From d32c2a288753921b989bb1d75fb5244fffb2bc72 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Christoph=20L=C3=A4ubrich?= <laeubi@laeubi-soft.de>
Date: Sun, 30 Jun 2024 08:10:32 +0200
Subject: [PATCH] Allow interfacing with other adapter frameworks by using a
 proxy

While the Eclipse Adapter Framework is very powerful it currently  does
not allow to interface with other adaption techniques (e.g. OSGi
Converter Specification).

This adds a new way to adapt a class of objects to a proxy that then is
asked for further adaption.
---
 .../eclipse/core/runtime/AdapterProxy.java    | 58 +++++++++++++++++++
 .../org/eclipse/core/runtime/Adapters.java    |  7 +++
 2 files changed, 65 insertions(+)
 create mode 100644 bundles/org.eclipse.equinox.common/src/org/eclipse/core/runtime/AdapterProxy.java

diff --git a/bundles/org.eclipse.equinox.common/src/org/eclipse/core/runtime/AdapterProxy.java b/bundles/org.eclipse.equinox.common/src/org/eclipse/core/runtime/AdapterProxy.java
new file mode 100644
index 00000000000..0bb9274214f
--- /dev/null
+++ b/bundles/org.eclipse.equinox.common/src/org/eclipse/core/runtime/AdapterProxy.java
@@ -0,0 +1,58 @@
+/*******************************************************************************
+ * Copyright (c) 2025 Christoph Läubrich 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:
+ *     Christoph Läubrich - initial API and implementation
+ *******************************************************************************/
+package org.eclipse.core.runtime;
+
+import org.osgi.annotation.versioning.ConsumerType;
+
+/**
+ * <p>
+ * An {@link AdapterProxy} can be used to interface the Eclipse Adapter
+ * Framework with other techniques. To do so one has to provide a generic
+ * {@link IAdapterFactory} that adapts this other frameworks objects to the
+ * {@link AdapterProxy} interface, then as a last resort, the Eclipse Adapter
+ * Framework will ask this proxy as if the original object would have
+ * implemented {@link IAdaptable}.
+ * </p>
+ * <p>
+ * One example is the OSGi <a href=
+ * "https://docs.osgi.org/specification/osgi.cmpn/7.0.0/util.converter.html">Converter
+ * Specification</a> that allows to adapt/convert objects in an extensible way,
+ * therefore it is not possible to register a "classic" {@link IAdapterFactory}
+ * because the types that are probably convertible are unknown in advance. Also
+ * the objects itself can't be made to implement the {@link IAdaptable}
+ * interface. An implementation then might look like this:
+ * </p>
+ * 
+ * <pre>
+ * &#64;Component
+ * &#64;AdapterTypes(adaptableClass = Object.class, adapterNames = AdapterProxy.class)
+ * public class OSGiConverterProxyFactory implements IAdapterFactory {
+ * 
+ * 	&#64;Reference
+ * 	private Converter converter;
+ * 
+ * 	public <T> T getAdapter(Object adaptableObject, Class<T> adapterType) {
+ * 		Converting converting = converter.convert(adaptableObject);
+ * 		return converting.to(adapterType);
+ * 	}
+ * 
+ * }
+ * </pre>
+ * 
+ * @since 3.20
+ */
+@ConsumerType
+public interface AdapterProxy extends IAdaptable {
+	// This is a specialized type that do not define any methods
+}
diff --git a/bundles/org.eclipse.equinox.common/src/org/eclipse/core/runtime/Adapters.java b/bundles/org.eclipse.equinox.common/src/org/eclipse/core/runtime/Adapters.java
index a3268aa0c40..51f9e9b0593 100644
--- a/bundles/org.eclipse.equinox.common/src/org/eclipse/core/runtime/Adapters.java
+++ b/bundles/org.eclipse.equinox.common/src/org/eclipse/core/runtime/Adapters.java
@@ -82,6 +82,13 @@ public static <T> T adapt(Object sourceObject, Class<T> adapter, boolean allowAc
 
 		String adapterId = adapter.getName();
 		Object result = queryAdapterManager(sourceObject, adapterId, allowActivation);
+		if (result == null) {
+			// Last resort, this object is maybe using a different adaption technique
+			if (queryAdapterManager(sourceObject, AdapterProxy.class.getName(),
+					allowActivation) instanceof AdapterProxy proxy) {
+				result = proxy.getAdapter(adapter);
+			}
+		}
 		if (result != null) {
 			// Sanity-check
 			if (!adapter.isInstance(result)) {