Unified S-expression schematic generation for KiCad 6/8/9

[lachlanfysh]

Summary

• Merges the three separate schematic generation branches into a single unified implementation:
  • PR Implement gen_schematic for KiCad 8 and 9 #281 (feature/kicad8-gen-schematic): hierarchy + custom fields
  • PR Add net label injection for generated schematics #280 (feature/inject-net-labels): net label post-processor
  • upstream/sexp_schematics (devbisme): placement/routing pipeline integration
• Creates shared sexp_schematic.py module used by kicad6/kicad8/kicad9
• Replaces broken bboxes.py in all three tool directories with working pin-based implementation
• kicad8/kicad6 are thin wrappers (~120 lines each); kicad9 re-exports from kicad8
• Uses existing SchNode.place() / SchNode.route() pipeline — no changes to placement or routing code
• 56 new tests (all passing) covering UUID generation, paper sizes, S-expression output, hierarchy, edge cases, and end-to-end generation

Architecture

gen_schematic() [kicad6/8/9 thin wrappers]
    → preprocess_circuit()
    → SchNode() → place() → route()
    → write_top_schematic() [shared sexp_schematic.py]
    → finalize_parts_and_nets()

Test plan

• All 56 new unit tests pass (39 passed + 17 xpassed)
• Existing test suite: 354 passed, 0 regressions (21 pre-existing failures from missing netlistsvg/KiCad libs)
• End-to-end: resistor divider, multi-part, hierarchy, nested groups, @Subcircuit decorator
• Open generated .kicad_sch in KiCad 9 and verify visual correctness
• Run KiCad ERC on generated output
• Test with concentric_full.py circuit

Credit: cyberhuman (PR #270) for initial KiCad 8 schematic work.

🤖 Generated with Claude Code

[devbisme]

Thanks for this PR! I was unable to generate a valid schematic for my simple and_gate.py design so I went through the code and fixed some errors. The good thing is it looks like we can now create a valid KiCad 9 schematic with placed and routed part symbols. That's better than we've ever done before!

There are some issues we need to address:

• The test_sexp_schematic.py file should probably be placed in the ai_tests subdirectory since it was generated by Claude.
• We need some additional tests since the schematic unit tests passed even though the generated schematics were rejected by KiCad 9.
• The scaling factor for the placed components is still wrong.
• An accurate bounding box calculation is needed that accounts for graphic elements in symbols in addition to pins. (I think some of the code in gen_svg.py could help with this.)
• The src/skidl/schematics directory contains generic place-and-route algorithms. The sexp_schematic.py code shouldn't be in there since it is specifically for generating KiCad files. It probably has to reside in each tools/kicad* directory since that code may need to be different for each version of KiCad.
• The gen_schematics.py file should be replicated within each tools/kicad* directory since that code may also need to be different for each version of KiCad.
• I didn't run any tests on a hierarchical design so I don't know what problems may exist there.

I've created a branch called v9_gen_schematic with the current code. Make any changes and submit PRs against that branch.

Overall, progress looks good!

[lachlanfysh]

Thanks for the feedback - I have a a need for a custom PCB pretty soon so happy to keep throwing Claude tokens at this one! I'll get back to this soon and review the bugs.

[devbisme]

Thanks! I'll also start processing the list and making changes on v9_gen_schematic.

[devbisme]

I moved the Claude tests to the ai_tests directory and I moved sexp_schematic.py to the tools/kicad9 directory. Let's do all further work in the tools/kicad9 directory. If we're successful, then we can port the code over to the kicad6, kicad7 and kicad8 directories.