Fix Java 1.6 compatibility and introduce animal-sniffer to prevent regressions

.gitignore

@@ -29,4 +29,5 @@ pom-jna-platform.xml.asc
 *.iml
 /contrib/platform/${build.generated.sources.dir}/
 /contrib/platform/${build}/
-/contrib/platform/nbproject/private/
+/contrib/platform/nbproject/private/
+/nbproject/private/

CHANGES.md

@@ -10,7 +10,7 @@ Features
 
 Bug Fixes
 ---------
-
+* [#1025](https://github.com/java-native-access/jna/pull/1025): Restore java 6 compatibility and introduce animal-sniffer to prevent regressions - [@matthiasblaesing](https://github.com/matthiasblaesing).
 
 Release 5.0.0
 =============

build.xml

@@ -1,5 +1,8 @@
 <?xml version="1.0" encoding="UTF-8"?>
-<project name="JNA" default="default" basedir="." xmlns:artifact="antlib:org.apache.maven.artifact.ant" xmlns:if="ant:if">
+<project name="JNA" default="default" basedir="." 
+         xmlns:artifact="antlib:org.apache.maven.artifact.ant"
+         xmlns:as="antlib:org.codehaus.mojo.animal_sniffer"
+         xmlns:if="ant:if">
   <description>Builds and tests JNA</description>
 
   <!-- Default build compiles all platform-independent stuff as well
@@ -136,6 +139,18 @@
   <target name="compile-test-single" depends="compile-tests"/>
   <target name="compile-single" depends="compile"/>
 
+  <!-- Prepare additional ant task -->
+  <path id="maven-ant-tasks.classpath">
+      <pathelement location="lib/animal-sniffer-ant-tasks-1.17.jar" />
+      <pathelement location="lib/maven-ant-tasks-2.1.3.jar" />
+  </path>
+  <typedef resource="org/apache/maven/artifact/ant/antlib.xml"
+           uri="antlib:org.apache.maven.artifact.ant"
+           classpathref="maven-ant-tasks.classpath" />
+  <typedef resource="org/codehaus/mojo/animal_sniffer/antlib.xml"
+           uri="antlib:org.codehaus.mojo.animal_sniffer"
+           classpathref="maven-ant-tasks.classpath" />
+
   <target name="-prepare-anttools">
       <mkdir dir="${build}/ant-tools" />
       <javac classpath="lib/ant.jar"
@@ -1127,6 +1142,17 @@ cd ..
   <!-- to where the test library (testlib) is found.                   -->
   <target name="test" depends="-enable-native,jar,compile-tests" unless="cross-compile"
           description="Run all unit tests">
+
+    <echo>Checking JDK compatibility 1.6</echo>
+
+    <echo></echo>
+
+    <as:check-signature signature="lib/java16-1.1.signature">
+        <path path="${classes}"/>
+    </as:check-signature>
+
+    <echo></echo>
+
     <property name="test.fork" value="yes"/>
     <property name="test.forkmode" value="perTest"/>
 
@@ -1370,12 +1396,6 @@ cd ..
     </artifact:mvn>
   </target>
 
-
-  <path id="maven-ant-tasks.classpath" path="lib/maven-ant-tasks-2.1.3.jar" />
-  <typedef resource="org/apache/maven/artifact/ant/antlib.xml"
-           uri="antlib:org.apache.maven.artifact.ant"
-           classpathref="maven-ant-tasks.classpath" />
-
   <!-- NOTE: The 'deploy' target works only if the version (jna.version in build.xml) ends in '-SNAPSHOT'. -->
   <target name="deploy" depends="dist" description="deploy snapshot version to Maven snapshot repository">
     <artifact:mvn failonerror="true">

contrib/platform/build.xml

@@ -1,5 +1,8 @@
 <?xml version="1.0" encoding="UTF-8"?>
-<project name="platform" default="default" basedir=".">
+<project name="platform"
+         default="default"
+         basedir="."
+         xmlns:as="antlib:org.codehaus.mojo.animal_sniffer">
     <description>Builds and tests platform-specific code.</description>
     <import file="nbproject/build-impl.xml"/>
     <!--
@@ -63,7 +66,16 @@
     nbproject/build-impl.xml file.
 
     -->
-
+
+    <!-- Prepare additional ant task -->
+    <path id="maven-ant-tasks.classpath">
+        <pathelement location="../../lib/animal-sniffer-ant-tasks-1.17.jar" />
+        <pathelement location="../../lib/maven-ant-tasks-2.1.3.jar" />
+    </path>
+    <typedef resource="org/codehaus/mojo/animal_sniffer/antlib.xml"
+             uri="antlib:org.codehaus.mojo.animal_sniffer"
+             classpathref="maven-ant-tasks.classpath" />
+
     <!-- the -init-macrodef-copylibs target superseeds the target defined in
     build-impl.xml. The classpath that the base copylibs target adds to the
     MANIFEST.MF interferes with spring-boot and tomcat   -->
@@ -98,7 +110,7 @@
             </sequential>
         </macrodef>
     </target>
-    
+
     <target name="-pre-jar">
         <tempfile deleteonexit="true" destdir="${build.dir}" property="tmp.manifest.file"/>
         <manifest file="${tmp.manifest.file}" mode="replace">
@@ -140,6 +152,17 @@ com.sun.jna.platform.wince;version=${osgi.version}
     </target>
 
     <target name="test" depends="init,compile,compile-test,-pre-test-run" description="Run platform unit tests.">
+
+      <echo>Checking JDK compatibility 1.6</echo>
+
+      <echo></echo>
+
+      <as:check-signature signature="../../lib/java16-1.1.signature" classpath="${javac.classpath}">
+          <path path="${build.classes.dir}"/>
+      </as:check-signature>
+
+      <echo></echo>
+
       <echo>Running platform tests: ${test.src.dir}</echo>
       <property name="test.fork" value="yes"/>
       <property name="reports.junit" location="${build}/reports/junit/${os.prefix}"/>

contrib/platform/src/com/sun/jna/platform/win32/COM/util/Convert.java

@@ -120,8 +120,9 @@ public static VARIANT toVariant(Object value) {
                         Constructor<VARIANT> constructor = null;
                         if (value != null) {
                                 for (Constructor<VARIANT> m : (Constructor<VARIANT>[]) VARIANT.class.getConstructors()) {
-                                        if (m.getParameterCount() > 0
-                                                && m.getParameterTypes()[0].isAssignableFrom(value.getClass())) {
+                                        Class<?>[] parameters = m.getParameterTypes();
+                                        if (parameters.length == 1
+                                                && parameters[0].isAssignableFrom(value.getClass())) {
                                                 constructor = m;
                                         }
                                 }

src/com/sun/jna/NativeString.java

@@ -21,9 +21,6 @@
  */
 package com.sun.jna;
 
-import java.nio.CharBuffer;
-
-
 /** Provides a temporary allocation of an immutable C string
  * (<code>const char*</code> or <code>const wchar_t*</code>) for use when
  * converting a Java String into a native memory function argument.
@@ -111,9 +108,7 @@ public boolean equals(Object other) {
     @Override
     public String toString() {
         boolean wide = WIDE_STRING.equals(encoding);
-        String s = wide ? "const wchar_t*" : "const char*";
-        s += "(" + (wide ? pointer.getWideString(0) : pointer.getString(0, encoding)) + ")";
-        return s;
+        return (wide ? pointer.getWideString(0) : pointer.getString(0, encoding));
     }
 
     public Pointer getPointer() {
@@ -132,7 +127,7 @@ public int length() {
 
     @Override
     public CharSequence subSequence(int start, int end) {
-        return CharBuffer.wrap(toString()).subSequence(start, end);
+        return toString().subSequence(start, end);
     }
 
     @Override