Nim/compiler/semcall.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 semantic checking for calls.
# included from sem.nim

proc sameMethodDispatcher(a, b: PSym): bool =
  result = false
  if a.kind == skMethod and b.kind == skMethod:
    var aa = lastSon(a.ast)
    var bb = lastSon(b.ast)
    if aa.kind == nkSym and bb.kind == nkSym:
      if aa.sym == bb.sym:
        result = true
    else:
      discard
      # generics have no dispatcher yet, so we need to compare the method
      # names; however, the names are equal anyway because otherwise we
      # wouldn't even consider them to be overloaded. But even this does
      # not work reliably! See tmultim6 for an example:
      # method collide[T](a: TThing, b: TUnit[T]) is instantiated and not
      # method collide[T](a: TUnit[T], b: TThing)! This means we need to
      # *instantiate* every candidate! However, we don't keep more than 2-3
      # candidated around so we cannot implement that for now. So in order
      # to avoid subtle problems, the call remains ambiguous and needs to
      # be disambiguated by the programmer; this way the right generic is
      # instantiated.

proc determineType(c: PContext, s: PSym)

proc pickBestCandidate(c: PContext, headSymbol: PNode,
                       n, orig: PNode,
                       initialBinding: PNode,
                       filter: TSymKinds,
                       best, alt: var TCandidate,
                       errors: var CandidateErrors) =
  var o: TOverloadIter
  # thanks to the lazy semchecking for operands, we need to iterate over the
  # symbol table *before* any call to 'initCandidate' which might invoke
  # semExpr which might modify the symbol table in cases like
  # 'init(a, 1, (var b = new(Type2); b))'.
  var symx = initOverloadIter(o, c, headSymbol)
  let symScope = o.lastOverloadScope

  var syms: seq[tuple[a: PSym, b: int]] = @[]
  while symx != nil:
    if symx.kind in filter: syms.add((symx, o.lastOverloadScope))
    symx = nextOverloadIter(o, c, headSymbol)
  if syms.len == 0: return

  var z: TCandidate
  initCandidate(c, best, syms[0][0], initialBinding, symScope)
  initCandidate(c, alt, syms[0][0], initialBinding, symScope)
  best.state = csNoMatch

  for i in 0 .. <syms.len:
    let sym = syms[i][0]
    determineType(c, sym)
    initCandidate(c, z, sym, initialBinding, syms[i][1])
    z.calleeSym = sym

    #if sym.name.s == "*" and (n.info ?? "temp5.nim") and n.info.line == 140:
    #  gDebug = true
    matches(c, n, orig, z)
    if errors != nil:
      errors.safeAdd(sym)
      if z.errors != nil:
        for err in z.errors:
          errors.add(err)
    if z.state == csMatch:
      # little hack so that iterators are preferred over everything else:
      if sym.kind == skIterator: inc(z.exactMatches, 200)
      case best.state
      of csEmpty, csNoMatch: best = z
      of csMatch:
        var cmp = cmpCandidates(best, z)
        if cmp < 0: best = z   # x is better than the best so far
        elif cmp == 0: alt = z # x is as good as the best so far
        else: discard
      #if sym.name.s == "cmp" and (n.info ?? "rstgen.nim") and n.info.line == 516:
      #  echo "Matches ", n.info, " ", typeToString(sym.typ)
      #  debug sym
      #  writeMatches(z)
      #  for i in 1 .. <len(z.call):
      #    z.call[i].typ.debug
      #  quit 1

proc notFoundError*(c: PContext, n: PNode, errors: CandidateErrors) =
  # Gives a detailed error message; this is separated from semOverloadedCall,
  # as semOverlodedCall is already pretty slow (and we need this information
  # only in case of an error).
  if c.compilesContextId > 0 and optReportConceptFailures notin gGlobalOptions:
    # fail fast:
    globalError(n.info, errTypeMismatch, "")
  if errors.isNil or errors.len == 0:
    localError(n.info, errExprXCannotBeCalled, n[0].renderTree)
    return

  # to avoid confusing errors like:
  #   got (SslPtr, SocketHandle)
  #   but expected one of:
  #   openssl.SSL_set_fd(ssl: SslPtr, fd: SocketHandle): cint
  # we do a pre-analysis. If all types produce the same string, we will add
  # module information.
  let proto = describeArgs(c, n, 1, preferName)

  var prefer = preferName
  for err in errors:
    var errProto = ""
    let n = err.typ.n
    for i in countup(1, n.len - 1):
      var p = n.sons[i]
      if p.kind == nkSym:
        add(errProto, typeToString(p.sym.typ, preferName))
        if i != n.len-1: add(errProto, ", ")
      # else: ignore internal error as we're already in error handling mode
    if errProto == proto:
      prefer = preferModuleInfo
      break
  # now use the information stored in 'prefer' to produce a nice error message:
  var result = msgKindToString(errTypeMismatch)
  add(result, describeArgs(c, n, 1, prefer))
  add(result, ')')
  var candidates = ""
  for err in errors:
    add(candidates, err.getProcHeader(prefer))
    add(candidates, "\n")
  if candidates != "":
    add(result, "\n" & msgKindToString(errButExpected) & "\n" & candidates)
  if c.compilesContextId > 0 and optReportConceptFailures in gGlobalOptions:
    globalError(n.info, errGenerated, result)
  else:
    localError(n.info, errGenerated, result)

proc gatherUsedSyms(c: PContext, usedSyms: var seq[PNode]) =
  for scope in walkScopes(c.currentScope):
    if scope.usingSyms != nil:
      for s in scope.usingSyms: usedSyms.safeAdd(s)

proc resolveOverloads(c: PContext, n, orig: PNode,
                      filter: TSymKinds;
                      errors: var CandidateErrors): TCandidate =
  var initialBinding: PNode
  var alt: TCandidate
  var f = n.sons[0]
  if f.kind == nkBracketExpr:
    # fill in the bindings:
    initialBinding = f
    f = f.sons[0]
  else:
    initialBinding = nil

  var usedSyms: seq[PNode]

  template pickBest(headSymbol: expr) =
    pickBestCandidate(c, headSymbol, n, orig, initialBinding,
                      filter, result, alt, errors)

  gatherUsedSyms(c, usedSyms)
  if usedSyms != nil:
    var hiddenArg = if usedSyms.len > 1: newNode(nkClosedSymChoice, n.info, usedSyms)
                    else: usedSyms[0]

    n.sons.insert(hiddenArg, 1)
    orig.sons.insert(hiddenArg, 1)

    pickBest(f)

    if result.state != csMatch:
      n.sons.delete(1)
      orig.sons.delete(1)
    else: return

  pickBest(f)

  let overloadsState = result.state
  if overloadsState != csMatch:
    if nfDotField in n.flags:
      internalAssert f.kind == nkIdent and n.sonsLen >= 2
      let calleeName = newStrNode(nkStrLit, f.ident.s).withInfo(n.info)

      # leave the op head symbol empty,
      # we are going to try multiple variants
      n.sons[0..1] = [nil, n[1], calleeName]
      orig.sons[0..1] = [nil, orig[1], calleeName]

      template tryOp(x) =
        let op = newIdentNode(getIdent(x), n.info)
        n.sons[0] = op
        orig.sons[0] = op
        pickBest(op)

      if nfExplicitCall in n.flags:
        tryOp ".()"

      if result.state in {csEmpty, csNoMatch}:
        tryOp "."

    elif nfDotSetter in n.flags:
      internalAssert f.kind == nkIdent and n.sonsLen == 3
      let calleeName = newStrNode(nkStrLit,
        f.ident.s[0..f.ident.s.len-2]).withInfo(n.info)
      let callOp = newIdentNode(getIdent".=", n.info)
      n.sons[0..1] = [callOp, n[1], calleeName]
      orig.sons[0..1] = [callOp, orig[1], calleeName]
      pickBest(callOp)

    if overloadsState == csEmpty and result.state == csEmpty:
      if nfDotField in n.flags and nfExplicitCall notin n.flags:
        localError(n.info, errUndeclaredField, considerQuotedIdent(f).s)
      else:
        localError(n.info, errUndeclaredRoutine, considerQuotedIdent(f).s)
      return
    elif result.state != csMatch:
      if nfExprCall in n.flags:
        localError(n.info, errExprXCannotBeCalled,
                   renderTree(n, {renderNoComments}))
      else:
        if {nfDotField, nfDotSetter} * n.flags != {}:
          # clean up the inserted ops
          n.sons.delete(2)
          n.sons[0] = f

        errors = @[]
        pickBest(f)
        #notFoundError(c, n, errors)

      return

  if alt.state == csMatch and cmpCandidates(result, alt) == 0 and
      not sameMethodDispatcher(result.calleeSym, alt.calleeSym):
    internalAssert result.state == csMatch
    #writeMatches(result)
    #writeMatches(alt)
    if c.compilesContextId > 0:
      # quick error message for performance of 'compiles' built-in:
      globalError(n.info, errGenerated, "ambiguous call")
    elif gErrorCounter == 0:
      # don't cascade errors
      var args = "("
      for i in countup(1, sonsLen(n) - 1):
        if i > 1: add(args, ", ")
        add(args, typeToString(n.sons[i].typ))
      add(args, ")")

      localError(n.info, errGenerated, msgKindToString(errAmbiguousCallXYZ) % [
        getProcHeader(result.calleeSym), getProcHeader(alt.calleeSym),
        args])


proc instGenericConvertersArg*(c: PContext, a: PNode, x: TCandidate) =
  if a.kind == nkHiddenCallConv and a.sons[0].kind == nkSym and
      isGenericRoutine(a.sons[0].sym):
    let finalCallee = generateInstance(c, a.sons[0].sym, x.bindings, a.info)
    a.sons[0].sym = finalCallee
    a.sons[0].typ = finalCallee.typ
    #a.typ = finalCallee.typ.sons[0]

proc instGenericConvertersSons*(c: PContext, n: PNode, x: TCandidate) =
  assert n.kind in nkCallKinds
  if x.genericConverter:
    for i in 1 .. <n.len:
      instGenericConvertersArg(c, n.sons[i], x)

proc indexTypesMatch(c: PContext, f, a: PType, arg: PNode): PNode =
  var m: TCandidate
  initCandidate(c, m, f)
  result = paramTypesMatch(m, f, a, arg, nil)
  if m.genericConverter and result != nil:
    instGenericConvertersArg(c, result, m)

proc inferWithMetatype(c: PContext, formal: PType,
                       arg: PNode, coerceDistincts = false): PNode =
  var m: TCandidate
  initCandidate(c, m, formal)
  m.coerceDistincts = coerceDistincts
  result = paramTypesMatch(m, formal, arg.typ, arg, nil)
  if m.genericConverter and result != nil:
    instGenericConvertersArg(c, result, m)
  if result != nil:
    # This almost exactly replicates the steps taken by the compiler during
    # param matching. It performs an embarrassing amount of back-and-forth
    # type jugling, but it's the price to pay for consistency and correctness
    result.typ = generateTypeInstance(c, m.bindings, arg.info,
                                      formal.skipTypes({tyCompositeTypeClass}))
  else:
    typeMismatch(arg, formal, arg.typ)
    # error correction:
    result = copyTree(arg)
    result.typ = formal

proc semResolvedCall(c: PContext, n: PNode, x: TCandidate): PNode =
  assert x.state == csMatch
  var finalCallee = x.calleeSym
  markUsed(n.sons[0].info, finalCallee)
  styleCheckUse(n.sons[0].info, finalCallee)
  if finalCallee.ast == nil:
    internalError(n.info, "calleeSym.ast is nil") # XXX: remove this check!
  if x.hasFauxMatch:
    result = x.call
    result.sons[0] = newSymNode(finalCallee, result.sons[0].info)
    if containsGenericType(result.typ) or x.fauxMatch == tyUnknown:
      result.typ = newTypeS(x.fauxMatch, c)
    return
  let gp = finalCallee.ast.sons[genericParamsPos]
  if gp.kind != nkEmpty:
    if x.calleeSym.kind notin {skMacro, skTemplate}:
      if x.calleeSym.magic in {mArrGet, mArrPut}:
        finalCallee = x.calleeSym
      else:
        finalCallee = generateInstance(c, x.calleeSym, x.bindings, n.info)
    else:
      # For macros and templates, the resolved generic params
      # are added as normal params.
      for s in instantiateGenericParamList(c, gp, x.bindings):
        case s.kind
          of skConst:
            x.call.add s.ast
          of skType:
            x.call.add newSymNode(s, n.info)
          else:
            internalAssert false

  result = x.call
  instGenericConvertersSons(c, result, x)
  result.sons[0] = newSymNode(finalCallee, result.sons[0].info)
  result.typ = finalCallee.typ.sons[0]

proc canDeref(n: PNode): bool {.inline.} =
  result = n.len >= 2 and (let t = n[1].typ;
    t != nil and t.skipTypes({tyGenericInst}).kind in {tyPtr, tyRef})

proc tryDeref(n: PNode): PNode =
  result = newNodeI(nkHiddenDeref, n.info)
  result.typ = n.typ.skipTypes(abstractInst).sons[0]
  result.addSon(n)

proc semOverloadedCall(c: PContext, n, nOrig: PNode,
                       filter: TSymKinds): PNode =
  var errors: CandidateErrors

  var r = resolveOverloads(c, n, nOrig, filter, errors)
  if r.state == csMatch: result = semResolvedCall(c, n, r)
  elif experimentalMode(c) and canDeref(n):
    # try to deref the first argument and then try overloading resolution again:
    n.sons[1] = n.sons[1].tryDeref
    var r = resolveOverloads(c, n, nOrig, filter, errors)
    if r.state == csMatch: result = semResolvedCall(c, n, r)
    else:
      # get rid of the deref again for a better error message:
      n.sons[1] = n.sons[1].sons[0]
      notFoundError(c, n, errors)
  else:
    notFoundError(c, n, errors)
  # else: result = errorNode(c, n)

proc explicitGenericInstError(n: PNode): PNode =
  localError(n.info, errCannotInstantiateX, renderTree(n))
  result = n

proc explicitGenericSym(c: PContext, n: PNode, s: PSym): PNode =
  var m: TCandidate
  initCandidate(c, m, s, n)
  var newInst = generateInstance(c, s, m.bindings, n.info)
  markUsed(n.info, s)
  styleCheckUse(n.info, s)
  result = newSymNode(newInst, n.info)

proc explicitGenericInstantiation(c: PContext, n: PNode, s: PSym): PNode =
  assert n.kind == nkBracketExpr
  for i in 1..sonsLen(n)-1:
    n.sons[i].typ = semTypeNode(c, n.sons[i], nil)
  var s = s
  var a = n.sons[0]
  if a.kind == nkSym:
    # common case; check the only candidate has the right
    # number of generic type parameters:
    if safeLen(s.ast.sons[genericParamsPos]) != n.len-1:
      let expected = safeLen(s.ast.sons[genericParamsPos])
      localError(n.info, errGenerated, "cannot instantiate: " & renderTree(n) &
         "; got " & $(n.len-1) & " type(s) but expected " & $expected)
      return n
    result = explicitGenericSym(c, n, s)
  elif a.kind in {nkClosedSymChoice, nkOpenSymChoice}:
    # choose the generic proc with the proper number of type parameters.
    # XXX I think this could be improved by reusing sigmatch.paramTypesMatch.
    # It's good enough for now.
    result = newNodeI(a.kind, n.info)
    for i in countup(0, len(a)-1):
      var candidate = a.sons[i].sym
      if candidate.kind in {skProc, skMethod, skConverter,
                            skIterator}:
        # it suffices that the candidate has the proper number of generic
        # type parameters:
        if safeLen(candidate.ast.sons[genericParamsPos]) == n.len-1:
          result.add(explicitGenericSym(c, n, candidate))
    # get rid of nkClosedSymChoice if not ambiguous:
    if result.len == 1 and a.kind == nkClosedSymChoice:
      result = result[0]
    # candidateCount != 1: return explicitGenericInstError(n)
  else:
    result = explicitGenericInstError(n)

proc searchForBorrowProc(c: PContext, startScope: PScope, fn: PSym): PSym =
  # Searchs for the fn in the symbol table. If the parameter lists are suitable
  # for borrowing the sym in the symbol table is returned, else nil.
  # New approach: generate fn(x, y, z) where x, y, z have the proper types
  # and use the overloading resolution mechanism:
  var call = newNodeI(nkCall, fn.info)
  var hasDistinct = false
  call.add(newIdentNode(fn.name, fn.info))
  for i in 1.. <fn.typ.n.len:
    let param = fn.typ.n.sons[i]
    let t = skipTypes(param.typ, abstractVar-{tyTypeDesc})
    if t.kind == tyDistinct or param.typ.kind == tyDistinct: hasDistinct = true
    call.add(newNodeIT(nkEmpty, fn.info, t.baseOfDistinct))
  if hasDistinct:
    var resolved = semOverloadedCall(c, call, call, {fn.kind})
    if resolved != nil:
      result = resolved.sons[0].sym