feat(tags): Create Flatten() method

internal/restic/tag_list.go

@@ -40,6 +40,20 @@ func (l TagLists) String() string {
 	return fmt.Sprintf("%v", []TagList(l))
 }
 
+// Flatten returns the list of all tags provided in TagLists
+func (l TagLists) Flatten() (tags TagList) {
+	tags = make([]string, 0)
+	for _, list := range l {
+		for _, tag := range list {
+			if tag != "" {
+				tags = append(tags, tag)
+			}
+		}
+	}
+
+	return tags
+}
+
 // Set updates the TagList's value.
 func (l *TagLists) Set(s string) error {
 	*l = append(*l, splitTagList(s))

internal/restic/tag_list_test.go

@@ -0,0 +1,45 @@
+package restic
+
+import (
+	rtest "github.com/restic/restic/internal/test"
+	"testing"
+)
+
+func TestTagLists_Flatten(t *testing.T) {
+	tests := []struct {
+		name string
+		l    TagLists
+		want TagList
+	}{
+		{
+			name: "4 tags",
+			l: TagLists{
+				TagList{
+					"tag1",
+					"tag2",
+				},
+				TagList{
+					"tag3",
+					"tag4",
+				},
+			},
+			want: TagList{"tag1", "tag2", "tag3", "tag4"},
+		},
+		{
+			name: "No tags",
+			l:    nil,
+			want: TagList{},
+		},
+		{
+			name: "Empty tags",
+			l:    TagLists{[]string{""}},
+			want: TagList{},
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got := tt.l.Flatten()
+			rtest.Equals(t, got, tt.want)
+		})
+	}
+}