[Truffle] Pulled in String#lines from Rubinius.

Author: nirvdrum

truffle/src/main/java/org/jruby/truffle/nodes/core/StringNodes.java

@@ -741,7 +741,7 @@ public RubyString eachChar(VirtualFrame frame, RubyString string, RubyProc block
 
     }
 
-    @CoreMethod(names = "each_line")
+    @CoreMethod(names = "each_line", optional = 1)
     public abstract static class EachLineNode extends YieldingCoreMethodNode {
 
         public EachLineNode(RubyContext context, SourceSection sourceSection) {
@@ -753,31 +753,41 @@ public EachLineNode(EachLineNode prev) {
         }
 
         @Specialization
-        public RubyArray eachLine(RubyString string) {
+        public RubyArray eachLine(RubyString string, @SuppressWarnings("unused") UndefinedPlaceholder separator) {
+            notDesignedForCompilation();
+
+            final RubyBasicObject globals = getContext().getCoreLibrary().getGlobalVariablesObject();
+            final RubyString recordSeparator = (RubyString) globals.getInstanceVariable("$/");
+            return eachLine(string, recordSeparator);
+        }
+
+        @Specialization
+        public RubyArray eachLine(RubyString string, RubyString separator) {
             notDesignedForCompilation();
 
             final List<Object> lines = new ArrayList<>();
 
             String str = string.toString();
+            String sep = separator.toString();
+
             int start = 0;
 
             while (start < str.length()) {
-                int end = str.indexOf('\n', start);
+                int end = str.indexOf(sep, start);
 
                 if (end == -1) {
                     lines.add(getContext().makeString(str.substring(start)));
                     break;
                 }
 
-                String line = str.substring(start, end+1);
-                start = end+1;
+                String line = str.substring(start, end + sep.length());
+                start = end + sep.length();
 
                 lines.add(getContext().makeString(line));
             }
 
             return RubyArray.fromObjects(getContext().getCoreLibrary().getArrayClass(), lines.toArray(new Object[lines.size()]));
         }
-
     }
 
     @CoreMethod(names = "empty?")

truffle/src/main/ruby/jruby/truffle/core/rubinius/kernel/common/string.rb

@@ -47,6 +47,16 @@ def chomp(separator=$/)
     str.chomp!(separator) || str
   end
 
+  def lines(sep=$/)
+    if block_given?
+      each_line(sep) do |line|
+        yield line
+      end
+    else
+      each_line(sep).to_a
+    end
+  end
+
   def start_with?(*prefixes)
     prefixes.each do |original_prefix|
       prefix = Rubinius::Type.check_convert_type original_prefix, String, :to_str