// Package types2 declares the data types and implements
// the algorithms for type-checking of Go packages. Use
// Config.Check to invoke the type checker for a package.
// Alternatively, create a new type checker with NewChecker
// and invoke it incrementally by calling Checker.Files.
//
// Type-checking consists of several interdependent phases:
//
// Name resolution maps each identifier (syntax.Name) in the program to the