ls: print "size":0 for empty files in JSON

[greatroar]

What does this PR change? What problem does it solve?

It causes restic ls --json to print empty files as having "size":0 instead of omitting the size, as was done previously.

It also removes unconditional panics introduced in 200f095, which broke JSON printing entirely.

Was the change discussed in an issue or in the forum before?

Fixes #3247.

Checklist

• I have read the Contribution Guidelines
• I have enabled maintainer edits for this PR
• I have added tests for all changes in this PR
• I have added documentation for the changes (in the manual)
• There's a new file in changelog/unreleased/ that describes the changes for our users (template here)
• I have run gofmt on the code in all commits
• All commit messages are formatted in the same style as the other commits in the repo
• I'm done, this Pull Request is ready for review

[fd0]

There's a better way (IMHO): Make Size a pointer to uint64, and set it to a non-nil value when the size should be printed. The code below misses error handling, but passes the tests you added:

type lsNode struct {
	Name       string      `json:"name"`
	Type       string      `json:"type"`
	Path       string      `json:"path"`
	UID        uint32      `json:"uid"`
	GID        uint32      `json:"gid"`
	Size       *uint64     `json:"size,omitempty"`
	Mode       os.FileMode `json:"mode,omitempty"`
	ModTime    time.Time   `json:"mtime,omitempty"`
	AccessTime time.Time   `json:"atime,omitempty"`
	ChangeTime time.Time   `json:"ctime,omitempty"`
	StructType string      `json:"struct_type"` // "node"
}

// Print node in our custom JSON format, followed by a newline.
func lsNodeJSON(w io.Writer, path string, node *restic.Node) {
	var size uint64

	n := lsNode{
		Name:       node.Name,
		Type:       node.Type,
		Path:       path,
		UID:        node.UID,
		GID:        node.GID,
		Mode:       node.Mode,
		ModTime:    node.ModTime,
		AccessTime: node.AccessTime,
		ChangeTime: node.ChangeTime,
		StructType: "node",
	}

	if node.Type == "file" {
		size = node.Size
		n.Size = &size
	}

	json.NewEncoder(w).Encode(n)
}

What do you think?

[greatroar]

Good idea, implemented that.

[MichaelEischer]

LGTM.

Feedback has been addressed