Fix String#unpack w* format issue

Author: bjfish

CHANGELOG.md

@@ -9,6 +9,7 @@ Bug fixes:
 * Fix error message when the method name is not a Symbol or String for `Kernel#respond_to?` (#2132, @ssnickolay)
 * Fixed setting of special variables in enumerators and enumerables (#1484).
 * Fixed return value of `Enumerable#count` and `Enumerable#uniq` with multiple yielded arguments (#2145, @LillianZ).
+* Fixed `String#unpack` for `w*` format (#2143).
 
 Compatibility:
 

spec/ruby/core/string/unpack/w_spec.rb

@@ -23,3 +23,13 @@
     "\x01\x02\x03".unpack("w w").should == [1, 2]
   end
 end
+
+describe "String#unpack with directive 'w*'" do
+
+  it "decodes BER-compressed integers" do
+    "\x01\x02\x03\x04".unpack("w*").should == [1, 2, 3, 4]
+    "\x00\xCE\x0F\x84\x80\x80\x80\x80\x80\x80\x80\x80\x00\x01\x00".unpack("w*").should == [0, 9999, 2**65, 1, 0]
+    "\x81\x80\x80\x80\x80\x80\x80\x80\x80\x00\x90\x80\x80\x80\x80\x80\x80\x80\x03\x01\x02".unpack("w*").should == [2**63, (2**60 + 3), 1, 2]
+  end
+
+end

src/main/java/org/truffleruby/core/format/read/bytes/ReadBERNode.java

@@ -70,23 +70,23 @@ public abstract class ReadBERNode extends FormatNode {
 
     @Specialization
     protected Object encode(VirtualFrame frame, byte[] source) {
-        final int position = getSourcePosition(frame);
-
         final ByteBuffer encode = wrapByteBuffer(frame, source);
-        int pos = encode.position();
+        int position = encode.position();
 
-        final long ul = encode.get(pos) & 0x7f;
+        final long ul = encode.get(position) & 0x7f;
 
-        if (simpleProfile.profile((encode.get(pos++) & 0x80) == 0)) {
-            setSourcePosition(frame, position + pos);
+        if (simpleProfile.profile((encode.get(position) & 0x80) == 0)) {
+            position++;
+            setSourcePosition(frame, position);
             return ul;
-        }
+        } else {
+            position++;
+            assert (ul & UL_MASK) == 0;
+            final BigIntegerAndPos bigIntegerAndPos = runLoop(encode, ul, position);
 
-        assert (ul & UL_MASK) == 0;
-        final BigIntegerAndPos bigIntegerAndPos = runLoop(encode, ul, pos);
-
-        setSourcePosition(frame, position + bigIntegerAndPos.getPos());
-        return fixnumOrBignumNode.fixnumOrBignum(bigIntegerAndPos.getBigInteger());
+            setSourcePosition(frame, bigIntegerAndPos.getPos());
+            return fixnumOrBignumNode.fixnumOrBignum(bigIntegerAndPos.getBigInteger());
+        }
     }
 
     @TruffleBoundary