Detect whether the return type of a call is similar to std::expected. This indicates that the caller wants to handle exceptions explicitly, so in case of error, we pass it through the the std::expected-like value. We still clear the exception state. The caller is responsible for freeing the jthrowable local reference. For this to work, we have to propagate errors through to the outer-most function. This includes allowing QJniObject to create QJniEnvironment instances that don't implicitly return a clean environment in the destructor. As long as we can call checkAndClearExceptions() in the public functions (unless the caller opts in), this should not break any existing code that expects QJniObject to implicitly clear exceptions. Add tests for all overloads to make sure that exceptions (from wrong class or method names, and thrown in methods) are caught. Add "Impl" helpers that do not handle exceptions if instantiated accordingly, and call those if we have to maintain compatibility in public functions while also enabling opt-in handling for modern APIs. Add tests that show that we can now handle exceptions ourselves for all public QJniObject APIs. If possible, we build the test with C++23 so that we can use std::expected; otherwise, try to use tl::expected by downloading the header-only implementation from github; and failing that, use a minimal implementation of a type that could be used instead and makes the test pass. Fixes: QTBUG-93800 Fixes: QTBUG-119791 Task-number: QTBUG-92952 Change-Id: I1cfac37ac9af8fd421bc0af030a1d448dd0e259e Reviewed-by: Assam Boudjelthia <assam.boudjelthia@qt.io>