Project sequence evidence through item mappings

internal/engine/compose_test.go

@@ -357,6 +357,78 @@ escaped/~:
 	}
 }
 
+func TestProjectedCompositionOriginsUseNoncontiguousItemMappings(t *testing.T) {
+	lowerRoot := parseCompositionDocument(t, "lower", `records:
+  - id: first
+    label: equal
+  - id: middle
+  - id: last
+    nested: {old: lower}
+`)
+	higherRoot := parseCompositionDocument(t, "higher", `records:
+  - id: last
+    nested: {new: higher}
+  - id: first
+    label: equal
+  - id: added
+`)
+	lower, _ := documentAtPath(lowerRoot, Keys("records"))
+	higher, _ := documentAtPath(higherRoot, Keys("records"))
+	combined, diagnostics := combineSequence(
+		lower, higher, sequenceCombinationPolicy(sequenceModeUpsert, "id"),
+		sequenceCombinationContext{destination: Keys("records")},
+	)
+	if len(diagnostics) != 0 {
+		t.Fatalf("combine diagnostics = %#v", diagnostics)
+	}
+	inputs := []*document.Node{lowerRoot, higherRoot}
+	ranges := []sequenceRange{
+		{
+			sourceIndex: 0, path: Keys("records"), start: 0, end: 3,
+			items: combined.lowerItems,
+		}, {
+			sourceIndex: 1, path: Keys("records"), start: 0, end: 3,
+			items: combined.higherItems,
+		},
+	}
+	origins := projectedCompositionOrigins(inputs, ranges)
+	if got, want := sequenceIdentityValues(combined.value, "id"), []string{"first", "middle", "last", "added"}; !reflect.DeepEqual(got, want) {
+		t.Fatalf("combined IDs = %#v, want %#v", got, want)
+	}
+	for path, want := range map[string][]string{
+		"/records/0/label":      {"higher"},
+		"/records/1/id":         {"lower"},
+		"/records/2/nested/new": {"higher"},
+		"/records/3/id":         {"higher"},
+		"/records/0/nested/new": nil,
+		"/records/2/nested/old": nil,
+	} {
+		origin := origins[path]
+		var got []string
+		for _, location := range origin.Locations {
+			got = append(got, location.SourceID)
+		}
+		if !reflect.DeepEqual(got, want) {
+			t.Errorf("origin sources at %s = %#v, want %#v", path, got, want)
+		}
+	}
+}
+
+func TestCloneSequenceRangesPreservesPreparedProjection(t *testing.T) {
+	ranges := []sequenceRange{{
+		start: 0, end: 1,
+		projection: newSequenceItemProjectionIndex([]sequenceItemProjection{{inputIndex: 0, outputIndex: 4}}),
+	}}
+	cloned := cloneSequenceRanges(ranges)
+	if output, ok := cloned[0].outputForInput(0); !ok || output != 4 {
+		t.Fatalf("cloned projection = %d, %v; want output index 4", output, ok)
+	}
+	cloned[0].projection.outputByInput[0] = 9
+	if output, ok := ranges[0].outputForInput(0); !ok || output != 4 {
+		t.Fatalf("cloned projection aliases original: %d, %v", output, ok)
+	}
+}
+
 func TestComposeDocumentsValidatesRegisteredSequenceSingletons(t *testing.T) {
 	tests := []struct {
 		name     string