Prepare coalesced resolution replay

internal/engine/resolution_index_test.go

@@ -1,11 +1,64 @@
 package engine
 
 import (
+	"reflect"
 	"testing"
 
 	"gitea.maximumdirect.net/eric/ConfigKit/internal/document"
 )
 
+func TestCoalescedResolutionSnapshotsMatchOrderedScan(t *testing.T) {
+	parsedDependency := parseOverrideTestPath(t, "/dependencies/item")
+	snapshots := []resolutionSnapshot{
+		{change: Change{Path: Keys("a", "b"), Reasons: []string{"child", "shared", "child"}, Dependencies: []Path{Keys("dependencies", "item")}, Origin: Origin{Operation: ChangeDerivedDefault}}},
+		{change: Change{Path: Keys("a", "c"), Reasons: []string{"other"}, Dependencies: []Path{Keys("other")}, Origin: Origin{Operation: ChangeDerivedDefault}}},
+		{change: Change{Path: Keys("a"), Reasons: []string{"parent"}, Dependencies: []Path{Keys("parent")}, Origin: Origin{Operation: ChangeDerivedDefault}}},
+		{change: Change{Path: Keys("a", "b", "grand"), Reasons: []string{"deep", "shared"}, Dependencies: []Path{parsedDependency, Keys("deep")}, Origin: Origin{Operation: ChangeDerivedDefault}}},
+		{change: Change{Path: Path{}, Reasons: []string{"root"}, Origin: Origin{Operation: ChangeDerivedDefault}}},
+		{change: Change{Path: Keys("outside"), Reasons: []string{"root child"}, Origin: Origin{Operation: ChangeDerivedDefault}}},
+		{change: Change{Path: Keys("a", "b", "normalization"), Reasons: []string{"normalized"}, Origin: Origin{Operation: ChangeNormalization}}},
+		{change: Change{Path: Keys("a", "none"), Reasons: []string{"parent child"}, Origin: Origin{Operation: ChangeDerivedDefault}}},
+	}
+	want := coalescedResolutionSnapshotsByScan(snapshots)
+	got := coalescedResolutionSnapshots(snapshots)
+	if !reflect.DeepEqual(got, want) {
+		t.Fatalf("coalesced snapshots differ from ordered scan:\n got: %#v\nwant: %#v", got, want)
+	}
+	if len(got) != 4 || got[0].change.Origin.Operation != ChangeNormalization ||
+		!reflect.DeepEqual(got[0].change.Reasons, []string{"child", "shared", "child", "deep", "normalized"}) ||
+		len(got[0].change.Dependencies) != 2 || got[3].change.Path.String() != "" {
+		t.Fatalf("coalesced ordering or unions changed: %#v", got)
+	}
+}
+
+func coalescedResolutionSnapshotsByScan(snapshots []resolutionSnapshot) []resolutionSnapshot {
+	groups := make([]resolutionSnapshot, 0, len(snapshots))
+	for _, snapshot := range snapshots {
+		merged := false
+		for i := range groups {
+			if !pathContains(groups[i].change.Path, snapshot.change.Path) {
+				continue
+			}
+			for _, reason := range snapshot.change.Reasons {
+				groups[i].change.Reasons = appendUniqueString(groups[i].change.Reasons, reason)
+			}
+			for _, dependency := range snapshot.change.Dependencies {
+				groups[i].change.Dependencies = appendUniquePath(groups[i].change.Dependencies, dependency)
+			}
+			if snapshot.change.Origin.Operation == ChangeNormalization {
+				groups[i].change.Origin.Operation = ChangeNormalization
+			}
+			merged = true
+			break
+		}
+		if !merged {
+			snapshot.change = cloneChange(snapshot.change)
+			groups = append(groups, snapshot)
+		}
+	}
+	return groups
+}
+
 func TestResolutionCoverageIndexMatchesOrderedScan(t *testing.T) {
 	paths := []Path{
 		Keys("group"),