fs: fix corruption of SizeSuffix with "B" suffix in config (eg --min-size)

Before this change, the config system round tripped fs.SizeSuffix
values through strings like this, corrupting them in the process.

    "2B" -> 2 -> "2" -> 2048

This caused `--min-size 2B` to be interpreted as `--min-size 2k`.

This fix makes sure SizeSuffix values have a "B" suffix when turned
into a string where necessary, so it becomes

    "2B" -> 2 -> "2B" -> 2

In rclone v2 we should probably declare unsuffixed SizeSuffix values
are in bytes not kBytes (done for rsync compatibility) but this would
be a backwards incompatible change which we don't want for v1.

Fixes #8437
Fixes #8212
Fixes #5169

fs/fs_test.go

@@ -261,6 +261,34 @@ func TestOptionString(t *testing.T) {
 	assert.Equal(t, "true", caseInsensitiveOption.String())
 }
 
+func TestOptionStringStringArray(t *testing.T) {
+	opt := Option{
+		Name:    "string_array",
+		Default: []string(nil),
+	}
+	assert.Equal(t, "", opt.String())
+	opt.Default = []string{}
+	assert.Equal(t, "", opt.String())
+	opt.Default = []string{"a", "b"}
+	assert.Equal(t, "a,b", opt.String())
+	opt.Default = []string{"hello, world!", "goodbye, world!"}
+	assert.Equal(t, `"hello, world!","goodbye, world!"`, opt.String())
+}
+
+func TestOptionStringSizeSuffix(t *testing.T) {
+	opt := Option{
+		Name:    "size_suffix",
+		Default: SizeSuffix(0),
+	}
+	assert.Equal(t, "0", opt.String())
+	opt.Default = SizeSuffix(-1)
+	assert.Equal(t, "off", opt.String())
+	opt.Default = SizeSuffix(100)
+	assert.Equal(t, "100B", opt.String())
+	opt.Default = SizeSuffix(1024)
+	assert.Equal(t, "1Ki", opt.String())
+}
+
 func TestOptionSet(t *testing.T) {
 	o := caseInsensitiveOption
 	assert.Equal(t, true, o.Value)

fs/registry.go

@@ -259,15 +259,27 @@ func (o *Option) IsDefault() bool {
 // String turns Option into a string
 func (o *Option) String() string {
 	v := o.GetValue()
-	if stringArray, isStringArray := v.([]string); isStringArray {
+	switch x := v.(type) {
+	case []string:
 		// Treat empty string array as empty string
 		// This is to make the default value of the option help nice
-		if len(stringArray) == 0 {
+		if len(x) == 0 {
 			return ""
 		}
 		// Encode string arrays as CSV
 		// The default Go encoding can't be decoded uniquely
-		return CommaSepList(stringArray).String()
+		return CommaSepList(x).String()
+	case SizeSuffix:
+		str := x.String()
+		// Suffix bare numbers with "B" unless they are 0
+		//
+		// This makes sure that fs.SizeSuffix roundtrips through string
+		if len(str) > 0 && str != "0" {
+			if lastDigit := str[len(str)-1]; lastDigit >= '0' && lastDigit <= '9' {
+				str += "B"
+			}
+		}
+		return str
 	}
 	return fmt.Sprint(v)
 }