seen: verify arrays (#663)

Fixes #662

internal/ast/ast.go

@@ -136,7 +136,6 @@ func (n *Node) Key() Iterator {
 // Guaranteed to be non-nil.
 // Panics if not called on a KeyValue node, or if the Children are malformed.
 func (n *Node) Value() *Node {
-	assertKind(KeyValue, *n)
 	return n.Child()
 }
 
@@ -144,9 +143,3 @@ func (n *Node) Value() *Node {
 func (n *Node) Children() Iterator {
 	return Iterator{node: n.Child()}
 }
-
-func assertKind(k Kind, n Node) {
-	if n.Kind != k {
-		panic(fmt.Errorf("method was expecting a %s, not a %s", k, n.Kind))
-	}
-}

internal/tracker/seen.go

@@ -232,9 +232,14 @@ func (s *SeenTracker) checkKeyValue(parentIdx int, node *ast.Node) error {
 	kind := valueKind
 	var err error
 
-	if node.Value().Kind == ast.InlineTable {
+	value := node.Value()
+
+	switch value.Kind {
+	case ast.InlineTable:
 		kind = tableKind
-		err = s.checkInlineTable(parentIdx, node.Value())
+		err = s.checkInlineTable(parentIdx, value)
+	case ast.Array:
+		err = s.checkArray(parentIdx, value)
 	}
 
 	s.entries[parentIdx].kind = kind
@@ -242,6 +247,32 @@ func (s *SeenTracker) checkKeyValue(parentIdx int, node *ast.Node) error {
 	return err
 }
 
+func (s *SeenTracker) checkArray(parentIdx int, node *ast.Node) error {
+	set := false
+	it := node.Children()
+	for it.Next() {
+		if set {
+			s.clear(parentIdx)
+		}
+		n := it.Node()
+		switch n.Kind {
+		case ast.InlineTable:
+			err := s.checkInlineTable(parentIdx, n)
+			if err != nil {
+				return err
+			}
+			set = true
+		case ast.Array:
+			err := s.checkArray(parentIdx, n)
+			if err != nil {
+				return err
+			}
+			set = true
+		}
+	}
+	return nil
+}
+
 func (s *SeenTracker) checkInlineTable(parentIdx int, node *ast.Node) error {
 	it := node.Children()
 	for it.Next() {

unmarshaler_test.go

@@ -1916,6 +1916,12 @@ func TestIssue658(t *testing.T) {
 	require.Error(t, err)
 }
 
+func TestIssue662(t *testing.T) {
+	var v map[string]interface{}
+	err := toml.Unmarshal([]byte("a=[{b=1,b=2}]"), &v)
+	require.Error(t, err)
+}
+
 //nolint:funlen
 func TestUnmarshalDecodeErrors(t *testing.T) {
 	examples := []struct {