catkin build ONLY the message target of a package

Question

I have packages as follows:

package_A/
|-- msg/
    |-- CustomMsg.msg
    \-- ... (other messages)
|-- include/ ... (some code)
|-- src/ ... (some Python and C++ code)

package_B/ ... (also depends on package_A/CustomMsg.msg)

my_msgs/
|-- msg/ ... (some messages; one depends on package_A/CustomMsg.msg)
\-- ... (srv and action definitions that depend on msg)

my_package_1/ ... (depends on my_msgs)

my_package_2/ ... (depends on my_msgs)

I'm working in Melodic and I have some bag data, pkl files, etc., but unfortunately, I need to work with that data in another distro where it's infeasible for me to setup my workspace again (package_A and package_B won't build because of various dependencies, for example). The way I see it, I have 2 options:

Option 1:

I only need the messages built to work with my data, but I cannot figure out a way to get catkin to only build the message targets and ignore the code that comes in package_A. Is there a way to do this?

CMake doesn't come naturally to me, so when trying to build catkin build package_A_generate_messages failed, I decided to come here for help. If there is a way to build just CustomMsg.msg, even better!

Option 2:

I know that you can work across distros if the message hashes remain unchanged. But I don't know how those hashes are generated. Is the package name taken into account? I think the answer is yes, but wanted to check what else might be. CustomMsg.msg actually has a pretty simple message definition, so if I redefine the message in my own (faux) package called package_A on the other machine and build, will I end up with the same hash, which will then allow me to reuse my data files?

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Originally posted by banerjs on ROS Answers with karma: 5 on 2019-07-30

Post score: 0

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Original comments

Comment by pcoenen on 2019-07-30:
I don't know if there is a way to force catkin to only generate messages, but you could comment out all the add_executable/library/dependencies and target_link_libraries in your packages CMakeLists.txt.

Comment by banerjs on 2019-07-30:
Yeah, that's essentially what I'm doing with option 2. I think it seems to be working; I'll post back here when I'm sure. Thanks!

Answer 1

What you ask for is impossible, as the message generation targets are only created upon a successful CMake configuration phase run.

Success of that phase depends on the find_package(..) and other statements in the CMakeLists.txt of all pkgs in a workspace to succeed. That can only happen if all dependencies are present (which would appear to be exactly your problem: "package_A and package_B won't build because of various dependencies, for example").

The targets are defined in the Makefile that CMake generates after all this succeeds. At that point it would be trivial to invoke only the message generation target:

catkin_make package_A_generate_messages

or:

catkin build --make-args package_A_generate_messages

I'm not aware of any option to CMake (which Catkin will invoke) to make it ignore failing commands, so editing the CMakeLists.txt of package_A and package_B would seem to be your only option.

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Originally posted by gvdhoorn with karma: 86574 on 2019-08-01

This answer was ACCEPTED on the original site

Post score: 1

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Original comments

Comment by banerjs on 2019-08-02:
Got it. That makes a lot of sense. Thanks!

Just so I have this clear, assume for instance that instead of missing dependencies, which is indeed my problem, the problem was that dependency APIs had changed (for instance the arguments to a function had changed; something only caught when an actual make command is run)---then the option of running some cmake command followed by a make <package>_generate_messages would have been doable, right?

Comment by gvdhoorn on 2019-08-02:
If CMake is happy with whatever it found for packages, and it's just compilation that would fail, then yes, I believe you should be able to run Catkin first (which is essentially CMake) and then the message generation targets should be there.

Answer 2

As far as I'm aware, there is no way to build only parts of a package such as messages. There is, however, a third option: Create a new package that contains only the messages. This actually a very common practice and would help avoid this issue.

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Originally posted by jayess with karma: 6155 on 2019-07-30

This answer was NOT ACCEPTED on the original site

Post score: 1

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Original comments

Comment by banerjs on 2019-07-30:
Yes, I know. But package_A and package_B are not maintained by me and while I do have access to the code, I do not want to incur the cost of a) collecting data again or of b) refactoring all the packages that depend on CustomMsg.msg since in reality there are many more than 3 or 4 packages in my workspace that depend on the message. So option 3, while valid, is a no-go.