Fix 592: RTextArea.setUI should not override non-UIResource Fonts

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

@@ -359,7 +359,10 @@ protected void installDefaults() {
 		super.installDefaults();
 
 		JTextComponent editor = getComponent();
-		editor.setFont(RTextAreaBase.getDefaultFont());
+		Font f = editor.getFont();
+		if (f == null || f instanceof UIResource) {
+			editor.setFont(RTextAreaBase.getDefaultFont());
+		}
 
 		// Nimbus (and possibly other Synth lafs) doesn't play by BasicLaf
 		// rules and doesn't set properties needed by custom BasicTextAreaUI's.
@@ -410,7 +413,7 @@ protected void installKeyboardActions() {
 	@Override
 	public void installUI(JComponent c) {
 		if (!(c instanceof RTextArea)) {
-			throw new Error("RTextAreaUI needs an instance of RTextArea!");
+			throw new IllegalArgumentException("RTextAreaUI needs an instance of RTextArea!");
 		}
 		super.installUI(c);
 	}

RSyntaxTextArea/src/test/java/org/fife/ui/rtextarea/RTextAreaUITest.java

@@ -0,0 +1,152 @@
+/*
+ * This library is distributed under a modified BSD license.  See the included
+ * LICENSE file for details.
+ */
+package org.fife.ui.rtextarea;
+
+import org.fife.ui.SwingRunnerExtension;
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.extension.ExtendWith;
+
+import javax.swing.*;
+import javax.swing.plaf.FontUIResource;
+import java.awt.*;
+
+
+/**
+ * Unit tests for {@code RTextAreaUI}.
+ */
+@ExtendWith(SwingRunnerExtension.class)
+class RTextAreaUITest extends AbstractRTextAreaTest {
+
+	@Test
+	void testCreateUI_error_notRTextArea() {
+		Assertions.assertThrows(IllegalArgumentException.class,
+			() -> RTextAreaUI.createUI(new JTextArea()));
+	}
+
+	@Test
+	void testCreateUI_happyPath() {
+		Assertions.assertDoesNotThrow(() -> RTextAreaUI.createUI(new RTextArea()));
+	}
+
+	@Test
+	void testInstallDefaults_doesNotOverrideRegularFont() {
+
+		RTextArea textArea = new RTextArea();
+		Font oldFont = new Font(FontUIResource.DIALOG, FontUIResource.ITALIC, 23);
+		textArea.setFont(oldFont);
+
+		RTextAreaUI ui = (RTextAreaUI)textArea.getUI();
+		ui.installDefaults();
+		Assertions.assertEquals(oldFont, textArea.getFont());
+	}
+
+	@Test
+	void testInstallDefaults_overridesFontUIResource() {
+
+		RTextArea textArea = new RTextArea();
+		Font oldFont = new FontUIResource(FontUIResource.DIALOG, FontUIResource.ITALIC, 23);
+		textArea.setFont(oldFont);
+
+		RTextAreaUI ui = (RTextAreaUI)textArea.getUI();
+		ui.installDefaults();
+		Assertions.assertEquals(RTextArea.getDefaultFont(), textArea.getFont());
+	}
+
+	@Test
+	void testInstallDefaults_overridesNullFont() {
+
+		RTextArea textArea = new RTextArea();
+		textArea.setFont(null);
+
+		RTextAreaUI ui = (RTextAreaUI)textArea.getUI();
+		ui.installDefaults();
+		Assertions.assertEquals(RTextArea.getDefaultFont(), textArea.getFont());
+	}
+
+	@Test
+	void testInstallUI_error_notRTextArea() {
+		Assertions.assertThrows(IllegalArgumentException.class, () -> {
+			RTextAreaUI ui = new RTextAreaUI(new RTextArea());
+			ui.installUI(new JTextArea());
+		}, "RTextAreaUI needs an instance of RTextArea!");
+	}
+
+	@Test
+	void testInstallUI_happyPath() {
+		Assertions.assertDoesNotThrow(() -> {
+			RTextArea textArea = new RTextArea();
+			RTextAreaUI ui = new RTextAreaUI(textArea);
+			ui.installUI(textArea);
+		});
+	}
+
+	@Test
+	void testPaintBackground_nullBackground_noError() {
+		Assertions.assertDoesNotThrow(() -> {
+			RTextArea textArea = new RTextArea();
+			RTextAreaUI ui = new RTextAreaUI(textArea);
+			ui.installUI(textArea);
+			textArea.setBackground(null);
+			ui.paintBackground(createTestGraphics());
+		});
+	}
+
+	@Test
+	void testPaintCurrentLineHighlight_false() {
+		Assertions.assertDoesNotThrow(() -> {
+			RTextArea textArea = new RTextArea();
+			RTextAreaUI ui = new RTextAreaUI(textArea);
+			ui.installUI(textArea);
+			textArea.setHighlightCurrentLine(false);
+			ui.paintCurrentLineHighlight(createTestGraphics(), textArea.getVisibleRect());
+		});
+	}
+
+	@Test
+	void testPaintCurrentLineHighlight_true() {
+		Assertions.assertDoesNotThrow(() -> {
+			RTextArea textArea = new RTextArea();
+			RTextAreaUI ui = new RTextAreaUI(textArea);
+			ui.installUI(textArea);
+			textArea.setHighlightCurrentLine(true);
+			ui.paintCurrentLineHighlight(createTestGraphics(), textArea.getVisibleRect());
+		});
+	}
+
+	@Test
+	void testPaintCurrentLineHighlight_true_andFadeCurrentLineHighlight() {
+		Assertions.assertDoesNotThrow(() -> {
+			RTextArea textArea = new RTextArea();
+			RTextAreaUI ui = new RTextAreaUI(textArea);
+			ui.installUI(textArea);
+			textArea.setHighlightCurrentLine(true);
+			textArea.setFadeCurrentLineHighlight(true);
+			ui.paintCurrentLineHighlight(createTestGraphics(), textArea.getVisibleRect());
+		});
+	}
+
+	@Test
+	void testPaintMarginLine_false() {
+		Assertions.assertDoesNotThrow(() -> {
+			RTextArea textArea = new RTextArea();
+			RTextAreaUI ui = new RTextAreaUI(textArea);
+			ui.installUI(textArea);
+			textArea.setMarginLineEnabled(false);
+			ui.paintMarginLine(createTestGraphics(), textArea.getVisibleRect());
+		});
+	}
+
+	@Test
+	void testPaintMarginLine_true() {
+		Assertions.assertDoesNotThrow(() -> {
+			RTextArea textArea = new RTextArea();
+			RTextAreaUI ui = new RTextAreaUI(textArea);
+			ui.installUI(textArea);
+			textArea.setMarginLineEnabled(true);
+			ui.paintMarginLine(createTestGraphics(), textArea.getVisibleRect());
+		});
+	}
+}