Fix parsing of backslashes at the end of field content

CHANGELOG.md

@@ -23,6 +23,7 @@ Note that this project **does not** adhere to [Semantic Versioning](http://semve
 ### Changed
 
 - 'Get full text' now also checks the file url. [#568](https://github.com/koppor/jabref/issues/568)
+- `log.txt` now contains an entry if a BibTeX entry could not be parsed.
 - We refined the 'main directory not found' error message. [#9625](https://github.com/JabRef/jabref/pull/9625)
 - We modified the `Add Group` dialog to use the most recently selected group hierarchical context [#9141](https://github.com/JabRef/jabref/issues/9141)
 
@@ -37,6 +38,7 @@ Note that this project **does not** adhere to [Semantic Versioning](http://semve
 - We fixed an issue where the command line export using `--exportMatches` flag does not create an output bib file [#9581](https://github.com/JabRef/jabref/issues/9581)
 - We fixed an issue where custom field in the custom entry types could not be set to mulitline [#9609](https://github.com/JabRef/jabref/issues/9609)
 - We fixed an issue where the Office XML exporter did not resolve BibTeX-Strings when exporting entries [forum#3741](https://discourse.jabref.org/t/exporting-bibtex-constant-strings-to-ms-office-2007-xml/3741)
+- JabRef is now more relaxed when parsing field content: In case a field content ended with `\`, the combination `\}` was treated as plain `}`. [#9668](https://github.com/JabRef/jabref/issues/9668)
 
 
 ### Removed

src/main/java/org/jabref/gui/ClipBoardManager.java

@@ -87,7 +87,7 @@ public static String getContents() {
         return result;
     }
 
-    public Optional<String> getBibTeXEntriesFromClipbaord() {
+    public Optional<String> getBibTeXEntriesFromClipboard() {
         return Optional.ofNullable(clipboard.getContent(DragAndDropDataFormats.ENTRIES)).map(String.class::cast);
     }
 

src/main/java/org/jabref/gui/externalfiles/ImportHandler.java

@@ -258,7 +258,7 @@ private void generateKeys(List<BibEntry> entries) {
     }
 
     public List<BibEntry> handleBibTeXData(String entries) {
-        BibtexParser parser = new BibtexParser(preferencesService.getImportFormatPreferences(), Globals.getFileUpdateMonitor());
+        BibtexParser parser = new BibtexParser(preferencesService.getImportFormatPreferences(), fileUpdateMonitor);
         try {
             return parser.parseEntries(new ByteArrayInputStream(entries.getBytes(StandardCharsets.UTF_8)));
         } catch (ParseException ex) {

src/main/java/org/jabref/gui/maintable/MainTable.java

@@ -322,9 +322,9 @@ private void clearAndSelectLast() {
 
     public void paste() {
         List<BibEntry> entriesToAdd;
-            entriesToAdd = this.clipBoardManager.getBibTeXEntriesFromClipbaord()
+            entriesToAdd = this.clipBoardManager.getBibTeXEntriesFromClipboard()
             .map(importHandler::handleBibTeXData)
-            .orElseGet(this::handleNonBibteXStringData);
+            .orElseGet(this::handleNonBibTeXStringData);
 
         for (BibEntry entry : entriesToAdd) {
             importHandler.importEntryWithDuplicateCheck(database, entry);
@@ -334,7 +334,7 @@ public void paste() {
         }
     }
 
-    private List<BibEntry> handleNonBibteXStringData() {
+    private List<BibEntry> handleNonBibTeXStringData() {
         String data = ClipBoardManager.getContents();
         List<BibEntry> entries = new ArrayList<>();
         try {

src/main/java/org/jabref/logic/importer/fileformat/BibtexParser.java

@@ -278,10 +278,10 @@ private void parseAndAddEntry(String type) {
 
             database.insertEntry(entry);
         } catch (IOException ex) {
-            // Trying to make the parser more robust.
+            // This makes the parser more robust:
             // If an exception is thrown when parsing an entry, drop the entry and try to resume parsing.
 
-            LOGGER.debug("Could not parse entry", ex);
+            LOGGER.warn("Could not parse entry", ex);
             parserResult.addWarning(Localization.lang("Error occurred when parsing entry") + ": '" + ex.getMessage()
                     + "'. " + "\n\n" + Localization.lang("JabRef skipped the entry."));
         }
@@ -290,7 +290,7 @@ private void parseAndAddEntry(String type) {
     private void parseJabRefComment(Map<String, String> meta) {
         StringBuilder buffer;
         try {
-            buffer = parseBracketedTextExactly();
+            buffer = parseBracketedFieldContent();
         } catch (IOException e) {
             // if we get an IO Exception here, then we have an unbracketed comment,
             // which means that we should just return and the comment will be picked up as arbitrary text
@@ -500,6 +500,16 @@ private int peek() throws IOException {
         return character;
     }
 
+    private char[] peek2() throws IOException {
+        char character1 = (char) read();
+        char character2 = (char) read();
+        unread(character2);
+        unread(character1);
+        return new char[] {
+                character1, character2
+        };
+    }
+
     private int read() throws IOException {
         int character = pushbackReader.read();
 
@@ -635,7 +645,7 @@ private String parseFieldContent(Field field) throws IOException {
                 // Value is a string enclosed in brackets. There can be pairs
                 // of brackets inside a field, so we need to count the
                 // brackets to know when the string is finished.
-                StringBuilder text = parseBracketedTextExactly();
+                StringBuilder text = parseBracketedFieldContent();
                 value.append(fieldContentFormatter.format(text, field));
             } else if (Character.isDigit((char) character)) { // value is a number
                 String number = parseTextToken();
@@ -668,7 +678,6 @@ private String parseTextToken() throws IOException {
             int character = read();
             if (character == -1) {
                 eof = true;
-
                 return token.toString();
             }
 
@@ -886,7 +895,11 @@ private boolean isClosingBracketNext() {
         }
     }
 
-    private StringBuilder parseBracketedTextExactly() throws IOException {
+    /**
+     * This is called if a field in the form of <code>field = {content}</code> is parsed.
+     * The global variable <code>character</code> contains <code>{</code>.
+     */
+    private StringBuilder parseBracketedFieldContent() throws IOException {
         StringBuilder value = new StringBuilder();
 
         consume('{');
@@ -898,7 +911,32 @@ private StringBuilder parseBracketedTextExactly() throws IOException {
         while (true) {
             character = (char) read();
 
-            boolean isClosingBracket = (character == '}') && (lastCharacter != '\\');
+            boolean isClosingBracket = false;
+            if (character == '}') {
+                if (lastCharacter == '\\') {
+                    // We hit `\}`
+                    // It could be that a user has a backslash at the end of the entry, but intended to put a file path
+                    // We want to be relaxed at that case
+                    // First described at https://github.com/JabRef/jabref/issues/9668
+                    char[] peek2 = peek2();
+                    if ((peek2[0] == ',') && ((peek2[1] == OS.NEWLINE.charAt(0)) || (peek2[1] == '\n'))) {
+                        // We hit '\}\r` or `\}\n`
+                        // Heuristics: Unwanted escaping of }
+                        //
+                        // Two consequences:
+                        //
+                        // 1. Keep `\` as read
+                        //   This is already done
+                        //
+                        // 2. Treat `}` as closing bracket
+                        isClosingBracket = true;
+                    } else {
+                        isClosingBracket = false;
+                    }
+                } else {
+                    isClosingBracket = true;
+                }
+            }
 
             if (isClosingBracket && (brackets == 0)) {
                 return value;

src/test/java/org/jabref/gui/externalfiles/ImportHandlerTest.java

@@ -0,0 +1,57 @@
+package org.jabref.gui.externalfiles;
+
+import java.util.List;
+
+import javax.swing.undo.UndoManager;
+
+import org.jabref.gui.DialogService;
+import org.jabref.gui.StateManager;
+import org.jabref.logic.importer.ImportFormatPreferences;
+import org.jabref.logic.importer.ImportFormatReader;
+import org.jabref.model.database.BibDatabaseContext;
+import org.jabref.model.entry.BibEntry;
+import org.jabref.model.entry.field.StandardField;
+import org.jabref.model.entry.types.StandardEntryType;
+import org.jabref.model.util.DummyFileUpdateMonitor;
+import org.jabref.preferences.FilePreferences;
+import org.jabref.preferences.PreferencesService;
+
+import org.junit.jupiter.api.Test;
+import org.mockito.Answers;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.when;
+
+class ImportHandlerTest {
+
+    @Test
+    void handleBibTeXData() {
+        ImportFormatPreferences importFormatPreferences = mock(ImportFormatPreferences.class, Answers.RETURNS_DEEP_STUBS);
+
+        PreferencesService preferencesService = mock(PreferencesService.class);
+        when(preferencesService.getImportFormatPreferences()).thenReturn(importFormatPreferences);
+        when(preferencesService.getFilePreferences()).thenReturn(mock(FilePreferences.class));
+
+        ImportHandler importHandler = new ImportHandler(
+                mock(BibDatabaseContext.class),
+                preferencesService,
+                new DummyFileUpdateMonitor(),
+                mock(UndoManager.class),
+                mock(StateManager.class),
+                mock(DialogService.class),
+                mock(ImportFormatReader.class));
+
+        List<BibEntry> bibEntries = importHandler.handleBibTeXData("""
+                @InProceedings{Wen2013,
+                  library          = {Tagungen\\2013\\KWTK45\\},
+                }
+                """);
+
+        BibEntry expected = new BibEntry(StandardEntryType.InProceedings)
+                .withCitationKey("Wen2013")
+                .withField(StandardField.LIBRARY, "Tagungen\\2013\\KWTK45\\");
+
+        assertEquals(List.of(expected), bibEntries.stream().toList());
+    }
+}

src/test/java/org/jabref/logic/bibtex/BibEntryWriterTest.java

@@ -184,7 +184,6 @@ void writeReallyUnknownTypeTest() throws Exception {
 
     @Test
     void roundTripTest() throws IOException {
-        // @formatter:off
         String bibtexEntry = """
                 @Article{test,
                   Author                   = {Foo Bar},
@@ -193,7 +192,63 @@ void roundTripTest() throws IOException {
                   Number                   = {1}
                 }
                 """.replaceAll("\n", OS.NEWLINE);
-        // @formatter:on
+
+        // read in bibtex string
+        ParserResult result = new BibtexParser(importFormatPreferences, fileMonitor).parse(new StringReader(bibtexEntry));
+        Collection<BibEntry> entries = result.getDatabase().getEntries();
+        BibEntry entry = entries.iterator().next();
+
+        // write out bibtex string
+        bibEntryWriter.write(entry, bibWriter, BibDatabaseMode.BIBTEX);
+
+        assertEquals(bibtexEntry, stringWriter.toString());
+    }
+
+    @Test
+    void roundTripKeepsFilePathWithBackslashes() throws IOException {
+        String bibtexEntry = """
+                @Article{,
+                  file = {Tagungen\\2013\\KWTK45},
+                }
+                """.replaceAll("\n", OS.NEWLINE);
+
+        // read in bibtex string
+        ParserResult result = new BibtexParser(importFormatPreferences, fileMonitor).parse(new StringReader(bibtexEntry));
+        Collection<BibEntry> entries = result.getDatabase().getEntries();
+        BibEntry entry = entries.iterator().next();
+
+        // write out bibtex string
+        bibEntryWriter.write(entry, bibWriter, BibDatabaseMode.BIBTEX);
+
+        assertEquals(bibtexEntry, stringWriter.toString());
+    }
+
+    @Test
+    void roundTripKeepsEscapedCharacters() throws IOException {
+        String bibtexEntry = """
+                @Article{,
+                  demofield = {Tagungen\\2013\\KWTK45},
+                }
+                """.replaceAll("\n", OS.NEWLINE);
+
+        // read in bibtex string
+        ParserResult result = new BibtexParser(importFormatPreferences, fileMonitor).parse(new StringReader(bibtexEntry));
+        Collection<BibEntry> entries = result.getDatabase().getEntries();
+        BibEntry entry = entries.iterator().next();
+
+        // write out bibtex string
+        bibEntryWriter.write(entry, bibWriter, BibDatabaseMode.BIBTEX);
+
+        assertEquals(bibtexEntry, stringWriter.toString());
+    }
+
+    @Test
+    void roundTripKeepsFilePathEndingWithBackslash() throws IOException {
+        String bibtexEntry = """
+                @Article{,
+                  file = {dir\\},
+                }
+                """.replaceAll("\n", OS.NEWLINE);
 
         // read in bibtex string
         ParserResult result = new BibtexParser(importFormatPreferences, fileMonitor).parse(new StringReader(bibtexEntry));

src/test/java/org/jabref/logic/importer/fileformat/BibtexParserTest.java

@@ -607,6 +607,32 @@ void parseRecognizesAbsoluteFile() throws IOException {
         assertEquals(Optional.of("D:\\Documents\\literature\\Tansel-PRL2006.pdf"), entry.getField(StandardField.FILE));
     }
 
+    @Test
+    void parseRecognizesFinalSlashAsSlash() throws Exception {
+        ParserResult result = parser
+                .parse(new StringReader("""
+        @misc{,
+          test = {wired\\},
+        }
+        """));
+
+        assertEquals(
+                List.of(new BibEntry()
+                .withField(new UnknownField("test"), "wired\\")),
+                result.getDatabase().getEntries()
+        );
+    }
+
+    /**
+     * JabRef's heuristics is not able to parse this special case.
+     */
+    @Test
+    void parseFailsWithFinalSlashAsSlashWhenSingleLine() throws Exception {
+        ParserResult parserResult = parser.parse(new StringReader("@misc{, test = {wired\\}}"));
+        // In case JabRef was more relaxed, `assertFalse` would be provided here.
+        assertTrue(parserResult.hasWarnings());
+    }
+
     @Test
     void parseRecognizesDateFieldWithConcatenation() throws IOException {
         ParserResult result = parser