Support "scope" for machine tag default semantics

[luisrayas3]

Proposed fix for #1884

[luisrayas3]

Open to alternatives to "scope" for the value that enables this behavior. "true_while_in_scope" seemed a bit verbose

[peci1]

I tested this PR and it works as advertised. Thanks!

I also added another value for the default argument - parent, which means that the machine becomes default in the parent context... that is useful if you want to define the machines in a separate launch file which is then included at relevant places in other launch files. It is just a few changed lines compared to this PR. Would you be interested in getting this feature here? On one hand, I consider this a useful feature, on the other hand, it might become a bit unintuitive when included files can change the default machine...

[peci1]

For those who do not want to wait until this PR is merged, I created a package that hacks roslaunch and adds this functionality: https://github.com/ctu-vras/scoped_roslaunch .

[ameysutavani]

Hello all,
Touch basing on this PR. Is is possible to get it merged?

[DanyResasco]

hi, I need this feature too. is it possible to get merged? @peci1 I'm tried to use your patch could you please tell me how to use it? Maybe I installed it wrong.

[130s]

I asked whether there's a room for merging a fix to the targeted issue #1884 (comment). That said, the way this PR suggests as of now seems to be adding a new capability ('scope'), which I'm not sure if we can still add to already-released core library. Just my feeling.

[peci1]

If the wiki docs have been correct for the past few years, then this PR is just fixing a bug. It adds the "new" functionality in order to keep code using the wrong (old, wiki-nonconformant) implementation working.

@130s Do you have a reference to a decision where OR decided not adding any new functionality into released core ROS1 packages? In earlier versions, it was quite common that released distros gained new functionality - if its implementation did not break ABI and API. I know everything is ROS 2 now, but Noetic still has quite some lifespan ahead and it would be sad to know it will not gain even non-intrusive features. Also, there is recent new functionality that has been accepted to roslaunch: #1937 (both into Melodic and Noetic). So it seems that adding new features should still be possible.

[DanyResasco]

Hi,
any update on this feature? The machine tag is not working as supposed to.