Java FFI: intro NitObject for references to Nit objects from Java

[nit.git] / src / ffi / java.nit

# This file is part of NIT ( http://www.nitlanguage.org ).
#
# Copyright 2013-2014 Alexis Laferrière <alexis.laf@xymus.net>
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

# FFI support for the Java language
#
# TODO support callbacks to super and casts
module java

import extern_classes
import c
import c_compiler_options

redef class FFILanguageAssignationPhase
        var java_language: FFILanguage = new JavaLanguage(self)
end

class JavaLanguage
        super FFILanguage

        redef fun identify_language(n) do return n.is_java

        redef fun compile_module_block(block, ccu, mmodule)
        do
                mmodule.ensure_java_files
                var java_file = mmodule.java_file
                assert java_file != null

                if block.is_inner_java then
                        java_file.class_content.add(block.code)
                else java_file.header.add(block.code)
        end

        redef fun compile_extern_method(block, m, ccu, mmodule)
        do
                ffi_ccu = ccu
                mmodule.ensure_java_files
                var java_file = mmodule.java_file
                assert java_file != null

                var mclass_type = m.parent.as(AClassdef).mclass.mclass_type
                var mmethodef = m.mpropdef
                var mproperty = m.mpropdef.mproperty

                # C function calling the Java method through JNI
                var fc = new ExternCFunction(m, mmodule)

                fc.exprs.add """
        jclass java_class;
        jmethodID java_meth_id;

        // retrieve the current JVM
        Sys sys = Pointer_sys(NULL);
        JNIEnv *nit_ffi_jni_env = Sys_jni_env(sys);

        // retrieve the implementation Java class
        java_class = Sys_load_jclass(sys, "{{{mmodule.impl_java_class_name}}}");
        if (java_class == NULL) {
                PRINT_ERROR("Nit FFI with Java error: failed to load class.\\n");
                (*nit_ffi_jni_env)->ExceptionDescribe(nit_ffi_jni_env);
                exit(1);
        }

        // register callbacks (only once per Nit module)
        if (!nit_ffi_with_java_registered_natives) nit_ffi_with_java_register_natives(nit_ffi_jni_env, java_class);
"""

                # Retrieve the Java implementation function id
                var java_fun_name = mproperty.build_cname(mclass_type, mmodule, "___java_impl", long_signature)
                var jni_format = mproperty.build_jni_format(mclass_type, mmodule)
                fc.exprs.add """
        // retreive the implementation static function
        java_meth_id = (*nit_ffi_jni_env)->GetStaticMethodID(nit_ffi_jni_env, java_class, "{{{java_fun_name}}}", "{{{jni_format}}}");
        if (java_meth_id == NULL) {
                PRINT_ERROR("Nit FFI with Java error: Java implementation not found.\\n");
                (*nit_ffi_jni_env)->ExceptionDescribe(nit_ffi_jni_env);
                exit(1);
        }
"""

                # Call the C Java implementation method from C
                var signature = mmethodef.msignature
                assert signature != null

                var jni_signature_alt
                var return_type
                var params = new Array[String]
                params.add "nit_ffi_jni_env"
                params.add "java_class"
                params.add "java_meth_id"

                if mproperty.is_init then
                        jni_signature_alt = mclass_type.jni_signature_alt
                        return_type = mclass_type
                else
                        params.add to_java_call_context.cast_to(mclass_type, "self")
                        if signature.return_mtype != null then
                                var ret_mtype = signature.return_mtype
                                ret_mtype = ret_mtype.resolve_for(mclass_type, mclass_type, mmodule, true)
                                return_type = signature.return_mtype
                                jni_signature_alt = return_type.jni_signature_alt
                        else
                                jni_signature_alt = "Void"
                                return_type = null
                        end
                end

                for p in signature.mparameters do
                        var param_mtype = p.mtype
                        param_mtype = param_mtype.resolve_for(mclass_type, mclass_type, mmodule, true)
                        params.add(to_java_call_context.cast_to(param_mtype, p.name))
                end

                var cname = "(*nit_ffi_jni_env)->CallStatic{jni_signature_alt}Method"
                var ccall
                if return_type != null then
                        ccall = "{return_type.jni_type} jni_res = {cname}({params.join(", ")});"
                else ccall = "{cname}({params.join(", ")});"

                fc.exprs.add """
        // execute implementation code
        {{{ccall}}}
        if ((*nit_ffi_jni_env)->ExceptionCheck(nit_ffi_jni_env)) {
                PRINT_ERROR("Nit FFI with Java error: Exception after call.\\n");
                (*nit_ffi_jni_env)->ExceptionDescribe(nit_ffi_jni_env);
                exit(1);
        }

        (*nit_ffi_jni_env)->DeleteLocalRef(nit_ffi_jni_env, java_class);
"""

                if return_type != null then
                        fc.exprs.add "\treturn {to_java_call_context.cast_from(return_type, "jni_res")};"
                end

                ccu.add_exported_function( fc )

                # Java implementation function in Java
                var java_csig = mproperty.build_csignature(mclass_type, mmodule, "___java_impl", long_signature, java_call_context)
                mmodule.java_file.class_content.add """
        public static {{{java_csig}}} {
                // from Nit FII at: {{{block.location}}}
                {{{block.code}}}
        }
"""

                mmodule.callbacks_used_from_java.join m.foreign_callbacks
        end

        redef fun compile_extern_class(block, m, ccu, mmodule) do end

        redef fun get_ftype(block, m) do return new ForeignJavaType(block.code)

        redef fun compile_to_files(mmodule, compdir)
        do
                var ffi_ccu = ffi_ccu
                assert ffi_ccu != null

                # Make sure we have a .java file
                mmodule.ensure_java_files

                # Needed compiler and linker options
                mmodule.insert_compiler_options

                # Enable linking C callbacks to java native methods
                mmodule.ensure_linking_callback_methods(ffi_ccu)

                # Function to build instances to the Java class NitObject
                var callbacks = mmodule.callbacks_used_from_java.callbacks
                if callbacks.not_empty then
                        var cf = new CFunction("jobject nit_ffi_with_java_new_nit_object(JNIEnv *env, void *data)")
                        cf.exprs.add """
        // retrieve the current JVM
        Sys sys = Pointer_sys(NULL);

        jclass java_class = Sys_load_jclass(sys, "nit/app/NitObject");
        if (java_class == NULL) {
                PRINT_ERROR("Nit FFI with Java error: failed to load class NitObject.\\n");
                (*env)->ExceptionDescribe(env);
                exit(1);
        }

        jmethodID java_init = (*env)->GetMethodID(env, java_class, "<init>", "(J)V");
        if (java_init == NULL) {
                PRINT_ERROR("Nit FFI with Java error: NitObject constructor not found.\\n");
                (*env)->ExceptionDescribe(env);
                exit(1);
        }

        jobject nit_object = (*env)->NewObject(env, java_class, java_init, (jlong)data);
        if (nit_object == NULL) {
                PRINT_ERROR("Nit FFI with Java error: NitObject construction failed.\\n");
                (*env)->ExceptionDescribe(env);
                exit(1);
        }

        return nit_object;
        """
                        ffi_ccu.add_local_function cf

                        # Function to extract the pointer held by instances of the Java class NitObject
                        cf = new CFunction("void *nit_ffi_with_java_nit_object_data(JNIEnv *env, jobject nit_object)")
                        cf.exprs.add """
        Sys sys = Pointer_sys(NULL);
        jclass java_class = Sys_load_jclass(sys, "nit/app/NitObject");
        if (java_class == NULL) {
                PRINT_ERROR("Nit FFI with Java error: failed to load class NitObject.\\n");
                (*env)->ExceptionDescribe(env);
                exit(1);
        }

        jfieldID java_field = (*env)->GetFieldID(env, java_class, "pointer", "J");
        if (java_field == NULL) {
                PRINT_ERROR("Nit FFI with Java error: NitObject field not found.\\n");
                (*env)->ExceptionDescribe(env);
                exit(1);
        }

        jlong data = (*env)->GetLongField(env, nit_object, java_field);

        return (void*)data;
        """
                        ffi_ccu.add_local_function cf
                end

                # Java implementation code
                var java_file = mmodule.java_file
                assert java_file != null
                var extern_java_file = java_file.write_to_files(compdir)
                mmodule.ffi_files.add(extern_java_file)
        end

        var ffi_ccu: nullable CCompilationUnit = null # HACK

        redef fun compile_callback(callback, mmodule, mainmodule, ccu)
        do
                ffi_ccu = ccu
                callback.compile_callback_to_java(mmodule, mainmodule, ccu)
        end
end

redef class MModule
        private var callbacks_used_from_java = new ForeignCallbackSet

        # Java source file extracted from user FFI code with generated structure
        var java_file: nullable JavaClassTemplate = null

        # Set up the templates of the Java implementation class
        private fun ensure_java_files
        do
                if java_file != null then return

                # Java implementation code
                java_file = new JavaClassTemplate(impl_java_class_name)
        end

        # Compile C code to call JNI and link C callbacks implementations to Java extern methods
        private fun ensure_linking_callback_methods(ccu: CCompilationUnit)
        do
                var callbacks = callbacks_used_from_java.callbacks
                if callbacks.is_empty then
                        ccu.body_decl.add "static int nit_ffi_with_java_registered_natives = 1;\n"
                        return
                end

                ccu.body_decl.add "static int nit_ffi_with_java_registered_natives = 0;\n"

                var jni_methods = new Array[String]
                for cb in callbacks do
                        jni_methods.add_all(cb.jni_methods_declaration(self))
                end
                for cb in callbacks_used_from_java.types do
                        jni_methods.add_all(cb.jni_methods_declaration(self))
                end

                var cf = new CFunction("void nit_ffi_with_java_register_natives(JNIEnv* env, jclass jclazz)")
                cf.exprs.add """
        nit_ffi_with_java_registered_natives = 1;

        jint n_methods = {{{jni_methods.length}}};
        JNINativeMethod methods[] = {
                {{{jni_methods.join(",\n\t\t")}}}
        };
        jint res = (*env)->RegisterNatives(env, jclazz, methods, n_methods);
        if (res != JNI_OK) {
                PRINT_ERROR("RegisterNatives failed\\n");
                (*env)->ExceptionDescribe(env);
                exit(1);
        }
                """
                ccu.add_local_function cf
        end

        # Tell the C compiler where to find jni.h and how to link with libjvm
        private fun insert_compiler_options
        do
                cflags.add_one("", "-I $(JAVA_HOME)/include/ -I $(JAVA_HOME)/include/linux/")
        end

        # Name of the generated Java class where to store all implementation methods of this module
        # as well as generated callbacks.
        private fun impl_java_class_name: String do return "Nit_{name}"
end

redef class AMethPropdef
        redef fun verify_nitni_callbacks(toolcontext)
        do
                super

                var block = n_extern_code_block
                if block != null and block.is_java then
                        insert_artificial_callbacks(toolcontext)
                end
        end

        # Insert additional explicit calls to get the current `JNIEnv`
        #
        # This forces declaration of callbacks to Nit. The callbacks will be available in Java
        # but will be used mainly by the FFI itself.
        #
        # The developer can also customize the JNIEnv used by the FFI by redefining `Sys::jni_env`.
        private fun insert_artificial_callbacks(toolcontext: ToolContext)
        do
                var fcc = foreign_callbacks

                var modelbuilder = toolcontext.modelbuilder
                var mmodule = mpropdef.mclassdef.mmodule

                # We use callbacks from the C FFI since they will be called from generated C
                var c_language_visitor = toolcontext.ffi_language_assignation_phase.as(FFILanguageAssignationPhase).c_language
                if not mmodule.ffi_callbacks.keys.has(c_language_visitor) then
                        mmodule.ffi_callbacks[c_language_visitor] = new HashSet[NitniCallback]
                end

                # Pointer::sys
                var pointer_class = modelbuilder.try_get_mclass_by_name(self, mmodule, "Pointer")
                assert pointer_class != null
                var pointer_sys_meth = modelbuilder.try_get_mproperty_by_name2(self, mmodule, pointer_class.mclass_type, "sys")
                assert pointer_sys_meth != null and pointer_sys_meth isa MMethod

                var explicit_call = new MExplicitCall(pointer_class.mclass_type, pointer_sys_meth, mmodule)
                fcc.callbacks.add(explicit_call)
                mmodule.ffi_callbacks[c_language_visitor].add(explicit_call)

                # Sys::jni_env
                var sys_class = modelbuilder.try_get_mclass_by_name(self, mmodule, "Sys")
                assert sys_class != null
                var sys_jni_env_meth = modelbuilder.try_get_mproperty_by_name2(self, mmodule, sys_class.mclass_type, "jni_env")
                if sys_jni_env_meth == null or not sys_jni_env_meth isa MMethod then
                        toolcontext.error(self.location, "Java FFI Error: you must import the `java` module when using the FFI with Java")
                        return
                end

                explicit_call = new MExplicitCall(sys_class.mclass_type, sys_jni_env_meth, mmodule)
                fcc.callbacks.add(explicit_call)
                mmodule.ffi_callbacks[c_language_visitor].add(explicit_call)

                # Sys::load_jclass
                var sys_jni_load_jclass_meth = modelbuilder.try_get_mproperty_by_name2(self, mmodule, sys_class.mclass_type, "load_jclass")
                assert sys_jni_load_jclass_meth != null
                assert sys_jni_load_jclass_meth isa MMethod

                explicit_call = new MExplicitCall(sys_class.mclass_type, sys_jni_load_jclass_meth, mmodule)
                fcc.callbacks.add(explicit_call)
                mmodule.ffi_callbacks[c_language_visitor].add(explicit_call)
                explicit_call.fill_type_for(fcc, mmodule)
        end
end

redef class AExternCodeBlock
        # Is this code block in Java?
        fun is_java: Bool do return is_default_java or (parent isa AModule and is_inner_java)

        # Is this code block in Java, with the default mode? (On module blocks it targets the file header)
        private fun is_default_java: Bool do return language_name != null and
                language_name_lowered == "java"

        # Is this code block in Java, and for a module block to generate in the class?
        private fun is_inner_java: Bool do return language_name != null and
                language_name_lowered == "java inner"
end

# Java class source template
class JavaClassTemplate
        super Template

        var java_class_name: String

        var header = new Template
        var class_content = new Template

        fun write_to_files(compdir: String): ExternFile
        do
                var filename = "{java_class_name}.java"
                var filepath = compdir/filename

                write_to_file filepath

                return new JavaFile(filename)
        end

        redef fun rendering
        do
                add header
                add "\n"
                add "public class {java_class_name} \{\n"
                add class_content
                add "\}"
        end
end

# A generated Java source file, represent the corresponding Makefile rules
class JavaFile
        super ExternFile

        # Full Java class name: package and class
        fun full_name: String do return filename.basename(".java")

        redef fun makefile_rule_name do return full_name.replace(".", "/") + ".class"
        redef fun makefile_rule_content do return "javac {filename} -d ."
        redef fun add_to_jar do return true
end

# Context in pure Java code
private class JavaCallContext
        super CallContext

        redef fun name_mtype(mtype) do return mtype.java_type
end

# Context in C, when call are from normal C to JNI
private class ToJavaCallContext
        super CallContext

        redef fun cast_to(mtype, name)
        do
                if mtype.java_is_nit_object then
                        return "nit_ffi_with_java_new_nit_object(nit_ffi_jni_env, {name})"
                else
                        return "({mtype.jni_type})({name})"
                end
        end

        redef fun cast_from(mtype, name)
        do
                if mtype.java_is_nit_object then
                        return "({mtype.cname})nit_ffi_with_java_nit_object_data(nit_ffi_jni_env, {name})"
                else
                        return "({mtype.cname})({name})"
                end
        end

        redef fun name_mtype(mtype) do return mtype.jni_type
end

# Context in C, when call are from JNI to normal C
private class FromJavaCallContext
        super CallContext

        redef fun cast_to(mtype, name)
        do
                if mtype.java_is_nit_object then
                        return "({mtype.cname})nit_ffi_with_java_nit_object_data(nit_ffi_jni_env, {name})"
                else
                        return "({mtype.cname})({name})"
                end
        end

        redef fun cast_from(mtype, name)
        do
                if mtype.java_is_nit_object then
                        return "nit_ffi_with_java_new_nit_object(nit_ffi_jni_env, {name})"
                else
                        return "({mtype.jni_type})({name})"
                end
        end

        redef fun name_mtype(mtype) do return mtype.jni_type
end

# Foreign type attach to Nit extern Java classes
class ForeignJavaType
        super ForeignType

        var java_type: String
end

redef class NitniCallback
        # Compile C and Java code to implement this callback
        fun compile_callback_to_java(mmodule: MModule, mainmodule: MModule, ccu: CCompilationUnit) do end

        # Returns the list of C functions to link with extern Java methods, as required
        # to enable this callback from Java code.
        #
        # Return used by `MModule::ensure_linking_callback_methods`
        #
        # TODO we return an Array to support cast and other features like that
        fun jni_methods_declaration(from_module: MModule): Array[String] do return new Array[String]
end

redef class MExplicitCall
        redef fun compile_callback_to_java(mmodule, mainmodule, ccu)
        do
                if not mmodule.callbacks_used_from_java.callbacks.has(self) then return

                var mproperty = mproperty
                assert mproperty isa MMethod

                # In C, indirection implementing the Java extern methods
                var csignature = mproperty.build_c_implementation_signature(recv_mtype, mmodule, "___indirect", long_signature, from_java_call_context)
                var cf = new CFunction("JNIEXPORT {csignature}")
                cf.exprs.add "\t{mproperty.build_ccall(recv_mtype, mainmodule, null, long_signature, from_java_call_context, null)}\n"
                ccu.add_non_static_local_function cf

                # In Java, declare the extern method as a private static local method
                var java_signature = mproperty.build_csignature(recv_mtype, mainmodule, null, short_signature, java_call_context)
                mmodule.java_file.class_content.add "private native static {java_signature};\n"
        end

        redef fun jni_methods_declaration(from_mmodule)
        do
                var mproperty = mproperty
                assert mproperty isa MMethod

                var java_name = mproperty.build_cname(recv_mtype, from_mmodule, null, short_signature)
                var jni_format = mproperty.build_jni_format(recv_mtype, from_mmodule)
                var c_name = mproperty.build_cname(recv_mtype, from_mmodule, "___indirect", long_signature)

                return ["""{"{{{java_name}}}", "{{{jni_format}}}", {{{c_name}}}}"""]
        end
end

redef class MType

        # Type name in Java
        #
        # * Primitives common to both languages use their Java primitive type
        # * Nit extern Java classes are represented by their full Java type
        # * Other Nit objects are represented by `NitObject` in Java, a class
        #   encapsulating the pointer to the underlying C structure.
        private fun java_type: String do return "nit.app.NitObject"

        # Is this type opaque in Java? As so it is represented by `nit.app.NitObject`.
        private fun java_is_nit_object: Bool do return true

        # JNI type name (in C)
        #
        # So this is a C type, usually defined in `jni.h`
        private fun jni_type: String do return "jobject"

        # JNI short type name (for signatures)
        #
        # Is used by `MMethod::build_jni_format` to pass a Java method signature
        # to the JNI function `GetStaticMetodId`.
        private fun jni_format: String do return "Lnit/app/NitObject;"

        # Type name appearing within JNI function names.
        #
        # Used by `JavaLanguage::compile_extern_method` when calling JNI's `CallStatic*Method`.
        # This strategy is used by JNI to type the return of callbacks to Java.
        private fun jni_signature_alt: String do return "Int"

        redef fun compile_callback_to_java(mmodule, mainmodule, ccu)
        do
                if self isa MClassType and mclass.ftype isa ForeignJavaType then return

                var java_file = mmodule.java_file
                if java_file == null or mmodule.callbacks_used_from_java.callbacks.is_empty then return

                for variation in ["incr", "decr"] do
                        var friendly_name = "{mangled_cname}_{variation}_ref"

                        # C
                        var csignature = "void {mmodule.impl_java_class_name}_{friendly_name}(JNIEnv *nit_ffi_jni_env, jclass clazz, jobject object)"
                        var cf = new CFunction("JNIEXPORT {csignature}")
                        cf.exprs.add "\tnitni_global_ref_{variation}(nit_ffi_with_java_nit_object_data(nit_ffi_jni_env, object));"
                        ccu.add_non_static_local_function cf

                        # Java
                        java_file.class_content.add "private native static void {friendly_name}(nit.app.NitObject object);\n"
                end
        end

        redef fun jni_methods_declaration(from_mmodule)
        do
                var arr = new Array[String]
                for variation in ["incr", "decr"] do
                        var friendly_name = "{mangled_cname}_{variation}_ref"
                        var jni_format = "(Lnit/app/NitObject;)V"
                        var cname = "{from_mmodule.impl_java_class_name}_{friendly_name}"
                        arr.add """{"{{{friendly_name}}}", "{{{jni_format}}}", {{{cname}}}}"""
                end

                return arr
        end
end

redef class MClassType
        redef fun java_type
        do
                var ftype = mclass.ftype
                if ftype isa ForeignJavaType then return ftype.java_type.
                        replace('/', ".").replace('$', ".").replace(' ', "").replace('\n',"")
                if mclass.name == "Bool" then return "boolean"
                if mclass.name == "Char" then return "int"
                if mclass.name == "Int" then return "long"
                if mclass.name == "Float" then return "double"
                if mclass.name == "Byte" then return "byte"
                if mclass.name == "Int8" then return "byte"
                if mclass.name == "Int16" then return "short"
                if mclass.name == "UInt16" then return "short"
                if mclass.name == "Int32" then return "int"
                if mclass.name == "UInt32" then return "int"
                return super
        end

        redef fun java_is_nit_object
        do
                var ftype = mclass.ftype
                if ftype isa ForeignJavaType then return false

                var java_primitives = once new HashSet[String].from(
                        ["Bool", "Char", "Int", "Float", "Byte", "Int8", "Int16", "UInt16", "Int32", "UInt32"])
                return not java_primitives.has(mclass.name)
        end

        redef fun jni_type
        do
                var ftype = mclass.ftype
                if ftype isa ForeignJavaType then return "jobject"
                if mclass.name == "Bool" then return "jboolean"
                if mclass.name == "Char" then return "jint"
                if mclass.name == "Int" then return "jlong"
                if mclass.name == "Float" then return "jdouble"
                if mclass.name == "Byte" then return "jbyte"
                if mclass.name == "Int8" then return "jbyte"
                if mclass.name == "Int16" then return "jshort"
                if mclass.name == "UInt16" then return "jshort"
                if mclass.name == "Int32" then return "jint"
                if mclass.name == "UInt32" then return "jint"
                return super
        end

        redef fun jni_format
        do
                var ftype = mclass.ftype
                if ftype isa ForeignJavaType then
                        var jni_type = ftype.java_type.
                                replace('.', "/").replace(' ', "").replace('\n', "")

                        # Remove parameters of generic types
                        loop
                                var i = jni_type.last_index_of('<')
                                if i >= 0 then
                                        var j = jni_type.index_of_from('>', i)
                                        if j == -1 then
                                                print "Error: missing closing '>' in extern Java type of \"{mclass.name}\""
                                                exit 1
                                        end
                                        jni_type = jni_type.substring(0, i) +
                                                jni_type.substring(j+1, jni_type.length)
                                else break
                        end

                        # Change `float[]` to `[float`
                        if jni_type.has('[') then
                                var depth = jni_type.chars.count('[')
                                var java_type = jni_type.replace("[]", "")
                                var short

                                if java_type == "boolean" then
                                        short = "Z"
                                else if java_type == "byte" then
                                        short = "B"
                                else if java_type == "char" then
                                        short = "C"
                                else if java_type == "short" then
                                        short = "S"
                                else if java_type == "int" then
                                        short = "I"
                                else if java_type == "long" then
                                        short = "J"
                                else if java_type == "float" then
                                        short = "F"
                                else if java_type == "double" then
                                        short = "D"
                                else
                                        short = "L{java_type};"
                                end

                                return "["*depth + short
                        end

                        return "L{jni_type};"
                end
                if mclass.name == "Bool" then return "Z"
                if mclass.name == "Char" then return "I"
                if mclass.name == "Int" then return "J"
                if mclass.name == "Float" then return "D"
                if mclass.name == "Byte" then return "B"
                if mclass.name == "Int8" then return "B"
                if mclass.name == "Int16" then return "S"
                if mclass.name == "UInt16" then return "S"
                if mclass.name == "Int32" then return "I"
                if mclass.name == "UInt32" then return "I"
                return super
        end

        redef fun jni_signature_alt
        do
                var ftype = mclass.ftype

                if ftype isa ForeignJavaType then return "Object"
                if mclass.name == "Bool" then return "Boolean"
                if mclass.name == "Char" then return "Int"
                if mclass.name == "Int" then return "Long"
                if mclass.name == "Float" then return "Double"
                if mclass.name == "Byte" then return "Byte"
                if mclass.name == "Int8" then return "Byte"
                if mclass.name == "Int16" then return "Short"
                if mclass.name == "UInt16" then return "Short"
                if mclass.name == "Int32" then return "Int"
                if mclass.name == "UInt32" then return "Int"
                return super
        end

        redef fun compile_callback_to_java(mmodule, mainmodule, ccu)
        do
                # Don't generate functions for reference counters on extern classes
                if mclass.ftype != null then return

                super
        end

        redef fun jni_methods_declaration(from_mmodule)
        do
                # Don't generate functions for reference counters on extern classes
                if mclass.ftype != null then return new Array[String]

                return super
        end
end

redef class MMethod
        # Returns the JNI signature format of this Nit method
        #
        # Example: a Nity signature `(Bool, Int, Float, JavaString)` is represented by
        # the JNI format `(ZIDLjava/lang/string;)V"
        private fun build_jni_format(recv_mtype: MClassType, from_mmodule: MModule): String
        do
                var mmethoddef = lookup_first_definition(from_mmodule, recv_mtype)
                var msignature = mmethoddef.msignature
                var format = new Array[String]

                format.add "("

                # receiver
                if not self.is_init then format.add recv_mtype.jni_format

                # parameters
                for p in msignature.mparameters do
                        var param_mtype = p.mtype.resolve_for(recv_mtype, recv_mtype, from_mmodule, true)
                        format.add param_mtype.jni_format
                end
                format.add ")"

                # return
                if self.is_init then
                        format.add recv_mtype.jni_format
                else
                        var return_mtype = msignature.return_mtype
                        if return_mtype != null then
                                return_mtype = return_mtype.resolve_for(recv_mtype, recv_mtype, from_mmodule, true)
                                format.add return_mtype.jni_format
                        else format.add "V"
                end

                return format.join
        end

        # Similar to `build_c_signature` but adapted to create the signature expected by JNI for C functions
        # implementing Java extern methods.
        #
        # Is used to generate FFI callbacks to Nit at `MExplicitCall::compile_callback_to_java`.
        private fun build_c_implementation_signature(recv_mtype: MClassType, from_mmodule: MModule,
                suffix: nullable String, length: SignatureLength, call_context: CallContext): String
        do
                var mmethoddef = lookup_first_definition(from_mmodule, recv_mtype)
                var signature = mmethoddef.msignature
                assert signature != null

                var creturn_type
                if self.is_init then
                        creturn_type = call_context.name_mtype(recv_mtype)
                else if signature.return_mtype != null then
                        var ret_mtype = signature.return_mtype
                        ret_mtype = ret_mtype.resolve_for(recv_mtype, recv_mtype, from_mmodule, true)
                        creturn_type = call_context.name_mtype(ret_mtype)
                else
                        creturn_type = "void"
                end

                var cname = build_cname(recv_mtype, from_mmodule, suffix, length)

                var cparams = new List[String]

                cparams.add "JNIEnv *nit_ffi_jni_env"
                cparams.add "jclass clazz"

                if not self.is_init then
                        cparams.add "{call_context.name_mtype(recv_mtype)} self"
                end
                for p in signature.mparameters do
                        var param_mtype = p.mtype.resolve_for(recv_mtype, recv_mtype, from_mmodule, true)
                        cparams.add "{call_context.name_mtype(param_mtype)} {p.name}"
                end

                return "{creturn_type} {cname}( {cparams.join(", ")} )"
        end
end

private fun java_call_context: JavaCallContext do return new JavaCallContext
private fun to_java_call_context: ToJavaCallContext do return new ToJavaCallContext
private fun from_java_call_context: FromJavaCallContext do return new FromJavaCallContext

redef class CCompilationUnit
        # Similar to `add_local_function` but not `static`
        #
        # Used when the signature contains a visibility attribute.
        private fun add_non_static_local_function(c_function: CFunction)
        do
                body_decl.add c_function.signature
                body_decl.add ";\n"

                body_impl.add "\n"
                body_impl.add c_function.to_writer
        end
end