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Fix an evaluated use of std::declval in qjnitypes.h

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While other compilers don't seem to have trouble with this, the latest
NDK (27) compiler does. That compiler diagnoses the empty-pack case, even though in that case there is no actual use of declval, as the pack-expanded expression contains no use of declval.
For other compilers, that may work for functions that have no arguments, but will not work for any function that does have arguments; in that case, the attempt to use declval will always be ill-formed, and there will be an attempt to use declval.

The fix is straightforward; we have a Ret(*)(Args...), its return type
is simply Ret. So use a simple trait instead of the result of a call.

Task-number: QTBUG-127468
Change-Id: I0dc9e1201914ab94acc2940870be7c6d8cb16c12
Pick-to: 6.7
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
(cherry picked from commit 236c6ec6f4c777d0534539f1c293cfc74006a6eb)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>
This commit is contained in:
Ville Voutilainen 2024-08-18 01:59:29 +03:00 committed by Qt Cherry-pick Bot
parent a75b432c8a
commit 1079d210d1
1 changed files with 8 additions and 6 deletions
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14
src/corelib/kernel/qjnitypes.h
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@ -220,12 +220,14 @@ static constexpr auto makeTupleFromArgs(Ret (*)(JNIEnv *, jclass, Args...), va_l
return makeTupleFromArgsHelper<Args...>(args);
}
// Get the return type of a function point
template <typename Ret, typename ...Args>
auto nativeFunctionReturnType(Ret(*function)(Args...))
template <typename>
struct NativeFunctionReturnType {};
template<typename Ret, typename... Args>
struct NativeFunctionReturnType<Ret(Args...)>
{
return function(std::declval<Args>()...);
}
using type = Ret;
};
} // namespace Detail
} // namespace QtJniMethods
@ -236,7 +238,7 @@ auto nativeFunctionReturnType(Ret(*function)(Args...))
// the actual function with. This then takes care of implicit conversions,
// e.g. a jobject becomes a QJniObject.
#define Q_DECLARE_JNI_NATIVE_METHOD_HELPER(Method) \
static decltype(QtJniMethods::Detail::nativeFunctionReturnType(Method)) \
static QtJniMethods::Detail::NativeFunctionReturnType<decltype(Method)>::type \
va_##Method(JNIEnv *env, jclass thiz, ...) \
{ \
va_list args; \