Android APIs use integer constants like enum values, so they are mapped to one of the integeral types (jint, jshort, jlong etc) on the C++ side. Enable C++ code to declare an equivalent enum (scoped or unscoped), and to use that enum as a type in JNI calls by treating it as the underlying type in the signature() generator. Add a helper type trait that maps enums to their underlying type and other integral types to themselves (we can't use std::underlying_type_t on a non-enum type). Add tests. Note: Java Enums are special classes with fields; this change does not add any special support for those. Change-Id: Iec430a1553152dcf7a24209aaebbeceb1c6e38a8 Reviewed-by: Petri Virkkunen <petri.virkkunen@qt.io> Reviewed-by: Zoltan Gera <zoltan.gera@qt.io> Reviewed-by: Juha Vuolle <juha.vuolle@qt.io>