disjoint checker is somewhat smarter

tests/overload/tspec.nim

@@ -0,0 +1,81 @@
+discard """
+  output: '''not a var
+not a var
+a var
+B
+int
+T
+int16
+T
+ref T
+123
+2
+1
+@[123, 2, 1]'''
+"""
+
+# Things that's even in the spec now!
+
+proc byvar(x: var int) = echo "a var"
+proc byvar(x: int) = echo "not a var"
+byvar(89)
+
+let letSym = 0
+var varSym = 13
+
+byvar(letSym)
+byvar(varSym)
+
+type
+  A = object of RootObj
+  B = object of A
+  C = object of B
+
+proc p(obj: A) =
+  echo "A"
+
+proc p(obj: B) =
+  echo "B"
+
+var c = C()
+# not ambiguous, calls 'B', not 'A' since B is a subtype of A
+# but not vice versa:
+p(c)
+
+proc pp(obj: A, obj2: B) = echo "A B"
+proc pp(obj: B, obj2: A) = echo "B A"
+
+# but this is ambiguous:
+#pp(c, c)
+
+proc takesInt(x: int) = echo "int"
+proc takesInt[T](x: T) = echo "T"
+proc takesInt(x: int16) = echo "int16"
+
+takesInt(4) # "int"
+var x: int32
+takesInt(x) # "T"
+var y: int16
+takesInt(y) # "int16"
+var z: range[0..4] = 0
+takesInt(z) # "T"
+
+proc gen[T](x: ref ref T) = echo "ref ref T"
+proc gen[T](x: ref T) = echo "ref T"
+proc gen[T](x: T) = echo "T"
+
+var ri: ref int
+gen(ri) # "ref T"
+
+
+template rem(x: expr) = discard
+#proc rem[T](x: T) = discard
+
+rem unresolvedExpression(undeclaredIdentifier)
+
+
+proc takeV[T](a: varargs[T]) =
+  for x in a: echo x
+
+takeV([123, 2, 1]) # takeV's T is "int", not "array of int"
+echo(@[123, 2, 1])