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type FileRev struct {
	Rev  string // requested revision
	Data []byte // file data
	Err  error  // error if any; os.IsNotExist(Err)==true if rev exists but file does not exist in that rev
}

type Repo interface {
	// List lists all tags with the given prefix.
	Tags(prefix string) (tags []string, err error)

	// Stat returns information about the revision rev.
	// A revision can be any identifier known to the underlying service:
	// commit hash, branch, tag, and so on.
	Stat(rev string) (*RevInfo, error)

	// Latest returns the latest revision on the default branch,
	// whatever that means in the underlying implementation.
	Latest() (*RevInfo, error)

	// ReadFile reads the given file in the file tree corresponding to revision rev.
	// It should refuse to read more than maxSize bytes.
	//
	// If the requested file does not exist it should return an error for which
	// os.IsNotExist(err) returns true.
	ReadFile(rev, file string, maxSize int64) (data []byte, err error)

	// ReadZip downloads a zip file for the subdir subdirectory
	// of the given revision to a new file in a given temporary directory.
	// It should refuse to read more than maxSize bytes.
	// It returns a ReadCloser for a streamed copy of the zip file.
	// All files in the zip file are expected to be
	// nested in a single top-level directory, whose name is not specified.
	ReadZip(rev, subdir string, maxSize int64) (zip io.ReadCloser, err error)

	// RecentTag returns the most recent tag on rev or one of its predecessors
	// with the given prefix. allowed may be used to filter out unwanted versions.
	RecentTag(rev, prefix string, allowed func(string) bool) (tag string, err error)

	// DescendsFrom reports whether rev or any of its ancestors has the given tag.
	//
	// DescendsFrom must return true for any tag returned by RecentTag for the
	// same revision.
	DescendsFrom(rev, tag string) (bool, error)
}

type RevInfo struct {
	Name    string    // complete ID in underlying repository
	Short   string    // shortened ID, for use in pseudo-version
	Version string    // version used in lookup
	Time    time.Time // commit time
	Tags    []string  // known tags for commit
}

type RunError struct {
	Cmd      string
	Err      error
	Stderr   []byte
	HelpText string
}

type UnknownRevisionError struct {
	Rev string
}

type VCSError struct {
	Err error
}