fix: dispose description window when toggled off, not just hide it

AutoComplete/src/main/java/org/fife/ui/autocomplete/AutoCompletePopupWindow.java

@@ -296,6 +296,36 @@ public Color getDescriptionWindowColor() {
     }
 
 
+	/**
+	 * Returns the description window, if it has been created.
+	 *
+	 * @return The description window, or {@code null} if it has not been
+	 *         created yet.
+	 */
+	AutoCompleteDescWindow getDescWindow() {
+		return descWindow;
+	}
+
+
+	/**
+	 * Disposes of the description window, if it has been created, and
+	 * discards our reference to it so it is lazily recreated the next time
+	 * it's needed. Simply hiding the description window is not enough here;
+	 * on some Linux/X11 window managers, quickly toggling a {@code JWindow}
+	 * visible and then invisible can leave a blank "ghost" window on screen
+	 * that never gets un-mapped or repainted. Disposing of the native peer
+	 * avoids that.
+	 *
+	 * @see AutoCompletion#setShowDescWindow(boolean)
+	 */
+	void disposeDescWindow() {
+		if (descWindow != null) {
+			descWindow.dispose();
+			descWindow = null;
+		}
+	}
+
+
 	/**
 	 * Returns the default list cell renderer used when a completion provider
 	 * does not supply its own.

AutoComplete/src/main/java/org/fife/ui/autocomplete/AutoCompletion.java

@@ -802,6 +802,11 @@ public boolean isPopupVisible() {
 		return popupWindow != null && popupWindow.isVisible();
 	}
 
+	// Returns the completion popup window, or null if not created yet.
+	AutoCompletePopupWindow getPopupWindow() {
+		return popupWindow;
+	}
+
 
 	/**
 	 * Refreshes the popup window. First, this method gets the possible
@@ -1151,6 +1156,11 @@ protected void setPopupVisible(boolean visible) {
 	 */
 	public void setShowDescWindow(boolean show) {
 		hidePopupWindow(); // Needed to force it to take effect
+		if (!show && popupWindow != null) {
+			// Dispose (rather than hide) the desc window on toggle-off, to avoid a
+			// Linux/X11 "ghost" window bug when hiding it instead; see issue #84.
+			popupWindow.disposeDescWindow();
+		}
 		showDescWindow = show;
 	}
 

AutoComplete/src/test/java/org/fife/ui/autocomplete/AutoCompletionTest.java

@@ -0,0 +1,88 @@
+/*
+ * This library is distributed under a modified BSD license.  See the included
+ * LICENSE.md file for details.
+ */
+package org.fife.ui.autocomplete;
+
+import java.awt.GraphicsEnvironment;
+import javax.swing.JFrame;
+import javax.swing.JTextArea;
+
+import org.junit.jupiter.api.AfterEach;
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Assumptions;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+
+class AutoCompletionTest {
+
+	private JFrame frame;
+
+
+	@BeforeEach
+	void setUp() {
+		Assumptions.assumeFalse(GraphicsEnvironment.isHeadless());
+	}
+
+
+	@AfterEach
+	void tearDown() {
+		if (frame != null) {
+			frame.dispose();
+			frame = null;
+		}
+	}
+
+
+	/**
+	 * Regression test for https://github.com/bobbylight/AutoComplete/issues/84 -
+	 * merely hiding the description window when it's toggled off could leave
+	 * a blank "ghost" window on screen on some Linux/X11 window managers.
+	 * The fix disposes of the description window's native peer instead of
+	 * just hiding it, so it must be lazily recreated the next time it's
+	 * shown.
+	 */
+	@Test
+	void setShowDescWindow_false_disposesExistingDescWindow() {
+
+		DefaultCompletionProvider provider = new DefaultCompletionProvider();
+		provider.addCompletion(new BasicCompletion(provider, "foo", "foo's summary"));
+		provider.addCompletion(new BasicCompletion(provider, "foobar", "foobar's summary"));
+
+		AutoCompletion ac = new AutoCompletion(provider);
+		ac.setShowDescWindow(true);
+		ac.setAutoCompleteEnabled(true);
+
+		JTextArea textArea = new JTextArea();
+		ac.install(textArea);
+
+		frame = new JFrame();
+		frame.add(textArea);
+		frame.pack();
+		frame.setVisible(true);
+
+		textArea.setText("foo");
+		textArea.setCaretPosition(textArea.getText().length());
+		ac.doCompletion();
+
+		AutoCompletePopupWindow popupWindow = ac.getPopupWindow();
+		Assertions.assertNotNull(popupWindow,
+				"Popup window should have been created by doCompletion()");
+		AutoCompleteDescWindow descWindow = popupWindow.getDescWindow();
+		Assertions.assertNotNull(descWindow,
+				"Description window should have been created since showDescWindow was true");
+		Assertions.assertTrue(descWindow.isDisplayable(),
+				"Description window's native peer should exist while showing");
+
+		ac.setShowDescWindow(false);
+
+		Assertions.assertNull(popupWindow.getDescWindow(),
+				"Description window should be disposed and discarded, not just hidden");
+		Assertions.assertFalse(descWindow.isDisplayable(),
+				"Description window's native peer should be destroyed by dispose()");
+
+	}
+
+
+}