//
// There are two modes of operation:
//
//  1. If infer == true, funcInst infers missing type arguments as needed and
//     instantiates the function x. The returned results are nil.
//
//  2. If infer == false and inst provides all type arguments, funcInst
//     instantiates the function x. The returned results are nil.
//     If inst doesn't provide enough type arguments, funcInst returns the

//
// There are two modes of operation:
//
//  1. If infer == true, funcInst infers missing type arguments as needed and
//     instantiates the function x. The returned results are nil.
//
//  2. If infer == false and inst provides all type arguments, funcInst
//     instantiates the function x. The returned results are nil.
//     If inst doesn't provide enough type arguments, funcInst returns the

	switch t := x.typ.(type) {
	case *Alias, *Named:
		if isGeneric(t) {
			what = "type"
		}
	case *Signature:
		if t.tparams != nil {
			if enableReverseTypeInference && T != nil {
				check.funcInst(T, x.Pos(), x, nil, true)
				return
			}
			what = "function"
		}
	}
	if what != "" {
		check.errorf(x.expr, WrongTypeArgCount, "cannot use generic %s %s without instantiation", what, x.expr)

	switch t := x.typ.(type) {
	case *Alias, *Named:
		if isGeneric(t) {
			what = "type"
		}
	case *Signature:
		if t.tparams != nil {
			if enableReverseTypeInference && T != nil {
				check.funcInst(T, x.Pos(), x, nil, true)
				return
			}
			what = "function"
		}
	}
	if what != "" {
		check.errorf(x.expr, WrongTypeArgCount, "cannot use generic %s %s without instantiation", what, x.expr)

			// This is ok; lazy type set computation will determine the actual type set
			// in normal form.
			return &Union{terms}
		}

	case *Interface:
		methods, mcopied := subst.funcList(t.methods)
		embeddeds, ecopied := subst.typeList(t.embeddeds)
		if mcopied || ecopied {
			iface := subst.check.newInterface()
			iface.embeddeds = embeddeds
			iface.embedPos = t.embedPos

			// This is ok; lazy type set computation will determine the actual type set
			// in normal form.
			return &Union{terms}
		}

	case *Interface:
		methods, mcopied := subst.funcList(t.methods)
		embeddeds, ecopied := subst.typeList(t.embeddeds)
		if mcopied || ecopied {
			iface := subst.check.newInterface()
			iface.embeddeds = embeddeds
			iface.embedPos = t.embedPos