Fix json tags for grouped snapshot output

This commit will add json tags to the structs for json output, so all
json variables of the snapshot command output are lowercase and
snake-case.

Furthermore it adds some internal code changes based on the feedback in
the pull request #2087.

cmd/restic/cmd_snapshots.go

@@ -51,9 +51,9 @@ func init() {
 }
 
 type groupKey struct {
-	Hostname string
+	Hostname string   `json:"hostname"`
-	Paths    []string
+	Paths    []string `json:"paths"`
-	Tags     []string
+	Tags     []string `json:"tags"`
 }
 
 func runSnapshots(opts SnapshotOptions, gopts GlobalOptions, args []string) error {
@@ -295,32 +295,33 @@ func PrintSnapshots(stdout io.Writer, list restic.Snapshots, reasons []restic.Ke
 // following snapshots belong to.
 // Prints nothing, if we did not group at all.
 func PrintSnapshotGroupHeader(stdout io.Writer, groupKeyJSON string, GroupByTag bool, GroupByHost bool, GroupByPath bool) error {
-	if GroupByTag || GroupByHost || GroupByPath {
+	if !GroupByTag && !GroupByHost && !GroupByPath {
-		var key groupKey
+		return nil
-		var err error
-
-		err = json.Unmarshal([]byte(groupKeyJSON), &key)
-		if err != nil {
-			return err
-		}
-
-		// Info
-		fmt.Fprintf(stdout, "snapshots")
-		var infoStrings []string
-		if GroupByTag {
-			infoStrings = append(infoStrings, "tags ["+strings.Join(key.Tags, ", ")+"]")
-		}
-		if GroupByHost {
-			infoStrings = append(infoStrings, "host ["+key.Hostname+"]")
-		}
-		if GroupByPath {
-			infoStrings = append(infoStrings, "paths ["+strings.Join(key.Paths, ", ")+"]")
-		}
-		if infoStrings != nil {
-			fmt.Fprintf(stdout, " for (%s)", strings.Join(infoStrings, ", "))
-		}
-		fmt.Fprintf(stdout, ":\n")
 	}
+	var key groupKey
+	var err error
+
+	err = json.Unmarshal([]byte(groupKeyJSON), &key)
+	if err != nil {
+		return err
+	}
+
+	// Info
+	fmt.Fprintf(stdout, "snapshots")
+	var infoStrings []string
+	if GroupByTag {
+		infoStrings = append(infoStrings, "tags ["+strings.Join(key.Tags, ", ")+"]")
+	}
+	if GroupByHost {
+		infoStrings = append(infoStrings, "host ["+key.Hostname+"]")
+	}
+	if GroupByPath {
+		infoStrings = append(infoStrings, "paths ["+strings.Join(key.Paths, ", ")+"]")
+	}
+	if infoStrings != nil {
+		fmt.Fprintf(stdout, " for (%s)", strings.Join(infoStrings, ", "))
+	}
+	fmt.Fprintf(stdout, ":\n")
 
 	return nil
 }
@@ -335,8 +336,8 @@ type Snapshot struct {
 
 // SnapshotGroup helps to print SnaphotGroups as JSON with their GroupReasons included.
 type SnapshotGroup struct {
-	GroupKey  groupKey
+	GroupKey  groupKey   `json:"group_key"`
-	Snapshots []Snapshot
+	Snapshots []Snapshot `json:"snapshots"`
 }
 
 // printSnapshotsJSON writes the JSON representation of list to stdout.
@@ -372,21 +373,21 @@ func printSnapshotGroupJSON(stdout io.Writer, snGroups map[string]restic.Snapsho
 		}
 
 		return json.NewEncoder(stdout).Encode(snapshotGroups)
-	} else {
-		// Old behavior
-		var snapshots []Snapshot
-
-		for _, list := range snGroups {
-			for _, sn := range list {
-				k := Snapshot{
-					Snapshot: sn,
-					ID:       sn.ID(),
-					ShortID:  sn.ID().Str(),
-				}
-				snapshots = append(snapshots, k)
-			}
-		}
-
-		return json.NewEncoder(stdout).Encode(snapshots)
 	}
+
+	// Old behavior
+	var snapshots []Snapshot
+
+	for _, list := range snGroups {
+		for _, sn := range list {
+			k := Snapshot{
+				Snapshot: sn,
+				ID:       sn.ID(),
+				ShortID:  sn.ID().Str(),
+			}
+			snapshots = append(snapshots, k)
+		}
+	}
+
+	return json.NewEncoder(stdout).Encode(snapshots)
 }