What UE 5.5 cannot do

Paths. scripts/… and references/… below are relative to the directory holding this SKILL.md. Your working directory is the user's project, not that directory, so prefix them with its absolute path or the command is not found.

5.5 and 5.8 are the same CARLA line, not parallel products. PythonAPI/carla/src/Sensor.cpp is byte-identical between the branches, Actor.cpp differs by 2 lines and World.cpp by 22. 5.8 is the later revision — the one released as CARLA 1.0 — so treat 5.5 as an earlier point release. It still declares 0.10.0, which is also what every ue58 build reported before that release, so the version string does not separate the two: the branch does.

The practical consequence: the ue58 skills are the procedures for 5.5 too, minus the five gaps below. There is no ue5 mirror of each skill because there is almost nothing to mirror.

Instructions

Progress:
- [ ] Step 1: bash scripts/check_env.sh
- [ ] Step 2: list  — the gaps, and which ue58 skill each one breaks
- [ ] Step 3: check — confirm against the tree in front of you
- [ ] Step 4: then use the ue58 skill, minus the MISSING lines

source scripts/env.sh

bash scripts/gaps.sh list      # needs no checkout
bash scripts/gaps.sh check     # this tree's gap markers
bash scripts/gaps.sh diff      # measured, if a ue58 tree is also present

The five gaps

Gap	What is absent on 5.5	What it breaks
ROS 2 middleware	ros2/middleware/ (RMW abstraction, QosProfile.h, ActiveMiddleware) and the CARLA_CYCLONEDDS_* / CARLA_ZENOH_C_* options	FastDDS only — --rmw cyclonedds / --rmw zenoh do not exist ([[run-carla-ue58-server]]); [[add-ros-publisher]]'s QosProfile.h step does not apply
Autoware	both publishers, the control subscriber, AutowareSteeringCompensation.h, sensor.other.autoware_gnss, sensor.other.vehicle_status	[[run-autoware-ue58]] has no 5.5 counterpart
DLSS + ray-traced lens	enable_dlss, dlss_screen_percentage, SceneCaptureCamera_RayTracedLens.cpp, CARLA_DLSS_SDK_PATH	sensor.camera.rt_lens does not exist; [[create-sensor]]'s DLSS attributes are 5.8-only
OFPA large-map mount	MountExternalPackageRoots in Carla.cpp	Town12 / Town13 / Town15 load with an empty World Partition and a black screen. 5.8 absorbed this patch upstream; on 5.5 it is still a manual fix
A few API additions	World.get_ego_spawn_points, World.set_publish_tf / get_publish_tf, World.spawn_custom_mesh, Actor.enable_constant_acceleration / disable_constant_acceleration	those calls raise AttributeError; the rest of the python-api group applies unchanged

What is identical — every ue58 finding transfers

CMake-only build (no Makefile, Util/Tools not Util/BuildTools); all six package targets; the MapsToCook default including uncookable Town15, so an out-of-the-box package build fails on 5.5 too; the single-dash -ros2 flag; the actor factories and their PropParameters.json / WalkerParameters.json / VehicleParameters.json registration; the entire CarlaTools header set.

The known defects are shared too, which means the ue58 notes apply verbatim: RecastBuilder missing from Util/DockerUtils/dist (map-import navmesh silently produces nothing), Environment.sh not setting CARLA_BUILD_TOOLS_FOLDER (so Import.sh invokes /Import.py and exits 2), and the #if 0 // @CARLAUE5 wheel block that stops GenerateNewVehicleBlueprint producing a drivable vehicle.

Examples

Example 1: "run Autoware against my 5.5 build"

list — gap 2. Not possible: none of the publishers, the subscriber or the two sensors exist. Say so; do not adapt [[run-autoware-ue58]]'s steps, they have nothing to bind to.

Example 2: "start the server with cyclonedds"

Gap 1. 5.5 has no middleware abstraction, so FastDDS is the only transport. -ros2 itself works.

Example 3: "load Town12 and it's black"

Gap 4, and it is the expected outcome on 5.5, not a broken install. The mount patch is absent, so the World Partition comes up empty. Either apply the patch or use a non-partitioned town.

Example 4: "is this checkout 5.5 or 5.8?"

check. It classifies by markers rather than by branch name — ros2/middleware, the Autoware publishers, MountExternalPackageRoots — and reports the engine branch the tree names for itself (ue5-dev-carla vs ue58-dev-carla).

Example 5: "import a prop on 5.5"

Nothing in gap 1-5 touches it: use [[import-carla-ue58-prop]] directly. Same for walkers, packaging, and running a server.

Troubleshooting

Problem: check says the tree has 5.8 markers Cause: CARLA_UE5_ROOT points at a ue58-dev checkout. Solution: use the ue58 skills directly — none of these gaps apply.

Problem: a ue58 skill's step fails on 5.5 and it is not in the gap list Cause: the list covers structural differences found by diffing the trees; a behavioural difference at runtime would not appear in it. Solution: say the behaviour is unverified on 5.5 — no 5.5 build has ever been run here — and investigate rather than assuming the gap list is exhaustive.

Problem: diff refuses to run Cause: it needs both trees. Solution: export CARLA_UE58_ROOT as well, or use list / check.

Outputs

Nothing is written and nothing is started: all three modes are read-only. list prints the gap catalogue, check reports which markers this tree has, and diff prints a measured comparison of the ROS 2 layer, the CMake options, the Python binding line counts and the declared versions.

Per-gap evidence — file paths, reference counts, and what each gap means for which skill — is in references/gaps.md.