Nim/compiler/semdestruct.nim

#
#
#           The Nimrod 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())
  rangeDestructorProc*: PSym

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 == tyGenericInvokation:
    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),
            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),
      newNode(nkDotExpr, field.info, @[holder, useSym(field)])])

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:
    var caseBranch = newNode(n[i].kind, n[i].info, n[i].sons[0 .. -2])
    
    let stmt = destroyFieldOrFields(c, n[i].lastSon, holder)
    if stmt == nil:
      caseBranch.addSon(newNode(nkStmtList, n[i].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: expr): stmt =
    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 = skipTypes(typ, {tyConst, tyMutable}).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})
  case t.kind
  of tySequence, tyArray, tyArrayConstr, tyOpenArray, tyVarargs:
    if instantiateDestructor(c, t.sons[0]) != nil:
      if rangeDestructorProc == nil:
        rangeDestructorProc = searchInScopes(c, getIdent"nimDestroyRange")
      t.destructor = rangeDestructorProc
      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 insertDestructors(c: PContext,
                       varSection: PNode): tuple[outer, inner: PNode] =
  # Accepts a var or let section.
  #
  # When a var section has variables with destructors
  # the var section is split up and finally blocks are inserted
  # immediately after all "destructable" vars
  #
  # In case there were no destrucable variables, the proc returns
  # (nil, nil) and the enclosing stmt-list requires no modifications.
  #
  # Otherwise, after the try blocks are created, the rest of the enclosing
  # stmt-list should be inserted in the most `inner` such block (corresponding
  # to the last variable).
  #
  # `outer` is a statement list that should replace the original var section.
  # It will include the new truncated var section followed by the outermost
  # try block.
  let totalVars = varSection.sonsLen
  for j in countup(0, totalVars - 1):
    let
      varId = varSection[j][0]
      varTyp = varId.sym.typ
      info = varId.info
    
    if varTyp == nil or sfGlobal in varId.sym.flags: continue
    let destructableT = instantiateDestructor(c, varTyp)
    
    if destructableT != nil:
      var tryStmt = newNodeI(nkTryStmt, info)

      if j < totalVars - 1:
        var remainingVars = newNodeI(varSection.kind, info)
        remainingVars.sons = varSection.sons[(j+1)..(-1)]
        let (outer, inner) = insertDestructors(c, remainingVars)
        if outer != nil:
          tryStmt.addSon(outer)
          result.inner = inner
        else:
          result.inner = newNodeI(nkStmtList, info)
          result.inner.addSon(remainingVars)
          tryStmt.addSon(result.inner)
      else:
        result.inner = newNodeI(nkStmtList, info)
        tryStmt.addSon(result.inner)
    
      tryStmt.addSon(
        newNode(nkFinally, info, @[
          semStmt(c, newNode(nkCall, info, @[
            useSym(destructableT.destructor),
            useSym(varId.sym)]))]))

      result.outer = newNodeI(nkStmtList, info)
      varSection.sons.setLen(j+1)
      result.outer.addSon(varSection)
      result.outer.addSon(tryStmt)

      return