Add last template function

`last` allows the user to select the last X items of
and array.

tpl/template_funcs.go

@@ -388,6 +388,42 @@ func First(limit interface{}, seq interface{}) (interface{}, error) {
 	return seqv.Slice(0, limitv).Interface(), nil
 }
 
+// Last is exposed to templates, to iterate over the last N items in a
+// rangeable list.
+func Last(limit interface{}, seq interface{}) (interface{}, error) {
+
+	if limit == nil || seq == nil {
+		return nil, errors.New("both limit and seq must be provided")
+	}
+
+	limitv, err := cast.ToIntE(limit)
+
+	if err != nil {
+		return nil, err
+	}
+
+	if limitv < 1 {
+		return nil, errors.New("can't return negative/empty count of items from sequence")
+	}
+
+	seqv := reflect.ValueOf(seq)
+	seqv, isNil := indirect(seqv)
+	if isNil {
+		return nil, errors.New("can't iterate over a nil value")
+	}
+
+	switch seqv.Kind() {
+	case reflect.Array, reflect.Slice, reflect.String:
+		// okay
+	default:
+		return nil, errors.New("can't iterate over " + reflect.ValueOf(seq).Type().String())
+	}
+	if limitv > seqv.Len() {
+		limitv = seqv.Len()
+	}
+	return seqv.Slice(seqv.Len()-limitv, seqv.Len()).Interface(), nil
+}
+
 // After is exposed to templates, to iterate over all the items after N in a
 // rangeable list. It's meant to accompany First
 func After(index interface{}, seq interface{}) (interface{}, error) {
@@ -1288,6 +1324,7 @@ func init() {
 		"relURL":      func(a string) template.HTML { return template.HTML(helpers.RelURL(a)) },
 		"markdownify": Markdownify,
 		"first":       First,
+		"last":        Last,
 		"after":       After,
 		"where":       Where,
 		"delimit":     Delimit,

tpl/template_funcs_test.go

@@ -253,6 +253,40 @@ func TestFirst(t *testing.T) {
 	}
 }
 
+func TestLast(t *testing.T) {
+	for i, this := range []struct {
+		count    interface{}
+		sequence interface{}
+		expect   interface{}
+	}{
+		{int(2), []string{"a", "b", "c"}, []string{"b", "c"}},
+		{int32(3), []string{"a", "b"}, []string{"a", "b"}},
+		{int64(2), []int{100, 200, 300}, []int{200, 300}},
+		{100, []int{100, 200}, []int{100, 200}},
+		{"1", []int{100, 200, 300}, []int{300}},
+		{int64(-1), []int{100, 200, 300}, false},
+		{"noint", []int{100, 200, 300}, false},
+		{1, nil, false},
+		{nil, []int{100}, false},
+		{1, t, false},
+	} {
+		results, err := Last(this.count, this.sequence)
+		if b, ok := this.expect.(bool); ok && !b {
+			if err == nil {
+				t.Errorf("[%d] First didn't return an expected error", i)
+			}
+		} else {
+			if err != nil {
+				t.Errorf("[%d] failed: %s", i, err)
+				continue
+			}
+			if !reflect.DeepEqual(results, this.expect) {
+				t.Errorf("[%d] First %d items, got %v but expected %v", i, this.count, results, this.expect)
+			}
+		}
+	}
+}
+
 func TestAfter(t *testing.T) {
 	for i, this := range []struct {
 		count    interface{}