Avoid duplicate extensions when creating scripts

Detect the script language from the supplied title before normalizing the
filename. This lets the editor recognize an existing extension and prevents
names such as Macro.ijm.ijm. Add regression coverage for already-suffixed
filenames.

Closes #78

Co-authored-by: Copilot <copilot@github.com>

Author: hinerm

src/main/java/org/scijava/ui/swing/script/TextEditor.java

@@ -102,14 +102,38 @@
 import java.util.concurrent.ExecutionException;
 import java.util.jar.JarEntry;
 import java.util.jar.JarOutputStream;
-import java.util.zip.ZipException;
 import java.util.regex.Matcher;
 import java.util.regex.Pattern;
+import java.util.zip.ZipException;
 
 import javax.script.ScriptEngine;
 import javax.script.ScriptException;
-import javax.swing.*;
-import javax.swing.border.BevelBorder;
+import javax.swing.AbstractAction;
+import javax.swing.AbstractButton;
+import javax.swing.BoxLayout;
+import javax.swing.ButtonGroup;
+import javax.swing.JButton;
+import javax.swing.JCheckBoxMenuItem;
+import javax.swing.JDialog;
+import javax.swing.JFrame;
+import javax.swing.JLabel;
+import javax.swing.JMenu;
+import javax.swing.JMenuBar;
+import javax.swing.JMenuItem;
+import javax.swing.JOptionPane;
+import javax.swing.JPanel;
+import javax.swing.JPopupMenu;
+import javax.swing.JRadioButtonMenuItem;
+import javax.swing.JScrollPane;
+import javax.swing.JSplitPane;
+import javax.swing.JTabbedPane;
+import javax.swing.JTextArea;
+import javax.swing.JTextField;
+import javax.swing.JTextPane;
+import javax.swing.JTree;
+import javax.swing.KeyStroke;
+import javax.swing.SwingUtilities;
+import javax.swing.UIManager;
 import javax.swing.event.ChangeEvent;
 import javax.swing.event.ChangeListener;
 import javax.swing.event.DocumentEvent;
@@ -1569,9 +1593,8 @@ public void createNewDocument(final String title, final String text) {
 		open(null);
 		final EditorPane editorPane = getEditorPane();
 		editorPane.setText(text);
-		setEditorPaneFileName(title);
-
 		editorPane.setLanguageByFileName(title);
+		setEditorPaneFileName(title);
 		updateLanguageMenu(editorPane.getCurrentLanguage());
 	}
 

src/test/java/org/scijava/ui/swing/script/EditorPaneFileNameTest.java

@@ -0,0 +1,34 @@
+package org.scijava.ui.swing.script;
+
+import static org.junit.Assert.assertEquals;
+
+import org.junit.After;
+import org.junit.Before;
+import org.junit.Test;
+import org.scijava.Context;
+
+public class EditorPaneFileNameTest {
+
+	private Context context;
+
+	@Before
+	public void setUp() {
+		context = new Context();
+	}
+
+	@After
+	public void tearDown() {
+		context.dispose();
+	}
+
+	@Test
+	public void testSuppliedLanguageExtensionIsNotDuplicated() {
+		final EditorPane editorPane = new EditorPane();
+		context.inject(editorPane);
+
+		editorPane.setLanguageByFileName("Macro.java");
+		editorPane.setFileName("Macro.java");
+
+		assertEquals("Macro.java", editorPane.getFileName());
+	}
+}