Reading diagnostics

When something is wrong, the compiler says what, where and what to change, in the layout rustc and ruff use.

error[name.unknown_reference]: Navigate.goal: nothing named 'gaol' matches @world/<goal or entity>
  --> demo.task:3:25
  |
3 |         Navigate(goal = @world/gaol)
  |                         ^^^^^^^^^^^ not declared
  |
  = help: did you mean 'goal'?

Part	Says
error[name.unknown_reference]	The level and the code. The code is stable; tools and tests match on it.
The message	The cause, in one sentence.
--> demo.task:3:25	The file, line and column of the cause.
The excerpt	The source line, with the exact bytes underlined.
= help:	What to change.
= note:	The facts the decision rested on.

The cause can be in a library as well as in the program: a problem with a part points into its component.yaml.

Errors and warnings

An error blocks: nothing is written. A warning does not. A validation rule that cannot decide, usually because a part does not state something, says so as a warning at the place it points at, and the summary counts it undecided:

warning[validation.assembly.footprint_known]: cannot decide: part 'imu_basic' of 'imu' declares no collision box, so the footprint may be larger than the known shapes
   --> demo.core:22:5
   |
22 |     IMU imu(ref = "imu_basic", glue = (0, 0.0001, 0.0344, 0, 0, -1))
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ no collision shape
   |
   = help: add a `collision` box to the part's component.yaml
   = note: evidence: x in [-0.177, 0.177] m, y in [-0.173, 0.173] m from chassis, pack, driver_l, driver_r, motor_lf, motor_lb, motor_rf, motor_rb, wheel_lf, wheel_lb, wheel_rf, wheel_rb

Checked demo.core demo.world demo.task (14 checks, 1 undecided)

--warnings-as-errors makes every warning block, and each one says so in a note.

Everything at once

The parser stops at the first syntax error. Every later phase checks the whole program and reports every problem it finds, so one compile shows everything it can:

error[validation.assembly.wheel_mounts_filled]: the shaft of 'motor_lf' carries no wheel
   --> demo.core:12:5
   |
12 |     Motor motor_lf(ref = "gearmotor_37d", glue = (0.1275, 0.1294, -0.0216, 0, 1, 0), command = @core/driver_l)
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ nothing on its shaft
   |
   = help: glue a wheel onto its shaft with glue = (0.1275, 0.1494, -0.0216, 0, 1, 0)
   = note: evidence: 4 motors drive 3 wheels on 4 drive mounts; 0 free wheels on 0 free wheel mounts

error[validation.assembly.glue_on_connector]: the glue of 'wheel_lf' matches no connector of the chassis or of a placed part; the nearest is 'motor_lf.shaft', 0.008 m away with direction cosine 1.00
   ...

error: 2 errors; demo.core demo.world demo.task did not compile

One misplaced wheel produced both: the glue matches no connector, so the motor's shaft it was meant for carries nothing.

For tools

--json writes the whole result to stdout: every diagnostic, every validation rule with its status and evidence, the robot as the compiler put it together (its parts and the facts the rules read), and the files written. --color never turns colour off; it is also off when NO_COLOR is set or the output is not a terminal.

Exit status	Means
0	Nothing blocked; warnings may have been printed
1	A diagnostic blocked
2	The command line itself was wrong

Diagnostics in the reference specifies every field and code.

Next

Running the output explains what the compiler writes and how to launch it.