Protobuf: Bug Report: The output file location of `protoc` is not expected under certain circumstances.

[zhengwx11]

protobuf version: 3.2
System: Ubuntu 16.04

When --proto-path is specified twice with certain setup, the --cpp_out will not be the direct output directory.

Set up

• .proto file: ~/project/proto/main.proto
• another .proto file: ~/project/proto/shared.proto

Process

1. change directory to ~/project/build/
2. run
   /usr/local/bin/protoc --cpp_out ~/project/build/ -I ~/project/ -I ~/project/proto/ ~/project/proto/hello.proto

Result
Output files are under ~/project/build/proto/ but not ~/project/build/, which is unexpected.

1. Remove first ipath:
   /usr/local/bin/protoc --cpp_out ~/project/build/ -I ~/project/proto/ ~/project/proto/hello.proto

Result
Output files are under ~/project/build/, which is expected.

[adhesiveNOR]

The correct command line parameter for --cpp_out is: protoc --cpp_out=~/project/build/

[zhengwx11]

@adhesiveNOR both forms are valid.

Part of the mechanism is explained in :
https://github.com/google/protobuf/issues/3044

Seems like searching in ipath is recursive. It goes deep down to the every leaf of directory tree. Multiple ipath are assigned priorities.

[xfxyjwf]

The directory layout of generated files is determined by their import name (the name you use in the 'import "path/to/other.proto";' statement to import that .proto file) and the import name as I explained in https://github.com/google/protobuf/issues/3044 is determined by matching the .proto file path against the --proto_path flags in order.

For

/usr/local/bin/protoc --cpp_out ~/project/build/ -I ~/project/ -I ~/project/proto/ ~/project/proto/hello.proto

The import name is "proto/hello.proto" because ~/project/proto/hello.proto matches the first "-I ~/project", and as such protoc will generate ~/project/build/proto/hellp.pb.h|cc.

If you instead do

/usr/local/bin/protoc --cpp_out ~/project/build/ -I ~/project/proto -I ~/project ~/project/proto/hello.proto

The import name will be "hello.proto" because "-I ~/project/proto" will be matched first.

Usually it's better to just put all .proto files in a single directory tree and specify the -I flag only once on the command line. More complex setup is usually not necessary and is very easy to get it wrong.