, InteriorField(PositionalField(i))); if_ok!(self.cat_pattern(subcmt, &**subpat, |x,y,z| op(x,y,z))); } } Some(&def::DefStruct(..)) => { for (i, subpat) in subpats.iter().enumerate() { let subpat_ty = if_ok!(self.pat_ty(&**subpat)); // see (*2) let cmt_field = self.cat_imm_interior( pat, cmt.clone(), subpat_ty, InteriorField(PositionalField(i))); if_ok!(self.cat_pattern(cmt_field, &**subpat, |x,y,z| op(x,y,z))); } } Some(&def::DefConst(..)) => { for subpat in subpats.iter() { if_ok!(self.cat_pattern(cmt.clone(), &**subpat, |x,y,z| op(x,y,z))); } } _ => { self.tcx().sess.span_bug( pat.span, "enum pattern didn't resolve to enum or struct"); } } } ast::PatIdent(_, _, Some(ref subpat)) => { if_ok!(self.cat_pattern(cmt, &**subpat, op)); } ast::PatIdent(_, _, None) => { // nullary variant or identifier: ignore } ast::PatStruct(_, ref field_pats, _) => { // {f1: p1, ..., fN: pN} for fp in field_pats.iter() { let field_ty = if_ok!(self.pat_ty(&*fp.node.pat)); // see (*2) let cmt_field = self.cat_field(pat, cmt.clone(), fp.node.ident.name, field_ty); if_ok!(self.cat_pattern(cmt_field, &*fp.node.pat, |x,y,z| op(x,y,z))); } } ast::PatTup(ref subpats) => { // (p1, ..., pN) for (i, subpat) in subpats.iter().enumerate() { let subpat_ty = if_ok!(self.pat_ty(&**subpat)); // see (*2) let subcmt = self.cat_imm_interior( pat, cmt.clone(), subpat_ty, InteriorField(PositionalField(i))); if_ok!(self.cat_pattern(subcmt, &**subpat, |x,y,z| op(x,y,z))); } } ast::PatBox(ref subpat) | ast::PatRegion(ref subpat) => { // @p1, ~p1, ref p1 let subcmt = self.cat_deref(pat, cmt, 0, false); if_ok!(self.cat_pattern(subcmt, &**subpat, op)); } ast::PatVec(ref before, ref slice, ref after) => { let elt_cmt = self.cat_index(pat, self.deref_vec(pat, cmt)); for before_pat in before.iter() { if_ok!(self.cat_pattern(elt_cmt.clone(), &**before_pat, |x,y,z| op(x,y,z))); } for slice_pat in slice.iter() { let slice_ty = if_ok!(self.pat_ty(&**slice_pat)); let slice_cmt = self.cat_rvalue_node(pat.id(), pat.span(), slice_ty); if_ok!(self.cat_pattern(slice_cmt, &**slice_pat, |x,y,z| op(x,y,z))); } for after_pat in after.iter() { if_ok!(self.cat_pattern(elt_cmt.clone(), &**after_pat, |x,y,z| op(x,y,z))); } } ast::PatLit(_) | ast::PatRange(_, _) => { /*always ok*/ } ast::PatMac(_) => { self.tcx().sess.span_bug(pat.span, "unexpanded macro"); } } Ok(()) } pub fn cmt_to_string(&self, cmt: &cmt_<'tcx>) -> String { fn upvar_to_string(upvar: &Upvar, is_copy: bool) -> String { if upvar.is_unboxed { let kind = match upvar.kind { ty::FnUnboxedClosureKind => "Fn", ty::FnMutUnboxedClosureKind => "FnMut", ty::FnOnceUnboxedClosureKind => "FnOnce" }; format!("captured outer variable in an `{}` closure", kind) } else { (match (upvar.kind, is_copy) { (ty::FnOnceUnboxedClosureKind, true) => "captured outer variable in a proc", _ => "captured outer variable" }).to_string() } } match cmt.cat { cat_static_item => { "static item".to_string() } cat_rvalue(..) => { "non-lvalue".to_string() } cat_local(vid) => { match self.tcx().map.find(vid) { Some(ast_map::NodeArg(_)) => { "argument".to_string() } _ => "local variable".to_string() } } cat_deref(_, _, pk) => { let upvar = cmt.upvar(); match upvar.as_ref().map(|i| &i.cat) { Some(&cat_upvar(ref var)) => { upvar_to_string(var, false) } Some(_) => unreachable!(), None => { match pk { Implicit(..) => { "dereference (dereference is implicit, due to indexing)".to_string() } OwnedPtr => format!("dereference of `{}`", ptr_sigil(pk)), _ => format!("dereference of `{}`-pointer", ptr_sigil(pk)) } } } } cat_interior(_, InteriorField(NamedField(_))) => { "field".to_string() } cat_interior(_, InteriorField(PositionalField(_))) => { "anonymous field".to_string() } cat_interior(_, InteriorElement(VecElement)) => { "vec content".to_string() } cat_interior(_, InteriorElement(OtherElement)) => { "indexed content".to_string() } cat_upvar(ref var) => { upvar_to_string(var, true) } cat_downcast(ref cmt, _) => { self.cmt_to_string(&**cmt) } } } } pub enum InteriorSafety { InteriorUnsafe, InteriorSafe } impl Copy for InteriorSafety {} pub enum AliasableReason { AliasableBorrowed, AliasableClosure(ast::NodeId), // Aliasable due to capture Fn closure env AliasableOther, AliasableStatic(InteriorSafety), AliasableStaticMut(InteriorSafety), } impl Copy for AliasableReason {} impl<'tcx> cmt_<'tcx> { pub fn guarantor(&self) -> cmt<'tcx> { //! Returns `self` after stripping away any owned pointer derefs or //! interior content. The return value is basically the `cmt` which //! determines how long the value in `self` remains live. match self.cat { cat_rvalue(..) | cat_static_item | cat_local(..) | cat_deref(_, _, UnsafePtr(..)) | cat_deref(_, _, BorrowedPtr(..)) | cat_deref(_, _, Implicit(..)) | cat_upvar(..) => { Rc::new((*self).clone()) } cat_downcast(ref b, _) | cat_interior(ref b, _) | cat_deref(ref b, _, OwnedPtr) => { b.guarantor() } } } /// Returns `Some(_)` if this lvalue represents a freely aliasable pointer type. pub fn freely_aliasable(&self, ctxt: &ty::ctxt<'tcx>) -> Option { // 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 { cat_deref(ref b, _, BorrowedPtr(ty::MutBorrow, _)) | cat_deref(ref b, _, Implicit(ty::MutBorrow, _)) | cat_deref(ref b, _, BorrowedPtr(ty::UniqueImmBorrow, _)) | cat_deref(ref b, _, Implicit(ty::UniqueImmBorrow, _)) | cat_downcast(ref b, _) | cat_deref(ref b, _, OwnedPtr) | cat_interior(ref b, _) => { // Aliasability depends on base cmt b.freely_aliasable(ctxt) } cat_rvalue(..) | cat_local(..) | cat_upvar(..) | cat_deref(_, _, UnsafePtr(..)) => { // yes, it's aliasable, but... None } cat_static_item(..) => { let int_safe = if ty::type_interior_is_unsafe(ctxt, self.ty) { InteriorUnsafe } else { InteriorSafe }; if self.mutbl.is_mutable() { Some(AliasableStaticMut(int_safe)) } else { Some(AliasableStatic(int_safe)) } } cat_deref(ref base, _, BorrowedPtr(ty::ImmBorrow, _)) | cat_deref(ref base, _, Implicit(ty::ImmBorrow, _)) => { match base.cat { cat_upvar(Upvar{ id, .. }) => Some(AliasableClosure(id.closure_expr_id)), _ => Some(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 { cat_deref(ref inner, _, _) => { match inner.cat { cat_deref(ref inner, _, _) => inner.clone(), cat_upvar(..) => inner.clone(), _ => unreachable!() } } _ => unreachable!() }) } NoteNone => None } } } impl<'tcx> Repr<'tcx> for cmt_<'tcx> { fn repr(&self, tcx: &ty::ctxt<'tcx>) -> String { format!("{{{} id:{} m:{} ty:{}}}", self.cat.repr(tcx), self.id, self.mutbl, self.ty.repr(tcx)) } } impl<'tcx> Repr<'tcx> for categorization<'tcx> { fn repr(&self, tcx: &ty::ctxt<'tcx>) -> String { match *self { cat_static_item | cat_rvalue(..) | cat_local(..) | cat_upvar(..) => { format!("{}", *self) } cat_deref(ref cmt, derefs, ptr) => { format!("{}-{}{}->", cmt.cat.repr(tcx), ptr_sigil(ptr), derefs) } cat_interior(ref cmt, interior) => { format!("{}.{}", cmt.cat.repr(tcx), interior.repr(tcx)) } cat_downcast(ref cmt, _) => { format!("{}->(enum)", cmt.cat.repr(tcx)) } } } } pub fn ptr_sigil(ptr: PointerKind) -> &'static str { match ptr { OwnedPtr => "Box", BorrowedPtr(ty::ImmBorrow, _) | Implicit(ty::ImmBorrow, _) => "&", BorrowedPtr(ty::MutBorrow, _) | Implicit(ty::MutBorrow, _) => "&mut", BorrowedPtr(ty::UniqueImmBorrow, _) | Implicit(ty::UniqueImmBorrow, _) => "&unique", UnsafePtr(_) => "*" } } impl<'tcx> Repr<'tcx> for InteriorKind { fn repr(&self, _tcx: &ty::ctxt) -> String { match *self { InteriorField(NamedField(fld)) => { token::get_name(fld).get().to_string() } InteriorField(PositionalField(i)) => format!("#{}", i), InteriorElement(_) => "[]".to_string(), } } } fn element_kind(t: Ty) -> ElementKind { match t.sty { ty::ty_rptr(_, ty::mt{ty, ..}) | ty::ty_uniq(ty) => match ty.sty { ty::ty_vec(_, None) => VecElement, _ => OtherElement }, ty::ty_vec(..) => VecElement, _ => OtherElement } }