classlib: fix ByteBuffer.slice

Probably fixes #607

classlib/src/main/java/org/teavm/classlib/java/nio/TByteBufferImpl.java

@@ -32,7 +32,8 @@ class TByteBufferImpl extends TByteBuffer {
 
     @Override
     public TByteBuffer slice() {
-        return new TByteBufferImpl(position, limit - position,  array, 0, limit - position, direct, readOnly);
+        return new TByteBufferImpl(position + start, limit - position,  array, 0, limit - position,
+                direct, readOnly);
     }
 
     @Override

tests/src/test/java/org/teavm/classlib/java/nio/ByteBufferTest.java

@@ -17,6 +17,7 @@ package org.teavm.classlib.java.nio;
 
 import static org.hamcrest.CoreMatchers.is;
 import static org.hamcrest.CoreMatchers.sameInstance;
+import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertThat;
 import static org.junit.Assert.fail;
 import java.nio.BufferOverflowException;
@@ -153,6 +154,18 @@ public class ByteBufferTest {
         assertThat(slice.get(1), is((byte) 25));
     }
 
+    @Test
+    public void sliceOfSlice() {
+        ByteBuffer buffer = ByteBuffer.allocate(100);
+        buffer.put(new byte[10]);
+        ByteBuffer slice1 = buffer.slice();
+        slice1.put(new byte[15]);
+        ByteBuffer slice2 = slice1.slice();
+
+        assertEquals(25, slice2.arrayOffset());
+        assertEquals(75, slice2.capacity());
+    }
+
     @Test
     public void slicePropertiesSameWithOriginal() {
         ByteBuffer buffer = ByteBuffer.allocate(100).asReadOnlyBuffer().slice();

tests/src/test/java/org/teavm/classlib/java/nio/IntBufferTest.java

@@ -17,6 +17,7 @@ package org.teavm.classlib.java.nio;
 
 import static org.hamcrest.CoreMatchers.is;
 import static org.hamcrest.CoreMatchers.sameInstance;
+import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertThat;
 import static org.junit.Assert.fail;
 import java.nio.BufferOverflowException;
@@ -132,6 +133,19 @@ public class IntBufferTest {
         assertThat(slice.get(1), is(25));
     }
 
+
+    @Test
+    public void sliceOfSlice() {
+        var buffer = IntBuffer.allocate(100);
+        buffer.put(new int[10]);
+        var slice1 = buffer.slice();
+        slice1.put(new int[15]);
+        var slice2 = slice1.slice();
+
+        assertEquals(25, slice2.arrayOffset());
+        assertEquals(75, slice2.capacity());
+    }
+
     @Test
     public void slicePropertiesSameWithOriginal() {
         IntBuffer buffer = IntBuffer.allocate(100).asReadOnlyBuffer().slice();