fs: Add --default-time flag to control unknown modtime of files/dirs

Before this patch, files or directories with unknown modtime would
appear as the current date.

When mounted some systems look at modification dates of directories to
see if they change and having them change whenever they drop out of
the directory cache is not optimal.

See #6986

docs/content/docs.md

@@ -992,6 +992,18 @@ Mode to run dedupe command in.  One of `interactive`, `skip`, `first`,
 `newest`, `oldest`, `rename`.  The default is `interactive`.  
 See the dedupe command for more information as to what these options mean.
 
+### --default-time TIME ###
+
+If a file or directory does have a modification time rclone can read
+then rclone will display this fixed time instead.
+
+The default is `2000-01-01 00:00:00 UTC`. This can be configured in
+any of the ways shown in [the time or duration options](#time-option).
+
+For example `--default-time 2020-06-01` to set the default time to the
+1st of June 2020 or `--default-time 0s` to set the default time to the
+time rclone started up.
+
 ### --disable FEATURE,FEATURE,... ###
 
 This disables a comma separated list of optional features. For example

fs/config.go

@@ -144,6 +144,7 @@ type ConfigInfo struct {
 	Metadata                bool
 	ServerSideAcrossConfigs bool
 	TerminalColorMode       TerminalColorMode
+	DefaultTime             Time // time that directories with no time should display
 }
 
 // NewConfig creates a new config with everything set to the default
@@ -185,6 +186,7 @@ func NewConfig() *ConfigInfo {
 	c.FsCacheExpireDuration = 300 * time.Second
 	c.FsCacheExpireInterval = 60 * time.Second
 	c.KvLockTime = 1 * time.Second
+	c.DefaultTime = Time(time.Date(2000, 1, 1, 0, 0, 0, 0, time.UTC))
 
 	// Perform a simple check for debug flags to enable debug logging during the flag initialization
 	for argIndex, arg := range os.Args {

fs/config/configflags/configflags.go

@@ -144,6 +144,7 @@ func AddFlags(ci *fs.ConfigInfo, flagSet *pflag.FlagSet) {
 	flags.BoolVarP(flagSet, &ci.Metadata, "metadata", "M", ci.Metadata, "If set, preserve metadata when copying objects")
 	flags.BoolVarP(flagSet, &ci.ServerSideAcrossConfigs, "server-side-across-configs", "", ci.ServerSideAcrossConfigs, "Allow server-side operations (e.g. copy) to work across different configs")
 	flags.FVarP(flagSet, &ci.TerminalColorMode, "color", "", "When to show colors (and other ANSI codes) AUTO|NEVER|ALWAYS")
+	flags.FVarP(flagSet, &ci.DefaultTime, "default-time", "", "Time to show if modtime is unknown for files and directories")
 }
 
 // ParseHeaders converts the strings passed in via the header flags into HTTPOptions

fs/dir.go

@@ -16,6 +16,8 @@ type Dir struct {
 }
 
 // NewDir creates an unspecialized Directory object
+//
+// If the modTime is unknown pass in time.Time{}
 func NewDir(remote string, modTime time.Time) *Dir {
 	return &Dir{
 		remote:  remote,
@@ -75,12 +77,14 @@ func (d *Dir) SetParentID(parent string) *Dir {
 }
 
 // ModTime returns the modification date of the file
-// It should return a best guess if one isn't available
+//
+// If one isn't available it returns the configured --default-dir-time
 func (d *Dir) ModTime(ctx context.Context) time.Time {
 	if !d.modTime.IsZero() {
 		return d.modTime
 	}
-	return time.Now()
+	ci := GetConfig(ctx)
+	return time.Time(ci.DefaultTime)
 }
 
 // Size returns the size of the file