add new --jni-generate-main parameter (#49)

* add new commandline parameter `--jni-generate-main` to resolve the currently discussed issue on how to provide a default JNI_OnLoad & JNI_OnUnload implementation without the user having to know about the internals.

The paramater, if true, generates a file `djinni_jni_main.cpp` that includes the `djinni/jni/djinni_jni_main.hpp` header provided by djinni-support-lib. That way by default the user automatically gets a default JNI_OnLoad implementation if he builds a shared library from all sources.

This is a breaking change because it generates a new type of file. This requires the upcoming djinni-support-lib v1.0.0, that comes with the required header file, to work properly.

docs/cli-usage.md

@@ -88,6 +88,7 @@ djinni \
 | `--jni-include-cpp-prefix <prefix>` | The prefix for `#includes` of the main header files from JNI C++ files. |
 | `--jni-namespace ...` | The namespace name to use for generated JNI C++ classes. |
 | `--jni-base-lib-include-prefix ...` | The JNI base support library's include path (default: `djinni/jni/`). |
+| `--jni-generate-main <true/false>` | Generate a source file (`djinni_jni_main.cpp`) that includes the default `JNI_OnLoad` & `JNI_OnUnload` implementation from the support library. (default: `true`) |
 
 ### Objective-C
 

docs/generated-code-usage.md

@@ -13,13 +13,14 @@ The following headers / code will be generated for each defined type:
 
 (+) Generated only for types that contain constants.
 
+Additionally `djinni_jni_main.cpp` is generated to provide a default implementation for `JNI_OnLoad` and `JNI_OnUnload`, if `--jni-generate-main=true`.
+
 Add all generated source files to your build target, and link the C++ code against the [djinni-support-lib](https://github.com/cross-language-cpp/djinni-support-lib).
 
 ### Our JNI approach
 JNI stands for [Java Native Interface](http://docs.oracle.com/javase/6/docs/technotes/guides/jni/spec/jniTOC.html), an extension of the Java language to allow interop with
 native (C/C++) code or libraries.
 
-
 For each type, built-in (`list`, `string`, etc.) or user-defined, Djinni produces a translator
 class with a `toJava` and `fromJava` function to translate back and forth.
 
@@ -39,12 +40,15 @@ class Main {
 If you package your native library in a jar, you can also use the [`NativeLibLoader`](https://github.com/cross-language-cpp/djinni-support-lib/blob/main/java/com/dropbox/djinni/NativeLibLoader.java)
 to help unpack and load your lib(s).
 
-When a native library is called, JNI calls a special function called [`JNI_OnLoad`](https://github.com/cross-language-cpp/djinni-support-lib/blob/main/djinni/jni/djinni_main.cpp#L23).
+Any library loaded from Java should provide the functions `JNI_OnLoad` and `JNI_OnUnload`.
+They are called by JNI when the library is loaded/unloaded.
 
-If your app doesn't use JNI except through Djinni, include [`djinni/jni/djinni_main.cpp`](https://github.com/cross-language-cpp/djinni-support-lib/blob/main/djinni/jni/djinni_main.cpp). 
-It defines default `JNI_Onload` and `JNI_OnUnload` functions for Djinni.
+Djinni uses these functions to initialize & cleanup internal structures.
+The generated file `djinni_jni_main.cpp` includes a default implementation of `JNI_Onload` and `JNI_OnUnload` functions 
+provided by the support library.
 
-If your app also includes a non-Djinni JNI interface, you'll need to define your own `JNI_OnLoad` and `JNI_OnUnload` functions.
+If you are building a library that does not use JNI except through Djinni, this default should work well for you.
+If want to provide your own implementation of `JNI_Onload` and `JNI_OnUnload`, the generation of `djinni_jni_main.cpp` can be disabled by setting `--jni-generate-main=false`.
 
 ## Objective-C / C++ Project
 

docs/setup.md

@@ -31,5 +31,5 @@ Add the generator as a build requirement in `conanfile.txt`:
 
 ```text
 [build_requires]
-djinni-generator/0.3.1
+djinni-generator/1.0.0
 ```

src/it/resources/expected/all_datatypes/generated-files.txt

@@ -1,5 +1,6 @@
 src/it/resources/result/all_datatypes/cpp-headers/all_datatypes.hpp
 src/it/resources/result/all_datatypes/java/AllDatatypes.java
+src/it/resources/result/all_datatypes/jni/djinni_jni_main.cpp
 src/it/resources/result/all_datatypes/jni-headers/all_datatypes.hpp
 src/it/resources/result/all_datatypes/jni/all_datatypes.cpp
 src/it/resources/result/all_datatypes/objc-headers/ITAllDatatypes.h

src/it/resources/expected/all_datatypes/jni/djinni_jni_main.cpp

@@ -0,0 +1,4 @@
+// AUTOGENERATED FILE - DO NOT MODIFY!
+// The file included here provides default JNI_OnLoad and JNI_OnUnload implementations.
+// Disable the generation of this file with `--jni-generate-main=false`.
+#include "djinni/jni/djinni_jni_main.hpp"

src/it/resources/expected/my_client_interface/generated-files.txt

@@ -1,5 +1,6 @@
 src/it/resources/result/my_client_interface/cpp-headers/my_client_interface.hpp
 src/it/resources/result/my_client_interface/java/MyClientInterface.java
+src/it/resources/result/my_client_interface/jni/djinni_jni_main.cpp
 src/it/resources/result/my_client_interface/jni-headers/my_client_interface.hpp
 src/it/resources/result/my_client_interface/jni/my_client_interface.cpp
 src/it/resources/result/my_client_interface/objc-headers/ITMyClientInterface.h

src/it/resources/expected/my_client_interface/jni/djinni_jni_main.cpp

@@ -0,0 +1,4 @@
+// AUTOGENERATED FILE - DO NOT MODIFY!
+// The file included here provides default JNI_OnLoad and JNI_OnUnload implementations.
+// Disable the generation of this file with `--jni-generate-main=false`.
+#include "djinni/jni/djinni_jni_main.hpp"

src/it/resources/expected/my_cpp_interface/generated-files.txt

@@ -1,6 +1,7 @@
 src/it/resources/result/my_cpp_interface/cpp-headers/my_cpp_interface.hpp
 src/it/resources/result/my_cpp_interface/cpp/my_cpp_interface.cpp
 src/it/resources/result/my_cpp_interface/java/MyCppInterface.java
+src/it/resources/result/my_cpp_interface/jni/djinni_jni_main.cpp
 src/it/resources/result/my_cpp_interface/jni-headers/my_cpp_interface.hpp
 src/it/resources/result/my_cpp_interface/jni/my_cpp_interface.cpp
 src/it/resources/result/my_cpp_interface/objc-headers/ITMyCppInterface.h

src/it/resources/expected/my_cpp_interface/jni/djinni_jni_main.cpp

@@ -0,0 +1,4 @@
+// AUTOGENERATED FILE - DO NOT MODIFY!
+// The file included here provides default JNI_OnLoad and JNI_OnUnload implementations.
+// Disable the generation of this file with `--jni-generate-main=false`.
+#include "djinni/jni/djinni_jni_main.hpp"

src/it/resources/expected/my_enum/generated-files.txt

@@ -1,5 +1,6 @@
 src/it/resources/result/my_enum/cpp-headers/my_enum.hpp
 src/it/resources/result/my_enum/java/MyEnum.java
+src/it/resources/result/my_enum/jni/djinni_jni_main.cpp
 src/it/resources/result/my_enum/jni-headers/my_enum.hpp
 src/it/resources/result/my_enum/objc-headers/ITMyEnum.h
 src/it/resources/result/my_enum/objcpp/ITMyEnum+Private.h

src/it/resources/expected/my_enum/jni/djinni_jni_main.cpp

@@ -0,0 +1,4 @@
+// AUTOGENERATED FILE - DO NOT MODIFY!
+// The file included here provides default JNI_OnLoad and JNI_OnUnload implementations.
+// Disable the generation of this file with `--jni-generate-main=false`.
+#include "djinni/jni/djinni_jni_main.hpp"

src/it/resources/expected/my_flags/generated-files.txt

@@ -1,5 +1,6 @@
 src/it/resources/result/my_flags/cpp-headers/my_flags.hpp
 src/it/resources/result/my_flags/java/MyFlags.java
+src/it/resources/result/my_flags/jni/djinni_jni_main.cpp
 src/it/resources/result/my_flags/jni-headers/my_flags.hpp
 src/it/resources/result/my_flags/objc-headers/ITMyFlags.h
 src/it/resources/result/my_flags/objcpp/ITMyFlags+Private.h

src/it/resources/expected/my_flags/jni/djinni_jni_main.cpp

@@ -0,0 +1,4 @@
+// AUTOGENERATED FILE - DO NOT MODIFY!
+// The file included here provides default JNI_OnLoad and JNI_OnUnload implementations.
+// Disable the generation of this file with `--jni-generate-main=false`.
+#include "djinni/jni/djinni_jni_main.hpp"

src/it/resources/expected/my_record/generated-files.txt

@@ -1,6 +1,7 @@
 src/it/resources/result/my_record/cpp-headers/my_record.hpp
 src/it/resources/result/my_record/cpp/my_record.cpp
 src/it/resources/result/my_record/java/MyRecord.java
+src/it/resources/result/my_record/jni/djinni_jni_main.cpp
 src/it/resources/result/my_record/jni-headers/my_record.hpp
 src/it/resources/result/my_record/jni/my_record.cpp
 src/it/resources/result/my_record/objc-headers/ITMyRecord.h

src/it/resources/expected/my_record/jni/djinni_jni_main.cpp

@@ -0,0 +1,4 @@
+// AUTOGENERATED FILE - DO NOT MODIFY!
+// The file included here provides default JNI_OnLoad and JNI_OnUnload implementations.
+// Disable the generation of this file with `--jni-generate-main=false`.
+#include "djinni/jni/djinni_jni_main.hpp"

src/it/resources/expected/using_custom_datatypes/generated-files.txt

@@ -2,6 +2,7 @@ src/it/resources/result/using_custom_datatypes/cpp-headers/custom_datatype.hpp
 src/it/resources/result/using_custom_datatypes/cpp-headers/other_record.hpp
 src/it/resources/result/using_custom_datatypes/java/CustomDatatype.java
 src/it/resources/result/using_custom_datatypes/java/OtherRecord.java
+src/it/resources/result/using_custom_datatypes/jni/djinni_jni_main.cpp
 src/it/resources/result/using_custom_datatypes/jni-headers/custom_datatype.hpp
 src/it/resources/result/using_custom_datatypes/jni/custom_datatype.cpp
 src/it/resources/result/using_custom_datatypes/jni-headers/other_record.hpp

src/it/resources/expected/using_custom_datatypes/jni/djinni_jni_main.cpp

@@ -0,0 +1,4 @@
+// AUTOGENERATED FILE - DO NOT MODIFY!
+// The file included here provides default JNI_OnLoad and JNI_OnUnload implementations.
+// Disable the generation of this file with `--jni-generate-main=false`.
+#include "djinni/jni/djinni_jni_main.hpp"

src/it/scala/djinni/GeneratorIntegrationTest.scala

@@ -26,7 +26,7 @@ class GeneratorIntegrationTest extends IntegrationTest with GivenWhenThen {
         Cpp(),
         CppHeaders("my_enum.hpp"),
         Java("MyEnum.java"),
-        Jni(),
+        Jni("djinni_jni_main.cpp"),
         JniHeaders("my_enum.hpp"),
         ObjC(),
         ObjCHeaders("ITMyEnum.h", "bridging-header.h"),
@@ -40,7 +40,7 @@ class GeneratorIntegrationTest extends IntegrationTest with GivenWhenThen {
         Cpp(),
         CppHeaders("my_flags.hpp"),
         Java("MyFlags.java"),
-        Jni(),
+        Jni("djinni_jni_main.cpp"),
         JniHeaders("my_flags.hpp"),
         ObjC(),
         ObjCHeaders("ITMyFlags.h"),
@@ -54,7 +54,7 @@ class GeneratorIntegrationTest extends IntegrationTest with GivenWhenThen {
         Cpp("my_record.cpp"),
         CppHeaders("my_record.hpp"),
         Java("MyRecord.java"),
-        Jni("my_record.cpp"),
+        Jni("my_record.cpp", "djinni_jni_main.cpp"),
         JniHeaders("my_record.hpp"),
         ObjC("ITMyRecord.mm"),
         ObjCHeaders("ITMyRecord.h", "bridging-header.h"),
@@ -69,7 +69,7 @@ class GeneratorIntegrationTest extends IntegrationTest with GivenWhenThen {
         Cpp("my_cpp_interface.cpp"),
         CppHeaders("my_cpp_interface.hpp"),
         Java("MyCppInterface.java"),
-        Jni("my_cpp_interface.cpp"),
+        Jni("my_cpp_interface.cpp", "djinni_jni_main.cpp"),
         JniHeaders("my_cpp_interface.hpp"),
         ObjC("ITMyCppInterface.mm"),
         ObjCHeaders("ITMyCppInterface.h", "bridging-header.h"),
@@ -83,7 +83,7 @@ class GeneratorIntegrationTest extends IntegrationTest with GivenWhenThen {
         Cpp(),
         CppHeaders("my_client_interface.hpp"),
         Java("MyClientInterface.java"),
-        Jni("my_client_interface.cpp"),
+        Jni("my_client_interface.cpp", "djinni_jni_main.cpp"),
         JniHeaders("my_client_interface.hpp"),
         ObjC(),
         ObjCHeaders("ITMyClientInterface.h", "bridging-header.h"),
@@ -97,7 +97,7 @@ class GeneratorIntegrationTest extends IntegrationTest with GivenWhenThen {
         Cpp(),
         CppHeaders("all_datatypes.hpp"),
         Java("AllDatatypes.java"),
-        Jni("all_datatypes.cpp"),
+        Jni("all_datatypes.cpp", "djinni_jni_main.cpp"),
         JniHeaders("all_datatypes.hpp"),
         ObjC("ITAllDatatypes.mm"),
         ObjCHeaders("ITAllDatatypes.h", "bridging-header.h"),
@@ -112,7 +112,7 @@ class GeneratorIntegrationTest extends IntegrationTest with GivenWhenThen {
         Cpp(),
         CppHeaders("custom_datatype.hpp", "other_record.hpp"),
         Java("CustomDatatype.java", "OtherRecord.java"),
-        Jni("custom_datatype.cpp", "other_record.cpp"),
+        Jni("custom_datatype.cpp", "other_record.cpp", "djinni_jni_main.cpp"),
         JniHeaders("custom_datatype.hpp", "other_record.hpp"),
         ObjC("ITCustomDatatype.mm", "ITOtherRecord.mm"),
         ObjCHeaders("ITCustomDatatype.h","ITOtherRecord.h", "bridging-header.h"),

src/main/scala/djinni/JNIGenerator.scala

@@ -35,6 +35,15 @@ class JNIGenerator(spec: Spec) extends Generator(spec) {
   def writeJniHppFile(name: String, origin: String, includes: Iterable[String], fwds: Iterable[String], f: IndentWriter => Unit, f2: IndentWriter => Unit = (w => {})) =
     writeHppFileGeneric(spec.jniHeaderOutFolder.get, spec.jniNamespace, spec.jniFileIdentStyle)(name, origin, includes, fwds, f, f2)
 
+  if(spec.jniGenerateMain) {
+    createFile(spec.jniOutFolder.get, "djinni_jni_main." + spec.cppExt, w => {
+      w.wl("// AUTOGENERATED FILE - DO NOT MODIFY!")
+      w.wl("// The file included here provides default JNI_OnLoad and JNI_OnUnload implementations.")
+      w.wl("// Disable the generation of this file with `--jni-generate-main=false`.")
+      w.wl(s"#include " + q(spec.jniBaseLibIncludePrefix + "djinni_jni_main.hpp"))
+    })
+  }
+
   class JNIRefs(name: String, cppPrefixOverride: Option[String]=None) {
     var jniHpp = mutable.TreeSet[String]()
     var jniCpp = mutable.TreeSet[String]()

src/main/scala/djinni/Main.scala

@@ -58,6 +58,7 @@ object Main {
     var jniFileIdentStyleOptional: Option[IdentConverter] = None
     var jniBaseLibClassIdentStyleOptional: Option[IdentConverter] = None
     var jniBaseLibIncludePrefix: String = "djinni/jni/"
+    var jniGenerateMain: Boolean = true
     var cppHeaderOutFolderOptional: Option[File] = None
     var cppExt: String = "cpp"
     var cppHeaderExt: String = "hpp"
@@ -185,6 +186,8 @@ object Main {
         .text("The namespace name to use for generated JNI C++ classes.")
       opt[String]("jni-base-lib-include-prefix").valueName("...").foreach(x => jniBaseLibIncludePrefix = x)
         .text("The JNI base support library's include path (default: djinni/jni/).")
+      opt[Boolean]("jni-generate-main").valueName("<true/false>").foreach(x => jniGenerateMain = x)
+        .text("Generate a source file (djinni_jni_main.cpp) that includes the default JNI_OnLoad & JNI_OnUnload implementation from the djinni-support-lib. (default: true)")
       note("\nObjective-C")
       opt[File]("objc-out").valueName("<out-folder>").foreach(x => objcOutFolder = Some(x))
         .text("The output folder for Objective-C files (Generator disabled if unspecified).")
@@ -427,6 +430,7 @@ object Main {
       jniClassIdentStyle,
       jniFileIdentStyle,
       jniBaseLibIncludePrefix,
+      jniGenerateMain,
       cppExt,
       cppHeaderExt,
       objcOutFolder,

src/main/scala/djinni/generator.scala

@@ -62,6 +62,7 @@ package object generatorTools {
                    jniClassIdentStyle: IdentConverter,
                    jniFileIdentStyle: IdentConverter,
                    jniBaseLibIncludePrefix: String,
+                   jniGenerateMain: Boolean,
                    cppExt: String,
                    cppHeaderExt: String,
                    objcOutFolder: Option[File],