encoding/protobuf/textproto: add encoder

Doesn't really copy positioning and all comments, but
the textproto API is sort of hit or miss anyway whether
this information is supported at all.
So good enough for now.

Issue #5

Change-Id: Ia0d09a0c4b92756f68c2a09a114311b363fef33a
Reviewed-on: https://cue-review.googlesource.com/c/cue/+/9370
Reviewed-by: CUE cueckoo <cueckoo@gmail.com>
Reviewed-by: Marcel van Lohuizen <mpvl@golang.org>

encoding/protobuf/pbinternal/attribute.go

@@ -16,6 +16,8 @@ package pbinternal
 
 import (
 	"strings"
+	"unicode"
+	"unicode/utf8"
 
 	"cuelang.org/go/cue"
 )
@@ -50,6 +52,8 @@ type Info struct {
 	ValueType     ValueType
 	Type          string
 
+	IsEnum bool
+
 	// For maps only
 	KeyType       ValueType // only for maps
 	KeyTypeString string
@@ -97,7 +101,7 @@ func FromValue(name string, v cue.Value) (info Info, err error) {
 
 	case cue.StructKind:
 		if strings.HasPrefix(info.Type, "map[") {
-			a := strings.SplitN(info.Type[len("map["):], ",", 2)
+			a := strings.SplitN(info.Type[len("map["):], "]", 2)
 			info.KeyTypeString = strings.TrimSpace(a[0])
 			switch info.KeyTypeString {
 			case "string":
@@ -133,6 +137,8 @@ func FromValue(name string, v cue.Value) (info Info, err error) {
 
 	case cue.IntKind:
 		info.ValueType = Int
+		r, _ := utf8.DecodeRuneInString(info.Type)
+		info.IsEnum = unicode.In(r, unicode.Upper)
 
 	case cue.FloatKind, cue.NumberKind:
 		info.ValueType = Float

encoding/protobuf/pbinternal/symbol.go

@@ -64,3 +64,47 @@ func matchBySymbol(v cue.Value, name string, x *ast.BasicLit) bool {
 
 	return false
 }
+
+// MatchByInt finds a symbol for a given enum value and sets it in x.
+func MatchByInt(v cue.Value, val int64) string {
+	if op, a := v.Expr(); op == cue.AndOp {
+		for _, v := range a {
+			if s := MatchByInt(v, val); s != "" {
+				return s
+			}
+		}
+	}
+	v = cue.Dereference(v)
+	return matchByInt(v, val)
+}
+
+func matchByInt(v cue.Value, val int64) string {
+	switch op, a := v.Expr(); op {
+	case cue.OrOp, cue.AndOp:
+		for _, v := range a {
+			if s := matchByInt(v, val); s != "" {
+				return s
+			}
+		}
+
+	default:
+		if i, err := v.Int64(); err != nil || i != val {
+			break
+		}
+
+		_, path := v.ReferencePath()
+		a := path.Selectors()
+		if len(a) == 0 {
+			break
+		}
+
+		sel := a[len(a)-1]
+		if !sel.IsDefinition() {
+			break
+		}
+
+		return sel.String()[1:]
+	}
+
+	return ""
+}

encoding/protobuf/textproto/encoder.go

@@ -0,0 +1,203 @@
+// Copyright 2021 CUE Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package textproto
+
+import (
+	"fmt"
+	"strings"
+
+	"cuelang.org/go/cue"
+	"cuelang.org/go/cue/errors"
+	"cuelang.org/go/encoding/protobuf/pbinternal"
+
+	"github.com/protocolbuffers/txtpbfmt/ast"
+	pbast "github.com/protocolbuffers/txtpbfmt/ast"
+	"github.com/protocolbuffers/txtpbfmt/parser"
+)
+
+// Encoder marshals CUE into text proto.
+//
+type Encoder struct {
+	// Schema
+}
+
+// NewEncoder returns a new encoder, where the given options are default
+// options.
+func NewEncoder(options ...Option) *Encoder {
+	return &Encoder{}
+}
+
+// Encode converts a CUE value to a text proto file.
+//
+// Fields do not need to have a @protobuf attribute except for in the following
+// cases:
+//
+//   - it is explicitly required that only fields with an attribute are exported
+//   - a struct represents a Protobuf map
+//   - custom naming
+//
+func (e *Encoder) Encode(v cue.Value, options ...Option) ([]byte, error) {
+	n := &pbast.Node{}
+	enc := &encoder{}
+
+	enc.encodeMsg(n, v)
+
+	if enc.errs != nil {
+		return nil, enc.errs
+	}
+
+	// Pretty printing does not do errors, and returns a string (why o why?).
+	s := parser.Pretty(n.Children, 0)
+	return []byte(s), nil
+}
+
+type encoder struct {
+	errs errors.Error
+}
+
+func (e *encoder) addErr(err error) {
+	e.errs = errors.Append(e.errs, errors.Promote(err, "textproto"))
+}
+
+func (e *encoder) encodeMsg(parent *pbast.Node, v cue.Value) {
+	i, err := v.Fields()
+	if err != nil {
+		e.addErr(err)
+		return
+	}
+	for i.Next() {
+		v := i.Value()
+		if !v.IsConcrete() {
+			continue
+		}
+
+		info, err := pbinternal.FromIter(i)
+		if err != nil {
+			e.addErr(err)
+		}
+
+		switch info.CompositeType {
+		case pbinternal.List:
+			elems, err := v.List()
+			if err != nil {
+				e.addErr(err)
+				return
+			}
+			for first := true; elems.Next(); first = false {
+				n := &pbast.Node{Name: info.Name}
+				if first {
+					copyMeta(n, v)
+				}
+				elem := elems.Value()
+				copyMeta(n, elem)
+				parent.Children = append(parent.Children, n)
+				e.encodeValue(n, elem)
+			}
+
+		case pbinternal.Map:
+			i, err := v.Fields()
+			if err != nil {
+				e.addErr(err)
+				return
+			}
+			for first := true; i.Next(); first = false {
+				n := &pbast.Node{Name: info.Name}
+				if first {
+					copyMeta(n, v)
+				}
+				parent.Children = append(parent.Children, n)
+				var key *pbast.Node
+				switch info.KeyType {
+				case pbinternal.String, pbinternal.Bytes:
+					key = pbast.StringNode("key", i.Label())
+				default:
+					key = &pbast.Node{
+						Name:   "key",
+						Values: []*ast.Value{{Value: i.Label()}},
+					}
+				}
+				n.Children = append(n.Children, key)
+
+				value := &pbast.Node{Name: "value"}
+				e.encodeValue(value, i.Value())
+				n.Children = append(n.Children, value)
+			}
+
+		default:
+			n := &pbast.Node{Name: info.Name}
+			copyMeta(n, v)
+			e.encodeValue(n, v)
+			// Don't add if there are no values or children.
+			parent.Children = append(parent.Children, n)
+		}
+	}
+}
+
+// copyMeta copies metadata from nodes to values.
+//
+// TODO: also copy positions. The textproto API is rather messy and complex,
+// though, and so far it seems to be quite buggy too. Not sure if it is worth
+// the effort.
+func copyMeta(x *pbast.Node, v cue.Value) {
+	for _, doc := range v.Doc() {
+		s := strings.TrimRight(doc.Text(), "\n")
+		for _, c := range strings.Split(s, "\n") {
+			x.PreComments = append(x.PreComments, "# "+c)
+		}
+	}
+}
+
+func (e *encoder) encodeValue(n *pbast.Node, v cue.Value) {
+	var value string
+	switch v.Kind() {
+	case cue.StructKind:
+		e.encodeMsg(n, v)
+
+	case cue.StringKind:
+		s, err := v.String()
+		if err != nil {
+			e.addErr(err)
+		}
+		sn := pbast.StringNode("foo", s)
+		n.Values = append(n.Values, sn.Values...)
+
+	case cue.BytesKind:
+		b, err := v.Bytes()
+		if err != nil {
+			e.addErr(err)
+		}
+		sn := pbast.StringNode("foo", string(b))
+		n.Values = append(n.Values, sn.Values...)
+
+	case cue.BoolKind:
+		value = fmt.Sprint(v)
+		n.Values = append(n.Values, &pbast.Value{Value: value})
+
+	case cue.IntKind, cue.FloatKind, cue.NumberKind:
+		d, _ := v.Decimal()
+		value := d.String()
+
+		if info, _ := pbinternal.FromValue("", v); !info.IsEnum {
+		} else if i, err := v.Int64(); err != nil {
+		} else if s := pbinternal.MatchByInt(v, i); s != "" {
+			value = s
+		}
+
+		n.Values = append(n.Values, &pbast.Value{Value: value})
+
+	default:
+		e.addErr(errors.Newf(v.Pos(), "textproto: unknown type %v", v.Kind()))
+	}
+}

encoding/protobuf/textproto/encoder_test.go

@@ -0,0 +1,73 @@
+// Copyright 2021 CUE Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package textproto_test
+
+import (
+	"strings"
+	"testing"
+
+	"cuelang.org/go/cue"
+	"cuelang.org/go/cue/errors"
+	"cuelang.org/go/encoding/protobuf/textproto"
+	"cuelang.org/go/internal/cuetest"
+	"cuelang.org/go/internal/cuetxtar"
+)
+
+func TestEncode(t *testing.T) {
+	test := cuetxtar.TxTarTest{
+		Root:   "./testdata/encoder",
+		Name:   "encode",
+		Update: cuetest.UpdateGoldenFiles,
+	}
+
+	r := cue.Runtime{}
+
+	test.Run(t, func(t *cuetxtar.Test) {
+		// TODO: use high-level API.
+
+		var schema, value cue.Value
+
+		for _, f := range t.Archive.Files {
+			switch {
+			case strings.HasSuffix(f.Name, ".cue"):
+				inst, err := r.Compile(f.Name, f.Data)
+				if err != nil {
+					t.WriteErrors(errors.Promote(err, "test"))
+					return
+				}
+				switch f.Name {
+				case "schema.cue":
+					schema = inst.Value()
+				case "value.cue":
+					value = inst.Value()
+				}
+			}
+		}
+
+		v := schema.Unify(value)
+		if err := v.Err(); err != nil {
+			t.WriteErrors(errors.Promote(err, "test"))
+			return
+		}
+
+		b, err := textproto.NewEncoder().Encode(v)
+		if err != nil {
+			t.WriteErrors(errors.Promote(err, "test"))
+			return
+		}
+		_, _ = t.Write(b)
+
+	})
+}