Index resolution coverage and document reads

internal/engine/document_walk.go

@@ -31,6 +31,10 @@ func indexDocument(node *document.Node, path Path, index map[string]*document.No
 }
 
 func documentAtPath(root *document.Node, path Path) (*document.Node, bool) {
+	return documentAtPathWithLookup(root, path, nil)
+}
+
+func documentAtPathWithLookup(root *document.Node, path Path, lookup *documentLookup) (*document.Node, bool) {
 	if root == nil || !path.valid() {
 		return nil, false
 	}
@@ -41,17 +45,21 @@ func documentAtPath(root *document.Node, path Path) (*document.Node, bool) {
 			if segment.kind == pathSegmentIndex {
 				return nil, false
 			}
-			found := false
-			for _, entry := range current.Mapping {
-				if entry.Key == segment.key {
-					current = entry.Value
-					found = true
-					break
+			entryIndex := -1
+			if lookup != nil {
+				entryIndex = lookup.find(current, segment.key)
+			} else {
+				for index, entry := range current.Mapping {
+					if entry.Key == segment.key {
+						entryIndex = index
+						break
+					}
 				}
 			}
-			if !found {
+			if entryIndex < 0 || entryIndex >= len(current.Mapping) {
 				return nil, false
 			}
+			current = current.Mapping[entryIndex].Value
 		case document.Sequence:
 			index, ok := schemaIndex(segment)
 			if !ok || index >= len(current.Sequence) {