The skip-trivial guard printed "Skipping" and then fuzzed anyway

[devdanzin]

The bug

skip_trivial_type has correctly identified cffi objects since #268. A PyPy stdlib module hands out a live FFI as an attribute — _curses_panel.ffi, _ssl.ffi, _lzma.ffi, at least ten of them — and type(ffi).__module__ really is _cffi_backend, so the check returns True.

It just never mattered. Two of the three emission sites put nothing in the guard's body except the print, and emitted the method fuzzing after the if rather than inside an else:

if skip_trivial_type(fuzz_target_module.ffi):
    print('Skipping deep diving on ...')      # <- the entire body
# General method fuzzing for fuzz_target_module.ffi
try:
    res_obj0m1 = callMethod("obj0m1", fuzz_target_module.ffi, "typeof", ...

So the script reported the skip and then called the object anyway.

ffi.memmove() and its siblings take their arguments as raw pointers and fault by contract on whatever they are handed — exactly as ctypes does on CPython — so a crash there is never a target defect. Five consecutive PyPy fleets kept dirs from this; the most recent is a _curses_panel SIGSEGV in fleet_10 whose last line before the fault is [obj12m14] FFI.memmove().

The fix

Both broken sites now open a real else:. The third already did, which is why it never contributed.

The plugin path is untouched: a dispatcher that opens its own trailing else still owns the fallback, and the new one is opened only when no dispatcher did. A pass keeps the block valid when an object turns out to have no methods to fuzz.

The golden snapshot moves accordingly — the method-fuzzing block is one level deeper, inside the else.

Tests

Asserting on the emitted text would not have caught this, because the print was always there. The new tests assert on the parsed structure:

• every if skip_trivial_type(x): carries the work in its orelse
• the taken branch only reports, never calls the object
• the emitted function skips a _cffi_backend-typed instance and leaves an ordinary object alone

All three fail on the pre-fix generator (verified by stashing the fix). 1303 tests pass; ruff check + ruff format --check clean.

🤖 Generated with Claude Code

https://claude.ai/code/session_01WPBSmN87d2BqUnrDbojUT1