Error on JDT configuration ignoring OSGi restrictions

ui/org.eclipse.pde.core/src/org/eclipse/pde/internal/core/PDECoreMessages.java

@@ -261,6 +261,8 @@ public class PDECoreMessages extends NLS {
 
 	public static String BuildErrorReporter_BuildEntryNotRequiredMatchesDefault;
 
+	public static String BuildErrorReporter_classpathAccessRulesDiscarded;
+
 	public static String BuildErrorReporter_sourceMissing;
 
 	public static String BuildErrorReporter_srcIncludesSourceFolder;

ui/org.eclipse.pde.core/src/org/eclipse/pde/internal/core/builders/BuildErrorReporter.java

@@ -162,6 +162,10 @@ public void addAttributes(Map<String, String> attributes) {
 	protected int fSrcLibSeverity;
 	protected int fOutputLibSeverity;
 	protected int fEncodingSeverity;
+	protected int fJDCTClasspathMissconfigurationSeverity = Boolean
+			.getBoolean("pde.acceptDiscardedForbiddenAccessRules") //$NON-NLS-1$
+					? CompilerFlags.WARNING
+					: CompilerFlags.ERROR;
 
 	public BuildErrorReporter(IFile buildFile) {
 		super(buildFile);
@@ -1108,6 +1112,13 @@ private void validateJavaCompilerSettings(IBuildEntry useJavaProjectSettings) {
 				String message = NLS.bind(PDECoreMessages.BuildErrorReporter_buildEntryInvalidWhenNoProjectSettings, PROPERTY_PROJECT_SETTINGS);
 				prepareCompilerError(PROPERTY_PROJECT_SETTINGS, null, message, PDEMarkerFactory.B_REMOVAL);
 			}
+
+			String forbiddenReferenceSeverity = options.get(JavaCore.COMPILER_PB_FORBIDDEN_REFERENCE);
+			if (forbiddenReferenceSeverity != null && !forbiddenReferenceSeverity.equals(JavaCore.ERROR)) {
+				String message = NLS.bind(PDECoreMessages.BuildErrorReporter_classpathAccessRulesDiscarded);
+				prepareError(null, null, message, PDEMarkerFactory.B_CLASSPATH_ACCESS_RULES,
+						fJDCTClasspathMissconfigurationSeverity, null, PDEMarkerFactory.CAT_OTHER);
+			}
 		}
 	}
 

ui/org.eclipse.pde.core/src/org/eclipse/pde/internal/core/builders/PDEMarkerFactory.java

@@ -91,6 +91,7 @@ public class PDEMarkerFactory {
 	public static final int B_REMOVAL = 0x2005;
 	public static final int B_REPLACE = 0x2006;
 	public static final int B_JAVA_ADDDITION = 0x2007;
+	public static final int B_CLASSPATH_ACCESS_RULES = 0x2008;
 
 	// plugin.xml fixes
 	public static final int P_ILLEGAL_XML_NODE = 0x3001;

ui/org.eclipse.pde.core/src/org/eclipse/pde/internal/core/pderesources.properties

@@ -103,6 +103,7 @@ BuildErrorReporter_buildEntryMissingProjectSpecificSettings=The ''{0}'' build en
 BuildErrorReporter_buildEntryMissingValidPath=The ''{0}'' build entry does not contain ''true'' or a path to an existing properties file
 BuildErrorReporter_buildEntryMissingValidRelativePath=The ''{0}'' build entry does not contain a path to an existing properties file
 BuildErrorReporter_BuildEntryNotRequiredMatchesDefault=The ''{0}'' build entry is not required because it matches the default value
+BuildErrorReporter_classpathAccessRulesDiscarded=OSGi access rules not enforced by classpath access rules, which can lead to classloading errors at runtime.
 BuildErrorReporter_entiresMustRefDirs={0}: entries ending in / must reference directories
 Builders_Manifest_deprecated_rootElement = The extension point ''{0}'' is deprecated
 BuildErrorReporter_classpathEntryMissing={0} is not included in any "source.*" build entry

ui/org.eclipse.pde.ui/src/org/eclipse/pde/internal/ui/PDEUIMessages.java

@@ -3461,5 +3461,6 @@ public class PDEUIMessages extends NLS {
 
 	public static String AddMatchingVersion;
 	public static String AddMatchingVersionDescription;
+	public static String EnableStrictClasspathAccessRules_label;
 
 }

ui/org.eclipse.pde.ui/src/org/eclipse/pde/internal/ui/correction/EnforceForbiddenAccessClasspathRules.java

@@ -0,0 +1,55 @@
+/*******************************************************************************
+ *  Copyright (c) 2026 Hannes Wellmann and others.
+ *
+ *  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:
+ *     Hannes Wellmann - initial API and implementation
+ *******************************************************************************/
+package org.eclipse.pde.internal.ui.correction;
+
+import org.eclipse.core.resources.IMarker;
+import org.eclipse.core.resources.IProject;
+import org.eclipse.core.resources.ProjectScope;
+import org.eclipse.core.runtime.ILog;
+import org.eclipse.core.runtime.preferences.IEclipsePreferences;
+import org.eclipse.jdt.core.JavaCore;
+import org.eclipse.pde.core.IBaseModel;
+import org.eclipse.pde.internal.ui.PDEUIMessages;
+import org.osgi.service.prefs.BackingStoreException;
+
+public class EnforceForbiddenAccessClasspathRules extends AbstractPDEMarkerResolution {
+
+	public EnforceForbiddenAccessClasspathRules(IMarker marker) {
+		super(AbstractPDEMarkerResolution.CONFIGURE_TYPE, marker);
+	}
+
+	@Override
+	public String getLabel() {
+		return PDEUIMessages.EnableStrictClasspathAccessRules_label;
+	}
+
+	@Override
+	public void run(IMarker marker) {
+		IProject project = marker.getResource().getProject();
+		IEclipsePreferences node = new ProjectScope(project).getNode("org.eclipse.jdt.core"); //$NON-NLS-1$
+		try {
+			node.sync();
+			node.put(JavaCore.COMPILER_PB_FORBIDDEN_REFERENCE, JavaCore.ERROR);
+			node.flush();
+		} catch (BackingStoreException e) {
+			ILog.get().error("Failed to update JDT Core preferences", e); //$NON-NLS-1$
+		}
+	}
+
+	@Override
+	protected void createChange(IBaseModel model) {
+		// handled by run
+	}
+}
+

ui/org.eclipse.pde.ui/src/org/eclipse/pde/internal/ui/correction/ResolutionGenerator.java

@@ -117,6 +117,8 @@ public IMarkerResolution[] getNonConfigSevResolutions(IMarker marker) {
 				return new IMarkerResolution[] {new RemoveBuildEntryResolution(AbstractPDEMarkerResolution.REMOVE_TYPE, marker)};
 			case PDEMarkerFactory.B_REPLACE :
 				return new IMarkerResolution[] {new ReplaceBuildEntryResolution(AbstractPDEMarkerResolution.RENAME_TYPE, marker)};
+			case PDEMarkerFactory.B_CLASSPATH_ACCESS_RULES:
+				return new IMarkerResolution[] { new EnforceForbiddenAccessClasspathRules(marker) };
 			case PDEMarkerFactory.P_ILLEGAL_XML_NODE :
 				return new IMarkerResolution[] {new RemoveNodeXMLResolution(AbstractPDEMarkerResolution.REMOVE_TYPE, marker)};
 			case PDEMarkerFactory.P_UNTRANSLATED_NODE :

ui/org.eclipse.pde.ui/src/org/eclipse/pde/internal/ui/pderesources.properties

@@ -1310,6 +1310,7 @@ UpdateClasspathJob_task = Update classpaths...
 UpdateClasspathJob_title = Updating Plug-in Classpaths
 AddMatchingVersion = Require latest available version range
 AddMatchingVersionDescription = Add a version range aligned with the latest compatible available version
+EnableStrictClasspathAccessRules_label=Enable strict enforcement of classpath access rules
 
 RuntimeWorkbenchShortcut_title=Select Configuration
 RuntimeWorkbenchShortcut_select_debug=Select a launch configuration to debug: