Modern C++ smoke probes (Phase 2.7)

Five small C++17 probes that exercise the language features most likely to interact poorly with the W65816 backend's i32 / i16 / pointer-cast codegen. Each probe builds through the buildGno.sh recipe (clang++ -O2 + crt0Gno + libcGno + libcxxabi + ExpressLoad OMF) and runs under real GNO/ME inside MAME. Success is verified by polling bank-2 memory for the per-probe sentinel 0x0099 plus a small set of computed-value anchors that pin down which surface area was exercised.

Why these five

Each was picked from docs/GAP_CLOSURE_PLAN.md Phase 2.7 to maximise the chance of catching an i32-codegen regression early:

Probe	Exercises
`rangeFor`	range-based for over `etl::array`
`genericLambda`	C++14 generic lambda + i32 capture-by-reference
`variadicTpl`	variadic template + initializer-list pack expand
`structBind`	C++17 structured bindings (aggregate + tuple proto)
`foldExpr`	C++17 left/right/binary fold expressions

The genericLambda probe is the highest-value one: the i32-by-reference capture path is where most recent codegen work has lived, so it's most likely to regress.

Build

bash tests/cxxSmoke/build.sh rangeFor       # build one probe
bash tests/cxxSmoke/runCxxSmoke.sh          # build + run all five under MAME
bash tests/cxxSmoke/runCxxSmoke.sh foldExpr # build + run one

Each MAME run takes roughly 3 minutes (GNO boot + login + shell + program launch + marker poll), so the full sweep is ~15 minutes.

What passes today (2026-06-01)

All five probes pass. No XFAILs.

Probe	Build	Run under GNO	Notes
`rangeFor`	OK	OK	sum=15 via etl::array iterator
`genericLambda`	OK	OK	i32 acc = 0x12445 (capture by &)
`variadicTpl`	OK	OK	sum 0x10+0x20+0x30+0x18 = 0x78
`structBind`	OK	OK	aggregate + tuple-protocol both
`foldExpr`	OK	OK	unary L/R + binary `,` folds

Marker contract

Each probe writes a small set of u16 values to bank 2 (the same region runInGno.sh polls). The last write is always the success sentinel 0x0099; earlier writes are the computed values that anchor the check to the right C++ surface. See the per-probe .cpp headers for the exact marker layout.

runInGno.sh --check 0x025002=0099 (etc.) is the verification gate. For headless-CI use, runCxxSmoke.sh wraps the build + check loop and prints a pass=N fail=M summary at the end.

Files

rangeFor.cpp — check 1
genericLambda.cpp — check 2
variadicTpl.cpp — check 3
structBind.cpp — check 4
foldExpr.cpp — check 5
build.sh — per-probe compile + link + OMF (mirrors demos/buildGno.sh)
runCxxSmoke.sh — full sweep harness

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