Add ~emersion/go-scfg as a subdirectory

1 files changed, 349 insertions, 0 deletions

diff --git a/scfg/unmarshal.go b/scfg/unmarshal.go
new file mode 100644
index 0000000..a99910f
--- /dev/null
+++ b/scfg/unmarshal.go
@@ -0,0 +1,349 @@
+package scfg
+
+import (
+	"encoding"
+	"fmt"
+	"io"
+	"reflect"
+	"strconv"
+)
+
+// Decoder reads and decodes an scfg document from an input stream.
+type Decoder struct {
+	r io.Reader
+}
+
+// NewDecoder returns a new decoder which reads from r.
+func NewDecoder(r io.Reader) *Decoder {
+	return &Decoder{r}
+}
+
+// Decode reads scfg document from the input and stores it in the value pointed
+// to by v.
+//
+// If v is nil or not a pointer, Decode returns an error.
+//
+// Blocks can be unmarshaled to:
+//
+//   - Maps. Each directive is unmarshaled into a map entry. The map key must
+//     be a string.
+//   - Structs. Each directive is unmarshaled into a struct field.
+//
+// Duplicate directives are not allowed, unless the struct field or map value
+// is a slice of values representing a directive: structs or maps.
+//
+// Directives can be unmarshaled to:
+//
+//   - Maps. The children block is unmarshaled into the map. Parameters are not
+//     allowed.
+//   - Structs. The children block is unmarshaled into the struct. Parameters
+//     are allowed if one of the struct fields contains the "param" option in
+//     its tag.
+//   - Slices. Parameters are unmarshaled into the slice. Children blocks are
+//     not allowed.
+//   - Arrays. Parameters are unmarshaled into the array. The number of
+//     parameters must match exactly the length of the array. Children blocks
+//     are not allowed.
+//   - Strings, booleans, integers, floating-point values, values implementing
+//     encoding.TextUnmarshaler. Only a single parameter is allowed and is
+//     unmarshaled into the value. Children blocks are not allowed.
+//
+// The decoding of each struct field can be customized by the format string
+// stored under the "scfg" key in the struct field's tag. The tag contains the
+// name of the field possibly followed by a comma-separated list of options.
+// The name may be empty in order to specify options without overriding the
+// default field name. As a special case, if the field name is "-", the field
+// is ignored. The "param" option specifies that directive parameters are
+// stored in this field (the name must be empty).
+func (dec *Decoder) Decode(v interface{}) error {
+	block, err := Read(dec.r)
+	if err != nil {
+		return err
+	}
+
+	rv := reflect.ValueOf(v)
+	if rv.Kind() != reflect.Ptr || rv.IsNil() {
+		return fmt.Errorf("scfg: invalid value for unmarshaling")
+	}
+
+	return unmarshalBlock(block, rv)
+}
+
+func unmarshalBlock(block Block, v reflect.Value) error {
+	v = unwrapPointers(v)
+	t := v.Type()
+
+	dirsByName := make(map[string][]*Directive, len(block))
+	for _, dir := range block {
+		dirsByName[dir.Name] = append(dirsByName[dir.Name], dir)
+	}
+
+	switch v.Kind() {
+	case reflect.Map:
+		if t.Key().Kind() != reflect.String {
+			return fmt.Errorf("scfg: map key type must be string")
+		}
+		if v.IsNil() {
+			v.Set(reflect.MakeMap(t))
+		} else if v.Len() > 0 {
+			clearMap(v)
+		}
+
+		for name, dirs := range dirsByName {
+			mv := reflect.New(t.Elem()).Elem()
+			if err := unmarshalDirectiveList(dirs, mv); err != nil {
+				return err
+			}
+			v.SetMapIndex(reflect.ValueOf(name), mv)
+		}
+	case reflect.Struct:
+		si, err := getStructInfo(t)
+		if err != nil {
+			return err
+		}
+
+		for name, dirs := range dirsByName {
+			fieldIndex, ok := si.children[name]
+			if !ok {
+				return newUnmarshalDirectiveError(dirs[0], "unknown directive")
+			}
+			fv := v.Field(fieldIndex)
+			if err := unmarshalDirectiveList(dirs, fv); err != nil {
+				return err
+			}
+		}
+	default:
+		return fmt.Errorf("scfg: unsupported type for unmarshaling blocks: %v", t)
+	}
+
+	return nil
+}
+
+func unmarshalDirectiveList(dirs []*Directive, v reflect.Value) error {
+	v = unwrapPointers(v)
+	t := v.Type()
+
+	if v.Kind() != reflect.Slice || !isDirectiveType(t.Elem()) {
+		if len(dirs) > 1 {
+			return newUnmarshalDirectiveError(dirs[1], "directive must not be specified more than once")
+		}
+		return unmarshalDirective(dirs[0], v)
+	}
+
+	sv := reflect.MakeSlice(t, len(dirs), len(dirs))
+	for i, dir := range dirs {
+		if err := unmarshalDirective(dir, sv.Index(i)); err != nil {
+			return err
+		}
+	}
+	v.Set(sv)
+	return nil
+}
+
+// isDirectiveType checks whether a type can only be unmarshaled as a
+// directive, not as a parameter. Accepting too many types here would result in
+// ambiguities, see:
+// https://lists.sr.ht/~emersion/public-inbox/%3C20230629132458.152205-1-contact%40emersion.fr%3E#%3Ch4Y2peS_YBqY3ar4XlmPDPiNBFpYGns3EBYUx3_6zWEhV2o8_-fBQveRujGADWYhVVCucHBEryFGoPtpC3d3mQ-x10pWnFogfprbQTSvtxc=@emersion.fr%3E
+func isDirectiveType(t reflect.Type) bool {
+	for t.Kind() == reflect.Ptr {
+		t = t.Elem()
+	}
+
+	textUnmarshalerType := reflect.TypeOf((*encoding.TextUnmarshaler)(nil)).Elem()
+	if reflect.PtrTo(t).Implements(textUnmarshalerType) {
+		return false
+	}
+
+	switch t.Kind() {
+	case reflect.Struct, reflect.Map:
+		return true
+	default:
+		return false
+	}
+}
+
+func unmarshalDirective(dir *Directive, v reflect.Value) error {
+	v = unwrapPointers(v)
+	t := v.Type()
+
+	if v.CanAddr() {
+		if _, ok := v.Addr().Interface().(encoding.TextUnmarshaler); ok {
+			if len(dir.Children) != 0 {
+				return newUnmarshalDirectiveError(dir, "directive requires zero children")
+			}
+			return unmarshalParamList(dir, v)
+		}
+	}
+
+	switch v.Kind() {
+	case reflect.Map:
+		if len(dir.Params) > 0 {
+			return newUnmarshalDirectiveError(dir, "directive requires zero parameters")
+		}
+		if err := unmarshalBlock(dir.Children, v); err != nil {
+			return err
+		}
+	case reflect.Struct:
+		si, err := getStructInfo(t)
+		if err != nil {
+			return err
+		}
+
+		if si.param >= 0 {
+			if err := unmarshalParamList(dir, v.Field(si.param)); err != nil {
+				return err
+			}
+		} else {
+			if len(dir.Params) > 0 {
+				return newUnmarshalDirectiveError(dir, "directive requires zero parameters")
+			}
+		}
+
+		if err := unmarshalBlock(dir.Children, v); err != nil {
+			return err
+		}
+	default:
+		if len(dir.Children) != 0 {
+			return newUnmarshalDirectiveError(dir, "directive requires zero children")
+		}
+		if err := unmarshalParamList(dir, v); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+func unmarshalParamList(dir *Directive, v reflect.Value) error {
+	switch v.Kind() {
+	case reflect.Slice:
+		t := v.Type()
+		sv := reflect.MakeSlice(t, len(dir.Params), len(dir.Params))
+		for i, param := range dir.Params {
+			if err := unmarshalParam(param, sv.Index(i)); err != nil {
+				return newUnmarshalParamError(dir, i, err)
+			}
+		}
+		v.Set(sv)
+	case reflect.Array:
+		if len(dir.Params) != v.Len() {
+			return newUnmarshalDirectiveError(dir, fmt.Sprintf("directive requires exactly %v parameters", v.Len()))
+		}
+		for i, param := range dir.Params {
+			if err := unmarshalParam(param, v.Index(i)); err != nil {
+				return newUnmarshalParamError(dir, i, err)
+			}
+		}
+	default:
+		if len(dir.Params) != 1 {
+			return newUnmarshalDirectiveError(dir, "directive requires exactly one parameter")
+		}
+		if err := unmarshalParam(dir.Params[0], v); err != nil {
+			return newUnmarshalParamError(dir, 0, err)
+		}
+	}
+
+	return nil
+}
+
+func unmarshalParam(param string, v reflect.Value) error {
+	v = unwrapPointers(v)
+	t := v.Type()
+
+	// TODO: improve our logic following:
+	// https://cs.opensource.google/go/go/+/refs/tags/go1.21.5:src/encoding/json/decode.go;drc=b9b8cecbfc72168ca03ad586cc2ed52b0e8db409;l=421
+	if v.CanAddr() {
+		if v, ok := v.Addr().Interface().(encoding.TextUnmarshaler); ok {
+			return v.UnmarshalText([]byte(param))
+		}
+	}
+
+	switch v.Kind() {
+	case reflect.String:
+		v.Set(reflect.ValueOf(param))
+	case reflect.Bool:
+		switch param {
+		case "true":
+			v.Set(reflect.ValueOf(true))
+		case "false":
+			v.Set(reflect.ValueOf(false))
+		default:
+			return fmt.Errorf("invalid bool parameter %q", param)
+		}
+	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
+		i, err := strconv.ParseInt(param, 10, t.Bits())
+		if err != nil {
+			return fmt.Errorf("invalid %v parameter: %v", t, err)
+		}
+		v.Set(reflect.ValueOf(i).Convert(t))
+	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64:
+		u, err := strconv.ParseUint(param, 10, t.Bits())
+		if err != nil {
+			return fmt.Errorf("invalid %v parameter: %v", t, err)
+		}
+		v.Set(reflect.ValueOf(u).Convert(t))
+	case reflect.Float32, reflect.Float64:
+		f, err := strconv.ParseFloat(param, t.Bits())
+		if err != nil {
+			return fmt.Errorf("invalid %v parameter: %v", t, err)
+		}
+		v.Set(reflect.ValueOf(f).Convert(t))
+	default:
+		return fmt.Errorf("unsupported type for unmarshaling parameter: %v", t)
+	}
+
+	return nil
+}
+
+func unwrapPointers(v reflect.Value) reflect.Value {
+	for v.Kind() == reflect.Ptr {
+		if v.IsNil() {
+			v.Set(reflect.New(v.Type().Elem()))
+		}
+		v = v.Elem()
+	}
+	return v
+}
+
+func clearMap(v reflect.Value) {
+	for _, k := range v.MapKeys() {
+		v.SetMapIndex(k, reflect.Value{})
+	}
+}
+
+type unmarshalDirectiveError struct {
+	lineno int
+	name   string
+	msg    string
+}
+
+func newUnmarshalDirectiveError(dir *Directive, msg string) *unmarshalDirectiveError {
+	return &unmarshalDirectiveError{
+		name:   dir.Name,
+		lineno: dir.lineno,
+		msg:    msg,
+	}
+}
+
+func (err *unmarshalDirectiveError) Error() string {
+	return fmt.Sprintf("line %v, directive %q: %v", err.lineno, err.name, err.msg)
+}
+
+type unmarshalParamError struct {
+	lineno     int
+	directive  string
+	paramIndex int
+	err        error
+}
+
+func newUnmarshalParamError(dir *Directive, paramIndex int, err error) *unmarshalParamError {
+	return &unmarshalParamError{
+		directive:  dir.Name,
+		lineno:     dir.lineno,
+		paramIndex: paramIndex,
+		err:        err,
+	}
+}
+
+func (err *unmarshalParamError) Error() string {
+	return fmt.Sprintf("line %v, directive %q, parameter %v: %v", err.lineno, err.directive, err.paramIndex+1, err.err)
+}