tests: align ffi gc trace expectation

Author: Frityet

notes/ffi-gc-trace-expectation.md

@@ -0,0 +1,15 @@
+# FFI GC Trace Expectation
+
+- `ffi.gc(cd, fn)` and `ffi.gc(cd, nil)` are currently interpreter fallback
+  paths: `recff_ffi_gc()` raises `LJ_TRERR_NYICONV` rather than recording the
+  public `ffi.gc` call.
+- `tests/t-ffi-gc-trace.lua` still expected three recorder traces, which was
+  stale after the recorder was made NYI again. The remaining traced coverage is
+  the metatype `__gc` allocation path, which still records through
+  `crec_alloc()`/`crec_finalizer()` and emits `lj_cdata_setfin`.
+- The test now asserts at least one metatype finalizer trace and keeps direct
+  `ffi.gc` / clear coverage as semantic checks.
+- The M7 suite still dump-checks `lj_cdata_setfin`, so loss of metatype
+  finalizer recording remains visible.
+- Verification:
+  - `tools/ci/lua_test.sh m7_ffi_finreg`

tests/t-ffi-gc-trace.lua

@@ -56,22 +56,22 @@ for _ = 1, rounds do clear_loop(n) end
 for _ = 1, rounds do metatype_loop(n) end
 
 local traces = trace_count(64)
-assert(traces >= 3, "expected ffi.gc recorder traces")
+assert(traces >= 1, "expected metatype __gc recorder trace")
 
 collectgarbage("restart")
 collectgarbage("collect")
 collectgarbage("collect")
 
 local expected = rounds * n
 assert(direct_finalized == expected,
-       ("direct traced ffi.gc finalized %d, expected %d"):
+       ("direct ffi.gc finalized %d, expected %d"):
        format(direct_finalized, expected))
 assert(cleared_finalized == 0,
-       ("traced ffi.gc clear finalized %d, expected 0"):
+       ("ffi.gc clear finalized %d, expected 0"):
        format(cleared_finalized))
 assert(mt_finalized == expected,
        ("traced ctype __gc finalized %d, expected %d"):
        format(mt_finalized, expected))
 
-print(("t-ffi-gc-trace OK: %d traces, %d direct finalizers, %d metatype finalizers"):
+print(("t-ffi-gc-trace OK: %d metatype traces, %d direct finalizers, %d metatype finalizers"):
       format(traces, direct_finalized, mt_finalized))