Synchronize local libraries with their files (merge external changes without a dialog)

CHANGELOG.md

@@ -17,6 +17,7 @@ Note that this project **does not** adhere to [Semantic Versioning](https://semv
 - We added `jabkit git merge-driver`, a Git merge driver that merges `.bib` files semantically. [#16838](https://github.com/JabRef/jabref/pull/16838)
 - We added tooltips with action descriptions to menu items. [#9615](https://github.com/JabRef/jabref/issues/9615)
 - We added "Contribute to JabRef" to the Help menu, linking to [contribute.jabref.org](https://contribute.jabref.org). [#17162](https://github.com/JabRef/jabref/pull/17162)
+- We added an option to automatically merge changes made to the library file outside JabRef into the open library. [#8431](https://github.com/JabRef/jabref/issues/8431)
 - We added EasyOCR, PaddleOCR, and AppleOCR as selectable OCR engines, alongside Tesseract and Docling. [#16866](https://github.com/JabRef/jabref/issues/16866)
 
 ### Changed
@@ -35,6 +36,7 @@ Note that this project **does not** adhere to [Semantic Versioning](https://semv
 - We fixed an issue where JabRef closed when a client of the integrated language server disconnected. [#17303](https://github.com/JabRef/jabref/pull/17303)
 - We fixed menu items not showing why they are disabled when a menu was opened for the first time. [#17200](https://github.com/JabRef/jabref/pull/17200)
 - We fixed an issue where entries of type Misc were penalized too strictly during duplicate detection. [#16578](https://github.com/JabRef/jabref/issues/16578)
+- We fixed an issue where accepting an external change to an entry lost its table position, selection, and open entry editor. [#16813](https://github.com/JabRef/jabref/pull/16813)
 - We fixed an issue where the "Simple HTML" export separated author initials with spaces. [#17306](https://github.com/JabRef/jabref/pull/17306)
 - We fixed an issue where the Hayagriva YAML export wrote braced author names, such as company names, as invalid YAML. [#17316](https://github.com/JabRef/jabref/issues/17316)
 - We fixed an issue where "Community forum" in the Help menu opened the donation page instead of the forum. [#17162](https://github.com/JabRef/jabref/pull/17162)

docs/requirements/ux.md

@@ -109,6 +109,15 @@ Since inspecting a library file means parsing it completely, the inspection is s
 
 Needs: impl
 
+## Automatically merging external changes into a library
+`req~ux.external-library-changes.automatic-merge~1`
+
+While a local library is set to automatically merge external changes (a per-library setting with a global default, off unless enabled), changes made to its file outside JabRef must be merged into the in-memory library without asking, and unsaved in-memory changes must not be reported as external changes.
+A review is only required for an item (entry field, entry type, metadata, preamble, string) that was changed differently in memory and in the file, or that was deleted on one side and changed on the other.
+Fields changed only in the file are taken over even when other fields of the same entry were changed in memory.
+
+Needs: impl
+
 ## Bulk entry deletion must keep main table responsive
 `req~ux.large-library.bulk-entry-removal~1`
 

jabgui/src/main/java/org/jabref/gui/collab/ChangeScanner.java

@@ -3,13 +3,16 @@
 import java.io.IOException;
 import java.nio.file.Path;
 import java.util.List;
+import java.util.Optional;
+import java.util.function.BooleanSupplier;
 
 import org.jabref.gui.DialogService;
 import org.jabref.gui.StateManager;
 import org.jabref.gui.preferences.GuiPreferences;
 import org.jabref.logic.importer.ImportFormatPreferences;
 import org.jabref.logic.importer.OpenDatabase;
 import org.jabref.logic.importer.ParserResult;
+import org.jabref.logic.sync.LibraryBaseline;
 import org.jabref.model.database.BibDatabaseContext;
 import org.jabref.model.util.DummyFileUpdateMonitor;
 
@@ -34,18 +37,32 @@ public ChangeScanner(BibDatabaseContext database,
     }
 
     public List<DatabaseChange> scanForChanges() {
-        if (database.getDatabasePath().isEmpty()) {
-            return List.of();
-        }
-
         try {
-            return getDatabaseChanges(database.getDatabasePath().get());
+            return scanForChanges(() -> true).orElse(List.of());
         } catch (IOException e) {
             LOGGER.warn("Error while parsing changed file.", e);
             return List.of();
         }
     }
 
+    /// @param readyToParse consulted right before the file is parsed, e.g. to wait until a sync client has finished writing it; `false` abandons the scan
+    /// @return the changes, or empty when the scan was abandoned
+    /// @throws IOException when the file could not be read; unlike no changes, a failed read must be retried
+    public Optional<List<DatabaseChange>> scanForChanges(BooleanSupplier readyToParse) throws IOException {
+        if (database.getDatabasePath().isEmpty()) {
+            return Optional.of(List.of());
+        }
+        if (!readyToParse.getAsBoolean()) {
+            return Optional.empty();
+        }
+        return Optional.of(getDatabaseChanges(database.getDatabasePath().get()));
+    }
+
+    /// @return the given external changes sorted by the side they happened on, see [ChangeTriage#triage]
+    public ChangeTriage.Triage triage(LibraryBaseline baseline, List<DatabaseChange> changes) {
+        return ChangeTriage.triage(baseline, changes, database, databaseChangeResolverFactory);
+    }
+
     public List<DatabaseChange> getDatabaseChanges(Path fileToCompare) throws IOException {
         ImportFormatPreferences importFormatPreferences = preferences.getImportFormatPreferences();
         ParserResult result = OpenDatabase.loadDatabase(fileToCompare, importFormatPreferences, new DummyFileUpdateMonitor());