[CMake] protobuf and imports relative to root (and --proto_path)

[David Jobet]

Hello, thanks for your answer.

Here's a mockup :
projectroot/lib1
projectroot/lib1/CMakeLists.txt
projectroot/lib1/a.proto
projectroot/lib1/b.proto
projectroot/lib1/test.cc

See below for the content of the files.

Here's the cmake output :
$ cmake --build build
[0/1] Re-running CMake...
-- Configuring done
-- Generating done
-- Build files have been written to: XXX/temp/build
[1/3] Building CXX object lib1/CMakeFiles/protolib1.dir/a.pb.cc.o
FAILED: lib1/CMakeFiles/protolib1.dir/a.pb.cc.o
XXX/bin/g++   -I. -isystem XXX/include -std=c++14 -Wall   -std=c++14
-MD -MT lib1/CMakeFiles/protolib1.dir/a.pb.cc.o -MF
lib1/CMakeFiles/protolib1.dir/a.pb.cc.o.d -o lib1/CMakeFiles/protoli
b1.dir/a.pb.cc.o -c lib1/a.pb.cc
lib1/a.pb.cc: In function 'void protobuf_AddDesc_a_2eproto()':
lib1/a.pb.cc:79:3: error: '::protobuf_AddDesc_lib1_2fb_2eproto' has
not been declared
  ::protobuf_AddDesc_lib1_2fb_2eproto();
  ^~
ninja: build stopped: subcommand failed.

Here's what's generated from b.proto :
$ cat build/lib1/b.pb.h | grep AddDesc
void  protobuf_AddDesc_b_2eproto();
 friend void  protobuf_AddDesc_b_2eproto();


If I remove the PROTOBUF_IMPORT_DIRS and add "PROTO_PATH
${CMAKE_SOURCE_DIR}" on protobuf_generate_cpp to use my patch (this
injects --proto_path on protoc command line), everything works.
e.g :
#set(PROTOBUF_IMPORT_DIRS ${CMAKE_SOURCE_DIR})
protobuf_generate_cpp(PROTO_SRCS PROTO_HRDS PROTO_PATH
${CMAKE_SOURCE_DIR} a.proto b.proto)

And indeed, the namespace is now correct :
$ cat build/lib1/b.pb.h | grep AddDesc
void  protobuf_AddDesc_lib1_2fb_2eproto();
 friend void  protobuf_AddDesc_lib1_2fb_2eproto();

Again, does anyone know how to make this works without the patch ?
If not, how do someone proposes a patch on cmake ? (posting to the
developper mailing list ?)

David


File contents

-----

$ cat lib1/CMakeLists.txt
project(lib1 LANGUAGES CXX C)

find_package(Protobuf REQUIRED)

set(PROTOBUF_IMPORT_DIRS ${CMAKE_SOURCE_DIR})
protobuf_generate_cpp(PROTO_SRCS PROTO_HRDS a.proto b.proto)
add_library(protolib1 STATIC ${PROTO_SRCS} ${PROTO_HRDS})
target_include_directories(protolib1 PUBLIC ${CMAKE_BINARY_DIR})
target_link_libraries(protolib1 PUBLIC protobuf::libprotobuf)

add_library(lib1 test.cc)
target_include_directories(lib1 PUBLIC ${CMAKE_CURRENT_SOURCE_DIR})
target_link_libraries(lib1 PRIVATE protolib1)

-----

$ cat lib1/a.proto
import "lib1/b.proto";

message A
{
 optional string toto = 1;
 optional BType  type = 2;
}

-----

$ cat lib1/b.proto
message BType
{
   optional double d = 1;
}

-----

$ cat lib1/test.cc
// Protocol buffer
#include <google/protobuf/text_format.h>
#include "lib1/a.pb.h"
On Thu, Aug 23, 2018 at 9:36 PM Alexander Neundorf <neundorf at kde.org> wrote:
>
> On 2018 M08 23, Thu 12:50:14 CEST David Jobet wrote:
> > Hello,
> >
> > I'm trying to port an existing project from premake to cmake.
> > I'm trying to avoid modifying the source files while doing so.
> >
> > Right now, we have several libraries (read in different directories) using
> > proto files with imports between them.
> > All imports are made relative to the root of the project.
> >
> > e.g :
> > work/lib1/sublib1/a.proto
> > work/lib1/sublib1/b.proto
> >
> > with a.proto having a link to b.proto like this "import
> > lib1/sublib1/b.proto"
> >
> > If I compile this with an unchanged FindProtobuf.cmake, I do this :
> >
> > protobuf_generate_cpp(PROTO_SRCS PROTO_HRDS a.proto b.proto)
> > add_library(...)
> >
> > the problem being that it looks like the "namespaces" generated by protoc
> > in b.proto do not match the one used in a.proto : it does not compile.
>
> do you mean protoc fails, or that the C++ compiler fails when compiling the
> generated file ?
> I'm also using proto files with imports between them and don't have problems
> with finding them.
> Are you setting the PROTOBUF_IMPORT_DIRS variable ?
>
> What I do have a problem is rerunning protoc automatically on proto-files which
> import proto files that have been modified.
> How do you handle this ?
>
> > Is there a way to make this work ?
> >
> > Otherwise, I made the patch below which solves my problem. Do you think it
> > could be included in cmake ?
> > it defines a new option PROTO_PATH, so the decl above becomes
> > protobuf_generate_cpp(PROTO_SRCS PROTO_HRDS PROTO_PATH ${CMAKE_SOURCE_DIR}
> > a.proto b.proto)
> >
> > With regards
> >
> > David
> >
> > $ diff share/cmake-3.10/Modules/FindProtobuf.cmake.orig
> > share/cmake-3.10/Modules/FindProtobuf.cmake
>
> can you please use diff -bup ?
> This makes the patch easier to read.
>
> Thanks
> Alex
>
> --
>
> Powered by www.kitware.com
>
> Please keep messages on-topic and check the CMake FAQ at: http://www.cmake.org/Wiki/CMake_FAQ
>
> Kitware offers various services to support the CMake community. For more information on each offering, please visit:
>
> CMake Support: http://cmake.org/cmake/help/support.html
> CMake Consulting: http://cmake.org/cmake/help/consulting.html
> CMake Training Courses: http://cmake.org/cmake/help/training.html
>
> Visit other Kitware open-source projects at http://www.kitware.com/opensource/opensource.html
>
> Follow this link to subscribe/unsubscribe:
> https://cmake.org/mailman/listinfo/cmake