catala/compiler/verification/io.ml

(* This file is part of the Catala compiler, a specification language for tax and social benefits
   computation rules. Copyright (C) 2022 Inria, contributor: Aymeric Fromherz
   <aymeric.fromherz@inria.fr>

   Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
   in compliance with the License. You may obtain a copy of the License at

   http://www.apache.org/licenses/LICENSE-2.0

   Unless required by applicable law or agreed to in writing, software distributed under the License
   is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
   or implied. See the License for the specific language governing permissions and limitations under
   the License. *)

open Utils
open Dcalc.Ast

module type Backend = sig
  type backend_context

  type vc_encoding

  val print_encoding : vc_encoding -> string

  type model

  type solver_result = ProvenTrue | ProvenFalse of model option | Unknown

  val solve_vc_encoding : backend_context -> vc_encoding -> solver_result

  val print_model : backend_context -> model -> string

  val is_model_empty : model -> bool
end

module SolverIO (B : Backend) = struct
  type vc_encoding_result = Success of B.vc_encoding * B.backend_context | Fail of string

  let print_positive_result (vc : Conditions.verification_condition) : string =
    match vc.Conditions.vc_kind with
    | Conditions.NoEmptyError ->
        Format.asprintf "%s This variable never returns an empty error"
          (Cli.print_with_style [ ANSITerminal.yellow ] "[%s.%s]"
             (Format.asprintf "%a" ScopeName.format_t vc.vc_scope)
             (Bindlib.name_of (Pos.unmark vc.vc_variable)))
    | Conditions.NoOverlappingExceptions ->
        Format.asprintf "%s No two exceptions to ever overlap for this variable"
          (Cli.print_with_style [ ANSITerminal.yellow ] "[%s.%s]"
             (Format.asprintf "%a" ScopeName.format_t vc.vc_scope)
             (Bindlib.name_of (Pos.unmark vc.vc_variable)))

  let print_negative_result (vc : Conditions.verification_condition) (ctx : B.backend_context)
      (model : B.model option) : string =
    let var_and_pos =
      match vc.Conditions.vc_kind with
      | Conditions.NoEmptyError ->
          Format.asprintf "%s This variable might return an empty error:\n%s"
            (Cli.print_with_style [ ANSITerminal.yellow ] "[%s.%s]"
               (Format.asprintf "%a" ScopeName.format_t vc.vc_scope)
               (Bindlib.name_of (Pos.unmark vc.vc_variable)))
            (Pos.retrieve_loc_text (Pos.get_position vc.vc_variable))
      | Conditions.NoOverlappingExceptions ->
          Format.asprintf "%s At least two exceptions overlap for this variable:\n%s"
            (Cli.print_with_style [ ANSITerminal.yellow ] "[%s.%s]"
               (Format.asprintf "%a" ScopeName.format_t vc.vc_scope)
               (Bindlib.name_of (Pos.unmark vc.vc_variable)))
            (Pos.retrieve_loc_text (Pos.get_position vc.vc_variable))
    in
    let counterexample : string option =
      match model with
      | None ->
          Some
            "The solver did not manage to generate a counterexample to explain the faulty behavior."
      | Some model ->
          if B.is_model_empty model then None
          else
            Some
              (Format.asprintf
                 "The solver generated the following counterexample to explain the faulty behavior:\n\
                  %s"
                 (B.print_model ctx model))
    in
    var_and_pos
    ^ match counterexample with None -> "" | Some counterexample -> "\n" ^ counterexample

  (** [encode_and_check_vc] spawns a new Z3 solver and tries to solve the expression [vc] **)
  let encode_and_check_vc (decl_ctx : decl_ctx)
      (vc : Conditions.verification_condition * vc_encoding_result) : unit =
    let vc, z3_vc = vc in

    Cli.debug_print
      (Format.asprintf "For this variable:\n%s\n"
         (Pos.retrieve_loc_text (Pos.get_position vc.Conditions.vc_guard)));
    Cli.debug_print
      (Format.asprintf "This verification condition was generated for %s:@\n%a"
         (Cli.print_with_style [ ANSITerminal.yellow ] "%s"
            (match vc.vc_kind with
            | Conditions.NoEmptyError -> "the variable definition never to return an empty error"
            | NoOverlappingExceptions -> "no two exceptions to ever overlap"))
         (Dcalc.Print.format_expr decl_ctx)
         vc.vc_guard);

    match z3_vc with
    | Success (encoding, backend_ctx) -> (
        Cli.debug_print
          (Format.asprintf "The translation to Z3 is the following:@\n%s"
             (B.print_encoding encoding));
        match B.solve_vc_encoding backend_ctx encoding with
        | ProvenTrue -> Cli.result_print (print_positive_result vc)
        | ProvenFalse model -> Cli.error_print (print_negative_result vc backend_ctx model)
        | Unknown -> failwith "The solver failed at proving or disproving the VC")
    | Fail msg -> Cli.error_print (Format.asprintf "The translation to Z3 failed:@\n%s" msg)
end