[feature] possibility to implement custom line number formatting

RSyntaxTextArea/src/main/java/org/fife/ui/rtextarea/Gutter.java

@@ -102,6 +102,11 @@ public class Gutter extends JPanel {
 	 */
 	private int lineNumberingStartIndex;
 
+	/**
+	 * Formats line numbers into a string to be displayed.
+	 */
+	private LineNumberFormatter lineNumberFormatter;
+
 	/**
 	 * The font used to render line numbers.
 	 */
@@ -152,6 +157,7 @@ public Gutter(RTextArea textArea) {
 		lineNumberColor = LineNumberList.DEFAULT_LINE_NUMBER_COLOR;
 		lineNumberFont = RTextArea.getDefaultFont();
 		lineNumberingStartIndex = 1;
+		lineNumberFormatter = LineNumberList.DEFAULT_LINE_NUMBER_FORMATTER;
 		iconRowHeaderInheritsGutterBackground = false;
 
 		setTextArea(textArea);
@@ -438,6 +444,17 @@ public int getLineNumberingStartIndex() {
 		return lineNumberingStartIndex;
 	}
 
+	/**
+	 * Returns the line number formatter. The default value is
+	 * {@link LineNumberList#DEFAULT_LINE_NUMBER_FORMATTER}
+	 *
+	 * @return The formatter
+	 * @see #setLineNumberFormatter(LineNumberFormatter)
+	 */
+	public LineNumberFormatter getLineNumberFormatter() {
+		return lineNumberFormatter;
+	}
+
 
 	/**
 	 * Returns <code>true</code> if the line numbers are enabled and visible.
@@ -919,6 +936,21 @@ public void setLineNumberingStartIndex(int index) {
 	}
 
 
+	/**
+	 * Sets a custom line number formatter. Can be called when other number
+	 * formats are needed like hindu-arabic numerals.
+	 *
+	 * @param formatter The new line number formatter
+	 * @see #getLineNumberFormatter()
+	 */
+	public void setLineNumberFormatter(LineNumberFormatter formatter) {
+		if (formatter != lineNumberFormatter) {
+			lineNumberFormatter = formatter;
+			lineNumberList.setLineNumberFormatter(formatter);
+		}
+	}
+
+
 	/**
 	 * Toggles whether line numbers are visible.<p>
 	 *
@@ -1004,6 +1036,8 @@ public void setTextArea(RTextArea textArea) {
 					getCurrentLineNumberColor());
 				lineNumberList.setLineNumberingStartIndex(
 						getLineNumberingStartIndex());
+				lineNumberList.setLineNumberFormatter(
+					getLineNumberFormatter());
 			}
 			else {
 				lineNumberList.setTextArea(textArea);

RSyntaxTextArea/src/main/java/org/fife/ui/rtextarea/LineNumberFormatter.java

@@ -0,0 +1,32 @@
+/*
+ * 29/07/2023
+ *
+ * LineNumber - Format line numbers into a comprehensible String.
+ *
+ * This library is distributed under a modified BSD license.  See the included
+ * LICENSE file for details.
+ */
+package org.fife.ui.rtextarea;
+
+/**
+ * Formats line numbers into a comprehensible String to be
+ * displayed to the user.
+ * */
+public interface LineNumberFormatter {
+	/**
+	 * Formats the given line number into a String.
+	 *
+	 * @param lineNumber the line number
+	 * @return the formatted line number
+	 */
+	String format(int lineNumber);
+
+	/**
+	 * Returns the maximum number of characters of any string returned
+	 * by {@link #format} provided a certain maximum line number.
+	 *
+	 * @param maxLineNumber the maximum line number
+	 * @return the maximum length
+	 */
+	int getMaxLength(int maxLineNumber);
+}

RSyntaxTextArea/src/main/java/org/fife/ui/rtextarea/LineNumberList.java

@@ -82,13 +82,19 @@ public class LineNumberList extends AbstractGutterComponent
 	 */
 	private int lineNumberingStartIndex;
 
+	/**
+	 * Formats line numbers into a string to be displayed.
+	 */
+	private LineNumberFormatter lineNumberFormatter = DEFAULT_LINE_NUMBER_FORMATTER;
+
 	/**
 	 * The color of current line number.
 	 */
 	private Color currentLineNumberColor;
 
 	public static final Color DEFAULT_LINE_NUMBER_COLOR = Color.GRAY;
 
+	public static final LineNumberFormatter DEFAULT_LINE_NUMBER_FORMATTER = new SimpleLineNumberFormatter();
 
 	/**
 	 * Constructs a new <code>LineNumberList</code> using default values for
@@ -197,6 +203,18 @@ public int getLineNumberingStartIndex() {
 	}
 
 
+	/**
+	 * Returns the line number formatter. The default value is
+	 * {@link LineNumberList#DEFAULT_LINE_NUMBER_FORMATTER}
+	 *
+	 * @return The formatter
+	 * @see #setLineNumberFormatter(LineNumberFormatter)
+	 */
+	public LineNumberFormatter getLineNumberFormatter() {
+		return lineNumberFormatter;
+	}
+
+
 	@Override
 	public Dimension getPreferredSize() {
 		int h = textArea!=null ? textArea.getHeight() : 100; // Arbitrary
@@ -392,7 +410,7 @@ protected void paintComponent(Graphics g) {
 			int rhs = getWidth() - rhsBorderWidth;
 			int line = topLine + 1; // TODO: Simplify me
 			while (y<visibleRect.y+visibleRect.height+ascent && line<=textArea.getLineCount()) {
-				String number = Integer.toString(line + getLineNumberingStartIndex() - 1);
+				String number = getLineNumberFormatter().format(line + getLineNumberingStartIndex() - 1);
 				int width = metrics.stringWidth(number);
 				if (currentLine + 1 == line + getLineNumberingStartIndex() - 1) {
 					Color color = currentLineNumberColor != null ? currentLineNumberColor :
@@ -659,6 +677,22 @@ public void setLineNumberingStartIndex(int index) {
 	}
 
 
+	/**
+	 * Sets a custom line number formatter. Can be called when other number
+	 * formats are needed like hindu-arabic numerals.
+	 *
+	 * @param formatter The new line number formatter
+	 * @see #getLineNumberFormatter()
+	 */
+	public void setLineNumberFormatter(LineNumberFormatter formatter) {
+		if (formatter != lineNumberFormatter) {
+			lineNumberFormatter = formatter;
+			updateCellWidths();
+			repaint();
+		}
+	}
+
+
 	/**
 	 * Sets the text area being displayed.
 	 *
@@ -719,13 +753,11 @@ void updateCellWidths() {
 			Font font = getFont();
 			if (font!=null) {
 				FontMetrics fontMetrics = getFontMetrics(font);
-				int count = 0;
 				int lineCount = textArea.getLineCount() +
 						getLineNumberingStartIndex() - 1;
-				do {
-					lineCount = lineCount/10;
-					count++;
-				} while (lineCount >= 10);
+				LineNumberFormatter formatter = getLineNumberFormatter() == null?
+					DEFAULT_LINE_NUMBER_FORMATTER: getLineNumberFormatter();
+				int count = formatter.getMaxLength(lineCount);
 				cellWidth += fontMetrics.charWidth('9')*(count+1) + 3;
 			}
 		}
@@ -817,4 +849,23 @@ public void uninstall(RTextArea textArea) {
 	}
 
 
+	private static class SimpleLineNumberFormatter implements LineNumberFormatter {
+		@Override
+		public String format(int lineNumber) {
+			return Integer.toString(lineNumber);
+		}
+
+		@Override
+		public int getMaxLength(int maxLineNumber) {
+			int count = 0;
+			do {
+				maxLineNumber = maxLineNumber /10;
+				count++;
+			} while (maxLineNumber >= 10);
+
+			return count;
+		}
+	}
+
+
 }

RSyntaxTextAreaDemo/src/main/java/org/fife/ui/rsyntaxtextarea/demo/DemoRootPane.java

@@ -25,6 +25,8 @@
 import org.fife.ui.rtextarea.FoldIndicatorStyle;
 import org.fife.ui.rtextarea.Gutter;
 import org.fife.ui.rtextarea.RTextScrollPane;
+import org.fife.ui.rtextarea.LineNumberFormatter;
+import org.fife.ui.rtextarea.LineNumberList;
 
 
 /**
@@ -140,6 +142,18 @@ private JMenuBar createMenuBar() {
 		foldStyleSubMenu.add(classicStyleItem);
 		foldStyleSubMenu.add(modernStyleItem);
 		menu.add(foldStyleSubMenu);
+		JMenu lineNumberFormatSubMenu = new JMenu("Line Number Format");
+		JRadioButtonMenuItem normalStyleItem = new JRadioButtonMenuItem(
+			new LineNumberFormatAction("Normal", LineNumberList.DEFAULT_LINE_NUMBER_FORMATTER));
+		JRadioButtonMenuItem hinduArabicStyleItem = new JRadioButtonMenuItem(
+			new LineNumberFormatAction("Hindu-Arabic", new HinduArabicLineNumberFormatter()));
+		normalStyleItem.setSelected(true);
+		bg = new ButtonGroup();
+		bg.add(normalStyleItem);
+		bg.add(hinduArabicStyleItem);
+		lineNumberFormatSubMenu.add(normalStyleItem);
+		lineNumberFormatSubMenu.add(hinduArabicStyleItem);
+		menu.add(lineNumberFormatSubMenu);
 		JCheckBoxMenuItem cbItem = new JCheckBoxMenuItem(new CodeFoldingAction());
 		cbItem.setSelected(true);
 		menu.add(cbItem);
@@ -409,6 +423,25 @@ public void actionPerformed(ActionEvent e) {
 
 	}
 
+	/**
+	 * Changes how line numbers are displayed.
+	 */
+	private class LineNumberFormatAction extends AbstractAction {
+
+		private final LineNumberFormatter formatter;
+
+		LineNumberFormatAction(String name, LineNumberFormatter formatter) {
+			this.formatter = formatter;
+			putValue(NAME, name);
+		}
+
+		@Override
+		public void actionPerformed(ActionEvent e) {
+			scrollPane.getGutter().setLineNumberFormatter(formatter);
+		}
+
+	}
+
 	/**
 	 * Changes the look and feel of the demo application.
 	 */
@@ -561,5 +594,35 @@ public void actionPerformed(ActionEvent e) {
 
 	}
 
+	/**
+	 * Formats line numbers into Hindu-Arabic numerals.
+	 */
+	private static class HinduArabicLineNumberFormatter implements LineNumberFormatter {
+		private static final String[] NUMERALS = {
+			"٠", "١", "٢", "٣", "٤", "٥", "٦", "٧", "٨", "٩"
+		};
+
+		@Override
+		public String format(int lineNumber) {
+			if (lineNumber == 0) {
+				return NUMERALS[0];
+			}
+
+			StringBuilder sb = new StringBuilder();
+			while (lineNumber > 0) {
+				int digit = lineNumber % 10;
+				sb.insert(0, NUMERALS[digit]);
+				lineNumber /= 10;
+			}
+
+			return sb.toString();
+		}
+
+		@Override
+		public int getMaxLength(int maxLineNumber) {
+			return String.valueOf(maxLineNumber).length();
+		}
+	}
+
 
 }