Audit ordinary list changes at field paths

internal/engine/resolution_compare.go

@@ -0,0 +1,52 @@
+package engine
+
+import (
+	"cmp"
+	"slices"
+
+	"go.maximumdirect.net/configkit/internal/document"
+)
+
+// compareResolutionValues reports field-level changes at stable list positions.
+func compareResolutionValues(before, after *document.Node) []documentDelta {
+	var deltas []documentDelta
+	var compare func(*document.Node, *document.Node, Path)
+	compare = func(left, right *document.Node, path Path) {
+		if left == nil || right == nil || left.Kind != right.Kind {
+			compareConfigurationValue(left, right, path, &deltas)
+			return
+		}
+		switch left.Kind {
+		case document.Mapping:
+			leftEntries := make(map[string]*document.Node, len(left.Mapping))
+			for _, entry := range left.Mapping {
+				leftEntries[entry.Key] = entry.Value
+			}
+			for _, entry := range right.Mapping {
+				compare(leftEntries[entry.Key], entry.Value, path.Key(entry.Key))
+				delete(leftEntries, entry.Key)
+			}
+			for key, value := range leftEntries {
+				compare(value, nil, path.Key(key))
+			}
+		case document.Sequence:
+			if len(left.Sequence) != len(right.Sequence) {
+				deltas = append(deltas, documentDelta{path: path.clone(), kind: documentReplaced})
+				return
+			}
+			for index := range left.Sequence {
+				compare(left.Sequence[index], right.Sequence[index], path.Index(index))
+			}
+		default:
+			compareConfigurationValue(left, right, path, &deltas)
+		}
+	}
+	compare(before, after, Path{})
+	slices.SortFunc(deltas, func(a, b documentDelta) int {
+		if order := cmp.Compare(a.path.String(), b.path.String()); order != 0 {
+			return order
+		}
+		return int(a.kind) - int(b.kind)
+	})
+	return deltas
+}