if T == nil {
					check.errorf(x, UntypedNilUse, "use of untyped nil in %s", context)
					x.mode = invalid
					return
				}
			} else if T == nil || isNonTypeParamInterface(T) {
				target = Default(x.typ)
			}
		} else { // go/types
			if T == nil || isNonTypeParamInterface(T) {
				if T == nil && x.typ == Typ[UntypedNil] {
					check.errorf(x, UntypedNilUse, "use of untyped nil in %s", context)
					x.mode = invalid
					return

}

// IsInterface reports whether t is an interface type.
func IsInterface(t Type) bool {
	_, ok := under(t).(*Interface)
	return ok
}

// isNonTypeParamInterface reports whether t is an interface type but not a type parameter.
func isNonTypeParamInterface(t Type) bool {
	return !isTypeParam(t) && IsInterface(t)
}

// isTypeParam reports whether t is a type parameter.
func isTypeParam(t Type) bool {

				if T == nil {
					check.errorf(x, UntypedNilUse, "use of untyped nil in %s", context)
					x.mode = invalid
					return
				}
			} else if T == nil || isNonTypeParamInterface(T) {
				target = Default(x.typ)
			}
		} else { // go/types
			if T == nil || isNonTypeParamInterface(T) {
				if T == nil && x.typ == Typ[UntypedNil] {
					check.errorf(x, UntypedNilUse, "use of untyped nil in %s", context)
					x.mode = invalid
					return

}

// IsInterface reports whether t is an interface type.
func IsInterface(t Type) bool {
	_, ok := under(t).(*Interface)
	return ok
}

// isNonTypeParamInterface reports whether t is an interface type but not a type parameter.
func isNonTypeParamInterface(t Type) bool {
	return !isTypeParam(t) && IsInterface(t)
}

// isTypeParam reports whether t is a type parameter.
func isTypeParam(t Type) bool {

		// - For constant integer to string conversions, keep the argument type.
		//   (See also the TODO below.)
		if isTypes2 && x.typ == Typ[UntypedNil] {
			// ok
		} else if isNonTypeParamInterface(T) || constArg && !isConstType(T) || !isTypes2 && x.isNil() {
			final = Default(x.typ) // default type of untyped nil is untyped nil
		} else if x.mode == constant_ && isInteger(x.typ) && allString(T) {
			final = x.typ

		// - For constant integer to string conversions, keep the argument type.
		//   (See also the TODO below.)
		if isTypes2 && x.typ == Typ[UntypedNil] {
			// ok
		} else if isNonTypeParamInterface(T) || constArg && !isConstType(T) || !isTypes2 && x.isNil() {
			final = Default(x.typ) // default type of untyped nil is untyped nil
		} else if x.mode == constant_ && isInteger(x.typ) && allString(T) {
			final = x.typ

		//           valid with interfaces), but in that case the assignability check should take
		//           care of the conversion. Verify and possibly eliminate this extra test.
		if isNonTypeParamInterface(x.typ) || isNonTypeParamInterface(y.typ) {
			return true
		}
		// A boolean type can only convert to another boolean type.
		if allBoolean(x.typ) != allBoolean(y.typ) {
			return false
		}

		//           valid with interfaces), but in that case the assignability check should take
		//           care of the conversion. Verify and possibly eliminate this extra test.
		if isNonTypeParamInterface(x.typ) || isNonTypeParamInterface(y.typ) {
			return true
		}
		// A boolean type can only convert to another boolean type.
		if allBoolean(x.typ) != allBoolean(y.typ) {
			return false
		}