Audit ordinary list changes at field paths

internal/engine/resolution.go

@@ -313,7 +313,7 @@ func runResolution[T any](configuration *T, resolver func(*T, *Resolution) error
 		state.addDiagnostic(CodeResolveInvalidValue, issue.path, "application resolution produced an invalid configuration value")
 		return resolutionResult{diagnostics: canonicalDiagnostics(state.diagnostics)}
 	}
-	deltas := compareConfigurationValues(decoded.final, after)
+	deltas := compareResolutionValues(decoded.final, after)
 	ordered := orderedResolutionRecords(state.records)
 	coverage := newResolutionCoverageIndexFromRecords(ordered)
 	beforeLookup := buildDocumentLookup(decoded.final)

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
+}

internal/engine/resolution_compare_test.go

@@ -0,0 +1,74 @@
+package engine
+
+import (
+	"errors"
+	"testing"
+)
+
+func TestResolutionAuditsOrdinaryListFields(t *testing.T) {
+	type item struct {
+		Count   int    `yaml:"count"`
+		Enabled bool   `yaml:"enabled"`
+		Nested  []*int `yaml:"nested"`
+	}
+	type config struct {
+		Items []item `yaml:"items"`
+	}
+	for _, test := range []struct {
+		name          string
+		other, resize bool
+		wantPath      string
+	}{
+		{name: "covered field"},
+		{name: "uncovered field", other: true, wantPath: "/items/0/enabled"},
+		{name: "length change", resize: true, wantPath: "/items"},
+	} {
+		t.Run(test.name, func(t *testing.T) {
+			result, err := testLoad(Bytes("items", []byte("items: [{count: 3, enabled: true, nested: [null]}]\n")), Options[config]{Definition: Definition[config]{
+				Resolve: func(value *config, r *Resolution) error {
+					value.Items[0].Count = 0
+					r.RecordNormalization(Keys("items").Index(0).Key("count"), "clear count")
+					if test.other {
+						value.Items[0].Enabled = false
+					}
+					if test.resize {
+						value.Items = append(value.Items, item{})
+					}
+					return nil
+				},
+			}})
+			if test.wantPath == "" {
+				if err != nil || result.Config.Items[0].Count != 0 {
+					t.Fatalf("result = %#v, error = %v", result, err)
+				}
+				return
+			}
+			var failure *LoadError
+			if !errors.As(err, &failure) {
+				t.Fatalf("error = %v", err)
+			}
+			found := false
+			for _, diagnostic := range failure.Diagnostics() {
+				if diagnostic.Code == CodeResolveUnrecordedChange && diagnostic.Path.String() == test.wantPath {
+					found = true
+				}
+			}
+			if !found {
+				t.Fatalf("diagnostics = %#v", failure.Diagnostics())
+			}
+		})
+	}
+}
+
+func TestResolutionComparisonKeepsDiffAtomic(t *testing.T) {
+	before := parseCompositionDocument(t, "before", "items: [{values: [true, null]}]")
+	after := parseCompositionDocument(t, "after", "items: [{values: [false, 0]}]")
+	deltas := compareResolutionValues(before, after)
+	if len(deltas) != 2 || deltas[0].path.String() != "/items/0/values/0" || deltas[1].path.String() != "/items/0/values/1" {
+		t.Fatalf("resolution deltas = %#v", deltas)
+	}
+	atomic := compareConfigurationValues(before, after)
+	if len(atomic) != 1 || atomic[0].path.String() != "/items" {
+		t.Fatalf("atomic deltas = %#v", atomic)
+	}
+}