// disambiguating package names in error messages.
	//
	// pkgPathMap is allocated lazily, so that we don't pay the price of building
	// it on the happy path. seenPkgMap tracks the packages that we've already
	// walked.
	pkgPathMap map[string]map[string]bool
	seenPkgMap map[*Package]bool

	// information collected during type-checking of a set of package files
	// (initialized by Files, valid only for the duration of check.Files;

	// disambiguating package names in error messages.
	//
	// pkgPathMap is allocated lazily, so that we don't pay the price of building
	// it on the happy path. seenPkgMap tracks the packages that we've already
	// walked.
	pkgPathMap map[string]map[string]bool
	seenPkgMap map[*Package]bool

	// information collected during type-checking of a set of package files
	// (initialized by Files, valid only for the duration of check.Files;