Decode typed configuration over defaults

decode.go

@@ -0,0 +1,455 @@
+package configkit
+
+import (
+	"encoding"
+	"math"
+	"reflect"
+	"regexp"
+	"strconv"
+	"time"
+
+	"gitea.maximumdirect.net/eric/ConfigKit/internal/document"
+)
+
+var integerPattern = regexp.MustCompile(`^-?(0|[1-9][0-9]*)$`)
+var unsignedIntegerPattern = regexp.MustCompile(`^(0|[1-9][0-9]*)$`)
+
+type decodeIssue struct {
+	code     Code
+	path     Path
+	message  string
+	location document.Location
+}
+
+type inputPresence struct {
+	null     bool
+	location document.Location
+}
+
+type decodedConfiguration struct {
+	value    reflect.Value
+	presence map[string]inputPresence
+	origins  map[string]Origin
+	baseline *document.Node
+	final    *document.Node
+}
+
+func decodeConfiguration(schema *schemaDescriptor, defaults reflect.Value, input *document.Node) (decodedConfiguration, []decodeIssue) {
+	if schema == nil || schema.root == nil || !defaults.IsValid() || defaults.Type() != schema.root.typeOf {
+		return decodedConfiguration{}, []decodeIssue{{code: CodeSchemaUnsupportedType, message: "configuration defaults do not match the schema"}}
+	}
+	baseline, projectionIssue := projectConfiguration(schema, defaults, defaultProjectionLimits())
+	if projectionIssue != nil {
+		return decodedConfiguration{}, []decodeIssue{decodeIssueFromProjection(projectionIssue)}
+	}
+	working, cloneIssue := cloneConfiguration(schema, defaults, defaultProjectionLimits())
+	if cloneIssue != nil {
+		return decodedConfiguration{}, []decodeIssue{decodeIssueFromProjection(cloneIssue)}
+	}
+
+	presence := make(map[string]inputPresence)
+	if input != nil {
+		collectPresence(input, Path{}, presence)
+		decoded, issues := decodeValue(input, working, schema.root, Path{}, schema)
+		if len(issues) != 0 {
+			return decodedConfiguration{}, issues
+		}
+		working = decoded
+	}
+	final, projectionIssue := projectConfiguration(schema, working, defaultProjectionLimits())
+	if projectionIssue != nil {
+		return decodedConfiguration{}, []decodeIssue{decodeIssueFromProjection(projectionIssue)}
+	}
+	origins := make(map[string]Origin)
+	collectOrigins(final, Path{}, presence, origins)
+	return decodedConfiguration{
+		value:    working,
+		presence: presence,
+		origins:  origins,
+		baseline: baseline,
+		final:    final,
+	}, nil
+}
+
+func decodeValue(node *document.Node, base reflect.Value, descriptor *typeDescriptor, path Path, schema *schemaDescriptor) (reflect.Value, []decodeIssue) {
+	if node.Kind == document.Null {
+		switch descriptor.kind {
+		case descriptorPointer, descriptorMap, descriptorSlice, descriptorDynamic:
+			return reflect.Zero(descriptor.typeOf), nil
+		default:
+			return reflect.Value{}, []decodeIssue{newDecodeIssue(CodeDecodeNull, path, node, "null is not allowed for this configuration type")}
+		}
+	}
+	if descriptor.kind == descriptorPointer {
+		var elementBase reflect.Value
+		if base.IsNil() {
+			elementBase = reflect.Zero(descriptor.typeOf.Elem())
+		} else {
+			elementBase = base.Elem()
+		}
+		decoded, issues := decodeValue(node, elementBase, descriptor.element, path, schema)
+		if len(issues) != 0 {
+			return reflect.Value{}, issues
+		}
+		result := reflect.New(descriptor.typeOf.Elem())
+		result.Elem().Set(decoded)
+		return result, nil
+	}
+
+	switch descriptor.kind {
+	case descriptorStruct:
+		return decodeStruct(node, base, descriptor, path, schema)
+	case descriptorMap:
+		return decodeMap(node, base, descriptor, path, schema)
+	case descriptorSlice:
+		return decodeSlice(node, descriptor, path, schema)
+	case descriptorArray:
+		return decodeArray(node, descriptor, path, schema)
+	case descriptorDynamic:
+		return decodeDynamic(node, base, path, schema)
+	case descriptorString:
+		if node.Kind != document.String {
+			return typeMismatch(path, node, "string")
+		}
+		result := reflect.New(descriptor.typeOf).Elem()
+		result.SetString(node.Text)
+		return result, nil
+	case descriptorBoolean:
+		if node.Kind != document.Boolean {
+			return typeMismatch(path, node, "boolean")
+		}
+		result := reflect.New(descriptor.typeOf).Elem()
+		result.SetBool(node.Text == "true")
+		return result, nil
+	case descriptorSigned:
+		if node.Kind != document.Number || !integerPattern.MatchString(node.Text) {
+			return typeMismatch(path, node, "integer")
+		}
+		value, err := strconv.ParseInt(node.Text, 10, descriptor.typeOf.Bits())
+		if err != nil {
+			return rangeFailure(path, node, "integer")
+		}
+		result := reflect.New(descriptor.typeOf).Elem()
+		result.SetInt(value)
+		return result, nil
+	case descriptorUnsigned:
+		if node.Kind != document.Number || !unsignedIntegerPattern.MatchString(node.Text) {
+			return typeMismatch(path, node, "unsigned integer")
+		}
+		value, err := strconv.ParseUint(node.Text, 10, descriptor.typeOf.Bits())
+		if err != nil {
+			return rangeFailure(path, node, "unsigned integer")
+		}
+		result := reflect.New(descriptor.typeOf).Elem()
+		result.SetUint(value)
+		return result, nil
+	case descriptorFloat:
+		if node.Kind != document.Number {
+			return typeMismatch(path, node, "number")
+		}
+		value, err := strconv.ParseFloat(node.Text, descriptor.typeOf.Bits())
+		if err != nil || math.IsNaN(value) || math.IsInf(value, 0) {
+			return rangeFailure(path, node, "number")
+		}
+		result := reflect.New(descriptor.typeOf).Elem()
+		result.SetFloat(value)
+		return result, nil
+	case descriptorDuration:
+		if node.Kind != document.String {
+			return typeMismatch(path, node, "duration string")
+		}
+		value, err := time.ParseDuration(node.Text)
+		if err != nil {
+			return reflect.Value{}, []decodeIssue{newDecodeIssue(CodeDecodeDuration, path, node, "duration string is invalid")}
+		}
+		result := reflect.New(descriptor.typeOf).Elem()
+		result.SetInt(int64(value))
+		return result, nil
+	case descriptorText:
+		if node.Kind != document.String {
+			return typeMismatch(path, node, "text string")
+		}
+		result := reflect.New(descriptor.typeOf).Elem()
+		unmarshaler := result.Addr().Interface().(encoding.TextUnmarshaler)
+		if err := unmarshaler.UnmarshalText([]byte(node.Text)); err != nil {
+			return reflect.Value{}, []decodeIssue{newDecodeIssue(CodeDecodeText, path, node, "text value is invalid for its configuration type")}
+		}
+		return result, nil
+	default:
+		return reflect.Value{}, []decodeIssue{newDecodeIssue(CodeSchemaUnsupportedType, path, node, "configuration type is not supported")}
+	}
+}
+
+func decodeStruct(node *document.Node, base reflect.Value, descriptor *typeDescriptor, path Path, schema *schemaDescriptor) (reflect.Value, []decodeIssue) {
+	if node.Kind != document.Mapping {
+		return typeMismatch(path, node, "mapping")
+	}
+	result := reflect.New(descriptor.typeOf).Elem()
+	result.Set(base)
+	var issues []decodeIssue
+	for _, entry := range node.Mapping {
+		childPath := path.Key(entry.Key)
+		if position, ok := descriptor.fieldByName[entry.Key]; ok {
+			field := descriptor.fields[position]
+			target, ok := fieldForDecode(result, field.index, true)
+			if !ok {
+				issues = append(issues, decodeIssue{code: CodeSchemaUnsupportedType, path: childPath, message: "configuration field could not be addressed", location: entry.ValueLocation})
+				continue
+			}
+			decoded, fieldIssues := decodeValue(entry.Value, target, field.descriptor, childPath, schema)
+			if len(fieldIssues) != 0 {
+				issues = append(issues, fieldIssues...)
+				continue
+			}
+			target.Set(decoded)
+			continue
+		}
+		if descriptor.inlineMap != nil {
+			if issue := decodeInlineMapEntry(result, *descriptor.inlineMap, entry, childPath, schema); issue != nil {
+				issues = append(issues, issue...)
+			}
+			continue
+		}
+		issues = append(issues, decodeIssue{code: CodeDecodeUnknownField, path: childPath, message: "configuration field is not declared", location: entry.KeyLocation})
+	}
+	return result, issues
+}
+
+func decodeInlineMapEntry(target reflect.Value, field fieldDescriptor, entry document.Entry, path Path, schema *schemaDescriptor) []decodeIssue {
+	mapValue, ok := fieldForDecode(target, field.index, true)
+	if !ok || mapValue.Kind() != reflect.Map {
+		return []decodeIssue{{code: CodeSchemaInline, path: path, message: "inline map could not be addressed", location: entry.KeyLocation}}
+	}
+	if mapValue.IsNil() {
+		mapValue.Set(reflect.MakeMap(mapValue.Type()))
+	}
+	key := reflect.New(mapValue.Type().Key()).Elem()
+	key.SetString(entry.Key)
+	base := mapValue.MapIndex(key)
+	if !base.IsValid() {
+		base = reflect.Zero(mapValue.Type().Elem())
+	}
+	decoded, issues := decodeValue(entry.Value, base, field.descriptor.element, path, schema)
+	if len(issues) == 0 {
+		mapValue.SetMapIndex(key, decoded)
+	}
+	return issues
+}
+
+func decodeMap(node *document.Node, base reflect.Value, descriptor *typeDescriptor, path Path, schema *schemaDescriptor) (reflect.Value, []decodeIssue) {
+	if node.Kind != document.Mapping {
+		return typeMismatch(path, node, "mapping")
+	}
+	result := base
+	if result.IsNil() {
+		result = reflect.MakeMap(descriptor.typeOf)
+	}
+	var issues []decodeIssue
+	for _, entry := range node.Mapping {
+		key := reflect.New(descriptor.typeOf.Key()).Elem()
+		key.SetString(entry.Key)
+		entryBase := result.MapIndex(key)
+		if !entryBase.IsValid() {
+			entryBase = reflect.Zero(descriptor.typeOf.Elem())
+		}
+		decoded, entryIssues := decodeValue(entry.Value, entryBase, descriptor.element, path.Key(entry.Key), schema)
+		if len(entryIssues) != 0 {
+			issues = append(issues, entryIssues...)
+			continue
+		}
+		result.SetMapIndex(key, decoded)
+	}
+	return result, issues
+}
+
+func decodeSlice(node *document.Node, descriptor *typeDescriptor, path Path, schema *schemaDescriptor) (reflect.Value, []decodeIssue) {
+	if node.Kind != document.Sequence {
+		return typeMismatch(path, node, "sequence")
+	}
+	result := reflect.MakeSlice(descriptor.typeOf, len(node.Sequence), len(node.Sequence))
+	var issues []decodeIssue
+	for i, child := range node.Sequence {
+		decoded, childIssues := decodeValue(child, reflect.Zero(descriptor.typeOf.Elem()), descriptor.element, path.Index(i), schema)
+		if len(childIssues) != 0 {
+			issues = append(issues, childIssues...)
+			continue
+		}
+		result.Index(i).Set(decoded)
+	}
+	return result, issues
+}
+
+func decodeArray(node *document.Node, descriptor *typeDescriptor, path Path, schema *schemaDescriptor) (reflect.Value, []decodeIssue) {
+	if node.Kind != document.Sequence {
+		return typeMismatch(path, node, "sequence")
+	}
+	if len(node.Sequence) != descriptor.length {
+		return reflect.Value{}, []decodeIssue{newDecodeIssue(CodeDecodeArrayLength, path, node, "configuration array has the wrong length")}
+	}
+	result := reflect.New(descriptor.typeOf).Elem()
+	var issues []decodeIssue
+	for i, child := range node.Sequence {
+		decoded, childIssues := decodeValue(child, reflect.Zero(descriptor.typeOf.Elem()), descriptor.element, path.Index(i), schema)
+		if len(childIssues) != 0 {
+			issues = append(issues, childIssues...)
+			continue
+		}
+		result.Index(i).Set(decoded)
+	}
+	return result, issues
+}
+
+func decodeDynamic(node *document.Node, base reflect.Value, path Path, schema *schemaDescriptor) (reflect.Value, []decodeIssue) {
+	if node.Kind == document.Mapping && base.IsValid() && !base.IsNil() {
+		concrete := base.Elem()
+		operation := valueOperation{schema: schema}
+		descriptor, issue := operation.dynamicDescriptor(concrete.Type(), path)
+		if issue == nil && acceptsMapping(descriptor) {
+			decoded, issues := decodeValue(node, concrete, descriptor, path, schema)
+			if len(issues) != 0 {
+				return reflect.Value{}, issues
+			}
+			result := reflect.New(base.Type()).Elem()
+			result.Set(decoded)
+			return result, nil
+		}
+	}
+	var value any
+	switch node.Kind {
+	case document.Null:
+		return reflect.Zero(base.Type()), nil
+	case document.String:
+		value = node.Text
+	case document.Boolean:
+		value = node.Text == "true"
+	case document.Number:
+		if integerPattern.MatchString(node.Text) {
+			parsed, err := strconv.ParseInt(node.Text, 10, 64)
+			if err != nil {
+				return rangeFailure(path, node, "dynamic integer")
+			}
+			value = parsed
+		} else {
+			parsed, err := strconv.ParseFloat(node.Text, 64)
+			if err != nil || math.IsNaN(parsed) || math.IsInf(parsed, 0) {
+				return rangeFailure(path, node, "dynamic number")
+			}
+			value = parsed
+		}
+	case document.Sequence:
+		sequence := make([]any, len(node.Sequence))
+		var issues []decodeIssue
+		for i, child := range node.Sequence {
+			decoded, childIssues := decodeDynamic(child, reflect.Zero(reflect.TypeFor[any]()), path.Index(i), schema)
+			if len(childIssues) != 0 {
+				issues = append(issues, childIssues...)
+				continue
+			}
+			sequence[i] = decoded.Interface()
+		}
+		if len(issues) != 0 {
+			return reflect.Value{}, issues
+		}
+		value = sequence
+	case document.Mapping:
+		mapping := make(map[string]any, len(node.Mapping))
+		var issues []decodeIssue
+		for _, entry := range node.Mapping {
+			decoded, childIssues := decodeDynamic(entry.Value, reflect.Zero(reflect.TypeFor[any]()), path.Key(entry.Key), schema)
+			if len(childIssues) != 0 {
+				issues = append(issues, childIssues...)
+				continue
+			}
+			mapping[entry.Key] = decoded.Interface()
+		}
+		if len(issues) != 0 {
+			return reflect.Value{}, issues
+		}
+		value = mapping
+	default:
+		return reflect.Value{}, []decodeIssue{newDecodeIssue(CodeDecodeType, path, node, "dynamic configuration value has an unsupported kind")}
+	}
+	result := reflect.New(base.Type()).Elem()
+	if value != nil {
+		result.Set(reflect.ValueOf(value))
+	}
+	return result, nil
+}
+
+func acceptsMapping(descriptor *typeDescriptor) bool {
+	for descriptor != nil && descriptor.kind == descriptorPointer {
+		descriptor = descriptor.element
+	}
+	return descriptor != nil && (descriptor.kind == descriptorStruct || descriptor.kind == descriptorMap || descriptor.kind == descriptorDynamic)
+}
+
+func fieldForDecode(root reflect.Value, index []int, allocate bool) (reflect.Value, bool) {
+	current := root
+	for position, fieldIndex := range index {
+		if current.Kind() != reflect.Struct {
+			return reflect.Value{}, false
+		}
+		current = current.Field(fieldIndex)
+		if position == len(index)-1 {
+			return current, current.CanSet()
+		}
+		for current.Kind() == reflect.Pointer {
+			if current.IsNil() {
+				if !allocate || !current.CanSet() {
+					return reflect.Value{}, false
+				}
+				current.Set(reflect.New(current.Type().Elem()))
+			}
+			current = current.Elem()
+		}
+	}
+	return reflect.Value{}, false
+}
+
+func collectPresence(node *document.Node, path Path, presence map[string]inputPresence) {
+	presence[path.String()] = inputPresence{null: node.Kind == document.Null, location: node.Location}
+	switch node.Kind {
+	case document.Mapping:
+		for _, entry := range node.Mapping {
+			collectPresence(entry.Value, path.Key(entry.Key), presence)
+		}
+	case document.Sequence:
+		for i, child := range node.Sequence {
+			collectPresence(child, path.Index(i), presence)
+		}
+	}
+}
+
+func collectOrigins(node *document.Node, path Path, presence map[string]inputPresence, origins map[string]Origin) {
+	if input, ok := presence[path.String()]; ok {
+		origins[path.String()] = Origin{Layer: LayerBase, Locations: []Location{{SourceID: input.location.SourceID, Line: input.location.Line, Column: input.location.Column}}}
+	} else {
+		origins[path.String()] = Origin{Layer: LayerDefault}
+	}
+	switch node.Kind {
+	case document.Mapping:
+		for _, entry := range node.Mapping {
+			collectOrigins(entry.Value, path.Key(entry.Key), presence, origins)
+		}
+	case document.Sequence:
+		for i, child := range node.Sequence {
+			collectOrigins(child, path.Index(i), presence, origins)
+		}
+	}
+}
+
+func decodeIssueFromProjection(issue *projectionIssue) decodeIssue {
+	return decodeIssue{code: issue.code, path: issue.path.clone(), message: issue.message}
+}
+
+func newDecodeIssue(code Code, path Path, node *document.Node, message string) decodeIssue {
+	return decodeIssue{code: code, path: path.clone(), message: message, location: node.Location}
+}
+
+func typeMismatch(path Path, node *document.Node, expected string) (reflect.Value, []decodeIssue) {
+	return reflect.Value{}, []decodeIssue{newDecodeIssue(CodeDecodeType, path, node, "configuration value must be a "+expected)}
+}
+
+func rangeFailure(path Path, node *document.Node, expected string) (reflect.Value, []decodeIssue) {
+	return reflect.Value{}, []decodeIssue{newDecodeIssue(CodeDecodeRange, path, node, expected+" is outside the supported range")}
+}

decode_test.go

@@ -0,0 +1,312 @@
+package configkit
+
+import (
+	"errors"
+	"math"
+	"reflect"
+	"strings"
+	"testing"
+	"time"
+
+	"gitea.maximumdirect.net/eric/ConfigKit/internal/document"
+)
+
+type namedSmall int8
+
+type validatedText string
+
+func (value validatedText) MarshalText() ([]byte, error) {
+	return []byte(value), nil
+}
+
+func (value *validatedText) UnmarshalText(text []byte) error {
+	if string(text) == "bad-secret-canary" {
+		return errors.New("CANARY_TEXT_ERROR: bad-secret-canary")
+	}
+	*value = validatedText(text)
+	return nil
+}
+
+func TestDecodeAppliesInputOverDetachedDefaults(t *testing.T) {
+	t.Parallel()
+
+	type nested struct {
+		A string `yaml:"a"`
+		B string `yaml:"b"`
+	}
+	type config struct {
+		Enabled      bool              `yaml:"enabled"`
+		Workers      int               `yaml:"workers"`
+		Label        string            `yaml:"label"`
+		Nested       nested            `yaml:"nested"`
+		EmptyMapping nested            `yaml:"empty_mapping"`
+		Objects      map[string]nested `yaml:"objects"`
+		Sequence     []string          `yaml:"sequence"`
+		Replacement  []string          `yaml:"replacement"`
+		Pointer      *nested           `yaml:"pointer"`
+		NilPointer   *nested           `yaml:"nil_pointer"`
+		Nullable     map[string]string `yaml:"nullable"`
+		Dynamic      any               `yaml:"dynamic"`
+		DynamicShape any               `yaml:"dynamic_shape"`
+		DynamicNull  any               `yaml:"dynamic_null"`
+		Fixed        [2]int            `yaml:"fixed"`
+		Small        namedSmall        `yaml:"small"`
+		Delay        time.Duration     `yaml:"delay"`
+		Custom       validatedText     `yaml:"custom"`
+	}
+	defaults := config{
+		Enabled:      true,
+		Workers:      4,
+		Label:        "default",
+		Nested:       nested{A: "keep", B: "before"},
+		EmptyMapping: nested{A: "keep-empty", B: "keep-empty"},
+		Objects: map[string]nested{
+			"existing": {A: "keep-map", B: "before"},
+		},
+		Sequence:     []string{"default"},
+		Replacement:  []string{"default"},
+		Pointer:      &nested{A: "keep-pointer", B: "before"},
+		Nullable:     map[string]string{"default": "value"},
+		Dynamic:      map[string]any{"keep": "default", "count": int64(4)},
+		DynamicShape: nested{A: "keep-dynamic", B: "before"},
+		DynamicNull:  "default",
+		Fixed:        [2]int{1, 2},
+		Small:        7,
+		Delay:        time.Second,
+		Custom:       "default",
+	}
+	input := `
+enabled: false
+workers: 0
+label: ""
+nested: {b: changed}
+empty_mapping: {}
+objects:
+  existing: {b: changed}
+  new: {b: added}
+sequence: []
+replacement: [one, two]
+pointer: {b: changed}
+nil_pointer: {b: added}
+nullable: null
+dynamic: {count: 0, fraction: 1.5}
+dynamic_shape: {b: changed}
+dynamic_null: null
+fixed: [3, 4]
+small: -8
+delay: 1.5s
+custom: accepted
+`
+	schema := mustSchemaFor[config](t)
+	documentRoot := parseDocumentForDecode(t, input)
+	decoded, issues := decodeConfiguration(schema, reflect.ValueOf(defaults), documentRoot)
+	if len(issues) != 0 {
+		t.Fatalf("decode issues = %#v", issues)
+	}
+	got := decoded.value.Interface().(config)
+	if got.Enabled || got.Workers != 0 || got.Label != "" {
+		t.Fatalf("explicit zero values lost: %#v", got)
+	}
+	if got.Nested != (nested{A: "keep", B: "changed"}) || got.EmptyMapping != defaults.EmptyMapping {
+		t.Fatalf("mapping defaults = %#v / %#v", got.Nested, got.EmptyMapping)
+	}
+	if got.Objects["existing"] != (nested{A: "keep-map", B: "changed"}) || got.Objects["new"] != (nested{B: "added"}) {
+		t.Fatalf("map defaults = %#v", got.Objects)
+	}
+	if got.Sequence == nil || len(got.Sequence) != 0 || !reflect.DeepEqual(got.Replacement, []string{"one", "two"}) {
+		t.Fatalf("sequence replacement = %#v / %#v", got.Sequence, got.Replacement)
+	}
+	if got.Pointer == defaults.Pointer || *got.Pointer != (nested{A: "keep-pointer", B: "changed"}) || got.NilPointer == nil || *got.NilPointer != (nested{B: "added"}) {
+		t.Fatalf("pointer defaults = %#v / %#v", got.Pointer, got.NilPointer)
+	}
+	if got.Nullable != nil || got.DynamicNull != nil {
+		t.Fatalf("null values = %#v / %#v", got.Nullable, got.DynamicNull)
+	}
+	dynamic := got.Dynamic.(map[string]any)
+	if dynamic["keep"] != "default" || dynamic["count"] != int64(0) || dynamic["fraction"] != float64(1.5) {
+		t.Fatalf("dynamic mapping = %#v", dynamic)
+	}
+	if got.DynamicShape != (nested{A: "keep-dynamic", B: "changed"}) {
+		t.Fatalf("dynamic concrete mapping = %#v", got.DynamicShape)
+	}
+	if got.Fixed != [2]int{3, 4} || got.Small != -8 || got.Delay != 1500*time.Millisecond || got.Custom != "accepted" {
+		t.Fatalf("scalar decoding = %#v", got)
+	}
+
+	for _, path := range []Path{Keys(), Keys("enabled"), Keys("nested"), Keys("nested", "b"), Keys("empty_mapping")} {
+		if _, ok := decoded.presence[path.String()]; !ok {
+			t.Errorf("explicit path %q missing", path.String())
+		}
+	}
+	if _, ok := decoded.presence[Keys("nested", "a").String()]; ok {
+		t.Fatal("parent mapping made omitted child explicit")
+	}
+	if decoded.origins[Keys("nested", "a").String()].Layer != LayerDefault || decoded.origins[Keys("nested", "b").String()].Layer != LayerBase {
+		t.Fatalf("origins = %#v", decoded.origins)
+	}
+	if decoded.origins[Keys("nested", "b").String()].Locations[0].Line == 0 {
+		t.Fatal("input origin lost source coordinates")
+	}
+
+	defaults.Objects["existing"] = nested{A: "mutated"}
+	defaults.Pointer.B = "mutated"
+	defaults.Sequence[0] = "mutated"
+	if got.Objects["existing"].A != "keep-map" || got.Pointer.B != "changed" || len(got.Sequence) != 0 {
+		t.Fatal("decoded value aliases defaults")
+	}
+	got.Pointer.B = "caller mutation"
+	if mappingValue(t, mappingValue(t, decoded.final, "pointer"), "b").Text != "changed" {
+		t.Fatal("final snapshot aliases returned typed value")
+	}
+	if mappingValue(t, mappingValue(t, decoded.baseline, "nested"), "b").Text != "before" {
+		t.Fatal("baseline snapshot was mutated by decode")
+	}
+}
+
+func TestDecodeDefaultsOnlyAndRepeatedResultsAreIndependent(t *testing.T) {
+	t.Parallel()
+
+	type config struct {
+		Values map[string][]string `yaml:"values"`
+	}
+	defaults := config{Values: map[string][]string{"one": {"a"}}}
+	schema := mustSchemaFor[config](t)
+	first, issues := decodeConfiguration(schema, reflect.ValueOf(defaults), nil)
+	if len(issues) != 0 {
+		t.Fatal(issues)
+	}
+	second, issues := decodeConfiguration(schema, reflect.ValueOf(defaults), nil)
+	if len(issues) != 0 {
+		t.Fatal(issues)
+	}
+	firstValue := first.value.Interface().(config)
+	secondValue := second.value.Interface().(config)
+	firstValue.Values["one"][0] = "changed"
+	if secondValue.Values["one"][0] != "a" || defaults.Values["one"][0] != "a" {
+		t.Fatal("repeated defaults-only results share aliases")
+	}
+	if len(first.presence) != 0 || first.origins[Keys("values", "one").String()].Layer != LayerDefault {
+		t.Fatalf("defaults-only metadata = %#v / %#v", first.presence, first.origins)
+	}
+}
+
+func TestDecodeCollectsIndependentTypeAndShapeFailures(t *testing.T) {
+	t.Parallel()
+
+	type nested struct {
+		Known int `yaml:"known"`
+	}
+	type config struct {
+		Small    int8          `yaml:"small"`
+		Unsigned uint8         `yaml:"unsigned"`
+		Number   float32       `yaml:"number"`
+		Text     string        `yaml:"text"`
+		Flag     bool          `yaml:"flag"`
+		Delay    time.Duration `yaml:"delay"`
+		Fixed    [2]int        `yaml:"fixed"`
+		Nested   nested        `yaml:"nested"`
+		Custom   validatedText `yaml:"custom"`
+		Dynamic  any           `yaml:"dynamic"`
+	}
+	input := `
+small: 128
+unsigned: -1
+number: 1e999
+text: 3
+flag: "true"
+delay: 10
+fixed: [1]
+nested: {first_unknown: 1, second_unknown: 2}
+custom: bad-secret-canary
+dynamic: 9223372036854775808
+`
+	schema := mustSchemaFor[config](t)
+	_, issues := decodeConfiguration(schema, reflect.ValueOf(config{Custom: "ok"}), parseDocumentForDecode(t, input))
+	if len(issues) != 11 {
+		t.Fatalf("issues = %d: %#v", len(issues), issues)
+	}
+	want := map[string]Code{
+		"/small":                 CodeDecodeRange,
+		"/unsigned":              CodeDecodeType,
+		"/number":                CodeDecodeRange,
+		"/text":                  CodeDecodeType,
+		"/flag":                  CodeDecodeType,
+		"/delay":                 CodeDecodeType,
+		"/fixed":                 CodeDecodeArrayLength,
+		"/nested/first_unknown":  CodeDecodeUnknownField,
+		"/nested/second_unknown": CodeDecodeUnknownField,
+		"/custom":                CodeDecodeText,
+		"/dynamic":               CodeDecodeRange,
+	}
+	for _, issue := range issues {
+		if wantCode, ok := want[issue.path.String()]; !ok || wantCode != issue.code {
+			t.Errorf("unexpected issue %#v", issue)
+		}
+		if issue.location.Line == 0 {
+			t.Errorf("issue lost input location: %#v", issue)
+		}
+		if strings.Contains(issue.message, "CANARY") || strings.Contains(issue.message, "bad-secret") {
+			t.Errorf("issue exposed value: %#v", issue)
+		}
+	}
+}
+
+func TestDecodeNullabilityAndNestedMapStrictness(t *testing.T) {
+	t.Parallel()
+
+	type nested struct {
+		Value int `yaml:"value"`
+	}
+	type config struct {
+		Scalar int               `yaml:"scalar"`
+		Object nested            `yaml:"object"`
+		Array  [1]int            `yaml:"array"`
+		Map    map[string]nested `yaml:"map"`
+	}
+	input := "scalar: null\nobject: null\narray: null\nmap:\n  item: {unknown: 1}\n"
+	_, issues := decodeConfiguration(mustSchemaFor[config](t), reflect.ValueOf(config{}), parseDocumentForDecode(t, input))
+	want := map[string]Code{
+		"/scalar":           CodeDecodeNull,
+		"/object":           CodeDecodeNull,
+		"/array":            CodeDecodeNull,
+		"/map/item/unknown": CodeDecodeUnknownField,
+	}
+	if len(issues) != len(want) {
+		t.Fatalf("issues = %#v", issues)
+	}
+	for _, issue := range issues {
+		if want[issue.path.String()] != issue.code {
+			t.Errorf("issue = %#v", issue)
+		}
+	}
+}
+
+func TestDecodeRejectsInvalidDefaultsBeforeApplyingInput(t *testing.T) {
+	t.Parallel()
+
+	type config struct {
+		Name   string         `yaml:"name"`
+		Extras map[string]any `yaml:",inline"`
+		Float  float64        `yaml:"float"`
+	}
+	schema := mustSchemaFor[config](t)
+	for name, defaults := range map[string]config{
+		"inline collision": {Name: "declared", Extras: map[string]any{"name": "duplicate"}},
+		"non-finite":       {Float: math.NaN()},
+	} {
+		t.Run(name, func(t *testing.T) {
+			if _, issues := decodeConfiguration(schema, reflect.ValueOf(defaults), parseDocumentForDecode(t, "{}\n")); len(issues) != 1 || !strings.HasPrefix(string(issues[0].code), "schema.") {
+				t.Fatalf("issues = %#v", issues)
+			}
+		})
+	}
+}
+
+func parseDocumentForDecode(t *testing.T, input string) *document.Node {
+	t.Helper()
+	parsed, diagnostics := parseSource(Bytes("decode.yml", []byte(input)), "source-1", defaultParseLimits())
+	if len(diagnostics) != 0 {
+		t.Fatalf("parse diagnostics = %#v", diagnostics)
+	}
+	return parsed.document
+}

docs/config.md

@@ -1,8 +1,9 @@
 # Configuration Input Contract
 
-This document owns ConfigKit's currently implemented source-input and YAML syntax
+This document owns ConfigKit's currently implemented source-input, YAML syntax,
-contracts. The parser and owned document representation are private; a public typed
+schema, typed-decoding, and ownership contracts. The parser, owned document
-loading lifecycle has not been implemented yet.
+representation, and decoder are private; a public typed loading lifecycle has not
+been implemented yet.
 
 ## Sources
 
@@ -101,8 +102,50 @@ tokens become indices only in a sequence. Sequence indices cannot have leading
 zeroes; fixed-array indices are bounds checked. Dynamic `any` and inline-map entries
 remain schema-valid for application-defined descendants.
 
-Descriptors do not yet decode documents. Document decoding will reuse this graph as
+Descriptors are reused by typed decoding, projection, and cloning so those operations
-its implementation lands.
+cannot acquire different field bindings.
+
+## Defaults and typed decoding
+
+The private decoder starts from an independently owned clone of the application's
+typed defaults and applies only explicitly present input nodes. Defaults therefore
+never become explicit, while equal-valued input remains explicit. Successful decode
+produces detached typed state, baseline and final canonical trees, an input-presence
+index, and default/input origins for the later public loading lifecycle.
+
+| Configured input | Effect on the typed baseline |
+| --- | --- |
+| Absent field | Retain the default |
+| Explicit false, zero, or empty string | Replace the default |
+| Partial mapping or string-keyed map | Recurse and retain omitted default children or entries |
+| Empty mapping | Retain existing mapping children |
+| Sequence, including an empty sequence | Replace the entire sequence |
+| Pointer object | Recurse into a non-nil default; otherwise allocate an object whose omitted children have ordinary Go zero values |
+| Allowed null | Replace the value with nil and suppress its default |
+
+Null is allowed only for pointers, maps, slices, and dynamic `any` values. It is an
+error for scalars, structs, and arrays. New map entries and sequence elements begin
+from their Go zero values; ConfigKit does not invent entry-level defaults.
+
+Decoding is strict at every typed depth. Unknown struct fields, type mismatches,
+invalid nulls, numeric overflow, and arrays with the wrong length are errors at the
+original semantic path and source coordinates. String-keyed maps accept arbitrary
+keys but preserve the strict schema of their values; inline maps accept unmatched
+keys according to their element descriptor. Multiple independent field failures are
+collected without publishing the partially decoded object.
+
+Booleans and strings are not coerced. Integer destinations require integer syntax
+and a value in the destination type's range. Float destinations accept finite JSON
+numbers representable by their destination precision. Dynamic numbers become
+`int64` for integer syntax and `float64` for fractional or exponent syntax, with
+range and finiteness checks. Named scalar types retain their identity. Durations
+decode only from strings accepted by `time.ParseDuration`; integers are rejected.
+Paired text scalars decode only from strings through `encoding.TextUnmarshaler`, and
+codec failures are classified without exposing application error text or input
+values.
+
+This decoder is currently an internal lifecycle foundation, not a public conversion
+API. Applications cannot call typed loading until `Load` is introduced.
 
 ## Typed projection and ownership
 

docs/internal/extraction.md

@@ -170,6 +170,19 @@ Assigned across schema, decoding, resolution, validation, and consumer examples:
   application-owned; every domain mutation is recorded. Campaign/session fallback,
   search paths, fetching, storage, and concrete default values remain in Narratio.
 
+Implementation record (2026-09-06): ConfigKit generalized Narratio's fresh-default,
+strict nested-type, and explicit-presence cases into `decode.go` and
+`decode_test.go`. The decoder applies the owned document tree over a detached typed
+baseline, treats mappings recursively and sequences atomically, preserves explicit
+false/zero/empty/null, rejects unknown nested fields, and returns private presence
+and default/input origin artifacts. Unlike Narratio's custom YAML hooks and
+pointer/zero inference, presence comes directly from the parsed tree and equal-valued
+input remains explicit. ConfigKit also adds destination-width numeric checks,
+dynamic `int64`/`float64`, exact arrays, duration strings, paired text codecs, safe
+multi-error collection, and repeated-result isolation. Resolution, validation,
+consumer defaults, and all campaign/session algorithms remain assigned to later
+work.
+
 ### Secrets bootstrap
 
 Assigned to the explicit bootstrap operation:

docs/internal/overview.md

@@ -7,18 +7,21 @@ module and package documentation boundary. Its implemented public primitives are
 - detached provenance and diagnostic record types with empty `Metadata` queries;
 - canonical, control-safe diagnostic rendering and structured `LoadError` access;
 - opaque file, byte, reader, and no-input source construction and bounded reads;
-- a parser-independent ordered tree in `internal/document`; and
+- a parser-independent ordered tree in `internal/document`;
 - the sole upstream YAML integration in `internal/yaml`, which translates validated
-  input into that owned tree and exposes no parser types outside its boundary; and
+  input into that owned tree and exposes no parser types outside its boundary;
 - a per-operation private reflection descriptor graph in `schema.go` for supported
   types, YAML field binding, inlining, secret tags, recursion, and semantic paths;
-  and
 - descriptor-driven canonical projection, detached typed cloning, cycle/limit
-  enforcement, and structural comparison in `projection.go`.
+  enforcement, and structural comparison in `projection.go`; and
+- strict schema-driven decoding over detached defaults in `decode.go`, including
+  mapping/sequence semantics, null and numeric policy, safe codec errors, presence,
+  baseline/final trees, and initial default/input origins.
 
-The [configuration contract](../config.md) owns implemented input, schema, and
+The [configuration contract](../config.md) owns implemented input, schema, decoding,
-ownership behavior. ConfigKit intentionally exposes no typed loading or decoding API yet.
+and ownership behavior. ConfigKit intentionally exposes no typed loading API yet;
-Private metadata population will be integrated when that lifecycle exists.
+the decoder and its initial metadata artifacts remain private until that lifecycle
+exists.
 
 The source-extraction inventory records the application foundations assigned to
 future implementation work:

docs/roadmap/implementation.md

@@ -2,7 +2,7 @@
 
 ## Status and ownership
 
-Status: implementation in progress; Stages 1–5 are complete and later stages are
+Status: implementation in progress; Stages 1–6 are complete and later stages are
 pending.
 
 Audience: a `gpt-5.6-terra` coding agent implementing one stage per prompt, in
@@ -564,7 +564,31 @@ Acceptance:
 
 ## Stage 6 — Decode scalar and container values over defaults
 
-Status: pending.
+Status: complete.
+
+Completion evidence (2026-09-06):
+
+- Added schema-driven typed decoding in [`decode.go`](../../decode.go), starting
+  from the Stage 5 detached clone and returning only private typed state, input
+  presence, projected baseline/final trees, and per-path default/base origins.
+- Implemented recursive mapping retention, atomic sequence replacement, exact array
+  lengths, pointer-object zero allocation versus non-nil retention, nullable-shape
+  clearing, strict nested map values, inline-map decoding, and unknown-field errors.
+- Added checked destination-width integers and floats, dynamic `int64`/`float64`,
+  named scalars, duration strings, paired text codecs, safe value-free failures, and
+  collection of independent decode errors at original semantic paths/coordinates.
+  The [current configuration contract](../config.md#defaults-and-typed-decoding) and
+  component inventory now own this behavior.
+- Adapted Narratio's fresh-default, presence, strict nested-type, and repeated-load
+  cases, replacing custom YAML hooks and pointer/zero guesses with tree-derived
+  presence; explicit empty and null are retained and equal-valued input is explicit.
+  Focused coverage includes the defaults operation table, new/existing map entries,
+  empty mappings/sequences, nil/non-nil pointer objects, default isolation, numeric
+  range and coercion failures, integer durations, inline collisions, nested unknown
+  fields, coordinates, safe codec failures, and independent repeated results.
+  Verified `go test ./...`, `go vet ./...`, `go build ./...`, `go mod tidy -diff`,
+  and `git diff --check` with Go 1.26.7 on linux/amd64. No deviations were required;
+  public loading and schema-version checks remain later work.
 
 Read: feature [defaults/null](initial.md#static-defaults-and-null) and typed decoding.
 

docs/roadmap/initial.md

@@ -552,69 +552,21 @@ Applications own flags and commands that select this behavior.
 
 ## Static defaults and null
 
-Applications supply a defaults factory that creates a fresh configuration per
+The defaults merge and nullability model is implemented privately. The
-load. Mutable maps, slices, and pointers must not be shared between factory
+[current defaults and typed-decoding contract](../config.md#defaults-and-typed-decoding)
-results. ConfigKit must not retain mutable aliases between returned loads or
+owns recursive mapping, atomic sequence, pointer allocation, explicit-presence,
-between the application result and its internal metadata snapshots.
+null, and detached-baseline behavior. The public defaults factory and result
-
+lifecycle remain target work in the sections below.
-Defaults obey the same recursive mapping/atomic replacement rules as a lower
-layer, rather than incidental decoder behavior:
-
-| Configured input | Effect on defaults |
-| --- | --- |
-| Absent field | Keep the default |
-| Explicit false, zero, or empty string | Replace the default |
-| Partial mapping, including a string-keyed Go map | Retain omitted default children/entries |
-| `{}` over an existing mapping | Retain its default children |
-| Sequence, including `[]` | Replace the entire default sequence |
-| Partial object represented by a pointer | Retain children of a non-nil default object; otherwise allocate and use ordinary zero values for omitted children |
-| Allowed null | Replace with nil; suppress lower defaults |
-
-The factory supplies actual defaults; ConfigKit does not invent per-entry
-defaults for newly introduced map entries or sequence elements. Application
-resolution may supply those. Go zero values are part of the initial typed
-baseline; do not imply that the application explicitly declared every zero as
-a domain default. Avoid serialization through `omitempty` that would erase
-baseline values or presence information.
-
-Null is valid for pointers, maps, slices, and dynamic `any` values. It is invalid
-for ordinary scalar fields, structs, and arrays. Thus `workers: null` cannot
-silently leave an integer default intact. Applications can further reject null
-through validation. Null never means reset to the application default.
 
 ## Typed decoding
 
-The schema-binding portion of this target is implemented. The [current application
+Schema binding and strict document-to-value decoding are implemented privately.
-schema contract](../config.md#application-schema-binding) owns root/type support,
+The [current application schema contract](../config.md#application-schema-binding)
-field and tag binding, inlining, text-codec pairing, and schema-aware path rules.
+owns root/type support, field and tag binding, inlining, codec pairing, and
-The remaining document-to-value behavior below is target decoding work.
+schema-aware path rules. The [current defaults and typed-decoding contract](../config.md#defaults-and-typed-decoding)
-
+owns strict conversions, container application, presence, safe failures, and initial
-Strictness must be enforced by ConfigKit across the effective tree:
+origins. Public lifecycle integration, layered provenance, secret handling, and
-
+rendering remain target work below.
-- Unknown struct fields, type mismatches, overflow, and invalid null are errors.
-- Without an inline map, unmatched keys remain errors. Default inline-map entries
-  colliding with declared fields are checked when runtime defaults are introduced.
-- String-keyed maps accept application-defined keys. Struct values inside them
-  remain strict. `map[string]any` permits arbitrary keys and recursively accepts
-  the supported scalar/container model; application validation owns its schema.
-- Do not coerce numbers or booleans to strings, or quoted numbers to numeric
-  fields. Integer targets require integer syntax and range checks. Float targets
-  accept finite decimal numbers subject to representable range checks.
-- Dynamic integer values use checked `int64`, and fractional/exponent values use
-  checked finite `float64`; values outside those ranges require a typed schema
-  or a quoted string rather than silent rounding of integer nodes.
-- Support `time.Duration` from a duration string. Custom scalar types must
-  implement both `encoding.TextUnmarshaler` and `encoding.TextMarshaler` so
-  decoding and inspection have an agreed representation. Duration integers are
-  rejected. See the [type and projection contract](#supported-types-and-projection).
-- Parser-specific unmarshal hooks are not a public extension mechanism. Do not
-  let them bypass key, null, or type policy. Custom structural decoders are
-  deferred; unsupported type shapes fail with a clear schema diagnostic.
-
-Keep parser nodes and errors internal under the
-[upstream isolation contract](#yaml-dependency-and-public-api-isolation).
-The field-binding model must also support defaults, provenance, secret
-classification, and rendering consistently.
 
 ## Recorded resolution and validation
 

records.go

@@ -64,6 +64,14 @@ const (
 	CodeSchemaCodec           Code = "schema.codec"
 	CodeSchemaNonFinite       Code = "schema.non_finite"
 	CodeSchemaDynamicType     Code = "schema.dynamic_type"
+
+	CodeDecodeType         Code = "decode.type"
+	CodeDecodeNull         Code = "decode.null"
+	CodeDecodeRange        Code = "decode.range"
+	CodeDecodeDuration     Code = "decode.duration"
+	CodeDecodeText         Code = "decode.text"
+	CodeDecodeUnknownField Code = "decode.unknown_field"
+	CodeDecodeArrayLength  Code = "decode.array_length"
 )
 
 // Location identifies a position in a configuration source. Zero line and column