`AssertionError` when running `Platform.build` with a `Module` using an `Instance`.

[cr1901]

The following code snippet triggers an assertion failure:

from nmigen import *
from nmigen_boards.tinyfpga_ax2 import *

from nmigen.build import *
from nmigen_boards.resources import *


plat = TinyFPGAAX2Platform()
plat.add_resources([Resource("led", 0, Pins("gpio_0:1"))])

class Test(Elaboratable):
    def __init__(self):
        pass

    def elaborate(self, plat):
        m = Module()
        led = plat.request("led")

        m.submodules += [
            Instance("top", o_o=led)
        ]

        return m

plan = plat.build(Test(), name="actual_top", do_build=False)

$ python mk_build.py
Traceback (most recent call last):
  File "mk_build.py", line 25, in <module>
    plan = plat.build(Test(), name="actual_top", do_build=False)
  File "C:/msys64/home/william/projects/fpga/nmigen/nmigen/nmigen/build/plat.py", line 95, in build
    plan = self.prepare(elaboratable, name, **kwargs)
  File "C:/msys64/home/william/projects/fpga/nmigen/nmigen/nmigen/build/plat.py", line 166, in prepare
    fragment._propagate_ports(ports=self.iter_ports(), all_undef_as_ports=False)
  File "C:/msys64/home/william/projects/fpga/nmigen/nmigen/nmigen/hdl/ir.py", line 462, in _propagate_ports
    self._prepare_use_def_graph(parent, level, uses, defs, ios, self)
  File "C:/msys64/home/william/projects/fpga/nmigen/nmigen/nmigen/hdl/ir.py", line 436, in _prepare_use_def_graph
    subfrag._prepare_use_def_graph(parent, level, uses, defs, ios, top)
  File "C:/msys64/home/william/projects/fpga/nmigen/nmigen/nmigen/hdl/ir.py", line 428, in _prepare_use_def_graph
    add_defs(value._lhs_signals())
  File "C:/msys64/home/william/projects/fpga/nmigen/nmigen/nmigen/hdl/ir.py", line 396, in add_defs
    assert defs[sig] is self
AssertionError

The error is that the Pins direction (an inout?) of the led Resource does not match what Instance expects (an output). I'm not sure why this AssertionError is triggered. Is there a good place to raise a "driver conflict in Instance" error before this assertion triggers?

Fix to stop the AssertionError:

plat.add_resources([Resource("led", 0, Pins("gpio_0:1", dir="o"))])

[awygle]

I believe this would be addressed by #596

[whitequark]

The error is that the Pins direction (an inout?)

That's not an inout. You're requesting a triple, implicitly. Use dir="o" when defining the LED resource, or better, LEDResources.

[cr1901]

#596 will close this.