How to use `M` para

[Aklscc]

A successful example

I have a project with structure as following:

hello/
`-- protobuf
    |-- animal.proto
    |-- cat.proto
    `-- food
        `-- food.proto

The content of proto is:

// cat.proto
import "food/food.proto"

// food.proto
option go_package="hello/protobuf/food"

I run protoc command in proto dir:

protoc --proto_path=. \
    --go_out=. \
    --go_opt=Mfood/food.proto=hello/protobuf/food
    cat.proto

Ok, it works fine.

A failed example

I changed the structure as following:

hello/
`-- protobuf
    |-- animal.proto
    |`--cat
    |    `--cat.proto
    `-- food
        `-- food.proto

And the content of proto is:

// cat.proto
import "food/food.proto"

// food.proto
option go_package="hello/protobuf/food"

I run the command in cat dir,

protoc --proto_path=. \
    --go_out=. \
    --go_opt=Mfood/food.proto=hello/protobuf/food
    cat.proto

So how does the M para work with proto-gen-go. How should I use it to replace --proto_path to pass import_path?