Deprecation timeline for RigidBodyTree and attic

[jwnimmer-tri]

FYI For the new APIs, see MultibodyPlant<T> documentation.

If you have questions or need help converting to MultibodyPlant please use https://drake.mit.edu/getting_help.html. If there are missing features that could block your workflow, please let us know NOW by commenting on this issue.

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We are wondering if it's time to finally remove the RigidBodyTree, RigidBodyPlant, and related attic code and examples from Drake master.

We would like to understand the useful timeline for keeping them -- what issues with MultibodyPlant do we need to solve first, how long do users need to finish their transition to MultibodyPlant, and therefore what is a good target date for removing the code.

We are hoping for a removal date in early 2020.

I'd like to ask any users who would like to influence this timeline to speak up here, or on #dynamics slack.

Known possible blockers:

• MultiBody dynamics, inertia, and autodiff benchmarking #10322
• Add a bushing force element (as a low-budget loop weld joint) #11831

Feature request buckets:

• MultibodyTree features requests. #5013
• RigidBodyTree to MultibodyTree Feature Migration #7025

See also #9783 for past work on the attic.

[jwnimmer-tri]

Given the above PRs and a few more PRs currently in flight, as of this week all code inside Drake that uses the //attic is either deprecated (for removal by 2020-06-01), or has already been removed.

The only remaining question on timing for removal of RigidBodyTree is coordinating with downstream users, especially with respect to any missing features of MultibodyPlant.

[jwnimmer-tri]

The only remaining question on timing for removal of RigidBodyTree is coordinating with downstream users, especially with respect to any missing features of MultibodyPlant.

We have surveyed most known users, and the following timeline seems suitable. Please let us know of any difficulties:

Proposed dates (approximate):

• 2020-04-10 add once-per-process runtime warning
• 2020-04-15 release 0.17; mention the upcoming deprecation in relnotes
• 2020-05-15 release 0.18; mention the upcoming deprecation in relnotes
• 2020-05-25 add deprecation markers
• 2020-06-15 release 0.19 will be the first with compiler warnings
• 2020-07-15 release 0.20 (and 0.21)
• 2020-08-17 release 0.22
• 2020-09-01 removal of attic
• Add tag "last_sha_with_rigid_body_tree" or something
• 2020-09-15 release 0.23 first without attic

[jwnimmer-tri]

The last numbered release that still had attic code was v0.22.0 on 2020-08-17.
The last git sha on master that still had attic code was 408ebc1 on 2020-08-31.