Error message should be reported after detecting protoc execution failure

[JackBoosY]

Hi guys, Recently, some issues in vcpkg reported that opencv4 or Darknet failed to build when using protoc(#10695 #11802 etc.). After an in-depth investigation, the reason for the build failure is that the library that protoc depends on has not been found or installed in the path where it is located. And I found that the execution command of protoc is written here: https://github.com/protocolbuffers/protobuf/blob/1dae8fdd6271d091bbf43c0fd5855603ba533c1d/cmake/protobuf-config.cmake.in#L126

Is there any way to write detailed logs to the log when protoc fails to execute?

Thanks.

What version of protobuf and what language are you using? Version: 3.12.0 Language: C++/CMake

What operating system (Linux, Windows, ...) and version? Windows What runtime / compiler are you using (e.g., python version or gcc version) N/A What did you do? Steps to reproduce the behavior(on Windows):

1. git clone https://github.com/microsoft/vcpkg.git
2. ./bootstrap-vcpkg.bat
3. ./vcpkg install protobuf
4. del PATH_TO_VCPKG/installed/x86-windows/tools/protobuf/libprotobuf.dll
5. ./vcpkg install opencv4
6. See error in PATH_TO_VCPKG/buildtrees/opencv4/install-x86-windows-dbg-out.log

What did you expect to see Report error info in log,

What did you see instead?

[233/470] cmd.exe /C "cd /D F:\vcpkg\buildtrees\opencv4\x86-windows-dbg\modules\dnn && F:\vcpkg\installed\x86-windows\tools\protobuf\protoc.exe --cpp_out F:/vcpkg/buildtrees/opencv4/x86-windows-dbg/modules/dnn -I F:/vcpkg/buildtrees/opencv4/src/4.1.1-fb9e10326a/modules/dnn/src/caffe -I F:/vcpkg/buildtrees/opencv4/src/4.1.1-fb9e10326a/modules/dnn/src/onnx -I F:/vcpkg/buildtrees/opencv4/src/4.1.1-fb9e10326a/modules/dnn/src/tensorflow F:/vcpkg/buildtrees/opencv4/src/4.1.1-fb9e10326a/modules/dnn/src/tensorflow/attr_value.proto" FAILED: modules/dnn/attr_value.pb.h modules/dnn/attr_value.pb.cc Make sure you include information that can help us debug (full error message, exception listing, stack trace, logs).

Anything else we should know about your project / environment vcpkg-latest

[elharo]

If I follow, this is a bug in vcpkg, not protoc. protoc can't log anything if it isn't even launched. If I'm misreading this, please reopen.

[JackBoosY]

@elharo Yeah that's caused by a vcpkg bug, but I wish to print some error message when add_custom_command run failed.

[elharo]

This change is not OK per the JSON spec. JSON allows "true" and "false" for boolean values. It does not allow TRUE, False, ERROR, etc.

[elharo]

sorry, commented on wrong issue.

[mkruskal-google]

Turning up the verbosity in CMake may help, but this doesn't seem like a problem protobuf can fix (it looks like a CMake/vcpkg issue to me)