[leafyoung]

Summary

Fd2dBlackScholesVanillaEngine::calculate() does:

const ext::shared_ptr<BasketPayoff> payoff =
    ext::dynamic_pointer_cast<BasketPayoff>(arguments_.payoff);

with no check that the cast succeeded. Its sibling FdNdimBlackScholesVanillaEngine performs the identical cast and immediately follows it with QL_REQUIRE(payoff, "basket payoff expected"); — Fd2dBlackScholesVanillaEngine is missing that guard. A failed cast leaves payoff null, which is stored and later dereferenced unconditionally in FdmLogBasketInnerValue::innerValue() via (*payoff_)(x) — undefined behavior instead of a clean, actionable error.

BasketOption's own constructor only accepts an ext::shared_ptr<BasketPayoff>, so this isn't reachable through normal BasketOption construction — but the engine's own getArguments()/calculate() interface is public API independent of any specific instrument wrapper (as the N-dim engine's existing guard already anticipates), and nothing stops a non-basket payoff from being set directly through it.

Fix

Added the same QL_REQUIRE(payoff, "basket payoff expected"); the N-dim sibling already has, right after the cast.

Test

Added testFd2dBlackScholesVanillaEngineRejectsNonBasketPayoff to test-suite/basketoption.cpp: drives the engine directly through getArguments()/calculate() with a non-basket payoff after confirming normal BasketOption usage still works. Without the fix this hits an uncaught Boost shared_ptr null-dereference assertion (px != 0) rather than the library's own clean error; with the fix it throws a QuantLib::Error as expected. Full BasketOptionTests suite (33 cases) passes with no regressions.

🤖 Co-worked with Claude Code

[Copilot]

🟡 Changes recommended

The new quote, process, exercise, and engine allocations use raw new wrapped in shared pointers instead of the repository-required auto with ext::make_shared convention.

1 open issue

• Use ext::make_shared for quote allocations · New

What changed in this PR

This PR makes Fd2dBlackScholesVanillaEngine reject non-basket payoffs with a clear QuantLib error instead of risking a null-pointer dereference, matching its N-dimensional sibling.

Changes:

• Adds a guard immediately after the basket-payoff cast.
• Adds a regression test covering normal basket pricing and rejection of a non-basket payoff through the engine’s public interface.

File	Description
test-suite/​basketoption.cpp	Tests valid basket pricing and rejection of an incompatible payoff.
ql/​pricingengines/​basket/​fd2dblackscholesvanillaengine.cpp	Requires the basket-payoff cast to succeed before proceeding.

_{Review effort: Balanced}