Hole spacing to a fixed via measured from where it is, with its own drill

A fixed via sits anywhere, not on a cell centre, and may have a bigger
drill than the router's via; checking hole spacing between cell centres
with one drill let the flight controller's routed 0.2 mm via come 0.19
mm from a hand-placed 0.25 mm one. The board now carries each fixed
via's drill (from KiCad's padstack name), and cells are checked against
fixed vias exactly.

tests/route/test_via_spacing.py

@@ -56,7 +56,7 @@ def test_connections_sharing_a_plane_via_write_it_once():
     assert len(set(vias)) == len(vias), "a shared via written more than once"
 
 
-def _router(dsn_text):
+def _router(dsn_text, via_drill_um=300):
     from freeroute.board import build_board
     from freeroute.route.grid_router import GridRouter
     from freeroute.route.pipeline import _rule_clearance_dsn, _rule_width_dsn
@@ -66,7 +66,7 @@ def _router(dsn_text):
     return GridRouter(
         build_board(dsn), trace_width=round(_rule_width_dsn(dsn) * s),
         clearance=round(_rule_clearance_dsn(dsn) * s), resolution=2, orthogonal=True,
-        via_drill=300 * s, hole_to_hole=250 * s,
+        via_drill=via_drill_um * s, hole_to_hole=250 * s,
     ), s
 
 
@@ -98,3 +98,29 @@ def test_a_via_in_a_pad_keeps_hole_spacing_from_a_fixed_via():
     router, s = _router(text)
     assert not router._hole_clear_at(IntPoint(3400 * s, -3000 * s))  # 0.4 mm < 0.55 mm
     assert router._hole_clear_at(IntPoint(3600 * s, -3000 * s))
+
+
+def test_hole_spacing_from_a_fixed_via_is_measured_from_where_it_really_is():
+    # a fixed via off the grid with its own 0.25 mm drill, and the router's
+    # via a smaller 0.2 mm one (the flight controller's case): a new via needs
+    # its centre 0.1 + 0.125 + 0.25 = 0.475 mm away, measured exactly, where
+    # one rule for all vias gave 0.2 + 0.25 = 0.45 from the cell centres
+    text = _THT.replace("(network (net SIG (pins J1-1))))",
+                        "(network (net SIG (pins J1-1)) (net GND))\n"
+                        "  (wiring (via \"Via[0-1]_500:250_um\"  3030 -3030 (net GND) (type route))))")
+    text = text.replace(
+        '(attach off)))\n  (network',
+        '(attach off))\n    (padstack "Via[0-1]_500:250_um" (shape (circle F.Cu 500)) '
+        '(shape (circle B.Cu 500)) (attach off)))\n  (network',
+    )
+    router, s = _router(text, via_drill_um=200)
+    via = next(v for v in router.board.get_items() if getattr(v, "drill", 0))
+    assert via.drill == 250 * s
+    loc = via.location
+    for cell in [(x, y) for x in range(router.cols) for y in range(router.rows)]:
+        c = router._cell_center(cell)
+        d = math.hypot(c.x - loc.x, c.y - loc.y)
+        if router.step * 1.5 < d < 470 * s:
+            assert not router._holes_clear(cell, 1), f"{d / s:.0f} um from the fixed via"
+        elif 560 * s < d < 700 * s and cell not in router._tht_block:
+            assert router._holes_clear(cell, 1)