path: root/compiler/InterpreterLoopsJoinCtxs.ml

open Types
open Values
open Contexts
open TypesUtils
open ValuesUtils
open InterpreterUtils
open InterpreterBorrows
open InterpreterLoopsCore
open InterpreterLoopsMatchCtxs
open Errors

(** The local logger *)
let log = Logging.loops_join_ctxs_log

(** Reorder the loans and borrows in the fresh abstractions.

    We do this in order to enforce some structure in the environments: this
    allows us to find fixed-points. Note that this function needs to be
    called typically after we merge abstractions together (see {!collapse_ctx}
    and {!reduce_ctx} for instance).
 *)
let reorder_loans_borrows_in_fresh_abs (span : Meta.span)
    (old_abs_ids : AbstractionId.Set.t) (ctx : eval_ctx) : eval_ctx =
  let reorder_in_fresh_abs (abs : abs) : abs =
    (* Split between the loans and borrows *)
    let is_borrow (av : typed_avalue) : bool =
      match av.value with
      | ABorrow _ -> true
      | ALoan _ -> false
      | _ -> craise __FILE__ __LINE__ span "Unexpected"
    in
    let aborrows, aloans = List.partition is_borrow abs.avalues in

    (* Reoder the borrows, and the loans.

       After experimenting, it seems that a good way of reordering the loans
       and the borrows to find fixed points is simply to sort them by increasing
       order of id (taking the smallest id of a set of ids, in case of sets).
    *)
    let get_borrow_id (av : typed_avalue) : BorrowId.id =
      match av.value with
      | ABorrow (AMutBorrow (_, bid, _) | ASharedBorrow (_, bid)) -> bid
      | _ -> craise __FILE__ __LINE__ span "Unexpected"
    in
    let get_loan_id (av : typed_avalue) : BorrowId.id =
      match av.value with
      | ALoan (AMutLoan (_, lid, _)) -> lid
      | ALoan (ASharedLoan (_, lids, _, _)) -> BorrowId.Set.min_elt lids
      | _ -> craise __FILE__ __LINE__ span "Unexpected"
    in
    (* We use ordered maps to reorder the borrows and loans *)
    let reorder (get_bid : typed_avalue -> BorrowId.id)
        (values : typed_avalue list) : typed_avalue list =
      List.map snd
        (BorrowId.Map.bindings
           (BorrowId.Map.of_list (List.map (fun v -> (get_bid v, v)) values)))
    in
    let aborrows = reorder get_borrow_id aborrows in
    let aloans = reorder get_loan_id aloans in
    let avalues = List.append aborrows aloans in
    { abs with avalues }
  in

  let reorder_in_abs (abs : abs) =
    if AbstractionId.Set.mem abs.abs_id old_abs_ids then abs
    else reorder_in_fresh_abs abs
  in

  let env = env_map_abs reorder_in_abs ctx.env in

  { ctx with env }

(** Reduce an environment.

    We do this to simplify an environment, for the purpose of finding a loop
    fixed point.

    We do the following:
    - we look for all the *new* dummy values (we use sets of old ids to decide
      wether a value is new or not) and convert them into abstractions
    - whenever there is a new abstraction in the context, and some of its
      its borrows are associated to loans in another new abstraction, we
      merge them.
    In effect, this allows us to merge newly introduced abstractions/borrows
    with their parent abstractions.
    
    For instance, when evaluating the first loop iteration, we start in the
    following environment:
    {[
      abs@0 { ML l0 }
      ls -> MB l0 (s2 : loops::List<T>)
      i -> s1 : u32
    ]}
    
    and get the following environment upon reaching the [Continue] statement:
    {[
      abs@0 { ML l0 }
      ls -> MB l4 (s@6 : loops::List<T>)
      i -> s@7 : u32
      _@1 -> MB l0 (loops::List::Cons (ML l1, ML l2))
      _@2 -> MB l2 (@Box (ML l4))                      // tail
      _@3 -> MB l1 (s@3 : T)                           // hd
    ]}
    
    In this new environment, the dummy variables [_@1], [_@2] and [_@3] are
    considered as new.
    
    We first convert the new dummy values to abstractions. It gives:
    {[
      abs@0 { ML l0 }
      ls -> MB l4 (s@6 : loops::List<T>)
      i -> s@7 : u32
      abs@1 { MB l0, ML l1, ML l2 }
      abs@2 { MB l2, ML l4 }
      abs@3 { MB l1 }
    ]}

    We finally merge the new abstractions together. It gives:
    {[
      abs@0 { ML l0 }
      ls -> MB l4 (s@6 : loops::List<T>)
      i -> s@7 : u32
      abs@4 { MB l0, ML l4 }
    ]}

    If [merge_funs] is None, we ensure that there are no markers in the environments.
    If [merge_funs] is Some _, we merge environments that contain borrow/loan pairs with the same markers, omitting
    pairs with the PNone marker (i.e., no marker)
 *)
let reduce_ctx_with_markers (merge_funs : merge_duplicates_funcs option)
    (span : Meta.span) (loop_id : LoopId.id) (old_ids : ids_sets)
    (ctx0 : eval_ctx) : eval_ctx =
  (* Debug *)
  log#ldebug
    (lazy
      ("reduce_ctx:\n\n- fixed_ids:\n" ^ show_ids_sets old_ids ^ "\n\n- ctx0:\n"
      ^ eval_ctx_to_string ~span:(Some span) ctx0
      ^ "\n\n"));

  let allow_markers = merge_funs <> None in

  let abs_kind : abs_kind = Loop (loop_id, None, LoopSynthInput) in
  let can_end = true in
  let destructure_shared_values = true in
  let is_fresh_abs_id (id : AbstractionId.id) : bool =
    not (AbstractionId.Set.mem id old_ids.aids)
  in
  let is_fresh_did (id : DummyVarId.id) : bool =
    not (DummyVarId.Set.mem id old_ids.dids)
  in
  (* Convert the dummy values to abstractions (note that when we convert
     values to abstractions, the resulting abstraction should be destructured) *)
  (* Note that we preserve the order of the dummy values: we replace them with
     abstractions in place - this makes matching easier *)
  let env =
    List.concat
      (List.map
         (fun ee ->
           match ee with
           | EAbs _ | EFrame | EBinding (BVar _, _) -> [ ee ]
           | EBinding (BDummy id, v) ->
               if is_fresh_did id then
                 let absl =
                   convert_value_to_abstractions span abs_kind can_end
                     destructure_shared_values ctx0 v
                 in
                 List.map (fun abs -> EAbs abs) absl
               else [ ee ])
         ctx0.env)
  in
  let ctx = { ctx0 with env } in
  log#ldebug
    (lazy
      ("reduce_ctx: after converting values to abstractions:\n"
     ^ show_ids_sets old_ids ^ "\n\n- ctx:\n"
      ^ eval_ctx_to_string ~span:(Some span) ctx
      ^ "\n\n"));

  log#ldebug
    (lazy
      ("reduce_ctx: after decomposing the shared values in the abstractions:\n"
     ^ show_ids_sets old_ids ^ "\n\n- ctx:\n"
      ^ eval_ctx_to_string ~span:(Some span) ctx
      ^ "\n\n"));

  (* Explore all the *new* abstractions, and compute various maps *)
  let explore (abs : abs) = is_fresh_abs_id abs.abs_id in
  let ids_maps = compute_abs_borrows_loans_maps span explore env in
  let {
    abs_ids;
    abs_to_borrows;
    abs_to_loans = _;
    borrow_to_abs = _;
    loan_to_abs;
  } =
    ids_maps
  in

  (* Merge the abstractions together *)
  let merged_abs : AbstractionId.id UnionFind.elem AbstractionId.Map.t =
    AbstractionId.Map.of_list
      (List.map (fun id -> (id, UnionFind.make id)) abs_ids)
  in

  let ctx = ref ctx in

  (* Merge all the mergeable abs.

     We iterate over the abstractions, then over the borrows in the abstractions.
     We do this because we want to control the order in which abstractions
     are merged (the ids are iterated in increasing order). Otherwise, we
     could simply iterate over all the borrows in [borrow_to_abs]...
  *)
  List.iter
    (fun abs_id0 ->
      let bids = AbstractionId.Map.find abs_id0 abs_to_borrows in
      let bids = MarkerBorrowId.Set.elements bids in
      List.iter
        (fun bid ->
          if not allow_markers then
            sanity_check __FILE__ __LINE__ (fst bid = PNone) span;
          match MarkerBorrowId.Map.find_opt bid loan_to_abs with
          | None -> (* Nothing to do *) ()
          | Some abs_ids1 ->
              if allow_markers && fst bid = PNone then ()
              else
                AbstractionId.Set.iter
                  (fun abs_id1 ->
                    (* We need to merge - unless we have already merged *)
                    (* First, find the representatives for the two abstractions (the
                       representative is the abstraction into which we merged) *)
                    let abs_ref0 =
                      UnionFind.find (AbstractionId.Map.find abs_id0 merged_abs)
                    in
                    let abs_id0 = UnionFind.get abs_ref0 in
                    let abs_ref1 =
                      UnionFind.find (AbstractionId.Map.find abs_id1 merged_abs)
                    in
                    let abs_id1 = UnionFind.get abs_ref1 in
                    (* If the two ids are the same, it means the abstractions were already merged *)
                    if abs_id0 = abs_id1 then ()
                    else (
                      (* We actually need to merge the abstractions *)

                      (* Debug *)
                      log#ldebug
                        (lazy
                          ("reduce_ctx: merging abstraction "
                          ^ AbstractionId.to_string abs_id1
                          ^ " into "
                          ^ AbstractionId.to_string abs_id0
                          ^ ":\n\n"
                          ^ eval_ctx_to_string ~span:(Some span) !ctx));

                      (* Update the environment - pay attention to the order: we
                         we merge [abs_id1] *into* [abs_id0] *)
                      let nctx, abs_id =
                        merge_into_abstraction span abs_kind can_end merge_funs
                          !ctx abs_id1 abs_id0
                      in
                      ctx := nctx;

                      (* Update the union find *)
                      let abs_ref_merged = UnionFind.union abs_ref0 abs_ref1 in
                      UnionFind.set abs_ref_merged abs_id))
                  abs_ids1)
        bids)
    abs_ids;

  log#ldebug
    (lazy
      ("reduce_ctx:\n\n- fixed_ids:\n" ^ show_ids_sets old_ids
     ^ "\n\n- after reduce:\n"
      ^ eval_ctx_to_string ~span:(Some span) !ctx
      ^ "\n\n"));

  (* Reorder the loans and borrows in the fresh abstractions *)
  let ctx = reorder_loans_borrows_in_fresh_abs span old_ids.aids !ctx in

  log#ldebug
    (lazy
      ("reduce_ctx:\n\n- fixed_ids:\n" ^ show_ids_sets old_ids
     ^ "\n\n- after reduce and reorder borrows/loans:\n"
      ^ eval_ctx_to_string ~span:(Some span) ctx
      ^ "\n\n"));

  (* Return the new context *)
  ctx

(* Reduce_ctx can only be called in a context with no markers *)
let reduce_ctx = reduce_ctx_with_markers None

(* Collapse an environment

   This is the second part of a join, where we attempt to simplify and remove all projection markers.
   This function is called after reducing the environments, and attempting to simplify all the pairs
   of borrows and loans.

   We traverse all abstractions, and merge abstractions when they contain the same element,
   but with dual markers (i.e., PLeft and PRight).

   For instance, if we have the abstractions

   abs@0 { | MB l0 _ |, ML l1 }
   abs@1 { ︙MB l0 _ ︙, ML l2 }

   we will merge abs@0 and abs@1 into a new abstraction abs@2, removing the marker for duplicated elements,
   and taking the join of the remaining elements

   abs@2 { MB l0 _, ML l1, ML l2 }

   Rem.: Doing this might introduce new pairs of borrow/loans to be merged in different abstractions: in the example above,
   this could occur if there was another abstraction in the context containing ML l0, which would need to be simplified through
   a further reduce.
   It is unclear whether this can happen in practice. If so, a solution would be to preprocess the environments when doing
   a join: while not in the current formalism, it is sound to split an element with no markers into a duplicated pair of the
   same element with left and right markers. Doing this before reduce would allow to reduce all possible pairs of borrow/loans,
   before finally collapsing and removing all markers.
*)
let collapse_ctx_markers (span : Meta.span) (loop_id : LoopId.id)
    (merge_funs : merge_duplicates_funcs) (old_ids : ids_sets) (ctx0 : eval_ctx)
    : eval_ctx =
  (* Debug *)
  log#ldebug
    (lazy
      ("collapse_ctx:\n\n- fixed_ids:\n" ^ show_ids_sets old_ids
     ^ "\n\n- ctx0:\n"
      ^ eval_ctx_to_string ~span:(Some span) ctx0
      ^ "\n\n"));

  let abs_kind : abs_kind = Loop (loop_id, None, LoopSynthInput) in
  let can_end = true in
  let is_fresh_abs_id (id : AbstractionId.id) : bool =
    not (AbstractionId.Set.mem id old_ids.aids)
  in

  (* Explore all the *new* abstractions, and compute various maps *)
  let explore (abs : abs) = is_fresh_abs_id abs.abs_id in
  let ids_maps = compute_abs_borrows_loans_maps span explore ctx0.env in
  let { abs_ids; abs_to_borrows; abs_to_loans; borrow_to_abs; loan_to_abs } =
    ids_maps
  in

  (* Merge the abstractions together *)
  let merged_abs : AbstractionId.id UnionFind.elem AbstractionId.Map.t =
    AbstractionId.Map.of_list
      (List.map (fun id -> (id, UnionFind.make id)) abs_ids)
  in

  let ctx = ref ctx0 in

  let invert_proj_marker = function
    | PNone -> craise __FILE__ __LINE__ span "Unreachable"
    | PLeft -> PRight
    | PRight -> PLeft
  in

  (* Merge all the mergeable abs where the same element in present in both abs,
     but with left and right markers respectively.

     We first check all borrows, then all loans
  *)
  List.iter
    (fun abs_id0 ->
      let bids = AbstractionId.Map.find abs_id0 abs_to_borrows in
      let bids = MarkerBorrowId.Set.elements bids in
      List.iter
        (fun (pm, bid) ->
          if pm = PNone then ()
          else
            (* We are looking for an element with the same borrow_id, but with the dual marker *)
            match
              MarkerBorrowId.Map.find_opt
                (invert_proj_marker pm, bid)
                borrow_to_abs
            with
            | None -> (* Nothing to do *) ()
            | Some abs_ids1 ->
                AbstractionId.Set.iter
                  (fun abs_id1 ->
                    (* We need to merge - unless we have already merged *)
                    (* First, find the representatives for the two abstractions (the
                       representative is the abstraction into which we merged) *)
                    let abs_ref0 =
                      UnionFind.find (AbstractionId.Map.find abs_id0 merged_abs)
                    in
                    let abs_id0 = UnionFind.get abs_ref0 in
                    let abs_ref1 =
                      UnionFind.find (AbstractionId.Map.find abs_id1 merged_abs)
                    in
                    let abs_id1 = UnionFind.get abs_ref1 in
                    (* If the two ids are the same, it means the abstractions were already merged *)
                    if abs_id0 = abs_id1 then ()
                    else (
                      (* We actually need to merge the abstractions *)

                      (* Debug *)
                      log#ldebug
                        (lazy
                          ("collapse_ctx: merging abstraction "
                          ^ AbstractionId.to_string abs_id1
                          ^ " into "
                          ^ AbstractionId.to_string abs_id0
                          ^ ":\n\n"
                          ^ eval_ctx_to_string ~span:(Some span) !ctx));

                      (* Update the environment - pay attention to the order: we
                         we merge [abs_id1] *into* [abs_id0] *)
                      let nctx, abs_id =
                        merge_into_abstraction span abs_kind can_end
                          (Some merge_funs) !ctx abs_id1 abs_id0
                      in
                      ctx := nctx;

                      (* Update the union find *)
                      let abs_ref_merged = UnionFind.union abs_ref0 abs_ref1 in
                      UnionFind.set abs_ref_merged abs_id))
                  abs_ids1)
        bids;
      (* We now traverse the loans *)
      let bids = AbstractionId.Map.find abs_id0 abs_to_loans in
      let bids = MarkerBorrowId.Set.elements bids in
      List.iter
        (fun (pm, bid) ->
          if pm = PNone then ()
          else
            (* We are looking for an element with the same borrow_id, but with the dual marker *)
            match
              MarkerBorrowId.Map.find_opt
                (invert_proj_marker pm, bid)
                loan_to_abs
            with
            | None -> (* Nothing to do *) ()
            | Some abs_ids1 ->
                AbstractionId.Set.iter
                  (fun abs_id1 ->
                    (* We need to merge - unless we have already merged *)
                    (* First, find the representatives for the two abstractions (the
                       representative is the abstraction into which we merged) *)
                    let abs_ref0 =
                      UnionFind.find (AbstractionId.Map.find abs_id0 merged_abs)
                    in
                    let abs_id0 = UnionFind.get abs_ref0 in
                    let abs_ref1 =
                      UnionFind.find (AbstractionId.Map.find abs_id1 merged_abs)
                    in
                    let abs_id1 = UnionFind.get abs_ref1 in
                    (* If the two ids are the same, it means the abstractions were already merged *)
                    if abs_id0 = abs_id1 then ()
                    else (
                      (* We actually need to merge the abstractions *)

                      (* Debug *)
                      log#ldebug
                        (lazy
                          ("collapse_ctx: merging abstraction "
                          ^ AbstractionId.to_string abs_id1
                          ^ " into "
                          ^ AbstractionId.to_string abs_id0
                          ^ ":\n\n"
                          ^ eval_ctx_to_string ~span:(Some span) !ctx));

                      (* Update the environment - pay attention to the order: we
                         we merge [abs_id1] *into* [abs_id0] *)
                      let nctx, abs_id =
                        merge_into_abstraction span abs_kind can_end
                          (Some merge_funs) !ctx abs_id1 abs_id0
                      in
                      ctx := nctx;

                      (* Update the union find *)
                      let abs_ref_merged = UnionFind.union abs_ref0 abs_ref1 in
                      UnionFind.set abs_ref_merged abs_id))
                  abs_ids1)
        bids)
    abs_ids;

  log#ldebug
    (lazy
      ("collapse_ctx:\n\n- fixed_ids:\n" ^ show_ids_sets old_ids
     ^ "\n\n- after collapse:\n"
      ^ eval_ctx_to_string ~span:(Some span) !ctx
      ^ "\n\n"));

  (* Reorder the loans and borrows in the fresh abstractions *)
  let ctx = reorder_loans_borrows_in_fresh_abs span old_ids.aids !ctx in

  log#ldebug
    (lazy
      ("collapse_ctx:\n\n- fixed_ids:\n" ^ show_ids_sets old_ids
     ^ "\n\n- after collapse and reorder borrows/loans:\n"
      ^ eval_ctx_to_string ~span:(Some span) ctx
      ^ "\n\n"));

  (* Return the new context *)
  ctx

(* Collapse two environments containing projection markers; this function is called after
   joining environments.

   The collapse is done in two steps.
   First, we reduce the environment, merging for instance abstractions containing MB l0 _ and ML l0,
   when both elements have the same marker, e.g., PNone, PLeft, or PRight.

   Second, we merge abstractions containing the same element with left and right markers respectively.

   At the end of the second step, all markers should have been removed from the resulting environment.
*)
let collapse_ctx (span : Meta.span) (loop_id : LoopId.id)
    (merge_funs : merge_duplicates_funcs) (old_ids : ids_sets) (ctx0 : eval_ctx)
    : eval_ctx =
  let ctx =
    reduce_ctx_with_markers (Some merge_funs) span loop_id old_ids ctx0
  in
  collapse_ctx_markers span loop_id merge_funs old_ids ctx

let mk_collapse_ctx_merge_duplicate_funs (span : Meta.span)
    (loop_id : LoopId.id) (ctx : eval_ctx) : merge_duplicates_funcs =
  (* Rem.: the merge functions raise exceptions (that we catch). *)
  let module S : MatchJoinState = struct
    let span = span
    let loop_id = loop_id
    let nabs = ref []
  end in
  let module JM = MakeJoinMatcher (S) in
  let module M = MakeMatcher (JM) in
  (* Functions to match avalues (see {!merge_duplicates_funcs}).

     Those functions are used to merge borrows/loans with the *same ids*.

     They will always be called on destructured avalues (whose children are
     [AIgnored] - we enforce that through sanity checks). We rely on the join
     matcher [JM] to match the concrete values (for shared loans for instance).
     Note that the join matcher doesn't implement match functions for avalues
     (see the comments in {!MakeJoinMatcher}.
  *)
  let merge_amut_borrows id ty0 _pm0 child0 _ty1 _pm1 child1 =
    (* Sanity checks *)
    sanity_check __FILE__ __LINE__ (is_aignored child0.value) span;
    sanity_check __FILE__ __LINE__ (is_aignored child1.value) span;

    (* We need to pick a type for the avalue. The types on the left and on the
       right may use different regions: it doesn't really matter (here, we pick
       the one from the left), because we will merge those regions together
       anyway (see the comments for {!merge_into_abstraction}).
    *)
    let ty = ty0 in
    let child = child0 in
    let value = ABorrow (AMutBorrow (PNone, id, child)) in
    { value; ty }
  in

  let merge_ashared_borrows id ty0 _pm0 ty1 _pm1 =
    (* Sanity checks *)
    let _ =
      let _, ty0, _ = ty_as_ref ty0 in
      let _, ty1, _ = ty_as_ref ty1 in
      sanity_check __FILE__ __LINE__
        (not (ty_has_borrows ctx.type_ctx.type_infos ty0))
        span;
      sanity_check __FILE__ __LINE__
        (not (ty_has_borrows ctx.type_ctx.type_infos ty1))
        span
    in

    (* Same remarks as for [merge_amut_borrows] *)
    let ty = ty0 in
    let value = ABorrow (ASharedBorrow (PNone, id)) in
    { value; ty }
  in

  let merge_amut_loans id ty0 _pm0 child0 _ty1 _pm1 child1 =
    (* Sanity checks *)
    sanity_check __FILE__ __LINE__ (is_aignored child0.value) span;
    sanity_check __FILE__ __LINE__ (is_aignored child1.value) span;

    (* Same remarks as for [merge_amut_borrows] *)
    let ty = ty0 in
    let child = child0 in
    let value = ALoan (AMutLoan (PNone, id, child)) in
    { value; ty }
  in
  let merge_ashared_loans ids ty0 _pm0 (sv0 : typed_value) child0 _ty1 _pm1
      (sv1 : typed_value) child1 =
    (* Sanity checks *)
    sanity_check __FILE__ __LINE__ (is_aignored child0.value) span;
    sanity_check __FILE__ __LINE__ (is_aignored child1.value) span;
    (* Same remarks as for [merge_amut_borrows].

       This time we need to also merge the shared values. We rely on the
       join matcher [JM] to do so.
    *)
    sanity_check __FILE__ __LINE__
      (not (value_has_loans_or_borrows ctx sv0.value))
      span;
    sanity_check __FILE__ __LINE__
      (not (value_has_loans_or_borrows ctx sv1.value))
      span;

    let ty = ty0 in
    let child = child0 in
    let sv = M.match_typed_values ctx ctx sv0 sv1 in
    let value = ALoan (ASharedLoan (PNone, ids, sv, child)) in
    { value; ty }
  in
  {
    merge_amut_borrows;
    merge_ashared_borrows;
    merge_amut_loans;
    merge_ashared_loans;
  }

let merge_into_abstraction (span : Meta.span) (loop_id : LoopId.id)
    (abs_kind : abs_kind) (can_end : bool) (ctx : eval_ctx)
    (aid0 : AbstractionId.id) (aid1 : AbstractionId.id) :
    eval_ctx * AbstractionId.id =
  let merge_funs = mk_collapse_ctx_merge_duplicate_funs span loop_id ctx in
  merge_into_abstraction span abs_kind can_end (Some merge_funs) ctx aid0 aid1

(** Collapse an environment, merging the duplicated borrows/loans.

    This function simply calls {!collapse_ctx} with the proper merging functions.

    We do this because when we join environments, we may introduce duplicated
    loans and borrows. See the explanations for {!join_ctxs}.
 *)
let collapse_ctx_with_merge (span : Meta.span) (loop_id : LoopId.id)
    (old_ids : ids_sets) (ctx : eval_ctx) : eval_ctx =
  let merge_funs = mk_collapse_ctx_merge_duplicate_funs span loop_id ctx in
  try collapse_ctx span loop_id merge_funs old_ids ctx
  with ValueMatchFailure _ -> craise __FILE__ __LINE__ span "Unexpected"

let join_ctxs (span : Meta.span) (loop_id : LoopId.id) (fixed_ids : ids_sets)
    (ctx0 : eval_ctx) (ctx1 : eval_ctx) : ctx_or_update =
  (* Debug *)
  log#ldebug
    (lazy
      ("join_ctxs:\n\n- fixed_ids:\n" ^ show_ids_sets fixed_ids
     ^ "\n\n- ctx0:\n"
      ^ eval_ctx_to_string_no_filter ~span:(Some span) ctx0
      ^ "\n\n- ctx1:\n"
      ^ eval_ctx_to_string_no_filter ~span:(Some span) ctx1
      ^ "\n\n"));

  let env0 = List.rev ctx0.env in
  let env1 = List.rev ctx1.env in
  let nabs = ref [] in

  (* Explore the environments. *)
  let join_suffixes (env0 : env) (env1 : env) : env =
    (* Debug *)
    log#ldebug
      (lazy
        ("join_suffixes:\n\n- fixed_ids:\n" ^ show_ids_sets fixed_ids
       ^ "\n\n- ctx0:\n"
        ^ eval_ctx_to_string_no_filter ~span:(Some span)
            { ctx0 with env = List.rev env0 }
        ^ "\n\n- ctx1:\n"
        ^ eval_ctx_to_string_no_filter ~span:(Some span)
            { ctx1 with env = List.rev env1 }
        ^ "\n\n"));

    (* Sanity check: there are no values/abstractions which should be in the prefix *)
    let check_valid (ee : env_elem) : unit =
      match ee with
      | EBinding (BVar _, _) ->
          (* Variables are necessarily in the prefix *)
          craise __FILE__ __LINE__ span "Unreachable"
      | EBinding (BDummy did, _) ->
          sanity_check __FILE__ __LINE__
            (not (DummyVarId.Set.mem did fixed_ids.dids))
            span
      | EAbs abs ->
          sanity_check __FILE__ __LINE__
            (not (AbstractionId.Set.mem abs.abs_id fixed_ids.aids))
            span
      | EFrame ->
          (* This should have been eliminated *)
          craise __FILE__ __LINE__ span "Unreachable"
    in

    (* Add projection marker to all abstractions in the left and right environments *)
    let add_marker (pm : proj_marker) (ee : env_elem) : env_elem =
      match ee with
      | EAbs abs ->
          EAbs
            {
              abs with
              avalues = List.map (add_marker_avalue span ctx0 pm) abs.avalues;
            }
      | x -> x
    in

    let env0 = List.map (add_marker PLeft) env0 in
    let env1 = List.map (add_marker PRight) env1 in

    List.iter check_valid env0;
    List.iter check_valid env1;
    (* Concatenate the suffixes and append the abstractions introduced while
       joining the prefixes *)
    let absl = List.map (fun abs -> EAbs abs) (List.rev !nabs) in
    List.concat [ env0; env1; absl ]
  in

  let module S : MatchJoinState = struct
    let span = span
    let loop_id = loop_id
    let nabs = nabs
  end in
  let module JM = MakeJoinMatcher (S) in
  let module M = MakeMatcher (JM) in
  (* Rem.: this function raises exceptions *)
  let rec join_prefixes (env0 : env) (env1 : env) : env =
    match (env0, env1) with
    | ( (EBinding (BDummy b0, v0) as var0) :: env0',
        (EBinding (BDummy b1, v1) as var1) :: env1' ) ->
        (* Debug *)
        log#ldebug
          (lazy
            ("join_prefixes: BDummys:\n\n- fixed_ids:\n" ^ "\n"
           ^ show_ids_sets fixed_ids ^ "\n\n- value0:\n"
            ^ env_elem_to_string span ctx0 var0
            ^ "\n\n- value1:\n"
            ^ env_elem_to_string span ctx1 var1
            ^ "\n\n"));

        (* Two cases: the dummy value is an old value, in which case the bindings
           must be the same and we must join their values. Otherwise, it means we
           are not in the prefix anymore *)
        if DummyVarId.Set.mem b0 fixed_ids.dids then (
          (* Still in the prefix: match the values *)
          sanity_check __FILE__ __LINE__ (b0 = b1) span;
          let b = b0 in
          let v = M.match_typed_values ctx0 ctx1 v0 v1 in
          let var = EBinding (BDummy b, v) in
          (* Continue *)
          var :: join_prefixes env0' env1')
        else (* Not in the prefix anymore *)
          join_suffixes env0 env1
    | ( (EBinding (BVar b0, v0) as var0) :: env0',
        (EBinding (BVar b1, v1) as var1) :: env1' ) ->
        (* Debug *)
        log#ldebug
          (lazy
            ("join_prefixes: BVars:\n\n- fixed_ids:\n" ^ "\n"
           ^ show_ids_sets fixed_ids ^ "\n\n- value0:\n"
            ^ env_elem_to_string span ctx0 var0
            ^ "\n\n- value1:\n"
            ^ env_elem_to_string span ctx1 var1
            ^ "\n\n"));

        (* Variable bindings *must* be in the prefix and consequently their
           ids must be the same *)
        sanity_check __FILE__ __LINE__ (b0 = b1) span;
        (* Match the values *)
        let b = b0 in
        let v = M.match_typed_values ctx0 ctx1 v0 v1 in
        let var = EBinding (BVar b, v) in
        (* Continue *)
        var :: join_prefixes env0' env1'
    | (EAbs abs0 as abs) :: env0', EAbs abs1 :: env1' ->
        (* Debug *)
        log#ldebug
          (lazy
            ("join_prefixes: Abs:\n\n- fixed_ids:\n" ^ "\n"
           ^ show_ids_sets fixed_ids ^ "\n\n- abs0:\n"
            ^ abs_to_string span ctx0 abs0
            ^ "\n\n- abs1:\n"
            ^ abs_to_string span ctx1 abs1
            ^ "\n\n"));

        (* Same as for the dummy values: there are two cases *)
        if AbstractionId.Set.mem abs0.abs_id fixed_ids.aids then (
          (* Still in the prefix: the abstractions must be the same *)
          sanity_check __FILE__ __LINE__ (abs0 = abs1) span;
          (* Continue *)
          abs :: join_prefixes env0' env1')
        else (* Not in the prefix anymore *)
          join_suffixes env0 env1
    | _ ->
        (* The elements don't match: we are not in the prefix anymore *)
        join_suffixes env0 env1
  in

  try
    (* Remove the frame delimiter (the first element of an environment is a frame delimiter) *)
    let env0, env1 =
      match (env0, env1) with
      | EFrame :: env0, EFrame :: env1 -> (env0, env1)
      | _ -> craise __FILE__ __LINE__ span "Unreachable"
    in

    log#ldebug
      (lazy
        ("- env0:\n" ^ show_env env0 ^ "\n\n- env1:\n" ^ show_env env1 ^ "\n\n"));

    let env = List.rev (EFrame :: join_prefixes env0 env1) in

    (* Construct the joined context - of course, the type, fun, etc. contexts
     * should be the same in the two contexts *)
    let {
      type_ctx;
      fun_ctx;
      global_ctx;
      trait_decls_ctx;
      trait_impls_ctx;
      region_groups;
      type_vars;
      const_generic_vars;
      const_generic_vars_map;
      norm_trait_types;
      env = _;
      ended_regions = ended_regions0;
    } =
      ctx0
    in
    let {
      type_ctx = _;
      fun_ctx = _;
      global_ctx = _;
      trait_decls_ctx = _;
      trait_impls_ctx = _;
      region_groups = _;
      type_vars = _;
      const_generic_vars = _;
      const_generic_vars_map = _;
      norm_trait_types = _;
      env = _;
      ended_regions = ended_regions1;
    } =
      ctx1
    in
    let ended_regions = RegionId.Set.union ended_regions0 ended_regions1 in
    Ok
      {
        type_ctx;
        fun_ctx;
        global_ctx;
        trait_decls_ctx;
        trait_impls_ctx;
        region_groups;
        type_vars;
        const_generic_vars;
        const_generic_vars_map;
        norm_trait_types;
        env;
        ended_regions;
      }
  with ValueMatchFailure e -> Error e

(** Destructure all the new abstractions *)
let destructure_new_abs (span : Meta.span) (loop_id : LoopId.id)
    (old_abs_ids : AbstractionId.Set.t) (ctx : eval_ctx) : eval_ctx =
  let abs_kind : abs_kind = Loop (loop_id, None, LoopSynthInput) in
  let can_end = true in
  let destructure_shared_values = true in
  let is_fresh_abs_id (id : AbstractionId.id) : bool =
    not (AbstractionId.Set.mem id old_abs_ids)
  in
  let env =
    env_map_abs
      (fun abs ->
        if is_fresh_abs_id abs.abs_id then
          let abs =
            destructure_abs span abs_kind can_end destructure_shared_values ctx
              abs
          in
          abs
        else abs)
      ctx.env
  in
  { ctx with env }

(** Refresh the ids of the fresh abstractions.

    We do this because {!prepare_ashared_loans} introduces some non-fixed
    abstractions in contexts which are later joined: we have to make sure two
    contexts we join don't have non-fixed abstractions with the same ids.
  *)
let refresh_abs (old_abs : AbstractionId.Set.t) (ctx : eval_ctx) : eval_ctx =
  let ids, _ = compute_ctx_ids ctx in
  let abs_to_refresh = AbstractionId.Set.diff ids.aids old_abs in
  let aids_subst =
    List.map
      (fun id -> (id, fresh_abstraction_id ()))
      (AbstractionId.Set.elements abs_to_refresh)
  in
  let aids_subst = AbstractionId.Map.of_list aids_subst in
  let subst id =
    match AbstractionId.Map.find_opt id aids_subst with
    | None -> id
    | Some id -> id
  in
  let env =
    Substitute.env_subst_ids
      (fun x -> x)
      (fun x -> x)
      (fun x -> x)
      (fun x -> x)
      (fun x -> x)
      subst ctx.env
  in
  { ctx with env }

let loop_join_origin_with_continue_ctxs (config : config) (span : Meta.span)
    (loop_id : LoopId.id) (fixed_ids : ids_sets) (old_ctx : eval_ctx)
    (ctxl : eval_ctx list) : (eval_ctx * eval_ctx list) * eval_ctx =
  (* # Join with the new contexts, one by one

     For every context, we repeteadly attempt to join it with the current
     result of the join: if we fail (because we need to end loans for instance),
     we update the context and retry.
     Rem.: we should never have to end loans in the aggregated context, only
     in the one we are trying to add to the join.
  *)
  let joined_ctx = ref old_ctx in
  let rec join_one_aux (ctx : eval_ctx) : eval_ctx =
    match join_ctxs span loop_id fixed_ids !joined_ctx ctx with
    | Ok nctx ->
        joined_ctx := nctx;
        ctx
    | Error err ->
        let ctx =
          match err with
          | LoanInRight bid ->
              InterpreterBorrows.end_borrow_no_synth config span bid ctx
          | LoansInRight bids ->
              InterpreterBorrows.end_borrows_no_synth config span bids ctx
          | AbsInRight _ | AbsInLeft _ | LoanInLeft _ | LoansInLeft _ ->
              craise __FILE__ __LINE__ span "Unexpected"
        in
        join_one_aux ctx
  in
  let join_one (ctx : eval_ctx) : eval_ctx =
    log#ldebug
      (lazy
        ("loop_join_origin_with_continue_ctxs:join_one: initial ctx:\n"
        ^ eval_ctx_to_string ~span:(Some span) ctx));

    (* Destructure the abstractions introduced in the new context *)
    let ctx = destructure_new_abs span loop_id fixed_ids.aids ctx in
    log#ldebug
      (lazy
        ("loop_join_origin_with_continue_ctxs:join_one: after destructure:\n"
        ^ eval_ctx_to_string ~span:(Some span) ctx));

    (* Reduce the context we want to add to the join *)
    let ctx = reduce_ctx span loop_id fixed_ids ctx in
    log#ldebug
      (lazy
        ("loop_join_origin_with_continue_ctxs:join_one: after reduce:\n"
        ^ eval_ctx_to_string ~span:(Some span) ctx));

    (* Refresh the fresh abstractions *)
    let ctx = refresh_abs fixed_ids.aids ctx in

    (* Join the two contexts  *)
    let ctx1 = join_one_aux ctx in
    log#ldebug
      (lazy
        ("loop_join_origin_with_continue_ctxs:join_one: after join:\n"
        ^ eval_ctx_to_string ~span:(Some span) ctx1));

    (* Collapse to eliminate the markers *)
    joined_ctx := collapse_ctx_with_merge span loop_id fixed_ids !joined_ctx;
    log#ldebug
      (lazy
        ("loop_join_origin_with_continue_ctxs:join_one: after join-collapse:\n"
        ^ eval_ctx_to_string ~span:(Some span) !joined_ctx));

    (* Reduce again to reach fixed point *)
    joined_ctx := reduce_ctx span loop_id fixed_ids !joined_ctx;
    log#ldebug
      (lazy
        ("loop_join_origin_with_continue_ctxs:join_one: after last reduce:\n"
        ^ eval_ctx_to_string ~span:(Some span) !joined_ctx));

    (* Sanity check *)
    if !Config.sanity_checks then Invariants.check_invariants span !joined_ctx;
    (* Return *)
    ctx1
  in

  let ctxl = List.map join_one ctxl in

  (* # Return *)
  ((old_ctx, ctxl), !joined_ctx)