A command for building and maintaing the module cache a.out <flags> <command> <args> The commands are 'create' which builds a new index, 'update', which attempts to update an existing index, 'query', which looks up things in the index.

Create always creates a new index for the go module cache that is in cachedir.

DirToImportPathVersion computes import path and semantic version.

ReadIndex reads the latest version of the on-disk index for the cache directory cd.

Update the index for the go module cache that is in cachedir, If there is no existing index it will build one.

CurrentVersion tells readers about the format of the index.

IndexDir is where the module index is stored.

An Entry contains information for an import path.

Index is returned by ReadIndex().

distinguish various types of directory names.