test_ucode: address UnusedElaboratable warning.

[kivikakk]

Fixes #17.

This is in fact an UnusedElaboratable being reported. If you stick # amaranth: UnusedElaboratable=no at the top of ucoderom.py, it goes away.

The origin is test_ucode_layout_gen:

sentinel/tests/sim/test_ucode.py

Lines 32 to 39 in 0bd1a79

	# This is a test by itself because creating the signature from the microcode
	# assembly file can be tricky.
	@pytest.mark.module(UCodeROM(main_file=StringIO(M5META_TEST_FILE),
	enum_map={"bar": Bar}))
	@pytest.mark.clks((1.0 / 12e6,))
	def test_ucode_layout_gen(sim_mod):
	_, m = sim_mod
	m.elaborate(None)

It doesn't happen if you run it in isolation, I'm guessing due to how all the MustUse machinery works (or some interaction with SimulatorFixture), but one other test before it is enough:

$ pdm test tests/sim/test_top.py::test_exception tests/sim/test_ucode.py::test_ucode_layout_gen
=================================== test session starts ===================================
platform darwin -- Python 3.12.3, pytest-8.1.1, pluggy-1.4.0
rootdir: /Users/kivikakk/g/sentinel
configfile: pyproject.toml
collected 2 items

tests/sim/test_top.py .                                                             [ 50%]
tests/sim/test_ucode.py .                                                           [100%]

==================================== 2 passed in 1.44s ====================================
/Users/kivikakk/g/sentinel/src/sentinel/ucoderom.py:69: UnusedElaboratable: <amaranth.hdl._dsl.Module object at 0x1072cb1d0> created but never used
  m = Module()
UnusedElaboratable: Enable tracemalloc to get the object allocation traceback

Fragment.get calls elaborate and sets the "used" flag, so this stops the warning.

[cr1901]

Looks fine to me... could you add a comment to the changed lines for future-me when I inevitably forget? I don't touch the Fragment stuff typically, so I'm not familiar with how it works.

$ pdm test tests/sim/test_top.py::test_exception tests/sim/test_ucode.py::test_ucode_layout_gen
=================================== test session starts ===================================
platform darwin -- Python 3.12.3, pytest-8.1.1, pluggy-1.4.0
rootdir: /Users/kivikakk/g/sentinel
configfile: pyproject.toml
collected 2 items

tests/sim/test_top.py .                                                             [ 50%]
tests/sim/test_ucode.py .                                                           [100%]

==================================== 2 passed in 1.44s ====================================
/Users/kivikakk/g/sentinel/src/sentinel/ucoderom.py:69: UnusedElaboratable: <amaranth.hdl._dsl.Module object at 0x1072cb1d0> created but never used
  m = Module()
UnusedElaboratable: Enable tracemalloc to get the object allocation traceback

Thank you for isolating the issue :). I still have to use grep -v UnusedEla to prevent my console from being overrun with spurious warnings, but at least it's a starting point.

[kivikakk]

I don't really know what you would like the comment to say (I can't say I'm overly familiar with Fragment either, but I looked at where MustUse is touched and there it was!), but I've done my best!

[cr1901]

Fair enough... merged :D! Thanks for the contribution :)!