path: root/src/InterpreterBorrowsCore.ml

(* This file defines the basic blocks to implement the semantics of borrows.
 * Note that those functions are not only used in InterpreterBorrows, but
 * also in Invariants or InterpreterProjectors *)

module T = Types
module V = Values
module C = Contexts
module Subst = Substitute
module L = Logging
open TypesUtils
open InterpreterUtils

(** The local logger *)
let log = L.borrows_log

(** TODO: cleanup this a bit, once we have a better understanding about
    what we need.
    TODO: I'm not sure in which file this should be moved... *)
type exploration_kind = {
  enter_shared_loans : bool;
  enter_mut_borrows : bool;
  enter_abs : bool;
      (** Note that if we allow to enter abs, we don't check whether we enter
          mutable/shared loans or borrows: there are no use cases requiring
          a finer control. *)
}
(** This record controls how some generic helper lookup/update
    functions behave, by restraining the kind of therms they can enter.
*)

let ek_all : exploration_kind =
  { enter_shared_loans = true; enter_mut_borrows = true; enter_abs = true }

type borrow_ids = Borrows of V.BorrowId.Set.t | Borrow of V.BorrowId.id
[@@deriving show]

exception FoundBorrowIds of borrow_ids

type priority_borrows_or_abs =
  | OuterBorrows of borrow_ids
  | OuterAbs of V.AbstractionId.id
  | InnerLoans of borrow_ids
[@@deriving show]

let update_if_none opt x = match opt with None -> Some x | _ -> opt

exception FoundPriority of priority_borrows_or_abs
(** Utility exception *)

type loan_or_borrow_content =
  | LoanContent of V.loan_content
  | BorrowContent of V.borrow_content
[@@deriving show]

type borrow_or_abs_id =
  | BorrowId of V.BorrowId.id
  | AbsId of V.AbstractionId.id

type borrow_or_abs_ids = borrow_or_abs_id list

let borrow_or_abs_id_to_string (id : borrow_or_abs_id) : string =
  match id with
  | AbsId id -> "abs@" ^ V.AbstractionId.to_string id
  | BorrowId id -> "l@" ^ V.BorrowId.to_string id

let borrow_or_abs_ids_chain_to_string (ids : borrow_or_abs_ids) : string =
  let ids = List.rev ids in
  let ids = List.map borrow_or_abs_id_to_string ids in
  String.concat " -> " ids

(** Add a borrow or abs id to a chain of ids, while checking that we don't loop *)
let add_borrow_or_abs_id_to_chain (msg : string) (id : borrow_or_abs_id)
    (ids : borrow_or_abs_ids) : borrow_or_abs_ids =
  if List.mem id ids then
    failwith
      (msg ^ "detected a loop in the chain of ids: "
      ^ borrow_or_abs_ids_chain_to_string (id :: ids))
  else id :: ids

(** Check if two different projections intersect. This is necessary when
    giving a symbolic value to an abstraction: we need to check that
    the regions which are already ended inside the abstraction don't
    intersect the regions over which we project in the new abstraction.
    Note that the two abstractions have different views (in terms of regions)
    of the symbolic value (hence the two region types).
*)
let rec projections_intersect (ty1 : T.rty) (rset1 : T.RegionId.Set.t)
    (ty2 : T.rty) (rset2 : T.RegionId.Set.t) : bool =
  match (ty1, ty2) with
  | T.Bool, T.Bool | T.Char, T.Char | T.Str, T.Str -> false
  | T.Integer int_ty1, T.Integer int_ty2 ->
      assert (int_ty1 = int_ty2);
      false
  | T.Adt (id1, regions1, tys1), T.Adt (id2, regions2, tys2) ->
      assert (id1 = id2);
      (* The intersection check for the ADTs is very crude: 
       * we check if some arguments intersect. As all the type and region
       * parameters should be used somewhere in the ADT (otherwise rustc
       * generates an error), it means that it should be equivalent to checking
       * whether two fields intersect (and anyway comparing the field types is
       * difficult in case of enumerations...).
       * If we didn't have the above property enforced by the rust compiler,
       * this check would still be a reasonable conservative approximation. *)
      let regions = List.combine regions1 regions2 in
      let tys = List.combine tys1 tys2 in
      List.exists
        (fun (r1, r2) -> region_in_set r1 rset1 && region_in_set r2 rset2)
        regions
      || List.exists
           (fun (ty1, ty2) -> projections_intersect ty1 rset1 ty2 rset2)
           tys
  | T.Array ty1, T.Array ty2 | T.Slice ty1, T.Slice ty2 ->
      projections_intersect ty1 rset1 ty2 rset2
  | T.Ref (r1, ty1, kind1), T.Ref (r2, ty2, kind2) ->
      (* Sanity check *)
      assert (kind1 = kind2);
      (* The projections intersect if the borrows intersect or their contents
       * intersect *)
      (region_in_set r1 rset1 && region_in_set r2 rset2)
      || projections_intersect ty1 rset1 ty2 rset2
  | T.TypeVar id1, T.TypeVar id2 ->
      assert (id1 = id2);
      false
  | _ ->
      log#lerror
        (lazy
          ("projections_intersect: unexpected inputs:" ^ "\n- ty1: "
         ^ T.show_rty ty1 ^ "\n- ty2: " ^ T.show_rty ty2));
      failwith "Unreachable"

(** Lookup a loan content.

    The loan is referred to by a borrow id.

    TODO: group abs_or_var_id and g_loan_content. 
 *)
let lookup_loan_opt (ek : exploration_kind) (l : V.BorrowId.id)
    (ctx : C.eval_ctx) : (abs_or_var_id * g_loan_content) option =
  (* We store here whether we are inside an abstraction or a value - note that we
   * could also track that with the environment, it would probably be more idiomatic
   * and cleaner *)
  let abs_or_var : abs_or_var_id option ref = ref None in

  let obj =
    object
      inherit [_] C.iter_eval_ctx as super

      method! visit_borrow_content env bc =
        match bc with
        | V.SharedBorrow bid ->
            (* Nothing specific to do *)
            super#visit_SharedBorrow env bid
        | V.InactivatedMutBorrow bid ->
            (* Nothing specific to do *)
            super#visit_InactivatedMutBorrow env bid
        | V.MutBorrow (bid, mv) ->
            (* Control the dive *)
            if ek.enter_mut_borrows then super#visit_MutBorrow env bid mv
            else ()

      method! visit_loan_content env lc =
        match lc with
        | V.SharedLoan (bids, sv) ->
            (* Check if this is the loan we are looking for, and control the dive *)
            if V.BorrowId.Set.mem l bids then
              raise (FoundGLoanContent (Concrete lc))
            else if ek.enter_shared_loans then
              super#visit_SharedLoan env bids sv
            else ()
        | V.MutLoan bid ->
            (* Check if this is the loan we are looking for *)
            if bid = l then raise (FoundGLoanContent (Concrete lc))
            else super#visit_MutLoan env bid
      (** We reimplement [visit_Loan] (rather than the more precise functions
          [visit_SharedLoan], etc.) on purpose: as we have an exhaustive match
          below, we are more resilient to definition updates (the compiler
          is our friend).
      *)

      method! visit_aloan_content env lc =
        match lc with
        | V.AMutLoan (bid, av) ->
            if bid = l then raise (FoundGLoanContent (Abstract lc))
            else super#visit_AMutLoan env bid av
        | V.ASharedLoan (bids, v, av) ->
            if V.BorrowId.Set.mem l bids then
              raise (FoundGLoanContent (Abstract lc))
            else super#visit_ASharedLoan env bids v av
        | V.AEndedMutLoan { given_back = _; child = _; given_back_meta = _ }
        | V.AEndedSharedLoan (_, _)
        | V.AIgnoredMutLoan (_, _)
        | V.AEndedIgnoredMutLoan
            { given_back = _; child = _; given_back_meta = _ }
        | V.AIgnoredSharedLoan _ ->
            super#visit_aloan_content env lc
      (** Note that we don't control diving inside the abstractions: if we
          allow to dive inside abstractions, we allow to go anywhere
          (because there are no use cases requiring finer control) *)

      method! visit_Var env bv v =
        assert (Option.is_none !abs_or_var);
        abs_or_var :=
          Some
            (VarId (match bv with Some bv -> Some bv.C.index | None -> None));
        super#visit_Var env bv v;
        abs_or_var := None

      method! visit_Abs env abs =
        assert (Option.is_none !abs_or_var);
        if ek.enter_abs then (
          abs_or_var := Some (AbsId abs.V.abs_id);
          super#visit_Abs env abs;
          abs_or_var := None)
        else ()
    end
  in
  (* We use exceptions *)
  try
    obj#visit_eval_ctx () ctx;
    None
  with FoundGLoanContent lc -> (
    match !abs_or_var with
    | Some abs_or_var -> Some (abs_or_var, lc)
    | None -> failwith "Inconsistent state")

(** Lookup a loan content.

    The loan is referred to by a borrow id.
    Raises an exception if no loan was found.
 *)
let lookup_loan (ek : exploration_kind) (l : V.BorrowId.id) (ctx : C.eval_ctx) :
    abs_or_var_id * g_loan_content =
  match lookup_loan_opt ek l ctx with
  | None -> failwith "Unreachable"
  | Some res -> res

(** Update a loan content.

    The loan is referred to by a borrow id.

    This is a helper function: it might break invariants.
 *)
let update_loan (ek : exploration_kind) (l : V.BorrowId.id)
    (nlc : V.loan_content) (ctx : C.eval_ctx) : C.eval_ctx =
  (* We use a reference to check that we update exactly one loan: when updating
   * inside values, we check we don't update more than one loan. Then, upon
   * returning we check that we updated at least once. *)
  let r = ref false in
  let update () : V.loan_content =
    assert (not !r);
    r := true;
    nlc
  in

  let obj =
    object
      inherit [_] C.map_eval_ctx as super

      method! visit_borrow_content env bc =
        match bc with
        | V.SharedBorrow _ | V.InactivatedMutBorrow _ ->
            (* Nothing specific to do *)
            super#visit_borrow_content env bc
        | V.MutBorrow (bid, mv) ->
            (* Control the dive into mutable borrows *)
            if ek.enter_mut_borrows then super#visit_MutBorrow env bid mv
            else V.MutBorrow (bid, mv)

      method! visit_loan_content env lc =
        match lc with
        | V.SharedLoan (bids, sv) ->
            (* Shared loan: check if this is the loan we are looking for, and
               control the dive. *)
            if V.BorrowId.Set.mem l bids then update ()
            else if ek.enter_shared_loans then
              super#visit_SharedLoan env bids sv
            else V.SharedLoan (bids, sv)
        | V.MutLoan bid ->
            (* Mut loan: checks if this is the loan we are looking for *)
            if bid = l then update () else super#visit_MutLoan env bid
      (** We reimplement [visit_loan_content] (rather than one of the sub-
          functions) on purpose: exhaustive matches are good for maintenance *)

      method! visit_abs env abs =
        if ek.enter_abs then super#visit_abs env abs else abs
      (** Note that once inside the abstractions, we don't control diving
          (there are no use cases requiring finer control).
          Also, as we give back a [loan_content] (and not an [aloan_content])
          we don't need to do reimplement the visit functions for the values
          inside the abstractions (rk.: there may be "concrete" values inside
          abstractions, so there is a utility in diving inside). *)
    end
  in

  let ctx = obj#visit_eval_ctx () ctx in
  (* Check that we updated at least one loan *)
  assert !r;
  ctx

(** Update a abstraction loan content.

    The loan is referred to by a borrow id.

    This is a helper function: it might break invariants.
 *)
let update_aloan (ek : exploration_kind) (l : V.BorrowId.id)
    (nlc : V.aloan_content) (ctx : C.eval_ctx) : C.eval_ctx =
  (* We use a reference to check that we update exactly one loan: when updating
   * inside values, we check we don't update more than one loan. Then, upon
   * returning we check that we updated at least once. *)
  let r = ref false in
  let update () : V.aloan_content =
    assert (not !r);
    r := true;
    nlc
  in

  let obj =
    object
      inherit [_] C.map_eval_ctx as super

      method! visit_aloan_content env lc =
        match lc with
        | V.AMutLoan (bid, av) ->
            if bid = l then update () else super#visit_AMutLoan env bid av
        | V.ASharedLoan (bids, v, av) ->
            if V.BorrowId.Set.mem l bids then update ()
            else super#visit_ASharedLoan env bids v av
        | V.AEndedMutLoan { given_back = _; child = _; given_back_meta = _ }
        | V.AEndedSharedLoan (_, _)
        | V.AIgnoredMutLoan (_, _)
        | V.AEndedIgnoredMutLoan
            { given_back = _; child = _; given_back_meta = _ }
        | V.AIgnoredSharedLoan _ ->
            super#visit_aloan_content env lc

      method! visit_abs env abs =
        if ek.enter_abs then super#visit_abs env abs else abs
      (** Note that once inside the abstractions, we don't control diving
          (there are no use cases requiring finer control). *)
    end
  in

  let ctx = obj#visit_eval_ctx () ctx in
  (* Check that we updated at least one loan *)
  assert !r;
  ctx

(** Lookup a borrow content from a borrow id. *)
let lookup_borrow_opt (ek : exploration_kind) (l : V.BorrowId.id)
    (ctx : C.eval_ctx) : g_borrow_content option =
  let obj =
    object
      inherit [_] C.iter_eval_ctx as super

      method! visit_borrow_content env bc =
        match bc with
        | V.MutBorrow (bid, mv) ->
            (* Check the borrow id and control the dive *)
            if bid = l then raise (FoundGBorrowContent (Concrete bc))
            else if ek.enter_mut_borrows then super#visit_MutBorrow env bid mv
            else ()
        | V.SharedBorrow bid ->
            (* Check the borrow id *)
            if bid = l then raise (FoundGBorrowContent (Concrete bc)) else ()
        | V.InactivatedMutBorrow bid ->
            (* Check the borrow id *)
            if bid = l then raise (FoundGBorrowContent (Concrete bc)) else ()

      method! visit_loan_content env lc =
        match lc with
        | V.MutLoan bid ->
            (* Nothing special to do *) super#visit_MutLoan env bid
        | V.SharedLoan (bids, sv) ->
            (* Control the dive *)
            if ek.enter_shared_loans then super#visit_SharedLoan env bids sv
            else ()

      method! visit_aborrow_content env bc =
        match bc with
        | V.AMutBorrow (mv, bid, av) ->
            if bid = l then raise (FoundGBorrowContent (Abstract bc))
            else super#visit_AMutBorrow env mv bid av
        | V.ASharedBorrow bid ->
            if bid = l then raise (FoundGBorrowContent (Abstract bc))
            else super#visit_ASharedBorrow env bid
        | V.AIgnoredMutBorrow (_, _)
        | V.AEndedMutBorrow _
        | V.AEndedIgnoredMutBorrow
            { given_back_loans_proj = _; child = _; given_back_meta = _ } ->
            super#visit_aborrow_content env bc
        | V.AProjSharedBorrow asb ->
            if borrow_in_asb l asb then
              raise (FoundGBorrowContent (Abstract bc))
            else ()

      method! visit_abs env abs =
        if ek.enter_abs then super#visit_abs env abs else ()
    end
  in
  (* We use exceptions *)
  try
    obj#visit_eval_ctx () ctx;
    None
  with FoundGBorrowContent lc -> Some lc

(** Lookup a borrow content from a borrow id.

    Raise an exception if no loan was found
*)
let lookup_borrow (ek : exploration_kind) (l : V.BorrowId.id) (ctx : C.eval_ctx)
    : g_borrow_content =
  match lookup_borrow_opt ek l ctx with
  | None -> failwith "Unreachable"
  | Some lc -> lc

(** Update a borrow content.

    The borrow is referred to by a borrow id.

    This is a helper function: it might break invariants.   
 *)
let update_borrow (ek : exploration_kind) (l : V.BorrowId.id)
    (nbc : V.borrow_content) (ctx : C.eval_ctx) : C.eval_ctx =
  (* We use a reference to check that we update exactly one borrow: when updating
   * inside values, we check we don't update more than one borrow. Then, upon
   * returning we check that we updated at least once. *)
  let r = ref false in
  let update () : V.borrow_content =
    assert (not !r);
    r := true;
    nbc
  in

  let obj =
    object
      inherit [_] C.map_eval_ctx as super

      method! visit_borrow_content env bc =
        match bc with
        | V.MutBorrow (bid, mv) ->
            (* Check the id and control dive *)
            if bid = l then update ()
            else if ek.enter_mut_borrows then super#visit_MutBorrow env bid mv
            else V.MutBorrow (bid, mv)
        | V.SharedBorrow bid ->
            (* Check the id *)
            if bid = l then update () else super#visit_SharedBorrow env bid
        | V.InactivatedMutBorrow bid ->
            (* Check the id *)
            if bid = l then update ()
            else super#visit_InactivatedMutBorrow env bid

      method! visit_loan_content env lc =
        match lc with
        | V.SharedLoan (bids, sv) ->
            (* Control the dive *)
            if ek.enter_shared_loans then super#visit_SharedLoan env bids sv
            else V.SharedLoan (bids, sv)
        | V.MutLoan bid ->
            (* Nothing specific to do *)
            super#visit_MutLoan env bid

      method! visit_abs env abs =
        if ek.enter_abs then super#visit_abs env abs else abs
    end
  in

  let ctx = obj#visit_eval_ctx () ctx in
  (* Check that we updated at least one borrow *)
  assert !r;
  ctx

(** Update an abstraction borrow content.

    The borrow is referred to by a borrow id.

    This is a helper function: it might break invariants.     
 *)
let update_aborrow (ek : exploration_kind) (l : V.BorrowId.id) (nv : V.avalue)
    (ctx : C.eval_ctx) : C.eval_ctx =
  (* We use a reference to check that we update exactly one borrow: when updating
   * inside values, we check we don't update more than one borrow. Then, upon
   * returning we check that we updated at least once. *)
  let r = ref false in
  let update () : V.avalue =
    assert (not !r);
    r := true;
    nv
  in

  let obj =
    object
      inherit [_] C.map_eval_ctx as super

      method! visit_ABorrow env bc =
        match bc with
        | V.AMutBorrow (mv, bid, av) ->
            if bid = l then update ()
            else V.ABorrow (super#visit_AMutBorrow env mv bid av)
        | V.ASharedBorrow bid ->
            if bid = l then update ()
            else V.ABorrow (super#visit_ASharedBorrow env bid)
        | V.AIgnoredMutBorrow _ | V.AEndedMutBorrow _
        | V.AEndedIgnoredMutBorrow _ ->
            super#visit_ABorrow env bc
        | V.AProjSharedBorrow asb ->
            if borrow_in_asb l asb then update ()
            else V.ABorrow (super#visit_AProjSharedBorrow env asb)

      method! visit_abs env abs =
        if ek.enter_abs then super#visit_abs env abs else abs
    end
  in

  let ctx = obj#visit_eval_ctx () ctx in
  (* Check that we updated at least one borrow *)
  assert !r;
  ctx

(** Auxiliary function: see its usage in [end_borrow_get_borrow_in_value] *)
let update_outer_borrows (outer : V.AbstractionId.id option * borrow_ids option)
    (x : borrow_ids) : V.AbstractionId.id option * borrow_ids option =
  let abs, opt = outer in
  (abs, update_if_none opt x)

(** Return the first loan we find in a value *)
let get_first_loan_in_value (v : V.typed_value) : V.loan_content option =
  let obj =
    object
      inherit [_] V.iter_typed_value

      method! visit_loan_content _ lc = raise (FoundLoanContent lc)
    end
  in
  (* We use exceptions *)
  try
    obj#visit_typed_value () v;
    None
  with FoundLoanContent lc -> Some lc

(** Return the first borrow we find in a value *)
let get_first_borrow_in_value (v : V.typed_value) : V.borrow_content option =
  let obj =
    object
      inherit [_] V.iter_typed_value

      method! visit_borrow_content _ bc = raise (FoundBorrowContent bc)
    end
  in
  (* We use exceptions *)
  try
    obj#visit_typed_value () v;
    None
  with FoundBorrowContent bc -> Some bc

(** Return the first loan or borrow content we find in a value (starting with
    the outer ones).
    
    [with_borrows]:
    - if true: return the first loan or borrow we find
    - if false: return the first loan we find, do not dive into borrowed values
 *)
let get_first_outer_loan_or_borrow_in_value (with_borrows : bool)
    (v : V.typed_value) : loan_or_borrow_content option =
  let obj =
    object
      inherit [_] V.iter_typed_value

      method! visit_borrow_content _ bc =
        if with_borrows then raise (FoundBorrowContent bc) else ()

      method! visit_loan_content _ lc = raise (FoundLoanContent lc)
    end
  in
  (* We use exceptions *)
  try
    obj#visit_typed_value () v;
    None
  with
  | FoundLoanContent lc -> Some (LoanContent lc)
  | FoundBorrowContent bc -> Some (BorrowContent bc)

type gproj_borrows =
  | AProjBorrows of V.AbstractionId.id * V.symbolic_value
  | ProjBorrows of V.symbolic_value

let proj_borrows_intersects_proj_loans
    (proj_borrows : T.RegionId.Set.t * V.symbolic_value * T.rty)
    (proj_loans : T.RegionId.Set.t * V.symbolic_value) : bool =
  let b_regions, b_sv, b_ty = proj_borrows in
  let l_regions, l_sv = proj_loans in
  if same_symbolic_id b_sv l_sv then
    projections_intersect l_sv.V.sv_ty l_regions b_ty b_regions
  else false

(** Result of looking up aproj_borrows which intersect a given aproj_loans in
    the context.

    Note that because we we force the expansion of primitively copyable values
    before giving them to abstractions, we only have the following possibilities:
    - no aproj_borrows, in which case the symbolic value was either dropped
      or is in the context
    - exactly one aproj_borrows over a non-shared value
    - potentially several aproj_borrows over shared values
    
    The result contains the ids of the abstractions in which the projectors were
    found, as well as the projection types used in those abstractions.
*)
type looked_up_aproj_borrows =
  | NonSharedProj of V.AbstractionId.id * T.rty
  | SharedProjs of (V.AbstractionId.id * T.rty) list

(** Lookup the aproj_borrows (including aproj_shared_borrows) over a
    symbolic value which intersect a given set of regions.
        
    [lookup_shared]: if `true` also explore projectors over shared values,
    otherwise ignore.
    
    This is a helper function: it might break invariants.
*)
let lookup_intersecting_aproj_borrows_opt (lookup_shared : bool)
    (regions : T.RegionId.Set.t) (sv : V.symbolic_value) (ctx : C.eval_ctx) :
    looked_up_aproj_borrows option =
  let found : looked_up_aproj_borrows option ref = ref None in
  let set_non_shared ((id, ty) : V.AbstractionId.id * T.rty) : unit =
    match !found with
    | None -> found := Some (NonSharedProj (id, ty))
    | Some _ -> failwith "Unreachable"
  in
  let add_shared (x : V.AbstractionId.id * T.rty) : unit =
    match !found with
    | None -> found := Some (SharedProjs [ x ])
    | Some (SharedProjs pl) -> found := Some (SharedProjs (x :: pl))
    | Some (NonSharedProj _) -> failwith "Unreachable"
  in
  let check_add_proj_borrows (is_shared : bool) abs sv' proj_ty =
    if
      proj_borrows_intersects_proj_loans
        (abs.V.regions, sv', proj_ty)
        (regions, sv)
    then
      let x = (abs.abs_id, proj_ty) in
      if is_shared then add_shared x else set_non_shared x
    else ()
  in
  let obj =
    object
      inherit [_] C.iter_eval_ctx as super

      method! visit_abs _ abs = super#visit_abs (Some abs) abs

      method! visit_abstract_shared_borrows abs asb =
        (* Sanity check *)
        (match !found with
        | Some (NonSharedProj _) -> failwith "Unreachable"
        | _ -> ());
        (* Explore *)
        if lookup_shared then
          let abs = Option.get abs in
          let check asb =
            match asb with
            | V.AsbBorrow _ -> ()
            | V.AsbProjReborrows (sv', proj_ty) ->
                let is_shared = true in
                check_add_proj_borrows is_shared abs sv' proj_ty
          in
          List.iter check asb
        else ()

      method! visit_aproj abs sproj =
        (let abs = Option.get abs in
         match sproj with
         | AProjLoans _ | AEndedProjLoans _ | AEndedProjBorrows _
         | AIgnoredProjBorrows ->
             ()
         | AProjBorrows (sv', proj_rty) ->
             let is_shared = false in
             check_add_proj_borrows is_shared abs sv' proj_rty);
        super#visit_aproj abs sproj
    end
  in
  (* Visit *)
  obj#visit_eval_ctx None ctx;
  (* Return *)
  !found

(** Lookup the aproj_borrows (not aproj_borrows_shared!) over a symbolic
    value which intersects a given set of regions.
    
    Note that there should be **at most one** (one reason is that we force
    the expansion of primitively copyable values before giving them to
    abstractions).
    
    Returns the id of the owning abstraction, and the projection type used in
    this abstraction.
*)
let lookup_intersecting_aproj_borrows_not_shared_opt
    (regions : T.RegionId.Set.t) (sv : V.symbolic_value) (ctx : C.eval_ctx) :
    (V.AbstractionId.id * T.rty) option =
  let lookup_shared = false in
  match lookup_intersecting_aproj_borrows_opt lookup_shared regions sv ctx with
  | None -> None
  | Some (NonSharedProj (abs_id, rty)) -> Some (abs_id, rty)
  | _ -> failwith "Unexpected"

(** Similar to [lookup_intersecting_aproj_borrows_opt], but updates the
    values.

    This is a helper function: it might break invariants.
 *)
let update_intersecting_aproj_borrows (can_update_shared : bool)
    (update_shared : V.AbstractionId.id -> T.rty -> V.abstract_shared_borrows)
    (update_non_shared : V.AbstractionId.id -> T.rty -> V.aproj)
    (regions : T.RegionId.Set.t) (sv : V.symbolic_value) (ctx : C.eval_ctx) :
    C.eval_ctx =
  (* Small helpers for sanity checks *)
  let shared = ref None in
  let add_shared () =
    match !shared with None -> shared := Some true | Some b -> assert b
  in
  let set_non_shared () =
    match !shared with
    | None -> shared := Some false
    | Some _ -> failwith "Found unexpected intersecting proj_borrows"
  in
  let check_proj_borrows is_shared abs sv' proj_ty =
    if
      proj_borrows_intersects_proj_loans
        (abs.V.regions, sv', proj_ty)
        (regions, sv)
    then (
      if is_shared then add_shared () else set_non_shared ();
      true)
    else false
  in
  (* The visitor *)
  let obj =
    object
      inherit [_] C.map_eval_ctx as super

      method! visit_abs _ abs = super#visit_abs (Some abs) abs

      method! visit_abstract_shared_borrows abs asb =
        (* Sanity check *)
        (match !shared with Some b -> assert b | _ -> ());
        (* Explore *)
        if can_update_shared then
          let abs = Option.get abs in
          let update (asb : V.abstract_shared_borrow) :
              V.abstract_shared_borrows =
            match asb with
            | V.AsbBorrow _ -> [ asb ]
            | V.AsbProjReborrows (sv', proj_ty) ->
                let is_shared = true in
                if check_proj_borrows is_shared abs sv' proj_ty then
                  update_shared abs.abs_id proj_ty
                else [ asb ]
          in
          List.concat (List.map update asb)
        else asb

      method! visit_aproj abs sproj =
        match sproj with
        | AProjLoans _ | AEndedProjLoans _ | AEndedProjBorrows _
        | AIgnoredProjBorrows ->
            super#visit_aproj abs sproj
        | AProjBorrows (sv', proj_rty) ->
            let abs = Option.get abs in
            let is_shared = true in
            if check_proj_borrows is_shared abs sv' proj_rty then
              update_non_shared abs.abs_id proj_rty
            else super#visit_aproj (Some abs) sproj
    end
  in
  (* Apply *)
  let ctx = obj#visit_eval_ctx None ctx in
  (* Check that we updated the context at least once *)
  assert (Option.is_some !shared);
  (* Return *)
  ctx

(** Simply calls [update_intersecting_aproj_borrows] to update a
    proj_borrows over a non-shared value.
    
    We check that we update exactly one proj_borrows.

    This is a helper function: it might break invariants.
 *)
let update_intersecting_aproj_borrows_non_shared (regions : T.RegionId.Set.t)
    (sv : V.symbolic_value) (nv : V.aproj) (ctx : C.eval_ctx) : C.eval_ctx =
  (* Small helpers *)
  let can_update_shared = false in
  let update_shared _ _ = failwith "Unexpected" in
  let updated = ref false in
  let update_non_shared _ _ =
    assert (not !updated);
    updated := true;
    nv
  in
  (* Update *)
  let ctx =
    update_intersecting_aproj_borrows can_update_shared update_shared
      update_non_shared regions sv ctx
  in
  (* Check that we updated at least once *)
  assert !updated;
  (* Return *)
  ctx

(** Simply calls [update_intersecting_aproj_borrows] to remove the
    proj_borrows over shared values.

    This is a helper function: it might break invariants.
 *)
let remove_intersecting_aproj_borrows_shared (regions : T.RegionId.Set.t)
    (sv : V.symbolic_value) (ctx : C.eval_ctx) : C.eval_ctx =
  (* Small helpers *)
  let can_update_shared = true in
  let update_shared _ _ = [] in
  let update_non_shared _ _ = failwith "Unexpected" in
  (* Update *)
  update_intersecting_aproj_borrows can_update_shared update_shared
    update_non_shared regions sv ctx

(** Updates the proj_loans intersecting some projection.

    This is a helper function: it might break invariants.

    Note that in practice, when we update a proj_loans, we always update exactly
    one aproj_loans, in a specific abstraction.
    
    We make this function more general, by checking projection intersections
    (rather than simply checking the abstraction and symbolic value ids)
    for sanity checking: we check whether we need to update a loan based
    on intersection criteria, but also check at the same time that we update
    *exactly one* projector.
    
    Note that the new value [nv] with which to replace the proj_loans could
    be untyped: we request a typed value for sanity checking.
    
    [subst]: takes as parameters the abstraction and the projection type
    where we perform the substitution.
 *)
let update_intersecting_aproj_loans (proj_regions : T.RegionId.Set.t)
    (proj_ty : T.rty) (sv : V.symbolic_value)
    (subst : V.abs -> T.rty -> V.aproj) (ctx : C.eval_ctx) : C.eval_ctx =
  (* Small helpers for sanity checks *)
  let updated = ref false in
  let update abs local_proj_ty : V.aproj =
    assert (not !updated);
    updated := true;
    subst abs local_proj_ty
  in
  (* The visitor *)
  let obj =
    object
      inherit [_] C.map_eval_ctx as super

      method! visit_abs _ abs = super#visit_abs (Some abs) abs

      method! visit_aproj abs sproj =
        match sproj with
        | AProjBorrows _ | AEndedProjLoans _ | AEndedProjBorrows _
        | AIgnoredProjBorrows ->
            super#visit_aproj abs sproj
        | AProjLoans sv' ->
            let abs = Option.get abs in
            if same_symbolic_id sv sv' then (
              assert (sv.sv_ty = sv'.sv_ty);
              if
                projections_intersect proj_ty proj_regions sv'.V.sv_ty
                  abs.regions
              then update abs sv'.V.sv_ty
              else super#visit_aproj (Some abs) sproj)
            else super#visit_aproj (Some abs) sproj
    end
  in
  (* Apply *)
  let ctx = obj#visit_eval_ctx None ctx in
  (* Check that we updated the context at least once *)
  assert !updated;
  (* Return *)
  ctx