contracts: Remove useless return parameter

[nit.git] / src / contracts.nit

# This file is part of NIT ( http://www.nitlanguage.org ).
#
# 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.

# Module to build contract
# This module provide extension of the modele to add contracts, the building phase and the "re-driving" to call the contract.
#
# FIXME Split the module in three parts: extension of the modele, building phase and the "re-driving"
module contracts

import parse_annotations
import phase
import semantize
intrude import model_contract
intrude import astbuilder
intrude import modelize_property
intrude import scope
intrude import typing

redef class ToolContext
        # Parses contracts annotations.
        var contracts_phase: Phase = new ContractsPhase(self, [modelize_property_phase,typing_phase])
end

private class ContractsPhase
        super Phase

        # The entry point of the contract phase
        # In reality, the contract phase is executed on each module
        # FIXME: Actually all method is checked to add method if any contract is inherited
        redef fun process_nmodule(nmodule)do
                # Check if the contracts are disabled
                if toolcontext.opt_no_contract.value then return
                nmodule.do_contracts(self.toolcontext)
        end
end

redef class AModule
        # Compile all contracts
        #
        # The implementation of the contracts is done in two visits.
        #
        # - First step, the visitor analyzes and constructs the contracts
        #   for each class (invariant) and method (expect, ensure).
        #
        # - Second step the visitor analyzes each `ASendExpr` to see
        #   if the callsite calls a method with a contract. If this is
        #       the case the callsite is replaced by another callsite to the contract method.
        fun do_contracts(toolcontext: ToolContext) do
                var ast_builder = new ASTBuilder(mmodule.as(not null))
                #
                var contract_visitor = new ContractsVisitor(toolcontext, toolcontext.modelbuilder.identified_modules.first, self, ast_builder)
                contract_visitor.enter_visit(self)
                #
                var callsite_visitor = new CallSiteVisitor(toolcontext, ast_builder)
                callsite_visitor.enter_visit(self)
        end
end

# Visitor to build all contracts.
private class ContractsVisitor
        super Visitor

        # Instance of the toolcontext
        var toolcontext: ToolContext

        # The main module
        # It's strore to define if the contract need to be build depending on the selected policy `--no-contract` `--full-contract` or default
        var mainmodule: MModule

        # Actual visited module
        var visited_module: AModule

        var ast_builder: ASTBuilder

        # The `ASignature` of the actual build contract
        var n_signature: ASignature is noinit

        # The `MSignature` of the actual build contract
        var m_signature: MSignature is noinit

        # The `current_location` can corresponding of the annotation or method location.
        var current_location: Location is noinit

        # Is the contrat is an introduction or not?
        # This attribute has the same value as the `is_intro` of the propdef attached to the contract.
        # Note : For MClassDef `is_intro_contract == false`. This is due to the fact that a method for checking invariants is systematically added to the root object class.
        var is_intro_contract: Bool is noinit

        # Actual visited class
        var visited_class: nullable AClassdef

        # is `no_contract` annotation was found
        var find_no_contract = false

        # The reference to the `in_contract` attribute.
        # This attribute is used to disable contract verification when you are already in a contract verification.
        # Keep the `in_contract` attribute to avoid searching at each contrat
        var in_contract_attribute: nullable MAttribute = null

        redef fun visit(node)
        do
                node.create_contracts(self)
                node.visit_all(self)
        end

        # Method use to define the signature part of the method `ASignature` and `MSignature`
        # The given `mcontract` provided `adapt_nsignature` and `adapt_msignature` to copy and adapt the given signature (`nsignature` and `msignature`)
        fun define_signature(mcontract: MContract, nsignature: nullable ASignature, msignature: nullable MSignature)
        do
                if nsignature != null and msignature != null then nsignature.ret_type = msignature.return_mtype
                self.n_signature = mcontract.adapt_nsignature(nsignature)
                self.m_signature = mcontract.adapt_msignature(msignature)
        end

        # Define the new contract take in consideration that an old contract exist or not
        private fun build_contract(n_annotation: AAnnotation, mcontract: MContract, mclassdef: MClassDef)
        do
                self.current_location = n_annotation.location
                # Retrieving the expression provided in the annotation
                var n_condition = n_annotation.construct_condition(self)
                var m_contractdef: AMethPropdef
                if is_intro_contract then
                        # Create new contract method
                        mcontract.create_intro_contract(self, n_condition, mclassdef)
                else
                        # Create a redef of contract to take in consideration the new condition
                        mcontract.create_subcontract(self, n_condition, mclassdef)
                end
        end

        # Verification if the construction of the contract is necessary.
        # Three cases are checked for `expect`:
        #
        # - Was the `--full-contract` option passed?
        # - Is the method is in the main package?
        # - Is the method is in a direct imported package?
        #
        fun check_usage_expect(actual_mmodule: MModule): Bool
        do
                var main_package = mainmodule.mpackage
                var actual_package = actual_mmodule.mpackage
                if main_package != null and actual_package != null then
                        var condition_direct_arc = toolcontext.modelbuilder.model.mpackage_importation_graph.has_arc(main_package, actual_package)
                        return toolcontext.opt_full_contract.value or condition_direct_arc or main_package == actual_package
                end
                return false
        end

        # Verification if the construction of the contract is necessary.
        # Two cases are checked for `ensure`:
        #
        # - Was the `--full-contract` option passed?
        # - Is the method is in the main package?
        #
        fun check_usage_ensure(actual_mmodule: MModule): Bool
        do
                return toolcontext.opt_full_contract.value or mainmodule.mpackage == actual_mmodule.mpackage
        end

        # Inject the incontract attribute (`_in_contract_`) in the `Sys` class
        # This attribute allows to check if the contract need to be executed
        private fun inject_incontract_in_sys
        do
                # If the `in_contract_attribute` already know just return
                if in_contract_attribute != null then return

                var sys_class = toolcontext.modelbuilder.get_mclass_by_name(visited_module, mainmodule, "Sys")

                # Try to get the `in_contract` property, if it has already defined in a previously visited module.
                var in_contract_property = toolcontext.modelbuilder.try_get_mproperty_by_name(visited_module, sys_class.intro, "__in_contract_")
                if in_contract_property != null then
                        self.in_contract_attribute = in_contract_property.as(MAttribute)
                        return
                end

                var bool_false = new AFalseExpr.make(mainmodule.bool_type)
                var n_in_contract_attribute = toolcontext.modelbuilder.create_attribute_from_name("__in_contract_", sys_class.intro, mainmodule.bool_type, public_visibility).create_setter(toolcontext.modelbuilder, true).define_default(bool_false)

                in_contract_attribute = n_in_contract_attribute.mpropdef.mproperty
        end

        # Return the `_in_contract_` attribute.
        # If the attribute `_in_contract_` does not exist it's injected with `inject_incontract_in_sys`
        private fun get_incontract: MAttribute
        do
                if self.in_contract_attribute == null then inject_incontract_in_sys
                return in_contract_attribute.as(not null)
        end

        # Return an `AIfExpr` with the contract encapsulated by an `if` to check if it's already in a contract verification.
        #
        # Example:
        # ~~~nitish
        # class A
        #       fun bar([...]) is except([...])
        #
        #       fun _contract_bar([...])
        #       do
        #               if not sys._in_contract_ then
        #                       sys._in_contract_ = true
        #                       _bar_expect([...])
        #                       sys._in_contract_ = false
        #               end
        #               bar([...])
        #       end
        #
        #       fun _bar_expect([...])
        # end
        # ~~~~
        #
        private fun encapsulated_contract_call(visited_method: AMethPropdef, call_to_contracts: Array[ACallExpr]): AIfExpr
        do
                var sys_property = toolcontext.modelbuilder.model.get_mproperties_by_name("sys").first.as(MMethod)
                var callsite_sys = ast_builder.create_callsite(toolcontext.modelbuilder, visited_method, sys_property, true)

                var incontract_attribute = get_incontract

                var callsite_get_incontract = ast_builder.create_callsite(toolcontext.modelbuilder, visited_method, incontract_attribute.getter.as(MMethod), false)
                var callsite_set_incontract = ast_builder.create_callsite(toolcontext.modelbuilder, visited_method, incontract_attribute.setter.as(MMethod), false)

                var n_condition = ast_builder.make_not(ast_builder.make_call(ast_builder.make_call(new ASelfExpr, callsite_sys, null), callsite_get_incontract, null))

                var n_if = ast_builder.make_if(n_condition, null)

                var if_then_block = n_if.n_then.as(ABlockExpr)

                if_then_block.add(ast_builder.make_call(ast_builder.make_call(new ASelfExpr, callsite_sys, null), callsite_set_incontract, [new ATrueExpr.make(mainmodule.bool_type)]))
                if_then_block.add_all(call_to_contracts)
                if_then_block.add(ast_builder.make_call(ast_builder.make_call(new ASelfExpr, callsite_sys, null), callsite_set_incontract, [new AFalseExpr.make(mainmodule.bool_type)]))

                return n_if
        end
end

# This visitor checks the `callsite` to see if the target `mpropdef` has a contract.
private class CallSiteVisitor
        super Visitor

        # Instance of the toolcontext
        var toolcontext: ToolContext

        var ast_builder: ASTBuilder

        # Actual visited method
        var visited_propdef: APropdef is noinit

        redef fun visit(node)
        do
                node.check_callsite(self)
                node.visit_all(self)
        end

        # Check if the callsite calls a method with a contract.
        # If it's the case the callsite is replaced by another callsite to the contract method.
        private fun drive_method_contract(callsite: CallSite): CallSite
        do
                var contract_facet = callsite.mproperty.mcontract_facet
                var visited_mpropdef = visited_propdef.mpropdef

                if visited_mpropdef isa MContract or visited_mpropdef isa MFacet then return callsite
                if visited_mpropdef == null or contract_facet == null then return callsite

                return ast_builder.create_callsite(toolcontext.modelbuilder, visited_propdef, contract_facet, callsite.recv_is_self)
        end
end

redef class ANode
        private fun create_contracts(v: ContractsVisitor) do end
        private fun check_callsite(v: CallSiteVisitor) do end
end

redef class AAnnotation

        # Returns the conditions of annotation parameters. If there are several parameters, the result is an `AAndExpr`
        # Example:
        # the contract `ensure(true, i == 10, f >= 1.0)`
        # return this condition `(true and i == 10 and f >= 1.0)`
        private fun construct_condition(v : ContractsVisitor): AExpr
        do
                var n_condition = n_args.first
                n_args.remove_at(0)
                for n_arg in n_args do n_condition = v.ast_builder.make_and(n_condition, n_arg)
                return n_condition
        end
end

redef class MContract

        # Define the name of the contract
        fun contract_name: String is abstract

        # Method use to diplay warning when the contract is not present at the introduction
        private fun no_intro_contract(v: ContractsVisitor, a: AAnnotation)do end

        # Creating specific inheritance block contract
        private fun create_nblock(v: ContractsVisitor, n_condition: AExpr, args: Array[AExpr]): ABlockExpr is abstract

        # Method to adapt the `n_mpropdef.n_block` to the contract
        private fun adapt_block_to_contract(v: ContractsVisitor, n_mpropdef: AMethPropdef) is abstract

        # Adapt the msignature specifically for the contract method
        private fun adapt_specific_msignature(m_signature: MSignature): MSignature do return m_signature.adapt_to_contract

        # Adapt the nsignature specifically for the contract method
        private fun adapt_specific_nsignature(n_signature: ASignature): ASignature do return n_signature.adapt_to_contract

        # Adapt the `m_signature` to the contract
        # If it is not null call the specific adapt `m_signature` for the contract
        private fun adapt_msignature(m_signature: nullable MSignature): MSignature
        do
                if m_signature == null then return new MSignature(new Array[MParameter])
                return adapt_specific_msignature(m_signature)
        end

        # Adapt the `n_signature` to the contract
        # If it is not null call the specific adapt `n_signature` for the contract
        private fun adapt_nsignature(n_signature: nullable ASignature): ASignature
        do
                if n_signature == null then return new ASignature
                return adapt_specific_nsignature(n_signature)
        end

        # Create a new empty contract
        private fun create_empty_contract(v: ContractsVisitor, mclassdef: MClassDef, msignature: nullable MSignature, n_signature: ASignature)
        do
                var n_contract_def = intro_mclassdef.mclass.create_empty_method(v, self, mclassdef, msignature, n_signature)
                n_contract_def.do_all(v.toolcontext)
        end

        # Create the initial contract (intro)
        # All contracts have the same implementation for the introduction.
        #
        # Example:
        # ~~~nitish
        # fun contrat([...])
        # do
        #       assert contract_condition
        # end
        # ~~~
        #
        private fun create_intro_contract(v: ContractsVisitor, n_condition: nullable AExpr, mclassdef: MClassDef)
        do
                var n_block = v.ast_builder.make_block
                if n_condition != null then
                        # Create a new tid to set the name of the assert for more explicit error
                        var tid = new TId.init_tk(self.location)
                        tid.text = "{self.contract_name}"
                        n_block.add v.ast_builder.make_assert(tid, n_condition, null)
                end
                make_contract(v, n_block, mclassdef)
        end

        # Create a contract with old (super) and the new conditions
        private fun create_subcontract(v: ContractsVisitor, ncondition: nullable AExpr, mclassdef: MClassDef)
        do
                var args = v.n_signature.make_parameter_read(v.ast_builder)
                var n_block = v.ast_builder.make_block
                if ncondition != null then n_block = self.create_nblock(v, ncondition, args)
                make_contract(v, n_block, mclassdef)
        end

        # Build a method with a specific block `n_block` in a specified `mclassdef`
        private fun make_contract(v: ContractsVisitor, n_block: AExpr, mclassdef: MClassDef)
        do
                var n_contractdef = intro_mclassdef.mclass.create_empty_method(v, self, mclassdef, v.m_signature, v.n_signature)
                n_contractdef.n_block = n_block
                # Define the location of the new method for corresponding of the annotation location
                n_contractdef.location = v.current_location
                n_contractdef.do_all(v.toolcontext)
        end
end

redef class MExpect

        # Define the name of the contract
        redef fun contract_name: String do return "expect"

        # Display warning if no contract is defined at introduction `expect`,
        # because if no contract is defined at the introduction the added
        # contracts will not cause any error even if they are not satisfied.
        #
        # Example:
        # ~~~nitish
        # class A
        #       fun bar [...]
        #       fun _bar_expect([...])
        #       do
        #               [empty contract]
        #       end
        # end
        #
        # redef class A
        #       redef fun bar is expect(contract_condition)
        #       redef fun _bar_expect([...])
        #       do
        #               if (contract_condition) then return
        #               super
        #       end
        # end
        # ~~~~
        #
        redef fun no_intro_contract(v: ContractsVisitor, a: AAnnotation)
        do
                v.toolcontext.warning(a.location,"","Useless contract: No contract defined at the introduction of the method")
        end

        redef fun create_nblock(v: ContractsVisitor, n_condition: AExpr, args: Array[AExpr]): ABlockExpr
        do
                # Creating the if expression with the new condition
                var if_block = v.ast_builder.make_if(n_condition, n_condition.mtype)
                # Creating and adding return expr to the then case
                if_block.n_then = v.ast_builder.make_return(null)
                # Creating the super call to the contract and adding this to else case
                if_block.n_else = v.ast_builder.make_super_call(args,null)
                var n_block = v.ast_builder.make_block
                n_block.add if_block
                return n_block
        end

        redef fun adapt_block_to_contract(v: ContractsVisitor, n_mpropdef: AMethPropdef)
        do
                var callsite = v.ast_builder.create_callsite(v.toolcontext.modelbuilder, n_mpropdef, self, true)
                var n_self = new ASelfExpr
                var args = n_mpropdef.n_signature.make_parameter_read(v.ast_builder)
                var n_callexpect = v.ast_builder.make_call(n_self,callsite,args)
                # Creation of the new instruction block with the call to expect condition
                var actual_expr = n_mpropdef.n_block
                var new_block = new ABlockExpr
                new_block.n_expr.push n_callexpect
                if actual_expr isa ABlockExpr then
                        new_block.n_expr.add_all(actual_expr.n_expr)
                else if actual_expr != null then
                        new_block.n_expr.push(actual_expr)
                end
                n_mpropdef.n_block = new_block
        end
end

redef class BottomMContract

        redef fun create_nblock(v: ContractsVisitor, n_condition: AExpr, args: Array[AExpr]): ABlockExpr
        do
                var tid = new TId.init_tk(v.current_location)
                tid.text = "{contract_name}"
                # Creating the assert expression with the new condition
                var assert_block = v.ast_builder.make_assert(tid,n_condition,null)
                # Creating the super call to the contract
                var super_call = v.ast_builder.make_super_call(args,null)
                # Define contract block
                var n_block = v.ast_builder.make_block
                # Adding the expressions to the block
                n_block.add super_call
                n_block.add assert_block
                return n_block
        end

        # Inject the `result` variable into the `n_block` of the given n_mpropdef`.
        #
        # The purpose of the variable is to capture return values to use it in contracts.
        private fun inject_result(v: ContractsVisitor, n_mpropdef: AMethPropdef, ret_type: MType): Variable
        do
                var actual_block = n_mpropdef.n_block
                # never happen. If it's the case the problem is in the contract facet building
                assert actual_block isa ABlockExpr

                var return_var: nullable Variable = null

                var return_expr = actual_block.n_expr.last.as(AReturnExpr)

                var returned_expr = return_expr.n_expr
                # The return node has no returned expression
                assert returned_expr != null

                # Check if the result variable already exit
                if returned_expr isa AVarExpr then
                        if returned_expr.variable.name == "result" then
                                return_var = returned_expr.variable
                        end
                end

                return_var = new Variable("result")
                # Creating a new variable to keep the old return of the method
                var assign_result = v.ast_builder.make_var_assign(return_var, returned_expr)
                # Remove the actual return
                actual_block.n_expr.pop
                # Set the return type
                return_var.declared_type = ret_type
                # Adding the reading expr of result variable to the block
                actual_block.add assign_result
                # Expr to read the result variable
                var read_result = v.ast_builder.make_var_read(return_var, ret_type)
                # Definition of the new return
                return_expr = v.ast_builder.make_return(read_result)
                actual_block.add return_expr
                return return_var
        end
end

redef class MEnsure

        # Define the name of the contract
        redef fun contract_name: String do return "ensure"

        redef fun adapt_specific_msignature(m_signature: MSignature): MSignature
        do
                return m_signature.adapt_to_ensurecondition
        end

        redef fun adapt_specific_nsignature(n_signature: ASignature): ASignature
        do
                return n_signature.adapt_to_ensurecondition
        end

        redef fun adapt_block_to_contract(v: ContractsVisitor, n_mpropdef: AMethPropdef)
        do
                var callsite = v.ast_builder.create_callsite(v.toolcontext.modelbuilder, n_mpropdef, self, true)
                var n_self = new ASelfExpr
                # argument to call the contract method
                var args = n_mpropdef.n_signature.make_parameter_read(v.ast_builder)
                # Inject the variable result
                # The cast is always safe because the online adapted method is the contract facet

                var actual_block = n_mpropdef.n_block
                # never happen. If it's the case the problem is in the contract facet building
                assert actual_block isa ABlockExpr

                var ret_type = n_mpropdef.mpropdef.mproperty.intro.msignature.return_mtype
                if ret_type != null then
                        var result_var = inject_result(v, n_mpropdef, ret_type)
                        # Expr to read the result variable
                        var read_result = v.ast_builder.make_var_read(result_var, ret_type)
                        var return_expr = actual_block.n_expr.pop
                        # Adding the read return to argument
                        args.add(read_result)
                        var n_callcontract = v.ast_builder.make_call(n_self,callsite,args)
                        actual_block.add_all([n_callcontract,return_expr])
                else
                        # build the call to the contract method
                        var n_callcontract = v.ast_builder.make_call(n_self,callsite,args)
                        actual_block.add n_callcontract
                end
        end
end

redef class MClass

        # This method create an abstract method representation with this MMethodDef an this AMethoddef
        private fun create_abstract_method(v: ContractsVisitor, mproperty: MMethod, mclassdef: MClassDef, msignature: nullable MSignature, n_signature: ASignature): AMethPropdef
        do
                # new methoddef definition
                var m_def = new MMethodDef(mclassdef, mproperty, v.current_location)
                # set the signature
                if msignature != null then m_def.msignature = msignature.clone
                # set the abstract flag
                m_def.is_abstract = true
                # Build the new node method
                var n_def = v.ast_builder.make_method(null,null,m_def,n_signature,null,null,null,null)
                # Define the location of the new method for corresponding of the actual method
                n_def.location = v.current_location
                # Association new npropdef to mpropdef
                v.toolcontext.modelbuilder.unsafe_add_mpropdef2npropdef(m_def,n_def)
                return n_def
        end

        # Create method with an empty block
        # the `mproperty` i.e the global property definition. The mclassdef to set where the method is declared and it's model `msignature` and ast `n_signature` signature
        private fun create_empty_method(v: ContractsVisitor, mproperty: MMethod, mclassdef: MClassDef, msignature: nullable MSignature, n_signature: ASignature): AMethPropdef
        do
                var n_def = create_abstract_method(v, mproperty, mclassdef, msignature, n_signature)
                n_def.mpropdef.is_abstract = false
                n_def.n_block = v.ast_builder.make_block
                return n_def
        end
end

redef class MMethodDef

        # Verification of the contract facet
        # Check if a contract facet already exists to use it again or if it is necessary to create it.
        private fun check_contract_facet(v: ContractsVisitor, n_signature: ASignature, classdef: MClassDef, mcontract: MContract, exist_contract: Bool)
        do
                var exist_contract_facet = mproperty.has_contract_facet
                if exist_contract_facet and exist_contract then return

                var contract_facet: AMethPropdef
                if not exist_contract_facet then
                        # If has no contract facet in intro just create it
                        if classdef != mproperty.intro_mclassdef then create_contract_facet(v, mproperty.intro_mclassdef, n_signature)
                        # If has no contract facet just create it
                        contract_facet = create_contract_facet(v, classdef, n_signature)
                else
                        # Check if the contract facet already exist in this context (in this classdef)
                        if classdef.mpropdefs_by_property.has_key(mproperty.mcontract_facet) then
                                # get the define
                                contract_facet = v.toolcontext.modelbuilder.mpropdef2node(classdef.mpropdefs_by_property[mproperty.mcontract_facet]).as(AMethPropdef)
                        else
                                # create a new contract facet definition
                                contract_facet = create_contract_facet(v, classdef, n_signature)
                                var block = v.ast_builder.make_block
                                # super call to the contract facet
                                var n_super_call = v.ast_builder.make_super_call(n_signature.make_parameter_read(v.ast_builder), null)
                                # verification for add a return or not
                                if contract_facet.mpropdef.msignature.return_mtype != null then
                                        block.add(v.ast_builder.make_return(n_super_call))
                                else
                                        block.add(n_super_call)
                                end
                                contract_facet.n_block = block
                        end
                end
                contract_facet.adapt_block_to_contract(v, mcontract, contract_facet)
                contract_facet.location = v.current_location
                contract_facet.do_all(v.toolcontext)
        end

        # Method to create a contract facet of the method
        private fun create_contract_facet(v: ContractsVisitor, classdef: MClassDef, n_signature: ASignature): AMethPropdef
        do
                var contract_facet = mproperty.build_contract_facet
                # Defines the contract phase is an init or not
                # it is necessary to use the contracts on constructor
                contract_facet.is_init = self.mproperty.is_init

                # check if the method has an `msignature` to copy it.
                var m_signature: nullable MSignature = null
                if mproperty.intro.msignature != null then m_signature = mproperty.intro.msignature.clone

                var n_contractdef = classdef.mclass.create_empty_method(v, contract_facet, classdef, m_signature, n_signature)
                # FIXME set the location because the callsite creation need the node location
                n_contractdef.location = v.current_location
                n_contractdef.validate

                var block = v.ast_builder.make_block
                var n_self = new ASelfExpr
                var args = n_contractdef.n_signature.make_parameter_read(v.ast_builder)
                var callsite = v.ast_builder.create_callsite(v.toolcontext.modelbuilder, n_contractdef, mproperty, true)
                var n_call = v.ast_builder.make_call(n_self, callsite, args)

                if m_signature.return_mtype == null then
                        block.add(n_call)
                else
                        block.add(v.ast_builder.make_return(n_call))
                end

                n_contractdef.n_block = block
                n_contractdef.do_all(v.toolcontext)
                return n_contractdef
        end

        # Entry point to build contract (define the contract facet and define the contract method verification)
        private fun construct_contract(v: ContractsVisitor, n_signature: ASignature, n_annotation: AAnnotation, mcontract: MContract, exist_contract: Bool)
        do
                if check_same_contract(v, n_annotation, mcontract) then return
                if not exist_contract and not is_intro then no_intro_contract(v, n_signature, mcontract, n_annotation)
                v.define_signature(mcontract, n_signature, mproperty.intro.msignature)

                v.build_contract(n_annotation, mcontract, mclassdef)
                check_contract_facet(v, n_signature.clone, mclassdef, mcontract, exist_contract)
                has_contract = true
        end

        # Create a contract on the introduction classdef of the property.
        # Display an warning message if necessary
        private fun no_intro_contract(v: ContractsVisitor, n_signature: ASignature, mcontract: MContract, n_annotation: AAnnotation)
        do
                mcontract.create_empty_contract(v, mcontract.intro_mclassdef, mcontract.adapt_msignature(self.mproperty.intro.msignature), mcontract.adapt_nsignature(n_signature))
                mcontract.no_intro_contract(v, n_annotation)
                mproperty.intro.has_contract = true
        end

        # Is the contract already defined in the context
        #
        # Exemple :
        # fun foo is expect([...]), expect([...])
        #
        # Here `check_same_contract` display an error when the second expect is processed
        private fun check_same_contract(v: ContractsVisitor, n_annotation: AAnnotation ,mcontract: MContract): Bool
        do
                if self.mclassdef.mpropdefs_by_property.has_key(mcontract) then
                        v.toolcontext.error(n_annotation.location, "The method already has a defined `{mcontract.contract_name}` contract at line {self.mclassdef.mpropdefs_by_property[mcontract].location.line_start}")
                        return true
                end
                return false
        end
end

redef class MPropDef
        # flag to indicate is the `MPropDef` has a contract
        var has_contract = false
end

redef class APropdef
        redef fun check_callsite(v)
        do
                v.visited_propdef = self
        end
end

redef class AMethPropdef

        # Entry point to create a contract (verification of inheritance, or new contract).
        redef fun create_contracts(v)
        do
                v.ast_builder.check_mmodule(mpropdef.mclassdef.mmodule)

                v.current_location = self.location
                v.is_intro_contract = mpropdef.is_intro

                if n_annotations != null then
                        for n_annotation in n_annotations.n_items do
                                check_annotation(v,n_annotation)
                        end
                end

                if not mpropdef.is_intro and not v.find_no_contract then
                        self.check_redef(v)
                end

                # reset the flag
                v.find_no_contract = false
        end

        # Verification of the annotation to know if it is a contract annotation.
        # If this is the case, we built the appropriate contract.
        private fun check_annotation(v: ContractsVisitor, n_annotation: AAnnotation)
        do
                if n_annotation.name == "expect" then
                        if not v.check_usage_expect(mpropdef.mclassdef.mmodule) then return
                        var exist_contract = mpropdef.mproperty.has_expect
                        mpropdef.construct_contract(v, self.n_signature.as(not null), n_annotation, mpropdef.mproperty.build_expect, exist_contract)
                else if n_annotation.name == "ensure" then
                        if not v.check_usage_ensure(mpropdef.mclassdef.mmodule) then return
                        var exist_contract = mpropdef.mproperty.has_ensure
                        mpropdef.construct_contract(v, self.n_signature.as(not null), n_annotation, mpropdef.mproperty.build_ensure, exist_contract)
                else if n_annotation.name == "no_contract" then
                        # no_contract found set the flag to true
                        v.find_no_contract = true
                end
        end

        # Verification if the method have an inherited contract to apply it.
        private fun check_redef(v: ContractsVisitor)
        do
                # Check if the method has an attached contract
                if not mpropdef.has_contract then
                        if mpropdef.mproperty.intro.has_contract then
                                mpropdef.has_contract = true
                        end
                end
        end

        # Adapt the block to use the contracts
        private fun adapt_block_to_contract(v: ContractsVisitor, contract: MContract, n_mpropdef: AMethPropdef)
        do
                contract.adapt_block_to_contract(v, n_mpropdef)
                mpropdef.has_contract = true
                n_mpropdef.do_all(v.toolcontext)
        end
end

redef class MSignature

        # Adapt signature for an contract
        #
        # The returned `MSignature` is the copy of `self` without return type.
        private fun adapt_to_contract: MSignature do return new MSignature(mparameters.to_a, null)

        # Adapt signature for a ensure contract
        #
        # The returned `MSignature` is the copy of `self` without return type.
        # The return type is replaced by a new parameter `result`
        private fun adapt_to_ensurecondition: MSignature
        do
                var rtype = return_mtype
                var msignature = adapt_to_contract
                if rtype != null then
                        msignature.mparameters.add(new MParameter("result", rtype, false))
                end
                return msignature
        end

        # The returned `MSignature` is the exact copy of `self`.
        private fun clone: MSignature do return new MSignature(mparameters.to_a, return_mtype)
end

redef class ASignature

        # Create an array of AVarExpr representing the read of every parameters
        private fun make_parameter_read(ast_builder: ASTBuilder): Array[AVarExpr]
        do
                var args = new Array[AVarExpr]
                for n_param in self.n_params do
                        var mtype = n_param.variable.declared_type
                        var variable = n_param.variable
                        if variable != null and mtype != null then
                                args.push ast_builder.make_var_read(variable, mtype)
                        end
                end
                return args
        end

        # Create a new ASignature adapted for contract
        #
        # The returned `ASignature` is the copy of `self` without return type.
        private fun adapt_to_contract: ASignature
        do
                var adapt_nsignature = self.clone
                if adapt_nsignature.n_type != null then adapt_nsignature.n_type.detach
                return adapt_nsignature
        end

        # Create a new ASignature adapted for ensure
        #
        # The returned `ASignature` is the copy of `self` without return type.
        # The return type is replaced by a new parameter `result`
        private fun adapt_to_ensurecondition: ASignature do
                var nsignature = adapt_to_contract
                if ret_type != null then
                        var variable = new Variable("result")
                        variable.declared_type = ret_type
                        nsignature.n_params.add new AParam.make(variable, ret_type.create_ast_representation)
                end
                return nsignature
        end
end

redef class ASendExpr
        redef fun check_callsite(v)
        do
                var actual_callsite = callsite
                if actual_callsite != null then
                        callsite = v.drive_method_contract(actual_callsite)
                end
        end
end

redef class ANewExpr
        redef fun check_callsite(v)
        do
                var actual_callsite = callsite
                if actual_callsite != null then
                        callsite = v.drive_method_contract(actual_callsite)
                end
        end
end