Fix "Recursive update' for scoped proxies (micronaut-projects#3824)

Author: dstepanov

inject/src/main/java/io/micronaut/context/DefaultBeanContext.java

@@ -107,7 +107,7 @@ public <BT extends BeanType<Object>> Stream<BT> reduce(Class<Object> beanType, S
 
     final Map<BeanKey, BeanRegistration> singletonObjects = new ConcurrentHashMap<>(100);
     final Map<BeanIdentifier, Object> singlesInCreation = new ConcurrentHashMap<>(5);
-    final Map<BeanKey, Object> scopedProxies = new ConcurrentHashMap<>(20);
+    final Map<BeanKey, Provider<Object>> scopedProxies = new ConcurrentHashMap<>(20);
 
     Set<Map.Entry<Class, List<BeanInitializedEventListener>>> beanInitializedEventListeners;
 
@@ -2313,7 +2313,7 @@ private <T> T getScopedBeanForDefinition(
             Class<?> proxiedType = resolveProxiedType(beanType, definition);
             BeanKey key = new BeanKey(proxiedType, qualifier);
             BeanDefinition<T> finalDefinition = definition;
-            return (T) scopedProxies.computeIfAbsent(key, (Function<BeanKey, T>) beanKey -> {
+            return (T) scopedProxies.computeIfAbsent(key, beanKey -> ProviderUtils.memoized(() -> {
                 Qualifier<T> q = qualifier;
                 if (q == null) {
                     q = finalDefinition.getDeclaredQualifier();
@@ -2328,7 +2328,7 @@ private <T> T getScopedBeanForDefinition(
                     throw new NoSuchBeanException(proxyDefinition.getBeanType(), qualifier);
                 }
                 return createBean;
-            });
+            })).get();
         } else {
             Optional<BeanResolutionContext.Segment<?>> currentSegment = resolutionContext.getPath().currentSegment();
             Optional<CustomScope> registeredScope = Optional.empty();

inject/src/main/java/io/micronaut/context/ProviderUtils.java

@@ -0,0 +1,82 @@
+/*
+ * Copyright 2017-2020 original 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 io.micronaut.context;
+
+
+import javax.inject.Provider;
+import javax.validation.constraints.NotNull;
+
+/**
+ * Helper methods for dealing with {@link javax.inject.Provider}.
+ *
+ * @author Denis Stepanov
+ * @since 2.0.2
+ */
+public class ProviderUtils {
+
+    /**
+     * Caches the result of provider in a thread safe manner.
+     *
+     * @param delegate The provider providing the result
+     * @param <T> The type of result
+     * @return A new provider that will cache the result
+     */
+    public static <T> Provider<T> memoized(Provider<T> delegate) {
+        return new MemoizingProvider<>(delegate);
+    }
+
+    /**
+     * A lazy provider.
+     *
+     * @param <T> The type
+     * @author Denis Stepanov
+     * @since 2.0.2
+     */
+    private static final class MemoizingProvider<T> implements Provider<T> {
+
+        private Provider<T> actual;
+        private Provider<T> delegate = this::initialize;
+        private boolean initialized;
+
+        MemoizingProvider(@NotNull Provider<T> actual) {
+            this.actual = actual;
+        }
+
+        @Override
+        public T get() {
+            return delegate.get();
+        }
+
+        private synchronized T initialize() {
+            if (!initialized) {
+                T value = actual.get();
+                delegate = () -> value;
+                initialized = true;
+                actual = null;
+            }
+            return delegate.get();
+        }
+
+        @Override
+        public String toString() {
+            if (initialized) {
+                return "Provider of " + delegate.get();
+            }
+            return "ProviderUtils.memoized(" + actual + ")";
+        }
+
+    }
+}