Fix KiCad 9 s-expression netlist import and export_netlist format flags

KiCad 9 defaults to s-expression netlist export, not XML. Add
_parse_kicad_sexp() parser with pinfunction/pintype metadata, update
auto-detection to distinguish (export from <export by content.

Fix export_netlist: use kicad-cli's actual format names (kicadsexpr,
kicadxml) instead of invalid 'kicad', use --format instead of -f, and
treat non-zero exit with valid output as success with warnings.

src/mckicad/tools/netlist.py

@@ -2,7 +2,8 @@
 
 Parses external netlist files into the component-pin-net graph that
 ``verify_connectivity`` and ``apply_batch`` consume.  Supports KiCad
-XML (.net) and CSV/TSV formats.
+s-expression (.net, default in KiCad 9+), KiCad XML (legacy), and
+CSV/TSV formats.
 """
 
 import csv
@@ -10,6 +11,7 @@ import io
 import json
 import logging
 import os
+import re
 from typing import Any
 import xml.etree.ElementTree as ET
 
@@ -90,6 +92,122 @@ def _parse_kicad_xml(content: str) -> dict[str, Any]:
     }
 
 
+def _parse_kicad_sexp(content: str) -> dict[str, Any]:
+    """Parse a KiCad s-expression netlist (.net file) into nets/components dicts.
+
+    This is the default export format for KiCad 9+, produced by
+    ``kicad-cli sch export netlist`` (``--format kicadsexpr``).
+
+    S-expression structure::
+
+        (export (version "E")
+          (components
+            (comp (ref "R1")
+              (value "1K")
+              (libsource (lib "Device") (part "R") (description "..."))
+              ...))
+          (nets
+            (net (code "1") (name "GND") (class "Default")
+              (node (ref "R2") (pin "1") (pinfunction "A") (pintype "passive"))
+              ...)))
+    """
+    _sexp_node = re.compile(
+        r'\(node\s+'
+        r'\(ref\s+"([^"]+)"\)\s*'
+        r'\(pin\s+"([^"]+)"\)'
+        r'(?:\s*\(pinfunction\s+"([^"]*?)"\))?'
+        r'(?:\s*\(pintype\s+"([^"]*?)"\))?'
+    )
+
+    # --- Parse components ---
+    components: dict[str, dict[str, str]] = {}
+    for comp_match in re.finditer(r'\(comp\s+\(ref\s+"([^"]+)"\)', content):
+        ref = comp_match.group(1)
+        # Extract the full (comp ...) block via bracket counting
+        start = comp_match.start()
+        depth = 0
+        end = start
+        for i in range(start, len(content)):
+            if content[i] == "(":
+                depth += 1
+            elif content[i] == ")":
+                depth -= 1
+                if depth == 0:
+                    end = i + 1
+                    break
+        comp_block = content[start:end]
+
+        # Pull value, footprint, libsource fields
+        value_m = re.search(r'\(value\s+"([^"]*?)"\)', comp_block)
+        fp_m = re.search(r'\(footprint\s+"([^"]*?)"\)', comp_block)
+        lib_m = re.search(r'\(lib\s+"([^"]*?)"\)', comp_block)
+        part_m = re.search(r'\(part\s+"([^"]*?)"\)', comp_block)
+
+        components[ref] = {
+            "value": value_m.group(1) if value_m else "",
+            "footprint": fp_m.group(1) if fp_m else "",
+            "lib": lib_m.group(1) if lib_m else "",
+            "part": part_m.group(1) if part_m else "",
+        }
+
+    # --- Parse nets ---
+    nets: dict[str, list[list[str]]] = {}
+    pin_metadata: dict[str, dict[str, dict[str, str]]] = {}  # ref -> pin -> {pinfunction, pintype}
+    connection_count = 0
+
+    # Find each (net ...) block
+    for net_start in re.finditer(r'\(net\s+\(code\s+"[^"]*"\)\s*\(name\s+"([^"]+)"\)', content):
+        net_name = net_start.group(1)
+
+        # Extract the full (net ...) block
+        start = net_start.start()
+        depth = 0
+        end = start
+        for i in range(start, len(content)):
+            if content[i] == "(":
+                depth += 1
+            elif content[i] == ")":
+                depth -= 1
+                if depth == 0:
+                    end = i + 1
+                    break
+        net_block = content[start:end]
+
+        pins: list[list[str]] = []
+        for node_m in _sexp_node.finditer(net_block):
+            ref = node_m.group(1)
+            pin = node_m.group(2)
+            pinfunction = node_m.group(3) or ""
+            pintype = node_m.group(4) or ""
+            if ref and pin:
+                pins.append([ref, pin])
+                connection_count += 1
+                # Store pin metadata for richer output
+                if pinfunction or pintype:
+                    pin_metadata.setdefault(ref, {})[pin] = {
+                        "pinfunction": pinfunction,
+                        "pintype": pintype,
+                    }
+        if pins:
+            nets[net_name] = pins
+
+    result: dict[str, Any] = {
+        "nets": nets,
+        "components": components,
+        "statistics": {
+            "net_count": len(nets),
+            "component_count": len(components),
+            "connection_count": connection_count,
+        },
+    }
+
+    # Include pin metadata when available (s-expression format is richer than XML/CSV)
+    if pin_metadata:
+        result["pin_metadata"] = pin_metadata
+
+    return result
+
+
 def _parse_csv(content: str) -> dict[str, Any]:
     """Parse a CSV/TSV netlist into nets/components dicts.
 
@@ -153,20 +271,27 @@ def _parse_csv(content: str) -> dict[str, Any]:
 def _detect_format(content: str, file_path: str) -> str:
     """Auto-detect netlist format from file extension and content."""
     ext = os.path.splitext(file_path)[1].lower()
+    stripped = content.lstrip()
 
-    # Extension-based detection
+    # Content-based detection takes priority (a .net file could be either format)
-    if ext == ".net":
+    if stripped.startswith("(export"):
+        return "kicad_sexp"
+    if stripped.startswith("<?xml") or stripped.startswith("<export"):
         return "kicad_xml"
+
+    # Extension-based fallback
+    if ext == ".net":
+        # KiCad 9+ defaults to s-expression; older versions used XML.
+        # If content detection didn't match either, try s-expression
+        # (covers cases with leading whitespace or comments).
+        if "(export" in stripped[:500]:
+            return "kicad_sexp"
+        return "kicad_sexp"  # Default for .net — KiCad 9+ is the common case
     if ext in (".csv", ".tsv"):
         return "csv"
     if ext == ".xml":
         return "kicad_xml"
 
-    # Content-based detection
-    stripped = content.lstrip()
-    if stripped.startswith("<?xml") or stripped.startswith("<export"):
-        return "kicad_xml"
-
     # Check for CSV header pattern
     first_line = stripped.split("\n", 1)[0].lower()
     if any(kw in first_line for kw in ("reference", "designator", "ref,")):
@@ -193,15 +318,19 @@ def import_netlist(
     or for generating ``apply_batch`` wiring instructions.
 
     Supported formats:
-    - ``kicad_xml`` — KiCad intermediate netlist (.net XML).  Most reliable
+    - ``kicad_sexp`` — KiCad s-expression netlist (.net), the default
-      source, exported via ``kicad-cli sch export netlist``.
+      format for KiCad 9+.  Exported via
+      ``kicad-cli sch export netlist --format kicadsexpr``.
+      Includes ``pinfunction`` and ``pintype`` metadata per pin.
+    - ``kicad_xml`` — KiCad XML netlist (legacy format, ``--format kicadxml``).
     - ``csv`` — CSV or TSV with Reference, Pin, and Net columns.  Common
       export from EDA tools (Altium, Eagle, etc.).
     - ``auto`` — detect format from file extension and content (default).
 
     Args:
         source_path: Path to the netlist file to import.
-        format: Netlist format (``auto``, ``kicad_xml``, ``csv``).
+        format: Netlist format (``auto``, ``kicad_sexp``, ``kicad_xml``,
+            ``csv``).
         output_path: Optional path to write the parsed result as JSON.
             Defaults to ``.mckicad/imported_netlist.json`` next to
             the source file.
@@ -211,6 +340,8 @@ def import_netlist(
         ``components`` (ref → metadata dict), and ``statistics``.
         The ``nets`` dict is directly compatible with
         ``verify_connectivity``'s ``expected`` parameter.
+        When format is ``kicad_sexp``, also includes ``pin_metadata``
+        with per-pin ``pinfunction`` and ``pintype``.
     """
     source_path = os.path.abspath(os.path.expanduser(source_path))
 
@@ -220,7 +351,7 @@ def import_netlist(
             "error": f"Source file not found: {source_path}",
         }
 
-    allowed_formats = ("auto", "kicad_xml", "csv")
+    allowed_formats = ("auto", "kicad_sexp", "kicad_xml", "csv")
     fmt = format.lower().strip()
     if fmt not in allowed_formats:
         return {
@@ -245,13 +376,15 @@ def import_netlist(
                 "success": False,
                 "error": (
                     "Could not auto-detect netlist format. "
-                    "Specify format='kicad_xml' or format='csv' explicitly."
+                    "Specify format='kicad_sexp', 'kicad_xml', or 'csv' explicitly."
                 ),
             }
 
     # Parse
     try:
-        if fmt == "kicad_xml":
+        if fmt == "kicad_sexp":
+            parsed = _parse_kicad_sexp(content)
+        elif fmt == "kicad_xml":
             parsed = _parse_kicad_xml(content)
         elif fmt == "csv":
             parsed = _parse_csv(content)

src/mckicad/tools/schematic_analysis.py

@@ -958,25 +958,33 @@ def get_component_pins(
 def export_netlist(
     schematic_path: str,
     output_path: str | None = None,
-    format: str = "kicad",
+    format: str = "kicadsexpr",
 ) -> dict[str, Any]:
     """Export a netlist from a KiCad schematic via kicad-cli.
 
-    Supported formats: ``kicad`` (default), ``spice``, ``cadstar``,
+    Supported formats: ``kicadsexpr`` (default, s-expression), ``kicadxml``
-    ``allegro``, ``pads``, ``orcadpcb2``.  The output file is written to
+    (legacy XML), ``spice``, ``spicemodel``, ``cadstar``, ``allegro``,
-    the ``.mckicad/`` sidecar directory by default.
+    ``pads``, ``orcadpcb2``.  The output file is written to the
+    ``.mckicad/`` sidecar directory by default.
+
+    The default ``kicadsexpr`` format can be re-imported via
+    ``import_netlist(format='kicad_sexp')`` for round-trip workflows.
 
     Args:
         schematic_path: Path to a .kicad_sch file.
         output_path: Destination file path.  Defaults to
                      ``.mckicad/netlist.<ext>`` next to the schematic.
-        format: Netlist format name.
+        format: Netlist format name as accepted by ``kicad-cli``.
 
     Returns:
         Dictionary with ``output_path`` and ``format``.
     """
     # Validate format first (cheap check, no filesystem access)
-    allowed_formats = ("kicad", "spice", "cadstar", "allegro", "pads", "orcadpcb2")
+    # Names must match kicad-cli's --format flag exactly
+    allowed_formats = (
+        "kicadsexpr", "kicadxml", "spice", "spicemodel",
+        "cadstar", "allegro", "pads", "orcadpcb2",
+    )
     fmt = format.lower().strip()
     if fmt not in allowed_formats:
         return {
@@ -997,8 +1005,10 @@ def export_netlist(
 
     # Determine file extension based on format
     ext_map = {
-        "kicad": ".net",
+        "kicadsexpr": ".net",
+        "kicadxml": ".net",
         "spice": ".cir",
+        "spicemodel": ".cir",
         "cadstar": ".frp",
         "allegro": ".net",
         "pads": ".asc",
@@ -1015,7 +1025,7 @@ def export_netlist(
     try:
         import subprocess
 
-        cmd = [cli_path, "sch", "export", "netlist", "-f", fmt, "-o", output_path, schematic_path]
+        cmd = [cli_path, "sch", "export", "netlist", "--format", fmt, "-o", output_path, schematic_path]
 
         logger.info("Exporting netlist: %s", " ".join(cmd))
 
@@ -1027,10 +1037,21 @@ def export_netlist(
             check=False,
         )
 
+        warnings: str | None = None
         if result.returncode != 0:
-            stderr = result.stderr.strip() if result.stderr else "Netlist export failed"
+            stderr = result.stderr.strip() if result.stderr else ""
-            logger.error("Netlist export failed (rc=%d): %s", result.returncode, stderr)
+            # kicad-cli may exit non-zero for warnings (missing fonts, library
-            return {"success": False, "error": f"kicad-cli netlist export failed: {stderr}"}
+            # warnings) yet still produce a valid output file.  Only fail if
+            # the output wasn't created.
+            if os.path.isfile(output_path) and os.path.getsize(output_path) > 0:
+                warnings = stderr or f"kicad-cli exited with code {result.returncode}"
+                logger.warning("Netlist export warnings (rc=%d): %s", result.returncode, warnings)
+            else:
+                logger.error("Netlist export failed (rc=%d): %s", result.returncode, stderr)
+                return {
+                    "success": False,
+                    "error": f"kicad-cli netlist export failed: {stderr or 'unknown error'}",
+                }
 
         if not os.path.isfile(output_path):
             return {"success": False, "error": "Netlist output file was not created"}
@@ -1038,13 +1059,16 @@ def export_netlist(
         file_size = os.path.getsize(output_path)
         logger.info("Netlist exported: %s (%d bytes, format=%s)", output_path, file_size, fmt)
 
-        return {
+        out: dict[str, Any] = {
             "success": True,
             "output_path": output_path,
             "format": fmt,
             "file_size": file_size,
             "schematic_path": schematic_path,
         }
+        if warnings:
+            out["warnings"] = warnings
+        return out
 
     except Exception as exc:
         logger.error("Netlist export failed: %s", exc, exc_info=True)

tests/test_netlist.py

@@ -131,6 +131,152 @@ class TestParseKicadXml:
             assert len(pin_pair) == 2
 
 
+@pytest.mark.unit
+class TestParseKicadSexp:
+    """Tests for KiCad s-expression netlist parsing (KiCad 9+ default)."""
+
+    def test_parse_sexp_netlist(self, tmp_output_dir):
+        """Parse a KiCad 9 s-expression netlist with components, nets, and pin metadata."""
+        from mckicad.tools.netlist import import_netlist
+
+        sexp_content = textwrap.dedent("""\
+            (export (version "E")
+              (design
+                (source "/path/to/project.kicad_sch")
+                (tool "Eeschema 9.0.7"))
+              (components
+                (comp (ref "R1")
+                  (value "10k")
+                  (footprint "Resistor_SMD:R_0402")
+                  (libsource (lib "Device") (part "R") (description "Resistor")))
+                (comp (ref "C1")
+                  (value "100nF")
+                  (footprint "Capacitor_SMD:C_0402")
+                  (libsource (lib "Device") (part "C") (description "Capacitor")))
+                (comp (ref "U1")
+                  (value "ESP32")
+                  (libsource (lib "MCU") (part "ESP32") (description "MCU"))))
+              (nets
+                (net (code "1") (name "GND") (class "Default")
+                  (node (ref "R1") (pin "2") (pinfunction "~") (pintype "passive"))
+                  (node (ref "C1") (pin "2") (pinfunction "~") (pintype "passive")))
+                (net (code "2") (name "VCC") (class "Power")
+                  (node (ref "R1") (pin "1") (pinfunction "~") (pintype "passive"))
+                  (node (ref "U1") (pin "1") (pinfunction "VDD") (pintype "power_in")))
+                (net (code "3") (name "/SPI/MOSI") (class "Default")
+                  (node (ref "U1") (pin "5") (pinfunction "MOSI") (pintype "bidirectional"))
+                  (node (ref "C1") (pin "1") (pinfunction "~") (pintype "passive")))))
+        """)
+        path = os.path.join(tmp_output_dir, "test.net")
+        with open(path, "w") as f:
+            f.write(sexp_content)
+
+        result = import_netlist(source_path=path)
+
+        assert result["success"] is True
+        assert result["format_detected"] == "kicad_sexp"
+        assert result["statistics"]["net_count"] == 3
+        assert result["statistics"]["component_count"] == 3
+        assert result["statistics"]["connection_count"] == 6
+
+        # Check nets structure
+        nets = result["nets"]
+        assert "GND" in nets
+        assert ["R1", "2"] in nets["GND"]
+        assert ["C1", "2"] in nets["GND"]
+        assert "VCC" in nets
+        assert "/SPI/MOSI" in nets  # hierarchical net name preserved
+
+        # Check components
+        assert "R1" in result["components"]
+        assert result["components"]["R1"]["value"] == "10k"
+        assert result["components"]["R1"]["lib"] == "Device"
+        assert result["components"]["U1"]["part"] == "ESP32"
+
+    def test_sexp_pin_metadata(self, tmp_output_dir):
+        """S-expression format includes pinfunction and pintype metadata."""
+        from mckicad.tools.netlist import import_netlist
+
+        sexp_content = textwrap.dedent("""\
+            (export (version "E")
+              (components
+                (comp (ref "U1")
+                  (value "IC")
+                  (libsource (lib "MCU") (part "IC") (description "IC"))))
+              (nets
+                (net (code "1") (name "SDA") (class "Default")
+                  (node (ref "U1") (pin "3") (pinfunction "SDA") (pintype "bidirectional"))
+                  (node (ref "R1") (pin "1") (pinfunction "~") (pintype "passive")))))
+        """)
+        path = os.path.join(tmp_output_dir, "meta.net")
+        with open(path, "w") as f:
+            f.write(sexp_content)
+
+        result = import_netlist(source_path=path)
+        assert result["success"] is True
+        assert "pin_metadata" in result
+
+        # U1 pin 3 should have pinfunction and pintype
+        assert "U1" in result["pin_metadata"]
+        assert "3" in result["pin_metadata"]["U1"]
+        assert result["pin_metadata"]["U1"]["3"]["pinfunction"] == "SDA"
+        assert result["pin_metadata"]["U1"]["3"]["pintype"] == "bidirectional"
+
+    def test_auto_detects_sexp_format(self, tmp_output_dir):
+        """Auto-detection picks kicad_sexp for s-expression .net files."""
+        from mckicad.tools.netlist import import_netlist
+
+        sexp = '(export (version "E")(components)(nets))'
+        path = os.path.join(tmp_output_dir, "test.net")
+        with open(path, "w") as f:
+            f.write(sexp)
+
+        result = import_netlist(source_path=path, format="auto")
+        assert result["success"] is True
+        assert result["format_detected"] == "kicad_sexp"
+
+    def test_sexp_verify_connectivity_compatible(self, tmp_output_dir):
+        """The nets dict from sexp parsing matches verify_connectivity shape."""
+        from mckicad.tools.netlist import import_netlist
+
+        sexp = textwrap.dedent("""\
+            (export (version "E")
+              (components
+                (comp (ref "U1") (value "IC") (libsource (lib "x") (part "y") (description "z"))))
+              (nets
+                (net (code "1") (name "NET1") (class "Default")
+                  (node (ref "U1") (pin "1") (pinfunction "A") (pintype "output"))
+                  (node (ref "R1") (pin "2") (pinfunction "~") (pintype "passive")))))
+        """)
+        path = os.path.join(tmp_output_dir, "compat.net")
+        with open(path, "w") as f:
+            f.write(sexp)
+
+        result = import_netlist(source_path=path)
+        assert result["success"] is True
+
+        nets = result["nets"]
+        assert "NET1" in nets
+        assert isinstance(nets["NET1"], list)
+        for pin_pair in nets["NET1"]:
+            assert isinstance(pin_pair, list)
+            assert len(pin_pair) == 2
+
+    def test_sexp_empty_sections(self, tmp_output_dir):
+        """Handle s-expression netlist with empty components and nets sections."""
+        from mckicad.tools.netlist import import_netlist
+
+        sexp = '(export (version "E")(components)(nets))'
+        path = os.path.join(tmp_output_dir, "empty_sections.net")
+        with open(path, "w") as f:
+            f.write(sexp)
+
+        result = import_netlist(source_path=path)
+        assert result["success"] is True
+        assert result["statistics"]["net_count"] == 0
+        assert result["statistics"]["component_count"] == 0
+
+
 @pytest.mark.unit
 class TestParseCsv:
     """Tests for CSV/TSV netlist parsing."""