Support backward-cpp

[j-rivero]

Related to gazebosim/gz-tools#63

The PR makes several things:

• remove Sid. ignition-tools is an official package in Sid started last week
• backward-cpp is available in Debian/Buster and Ubuntu/Focal on but not on Bionic. Missed the build-dep on control file, fixed here.
• For BIonic: custom rules and control file to use the vendor backward-cpp.

[chapulina]

This kinda goes against the undocumented rule we have against adding dependencies in minor releases. In this case I guess the alternative would be vendoring, which I don't think is recommended.

Do you think the addition of this dependency could negatively impact downstream users? Note that ign-tools1 is a dependency of pretty much all simulators we maintain right now.

[j-rivero]

Do you think the addition of this dependency could negatively impact downstream users? Note that ign-tools1 is a dependency of pretty much all simulators we maintain right now.

This case is a bit special since the dependency is only a build-dep, headers go into the build and no more is needed, if I understand the scenario correctly. If this is right, we are not modifying the dependency chain for consumers of the library just altering the build conditions providing the necessary source code for platforms without backwards-cpp. Seems safe to me to make an exception to the rule.

[chapulina]

Cool, I agree that it's ok if it's only needed while building. To be honest, I haven't looked into how it's all hooked up. I just noticed some failing downstream CI that couldn't find backward though.

[chapulina]

Let's give it a try!

[j-rivero]

Double checking things, seems like the new code does produce a new library:

++ cat /var/lib/jenkins/workspace/ignition_tools-ci-ign-tools1-bionic-amd64/make_jobs
+ make -j4
Scanning dependencies of target backward
[ 50%] Building CXX object src/CMakeFiles/backward.dir/backward.cc.o
[100%] Linking CXX shared library libignition-tools-backward.so
[100%] Built target backward
+ echo '# END SECTION'
# END SECTION
+ echo '# BEGIN SECTION: installing'

I assume that the library is needed to use the new functionality, is this right @azeey? If it is, we need a new package (i.e: libignition-tools-backwards) created from here and more modifications to this PR.

[azeey]

I assume that the library is needed to use the new functionality

That's correct.

[chapulina]

In that case, is there a way to setup the core ign-tools to skip backwards utilization if it's not present at runtime? So we keep the core of ign-tools C++-free and don't add a new dependency to existing users.

[azeey]

That's what it does right now. It tries to load the library and prints a message if it fails https://github.com/ignitionrobotics/ign-tools/blob/6cf3e3521f701d79f1c1e11b2b6d9e3de7f946fe/src/ign.in#L292-L297.

Seeing that Backward was a header-only library, I was hoping we can just drop it in the code and not have to deal with packaging issues. I guess it's not that simple.

[j-rivero]

That's what it does right now. It tries to load the library and prints a message if it fails https://github.com/ignitionrobotics/ign-tools/blob/6cf3e3521f701d79f1c1e11b2b6d9e3de7f946fe/src/ign.in#L292-L297.

Maybeeee a warning? not under the scope of this work, just a comment.

Seeing that Backward was a header-only library, I was hoping we can just drop it in the code and not have to deal with packaging issues. I guess it's not that simple.

That usually happens when we have C/C++ libraries and header only libraries are introduced in the code and just mixed at compilation time with no other requirements or effects. In this case, the library has no C/C++ code so somehow the feature needs a place to live in :)

I'm including the library together with the main package 2e6dc66. Let me role a prerelease to see if things are working.

[j-rivero]

I'm including the library together with the main package 2e6dc66. Let me role a prerelease to see if things are working.

1.4.0 Focal/amd64 from prerelease repository:

❯ ign log
Record and playback Ignition Transport topics.                        

  ign log record|playback [options]                                     
                                                                        
Options:                                                              

  -h [ --help ]              Print this help message.                   
  -v [ --verbose ] LEVEL     Set verbosity level 0-4 (default 1).       
                                                                        

~/code 
❯ sudo rm /usr/lib/x86_64-linux-gnu/libignition-tools-backward.so

~/code 
❯ ign log
Library error: libignition-tools-backward.so not found. Improved backtrace generation will be disabled
Record and playback Ignition Transport topics.                        

  ign log record|playback [options]                                     
                                                                        
Options:                                                              

  -h [ --help ]              Print this help message.                   
  -v [ --verbose ] LEVEL     Set verbosity level 0-4 (default 1).