internal/protobuf: record position information

for both errors and in the AST.

Removes the error type, which now implements the
standard CUE error conventions.

Change-Id: I7a4198a9cf9b38622f14f63df827f3f9730fe4b5
Reviewed-on: https://cue-review.googlesource.com/c/cue/+/2341
Reviewed-by: Marcel van Lohuizen <mpvl@golang.org>

internal/protobuf/errors.go

@@ -0,0 +1,53 @@
+// Copyright 2019 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 protobuf
+
+import (
+	"fmt"
+	"strings"
+
+	"cuelang.org/go/cue/token"
+)
+
+// protobufError implements cue/Error
+type protobufError struct {
+	path []string
+	pos  token.Pos
+	err  error
+}
+
+func (e *protobufError) Position() token.Pos {
+	return e.pos
+}
+
+func (e *protobufError) InputPositions() []token.Pos {
+	return nil
+}
+
+func (e *protobufError) Error() string {
+	if e.path == nil {
+		return fmt.Sprintf("protobuf: %s: %v", e.pos, e.err)
+	}
+	path := strings.Join(e.path, ".")
+	return fmt.Sprintf("protobuf: %s:%s: %v", e.pos, path, e.err)
+}
+
+func (e *protobufError) Path() []string {
+	return e.path
+}
+
+func (e *protobufError) Msg() (format string, args []interface{}) {
+	return "error parsing protobuf: %v", []interface{}{e.err}
+}