Add _state suffix to //state subelements

[scpeters]

🦟 Bug fix

Part of #632, alternative to #1377

Summary

There is some overlap in the names used for elements in the //world/state specification and elsewhere, for example the model_state.sdf file included in state.sdf defines an element named model. This has caused challenges with aliasing in XSD (see #632 and #643), and it would be simpler if some of these elements had different names, so a _state suffix is appended to several subelements of the //state element. Additionally, the //joint_state definition is moved to its own file and included from state.sdf so that a //state/joint_state element can specify the state of a //world/joint.

I made a similar attempt at renaming these state elements in #1377 trying also to support backwards compatibility with a 1_11.convert file but only achieving partial functionality. Given that the //state element hasn't been used in any version of gz-sim, this pull request opts for a breaking change instead of partial support for backwards compatibility.

Checklist

• Signed all commits for DCO
• Added tests
• Updated documentation (as needed)
• Updated migration guide (as needed)
• Consider updating Python bindings (if the library has them)
• codecheck passed (See contributing)
• All tests passed (See test coverage)
• While waiting for a review on your PR, please help review another open pull request to support the maintainers

Note to maintainers: Remember to use Squash-Merge and edit the commit message to match the pull request summary while retaining Signed-off-by messages.

[jennuine]

LGTM, in each of the *_state.sdf can we add a little more description on what state is? For example, what is joint_state vs. normal joint. Alternatively, adding a more thorough comment in state.sdf would be helpful.

Also, since this is a breaking change, shouldn't we add a method of conversion in https://github.com/gazebosim/sdformat/blob/sdformat14_14.0.0/sdf/1.11/1_10.convert ?

[scpeters]

LGTM, in each of the *_state.sdf can we add a little more description on what state is? For example, what is joint_state vs. normal joint. Alternatively, adding a more thorough comment in state.sdf would be helpful.

👍

Also, since this is a breaking change, shouldn't we add a method of conversion in https://github.com/gazebosim/sdformat/blob/sdformat14_14.0.0/sdf/1.11/1_10.convert ?

I tried to add that in #1377, but it was difficult to handle multiple levels of nested models. My last commit in that PR (e9de659) added a failing test showing what wasn't yet working (see jenkins job result). The //state elements were used in gazebo-classic log files but haven't been used with gz-sim, and enabling automatic conversion would have required substantial updates to the sdf::Converter class, so I'm proposing a breaking change here. I believe @azeey concurred during a weekly meeting

[scpeters]

LGTM, in each of the *_state.sdf can we add a little more description on what state is? For example, what is joint_state vs. normal joint. Alternatively, adding a more thorough comment in state.sdf would be helpful.

👍

I've updated the description of state elements in cd32f6e

[scpeters]

while updating state descriptions (see cd32f6e), I decided to allow joints in //state/insertions for consistency with //state/joint_state in 33d6634

[azeey]

LGTM, in each of the *_state.sdf can we add a little more description on what state is? For example, what is joint_state vs. normal joint. Alternatively, adding a more thorough comment in state.sdf would be helpful.

👍

Also, since this is a breaking change, shouldn't we add a method of conversion in https://github.com/gazebosim/sdformat/blob/sdformat14_14.0.0/sdf/1.11/1_10.convert ?

I tried to add that in #1377, but it was difficult to handle multiple levels of nested models. My last commit in that PR (e9de659) added a failing test showing what wasn't yet working (see jenkins job result). The //state elements were used in gazebo-classic log files but haven't been used with gz-sim, and enabling automatic conversion would have required substantial updates to the sdf::Converter class, so I'm proposing a breaking change here. I believe @azeey concurred during a weekly meeting

Yes, like @scpeters said, gz-sim hasn't been using the //state element, so not having an automatic conversion is not a blocker.