fs: allow boolean features to be enabled with --disable !Feature

docs/content/docs.md

@@ -1002,10 +1002,24 @@ To see a list of which features can be disabled use:
 
     --disable help
 
+The features a remote has can be seen in JSON format with:
+
+    rclone backend features remote:
+
 See the overview [features](/overview/#features) and
 [optional features](/overview/#optional-features) to get an idea of
 which feature does what.
 
+Note that some features can be set to `true` if they are `true`/`false`
+feature flag features by prefixing them with `!`. For example the
+`CaseInsensitive` feature can be forced to `false` with `--disable CaseInsensitive`
+and forced to `true` with `--disable '!CaseInsensitive'`. In general
+it isn't a good idea doing this but it may be useful in extremis.
+
+(Note that `!` is a shell command which you will
+need to escape with single quotes or a backslash on unix like
+platforms.)
+
 This flag can be useful for debugging and in exceptional circumstances
 (e.g. Google Drive limiting the total volume of Server Side Copies to
 100 GiB/day).

fs/features.go

@@ -172,6 +172,12 @@ type Features struct {
 // Disable nil's out the named feature.  If it isn't found then it
 // will log a message.
 func (ft *Features) Disable(name string) *Features {
+	// Prefix boolean values with ! to set the feature
+	invert := false
+	if strings.HasPrefix(name, "!") {
+		name = name[1:]
+		invert = true
+	}
 	v := reflect.ValueOf(ft).Elem()
 	vType := v.Type()
 	for i := 0; i < v.NumField(); i++ {
@@ -180,6 +186,14 @@ func (ft *Features) Disable(name string) *Features {
 		if strings.EqualFold(name, vName) {
 			if !field.CanSet() {
 				Errorf(nil, "Can't set Feature %q", name)
+			} else {
+				if invert {
+					if field.Type().Kind() == reflect.Bool {
+						field.Set(reflect.ValueOf(true))
+						Debugf(nil, "Set feature %q", name)
+					} else {
+						Errorf(nil, "Can't set Feature %q to true", name)
+					}
 				} else {
 					zero := reflect.Zero(field.Type())
 					field.Set(zero)
@@ -187,6 +201,7 @@ func (ft *Features) Disable(name string) *Features {
 				}
 			}
 		}
+	}
 	return ft
 }