Fix for entering a backslash in the custom entry preview dialog

CHANGELOG.md

@@ -111,6 +111,7 @@ Note that this project **does not** adhere to [Semantic Versioning](http://semve
 - We fixed an issue where the RFC fetcher is not compatible with the draft [7305](https://github.com/JabRef/jabref/issues/7305)
 - We fixed an issue where duplicate files (both file names and contents are the same) is downloaded and add to linked files [#6197](https://github.com/JabRef/jabref/issues/6197)
 - We fixed an issue where changing the appearance of the preview tab did not trigger a restart warning. [#5464](https://github.com/JabRef/jabref/issues/5464)
+- We fixed an issue where editing "Custom preview style" triggers exception. [#7526](https://github.com/JabRef/jabref/issues/7526)
 - We fixed an issue where a title with multiple applied formattings in EndNote was not imported correctly [forum#2734](https://discourse.jabref.org/t/importing-endnote-label-field-to-jabref-from-xml-file/2734)
 - We fixed an issue where a `report` in EndNote was imported as `article` [forum#2734](https://discourse.jabref.org/t/importing-endnote-label-field-to-jabref-from-xml-file/2734)
 - We fixed an issue where the field `publisher` in EndNote was not imported in JabRef [forum#2734](https://discourse.jabref.org/t/importing-endnote-label-field-to-jabref-from-xml-file/2734)

src/main/java/org/jabref/logic/layout/LayoutHelper.java

@@ -188,7 +188,7 @@ private void doBracketedOptionField() throws IOException {
         }
     }
 
-    private void parse() throws IOException, StringIndexOutOfBoundsException {
+    private void parse() throws IOException {
         skipWhitespace();
 
         int c;
@@ -254,11 +254,15 @@ private void parseField() throws IOException {
 
                 if (name.isEmpty()) {
                     StringBuilder lastFive = new StringBuilder(10);
-                    for (StringInt entry : parsedEntries.subList(Math.max(0, parsedEntries.size() - 6),
-                            parsedEntries.size() - 1)) {
-                        lastFive.append(entry.s);
+                    if (parsedEntries.isEmpty()) {
+                        lastFive.append("unknown");
+                    } else {
+                        for (StringInt entry : parsedEntries.subList(Math.max(0, parsedEntries.size() - 6),
+                                parsedEntries.size() - 1)) {
+                            lastFive.append(entry.s);
+                        }
                     }
-                    throw new StringIndexOutOfBoundsException(
+                    throw new IOException(
                             "Backslash parsing error near \'" + lastFive.toString().replace("\n", " ") + '\'');
                 }
 

src/test/java/org/jabref/logic/layout/LayoutHelperTest.java

@@ -0,0 +1,39 @@
+package org.jabref.logic.layout;
+
+import java.io.IOException;
+import java.io.StringReader;
+
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertNotNull;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+import static org.mockito.Mockito.mock;
+
+class LayoutHelperTest {
+
+    @Test
+    public void backslashDoesNotTriggerException() {
+        StringReader stringReader = new StringReader("\\");
+        LayoutFormatterPreferences layoutFormatterPreferences = mock(LayoutFormatterPreferences.class);
+        LayoutHelper layoutHelper = new LayoutHelper(stringReader, layoutFormatterPreferences);
+        assertThrows(IOException.class, () -> layoutHelper.getLayoutFromText());
+    }
+
+    @Test
+    public void unbalancedBeginEndIsParsed() throws Exception {
+        StringReader stringReader = new StringReader("\\begin{doi}, DOI: \\doi");
+        LayoutFormatterPreferences layoutFormatterPreferences = mock(LayoutFormatterPreferences.class);
+        LayoutHelper layoutHelper = new LayoutHelper(stringReader, layoutFormatterPreferences);
+        Layout layout = layoutHelper.getLayoutFromText();
+        assertNotNull(layout);
+    }
+
+    @Test
+    public void minimalExampleWithDoiGetsParsed() throws Exception {
+        StringReader stringReader = new StringReader("\\begin{doi}, DOI: \\doi\\end{doi}");
+        LayoutFormatterPreferences layoutFormatterPreferences = mock(LayoutFormatterPreferences.class);
+        LayoutHelper layoutHelper = new LayoutHelper(stringReader, layoutFormatterPreferences);
+        Layout layout = layoutHelper.getLayoutFromText();
+        assertNotNull(layout);
+    }
+}