Draw completion proposals always as focused

When opening the completion proposals via the keyboard, the focus will stay in the editor to be able to accept further user input. This is causing the completion proposal to be drawn in non focus colors. This colors can lead to UX problems, especially in dark theme.
With this fix, the completion proposals are always drawn in focused colors.

Fixes #1688

Author: Christopher-Hermann

bundles/org.eclipse.jface.text/src/org/eclipse/jface/contentassist/CompletionProposalDrawSupport.java

@@ -0,0 +1,59 @@
+/*******************************************************************************
+ * Copyright (c) 2024 SAP SE.
+ *
+ * This program and the accompanying materials
+ * are made available under the terms of the Eclipse Public License 2.0
+ * which accompanies this distribution, and is available at
+ * https://www.eclipse.org/legal/epl-2.0/
+ *
+ * SPDX-License-Identifier: EPL-2.0
+ *
+ * Contributors:
+ *     SAP SE - initial API and implementation
+ *******************************************************************************/
+package org.eclipse.jface.contentassist;
+
+import org.eclipse.swt.SWT;
+import org.eclipse.swt.graphics.Color;
+import org.eclipse.swt.widgets.Event;
+import org.eclipse.swt.widgets.Listener;
+import org.eclipse.swt.widgets.Table;
+
+import org.eclipse.jface.internal.text.TableOwnerDrawSupport;
+
+/**
+ * Provides custom drawing support for completion proposals. This class ensures that completion
+ * proposals are always rendered with a focused appearance.
+ *
+ * <p>
+ * This drawing behavior addresses the particular situation where the code completion is triggered
+ * via keyboard shortcut, leaving the editor focused. In such cases, without this custom drawing
+ * support, the completion proposal would appear unfocused, leading to a suboptimal coloring.
+ * </p>
+ */
+public class CompletionProposalDrawSupport implements Listener {
+
+	private TableOwnerDrawSupport fTableOwnerDrawSupport;
+
+	private CompletionProposalDrawSupport(Table table) {
+		fTableOwnerDrawSupport= new TableOwnerDrawSupport(table);
+	}
+
+	public static void install(Table table) {
+		CompletionProposalDrawSupport listener= new CompletionProposalDrawSupport(table);
+		table.addListener(SWT.Dispose, listener);
+		table.addListener(SWT.MeasureItem, listener);
+		table.addListener(SWT.EraseItem, listener);
+		table.addListener(SWT.PaintItem, listener);
+	}
+
+	@Override
+	public void handleEvent(Event event) {
+		Color background= event.item.getDisplay().getSystemColor(SWT.COLOR_TITLE_BACKGROUND);
+		Color forground= event.item.getDisplay().getSystemColor(SWT.COLOR_WHITE);
+		event.gc.setBackground(background);
+		event.gc.setForeground(forground);
+		fTableOwnerDrawSupport.handleEvent(event);
+	}
+
+}

bundles/org.eclipse.jface.text/src/org/eclipse/jface/internal/text/TableOwnerDrawSupport.java

@@ -70,7 +70,7 @@ private static StyleRange[] getStyledRanges(TableItem item, int column) {
 		return (StyleRange[])item.getData(STYLED_RANGES_KEY + column);
 	}
 
-	private TableOwnerDrawSupport(Table table) {
+	public TableOwnerDrawSupport(Table table) {
 		int orientation= table.getStyle() & (SWT.LEFT_TO_RIGHT | SWT.RIGHT_TO_LEFT);
 		fSharedLayout= new TextLayout(table.getDisplay());
 		fSharedLayout.setOrientation(orientation);

bundles/org.eclipse.jface.text/src/org/eclipse/jface/internal/text/link/contentassist/CompletionProposalPopup2.java

@@ -39,6 +39,7 @@
 import org.eclipse.swt.widgets.Table;
 import org.eclipse.swt.widgets.TableItem;
 
+import org.eclipse.jface.contentassist.CompletionProposalDrawSupport;
 import org.eclipse.jface.internal.text.TableOwnerDrawSupport;
 import org.eclipse.jface.preference.JFacePreferences;
 import org.eclipse.jface.resource.ColorRegistry;
@@ -269,7 +270,7 @@ private void createProposalSelector() {
 
 		fIsColoredLabelsSupportEnabled= fContentAssistant.isColoredLabelsSupportEnabled();
 		if (fIsColoredLabelsSupportEnabled)
-			TableOwnerDrawSupport.install(fProposalTable);
+			CompletionProposalDrawSupport.install(fProposalTable);
 
 		fProposalTable.setLocation(0, 0);
 		if (fAdditionalInfoController != null)

bundles/org.eclipse.jface.text/src/org/eclipse/jface/text/contentassist/CompletionProposalPopup.java

@@ -76,6 +76,7 @@
 
 import org.eclipse.jface.bindings.keys.KeySequence;
 import org.eclipse.jface.bindings.keys.SWTKeySupport;
+import org.eclipse.jface.contentassist.CompletionProposalDrawSupport;
 import org.eclipse.jface.contentassist.IContentAssistSubjectControl;
 import org.eclipse.jface.internal.text.InformationControlReplacer;
 import org.eclipse.jface.internal.text.TableOwnerDrawSupport;
@@ -613,7 +614,7 @@ void createProposalSelector() {
 
 		fIsColoredLabelsSupportEnabled= fContentAssistant.isColoredLabelsSupportEnabled();
 		if (fIsColoredLabelsSupportEnabled)
-			TableOwnerDrawSupport.install(fProposalTable);
+			CompletionProposalDrawSupport.install(fProposalTable);
 
 		fProposalTable.setLocation(0, 0);
 		if (fAdditionalInfoController != null)