syntax: New escape block management

[nit.git] / src / syntax / control_flow.nit

# This file is part of NIT ( http://www.nitlanguage.org ).
#
# Copyright 2008 Jean Privat <jean@pryen.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.

# Analysis control flow in property bodies, statements and expressions
package control_flow

import syntax_base

redef class MMSrcModule
        # Walk trough the module and type statments and expressions
        # Require than supermodules are processed
        meth do_control_flow(tc: ToolContext)
        do
                var tv = new ControlFlowVisitor(tc, self)
                tv.visit(node)
        end
end

redef class Variable
        # Is the variable must be set before being used ?
        meth must_be_set: Bool do return false
end

redef class VarVariable
        redef meth must_be_set do return true
end



# Control flow visitor
# * Check reachability in methods
# * Associate breaks and continues
# * Check some other warning
private class ControlFlowVisitor
special AbsSyntaxVisitor
        redef meth visit(n)
        do
                if n != null then n.accept_control_flow(self)
        end

        # Number of nested once
        readable writable attr _once_count: Int = 0

        # Current knowledge about variables types
        readable writable attr _control_flow_ctx: ControlFlowContext

        meth check_is_set(n: PNode, v: Variable)
        do
                if v.must_be_set and not control_flow_ctx.is_set(v) then
                        error(n, "Error: variable '{v}' is possibly unset.")
                        var cfc = control_flow_ctx
                        while cfc != null do
                                print("cfc: " + cfc.set_variables.join(" "))
                                cfc = cfc.prev
                        end
                end
        end

        meth mark_is_set(v: Variable)
        do
                control_flow_ctx.set_variables.add(v)
        end

        init(tc, m) do super
end

private class ControlFlowContext
        # Previous control flow context if any
        readable attr _prev: ControlFlowContext

        # Is a control flow break met? (return, break, continue)
        readable writable attr _unreash: Bool = false

        # Is a control flow already broken?
        # Used to avoid repeating the same error message
        readable writable attr _already_unreash: Bool = false

        # Set of variable that are set (assigned)
        readable attr _set_variables: HashSet[Variable] = new HashSet[Variable]

        # Is a variable set?
        meth is_set(v: Variable): Bool
        do
                return _set_variables.has(v) or (_prev != null and _prev.is_set(v))
        end

        meth sub: ControlFlowContext
        do
                return new ControlFlowContext.with_prev(self)
        end

        init
        do 
        end

        init with_prev(p: ControlFlowContext)
        do
                _prev = p
                _unreash = p.unreash
                _already_unreash = p.already_unreash
        end
end

###############################################################################

redef class PNode
        private meth accept_control_flow(v: ControlFlowVisitor) 
        do
                accept_abs_syntax_visitor(v)
        end
end

redef class AMethPropdef
        redef meth accept_control_flow(v)
        do
                v.control_flow_ctx = new ControlFlowContext
                super
        end
end

redef class AConcreteMethPropdef
        redef meth accept_control_flow(v)
        do
                super
                if v.control_flow_ctx.unreash == false and method.signature.return_type != null then
                        v.error(self, "Control error: Reached end of function (a 'return' with a value was expected).")
                end
        end
end

redef class AVardeclExpr
        redef meth accept_control_flow(v)
        do
                super
                if n_expr != null then v.mark_is_set(variable)
        end
end

redef class ABlockExpr
        redef meth accept_control_flow(v)
        do
                for e in n_expr do
                        if v.control_flow_ctx.unreash and not v.control_flow_ctx.already_unreash then
                                v.control_flow_ctx.already_unreash = true
                                v.warning(e, "Warning: unreachable statement.")
                        end
                        v.visit(e)
                end
        end
end

redef class AReturnExpr
        redef meth accept_control_flow(v)
        do
                super
                v.control_flow_ctx.unreash = true
        end
end

redef class ABreakExpr
        redef meth accept_control_flow(v)
        do
                super
                v.control_flow_ctx.unreash = true
        end
end
redef class AContinueExpr
        redef meth accept_control_flow(v)
        do
                super
                v.control_flow_ctx.unreash = true
        end
end

redef class AAbortExpr
        redef meth accept_control_flow(v)
        do
                super
                v.control_flow_ctx.unreash = true
        end
end

redef class AClosureCallExpr
        redef meth accept_control_flow(v)
        do
                super
                if variable.closure.is_break then v.control_flow_ctx.unreash = true
        end
end

redef class AIfExpr
        redef meth accept_control_flow(v)
        do
                v.visit(n_expr)

                var old_control_flow_ctx = v.control_flow_ctx
                v.control_flow_ctx = v.control_flow_ctx.sub

                v.visit(n_then)

                if n_else == null then
                        # Restore control flow ctx since the 'then" block is optional
                        v.control_flow_ctx = old_control_flow_ctx
                else
                        # Remember what appens in the 'then'
                        var then_control_flow_ctx = v.control_flow_ctx
                        # Reset to execute the 'else'
                        v.control_flow_ctx = old_control_flow_ctx.sub

                        v.visit(n_else)

                        # Merge then and else in the old control_flow
                        old_control_flow_ctx.unreash = v.control_flow_ctx.unreash and then_control_flow_ctx.unreash

                        if v.control_flow_ctx.unreash then v.control_flow_ctx = then_control_flow_ctx
                        if then_control_flow_ctx.unreash then then_control_flow_ctx = v.control_flow_ctx
                        for variable in v.control_flow_ctx.set_variables do
                                if then_control_flow_ctx.is_set(variable) then
                                        old_control_flow_ctx.set_variables.add(variable)
                                end
                        end
                        v.control_flow_ctx = old_control_flow_ctx
                end
        end
end

class AControlableBlock
special PExpr
        redef meth accept_control_flow(v)
        do
                # Store old control flow values
                var old_control_flow_ctx = v.control_flow_ctx
                v.control_flow_ctx = v.control_flow_ctx.sub

                super

                # Check control flow if any
                check_control_flow(v)

                # Restore control flow value since all controlable blocks are optionnal
                v.control_flow_ctx = old_control_flow_ctx
        end

        private meth check_control_flow(v: ControlFlowVisitor) do end
end

redef class AWhileExpr
special AControlableBlock
end

redef class AForExpr
special AControlableBlock
end

redef class AVarExpr
        redef meth accept_control_flow(v)
        do
                super
                v.check_is_set(self, variable)
        end
end

redef class AVarAssignExpr
        redef meth accept_control_flow(v)
        do
                super
                v.mark_is_set(variable)
        end
end

redef class AVarReassignExpr
        redef meth accept_control_flow(v)
        do
                super
                v.check_is_set(self, variable)
                v.mark_is_set(variable)
        end
end

redef class AClosureDecl
        redef meth accept_control_flow(v)
        do
                if n_expr != null then
                        var old_control_flow_ctx = v.control_flow_ctx
                        v.control_flow_ctx = v.control_flow_ctx.sub

                        super

                        if v.control_flow_ctx.unreash == false then
                                if variable.closure.signature.return_type != null then
                                        v.error(self, "Control error: Reached end of bloc (a 'continue' with a value was expected).")
                                else if variable.closure.is_break then
                                        v.error(self, "Control error: Reached end of break bloc (an 'abort' was expected).")
                                end
                        end

                        v.control_flow_ctx = old_control_flow_ctx
                end
        end
end

redef class AClosureDef
special AControlableBlock
        redef meth accept_control_flow(v)
        do
                for va in variables do v.mark_is_set(va)
                super
        end

        redef meth check_control_flow(v)
        do
                if v.control_flow_ctx.unreash == false then
                        if closure.signature.return_type != null then
                                v.error(self, "Control error: Reached end of bloc (a 'continue' with a value was expected).")
                        else if closure.is_break then
                                v.error(self, "Control error: Reached end of break bloc (a 'break' was expected).")
                        end
                end
        end
end

redef class AOnceExpr
        redef meth accept_control_flow(v)
        do
                if v.once_count > 0 then
                        v.warning(self, "Useless once in a once expression.")
                end
                v.once_count = v.once_count + 1

                super

                v.once_count = v.once_count - 1
        end
end