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(************************************************************************)
(*         *   The Coq Proof Assistant / The Coq Development Team       *)
(*  v      *   INRIA, CNRS and contributors - Copyright 1999-2019       *)
(* <O___,, *       (see CREDITS file for the list of authors)           *)
(*   \VV/  **************************************************************)
(*    //   *    This file is distributed under the terms of the         *)
(*         *     GNU Lesser General Public License Version 2.1          *)
(*         *     (see LICENSE file for the text of the license)         *)
(************************************************************************)

open Pp
open CErrors
open Util
open Names
open Nameops
open Termops
open Constr
open Context
open Namegen
open Environ
open Evd
open EConstr
open Vars
open Reduction
open Reductionops
open Tacred
open Pretype_errors
open Evarutil
open Unification
open Tactypes

(******************************************************************)
(* Clausal environments *)

type clausenv = {
  env      : env;
  evd      : evar_map;
  templval : constr freelisted;
  templtyp : constr freelisted }

let cl_env ce = ce.env
let cl_sigma ce =  ce.evd

let clenv_nf_meta clenv c = nf_meta clenv.evd c
let clenv_term clenv c = meta_instance clenv.evd c
let clenv_meta_type clenv mv = Typing.meta_type clenv.evd mv
let clenv_value clenv = meta_instance clenv.evd clenv.templval
let clenv_type clenv = meta_instance clenv.evd clenv.templtyp

let refresh_undefined_univs clenv =
  match EConstr.kind clenv.evd clenv.templval.rebus with
  | Var _ -> clenv, Univ.empty_level_subst
  | App (f, args) when isVar clenv.evd f -> clenv, Univ.empty_level_subst
  | _ ->  
    let evd', subst = Evd.refresh_undefined_universes clenv.evd in
    let map_freelisted f = { f with rebus = subst_univs_level_constr subst f.rebus } in
      { clenv with evd = evd'; templval = map_freelisted clenv.templval;
        templtyp = map_freelisted clenv.templtyp }, subst

let clenv_hnf_constr ce t = hnf_constr (cl_env ce) (cl_sigma ce) t

let clenv_get_type_of ce c = Retyping.get_type_of (cl_env ce) (cl_sigma ce) c

exception NotExtensibleClause

let clenv_push_prod cl =
  let typ = whd_all (cl_env cl) (cl_sigma cl) (clenv_type cl) in
  let rec clrec typ = match EConstr.kind cl.evd typ with
    | Cast (t,_,_) -> clrec t
    | Prod (na,t,u) ->
        let mv = new_meta () in
        let dep = not (noccurn (cl_sigma cl) 1 u) in
        let na' = if dep then na.binder_name else Anonymous in
        let e' = meta_declare mv t ~name:na' cl.evd in
        let concl = if dep then subst1 (mkMeta mv) u else u in
        let def = applist (cl.templval.rebus,[mkMeta mv]) in
        { templval = mk_freelisted def;
          templtyp = mk_freelisted concl;
          evd = e';
          env = cl.env }
    | _ -> raise NotExtensibleClause
  in clrec typ

(* Instantiate the first [bound] products of [t] with metas (all products if
   [bound] is [None]; unfold local defs *)

(** [clenv_environments sigma n t] returns [sigma',lmeta,ccl] where
   [lmetas] is a list of metas to be applied to a proof of [t] so that
   it produces the unification pattern [ccl]; [sigma'] is [sigma]
   extended with [lmetas]; if [n] is defined, it limits the size of
   the list even if [ccl] is still a product; otherwise, it stops when
   [ccl] is not a product; example: if [t] is [forall x y, x=y -> y=x]
   and [n] is [None], then [lmetas] is [Meta n1;Meta n2;Meta n3] and
   [ccl] is [Meta n1=Meta n2]; if [n] is [Some 1], [lmetas] is [Meta n1]
   and [ccl] is [forall y, Meta n1=y -> y=Meta n1] *)

let clenv_environments evd bound t =
  let open EConstr in
  let open Vars in
  let rec clrec (e,metas) n t =
    match n, EConstr.kind evd t with
      | (Some 0, _) -> (e, List.rev metas, t)
      | (n, Cast (t,_,_)) -> clrec (e,metas) n t
      | (n, Prod (na,t1,t2)) ->
          let mv = new_meta () in
          let dep = not (noccurn evd 1 t2) in
          let na' = if dep then na.binder_name else Anonymous in
          let e' = meta_declare mv t1 ~name:na' e in
          clrec (e', (mkMeta mv)::metas) (Option.map ((+) (-1)) n)
            (if dep then (subst1 (mkMeta mv) t2) else t2)
      | (n, LetIn (na,b,_,t)) -> clrec (e,metas) n (subst1 b t)
      | (n, _) -> (e, List.rev metas, t)
  in
  clrec (evd,[]) bound t

let mk_clenv_from_env env sigma n (c,cty) =
  let evd = clear_metas sigma in
  let (evd,args,concl) = clenv_environments evd n cty in
  { templval = mk_freelisted (applist (c,args));
    templtyp = mk_freelisted concl;
    evd = evd;
    env = env }

let mk_clenv_from_n gls n (c,cty) =
  let env = Proofview.Goal.env gls in
  let sigma = Tacmach.New.project gls in
  mk_clenv_from_env env sigma n (c, cty)

let mk_clenv_from gls = mk_clenv_from_n gls None

let mk_clenv_type_of gls t = mk_clenv_from gls (t,Tacmach.New.pf_unsafe_type_of gls t)

(******************************************************************)

(* [mentions clenv mv0 mv1] is true if mv1 is defined and mentions
 * mv0, or if one of the free vars on mv1's freelist mentions
 * mv0 *)

let mentions clenv mv0 =
  let rec menrec mv1 =
    Int.equal mv0 mv1 ||
    let mlist =
      try match meta_opt_fvalue clenv.evd mv1 with
      | Some (b,_) -> b.freemetas
      | None -> Metaset.empty
      with Not_found -> Metaset.empty in
    Metaset.exists menrec mlist
  in menrec

let error_incompatible_inst clenv mv  =
  let na = meta_name clenv.evd mv in
  match na with
      Name id ->
        user_err ~hdr:"clenv_assign"
          (str "An incompatible instantiation has already been found for " ++
           Id.print id)
    | _ ->
        anomaly ~label:"clenv_assign" (Pp.str "non dependent metavar already assigned.")

(* TODO: replace by clenv_unify (mkMeta mv) rhs ? *)
let clenv_assign mv rhs clenv =
  let rhs_fls = mk_freelisted rhs in
  if Metaset.exists (mentions clenv mv) rhs_fls.freemetas then
    user_err Pp.(str "clenv_assign: circularity in unification");
  try
    if meta_defined clenv.evd mv then
      if not (EConstr.eq_constr clenv.evd (fst (meta_fvalue clenv.evd mv)).rebus rhs) then
        error_incompatible_inst clenv mv
      else
        clenv
    else
      let st = (Conv,TypeNotProcessed) in
      {clenv with evd = meta_assign mv (rhs_fls.rebus,st) clenv.evd}
  with Not_found ->
    user_err Pp.(str "clenv_assign: undefined meta")



(* [clenv_dependent hyps_only clenv]
 * returns a list of the metavars which appear in the template of clenv,
 * and which are dependent, This is computed by taking the metavars of the
 * template in right-to-left order, and collecting the metavars which appear
 * in their types, and adding in all the metavars appearing in the
 * type of clenv.
 * If [hyps_only] then metavariables occurring in the concl are _excluded_
 * If [iter] is also set then all metavariables *recursively* occurring
 * in the concl are _excluded_

   Details of the strategies used for computing the set of unresolved
   dependent metavariables

   We typically have a clause of the form

   lem(?T:Type,?T,?U:Type,?V:Type,?x:?T,?y:?U,?z:?V,?H:hyp(?x,?z)) :concl(?y,?z)

   Then, we compute:
   A  = the set of all unresolved metas
   C  = the set of metas occurring in concl (here ?y, ?z)
   C* = the recursive closure of C wrt types (here ?y, ?z, ?U, ?V)
   D  = the set of metas occurring in a type of meta (here ?x, ?T, ?z, ?U, ?V)
   NL = the set of duplicated metas even if non dependent (here ?T)
       (we make the assumption that duplicated metas have internal dependencies)

   Then, for the "apply"-style tactic (hyps_only), missing metas are
     A inter ((D minus C) union NL)

   for the optimized "apply"-style tactic (taking in care, f_equal style
   lemma, from 2/8/10, Coq > 8.3), missing metas are
     A inter (( D minus C* ) union NL)

   for the "elim"-style tactic, missing metas are
     A inter (D union C union NL)

   In any case, we respect the order given in A.
*)

let clenv_metas_in_type_of_meta evd mv =
  (mk_freelisted (meta_instance evd (meta_ftype evd mv))).freemetas

let dependent_in_type_of_metas clenv mvs =
  List.fold_right
    (fun mv -> Metaset.union (clenv_metas_in_type_of_meta clenv.evd mv))
    mvs Metaset.empty

let dependent_closure clenv mvs =
  let rec aux mvs acc =
    Metaset.fold
      (fun mv deps ->
        let metas_of_meta_type = clenv_metas_in_type_of_meta clenv.evd mv in
        aux metas_of_meta_type (Metaset.union deps metas_of_meta_type))
      mvs acc in
  aux mvs mvs

let clenv_dependent_gen hyps_only ?(iter=true) clenv =
  let all_undefined = undefined_metas clenv.evd in
  let deps_in_concl = (mk_freelisted (clenv_type clenv)).freemetas in
  let deps_in_hyps = dependent_in_type_of_metas clenv all_undefined in
  let deps_in_concl =
    if hyps_only && iter then dependent_closure clenv deps_in_concl
    else deps_in_concl in
  List.filter
    (fun mv ->
      if hyps_only then
        Metaset.mem mv deps_in_hyps && not (Metaset.mem mv deps_in_concl)
      else
        Metaset.mem mv deps_in_hyps || Metaset.mem mv deps_in_concl)
    all_undefined

let clenv_missing ce = clenv_dependent_gen true ce
let clenv_dependent ce = clenv_dependent_gen false ce

(******************************************************************)

let clenv_unify ?(flags=default_unify_flags ()) cv_pb t1 t2 clenv =
  { clenv with
      evd = w_unify ~flags clenv.env clenv.evd cv_pb t1 t2 }

let clenv_unify_meta_types ?(flags=default_unify_flags ()) clenv =
  { clenv with evd = w_unify_meta_types ~flags:flags clenv.env clenv.evd }

let clenv_unique_resolver_gen ?(flags=default_unify_flags ()) clenv concl =
  if isMeta clenv.evd (fst (decompose_app_vect clenv.evd (whd_nored clenv.evd clenv.templtyp.rebus))) then
    clenv_unify CUMUL ~flags (clenv_type clenv) concl
      (clenv_unify_meta_types ~flags clenv)
  else
    clenv_unify CUMUL ~flags
      (meta_reducible_instance clenv.evd clenv.templtyp) concl clenv

let old_clenv_unique_resolver ?flags clenv gl =
  let concl = Goal.V82.concl clenv.evd (sig_it gl) in
  clenv_unique_resolver_gen ?flags clenv concl

let clenv_unique_resolver ?flags clenv gl =
  let concl = Proofview.Goal.concl gl in
  clenv_unique_resolver_gen ?flags clenv concl

let adjust_meta_source evd mv = function
  | loc,Evar_kinds.VarInstance id ->
    let rec match_name c l =
      match EConstr.kind evd c, l with
      | Lambda ({binder_name=Name id},_,c), a::l when EConstr.eq_constr evd a (mkMeta mv) -> Some id
      | Lambda (_,_,c), a::l -> match_name c l
      | _ -> None in
    (* This is very ad hoc code so that an evar inherits the name of the binder
       in situations like "ex_intro (fun x => P) ?ev p" *)
    let f = function (mv',(Cltyp (_,t) | Clval (_,_,t))) ->
      if Metaset.mem mv t.freemetas then
        let f,l = decompose_app evd t.rebus in
        match EConstr.kind evd f with
        | Meta mv'' ->
          (match meta_opt_fvalue evd mv'' with
          | Some (c,_) -> match_name c.rebus l
          | None -> None)
        | _ -> None
      else None in
    let id = try List.find_map f (Evd.meta_list evd) with Not_found -> id in
    loc,Evar_kinds.VarInstance id
  | src -> src

(* [clenv_pose_metas_as_evars clenv dep_mvs]
 * For each dependent evar in the clause-env which does not have a value,
 * pose a value for it by constructing a fresh evar.  We do this in
 * left-to-right order, so that every evar's type is always closed w.r.t.
 * metas.

 * Node added 14/4/08 [HH]: before this date, evars were collected in
   clenv_dependent by collect_metas in the fold_constr order which is
   (almost) the left-to-right order of dependencies in term. However,
   due to K-redexes, collect_metas was sometimes missing some metas.
   The call to collect_metas has been replaced by a call to
   undefined_metas, but then the order was the one of definition of
   the metas (numbers in increasing order) which is _not_ the
   dependency order when a clenv_fchain occurs (because clenv_fchain
   plugs a term with a list of consecutive metas in place of a - a priori -
   arbitrary metavariable belonging to another sequence of consecutive metas:
   e.g., clenv_fchain may plug (H ?1 ?2) at the position ?6 of
   (nat_ind ?3 ?4 ?5 ?6), leading to a dependency order 3<4<5<1<2).
   To ensure the dependency order, we check that the type of each meta
   to pose is already meta-free, otherwise we postpone the transformation,
   hoping that no cycle may happen.

   Another approach could have been to use decimal numbers for metas so that
   in the example above, (H ?1 ?2) would have been renumbered (H ?6.1 ?6.2)
   then making the numeric order match the dependency order.
*)

let clenv_pose_metas_as_evars clenv dep_mvs =
  let rec fold clenv evs = function
  | [] -> clenv, evs
  | mv::mvs ->
      let ty = clenv_meta_type clenv mv in
      (* Postpone the evar-ization if dependent on another meta *)
      (* This assumes no cycle in the dependencies - is it correct ? *)
      if occur_meta clenv.evd ty then fold clenv evs (mvs@[mv])
      else
        let src = evar_source_of_meta mv clenv.evd in
        let src = adjust_meta_source clenv.evd mv src in
        let evd = clenv.evd in
        let (evd, evar) = new_evar (cl_env clenv) evd ~src ty in
        let clenv = clenv_assign mv evar {clenv with evd=evd} in
        fold clenv (fst (destEvar evd evar) :: evs) mvs in
  fold clenv [] dep_mvs

(******************************************************************)

(* [clenv_fchain mv clenv clenv']
 *
 * Resolves the value of "mv" (which must be undefined) in clenv to be
 * the template of clenv' be the value "c", applied to "n" fresh
 * metavars, whose types are chosen by destructing "clf", which should
 * be a clausale forme generated from the type of "c".  The process of
 * resolution can cause unification of already-existing metavars, and
 * of the fresh ones which get created.  This operation is a composite
 * of operations which pose new metavars, perform unification on
 * terms, and make bindings.

   Otherwise said, from

     [clenv] = [env;sigma;metas |- c:T]
     [clenv'] = [env';sigma';metas' |- d:U]
     [mv] = [mi] of type [Ti] in [metas]

   then, if the unification of [Ti] and [U] produces map [rho], the
   chaining is [env';sigma';rho'(metas),rho(metas') |- c:rho'(T)] for
   [rho'] being [rho;mi:=d].

   In particular, it assumes that [env'] and [sigma'] extend [env] and [sigma].
*)

let fchain_flags () =
  { (default_unify_flags ()) with
    allow_K_in_toplevel_higher_order_unification = true }

let clenv_fchain ?with_univs ?(flags=fchain_flags ()) mv clenv nextclenv =
  (* Add the metavars of [nextclenv] to [clenv], with their name-environment *)
  let clenv' =
    { templval = clenv.templval;
      templtyp = clenv.templtyp;
      evd = meta_merge ?with_univs nextclenv.evd clenv.evd;
      env = nextclenv.env } in
  (* unify the type of the template of [nextclenv] with the type of [mv] *)
  let clenv'' =
    clenv_unify ~flags CUMUL
      (clenv_term clenv' nextclenv.templtyp)
      (clenv_meta_type clenv' mv)
      clenv' in
  (* assign the metavar *)
  let clenv''' =
    clenv_assign mv (clenv_term clenv' nextclenv.templval) clenv''
  in
  clenv'''

(***************************************************************)
(* Bindings *)

type arg_bindings = constr explicit_bindings

(* [clenv_independent clenv]
 * returns a list of metavariables which appear in the term cval,
 * and which are not dependent.  That is, they do not appear in
 * the types of other metavars which are in cval, nor in the type
 * of cval, ctyp. *)

let clenv_independent clenv =
  let mvs = collect_metas clenv.evd (clenv_value clenv) in
  let ctyp_mvs = (mk_freelisted (clenv_type clenv)).freemetas in
  let deps = Metaset.union (dependent_in_type_of_metas clenv mvs) ctyp_mvs in
  List.filter (fun mv -> not (Metaset.mem mv deps)) mvs

let qhyp_eq h1 h2 = match h1, h2 with
| NamedHyp n1, NamedHyp n2 -> Id.equal n1 n2
| AnonHyp i1, AnonHyp i2 -> Int.equal i1 i2
| _ -> false

let check_bindings bl =
  match List.duplicates qhyp_eq (List.map (fun {CAst.v=x} -> fst x) bl) with
    | NamedHyp s :: _ ->
        user_err 
          (str "The variable " ++ Id.print s ++
           str " occurs more than once in binding list.");
    | AnonHyp n :: _ ->
        user_err 
          (str "The position " ++ int n ++
           str " occurs more than once in binding list.")
    | [] -> ()

let explain_no_such_bound_variable evd id =
  let fold l (n, clb) =
    let na = match clb with
    | Cltyp (na, _) -> na
    | Clval (na, _, _) -> na
    in
    if na != Anonymous then Name.get_id na :: l else l
  in
  let mvl = List.fold_left fold [] (Evd.meta_list evd) in
  user_err ~hdr:"Evd.meta_with_name"
    (str"No such bound variable " ++ Id.print id ++
     (if mvl == [] then str " (no bound variables at all in the expression)."
      else
        (str" (possible name" ++
         str (if List.length mvl == 1 then " is: " else "s are: ") ++
         pr_enum Id.print mvl ++ str").")))

let meta_with_name evd id =
  let na = Name id in
  let fold (l1, l2 as l) (n, clb) =
    let (na',def) = match clb with
    | Cltyp (na, _) -> (na, false)
    | Clval (na, _, _) -> (na, true)
    in
    if Name.equal na na' then if def then (n::l1,l2) else (n::l1,n::l2)
    else l
  in
  let (mvl, mvnodef) = List.fold_left fold ([], []) (Evd.meta_list evd) in
  match mvnodef, mvl with
    | _,[]  ->
      explain_no_such_bound_variable evd id
    | ([n],_|_,[n]) ->
        n
    | _  ->
        user_err ~hdr:"Evd.meta_with_name"
          (str "Binder name \"" ++ Id.print id ++
           strbrk "\" occurs more than once in clause.")

let meta_of_binder clause loc mvs = function
  | NamedHyp s -> meta_with_name clause.evd s
  | AnonHyp n ->
      try List.nth mvs (n-1)
      with (Failure _|Invalid_argument _) ->
        user_err  (str "No such binder.")

let error_already_defined b =
  match b with
    | NamedHyp id ->
        user_err 
          (str "Binder name \"" ++ Id.print id ++
           str"\" already defined with incompatible value.")
    | AnonHyp n ->
        anomaly
          (str "Position " ++ int n ++ str" already defined.")

let clenv_unify_binding_type clenv c t u =
  if isMeta clenv.evd (fst (decompose_app_vect clenv.evd (whd_nored clenv.evd u))) then
    (* Not enough information to know if some subtyping is needed *)
    CoerceToType, clenv, c
  else
    (* Enough information so as to try a coercion now *)
    try
      let evd,c = w_coerce_to_type (cl_env clenv) clenv.evd c t u in
      TypeProcessed, { clenv with evd = evd }, c
    with 
      | PretypeError (_,_,ActualTypeNotCoercible (_,_,
          (NotClean _ | ConversionFailed _))) as e ->
          raise e
      | e when precatchable_exception e ->
          TypeNotProcessed, clenv, c

let clenv_assign_binding clenv k c =
  let k_typ = clenv_hnf_constr clenv (clenv_meta_type clenv k) in
  let c_typ = nf_betaiota clenv.env clenv.evd (clenv_get_type_of clenv c) in
  let status,clenv',c = clenv_unify_binding_type clenv c c_typ k_typ in
  { clenv' with evd = meta_assign k (c,(Conv,status)) clenv'.evd }

let clenv_match_args bl clenv =
  if List.is_empty bl then
    clenv
  else
    let mvs = clenv_independent clenv in
    check_bindings bl;
    List.fold_left
      (fun clenv {CAst.loc;v=(b,c)} ->
        let k = meta_of_binder clenv loc mvs b in
        if meta_defined clenv.evd k then
          if EConstr.eq_constr clenv.evd (fst (meta_fvalue clenv.evd k)).rebus c then clenv
          else error_already_defined b
        else
          clenv_assign_binding clenv k c)
      clenv bl

exception NoSuchBinding

let clenv_constrain_last_binding c clenv =
  let all_mvs = collect_metas clenv.evd clenv.templval.rebus in
  let k = try List.last all_mvs with Failure _ -> raise NoSuchBinding in
  clenv_assign_binding clenv k c

let error_not_right_number_missing_arguments n =
  user_err 
    (strbrk "Not the right number of missing arguments (expected " ++
      int n ++ str ").")

let clenv_constrain_dep_args hyps_only bl clenv =
  if List.is_empty bl then
    clenv
  else
    let occlist = clenv_dependent_gen hyps_only clenv in
    if Int.equal (List.length occlist) (List.length bl) then
      List.fold_left2 clenv_assign_binding clenv occlist bl
    else
      if hyps_only then
        (* Tolerance for compatibility <= 8.3 *)
        let occlist' = clenv_dependent_gen hyps_only ~iter:false clenv in
        if Int.equal (List.length occlist') (List.length bl) then
          List.fold_left2 clenv_assign_binding clenv occlist' bl
        else
          error_not_right_number_missing_arguments (List.length occlist)
      else
        error_not_right_number_missing_arguments (List.length occlist)

(****************************************************************)
(* Clausal environment for an application *)

let make_clenv_binding_gen hyps_only n env sigma (c,t) = function
  | ImplicitBindings largs ->
      let clause = mk_clenv_from_env env sigma n (c,t) in
      clenv_constrain_dep_args hyps_only largs clause
  | ExplicitBindings lbind ->
      let t = rename_bound_vars_as_displayed sigma Id.Set.empty [] t in
      let clause = mk_clenv_from_env env sigma n
        (c, t)
      in clenv_match_args lbind clause
  | NoBindings ->
      mk_clenv_from_env env sigma n (c,t)

let make_clenv_binding_env_apply env sigma n =
  make_clenv_binding_gen true n env sigma

let make_clenv_binding_env env sigma =
  make_clenv_binding_gen false None env sigma
        
let make_clenv_binding_apply env sigma n = make_clenv_binding_gen true n env sigma
let make_clenv_binding env sigma = make_clenv_binding_gen false None env sigma

(****************************************************************)
(* Pretty-print *)

let pr_clenv clenv =
  h 0
    (str"TEMPL: " ++ Termops.Internal.print_constr_env clenv.env clenv.evd clenv.templval.rebus ++
     str" : " ++ Termops.Internal.print_constr_env clenv.env clenv.evd clenv.templtyp.rebus ++ fnl () ++
     pr_evar_map (Some 2) clenv.env clenv.evd)

(****************************************************************)
(** Evar version of mk_clenv *)

type hole = {
  hole_evar : EConstr.constr;
  hole_type : EConstr.types;
  hole_deps  : bool;
  hole_name : Name.t;
}

type clause = {
  cl_holes : hole list;
  cl_concl : EConstr.types;
}

let make_evar_clause env sigma ?len t =
  let open EConstr in
  let open Vars in
  let bound = match len with
  | None -> -1
  | Some n -> assert (0 <= n); n
  in
  (* FIXME: do the renaming online *)
  let t = rename_bound_vars_as_displayed sigma Id.Set.empty [] t in
  let rec clrec (sigma, holes) inst n t =
    if n = 0 then (sigma, holes, t)
    else match EConstr.kind sigma t with
    | Cast (t, _, _) -> clrec (sigma, holes) inst n t
    | Prod (na, t1, t2) ->
      (* Share the evar instances as we are living in the same context *)
      let inst, ctx, args, subst = match inst with
      | None ->
        (* Dummy type *)
        let ctx, _, args, subst = push_rel_context_to_named_context env sigma mkProp in
        Some (ctx, args, subst), ctx, args, subst
      | Some (ctx, args, subst) -> inst, ctx, args, subst
      in
      let (sigma, ev) = new_evar_instance ~typeclass_candidate:false ctx sigma (csubst_subst subst t1) args in
      let dep = not (noccurn sigma 1 t2) in
      let hole = {
        hole_evar = ev;
        hole_type = t1;
        hole_deps = dep;
        (* We fix it later *)
        hole_name = na.binder_name;
      } in
      let t2 = if dep then subst1 ev t2 else t2 in
      clrec (sigma, hole :: holes) inst (pred n) t2
    | LetIn (na, b, _, t) -> clrec (sigma, holes) inst n (subst1 b t)
    | _ -> (sigma, holes, t)
  in
  let (sigma, holes, t) = clrec (sigma, []) None bound t in
  let holes = List.rev holes in
  let clause = { cl_concl = t; cl_holes = holes } in
  (sigma, clause)

let explain_no_such_bound_variable holes id =
  let fold h accu = match h.hole_name with
  | Anonymous -> accu
  | Name id -> id :: accu
  in
  let mvl = List.fold_right fold holes [] in
  let expl = match mvl with
  | [] -> str " (no bound variables at all in the expression)."
  | [id] -> str "(possible name is: " ++ Id.print id ++ str ")."
  | _ -> str "(possible names are: " ++ pr_enum Id.print mvl ++ str ")."
  in
  user_err  (str "No such bound variable " ++ Id.print id ++ expl)

let evar_with_name holes id =
  let map h = match h.hole_name with
  | Anonymous -> None
  | Name id' -> if Id.equal id id' then Some h else None
  in
  let hole = List.map_filter map holes in
  match hole with
  | [] -> explain_no_such_bound_variable holes id
  | [h] -> h.hole_evar
  | _ ->
    user_err 
      (str "Binder name \"" ++ Id.print id ++
        str "\" occurs more than once in clause.")

let evar_of_binder holes = function
| NamedHyp s -> evar_with_name holes s
| AnonHyp n ->
  try
    let nondeps = List.filter (fun hole -> not hole.hole_deps) holes in
    let h = List.nth nondeps (pred n) in
    h.hole_evar
  with e when CErrors.noncritical e ->
    user_err  (str "No such binder.")

let define_with_type sigma env ev c =
  let open EConstr in
  let t = Retyping.get_type_of env sigma ev in
  let ty = Retyping.get_type_of env sigma c in
  let j = Environ.make_judge c ty in
  let (sigma, j) = Coercion.inh_conv_coerce_to ~program_mode:false true env sigma j t in
  let (ev, _) = destEvar sigma ev in
  let sigma = Evd.define ev j.Environ.uj_val sigma in
  sigma

let solve_evar_clause env sigma hyp_only clause = function
| NoBindings -> sigma
| ImplicitBindings largs ->
  let open EConstr in
  let fold holes h =
    if h.hole_deps then
      (* Some subsequent term uses the hole *)
      let (ev, _) = destEvar sigma h.hole_evar in
      let is_dep hole = occur_evar sigma ev hole.hole_type in
      let in_hyp = List.exists is_dep holes in
      let in_ccl = occur_evar sigma ev clause.cl_concl in
      let dep = if hyp_only then in_hyp && not in_ccl else in_hyp || in_ccl in
      let h = { h with hole_deps = dep } in
      h :: holes
    else
      (* The hole does not occur anywhere *)
      h :: holes
  in
  let holes = List.fold_left fold [] (List.rev clause.cl_holes) in
  let map h = if h.hole_deps then Some h.hole_evar else None in
  let evs = List.map_filter map holes in
  let len = List.length evs in
  if Int.equal len (List.length largs) then
    let fold sigma ev arg = define_with_type sigma env ev arg in
    let sigma = List.fold_left2 fold sigma evs largs in
    sigma
  else
    error_not_right_number_missing_arguments len
| ExplicitBindings lbind ->
  let () = check_bindings lbind in
  let fold sigma {CAst.v=(binder, c)} =
    let ev = evar_of_binder clause.cl_holes binder in
    define_with_type sigma env ev c
  in
  let sigma = List.fold_left fold sigma lbind in
  sigma
proofs/clenv.ml

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