Avoid duplicate intermediate source history

facade_tier_history_test.go

@@ -0,0 +1,43 @@
+package configkit_test
+
+import (
+	"testing"
+
+	configkit "gitea.maximumdirect.net/eric/ConfigKit"
+)
+
+func TestTierHistoryRecordsEachContributionOnce(t *testing.T) {
+	t.Parallel()
+	for _, middle := range []string{"mid", "low"} {
+		t.Run(middle, func(t *testing.T) {
+			result, err := configkit.LoadLayered[map[string]any](
+				configkit.Input{Source: configkit.Bytes("main", []byte("x: high\n"))},
+				configkit.LayeredOptions[map[string]any]{Underlays: []configkit.Underlay{
+					{Inputs: []configkit.Input{{Source: configkit.Bytes("low", []byte("x: low\n"))}}},
+					{Inputs: []configkit.Input{{Source: configkit.Bytes("middle", []byte("x: "+middle+"\n"))}}},
+				}},
+			)
+			if err != nil {
+				t.Fatal(err)
+			}
+			history := result.Metadata().History(configkit.Keys("x"))
+			if len(history) != 3 {
+				t.Fatalf("history has %d records; want the three independent contributions", len(history))
+			}
+			for index, sourceID := range []string{"source-2", "source-3", "source-1"} {
+				change := history[index]
+				if len(change.Origin.Locations) != 1 || change.Origin.Locations[0].SourceID != sourceID {
+					t.Fatalf("contribution %d has origin %#v", index, change.Origin)
+				}
+				if index == 0 {
+					if len(change.Previous) != 0 {
+						t.Fatal("first source contribution has a previous origin")
+					}
+				} else if len(change.Previous) != 1 || len(change.Previous[0].Locations) != 1 ||
+					change.Previous[0].Locations[0] != history[index-1].Origin.Locations[0] {
+					t.Fatalf("contribution %d has incorrect previous origin %#v", index, change.Previous)
+				}
+			}
+		})
+	}
+}