Reuse owned assembly across configuration layers

internal/engine/overlay_test.go

@@ -76,3 +76,44 @@ to_scalar: scalar
 		t.Fatal("overlay result aliases an input document")
 	}
 }
+
+func TestOwnedOverlayKeepsCompositeContributorsAndAcquiredInputs(t *testing.T) {
+	baseInput := parseCompositionDocument(t, "source-1", "catalog:\n  base: true\n")
+	base, diagnostics := composeDocuments(baseInput)
+	if len(diagnostics) != 0 {
+		t.Fatal(diagnostics)
+	}
+	first := parseCompositionDocument(t, "source-2", "catalog:\n  first: true\n")
+	second := parseCompositionDocument(t, "source-3", "catalog:\n  second: true\n")
+	firstBefore, secondBefore := document.Clone(first), document.Clone(second)
+	incoming, diagnostics := composeDocuments(first, second)
+	if len(diagnostics) != 0 {
+		t.Fatal(diagnostics)
+	}
+	assembly := newAssemblyAccumulator(base)
+	if diagnostics := assembly.applyOverlay(incoming.root, incoming.origins, incoming.applications, LayerOverlay); len(diagnostics) != 0 {
+		t.Fatal(diagnostics)
+	}
+	for _, key := range []string{"base", "first", "second"} {
+		if _, ok := documentAtPath(assembly.current.root, Keys("catalog", key)); !ok {
+			t.Fatalf("catalog is missing %q", key)
+		}
+	}
+	origin := assembly.current.origins[Keys("catalog").String()]
+	if got, want := origin.Locations, []Location{{SourceID: "source-1", Line: 2, Column: 3}, {SourceID: "source-2", Line: 2, Column: 3}, {SourceID: "source-3", Line: 2, Column: 3}}; !reflect.DeepEqual(got, want) {
+		t.Fatalf("catalog origin locations = %#v, want %#v", got, want)
+	}
+	if len(assembly.current.applications) != 3 {
+		t.Fatalf("history applications = %d, want three source contributions", len(assembly.current.applications))
+	}
+	for _, application := range assembly.current.applications[1:] {
+		if application.layer != LayerOverlay {
+			t.Fatalf("incoming application layer = %q", application.layer)
+		}
+	}
+	assembly.current.root.Mapping[0].Value.Mapping[1].Value.Text = "false"
+	if !reflect.DeepEqual(first, firstBefore) || !reflect.DeepEqual(second, secondBefore) ||
+		!reflect.DeepEqual(first, assembly.current.applications[1].value) || !reflect.DeepEqual(second, assembly.current.applications[2].value) {
+		t.Fatal("working tree mutation changed an acquired input")
+	}
+}