Ignore non-displayable fields for indent during writing

src/main/java/net/sf/jabref/bibtex/BibEntryWriter.java

@@ -154,9 +154,16 @@ private boolean writeField(BibEntry entry, Writer out, String name, boolean prep
         }
     }
 
+    /**
+     * Determine length of longest field key.
+     * Only displayable fields are regarded as writable-only fields are not shown in the UI, but the user expects the entry to be rendered as shown in the UI
+     * This is a quick fix for https://github.com/JabRef/jabref/issues/834
+     * TODO: Long term fix: Fix https://github.com/JabRef/jabref/issues/574
+     */
     private int getLengthOfLongestFieldName(BibEntry entry) {
-        Predicate<String> isNotBibtexKey = field -> !"bibtexkey".equals(field);
-        return entry.getFieldNames().stream().filter(isNotBibtexKey).mapToInt(field -> field.length()).max().orElse(0);
+        Predicate<String> isDisplayableField = field -> InternalBibtexFields.isDisplayableField(field);
+        return entry.getFieldNames().stream().filter(isDisplayableField).mapToInt(field -> field.length()).max()
+                .orElse(0);
     }
 
     /**

src/main/java/net/sf/jabref/gui/InternalBibtexFields.java

@@ -169,6 +169,9 @@ private InternalBibtexFields() {
         // some semi-standard fields
         dummy = new BibtexSingleField(BibEntry.KEY_FIELD, true);
         dummy.setPrivate();
+        // the field is displayed and written with a special handling. Therefore, we set displayable and writable to false
+        dummy.setWriteable(false);
+        dummy.setDisplayable(false);
         add(dummy);
 
         dummy = new BibtexSingleField("doi", true, GUIGlobals.SMALL_W);

src/test/java/net/sf/jabref/bibtex/BibEntryWriterTest.java

@@ -42,10 +42,10 @@ public void setUpWriter() {
         writer = new BibEntryWriter(new LatexFieldFormatter(), true);
     }
 
-    @Test
-    public void testSerialization() throws IOException {
-        StringWriter stringWriter = new StringWriter();
-
+    /**
+     * Generates a BibEntry with type "article", key "1234", and some test data
+     */
+    private static BibEntry generateArticle1234() {
         BibEntry entry = new BibEntry("1234", "article");
         //set a required field
         entry.setField("author", "Foo Bar");
@@ -54,7 +54,14 @@ public void testSerialization() throws IOException {
         entry.setField("number", "1");
         entry.setField("note", "some note");
 
-        writer.write(entry, stringWriter, BibDatabaseMode.BIBTEX);
+        return entry;
+    }
+
+    @Test
+    public void testSerialization() throws IOException {
+        StringWriter stringWriter = new StringWriter();
+
+        writer.write(generateArticle1234(), stringWriter, BibDatabaseMode.BIBTEX);
 
         String actual = stringWriter.toString();
 
@@ -70,6 +77,31 @@ public void testSerialization() throws IOException {
         assertEquals(expected, actual);
     }
 
+    @Test
+    public void testSerializationOfNonDisplayableFields() throws IOException {
+        StringWriter stringWriter = new StringWriter();
+
+        BibEntry entry = generateArticle1234();
+        // mark entry; __markedentry is a writable field, but not a displayable
+        // we cannot use `EntryMarker.markEntry(entry, 1, false, nc);`, because even though Globals.DEFAEULT_OWNER is "jabref", the entry is marked by "travis" on TravisCI
+        entry.setField("__markedentry", "[[jabref]:1]");
+
+        writer.write(entry, stringWriter, BibDatabaseMode.BIBTEX);
+
+        String actual = stringWriter.toString();
+
+        // @formatter:off
+        String expected = Globals.NEWLINE + "@Article{," + Globals.NEWLINE +
+                "  author =  {Foo Bar}," + Globals.NEWLINE +
+                "  journal = {International Journal of Something}," + Globals.NEWLINE +
+                "  number =  {1}," + Globals.NEWLINE +
+                "  note =    {some note}," + Globals.NEWLINE +
+                "  __markedentry = {[[jabref]:1]}" + Globals.NEWLINE +
+                "}" + Globals.NEWLINE;
+        // @formatter:on
+        assertEquals(expected, actual);
+    }
+
     @Test
     public void roundTripTest() throws IOException {
         // @formatter:off