compiler/rustc_middle/src/ty/closure.rs - toolchain/rustc - Git at Google

 use crate::hir::place::{
     Place as HirPlace, PlaceBase as HirPlaceBase, ProjectionKind as HirProjectionKind,
 };
 use crate::ty;

 use rustc_data_structures::fx::{FxHashMap, FxIndexMap};
 use rustc_hir as hir;
 use rustc_hir::def_id::{DefId, LocalDefId};
 use rustc_span::Span;

 use super::{Ty, TyCtxt};

 use self::BorrowKind::*;

 #[derive(
     Clone,
     Copy,
     Debug,
     PartialEq,
     Eq,
     Hash,
     TyEncodable,
     TyDecodable,
     TypeFoldable,
     HashStable
 )]
 pub struct UpvarPath {
     pub hir_id: hir::HirId,
 }

 /// Upvars do not get their own `NodeId`. Instead, we use the pair of
 /// the original var ID (that is, the root variable that is referenced
 /// by the upvar) and the ID of the closure expression.
 #[derive(Clone, Copy, PartialEq, Eq, Hash, TyEncodable, TyDecodable, TypeFoldable, HashStable)]
 pub struct UpvarId {
     pub var_path: UpvarPath,
     pub closure_expr_id: LocalDefId,
 }

 impl UpvarId {
     pub fn new(var_hir_id: hir::HirId, closure_def_id: LocalDefId) -> UpvarId {
         UpvarId { var_path: UpvarPath { hir_id: var_hir_id }, closure_expr_id: closure_def_id }
     }
 }

 /// Information describing the capture of an upvar. This is computed
 /// during `typeck`, specifically by `regionck`.
 #[derive(PartialEq, Clone, Debug, Copy, TyEncodable, TyDecodable, TypeFoldable, HashStable)]
 pub enum UpvarCapture<'tcx> {
     /// Upvar is captured by value. This is always true when the
     /// closure is labeled `move`, but can also be true in other cases
     /// depending on inference.
     ///
     /// If the upvar was inferred to be captured by value (e.g. `move`
     /// was not used), then the `Span` points to a usage that
     /// required it. There may be more than one such usage
     /// (e.g. `|| { a; a; }`), in which case we pick an
     /// arbitrary one.
     ByValue(Option<Span>),

     /// Upvar is captured by reference.
     ByRef(UpvarBorrow<'tcx>),
 }

 #[derive(PartialEq, Clone, Copy, TyEncodable, TyDecodable, TypeFoldable, HashStable)]
 pub struct UpvarBorrow<'tcx> {
     /// The kind of borrow: by-ref upvars have access to shared
     /// immutable borrows, which are not part of the normal language
     /// syntax.
     pub kind: BorrowKind,

     /// Region of the resulting reference.
     pub region: ty::Region<'tcx>,
 }

 pub type UpvarListMap = FxHashMap<DefId, FxIndexMap<hir::HirId, UpvarId>>;
 pub type UpvarCaptureMap<'tcx> = FxHashMap<UpvarId, UpvarCapture<'tcx>>;

 /// Given the closure DefId this map provides a map of root variables to minimum
 /// set of `CapturedPlace`s that need to be tracked to support all captures of that closure.
 pub type MinCaptureInformationMap<'tcx> = FxHashMap<DefId, RootVariableMinCaptureList<'tcx>>;

 /// Part of `MinCaptureInformationMap`; Maps a root variable to the list of `CapturedPlace`.
 /// Used to track the minimum set of `Place`s that need to be captured to support all
 /// Places captured by the closure starting at a given root variable.
 ///
 /// This provides a convenient and quick way of checking if a variable being used within
 /// a closure is a capture of a local variable.
 pub type RootVariableMinCaptureList<'tcx> = FxIndexMap<hir::HirId, MinCaptureList<'tcx>>;

 /// Part of `MinCaptureInformationMap`; List of `CapturePlace`s.
 pub type MinCaptureList<'tcx> = Vec<CapturedPlace<'tcx>>;

 /// Represents the various closure traits in the language. This
 /// will determine the type of the environment (`self`, in the
 /// desugaring) argument that the closure expects.
 ///
 /// You can get the environment type of a closure using
 /// `tcx.closure_env_ty()`.
 #[derive(Clone, Copy, PartialOrd, Ord, PartialEq, Eq, Hash, Debug, TyEncodable, TyDecodable)]
 #[derive(HashStable)]
 pub enum ClosureKind {
     // Warning: Ordering is significant here! The ordering is chosen
     // because the trait Fn is a subtrait of FnMut and so in turn, and
     // hence we order it so that Fn < FnMut < FnOnce.
     Fn,
     FnMut,
     FnOnce,
 }

 impl<'tcx> ClosureKind {
     // This is the initial value used when doing upvar inference.
     pub const LATTICE_BOTTOM: ClosureKind = ClosureKind::Fn;

     /// Returns `true` if a type that impls this closure kind
     /// must also implement `other`.
     pub fn extends(self, other: ty::ClosureKind) -> bool {
         matches!(
             (self, other),
             (ClosureKind::Fn, ClosureKind::Fn)
                 | (ClosureKind::Fn, ClosureKind::FnMut)
                 | (ClosureKind::Fn, ClosureKind::FnOnce)
                 | (ClosureKind::FnMut, ClosureKind::FnMut)
                 | (ClosureKind::FnMut, ClosureKind::FnOnce)
                 | (ClosureKind::FnOnce, ClosureKind::FnOnce)
         )
     }

     /// Returns the representative scalar type for this closure kind.
     /// See `TyS::to_opt_closure_kind` for more details.
     pub fn to_ty(self, tcx: TyCtxt<'tcx>) -> Ty<'tcx> {
         match self {
             ty::ClosureKind::Fn => tcx.types.i8,
             ty::ClosureKind::FnMut => tcx.types.i16,
             ty::ClosureKind::FnOnce => tcx.types.i32,
         }
     }
 }

 /// A composite describing a `Place` that is captured by a closure.
 #[derive(PartialEq, Clone, Debug, TyEncodable, TyDecodable, TypeFoldable, HashStable)]
 pub struct CapturedPlace<'tcx> {
     /// The `Place` that is captured.
     pub place: HirPlace<'tcx>,

     /// `CaptureKind` and expression(s) that resulted in such capture of `place`.
     pub info: CaptureInfo<'tcx>,

     /// Represents if `place` can be mutated or not.
     pub mutability: hir::Mutability,
 }

 impl CapturedPlace<'tcx> {
     /// Returns the hir-id of the root variable for the captured place.
     /// e.g., if `a.b.c` was captured, would return the hir-id for `a`.
     pub fn get_root_variable(&self) -> hir::HirId {
         match self.place.base {
             HirPlaceBase::Upvar(upvar_id) => upvar_id.var_path.hir_id,
             base => bug!("Expected upvar, found={:?}", base),
         }
     }

     /// Returns the `LocalDefId` of the closure that captured this Place
     pub fn get_closure_local_def_id(&self) -> LocalDefId {
         match self.place.base {
             HirPlaceBase::Upvar(upvar_id) => upvar_id.closure_expr_id,
             base => bug!("expected upvar, found={:?}", base),
         }
     }

     /// Return span pointing to use that resulted in selecting the current capture kind
     pub fn get_capture_kind_span(&self, tcx: TyCtxt<'tcx>) -> Span {
         if let Some(capture_kind_expr_id) = self.info.capture_kind_expr_id {
             tcx.hir().span(capture_kind_expr_id)
         } else if let Some(path_expr_id) = self.info.path_expr_id {
             tcx.hir().span(path_expr_id)
         } else {
             // Fallback on upvars mentioned if neither path or capture expr id is captured

             // Safe to unwrap since we know this place is captured by the closure, therefore the closure must have upvars.
             tcx.upvars_mentioned(self.get_closure_local_def_id()).unwrap()
                 [&self.get_root_variable()]
                 .span
         }
     }
 }

 /// Return true if the `proj_possible_ancestor` represents an ancestor path
 /// to `proj_capture` or `proj_possible_ancestor` is same as `proj_capture`,
 /// assuming they both start off of the same root variable.
 ///
 /// **Note:** It's the caller's responsibility to ensure that both lists of projections
 ///           start off of the same root variable.
 ///
 /// Eg: 1. `foo.x` which is represented using `projections=[Field(x)]` is an ancestor of
 ///        `foo.x.y` which is represented using `projections=[Field(x), Field(y)]`.
 ///        Note both `foo.x` and `foo.x.y` start off of the same root variable `foo`.
 ///     2. Since we only look at the projections here function will return `bar.x` as an a valid
 ///        ancestor of `foo.x.y`. It's the caller's responsibility to ensure that both projections
 ///        list are being applied to the same root variable.
 pub fn is_ancestor_or_same_capture(
     proj_possible_ancestor: &[HirProjectionKind],
     proj_capture: &[HirProjectionKind],
 ) -> bool {
     // We want to make sure `is_ancestor_or_same_capture("x.0.0", "x.0")` to return false.
     // Therefore we can't just check if all projections are same in the zipped iterator below.
     if proj_possible_ancestor.len() > proj_capture.len() {
         return false;
     }

     proj_possible_ancestor.iter().zip(proj_capture).all(|(a, b)| a == b)
 }

 /// Part of `MinCaptureInformationMap`; describes the capture kind (&, &mut, move)
 /// for a particular capture as well as identifying the part of the source code
 /// that triggered this capture to occur.
 #[derive(PartialEq, Clone, Debug, Copy, TyEncodable, TyDecodable, TypeFoldable, HashStable)]
 pub struct CaptureInfo<'tcx> {
     /// Expr Id pointing to use that resulted in selecting the current capture kind
     ///
     /// Eg:
     /// ```rust,no_run
     /// let mut t = (0,1);
     ///
     /// let c = || {
     ///     println!("{}",t); // L1
     ///     t.1 = 4; // L2
     /// };
     /// ```
     /// `capture_kind_expr_id` will point to the use on L2 and `path_expr_id` will point to the
     /// use on L1.
     ///
     /// If the user doesn't enable feature `capture_disjoint_fields` (RFC 2229) then, it is
     /// possible that we don't see the use of a particular place resulting in capture_kind_expr_id being
     /// None. In such case we fallback on uvpars_mentioned for span.
     ///
     /// Eg:
     /// ```rust,no_run
     /// let x = 5;
     ///
     /// let c = || {
     ///     let _ = x
     /// };
     /// ```
     ///
     /// In this example, if `capture_disjoint_fields` is **not** set, then x will be captured,
     /// but we won't see it being used during capture analysis, since it's essentially a discard.
     pub capture_kind_expr_id: Option<hir::HirId>,
     /// Expr Id pointing to use that resulted the corresponding place being captured
     ///
     /// See `capture_kind_expr_id` for example.
     ///
     pub path_expr_id: Option<hir::HirId>,

     /// Capture mode that was selected
     pub capture_kind: UpvarCapture<'tcx>,
 }

 pub fn place_to_string_for_capture(tcx: TyCtxt<'tcx>, place: &HirPlace<'tcx>) -> String {
     let name = match place.base {
         HirPlaceBase::Upvar(upvar_id) => tcx.hir().name(upvar_id.var_path.hir_id).to_string(),
         _ => bug!("Capture_information should only contain upvars"),
     };
     let mut curr_string = name;

     for (i, proj) in place.projections.iter().enumerate() {
         match proj.kind {
             HirProjectionKind::Deref => {
                 curr_string = format!("*{}", curr_string);
             }
             HirProjectionKind::Field(idx, variant) => match place.ty_before_projection(i).kind() {
                 ty::Adt(def, ..) => {
                     curr_string = format!(
                         "{}.{}",
                         curr_string,
                         def.variants[variant].fields[idx as usize].ident.name.as_str()
                     );
                 }
                 ty::Tuple(_) => {
                     curr_string = format!("{}.{}", curr_string, idx);
                 }
                 _ => {
                     bug!(
                         "Field projection applied to a type other than Adt or Tuple: {:?}.",
                         place.ty_before_projection(i).kind()
                     )
                 }
             },
             proj => bug!("{:?} unexpected because it isn't captured", proj),
         }
     }

     curr_string.to_string()
 }

 #[derive(Clone, PartialEq, Debug, TyEncodable, TyDecodable, TypeFoldable, Copy, HashStable)]
 pub enum BorrowKind {
     /// Data must be immutable and is aliasable.
     ImmBorrow,

     /// Data must be immutable but not aliasable. This kind of borrow
     /// cannot currently be expressed by the user and is used only in
     /// implicit closure bindings. It is needed when the closure
     /// is borrowing or mutating a mutable referent, e.g.:
     ///
     /// ```
     /// let x: &mut isize = ...;
     /// let y = || *x += 5;
     /// ```
     ///
     /// If we were to try to translate this closure into a more explicit
     /// form, we'd encounter an error with the code as written:
     ///
     /// ```
     /// struct Env { x: & &mut isize }
     /// let x: &mut isize = ...;
     /// let y = (&mut Env { &x }, fn_ptr);  // Closure is pair of env and fn
     /// fn fn_ptr(env: &mut Env) { **env.x += 5; }
     /// ```
     ///
     /// This is then illegal because you cannot mutate a `&mut` found
     /// in an aliasable location. To solve, you'd have to translate with
     /// an `&mut` borrow:
     ///
     /// ```
     /// struct Env { x: & &mut isize }
     /// let x: &mut isize = ...;
     /// let y = (&mut Env { &mut x }, fn_ptr); // changed from &x to &mut x
     /// fn fn_ptr(env: &mut Env) { **env.x += 5; }
     /// ```
     ///
     /// Now the assignment to `**env.x` is legal, but creating a
     /// mutable pointer to `x` is not because `x` is not mutable. We
     /// could fix this by declaring `x` as `let mut x`. This is ok in
     /// user code, if awkward, but extra weird for closures, since the
     /// borrow is hidden.
     ///
     /// So we introduce a "unique imm" borrow -- the referent is
     /// immutable, but not aliasable. This solves the problem. For
     /// simplicity, we don't give users the way to express this
     /// borrow, it's just used when translating closures.
     UniqueImmBorrow,

     /// Data is mutable and not aliasable.
     MutBorrow,
 }

 impl BorrowKind {
     pub fn from_mutbl(m: hir::Mutability) -> BorrowKind {
         match m {
             hir::Mutability::Mut => MutBorrow,
             hir::Mutability::Not => ImmBorrow,
         }
     }

     /// Returns a mutability `m` such that an `&m T` pointer could be used to obtain this borrow
     /// kind. Because borrow kinds are richer than mutabilities, we sometimes have to pick a
     /// mutability that is stronger than necessary so that it at least *would permit* the borrow in
     /// question.
     pub fn to_mutbl_lossy(self) -> hir::Mutability {
         match self {
             MutBorrow => hir::Mutability::Mut,
             ImmBorrow => hir::Mutability::Not,

             // We have no type corresponding to a unique imm borrow, so
             // use `&mut`. It gives all the capabilities of an `&uniq`
             // and hence is a safe "over approximation".
             UniqueImmBorrow => hir::Mutability::Mut,
         }
     }
 }
	use crate::hir::place::{
	Place as HirPlace, PlaceBase as HirPlaceBase, ProjectionKind as HirProjectionKind,
	};
	use crate::ty;

	use rustc_data_structures::fx::{FxHashMap, FxIndexMap};
	use rustc_hir as hir;
	use rustc_hir::def_id::{DefId, LocalDefId};
	use rustc_span::Span;

	use super::{Ty, TyCtxt};

	use self::BorrowKind::*;

	#[derive(
	Clone,
	Copy,
	Debug,
	PartialEq,
	Eq,
	Hash,
	TyEncodable,
	TyDecodable,
	TypeFoldable,
	HashStable
	)]
	pub struct UpvarPath {
	pub hir_id: hir::HirId,
	}

	/// Upvars do not get their own `NodeId`. Instead, we use the pair of
	/// the original var ID (that is, the root variable that is referenced
	/// by the upvar) and the ID of the closure expression.
	#[derive(Clone, Copy, PartialEq, Eq, Hash, TyEncodable, TyDecodable, TypeFoldable, HashStable)]
	pub struct UpvarId {
	pub var_path: UpvarPath,
	pub closure_expr_id: LocalDefId,
	}

	impl UpvarId {
	pub fn new(var_hir_id: hir::HirId, closure_def_id: LocalDefId) -> UpvarId {
	UpvarId { var_path: UpvarPath { hir_id: var_hir_id }, closure_expr_id: closure_def_id }
	}
	}

	/// Information describing the capture of an upvar. This is computed
	/// during `typeck`, specifically by `regionck`.
	#[derive(PartialEq, Clone, Debug, Copy, TyEncodable, TyDecodable, TypeFoldable, HashStable)]
	pub enum UpvarCapture<'tcx> {
	/// Upvar is captured by value. This is always true when the
	/// closure is labeled `move`, but can also be true in other cases
	/// depending on inference.
	///
	/// If the upvar was inferred to be captured by value (e.g. `move`
	/// was not used), then the `Span` points to a usage that
	/// required it. There may be more than one such usage
	/// (e.g. `\|\| { a; a; }`), in which case we pick an
	/// arbitrary one.
	ByValue(Option<Span>),

	/// Upvar is captured by reference.
	ByRef(UpvarBorrow<'tcx>),
	}

	#[derive(PartialEq, Clone, Copy, TyEncodable, TyDecodable, TypeFoldable, HashStable)]
	pub struct UpvarBorrow<'tcx> {
	/// The kind of borrow: by-ref upvars have access to shared
	/// immutable borrows, which are not part of the normal language
	/// syntax.
	pub kind: BorrowKind,

	/// Region of the resulting reference.
	pub region: ty::Region<'tcx>,
	}

	pub type UpvarListMap = FxHashMap<DefId, FxIndexMap<hir::HirId, UpvarId>>;
	pub type UpvarCaptureMap<'tcx> = FxHashMap<UpvarId, UpvarCapture<'tcx>>;

	/// Given the closure DefId this map provides a map of root variables to minimum
	/// set of `CapturedPlace`s that need to be tracked to support all captures of that closure.
	pub type MinCaptureInformationMap<'tcx> = FxHashMap<DefId, RootVariableMinCaptureList<'tcx>>;

	/// Part of `MinCaptureInformationMap`; Maps a root variable to the list of `CapturedPlace`.
	/// Used to track the minimum set of `Place`s that need to be captured to support all
	/// Places captured by the closure starting at a given root variable.
	///
	/// This provides a convenient and quick way of checking if a variable being used within
	/// a closure is a capture of a local variable.
	pub type RootVariableMinCaptureList<'tcx> = FxIndexMap<hir::HirId, MinCaptureList<'tcx>>;

	/// Part of `MinCaptureInformationMap`; List of `CapturePlace`s.
	pub type MinCaptureList<'tcx> = Vec<CapturedPlace<'tcx>>;

	/// Represents the various closure traits in the language. This
	/// will determine the type of the environment (`self`, in the
	/// desugaring) argument that the closure expects.
	///
	/// You can get the environment type of a closure using
	/// `tcx.closure_env_ty()`.
	#[derive(Clone, Copy, PartialOrd, Ord, PartialEq, Eq, Hash, Debug, TyEncodable, TyDecodable)]
	#[derive(HashStable)]
	pub enum ClosureKind {
	// Warning: Ordering is significant here! The ordering is chosen
	// because the trait Fn is a subtrait of FnMut and so in turn, and
	// hence we order it so that Fn < FnMut < FnOnce.
	Fn,
	FnMut,
	FnOnce,
	}

	impl<'tcx> ClosureKind {
	// This is the initial value used when doing upvar inference.
	pub const LATTICE_BOTTOM: ClosureKind = ClosureKind::Fn;

	/// Returns `true` if a type that impls this closure kind
	/// must also implement `other`.
	pub fn extends(self, other: ty::ClosureKind) -> bool {
	matches!(
	(self, other),
	(ClosureKind::Fn, ClosureKind::Fn)
	\| (ClosureKind::Fn, ClosureKind::FnMut)
	\| (ClosureKind::Fn, ClosureKind::FnOnce)
	\| (ClosureKind::FnMut, ClosureKind::FnMut)
	\| (ClosureKind::FnMut, ClosureKind::FnOnce)
	\| (ClosureKind::FnOnce, ClosureKind::FnOnce)
	)
	}

	/// Returns the representative scalar type for this closure kind.
	/// See `TyS::to_opt_closure_kind` for more details.
	pub fn to_ty(self, tcx: TyCtxt<'tcx>) -> Ty<'tcx> {
	match self {
	ty::ClosureKind::Fn => tcx.types.i8,
	ty::ClosureKind::FnMut => tcx.types.i16,
	ty::ClosureKind::FnOnce => tcx.types.i32,
	}
	}
	}

	/// A composite describing a `Place` that is captured by a closure.
	#[derive(PartialEq, Clone, Debug, TyEncodable, TyDecodable, TypeFoldable, HashStable)]
	pub struct CapturedPlace<'tcx> {
	/// The `Place` that is captured.
	pub place: HirPlace<'tcx>,

	/// `CaptureKind` and expression(s) that resulted in such capture of `place`.
	pub info: CaptureInfo<'tcx>,

	/// Represents if `place` can be mutated or not.
	pub mutability: hir::Mutability,
	}

	impl CapturedPlace<'tcx> {
	/// Returns the hir-id of the root variable for the captured place.
	/// e.g., if `a.b.c` was captured, would return the hir-id for `a`.
	pub fn get_root_variable(&self) -> hir::HirId {
	match self.place.base {
	HirPlaceBase::Upvar(upvar_id) => upvar_id.var_path.hir_id,
	base => bug!("Expected upvar, found={:?}", base),
	}
	}

	/// Returns the `LocalDefId` of the closure that captured this Place
	pub fn get_closure_local_def_id(&self) -> LocalDefId {
	match self.place.base {
	HirPlaceBase::Upvar(upvar_id) => upvar_id.closure_expr_id,
	base => bug!("expected upvar, found={:?}", base),
	}
	}

	/// Return span pointing to use that resulted in selecting the current capture kind
	pub fn get_capture_kind_span(&self, tcx: TyCtxt<'tcx>) -> Span {
	if let Some(capture_kind_expr_id) = self.info.capture_kind_expr_id {
	tcx.hir().span(capture_kind_expr_id)
	} else if let Some(path_expr_id) = self.info.path_expr_id {
	tcx.hir().span(path_expr_id)
	} else {
	// Fallback on upvars mentioned if neither path or capture expr id is captured

	// Safe to unwrap since we know this place is captured by the closure, therefore the closure must have upvars.
	tcx.upvars_mentioned(self.get_closure_local_def_id()).unwrap()
	[&self.get_root_variable()]
	.span
	}
	}
	}

	/// Return true if the `proj_possible_ancestor` represents an ancestor path
	/// to `proj_capture` or `proj_possible_ancestor` is same as `proj_capture`,
	/// assuming they both start off of the same root variable.
	///
	/// Note: It's the caller's responsibility to ensure that both lists of projections
	/// start off of the same root variable.
	///
	/// Eg: 1. `foo.x` which is represented using `projections=[Field(x)]` is an ancestor of
	/// `foo.x.y` which is represented using `projections=[Field(x), Field(y)]`.
	/// Note both `foo.x` and `foo.x.y` start off of the same root variable `foo`.
	/// 2. Since we only look at the projections here function will return `bar.x` as an a valid
	/// ancestor of `foo.x.y`. It's the caller's responsibility to ensure that both projections
	/// list are being applied to the same root variable.
	pub fn is_ancestor_or_same_capture(
	proj_possible_ancestor: &[HirProjectionKind],
	proj_capture: &[HirProjectionKind],
	) -> bool {
	// We want to make sure `is_ancestor_or_same_capture("x.0.0", "x.0")` to return false.
	// Therefore we can't just check if all projections are same in the zipped iterator below.
	if proj_possible_ancestor.len() > proj_capture.len() {
	return false;
	}

	proj_possible_ancestor.iter().zip(proj_capture).all(\|(a, b)\| a == b)
	}

	/// Part of `MinCaptureInformationMap`; describes the capture kind (&, &mut, move)
	/// for a particular capture as well as identifying the part of the source code
	/// that triggered this capture to occur.
	#[derive(PartialEq, Clone, Debug, Copy, TyEncodable, TyDecodable, TypeFoldable, HashStable)]
	pub struct CaptureInfo<'tcx> {
	/// Expr Id pointing to use that resulted in selecting the current capture kind
	///
	/// Eg:
	/// ```rust,no_run
	/// let mut t = (0,1);
	///
	/// let c = \|\| {
	/// println!("{}",t); // L1
	/// t.1 = 4; // L2
	/// };
	/// ```
	/// `capture_kind_expr_id` will point to the use on L2 and `path_expr_id` will point to the
	/// use on L1.
	///
	/// If the user doesn't enable feature `capture_disjoint_fields` (RFC 2229) then, it is
	/// possible that we don't see the use of a particular place resulting in capture_kind_expr_id being
	/// None. In such case we fallback on uvpars_mentioned for span.
	///
	/// Eg:
	/// ```rust,no_run
	/// let x = 5;
	///
	/// let c = \|\| {
	/// let _ = x
	/// };
	/// ```
	///
	/// In this example, if `capture_disjoint_fields` is not set, then x will be captured,
	/// but we won't see it being used during capture analysis, since it's essentially a discard.
	pub capture_kind_expr_id: Option<hir::HirId>,
	/// Expr Id pointing to use that resulted the corresponding place being captured
	///
	/// See `capture_kind_expr_id` for example.
	///
	pub path_expr_id: Option<hir::HirId>,

	/// Capture mode that was selected
	pub capture_kind: UpvarCapture<'tcx>,
	}

	pub fn place_to_string_for_capture(tcx: TyCtxt<'tcx>, place: &HirPlace<'tcx>) -> String {
	let name = match place.base {
	HirPlaceBase::Upvar(upvar_id) => tcx.hir().name(upvar_id.var_path.hir_id).to_string(),
	_ => bug!("Capture_information should only contain upvars"),
	};
	let mut curr_string = name;

	for (i, proj) in place.projections.iter().enumerate() {
	match proj.kind {
	HirProjectionKind::Deref => {
	curr_string = format!("*{}", curr_string);
	}
	HirProjectionKind::Field(idx, variant) => match place.ty_before_projection(i).kind() {
	ty::Adt(def, ..) => {
	curr_string = format!(
	"{}.{}",
	curr_string,
	def.variants[variant].fields[idx as usize].ident.name.as_str()
	);
	}
	ty::Tuple(_) => {
	curr_string = format!("{}.{}", curr_string, idx);
	}
	_ => {
	bug!(
	"Field projection applied to a type other than Adt or Tuple: {:?}.",
	place.ty_before_projection(i).kind()
	)
	}
	},
	proj => bug!("{:?} unexpected because it isn't captured", proj),
	}
	}

	curr_string.to_string()
	}

	#[derive(Clone, PartialEq, Debug, TyEncodable, TyDecodable, TypeFoldable, Copy, HashStable)]
	pub enum BorrowKind {
	/// Data must be immutable and is aliasable.
	ImmBorrow,

	/// Data must be immutable but not aliasable. This kind of borrow
	/// cannot currently be expressed by the user and is used only in
	/// implicit closure bindings. It is needed when the closure
	/// is borrowing or mutating a mutable referent, e.g.:
	///
	/// ```
	/// let x: &mut isize = ...;
	/// let y = \|\| *x += 5;
	/// ```
	///
	/// If we were to try to translate this closure into a more explicit
	/// form, we'd encounter an error with the code as written:
	///
	/// ```
	/// struct Env { x: & &mut isize }
	/// let x: &mut isize = ...;
	/// let y = (&mut Env { &x }, fn_ptr); // Closure is pair of env and fn
	/// fn fn_ptr(env: &mut Env) { **env.x += 5; }
	/// ```
	///
	/// This is then illegal because you cannot mutate a `&mut` found
	/// in an aliasable location. To solve, you'd have to translate with
	/// an `&mut` borrow:
	///
	/// ```
	/// struct Env { x: & &mut isize }
	/// let x: &mut isize = ...;
	/// let y = (&mut Env { &mut x }, fn_ptr); // changed from &x to &mut x
	/// fn fn_ptr(env: &mut Env) { **env.x += 5; }
	/// ```
	///
	/// Now the assignment to `**env.x` is legal, but creating a
	/// mutable pointer to `x` is not because `x` is not mutable. We
	/// could fix this by declaring `x` as `let mut x`. This is ok in
	/// user code, if awkward, but extra weird for closures, since the
	/// borrow is hidden.
	///
	/// So we introduce a "unique imm" borrow -- the referent is
	/// immutable, but not aliasable. This solves the problem. For
	/// simplicity, we don't give users the way to express this
	/// borrow, it's just used when translating closures.
	UniqueImmBorrow,

	/// Data is mutable and not aliasable.
	MutBorrow,
	}

	impl BorrowKind {
	pub fn from_mutbl(m: hir::Mutability) -> BorrowKind {
	match m {
	hir::Mutability::Mut => MutBorrow,
	hir::Mutability::Not => ImmBorrow,
	}
	}

	/// Returns a mutability `m` such that an `&m T` pointer could be used to obtain this borrow
	/// kind. Because borrow kinds are richer than mutabilities, we sometimes have to pick a
	/// mutability that is stronger than necessary so that it at least would permit the borrow in
	/// question.
	pub fn to_mutbl_lossy(self) -> hir::Mutability {
	match self {
	MutBorrow => hir::Mutability::Mut,
	ImmBorrow => hir::Mutability::Not,

	// We have no type corresponding to a unique imm borrow, so
	// use `&mut`. It gives all the capabilities of an `&uniq`
	// and hence is a safe "over approximation".
	UniqueImmBorrow => hir::Mutability::Mut,
	}
	}
	}