Generate Go file for protos with import dependencies using Protoc, a Reader service added to the proto

proto_folder\car\car_info.proto

syntax = "proto3";
package car;

import "common/vehicle_info.proto";

message Car {
    vehicle.Vehicle info = 1;
    string carType = 2;
}

service Reader {
    rpc GetPriceInfo(GetPriceInfoRequest) returns (GetPriceInfoResponse);
}

message GetPriceInfoRequest {
    string manufacturer = 1;
    string model = 2;
}

message GetPriceInfoResponse {
    vehicle.PurchaseEntity info = 1;
}

proto_folder\common\vehicle_info.proto

syntax = "proto3";
package vehicle;

message PurchaseEntity {
    string manufacturer = 1;
    string model = 2;
    int32 price = 3;
}

message Vehicle {
    PurchaseEntity info = 1;
    string engineType = 2;
    int32 wheelCount = 3;
    int32 registrationNumber = 4;
}

Here are some way to fix the error like 'protoc-gen-go: unable to determine Go import path for "common/vehicle_info.proto"' error while go file generation.

Generate with adding go_package in proto file itself
Update common/vehicle_info.proto file with option go_package="generated_code_with_go_package/vehicle_pkg"; line.

syntax = "proto3";
package vehicle;
option go_package="generated_code_with_go_package/vehicle_pkg"; // <--- this will generate go file under the package path
message PurchaseEntity {
.....

The earlier update allow us to generate the go file using the below command

protoc ^
    --proto_path=./proto_folder  ^
    --go_out=./generated_codes  ^
    common/vehicle_info.proto

This will generate go file in generated_codes\generated_code_with_go_package\vehicle_pkg

Alternatively you could mention the package path in go_opt option

protoc ^
    --proto_path=./proto_folder  ^
    --go_out=./generated_codes  ^
    --go_opt=Mcommon/vehicle_info.proto=generated_code_with_go_opt/vehicle_pkg ^
    common/vehicle_info.proto

Now to generate the go file of our targeted proto proto_folder\car\car_info.proto use the below command

protoc ^
    --proto_path=./proto_folder  ^
    --go_out=./generated_codes  ^
    --go_opt=Mcommon/vehicle_info.proto=generated_code_with_go_opt/vehicle_pkg ^
    --go_opt=Mcar/car_info.proto=generated_code_with_go_opt/car_pkg ^
    car/car_info.proto

This will generate generated_codes\generated_code_with_go_opt\car_pkg\car_info.pb.go go file.

You could generate them together using this simple command but for that both proto should define the expected package path through go_package option.

protoc ^
    --proto_path=./proto_folder  ^
    --go_out=./generated_codes  ^
    car/car_info.proto ^
    common/vehicle_info.proto

Otherwise as mentioned earlier include the go_opt option in protoc command.

protoc ^
    --proto_path=./proto_folder  ^
    --go_out=./generated_codes  ^
    --go_opt=Mcommon/vehicle_info.proto=generated_code_with_go_opt/vehicle_pkg ^
    common/vehicle_info.proto ^
    --go_opt=Mcar/car_info.proto=generated_code_with_go_opt/car_pkg ^
    car/car_info.proto

Step by step action can be found in the medium.

Note that i was using windows for my development thus the use of ^ for multi line command replace it with \ for linux based os.

The above method will only generate the message part of the proto.

If you want to generate you service code too, you have to do one more step.

protoc ^
--proto_path=./proto_folder ^
--go-grpc_out=./generated_codes ^
--go-grpc_opt=Mcar/car_info.proto=generated_code_with_go_opt/car_pkg ^
car/car_info.proto

They have separated these step into two to make the code/release more maintainable.

The difference,
generation of message uses go_out with go_opt.
but for service part we use go-grpc_out with go-grpc_opt

You can generate them together using..

protoc ^
    --proto_path=./proto_folder     ^
                                    ^
    --go_out=./generated_codes      ^
    --go_opt=Mcommon/vehicle_info.proto=generated_code_with_go_opt/vehicle_pkg ^
    --go_opt=Mcar/car_info.proto=generated_code_with_go_opt/car_pkg ^
                                    ^
    --go-grpc_out=./generated_codes ^
    --go-grpc_opt=Mcar/car_info.proto=generated_code_with_go_opt/car_pkg ^
                                    ^
    common/vehicle_info.proto       ^
    car/car_info.proto