- Analyzer: new `W0108` warning when an array's byte size exceeds
256. The codegen lowers `arr[i]` to `LDA base,X` and the 6502's
X register is 8 bits, so elements past byte 255 are unreachable.
The old debug bounds check silently skipped arrays in that range;
it now clamps the compare to 255 and the analyzer diagnoses the
declaration up front.
- UxROM `__bank_select`: the routine previously wrote the bank
number to a fixed `$FFF0`, which works on emulators that don't
simulate bus conflicts (jsnes, Mesen permissive) but is broken
on real hardware because a single ROM byte can't match every
possible bank number. Fixed by `TAX; STA __bank_select_table,X`
— the store lands at `table + bank_num`, whose ROM byte is
exactly `bank_num`, so CPU bus = A = ROM = no conflict. New
`LabelAbsoluteX` addressing-mode variant in the assembler
resolves the table's base address through the existing fixup
pass. The two existing UxROM example ROMs shift a few bytes
but their goldens still match (jsnes is bus-conflict-permissive).
- Source maps: new `source_map_survives_aggressive_peephole_folding`
regression test. The reviewer was worried peephole could drop
`__src_<N>` labels and silently leave stale source-map entries.
Peephole actually treats labels as block boundaries and never
deletes them — the test pins that down by compiling a program
tailored to trip every peephole fold and asserting every
codegen-recorded source marker survives into the final linker
label table.
- Frame-overrun counter: new `debug_frame_overrun_counter_reads_back_from_user_code`
end-to-end test that proves the contract works: NMI emits
`INC $07FF`, user `peek(0x07FF)` lowers to `LDA $07FF`, and the
RAM allocator doesn't hand out `$07FF` to a user variable.
https://claude.ai/code/session_01MaNVcDmK9gsspRkdxowQAM
The compiler is deterministic: rebuilding any example produces
a byte-identical ROM, verified across all 22 examples and all
four mappers (NROM, MMC1, UxROM, MMC3). That means the .nes
files are reproducible artefacts and can live next to their
sources without drift.
Benefits:
- Users can clone the repo and open any example in an emulator
without installing a Rust toolchain or running the compiler.
- The emulator harness can trust examples/*.nes directly, so its
CI job no longer needs a compiler build or a "compile all
examples" loop — it just boots jsnes against the committed
ROMs and diffs each against its golden.
- ROM diffs in PRs are now meaningful: "this compiler change
flipped 17 bytes in hello_sprite.nes" is visible review
signal, not hidden behind the emulator golden.
Guard rails so the ROMs don't drift from their sources:
- .gitignore no longer excludes *.nes.
- The `examples` CI job rebuilds every .ne into /tmp and fails
loudly (with a GitHub error annotation pointing at the exact
cargo command to rerun) if any committed ROM differs.
- scripts/pre-commit does the same check locally.
- CLAUDE.md now states that editing a .ne file requires
rebuilding its .nes in the same commit, so future agents
won't miss the invariant.
Total footprint: 22 ROMs, 624 KB (avg 28 KB each — most are
NROM 24 KB; two banked examples are larger).
https://claude.ai/code/session_01BcCcHi6FUmTh8jC7UgkA3A
