Keep unkwown meta data

CHANGELOG.md

@@ -65,6 +65,7 @@ We refer to [GitHub issues](https://github.com/JabRef/jabref/issues) by using `#
 - Entries with a single corporate author are now correclty exported to the corresponding `corporate` author field in MS-Office XML. [#1497](https://github.com/JabRef/jabref/issues/1497)
 - Improved author handling in MS-Office Import/Export
 - The `day` part of the biblatex `date` field is now exported to the corresponding `day` field in MS-Office XML. [#2691](https://github.com/JabRef/jabref/issues/2691)
+- JabRef will now no longer delete meta data it does not know, but keeps such entrys and tries to keep their formatting as far as possible
 - Single underscores are not converted during the LaTeX to unicode conversion, which does not follow the rules of LaTeX, but is what users require. [#2664](https://github.com/JabRef/jabref/issues/2664)
 - The bibtexkey field is not converted to unicode 
 

src/main/java/org/jabref/logic/exporter/MetaDataSerializer.java

@@ -55,6 +55,18 @@ public static Map<String, String> getSerializedStringMap(MetaData metaData,
         // Skip this if only the root node exists (which is always the AllEntriesGroup).
         metaData.getGroups().filter(root -> root.getNumberOfChildren() > 0).ifPresent(
                 root -> serializedMetaData.put(MetaData.GROUPSTREE, serializeGroups(root)));
+
+        // finally add all unknown meta data items to the serialization map
+        Map<String, List<String>> unknownMetaData = metaData.getUnknownMetaData();
+        for(Map.Entry<String, List<String>> entry : unknownMetaData.entrySet()){
+            StringBuilder value = new StringBuilder();
+            value.append(OS.NEWLINE);
+            for(String line: entry.getValue()){
+                value.append(line.replaceAll(";", "\\\\;") + MetaData.SEPARATOR_STRING + OS.NEWLINE);
+            }
+            serializedMetaData.put(entry.getKey(), value.toString());
+        }
+
         return serializedMetaData;
     }
 

src/main/java/org/jabref/logic/importer/util/MetaDataParser.java

@@ -87,10 +87,9 @@ public static MetaData parse(MetaData metaData, Map<String, String> data, Charac
                 case MetaData.SAVE_ORDER_CONFIG:
                     metaData.setSaveOrderConfig(SaveOrderConfig.parse(value));
                     break;
-                case "groupsversion":
-                case "groups":
-                    // These keys were used in previous JabRef versions, we will not support them anymore -> ignored
-                    break;
+                default:
+                    // Keep meta data items that we do not know in the file
+                    metaData.putUnkownMetaDataItem(entry.getKey(), value);
             }
         }
         if (!defaultCiteKeyPattern.isEmpty() || !nonDefaultCiteKeyPatterns.isEmpty()) {

src/main/java/org/jabref/model/metadata/MetaData.java

@@ -51,7 +51,7 @@ public class MetaData {
     private boolean isProtected;
     private String defaultFileDirectory;
     private ContentSelectors contentSelectors = new ContentSelectors();
-
+    private Map<String, List<String>> unkownMetaData = new HashMap<>();
 
     /**
      * Constructs an empty metadata.
@@ -100,8 +100,8 @@ public AbstractBibtexKeyPattern getCiteKeyPattern(GlobalBibtexKeyPattern globalP
     /**
      * Updates the stored key patterns to the given key patterns.
      *
-     * @param bibtexKeyPattern the key patterns to update to. <br />
-     *                     A reference to this object is stored internally and is returned at getCiteKeyPattern();
+     * @param bibtexKeyPattern the key patterns to update to. <br /> A reference to this object is stored internally and
+     *                         is returned at getCiteKeyPattern();
      */
     public void setCiteKeyPattern(AbstractBibtexKeyPattern bibtexKeyPattern) {
         Objects.requireNonNull(bibtexKeyPattern);
@@ -274,6 +274,17 @@ public Map<String, String> getUserFileDirectories() {
         return Collections.unmodifiableMap(userFileDirectory);
     }
 
+    public Map<String, List<String>> getUnknownMetaData() {
+        return Collections.unmodifiableMap(unkownMetaData);
+    }
+
+    public void putUnkownMetaDataItem(String key, List<String> value) {
+        Objects.requireNonNull(key);
+        Objects.requireNonNull(value);
+
+        unkownMetaData.put(key, value);
+    }
+
     @Override
     public boolean equals(Object o) {
         if (this == o) {

src/test/java/org/jabref/logic/exporter/BibtexDatabaseWriterTest.java

@@ -338,6 +338,22 @@ public void roundtripWithUserCommentBeforeStringAndChange() throws Exception {
         }
     }
 
+    @Test
+    public void roundtripWithUnknownMetaData() throws Exception {
+        Path testBibtexFile = Paths.get("src/test/resources/testbib/unknownMetaData.bib");
+        Charset encoding = StandardCharsets.UTF_8;
+        ParserResult result = new BibtexParser(importFormatPreferences).parse(Importer.getReader(testBibtexFile, encoding));
+
+        SavePreferences preferences = new SavePreferences().withEncoding(encoding).withSaveInOriginalOrder(true);
+        BibDatabaseContext context = new BibDatabaseContext(result.getDatabase(), result.getMetaData(),
+                new Defaults(BibDatabaseMode.BIBTEX));
+
+        StringSaveSession session = databaseWriter.savePartOfDatabase(context, result.getDatabase().getEntries(), preferences);
+        try (Scanner scanner = new Scanner(testBibtexFile,encoding.name())) {
+            assertEquals(scanner.useDelimiter("\\A").next(), session.getStringValue());
+        }
+    }
+
     @Test
     public void writeSavedSerializationOfEntryIfUnchanged() throws Exception {
         BibEntry entry = new BibEntry();

src/test/resources/testbib/unknownMetaData.bib

@@ -0,0 +1,17 @@
+% Encoding: UTF-8
+
+@Article{author2017title,
+  author  = {Author},
+  title   = {Title},
+  journal = {Journal},
+  year    = {2017},
+  groups  = {group},
+}
+
+@Comment{jabref-meta: databaseType:bibtex;}
+
+@Comment{jabref-meta: unkown:
+0 AllEntriesGroup:;
+1 ExplicitGroup:group\;0\;;
+1 ExplicitGroup:anothergroup\;0\;;
+}