[enhancement] add new exist serialization option

"exist:insert-final-newline" enforces a newline at the end of an XML document.

Since a lot of editors will insert a newline at the end of a file, this option
will lead to less meaningless changes in version control (e.g. git).
Also, tools like diff can do a better job when each file ends with a newline.

Author: line-o

exist-core/src/main/java/org/exist/storage/serializers/EXistOutputKeys.java

@@ -104,4 +104,14 @@ public class EXistOutputKeys {
      * Set to "yes" to enable xdm-serialization rules, false otherwise.
      */
     public final static String XDM_SERIALIZATION = "xdm-serialization";
+
+    /**
+     * Enforce newline at the end of an XML document.
+     *
+     * Since a lot of editors set this enforcing it on
+     * serialization out of exist-db will lead to less
+     * meaningless changes in git and tools like diff will
+     * be able to provide more meaningful as well.
+     */
+    public final static String INSERT_FINAL_NEWLINE = "insert-final-newline";
 }

exist-core/src/main/java/org/exist/util/serializer/IndentingXMLWriter.java

@@ -140,6 +140,14 @@ public void processingInstruction(final String target, final String data) throws
         afterTag = true;
     }
 
+    @Override
+    public void endDocument() throws TransformerException {
+        super.endDocument();
+        if ("yes".equals(outputProperties.getProperty(EXistOutputKeys.INSERT_FINAL_NEWLINE, "no"))) {
+            super.characters("\n");
+        }
+    }
+
     @Override
     public void endDocumentType() throws TransformerException {
         super.endDocumentType();