proto importing from parent directory does not work

Can't figure out how to do imports in proto, some help much appreciated.

The file structure:

• proto
  • api
    • item.proto
  • item.proto

I'm trying to import proto/item.proto into proto/api/item.proto

proto/api/item.proto:

syntax = "proto2";
import "item.proto"

service ItemService {

  rpc ListItems(ListItemsRequest) returns (ListItemsResponse);
}

message ListItemsRequest {
  //Empty message
}

message ListItemsResponse {

  option (grpc.gateway.protoc_gen_openapiv2.options.openapiv2_schema) = {
    json_schema: {
      required:["items"]
    }
  };

  repeated .item.Item wallets = 1;
}

Line for generating:

protoc \
    --proto_path=proto/ \
    --proto_path=third_party/grpc-gateway/third_party/googleapis \
    --proto_path=third_party/grpc-gateway \
    --include_source_info \
    --include_imports \
    --descriptor_set_out="$DESCRIPTOR_OUT" \
    --cpp_out="$CPP_OUT" \
    --grpc_out="$CPP_OUT" \
    --plugin=protoc-gen-grpc=`which grpc_cpp_plugin` \
    proto/api/item.proto

Spits out error:

api/item.proto:57:12: ".item.Item" is not defined.

I assume that you did not add a package specifier to the proto/item.proto file. See this, and this. If you specify a package in the imported file, you should get no errors:

syntax = "proto2";
package item;

message Item {}

You could also not add a package specifier to the imported file, and drop the package from the message name (in proto/api/item.proto):

message ListItemsResponse {
    repeated .Item wallets = 1;
}

As a side note, the protobuf documentation recommends that you always import files relative to the project root. I assume that this method can help in keeping the project manageable, I could not find any technical reason to recommend this. Something like this:

proto/api/item.proto:

syntax = "proto2";
package api.item;

import "proto/item.proto";

...

and generating with

protoc \
    --proto_path=. \
    ... \
    proto/api/item.proto