Add compile-time generation of JNI class names

As with method signatures, register class names using template function
specialization in the QtJniTypes namespace, and then declare C++ types
as JNI classes with a class name string. Such classes implicitly get
registered as JNI types as well.

Add a QJniObject construct method (since C++ constructors that are
templates cannot be explicitly instantiated with a type), and a
QJniEnvironment::findClass overload.

Add test coverage, also for the recently added macros for native
methods.

As a drive-by, change the name of the Q_JNI_DECLARE_NATIVE_METHOD
macro to Q_DECLARE_JNI_NATIVE_METHOD for consistency.

Change-Id: Ic19562d78da726f202b3bdf4e9354e8ad24d8bd9
Reviewed-by: Ivan Solovev <ivan.solovev@qt.io>
Reviewed-by: Assam Boudjelthia <assam.boudjelthia@qt.io>

3 files changed, 47 insertions, 2 deletions

diff --git a/src/corelib/kernel/qjnienvironment.h b/src/corelib/kernel/qjnienvironment.h
index 6cc8693227..f7ffa836c2 100644
--- a/src/corelib/kernel/qjnienvironment.h
+++ b/src/corelib/kernel/qjnienvironment.h
@@ -24,6 +24,8 @@ public:
     JNIEnv &operator*() const;
     JNIEnv *jniEnv() const;
     jclass findClass(const char *className);
+    template<typename Class>
+    jclass findClass() { return findClass(QtJniTypes::className<Class>().data()); }
     jmethodID findMethod(jclass clazz, const char *methodName, const char *signature);
     template<typename ...Args>
     jmethodID findMethod(jclass clazz, const char *methodName) {
diff --git a/src/corelib/kernel/qjniobject.h b/src/corelib/kernel/qjniobject.h
index bbaa6ee70c..3c7ca13ff2 100644
--- a/src/corelib/kernel/qjniobject.h
+++ b/src/corelib/kernel/qjniobject.h
@@ -45,6 +45,14 @@ public:
     inline QJniObject(QtJniTypes::Object wrapper) noexcept : QJniObject(jobject(wrapper)) {}
     ~QJniObject();
 
+    template<typename Class, typename ...Args>
+    static inline QJniObject construct(Args &&...args)
+    {
+        return QJniObject(QtJniTypes::className<Class>().data(),
+                          QtJniTypes::constructorSignature<Args...>().data(),
+                          std::forward<Args>(args)...);
+    }
+
     jobject object() const;
     template <typename T> T object() const
     {
diff --git a/src/corelib/kernel/qjnitypes.h b/src/corelib/kernel/qjnitypes.h
index 0ebc1a6bc9..ecb8ae02f9 100644
--- a/src/corelib/kernel/qjnitypes.h
+++ b/src/corelib/kernel/qjnitypes.h
@@ -214,6 +214,21 @@ constexpr auto typeSignature()
         staticAssertTypeMismatch();
 }
 
+template<bool flag = false>
+static void staticAssertClassNotRegistered()
+{
+    static_assert(flag, "Class not registered, use Q_DECLARE_JNI_CLASS");
+}
+
+template<typename T>
+constexpr auto className()
+{
+    if constexpr(std::is_same<T, jstring>::value)
+        return String("java/lang/String");
+    else
+        staticAssertClassNotRegistered();
+}
+
 template<typename T>
 static constexpr bool isPrimitiveType()
 {
@@ -298,13 +313,17 @@ struct Object
 
 } // namespace QtJniTypes
 
-#define Q_DECLARE_JNI_TYPE(Type, Signature)                      \
+#define Q_DECLARE_JNI_TYPE_HELPER(Type)                         \
 namespace QtJniTypes {                                          \
 struct Type : Object                                            \
 {                                                               \
     constexpr Type(jobject o) noexcept : Object{o} {}           \
 };                                                              \
 }                                                               \
+
+
+#define Q_DECLARE_JNI_TYPE(Type, Signature)                     \
+Q_DECLARE_JNI_TYPE_HELPER(Type)                                 \
 template<>                                                      \
 constexpr auto QtJniTypes::typeSignature<QtJniTypes::Type>()    \
 {                                                               \
@@ -315,7 +334,23 @@ constexpr auto QtJniTypes::typeSignature<QtJniTypes::Type>()    \
     return QtJniTypes::String(Signature);                       \
 }                                                               \
 
-#define Q_JNI_DECLARE_NATIVE_METHOD(Method)                     \
+#define Q_DECLARE_JNI_CLASS(Type, Signature)                    \
+Q_DECLARE_JNI_TYPE_HELPER(Type)                                 \
+template<>                                                      \
+constexpr auto QtJniTypes::className<QtJniTypes::Type>()        \
+{                                                               \
+    return QtJniTypes::String(Signature);                       \
+}                                                               \
+template<>                                                      \
+constexpr auto QtJniTypes::typeSignature<QtJniTypes::Type>()    \
+{                                                               \
+    return QtJniTypes::String("L")                              \
+         + QtJniTypes::String(Signature)                        \
+         + QtJniTypes::String(";");                             \
+}                                                               \
+
+
+#define Q_DECLARE_JNI_NATIVE_METHOD(Method)                     \
 namespace QtJniMethods {                                        \
 static constexpr auto Method##_signature =                      \
     QtJniTypes::nativeMethodSignature(Method);                  \