tpl/collections: Fix union when the first slice is empty

Fixes #3686

diff --git a/tpl/collections/collections.go b/tpl/collections/collections.go
index 103cb38604dd206f616826386eff7caa6b36c99d..bc80acbbec6361bc415f9c2eac9d8257a167b7f5 100644 (file)
--- a/tpl/collections/collections.go
+++ b/tpl/collections/collections.go
@@ -494,6 +494,7 @@ type intersector struct {
 }
 
 func (i *intersector) appendIfNotSeen(v reflect.Value) {
+
        vi := v.Interface()
        if !i.seen[vi] {
                i.r = reflect.Append(i.r, v)
@@ -565,6 +566,14 @@ func (ns *Namespace) Union(l1, l2 interface{}) (interface{}, error) {
                                }
                        }
 
+                       if !l1vv.IsValid() {
+                               // The first slice may be empty. Pick the first value of the second
+                               // to use as a prototype.
+                               if l2v.Len() > 0 {
+                                       l1vv = l2v.Index(0)
+                               }
+                       }
+
                        for j := 0; j < l2v.Len(); j++ {
                                l2vv := l2v.Index(j)
 

diff --git a/tpl/collections/collections_test.go b/tpl/collections/collections_test.go
index 46bef9483063f8b30fd0fb8c1611a5a65496f35f..239affad15692cf6f46d69bdd2c7e11f0c8c0e6c 100644 (file)
--- a/tpl/collections/collections_test.go
+++ b/tpl/collections/collections_test.go
@@ -666,6 +666,13 @@ func TestUnion(t *testing.T) {
                {pagesVals{p1v}, pagesVals{p3v, p3v}, pagesVals{p1v, p3v}, false},
                {[]interface{}{p1, p4}, []interface{}{p4, p2, p2}, []interface{}{p1, p4, p2}, false},
                {[]interface{}{p1v}, []interface{}{p3v, p3v}, []interface{}{p1v, p3v}, false},
+               // #3686
+               {[]interface{}{p1v}, []interface{}{}, []interface{}{p1v}, false},
+               {[]interface{}{}, []interface{}{p1v}, []interface{}{p1v}, false},
+               {pagesPtr{p1}, pagesPtr{}, pagesPtr{p1}, false},
+               {pagesVals{p1v}, pagesVals{}, pagesVals{p1v}, false},
+               {pagesPtr{}, pagesPtr{p1}, pagesPtr{p1}, false},
+               {pagesVals{}, pagesVals{p1v}, pagesVals{p1v}, false},
 
                // errors
                {"not array or slice", []string{"a"}, false, true},