highlight current line in issue editor pane (#3573)

key.ui/src/main/java/de/uka/ilkd/key/gui/actions/EditSourceFileAction.java

@@ -25,6 +25,7 @@
 import de.uka.ilkd.key.gui.sourceview.KeYEditorLexer;
 import de.uka.ilkd.key.gui.sourceview.SourceHighlightDocument;
 import de.uka.ilkd.key.gui.sourceview.TextLineNumber;
+import de.uka.ilkd.key.gui.utilities.CurrentLineHighlighter;
 import de.uka.ilkd.key.java.Position;
 import de.uka.ilkd.key.parser.Location;
 import de.uka.ilkd.key.util.ExceptionTools;
@@ -135,6 +136,7 @@ public void addNotify() {
                 textAreaGoto(this, location.getPosition());
             }
         };
+        textPane.setHighlighter(new CurrentLineHighlighter(textPane.getHighlighter()));
         Optional<URI> fileOpt = location.getFileURI();
         if (fileOpt.isEmpty()) {
             JTextPane jTextPane = new JTextPane();

key.ui/src/main/java/de/uka/ilkd/key/gui/utilities/CurrentLineHighlighter.java

@@ -0,0 +1,91 @@
+/* This file is part of KeY - https://key-project.org
+ * KeY is licensed under the GNU General Public License Version 2
+ * SPDX-License-Identifier: GPL-2.0-only */
+package de.uka.ilkd.key.gui.utilities;
+
+import java.awt.*;
+import javax.swing.text.BadLocationException;
+import javax.swing.text.Highlighter;
+import javax.swing.text.JTextComponent;
+
+/**
+ * Swing highlighter that highlights the current line in a JTextComponent.
+ *
+ * It delegates all other methods to the standard Highlighter such that it can be used as a drop-in
+ * replacement.
+ *
+ * @author Mattias Ulbrich
+ */
+public class CurrentLineHighlighter implements Highlighter {
+    private static final Color DEFAULT_COLOR = new Color(0, 0, 0, 15);
+
+    private final Highlighter delegate;
+    private final Color color;
+
+    private JTextComponent component;
+
+    public CurrentLineHighlighter(Highlighter delegate) {
+        this(delegate, DEFAULT_COLOR);
+    }
+
+    public CurrentLineHighlighter(Highlighter delegate, Color color) {
+        this.delegate = delegate;
+        this.color = color;
+    }
+
+    @Override
+    public void install(JTextComponent jTextComponent) {
+        delegate.install(jTextComponent);
+        this.component = jTextComponent;
+        component.addCaretListener(e -> component.repaint());
+    }
+
+    @Override
+    public void deinstall(JTextComponent jTextComponent) {
+        delegate.deinstall(jTextComponent);
+    }
+
+    @Override
+    public void paint(Graphics graphics) {
+        delegate.paint(graphics);
+        if (component != null) {
+            int caretPosition = component.getCaretPosition();
+            int currentRow =
+                component.getDocument().getDefaultRootElement().getElementIndex(caretPosition);
+            try {
+                Rectangle modelToView = component.modelToView(component.getDocument()
+                        .getDefaultRootElement().getElement(currentRow).getStartOffset());
+                graphics.setColor(color);
+                graphics.fillRect(0, modelToView.y, component.getWidth(), modelToView.height);
+            } catch (BadLocationException e) {
+                e.printStackTrace();
+            }
+        }
+    }
+
+    @Override
+    public Object addHighlight(int i, int i1, HighlightPainter highlightPainter)
+            throws BadLocationException {
+        return delegate.addHighlight(i, i1, highlightPainter);
+    }
+
+    @Override
+    public void removeHighlight(Object o) {
+        delegate.removeHighlight(o);
+    }
+
+    @Override
+    public void removeAllHighlights() {
+        delegate.removeAllHighlights();
+    }
+
+    @Override
+    public void changeHighlight(Object o, int i, int i1) throws BadLocationException {
+        delegate.changeHighlight(o, i, i1);
+    }
+
+    @Override
+    public Highlight[] getHighlights() {
+        return delegate.getHighlights();
+    }
+}