Fix return type of Native#loadLibrary to match unconstrained generic type

Author: Lyor Goldstein

CHANGES.md

@@ -33,6 +33,7 @@ Bug Fixes
 * [#549](https://github.com/java-native-access/jna/pull/549): Fixed bug in types derived from XID - [@twall](https://github.com/twall).
 * [#536](https://github.com/java-native-access/jna/pull/536): Fixed bug in determining the Library and options associated with types defined outside of a Library - [@twall](https://github.com/twall).
 * [#531](https://github.com/java-native-access/jna/pull/531): Ensure direct-mapped callbacks use the right calling convention - [@twall](https://github.com/twall).
+* [#565](https://github.com/java-native-access/jna/pull/565): Fix return type of Native#loadLibrary to match unconstrained generic [@lgoldstein](https://github.com/lgoldstein)
 
 Release 4.2.1
 =============

contrib/platform/src/com/sun/jna/platform/mac/MacFileUtils.java

@@ -32,7 +32,7 @@ public class MacFileUtils extends FileUtils {
 
     public interface FileManager extends Library {
 
-        public FileManager INSTANCE = (FileManager)Native.loadLibrary("CoreServices", FileManager.class);
+        FileManager INSTANCE = Native.loadLibrary("CoreServices", FileManager.class);
 
         int kFSFileOperationDefaultOptions = 0;
         int kFSFileOperationsOverwrite = 0x01;

contrib/platform/src/com/sun/jna/platform/unix/X11.java

@@ -278,7 +278,7 @@ class XImage extends PointerType { }
 
     /** Definition (incomplete) of the Xext library. */
     interface Xext extends Library {
-        Xext INSTANCE = (Xext)Native.loadLibrary("Xext", Xext.class);
+        Xext INSTANCE = Native.loadLibrary("Xext", Xext.class);
         // Shape Kinds
         int ShapeBounding = 0;
         int ShapeClip = 1;
@@ -296,7 +296,7 @@ void XShapeCombineMask(Display display, Window window, int dest_kind,
 
     /** Definition (incomplete) of the Xrender library. */
     interface Xrender extends Library {
-        Xrender INSTANCE = (Xrender)Native.loadLibrary("Xrender", Xrender.class);
+        Xrender INSTANCE = Native.loadLibrary("Xrender", Xrender.class);
         class XRenderDirectFormat extends Structure {
             public short red, redMask;
             public short green, greenMask;
@@ -338,7 +338,7 @@ protected List getFieldOrder() {
     /** Definition of the Xevie library. */
     interface Xevie extends Library {
         /** Instance of Xevie. Note: This extension has been removed from xorg/xserver on Oct 22, 2008 because it is broken and maintainerless. */
-        Xevie INSTANCE = (Xevie)Native.loadLibrary("Xevie", Xevie.class);
+        Xevie INSTANCE = Native.loadLibrary("Xevie", Xevie.class);
         int XEVIE_UNMODIFIED = 0;
         int XEVIE_MODIFIED   = 1;
         // Bool XevieQueryVersion (Display* display, int* major_version, int* minor_version);
@@ -355,7 +355,7 @@ interface Xevie extends Library {
 
     /** Definition of the XTest library. */
     interface XTest extends Library {
-        XTest INSTANCE = (XTest)Native.loadLibrary("Xtst", XTest.class);///usr/lib/libxcb-xtest.so.0
+        XTest INSTANCE = Native.loadLibrary("Xtst", XTest.class);///usr/lib/libxcb-xtest.so.0
         boolean XTestQueryExtension(Display display, IntByReference event_basep, IntByReference error_basep, IntByReference majorp, IntByReference minorp);
         boolean XTestCompareCursorWithWindow(Display display, Window window, Cursor cursor);
         boolean XTestCompareCurrentCursorWithWindow(Display display, Window window);
@@ -393,7 +393,7 @@ protected List getFieldOrder() {
         }
     }
 
-    X11 INSTANCE = (X11)Native.loadLibrary("X11", X11.class);
+    X11 INSTANCE = Native.loadLibrary("X11", X11.class);
 
     /*
       typedef struct {

src/com/sun/jna/Native.java

@@ -446,7 +446,7 @@ public static List<String> toStringList(char[] buf, int offset, int len) {
      * @throws UnsatisfiedLinkError if the library cannot be found or
      * dependent libraries are missing.
      */
-    public static <T extends Library> T loadLibrary(Class<T> interfaceClass) {
+    public static <T> T loadLibrary(Class<T> interfaceClass) {
         return loadLibrary(null, interfaceClass);
     }
 
@@ -465,7 +465,7 @@ public static <T extends Library> T loadLibrary(Class<T> interfaceClass) {
      * dependent libraries are missing.
      * @see #loadLibrary(String, Class, Map)
      */
-    public static <T extends Library> T loadLibrary(Class<T> interfaceClass, Map options) {
+    public static <T> T loadLibrary(Class<T> interfaceClass, Map options) {
         return loadLibrary(null, interfaceClass, options);
     }
 
@@ -483,7 +483,7 @@ public static <T extends Library> T loadLibrary(Class<T> interfaceClass, Map opt
      * dependent libraries are missing.
      * @see #loadLibrary(String, Class, Map)
      */
-    public static <T extends Library> T loadLibrary(String name, Class<T> interfaceClass) {
+    public static <T> T loadLibrary(String name, Class<T> interfaceClass) {
         return loadLibrary(name, interfaceClass, Collections.emptyMap());
     }
 
@@ -503,7 +503,12 @@ public static <T extends Library> T loadLibrary(String name, Class<T> interfaceC
      * @throws UnsatisfiedLinkError if the library cannot be found or
      * dependent libraries are missing.
      */
-    public static <T extends Library> T loadLibrary(String name, Class<T> interfaceClass, Map options) {
+    public static <T> T loadLibrary(String name, Class<T> interfaceClass, Map options) {
+        if (!Library.class.isAssignableFrom(interfaceClass)) {
+            throw new IllegalArgumentException("Interface (" + interfaceClass.getSimpleName() + ")"
+                    + " of library=" + name + " does not extend " + Library.class.getSimpleName());
+        }
+
         Library.Handler handler = new Library.Handler(name, interfaceClass, options);
         ClassLoader loader = interfaceClass.getClassLoader();
         Object proxy = Proxy.newProxyInstance(loader, new Class[] {interfaceClass}, handler);
@@ -1396,7 +1401,7 @@ public static boolean registered(Class<?> cls) {
     /** Unregister the native methods for the given class. */
     private static native void unregister(Class<?> cls, long[] handles);
 
-    private static String getSignature(Class<?> cls) {
+    static String getSignature(Class<?> cls) {
         if (cls.isArray()) {
             return "[" + getSignature(cls.getComponentType());
         }