urdf: fix test and clean up internals

[scpeters]

🦟 Bug fix

Fixes incorrect kinematics in a URDF test file and updates test accordingly. Also clean up some internal parser functions.

Summary

The urdf_gazebo_extensions.urdf file had incorrect kinematics with link3 being the child of two different joints. This adds a link4 and replaces joint13 with joint14 connecting link1 to link4. This also fixes some expectations about the implicit_spring_damper tags.

I also cleaned up some of the internals of parser_urdf in 90595c0:

• remove unused variables
• remove unused function parameters
• make input function parameters const

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.

[codecov]

Codecov Report

Merging #1126 (b361b5b) into sdf9 (3b82d6a) will not change coverage.
The diff coverage is n/a.

❗ Current head b361b5b differs from pull request most recent head 90595c0. Consider uploading reports for the commit 90595c0 to get more accurate results

@@           Coverage Diff           @@
##             sdf9    #1126   +/-   ##
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  Coverage   87.81%   87.81%           
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  Files          64       64           
  Lines       10099    10099           
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  Hits         8868     8868           
  Misses       1231     1231           

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[j-rivero]

LGTM. One silly question probably: why was necessary to rename the name joint13 to joint14 in the test/integration/urdf_gazebo_extensions.urdf file?

[scpeters]

LGTM. One silly question probably: why was necessary to rename the name joint13 to joint14 in the test/integration/urdf_gazebo_extensions.urdf file?

the naming scheme in this file uses single digits for links and pairs of digits for the joints corresponding to the parent and child link. So the change of the joint name from joint13 to joint14 isn't significant in itself, but the implied change of the child link from link3 to link4 is significant for the kinematics, since link3 was the child of both joint23 and joint13, which is not allowed in URDF. After this change, link3 has only one parent joint.