Implement Specctra SES session-file writer

Ports the write path of io/specctra/SesWriter.java to emit a valid
session from a parsed DsnBoard plus a RoutingResult. Each _write_*
function mirrors a write* method upstream:

- session scope with base_design, placement (resolution + components
  echoed from the DSN), an empty was_is, and routes
- routes carries resolution, a reduced parser scope, library_out with
  the via padstacks, and network_out
- network_out emits (net (wire (path layer width x1 y1 ...)) (via
  padstack x y)) for each routed net; integer coordinates via round-
  half-up to match Java Math.round

write_ses(board) with no result produces a valid no-op session,
proving the DSN-in / SES-out round trip. Only routes > network_out is
required by SesReader and kicad-cli; the rest is echoed for a
well-formed file.

18 tests: indent/quoting rules, no-op session structure, placement and
library_out echo, routed wire/via serialization, integer rounding, and
round-trips re-parsed through the project's own DSN tokenizer/sexp
(64 tests total across the suite, all green; ruff clean).
This commit is contained in:
Ryan Malloy 2026-07-11 16:34:19 -06:00
parent 650c732a30
commit 12b0a231f0
4 changed files with 525 additions and 0 deletions

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"""Specctra SES (session) writing for freeroute.
Public API::
from freeroute.dsn import parse_dsn
from freeroute.ses import write_ses, RoutingResult, RoutedWire, RoutedVia
board = parse_dsn(dsn_text)
ses_text = write_ses(board) # valid no-op session
# ... or with routed geometry:
result = RoutingResult()
result.add_wire("NET_A", RoutedWire("Top", 200, [0, 0, 1000, 0]))
ses_text = write_ses(board, result)
"""
from __future__ import annotations
from .indent import Identifier, IndentWriter
from .model import RoutedNet, RoutedVia, RoutedWire, RoutingResult
from .writer import write_ses, write_ses_file
__all__ = [
"write_ses",
"write_ses_file",
"RoutingResult",
"RoutedNet",
"RoutedWire",
"RoutedVia",
"Identifier",
"IndentWriter",
]

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src/freeroute/ses/writer.py Normal file
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"""Specctra SES session-file writer.
Ports the write path of FreeRouting's ``io/specctra/SesWriter.java`` to operate
on this project's parsed :class:`~freeroute.dsn.model.DsnBoard` plus an
in-memory :class:`~freeroute.ses.model.RoutingResult`. The emitted structure is::
(session <name>
(base_design <name>)
(placement
(resolution <unit> <n>)
(component <image> (place <ref> x y front|back rot) ...))
(was_is)
(routes
(resolution <unit> <n>)
(parser ...)
(library_out (padstack <name> (shape (...)) (attach off)))
(network_out
(net <name>
(wire (path <layer> <width> x1 y1 ...))
(via <padstack> x y)))))
FreeRouting's ``SesReader`` (and, in practice, ``kicad-cli pcb import
specctra-ses``) only *require* the ``routes > network_out > net > wire/via``
subtree plus the ``routes`` ``resolution`` for coordinate scaling; the other
scopes are echoed for a well-formed file and skipped on read. Each ``_write_*``
here corresponds to a ``write*`` method in ``SesWriter``.
"""
from __future__ import annotations
import math
from freeroute.dsn.model import DsnBoard
from freeroute.dsn.shapes import Circle, Path, Polygon, Rectangle, Shape
from .indent import Identifier, IndentWriter
from .model import RoutedNet, RoutedVia, RoutedWire, RoutingResult
__all__ = ["write_ses", "write_ses_file"]
def _iround(value: float) -> int:
"""Round half up, matching Java's ``(int) Math.round(x)``."""
return math.floor(value + 0.5)
def write_ses(
board: DsnBoard,
result: RoutingResult | None = None,
design_name: str | None = None,
) -> str:
"""Serialize ``board`` + ``result`` to a Specctra SES string.
``result`` may be ``None`` (or empty) for a valid no-op session that carries
no wires or vias enough to prove the DSN-in / SES-out round trip.
``design_name`` defaults to the board's pcb name; the session name is the
design name with a ``.dsn`` suffix rewritten to ``.ses``.
"""
if result is None:
result = RoutingResult()
design = design_name if design_name is not None else board.name
session_name = design.replace(".dsn", ".ses")
ident = Identifier(string_quote=board.parser.string_quote)
out = IndentWriter()
_write_session_scope(out, ident, board, result, session_name, design)
text = out.getvalue()
if not text.endswith("\n"):
text += "\n"
return text
def write_ses_file(
board: DsnBoard,
path: str,
result: RoutingResult | None = None,
design_name: str | None = None,
) -> None:
"""Write the SES output to ``path`` (UTF-8)."""
with open(path, "w", encoding="utf-8") as fh:
fh.write(write_ses(board, result, design_name))
# --- scope writers (mirror SesWriter.write*) ---------------------------------
def _write_session_scope(
out: IndentWriter,
ident: Identifier,
board: DsnBoard,
result: RoutingResult,
session_name: str,
design_name: str,
) -> None:
out.start_scope(new_line=False)
out.write("session ")
ident.write(session_name, out)
out.new_line()
out.write("(base_design ")
ident.write(design_name, out)
out.write(")")
_write_placement(out, ident, board)
_write_was_is(out)
_write_routes(out, ident, board, result)
out.end_scope()
def _write_resolution(out: IndentWriter, board: DsnBoard) -> None:
out.new_line()
out.write(f"(resolution {board.resolution.unit} {board.resolution.value})")
def _write_placement(out: IndentWriter, ident: Identifier, board: DsnBoard) -> None:
out.start_scope()
out.write("placement")
_write_resolution(out, board)
for placement in board.placements:
placed = [p for p in placement.places if p.x is not None and p.y is not None]
if not placed:
continue
out.start_scope()
out.write("component ")
ident.write(placement.lib_name, out)
for place in placed:
out.new_line()
out.write("(place ")
ident.write(place.name, out)
out.write(f" {_iround(place.x)} {_iround(place.y)}")
out.write(" front " if place.is_front else " back ")
out.write(str(_iround(place.rotation)))
if place.position_fixed:
out.new_line()
out.write(" (lock_type position)")
out.write(")")
out.end_scope()
out.end_scope()
def _write_was_is(out: IndentWriter) -> None:
# No pin/gate swaps are modelled yet, so this scope is intentionally empty.
out.start_scope()
out.write("was_is")
out.end_scope()
def _write_routes(
out: IndentWriter, ident: Identifier, board: DsnBoard, result: RoutingResult
) -> None:
out.start_scope()
out.write("routes ")
_write_resolution(out, board)
_write_parser(out, ident, board)
_write_library_out(out, ident, board)
_write_network_out(out, ident, result)
out.end_scope()
def _write_parser(out: IndentWriter, ident: Identifier, board: DsnBoard) -> None:
# Reduced parser scope (SesWriter passes p_reduced=true): omit string_quote /
# space_in_quoted_tokens / generated_by_freerouting; echo host_cad/version.
out.start_scope()
out.write("parser")
if board.parser.host_cad is not None:
out.new_line()
out.write("(host_cad ")
ident.write(board.parser.host_cad, out)
out.write(")")
if board.parser.host_version is not None:
out.new_line()
out.write("(host_version ")
ident.write(board.parser.host_version, out)
out.write(")")
out.end_scope()
def _write_library_out(out: IndentWriter, ident: Identifier, board: DsnBoard) -> None:
out.start_scope()
out.write("library_out ")
for name in board.via_padstack_names:
padstack = board.padstack(name)
if padstack is not None:
_write_padstack(out, ident, padstack)
out.end_scope()
def _write_padstack(out: IndentWriter, ident: Identifier, padstack) -> None:
out.start_scope()
out.write("padstack ")
ident.write(padstack.name, out)
for shape in padstack.shapes:
out.start_scope()
out.write("shape")
_write_shape_int(out, ident, shape)
out.end_scope()
if not padstack.attach_allowed:
out.new_line()
out.write("(attach off)")
out.end_scope()
def _write_shape_int(out: IndentWriter, ident: Identifier, shape: Shape) -> None:
"""Write a padstack shape with integer coordinates (mirrors write_scope_int)."""
out.start_scope()
if isinstance(shape, Rectangle):
out.write("rect ")
ident.write(shape.layer, out)
for c in shape.coords[:4]:
out.write(f" {_iround(c)}")
elif isinstance(shape, Circle):
out.write("circle ")
ident.write(shape.layer, out)
out.write(f" {_iround(shape.diameter)}")
if shape.center_x or shape.center_y:
out.write(f" {_iround(shape.center_x)} {_iround(shape.center_y)}")
elif isinstance(shape, Polygon):
out.write("polygon ")
ident.write(shape.layer, out)
out.write(f" {_iround(shape.aperture_width)}")
for c in shape.coords:
out.write(f" {_iround(c)}")
elif isinstance(shape, Path):
out.write("path ")
ident.write(shape.layer, out)
out.write(f" {_iround(shape.width)}")
for c in shape.coords:
out.write(f" {_iround(c)}")
else: # pragma: no cover - defensive: unknown shape type
out.write("rect ")
ident.write(shape.layer, out)
out.end_scope()
def _write_network_out(out: IndentWriter, ident: Identifier, result: RoutingResult) -> None:
out.start_scope()
out.write("network_out ")
for net in result.routed_nets():
_write_net(out, ident, net)
out.end_scope()
def _write_net(out: IndentWriter, ident: Identifier, net: RoutedNet) -> None:
out.start_scope()
out.write("net ")
ident.write(net.name, out)
for wire in net.wires:
_write_wire(out, ident, wire)
for via in net.vias:
_write_via(out, ident, via)
out.end_scope()
def _write_wire(out: IndentWriter, ident: Identifier, wire: RoutedWire) -> None:
out.start_scope()
out.write("wire")
_write_path(out, ident, wire.layer, wire.width, wire.coords)
if wire.fixed:
out.new_line()
out.write("(type fix)")
out.end_scope()
def _write_path(
out: IndentWriter,
ident: Identifier,
layer: str,
width: float,
coords: list[float],
) -> None:
out.start_scope()
out.write("path ")
ident.write(layer, out)
out.write(" ")
out.write(str(_iround(width)))
corner_count = len(coords) // 2
for i in range(corner_count):
out.new_line()
out.write(str(_iround(coords[2 * i])))
out.write(" ")
out.write(str(_iround(coords[2 * i + 1])))
out.end_scope()
def _write_via(out: IndentWriter, ident: Identifier, via: RoutedVia) -> None:
out.start_scope()
out.write("via ")
ident.write(via.padstack, out)
out.write(f" {_iround(via.x)} {_iround(via.y)}")
if via.fixed:
out.new_line()
out.write("(type fix)")
out.end_scope()

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tests/ses/test_indent.py Normal file
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"""Tests for the SES indent writer and identifier quoting."""
from __future__ import annotations
from freeroute.ses.indent import Identifier, IndentWriter
def test_nested_scopes_indent_by_two_spaces():
out = IndentWriter()
out.start_scope(new_line=False)
out.write("session x")
out.start_scope()
out.write("routes")
out.end_scope()
out.end_scope()
assert out.getvalue() == "(session x\n (routes\n )\n)"
def test_new_line_uses_current_indent():
out = IndentWriter()
out.start_scope(new_line=False)
out.write("a")
out.new_line()
out.write("(b)")
out.end_scope()
assert out.getvalue() == "(a\n (b)\n)"
def test_plain_name_not_quoted():
ident = Identifier()
assert ident.format("Top") == "Top"
assert ident.format("U1") == "U1"
assert ident.format("F.Cu") == "F.Cu" # '.' is not reserved
def test_reserved_chars_force_quotes():
ident = Identifier()
assert ident.format("NET_A") == '"NET_A"' # underscore reserved
assert ident.format("a-b") == '"a-b"' # hyphen reserved
assert ident.format("with space") == '"with space"'
assert ident.format("Via[0-1]_600:300_um") == '"Via[0-1]_600:300_um"'
def test_leading_digit_forces_quotes():
ident = Identifier()
assert ident.format("2layer") == '"2layer"'
assert ident.format("-3x") == '"-3x"'
def test_non_ascii_forces_quotes():
ident = Identifier()
assert ident.format("Паяльная") == '"Паяльная"'
def test_surrounding_quotes_stripped_before_reprocessing():
ident = Identifier()
# already-quoted plain name comes back unquoted
assert ident.format('"Top"') == "Top"
def test_embedded_quote_removed():
ident = Identifier()
assert ident.format('a"b') == "ab"

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tests/ses/test_writer.py Normal file
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"""End-to-end tests for the SES writer.
Where possible these re-parse the emitted SES with the project's own tokenizer /
S-expression parser (:mod:`freeroute.dsn.sexp`) and assert structural
invariants, mirroring what FreeRouting's ``SesReader`` and ``kicad-cli pcb
import specctra-ses`` walk: ``session > routes > network_out > net >
wire(path)/via``.
"""
from __future__ import annotations
from pathlib import Path
import pytest
from freeroute.dsn import parse_dsn
from freeroute.dsn.sexp import SExp, parse
from freeroute.ses import RoutedVia, RoutedWire, RoutingResult, write_ses
FIXTURES = Path(__file__).parent.parent / "dsn" / "fixtures"
def load_board(name: str):
return parse_dsn((FIXTURES / name).read_text())
@pytest.fixture
def board():
return load_board("smd_demo.dsn")
def child(node: SExp, head: str) -> SExp:
found = node.child(head)
assert found is not None, f"missing ({head} ...) scope"
return found
# --- no-op session -----------------------------------------------------------
def test_noop_session_is_parseable_and_well_formed(board):
text = write_ses(board)
top = parse(text) # must be a single balanced S-expression
assert top.head == "session"
# session name argument: design name with .dsn -> .ses
assert top.values()[0].text == "smd-demo.ses"
def test_noop_session_has_required_scopes(board):
top = parse(write_ses(board))
assert child(top, "base_design").values()[0].text == "smd-demo.dsn"
assert top.child("placement") is not None
assert top.child("was_is") is not None
routes = child(top, "routes")
# routes must carry a resolution (KiCad scales session coords by it)
assert child(routes, "resolution").values()[0].text == "um"
assert routes.child("network_out") is not None
def test_noop_network_out_is_empty(board):
routes = child(parse(write_ses(board)), "routes")
network = child(routes, "network_out")
assert network.children("net") == []
def test_placement_echoes_components(board):
placement = child(parse(write_ses(board)), "placement")
comps = placement.children("component")
names = [c.values()[0].text for c in comps]
assert names == ["MiniQFN-6", "0603"]
# U1 place: coords rounded to int, side, rotation
u1 = comps[0].child("place")
vals = [v.text for v in u1.values()]
assert vals == ["U1", "75000", "-45000", "front", "90"]
def test_library_out_echoes_via_padstack(board):
routes = child(parse(write_ses(board)), "routes")
lib = child(routes, "library_out")
pads = lib.children("padstack")
assert [p.values()[0].text for p in pads] == ["Via[0-1]_600:300_um"]
# --- routed geometry ---------------------------------------------------------
@pytest.fixture
def routed():
result = RoutingResult()
result.add_wire("NET_A", RoutedWire(layer="Top", width=200, coords=[0, 0, 1000, -500]))
result.add_via("NET_A", RoutedVia(padstack="Via[0-1]_600:300_um", x=1000, y=-500))
result.add_wire("NET_B", RoutedWire(layer="Bottom", width=250, coords=[10, 10, 20, 20]))
return result
def test_routed_network_out_has_nets(board, routed):
routes = child(parse(write_ses(board, routed)), "routes")
network = child(routes, "network_out")
nets = network.children("net")
assert [n.values()[0].text for n in nets] == ["NET_A", "NET_B"]
def test_routed_wire_path_and_via(board, routed):
routes = child(parse(write_ses(board, routed)), "routes")
net_a = child(routes, "network_out").children("net")[0]
wire = child(net_a, "wire")
path = child(wire, "path")
pvals = [v.text for v in path.values()]
# (path <layer> <width> x1 y1 x2 y2)
assert pvals == ["Top", "200", "0", "0", "1000", "-500"]
via = child(net_a, "via")
vvals = [v.text for v in via.values()]
assert vvals == ["Via[0-1]_600:300_um", "1000", "-500"]
def test_coordinates_are_integers(board):
result = RoutingResult()
result.add_wire("NET_A", RoutedWire(layer="Top", width=199.6, coords=[0.4, -0.4, 2.5, 3.5]))
routes = child(parse(write_ses(board, result)), "routes")
path = child(child(child(routes, "network_out").children("net")[0], "wire"), "path")
pvals = [v.text for v in path.values()]
# width 199.6 -> 200; coords 0.4->0, -0.4->0, 2.5->3, 3.5->4 (round half up)
assert pvals == ["Top", "200", "0", "0", "3", "4"]
assert all("." not in v for v in pvals)
def test_empty_result_matches_noop(board):
assert write_ses(board, RoutingResult()) == write_ses(board)
def test_round_trip_from_empty_board_fixture():
board = load_board("empty_board.dsn")
top = parse(write_ses(board))
assert top.head == "session"
assert top.values()[0].text == "freeroute-empty.ses"
# empty board has no placements -> placement scope has no components
assert child(top, "placement").children("component") == []