Nim/compiler/semdestruct.nim

#
#
#           The Nim Compiler
#        (c) Copyright 2013 Andreas Rumpf
#
#    See the file "copying.txt", included in this
#    distribution, for details about the copyright.
#

## This module implements destructors.

# included from sem.nim

# special marker values that indicates that we are
# 1) AnalyzingDestructor: currently analyzing the type for destructor
# generation (needed for recursive types)
# 2) DestructorIsTrivial: completed the analysis before and determined
# that the type has a trivial destructor
var analyzingDestructor, destructorIsTrivial: PSym
new(analyzingDestructor)
new(destructorIsTrivial)

var
  destructorName = getIdent"destroy_"
  destructorParam = getIdent"this_"
  destructorPragma = newIdentNode(getIdent"destructor", unknownLineInfo())

proc instantiateDestructor(c: PContext, typ: PType): PType

proc doDestructorStuff(c: PContext, s: PSym, n: PNode) =
  var t = s.typ.sons[1].skipTypes({tyVar})
  if t.kind == tyGenericInvocation:
    for i in 1 .. <t.sonsLen:
      if t.sons[i].kind != tyGenericParam:
        localError(n.info, errDestructorNotGenericEnough)
        return
    t = t.base
  elif t.kind == tyCompositeTypeClass:
    t = t.base
    if t.kind != tyGenericBody:
      localError(n.info, errDestructorNotGenericEnough)
      return

  t.destructor = s
  # automatically insert calls to base classes' destructors
  if n.sons[bodyPos].kind != nkEmpty:
    for i in countup(0, t.sonsLen - 1):
      # when inheriting directly from object
      # there will be a single nil son
      if t.sons[i] == nil: continue
      let destructableT = instantiateDestructor(c, t.sons[i])
      if destructableT != nil:
        n.sons[bodyPos].addSon(newNode(nkCall, t.sym.info, @[
            useSym(destructableT.destructor, c.graph.usageSym),
            n.sons[paramsPos][1][0]]))

proc destroyFieldOrFields(c: PContext, field: PNode, holder: PNode): PNode

proc destroySym(c: PContext, field: PSym, holder: PNode): PNode =
  let destructableT = instantiateDestructor(c, field.typ)
  if destructableT != nil:
    result = newNode(nkCall, field.info, @[
      useSym(destructableT.destructor, c.graph.usageSym),
      newNode(nkDotExpr, field.info, @[holder, useSym(field, c.graph.usageSym)])])

proc destroyCase(c: PContext, n: PNode, holder: PNode): PNode =
  var nonTrivialFields = 0
  result = newNode(nkCaseStmt, n.info, @[])
  # case x.kind
  result.addSon(newNode(nkDotExpr, n.info, @[holder, n.sons[0]]))
  for i in countup(1, n.len - 1):
    # of A, B:
    let ni = n[i]
    var caseBranch = newNode(ni.kind, ni.info, ni.sons[0..ni.len-2])

    let stmt = destroyFieldOrFields(c, ni.lastSon, holder)
    if stmt == nil:
      caseBranch.addSon(newNode(nkStmtList, ni.info, @[]))
    else:
      caseBranch.addSon(stmt)
      nonTrivialFields += stmt.len

    result.addSon(caseBranch)

  # maybe no fields were destroyed?
  if nonTrivialFields == 0:
    result = nil

proc destroyFieldOrFields(c: PContext, field: PNode, holder: PNode): PNode =
  template maybeAddLine(e) =
    let stmt = e
    if stmt != nil:
      if result == nil: result = newNode(nkStmtList)
      result.addSon(stmt)

  case field.kind
  of nkRecCase:
    maybeAddLine destroyCase(c, field, holder)
  of nkSym:
    maybeAddLine destroySym(c, field.sym, holder)
  of nkRecList:
    for son in field:
      maybeAddLine destroyFieldOrFields(c, son, holder)
  else:
    internalAssert false

proc generateDestructor(c: PContext, t: PType): PNode =
  ## generate a destructor for a user-defined object or tuple type
  ## returns nil if the destructor turns out to be trivial

  # XXX: This may be true for some C-imported types such as
  # Tposix_spawnattr
  if t.n == nil or t.n.sons == nil: return
  internalAssert t.n.kind == nkRecList
  let destructedObj = newIdentNode(destructorParam, unknownLineInfo())
  # call the destructods of all fields
  result = destroyFieldOrFields(c, t.n, destructedObj)
  # base classes' destructors will be automatically called by
  # semProcAux for both auto-generated and user-defined destructors

proc instantiateDestructor(c: PContext, typ: PType): PType =
  # returns nil if a variable of type `typ` doesn't require a
  # destructor. Otherwise, returns the type, which holds the
  # destructor that must be used for the varialbe.
  # The destructor is either user-defined or automatically
  # generated by the compiler in a member-wise fashion.
  var t = typ.skipGenericAlias
  let typeHoldingUserDefinition = if t.kind == tyGenericInst: t.base else: t

  if typeHoldingUserDefinition.destructor != nil:
    # XXX: This is not entirely correct for recursive types, but we need
    # it temporarily to hide the "destroy is already defined" problem
    if typeHoldingUserDefinition.destructor notin
        [analyzingDestructor, destructorIsTrivial]:
      return typeHoldingUserDefinition
    else:
      return nil

  t = t.skipTypes({tyGenericInst, tyAlias})
  case t.kind
  of tySequence, tyArray, tyOpenArray, tyVarargs:
    t.destructor = analyzingDestructor
    if instantiateDestructor(c, t.sons[0]) != nil:
      t.destructor = getCompilerProc"nimDestroyRange"
      return t
    else:
      return nil
  of tyTuple, tyObject:
    t.destructor = analyzingDestructor
    let generated = generateDestructor(c, t)
    if generated != nil:
      internalAssert t.sym != nil
      var i = t.sym.info
      let fullDef = newNode(nkProcDef, i, @[
        newIdentNode(destructorName, i),
        emptyNode,
        emptyNode,
        newNode(nkFormalParams, i, @[
          emptyNode,
          newNode(nkIdentDefs, i, @[
            newIdentNode(destructorParam, i),
            symNodeFromType(c, makeVarType(c, t), t.sym.info),
            emptyNode]),
          ]),
        newNode(nkPragma, i, @[destructorPragma]),
        emptyNode,
        generated
        ])
      let semantizedDef = semProc(c, fullDef)
      t.destructor = semantizedDef[namePos].sym
      return t
    else:
      t.destructor = destructorIsTrivial
      return nil
  else:
    return nil

proc createDestructorCall(c: PContext, s: PSym): PNode =
  let varTyp = s.typ
  if varTyp == nil or sfGlobal in s.flags: return
  let destructableT = instantiateDestructor(c, varTyp)
  if destructableT != nil:
    let call = semStmt(c, newNode(nkCall, s.info, @[
      useSym(destructableT.destructor, c.graph.usageSym),
      useSym(s, c.graph.usageSym)]))
    result = newNode(nkDefer, s.info, @[call])