Support explicitly setting field tags

ygen/protogen.go

@@ -21,6 +21,7 @@ import (
 	"path/filepath"
 	"regexp"
 	"sort"
+	"strconv"
 	"strings"
 	"text/template"
 
@@ -1094,6 +1095,38 @@ func safeProtoIdentifierName(name string) string {
 
 // protoTagForEntry returns a protobuf tag value for the entry e.
 func protoTagForEntry(e *yang.Entry) (uint32, error) {
+	var offset uint32
+	for _, ext := range e.Exts {
+		if ext.Keyword == "occodegenext:field-number-offset" {
+			off, err := strconv.ParseUint(ext.Argument, 10, 32)
+			if err != nil {
+				return 0, fmt.Errorf("could not parse %s %s: %s", ext.Keyword, ext.Argument, err)
+			}
+			offset = uint32(off)
+			if offset == 0 {
+				return 0, fmt.Errorf("%s cannot be 0", ext.Keyword)
+			}
+			break
+		}
+	}
+	for _, ext := range e.Exts {
+		if ext.Keyword == "occodegenext:field-number" {
+			fn, err := strconv.ParseUint(ext.Argument, 10, 32)
+			if err != nil {
+				return 0, fmt.Errorf("could not parse %s %s: %s", ext.Keyword, ext.Argument, err)
+			}
+			if fn == 0 {
+				return 0, fmt.Errorf("%s cannot be 0", ext.Keyword)
+			}
+			annotatedFieldNumber := uint32(fn) + offset
+			if annotatedFieldNumber >= 19000 && annotatedFieldNumber <= 19999 {
+				return 0, fmt.Errorf("%s field number %d in Protobuf reserved range",
+					e.Name, annotatedFieldNumber)
+			}
+			return annotatedFieldNumber, nil
+		}
+	}
+
 	return fieldTag(e.Path())
 }
 

ygen/protogen_test.go

@@ -654,6 +654,102 @@ func TestGenProto3Msg(t *testing.T) {
 				}},
 			},
 		},
+	}, {
+		name: "simple message with only scalar fields and field number extensions",
+		inMsg: &Directory{
+			Name: "MessageName",
+			Entry: &yang.Entry{
+				Name: "message-name",
+				Dir:  map[string]*yang.Entry{},
+				Kind: yang.DirectoryEntry,
+			},
+			Fields: map[string]*yang.Entry{
+				"field-one": {
+					Name: "field-one",
+					Type: &yang.YangType{Kind: yang.Ystring},
+					Exts: []*yang.Statement{
+						{
+							Keyword:  "occodegenext:field-number-offset",
+							Argument: "100",
+						},
+					},
+				},
+				"field-two": {
+					Name: "field-two",
+					Type: &yang.YangType{Kind: yang.Yint8},
+					Exts: []*yang.Statement{
+						{
+							Keyword:  "occodegenext:field-number",
+							Argument: "1",
+						},
+					},
+				},
+				"field-three": {
+					Name: "field-three",
+					Type: &yang.YangType{Kind: yang.Yint8},
+					Exts: []*yang.Statement{
+						{
+							Keyword:  "occodegenext:field-number",
+							Argument: "1",
+						},
+						{
+							Keyword:  "occodegenext:field-number-offset",
+							Argument: "100",
+						},
+					},
+				},
+			},
+			Path: []string{"", "root", "message-name"},
+		},
+		inBasePackage: "base",
+		inEnumPackage: "enums",
+		wantMsgs: map[string]*protoMsg{
+			"MessageName": {
+				Name:     "MessageName",
+				YANGPath: "/root/message-name",
+				Fields: []*protoMsgField{{
+					Tag:  410095931,
+					Name: "field_one",
+					Type: "ywrapper.StringValue",
+				}, {
+					Tag:  1,
+					Name: "field_two",
+					Type: "ywrapper.IntValue",
+				}, {
+					Tag:  101,
+					Name: "field_three",
+					Type: "ywrapper.IntValue",
+				}},
+			},
+		},
+	}, {
+		name: "message with field number in reserved range",
+		inMsg: &Directory{
+			Name: "MessageName",
+			Entry: &yang.Entry{
+				Name: "message-name",
+				Dir:  map[string]*yang.Entry{},
+				Kind: yang.DirectoryEntry,
+			},
+			Fields: map[string]*yang.Entry{
+				"field-one": {
+					Name: "field-one",
+					Type: &yang.YangType{Kind: yang.Ystring},
+					Exts: []*yang.Statement{
+						{
+							Keyword:  "occodegenext:field-number",
+							Argument: "1",
+						},
+						{
+							Keyword:  "occodegenext:field-number-offset",
+							Argument: "18999",
+						},
+					},
+				},
+			},
+			Path: []string{"", "root", "message-name"},
+		},
+		wantErr: true,
 	}}
 
 	for _, tt := range tests {