perf(encode): write scalars and scalar arrays without boxing

Assisted-by: GLM 5.3 Flash

encode.go

@@ -303,8 +303,9 @@ const (
 type entry struct {
 	kind entryKind
 	key  string
-	val  any      // entryScalar
-	doc  *tomlDoc // entryTable
+	val  any           // entryScalar, boxed
+	rv   reflect.Value // entryScalar, the value the walk kept unboxed
+	doc  *tomlDoc      // entryTable
 	docs []*tomlDoc
 
 	// inline forces a table entry to emit as `key = {…}`; it is set by the
@@ -359,6 +360,12 @@ func (d *tomlDoc) addScalar(key string, val any) {
 	d.entries = append(d.entries, entry{kind: entryScalar, key: key, val: val})
 }
 
+// addScalarReflect adds a scalar whose value stays in its reflect cell until
+// emission writes it, the path that keeps plain scalars from being boxed.
+func (d *tomlDoc) addScalarReflect(key string, v reflect.Value) {
+	d.entries = append(d.entries, entry{kind: entryScalar, key: key, rv: v})
+}
+
 func (d *tomlDoc) addTable(key string, sub *tomlDoc) *entry {
 	e := entry{kind: entryTable, key: key, doc: sub}
 	d.entries = append(d.entries, e)
@@ -712,6 +719,19 @@ func addField(doc *tomlDoc, name string, v reflect.Value, path encPath, forceInl
 	case reflect.Slice, reflect.Array:
 		return addArrayValue(doc, name, v, path, forceInline)
 	default:
+		// A plain scalar stays in its reflect cell until emission, which
+		// writes it without the boxing Interface() would cost. The kinds the
+		// boxed rules rewrite (duration, Number, the date-time structs) take
+		// the boxed path as before.
+		if t := v.Type(); t != durationType && t != numberType {
+			switch v.Kind() {
+			case reflect.String, reflect.Bool, reflect.Int, reflect.Int8, reflect.Int16,
+				reflect.Int32, reflect.Int64, reflect.Uint, reflect.Uint8, reflect.Uint16,
+				reflect.Uint32, reflect.Uint64, reflect.Float32, reflect.Float64:
+				doc.addScalarReflect(name, v)
+				return nil
+			}
+		}
 		val, err := normaliseValue(v)
 		if err != nil {
 			return fmt.Errorf("interpres: %s: %w", path.key(name), err)
@@ -762,39 +782,92 @@ func addArrayValue(doc *tomlDoc, name string, v reflect.Value, path encPath, for
 	// names them.
 	apath := path.key(name)
 
-	// Every element is resolved through MarshalTOML first, so an element that
-	// renders itself as a scalar, a table or a value array is classified by
-	// what it produces rather than by its Go kind, and its method runs once.
-	elems := make([]reflect.Value, n)
-	for i := range n {
-		if i%ctxCheckInterval == 0 {
-			if err := doc.checkCtx(); err != nil {
-				return err
+	// The per-element resolution runs only where the array could still take
+	// the [[header]] form: an interface element can never (its [[form]] would
+	// re-parse as []map[string]any), and a plain scalar element can only when
+	// a Marshaler rewrites it into a table. Everywhere else the array is a
+	// value array and the elements are written straight from the slice.
+	elem := v.Type().Elem()
+	maybeTables := true
+	if elem.Kind() == reflect.Interface {
+		maybeTables = false
+	} else {
+		switch elem.Kind() {
+		case reflect.Struct, reflect.Map, reflect.Pointer:
+		default:
+			f := encTypeFlags(elem)
+			if f&encFlagMarshaler == 0 && f&encFlagAddrMarshaler == 0 {
+				maybeTables = false
 			}
 		}
-		ev, err := resolveElement(v.Index(i), apath.elem(i))
-		if err != nil {
-			return err
+	}
+
+	// A typed array of plain scalars takes the direct emission path: no
+	// per-element slice, no boxing, and no error the boxed rules could raise.
+	// Everything wider, []any first among it, keeps the boxed path, because
+	// its element errors carry the element's path.
+	directValueArray := false
+	switch elem.Kind() {
+	case reflect.String, reflect.Bool, reflect.Int, reflect.Int8, reflect.Int16,
+		reflect.Int32, reflect.Int64, reflect.Float32, reflect.Float64:
+		f := encTypeFlags(elem)
+		if elem != durationType && elem != numberType &&
+			f&(encFlagMarshaler|encFlagAddrMarshaler|encFlagTextMarshaler|encFlagAddrTextMarshaler) == 0 {
+			directValueArray = true
+		}
+	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64:
+		f := encTypeFlags(elem)
+		if f&(encFlagMarshaler|encFlagAddrMarshaler|encFlagTextMarshaler|encFlagAddrTextMarshaler) == 0 {
+			directValueArray = true
+			// The one error the boxed path raises for these is the int64
+			// overflow, checked here so the direct path keeps the contract.
+			for i := range n {
+				if u := v.Index(i).Uint(); u > math.MaxInt64 {
+					return &EncodeError{Path: apath.elem(i).segments(), Err: fmt.Errorf("unsigned value %d overflows int64", u)}
+				}
+			}
+		}
+	}
+
+	var elems []reflect.Value
+	if maybeTables {
+		// Every element is resolved through MarshalTOML first, so an element
+		// that renders itself as a scalar, a table or a value array is
+		// classified by what it produces rather than by its Go kind, and its
+		// method runs once.
+		elems = make([]reflect.Value, n)
+		for i := range n {
+			if i%ctxCheckInterval == 0 {
+				if err := doc.checkCtx(); err != nil {
+					return err
+				}
+			}
+			ev, err := resolveElement(v.Index(i), apath.elem(i))
+			if err != nil {
+				return err
+			}
+			elems[i] = ev
 		}
-		elems[i] = ev
 	}
 
 	// An array keeps the [[header]] form only when every element is a table.
 	// TOML lets one array mix tables with scalars, and that mix renders as a
 	// value array with the table elements written inline.
-	allTables := true
-	for _, ev := range elems {
-		if !ev.IsValid() || !isTableElementValue(ev) {
+	allTables := maybeTables
+	if allTables {
+		for _, ev := range elems {
+			if !ev.IsValid() || !isTableElementValue(ev) {
+				allTables = false
+				break
+			}
+		}
+		// A []any of tables is what Parse produces for a value array of inline
+		// tables; the [[header]] form would re-parse as []map[string]any and so
+		// change the value's Go type across a round-trip. The header form is
+		// reserved for typed table slices.
+		if v.Type().Elem().Kind() == reflect.Interface {
 			allTables = false
-			break
 		}
-	}
-	// A []any of tables is what Parse produces for a value array of inline
-	// tables; the [[header]] form would re-parse as []map[string]any and so
-	// change the value's Go type across a round-trip. The header form is
-	// reserved for typed table slices.
-	if v.Type().Elem().Kind() == reflect.Interface {
-		allTables = false
 	}
 	// A `,inline` tag on an array of tables asks for a form that would change
 	// the value's Go type on re-parse, so the error is the honest answer.
@@ -839,15 +912,24 @@ func addArrayValue(doc *tomlDoc, name string, v reflect.Value, path encPath, for
 		return nil
 	}
 
+	if directValueArray {
+		doc.addScalarReflect(name, v)
+		return nil
+	}
+
 	// Value array. Table elements normalise to map[string]any and the emitter
 	// writes them as inline tables.
 	items := make([]any, n)
-	for i, ev := range elems {
+	for i := range n {
 		if i%ctxCheckInterval == 0 {
 			if err := doc.checkCtx(); err != nil {
 				return err
 			}
 		}
+		ev := v.Index(i)
+		if elems != nil {
+			ev = elems[i]
+		}
 		val, err := normaliseValue(ev)
 		if err != nil {
 			return &EncodeError{Path: apath.elem(i).segments(), Err: err}
@@ -858,6 +940,149 @@ func addArrayValue(doc *tomlDoc, name string, v reflect.Value, path encPath, for
 	return nil
 }
 
+// writeArrayValue writes a value array from its reflect value, its elements
+// written one by one, each falling back to the boxed path only where the
+// boxed rules rewrite it.
+func (e *encoder) writeArrayValue(v reflect.Value, depth int) error {
+	if atDepthLimit(depth) {
+		return errDepthLimit()
+	}
+	e.buf.WriteByte('[')
+	for i := range v.Len() {
+		if i > 0 {
+			e.buf.WriteString(", ")
+		}
+		if err := e.writeArrayElem(v.Index(i), depth+1); err != nil {
+			return err
+		}
+	}
+	e.buf.WriteByte(']')
+	return nil
+}
+
+// writeArrayElem writes one element of a value array. The kinds the boxed
+// rules rewrite are handed to normaliseValue and the boxed writer; the rest
+// write directly, including nested arrays and inline tables.
+func (e *encoder) writeArrayElem(v reflect.Value, depth int) error {
+	if v.Kind() == reflect.Interface {
+		if v.IsNil() {
+			return fmt.Errorf("interpres: cannot encode nil value")
+		}
+		v = v.Elem()
+	}
+	switch v.Kind() {
+	case reflect.Slice, reflect.Array:
+		return e.writeArrayValue(v, depth)
+	case reflect.Map:
+		return e.writeInlineMapFromReflect(v, depth)
+	}
+	if _, isMarshaler := marshalerOf(v); isMarshaler {
+		return e.writeNormalisedElem(v, depth)
+	}
+	if _, isText, err := textValue(v); err != nil || isText {
+		if err != nil {
+			return err
+		}
+		return e.writeNormalisedElem(v, depth)
+	}
+	switch v.Kind() {
+	case reflect.String, reflect.Bool, reflect.Int, reflect.Int8, reflect.Int16,
+		reflect.Int32, reflect.Int64, reflect.Uint, reflect.Uint8, reflect.Uint16,
+		reflect.Uint32, reflect.Uint64, reflect.Float32, reflect.Float64:
+		if t := v.Type(); t != durationType && t != numberType {
+			return e.writeScalarValue(v)
+		}
+	}
+	return e.writeNormalisedElem(v, depth)
+}
+
+// writeNormalisedElem normalises one element through the boxed rules and
+// writes the result.
+func (e *encoder) writeNormalisedElem(v reflect.Value, depth int) error {
+	val, err := normaliseValueAt(v, depth)
+	if err != nil {
+		return err
+	}
+	return e.writeValue(val)
+}
+
+// writeInlineMapFromReflect renders a map from its reflect value as an inline
+// table, the shape the boxed path gives the table elements of a value array:
+// sorted keys, single line when it fits, across lines when it does not.
+func (e *encoder) writeInlineMapFromReflect(v reflect.Value, depth int) error {
+	if e.limit >= noInlineBreak {
+		return e.writeInlineMapFlatReflect(v, depth)
+	}
+	flat := e.flat()
+	err := flat.writeInlineMapFlatReflect(v, depth)
+	if err != nil {
+		flat.release()
+		return err
+	}
+	fits := e.column()+flat.buf.Len() <= e.limit
+	if fits {
+		e.buf.Write(flat.buf.Bytes())
+	}
+	flat.release()
+	if fits {
+		return nil
+	}
+	return e.writeInlineMapMultilineReflect(v, depth)
+}
+
+// writeInlineMapFlatReflect renders the single-line form.
+func (e *encoder) writeInlineMapFlatReflect(v reflect.Value, depth int) error {
+	if v.Type().Key().Kind() != reflect.String {
+		return fmt.Errorf("map key must be string, got %s", v.Type().Key())
+	}
+	keys := make([]string, 0, v.Len())
+	for _, k := range v.MapKeys() {
+		keys = append(keys, k.String())
+	}
+	slices.Sort(keys)
+	e.buf.WriteByte('{')
+	for i, k := range keys {
+		if i > 0 {
+			e.buf.WriteString(", ")
+		}
+		if err := e.writeKey(k); err != nil {
+			return err
+		}
+		e.buf.WriteString(" = ")
+		if err := e.writeArrayElem(v.MapIndex(reflect.ValueOf(k)), depth+1); err != nil {
+			return err
+		}
+	}
+	e.buf.WriteByte('}')
+	return nil
+}
+
+// writeInlineMapMultilineReflect renders the across-lines form.
+func (e *encoder) writeInlineMapMultilineReflect(v reflect.Value, depth int) error {
+	keys := make([]string, 0, v.Len())
+	for _, k := range v.MapKeys() {
+		keys = append(keys, k.String())
+	}
+	slices.Sort(keys)
+	e.buf.WriteString("{\n")
+	e.inlineDepth++
+	for _, k := range keys {
+		e.writeInlineIndent()
+		if err := e.writeKey(k); err != nil {
+			return err
+		}
+		e.buf.WriteString(" = ")
+		if err := e.writeArrayElem(v.MapIndex(reflect.ValueOf(k)), depth+1); err != nil {
+			return err
+		}
+		e.buf.WriteString(",\n")
+	}
+	e.inlineDepth--
+	e.writeInlineIndent()
+	e.buf.WriteByte('}')
+	return nil
+}
+
 // marshalerOf finds the Marshaler a value carries: on the value itself, or on
 // its address, so a pointer-receiver MarshalTOML is found on an addressable
 // struct field or slice element, exactly as textMarshalerOf finds MarshalText.
@@ -1296,13 +1521,51 @@ func (e *encoder) writeKV(ent *entry) error {
 		return err
 	}
 	e.buf.WriteString(" = ")
-	if err := e.writeValue(ent.val); err != nil {
+	if err := e.writeEntryValue(ent); err != nil {
 		return err
 	}
 	e.buf.WriteByte('\n')
 	return nil
 }
 
+// writeEntryValue writes a scalar entry's value: from the reflect cell the
+// walk kept when it can be written unboxed, from the boxed value otherwise.
+func (e *encoder) writeEntryValue(ent *entry) error {
+	if ent.rv.IsValid() {
+		switch ent.rv.Kind() {
+		case reflect.Slice, reflect.Array:
+			return e.writeArrayValue(ent.rv, 0)
+		}
+		return e.writeScalarValue(ent.rv)
+	}
+	return e.writeValue(ent.val)
+}
+
+// writeScalarValue writes a scalar from its reflect value, boxing only the
+// kinds the boxed writer handles specially.
+func (e *encoder) writeScalarValue(v reflect.Value) error {
+	switch v.Kind() {
+	case reflect.String:
+		return e.writeStringVal(v.String())
+	case reflect.Bool:
+		e.buf.WriteString(strconv.FormatBool(v.Bool()))
+		return nil
+	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
+		e.buf.WriteString(strconv.FormatInt(v.Int(), 10))
+		return nil
+	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64:
+		u := v.Uint()
+		if u > math.MaxInt64 {
+			return fmt.Errorf("unsigned value %d overflows int64", u)
+		}
+		e.buf.WriteString(strconv.FormatUint(u, 10))
+		return nil
+	case reflect.Float32, reflect.Float64:
+		return e.writeFloat(v.Float())
+	}
+	return e.writeValue(v.Interface())
+}
+
 func (e *encoder) writeKeyPath(path []string) error {
 	for i, p := range path {
 		if i > 0 {
@@ -1573,7 +1836,7 @@ func (e *encoder) writeInlineDocEntry(ent entry) error {
 	case entryArray:
 		return errInlineArrayOfTables
 	default:
-		return e.writeValue(ent.val)
+		return e.writeEntryValue(&ent)
 	}
 }