// satisfy returns the set of interface satisfaction constraints.
func (r *Unexporter) satisfy() map[satisfy.Constraint]bool {
	if r.satisfyConstraints == nil {
		// Compute on demand: it's expensive.
		var f satisfy.Finder
		for _, info := range r.packages {
			f.Find(&info.Info, info.Files)
		}
		r.satisfyConstraints = f.Result
	}
	return r.satisfyConstraints
}

func calculateConstraints(u *Unexporter) {
	constraints := make(map[satisfy.Constraint]map[*types.Package]bool)

	for _, info := range u.prog.Imported {
		var finder satisfy.Finder
		finder.Find(&info.Info, info.Files)

		for constraint := range finder.Result {
			if _, ok := constraints[constraint]; !ok {
				constraints[constraint] = make(map[*types.Package]bool)
			}
			constraints[constraint][info.Pkg] = true
		}
	}
	u.f = constraints
}

// findAssignments returns the set of types to or from which type T is
// assigned in the program syntax.
func (r *renamer) findAssignments(T types.Type) map[types.Type]bool {
	if r.satisfyConstraints == nil {
		// Compute on demand: it's expensive.
		var f satisfy.Finder
		for _, info := range r.packages {
			f.Find(&info.Info, info.Files)
		}
		r.satisfyConstraints = f.Result
	}

	result := make(map[types.Type]bool)
	for key := range r.satisfyConstraints {
		// key = (lhs, rhs) where lhs is always an interface.
		if types.Identical(key.RHS, T) {
			result[key.LHS] = true
		}
		if isInterface(T) && types.Identical(key.LHS, T) {
			// must check both sides
			result[key.RHS] = true
		}
	}
	return result
}