Kotlin: Switch to JNA direct mapping

According to https://github.com/java-native-access/jna/blob/master/www/DirectMapping.md
direct mapping can improve performance substantially, maybe even that of custom JNI.
Given we know all methods it's easy to switch it all over.

Note that I have not run any actual benchmark to see how it helps.

Author: badboy

uniffi_bindgen/src/bindings/kotlin/gen_kotlin/mod.rs

@@ -669,7 +669,7 @@ mod filters {
     ) -> Result<String, askama::Error> {
         let ffi_func = callable.ffi_rust_future_poll(ci);
         Ok(format!(
-            "{{ future, callback, continuation -> UniffiLib.INSTANCE.{ffi_func}(future, callback, continuation) }}"
+            "{{ future, callback, continuation -> UniffiLib.{ffi_func}(future, callback, continuation) }}"
         ))
     }
 
@@ -678,7 +678,7 @@ mod filters {
         ci: &ComponentInterface,
     ) -> Result<String, askama::Error> {
         let ffi_func = callable.ffi_rust_future_complete(ci);
-        let call = format!("UniffiLib.INSTANCE.{ffi_func}(future, continuation)");
+        let call = format!("UniffiLib.{ffi_func}(future, continuation)");
         let call = match callable.return_type() {
             Some(Type::External {
                 kind: ExternalKind::DataClass,
@@ -699,9 +699,7 @@ mod filters {
         ci: &ComponentInterface,
     ) -> Result<String, askama::Error> {
         let ffi_func = callable.ffi_rust_future_free(ci);
-        Ok(format!(
-            "{{ future -> UniffiLib.INSTANCE.{ffi_func}(future) }}"
-        ))
+        Ok(format!("{{ future -> UniffiLib.{ffi_func}(future) }}"))
     }
 
     /// Remove the "`" chars we put around function/variable names

uniffi_bindgen/src/bindings/kotlin/templates/NamespaceLibraryTemplate.kt

@@ -59,28 +59,25 @@ internal open class {{ ffi_struct.name()|ffi_struct_name }}(
 // A JNA Library to expose the extern-C FFI definitions.
 // This is an implementation detail which will be called internally by the public API.
 
-internal interface UniffiLib : Library {
-    companion object {
-        internal val INSTANCE: UniffiLib by lazy {
-            loadIndirect<UniffiLib>(componentName = "{{ ci.namespace() }}")
-            .also { lib: UniffiLib ->
-                uniffiCheckContractApiVersion(lib)
-                uniffiCheckApiChecksums(lib)
-                {% for fn in self.initialization_fns() -%}
-                {{ fn }}(lib)
-                {% endfor -%}
-            }
-        }
-        {% if ci.contains_object_types() %}
-        // The Cleaner for the whole library
-        internal val CLEANER: UniffiCleaner by lazy {
-            UniffiCleaner.create()
-        }
-        {%- endif %}
+internal object UniffiLib {
+    {% if ci.contains_object_types() %}
+    // The Cleaner for the whole library
+    internal val CLEANER: UniffiCleaner by lazy {
+        UniffiCleaner.create()
+    }
+    {% endif %}
+
+    init {
+        Native.register(findLibraryName(componentName = "{{ ci.namespace() }}"))
+        uniffiCheckContractApiVersion(this)
+        uniffiCheckApiChecksums(this)
+        {% for fn in self.initialization_fns() -%}
+        {{ fn }}(this)
+        {% endfor %}
     }
 
     {% for func in ci.iter_ffi_function_definitions() -%}
-    fun {{ func.name() }}(
+    @JvmStatic external fun {{ func.name() }}(
         {%- call kt::arg_list_ffi_decl(func) %}
     ): {% match func.return_type() %}{% when Some with (return_type) %}{{ return_type.borrow()|ffi_type_name_by_value }}{% when None %}Unit{% endmatch %}
     {% endfor %}

uniffi_bindgen/src/bindings/kotlin/templates/ObjectTemplate.kt

@@ -195,15 +195,15 @@ open class {{ impl_class_name }}: Disposable, AutoCloseable, {{ interface_name }
         override fun run() {
             pointer?.let { ptr ->
                 uniffiRustCall { status ->
-                    UniffiLib.INSTANCE.{{ obj.ffi_object_free().name() }}(ptr, status)
+                    UniffiLib.{{ obj.ffi_object_free().name() }}(ptr, status)
                 }
             }
         }
     }
 
     fun uniffiClonePointer(): Pointer {
         return uniffiRustCall() { status ->
-            UniffiLib.INSTANCE.{{ obj.ffi_object_clone().name() }}(pointer!!, status)
+            UniffiLib.{{ obj.ffi_object_clone().name() }}(pointer!!, status)
         }
     }
 

uniffi_bindgen/src/bindings/kotlin/templates/RustBufferTemplate.kt

@@ -22,7 +22,7 @@ open class RustBuffer : Structure() {
     companion object {
         internal fun alloc(size: ULong = 0UL) = uniffiRustCall() { status ->
             // Note: need to convert the size to a `Long` value to make this work with JVM.
-            UniffiLib.INSTANCE.{{ ci.ffi_rustbuffer_alloc().name() }}(size.toLong(), status)
+            UniffiLib.{{ ci.ffi_rustbuffer_alloc().name() }}(size.toLong(), status)
         }.also {
             if(it.data == null) {
                throw RuntimeException("RustBuffer.alloc() returned null data pointer (size=${size})")
@@ -38,7 +38,7 @@ open class RustBuffer : Structure() {
         }
 
         internal fun free(buf: RustBuffer.ByValue) = uniffiRustCall() { status ->
-            UniffiLib.INSTANCE.{{ ci.ffi_rustbuffer_free().name() }}(buf, status)
+            UniffiLib.{{ ci.ffi_rustbuffer_free().name() }}(buf, status)
         }
     }
 

uniffi_bindgen/src/bindings/kotlin/templates/macros.kt

@@ -21,7 +21,7 @@
     {%- else %}
     uniffiRustCall()
     {%- endmatch %} { _status ->
-    UniffiLib.INSTANCE.{{ func.ffi_func().name() }}(
+    UniffiLib.{{ func.ffi_func().name() }}(
         {% if func.takes_self() %}it, {% endif -%}
         {% call arg_list_lowered(func) -%}
         _status)
@@ -60,13 +60,13 @@
     uniffiRustCallAsync(
 {%- if callable.takes_self() %}
         callWithPointer { thisPtr ->
-            UniffiLib.INSTANCE.{{ callable.ffi_func().name() }}(
+            UniffiLib.{{ callable.ffi_func().name() }}(
                 thisPtr,
                 {% call arg_list_lowered(callable) %}
             )
         },
 {%- else %}
-        UniffiLib.INSTANCE.{{ callable.ffi_func().name() }}({% call arg_list_lowered(callable) %}),
+        UniffiLib.{{ callable.ffi_func().name() }}({% call arg_list_lowered(callable) %}),
 {%- endif %}
         {{ callable|async_poll(ci) }},
         {{ callable|async_complete(ci) }},