Stupid logic error in build_stat

[simoncozens]

Found while porting. I can't think of a way to trigger this, but it just looks wrong:

axisregistry/Lib/axisregistry/__init__.py

Lines 229 to 249 in 3db2ff6

	for axis, fallback in fallbacks_in_names:
	if axis in seen_axes:
	continue
	a = {
	"tag": axis,
	"name": axis_registry[axis].display_name,
	"values": [{"name": fallback.name, "value": fallback.value, "flags": 0x0}],
	}
	if axis in LINKED_VALUES and fallback.value in LINKED_VALUES[axis]:
	linked_value = LINKED_VALUES[axis][fallback.value]
	a["values"][0]["linkedValue"] = linked_value
	res.append(a)
	for axis, fallback in fallbacks_in_siblings:
	if axis in seen_axes:
	continue
	elided_value = axis_registry[axis].default_value
	elided_fallback = axis_registry.fallback_for_value(axis, elided_value)
	a = {
	"tag": axis,
	"name": axis_registry[axis].display_name,

Suppose an axis is in fallbacks_in_names but not in fallbacks_in_fvar; it gets added during the first loop above. But suppose it is also in fallbacks_in_siblings. Because we didn't do a seen_axes.add(axis) during the fallbacks_in_names loop, it gets added twice.

[simoncozens]

In fact, I don't need a way to trigger it, we explicitly test for the axis being added twice.

axisregistry/tests/data/OpenSans-Italic[wdth,wght]_STAT.ttx

Lines 15 to 24 in 3db2ff6

	<Axis index="2">
	<AxisTag value="ital"/>
	<AxisNameID value="260"/> <!-- Italic -->
	<AxisOrdering value="2"/>
	</Axis>
	<Axis index="3">
	<AxisTag value="ital"/>
	<AxisNameID value="260"/> <!-- Italic -->
	<AxisOrdering value="3"/>
	</Axis>