fix nim-lang#6981 and nim-lang#9831 too

compiler/semcall.nim

@@ -340,7 +340,7 @@ proc getMsgDiagnostic(c: PContext, flags: TExprFlags, n, f: PNode): string =
       sym = nextOverloadIter(o, c, f)
 
   let ident = considerQuotedIdent(c, f, n).s
-  if {nfDotField, nfDotSetter, nfExplicitCall} * n.flags <= {nfDotField, nfDotSetter}:
+  if nfExplicitCall notin n.flags and {nfDotField, nfDotSetter} * n.flags != {}:
     let sym = n[1].typ.typSym
     var typeHint = ""
     if sym == nil:

compiler/semexprs.nim

@@ -535,7 +535,7 @@ proc overloadedCallOpr(c: PContext, n: PNode): PNode =
     result = newNodeI(nkCall, n.info)
     result.add newIdentNode(par, n.info)
     for i in 0..<n.len: result.add n[i]
-    result = semExpr(c, result)
+    result = semExpr(c, result, flags = {efNoUndeclared})
 
 proc changeType(c: PContext; n: PNode, newType: PType, check: bool) =
   case n.kind
@@ -988,6 +988,8 @@ proc semIndirectOp(c: PContext, n: PNode, flags: TExprFlags; expectedType: PType
     let t = n[0].typ
     if t != nil and t.kind in {tyVar, tyLent}:
       n[0] = newDeref(n[0])
+    elif isSymChoice(n[0]):
+      return semDirectOp(c, n, flags, expectedType)
     elif n[0].kind == nkBracketExpr:
       let s = bracketedMacro(n[0])
       if s != nil:
@@ -1042,10 +1044,10 @@ proc semIndirectOp(c: PContext, n: PNode, flags: TExprFlags; expectedType: PType
       instGenericConvertersSons(c, result, m)
 
   else:
-    result = overloadedCallOpr(c, n)
+    result = overloadedCallOpr(c, n) # this uses efNoUndeclared
     # Now that nkSym does not imply an iteration over the proc/iterator space,
     # the old ``prc`` (which is likely an nkIdent) has to be restored:
-    if result == nil:
+    if result == nil or result.kind == nkEmpty:
       # XXX: hmm, what kind of symbols will end up here?
       # do we really need to try the overload resolution?
       n[0] = prc

tests/specialops/terrmsgs.nim

@@ -53,7 +53,7 @@ block:
 
     # non-routine type shows `()` overloads:
     b(123) #[tt.Error
-     ^ type mismatch: got <Bar, int literal(123)>]#
+     ^ attempting to call routine: 'b']#
 
 # issue #7777
 
@@ -74,3 +74,10 @@ block:
 
   var tt: TestType
   discard tt.field
+
+block: # related to issue #6981
+  proc `()`(a:string, b:string):string = a & b
+  proc mewSeq[T](a,b:int)=discard
+  proc mewSeq[T](c:int)= discard
+  mewSeq[int]() #[tt.Error
+             ^ type mismatch: got <>]#

tests/specialops/tnewseq.nim

@@ -0,0 +1,22 @@
+# issue #6981
+
+import std/assertions
+
+{.experimental: "callOperator".}
+
+block: # issue #6981
+  proc `()`(a:string, b:string):string = a & b
+
+  var s = newSeq[int](3)
+
+  doAssert s == @[0, 0, 0]
+
+block: # generalized example from #6981
+  proc mewSeq[T](a: int)=discard
+  proc mewSeq[T]()= discard
+  mewSeq[int]()
+
+block: # issue #9831
+  type Foo = object
+  proc `()`(foo: Foo) = discard
+  let x = newSeq[int]()