Reintroduce previous EnvironmentPostProcessor in deprecated form

Restore previous `EnvironmentPostProcessor` in deprecated form to help
lessen upgrade pain.

Closes gh-47272

Author: philwebb

buildSrc/src/main/java/org/springframework/boot/build/architecture/ArchitectureRules.java

@@ -130,7 +130,12 @@ static ArchRule allBeanMethodsShouldReturnNonPrivateType() {
 	}
 
 	private static ArchRule allPackagesShouldBeFreeOfTangles() {
-		return SlicesRuleDefinition.slices().matching("(**)").should().beFreeOfCycles();
+		return SlicesRuleDefinition.slices()
+			.matching("(**)")
+			.should()
+			.beFreeOfCycles()
+			.ignoreDependency("org.springframework.boot.env.EnvironmentPostProcessor",
+					"org.springframework.boot.SpringApplication");
 	}
 
 	private static ArchRule allBeanPostProcessorBeanMethodsShouldBeStaticAndNotCausePrematureInitialization() {

core/spring-boot/src/main/java/org/springframework/boot/env/EnvironmentPostProcessor.java

@@ -0,0 +1,65 @@
+/*
+ * Copyright 2012-present the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.boot.env;
+
+import org.springframework.boot.bootstrap.BootstrapContext;
+import org.springframework.boot.bootstrap.BootstrapRegistry;
+import org.springframework.boot.bootstrap.ConfigurableBootstrapContext;
+import org.springframework.boot.logging.DeferredLogFactory;
+import org.springframework.core.env.ConfigurableEnvironment;
+import org.springframework.core.env.Environment;
+
+/**
+ * Allows for customization of the application's {@link Environment} prior to the
+ * application context being refreshed.
+ * <p>
+ * EnvironmentPostProcessor implementations have to be registered in
+ * {@code META-INF/spring.factories}, using the fully qualified name of this class as the
+ * key. Implementations may implement the {@link org.springframework.core.Ordered Ordered}
+ * interface or use an {@link org.springframework.core.annotation.Order @Order} annotation
+ * if they wish to be invoked in specific order.
+ * <p>
+ * Since Spring Boot 2.4, {@code EnvironmentPostProcessor} implementations may optionally
+ * take the following constructor parameters:
+ * <ul>
+ * <li>{@link DeferredLogFactory} - A factory that can be used to create loggers with
+ * output deferred until the application has been fully prepared (allowing the environment
+ * itself to configure logging levels).</li>
+ * <li>{@link ConfigurableBootstrapContext} - A bootstrap context that can be used to
+ * store objects that may be expensive to create, or need to be shared
+ * ({@link BootstrapContext} or {@link BootstrapRegistry} may also be used).</li>
+ * </ul>
+ *
+ * @author Andy Wilkinson
+ * @author Stephane Nicoll
+ * @since 1.3.0
+ * @deprecated since 4.0.0 for removal in 4.2.0 in favor of
+ * {@link org.springframework.boot.EnvironmentPostProcessor}
+ */
+@FunctionalInterface
+@Deprecated(since = "4.0.0", forRemoval = true)
+public interface EnvironmentPostProcessor {
+
+	/**
+	 * Post-process the given {@code environment}.
+	 * @param environment the environment to post-process
+	 * @param application the application to which the environment belongs
+	 */
+	void postProcessEnvironment(ConfigurableEnvironment environment,
+			org.springframework.boot.SpringApplication application);
+
+}

core/spring-boot/src/main/java/org/springframework/boot/support/SpringFactoriesEnvironmentPostProcessorsFactory.java

@@ -16,13 +16,18 @@
 
 package org.springframework.boot.support;
 
+import java.util.ArrayList;
 import java.util.List;
+import java.util.stream.Collectors;
 
 import org.springframework.boot.EnvironmentPostProcessor;
+import org.springframework.boot.SpringApplication;
 import org.springframework.boot.bootstrap.BootstrapContext;
 import org.springframework.boot.bootstrap.BootstrapRegistry;
 import org.springframework.boot.bootstrap.ConfigurableBootstrapContext;
 import org.springframework.boot.logging.DeferredLogFactory;
+import org.springframework.core.annotation.AnnotationAwareOrderComparator;
+import org.springframework.core.env.ConfigurableEnvironment;
 import org.springframework.core.io.support.SpringFactoriesLoader;
 import org.springframework.core.io.support.SpringFactoriesLoader.ArgumentResolver;
 
@@ -46,7 +51,34 @@ public List<EnvironmentPostProcessor> getEnvironmentPostProcessors(DeferredLogFa
 		argumentResolver = argumentResolver.and(ConfigurableBootstrapContext.class, bootstrapContext);
 		argumentResolver = argumentResolver.and(BootstrapContext.class, bootstrapContext);
 		argumentResolver = argumentResolver.and(BootstrapRegistry.class, bootstrapContext);
-		return this.loader.load(EnvironmentPostProcessor.class, argumentResolver);
+		List<Object> postProcessors = new ArrayList<>();
+		postProcessors.addAll(this.loader.load(EnvironmentPostProcessor.class, argumentResolver));
+		postProcessors.addAll(loadDeprecatedPostProcessors());
+		AnnotationAwareOrderComparator.sort(postProcessors);
+		return postProcessors.stream().map(Adapter::apply).collect(Collectors.toCollection(ArrayList::new));
+	}
+
+	@SuppressWarnings("removal")
+	private List<org.springframework.boot.env.EnvironmentPostProcessor> loadDeprecatedPostProcessors() {
+		return this.loader.load(org.springframework.boot.env.EnvironmentPostProcessor.class);
+	}
+
+	@SuppressWarnings("removal")
+	record Adapter(
+			org.springframework.boot.env.EnvironmentPostProcessor postProcessor) implements EnvironmentPostProcessor {
+
+		@Override
+		public void postProcessEnvironment(ConfigurableEnvironment environment, SpringApplication application) {
+			this.postProcessor.postProcessEnvironment(environment, application);
+		}
+
+		static EnvironmentPostProcessor apply(Object source) {
+			if (source instanceof EnvironmentPostProcessor environmentPostProcessor) {
+				return environmentPostProcessor;
+			}
+			return new Adapter((org.springframework.boot.env.EnvironmentPostProcessor) source);
+		}
+
 	}
 
 }