Explain defaults restored during final decoding

explain_test.go

@@ -326,3 +326,42 @@ func historyValueLayers(explanation Explanation) []Layer {
 	}
 	return layers
 }
+
+func TestExplanationReconcilesDefaultsAfterInputReplacement(t *testing.T) {
+	type cfg struct {
+		M map[string]int `yaml:"m"`
+	}
+	for _, base := range []string{"null", "replaced-text"} {
+		for _, cli := range []bool{false, true} {
+			t.Run(fmt.Sprintf("%s/cli=%v", base, cli), func(t *testing.T) {
+				root := t.TempDir()
+				main := writeImportFile(t, root, "main.yml", "m: "+base+"\n")
+				opts := Options[cfg]{Definition: Definition[cfg]{Defaults: func() cfg { return cfg{M: map[string]int{"a": 1}} }}}
+				if cli {
+					opts.Overrides = []Override{{Path: Keys("m"), Value: map[string]any{"b": 2}, Flag: "--m"}}
+				} else {
+					writeImportFile(t, root, "profiles/p.yml", "m: {b: 2}\n")
+					opts.Profile = "p"
+				}
+				result, err := Load(File(main), opts)
+				if err != nil {
+					t.Fatal(err)
+				}
+				for _, path := range []Path{Keys("m"), Keys("m", "a")} {
+					explanation, ok := result.Explain(path)
+					if !ok {
+						t.Fatal("missing explanation")
+					}
+					last := explanation.History[len(explanation.History)-1]
+					if last.After != explanation.Effective || last.Origin.Operation != ChangeDecoding {
+						t.Fatalf("history does not reconcile final value: %#v", explanation)
+					}
+					info, _ := result.Metadata().Lookup(path)
+					if last.Origin.Layer != info.Origin.Layer {
+						t.Fatal("decoding lost effective origin")
+					}
+				}
+			})
+		}
+	}
+}