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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)

	// ReadFileRevs reads a single file at multiple versions.
	// It should refuse to read more than maxSize bytes.
	// The result is a map from each requested rev strings
	// to the associated FileRev. The map must have a non-nil
	// entry for every requested rev (unless ReadFileRevs returned an error).
	// A file simply being missing or even corrupted in revs[i]
	// should be reported only in files[revs[i]].Err, not in the error result
	// from ReadFileRevs.
	// The overall call should return an error (and no map) only
	// in the case of a problem with obtaining the data, such as
	// a network failure.
	// Implementations may assume that revs only contain tags,
	// not direct commit hashes.
	ReadFileRevs(revs []string, file string, maxSize int64) (files map[string]*FileRev, 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,
	// along with the actual subdirectory (possibly shorter than subdir)
	// contained in 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, actualSubdir string, err error)

	// RecentTag returns the most recent tag at or before the given rev
	// with the given prefix. It should make a best-effort attempt to
	// find a tag that is a valid semantic version (following the prefix),
	// or else the result is not useful to the caller, but it need not
	// incur great expense in doing so. For example, the git implementation
	// of RecentTag limits git's search to tags matching the glob expression
	// "v[0-9]*.[0-9]*.[0-9]*" (after the prefix).
	RecentTag(rev, prefix string) (tag string, err 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
}