tpl: Fix panic in pairList.Less

While sorting on data sources with missing fields, a panic can occur in
pairList.Less if `Interface()` is called on a invalid `reflect.Value`.
This commit detects an invalid Value and replacing it with a zero value
for the comparison.

diff --git a/tpl/template_funcs.go b/tpl/template_funcs.go
index e9cc26869f5808d3d3ad3f1fdf8ab6ad9133dfab..ad5b8db1e35bd0d0e82d87eab589a4f79ad3925e 100644 (file)
--- a/tpl/template_funcs.go
+++ b/tpl/template_funcs.go
@@ -1054,7 +1054,24 @@ type pairList struct {
 func (p pairList) Swap(i, j int) { p.Pairs[i], p.Pairs[j] = p.Pairs[j], p.Pairs[i] }
 func (p pairList) Len() int      { return len(p.Pairs) }
 func (p pairList) Less(i, j int) bool {
-       return lt(p.Pairs[i].SortByValue.Interface(), p.Pairs[j].SortByValue.Interface())
+       iv := p.Pairs[i].SortByValue
+       jv := p.Pairs[j].SortByValue
+
+       if iv.IsValid() {
+               if jv.IsValid() {
+                       // can only call Interface() on valid reflect Values
+                       return lt(iv.Interface(), jv.Interface())
+               }
+               // if j is invalid, test i against i's zero value
+               return lt(iv.Interface(), reflect.Zero(iv.Type()))
+       }
+
+       if jv.IsValid() {
+               // if i is invalid, test j against j's zero value
+               return lt(reflect.Zero(jv.Type()), jv.Interface())
+       }
+
+       return false
 }
 
 // sorts a pairList and returns a slice of sorted values

diff --git a/tpl/template_funcs_test.go b/tpl/template_funcs_test.go
index a36629afdd3bd9519e66dc4dd0d1e3b0eb870e8b..4b49da41b04445a2f5b84943622d5972c8e87714 100644 (file)
--- a/tpl/template_funcs_test.go
+++ b/tpl/template_funcs_test.go
@@ -1535,6 +1535,21 @@ func TestSort(t *testing.T) {
                        "asc",
                        []map[string]mid{{"foo": mid{Tst: TstX{A: "a", B: "b"}}}, {"foo": mid{Tst: TstX{A: "c", B: "d"}}}, {"foo": mid{Tst: TstX{A: "e", B: "f"}}}},
                },
+               // interface slice with missing elements
+               {
+                       []interface{}{
+                               map[interface{}]interface{}{"Title": "Foo", "Weight": 10},
+                               map[interface{}]interface{}{"Title": "Bar"},
+                               map[interface{}]interface{}{"Title": "Zap", "Weight": 5},
+                       },
+                       "Weight",
+                       "asc",
+                       []interface{}{
+                               map[interface{}]interface{}{"Title": "Bar"},
+                               map[interface{}]interface{}{"Title": "Zap", "Weight": 5},
+                               map[interface{}]interface{}{"Title": "Foo", "Weight": 10},
+                       },
+               },
                // test error cases
                {(*[]TstX)(nil), nil, "asc", false},
                {TstX{A: "a", B: "b"}, nil, "asc", false},