allow registering bean definitions prior to startup (#10800)

context/src/main/java/io/micronaut/runtime/Micronaut.java

@@ -18,6 +18,7 @@
 import io.micronaut.context.ApplicationContext;
 import io.micronaut.context.ApplicationContextBuilder;
 import io.micronaut.context.DefaultApplicationContextBuilder;
+import io.micronaut.context.RuntimeBeanDefinition;
 import io.micronaut.context.banner.Banner;
 import io.micronaut.context.banner.MicronautBanner;
 import io.micronaut.context.banner.ResourceBanner;
@@ -220,6 +221,11 @@ private static long elapsedMillis(long startNanos) {
         return (Micronaut) super.singletons(beans);
     }
 
+    @Override
+    public Micronaut beanDefinitions(@NonNull RuntimeBeanDefinition<?>... definitions) {
+        return (Micronaut) super.beanDefinitions(definitions);
+    }
+
     @Override
     public @NonNull Micronaut propertySources(@Nullable PropertySource... propertySources) {
         return (Micronaut) super.propertySources(propertySources);

inject-java/src/test/groovy/io/micronaut/inject/beans/RuntimeBeanDefinitionSpec.groovy

@@ -17,6 +17,19 @@ class RuntimeBeanDefinitionSpec extends AbstractTypeElementSpec {
     @Shared
     BeanContext sharedContext = BeanContext.build()
 
+    void "test runtime bean definition registered with builder"() {
+        given:
+        def foo = new Foo()
+        def context = ApplicationContext.builder()
+            .beanDefinitions(RuntimeBeanDefinition.of(foo))
+            .build()
+            .start()
+
+        expect:
+        context.getBeanDefinition(Foo)
+        context.getBean(Foo).is(foo)
+    }
+
     void 'test simple runtime bean definition'() {
         given:
 

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

@@ -96,6 +96,16 @@ public interface ApplicationContextBuilder {
      */
     @NonNull ApplicationContextBuilder singletons(@Nullable Object... beans);
 
+    /**
+     * Register additional runtime bean definitions prior to startup.
+     * @param definitions The definitions.
+     * @return The context builder
+     * @since 4.5.0
+     */
+    default @NonNull ApplicationContextBuilder beanDefinitions(@NonNull RuntimeBeanDefinition<?>... definitions) {
+        return this;
+    };
+
     /**
      * If set to {@code true} (the default is {@code true}) Micronaut will attempt to automatically deduce the environment
      * it is running in using environment variables and/or stack trace inspection.

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

@@ -49,6 +49,7 @@
  */
 public class DefaultApplicationContextBuilder implements ApplicationContextBuilder, ApplicationContextConfiguration {
     private final List<Object> singletons = new ArrayList<>();
+    private final List<RuntimeBeanDefinition<?>> beanDefinitions = new ArrayList<>();
     private final List<String> environments = new ArrayList<>();
     private final List<String> defaultEnvironments = new ArrayList<>();
     private final List<String> packages = new ArrayList<>();
@@ -153,6 +154,14 @@ public Set<Class<? extends Annotation>> getEagerInitAnnotated() {
         return this;
     }
 
+    @Override
+    public ApplicationContextBuilder beanDefinitions(@NonNull RuntimeBeanDefinition<?>... definitions) {
+        if (definitions != null) {
+            beanDefinitions.addAll(Arrays.asList(definitions));
+        }
+        return this;
+    }
+
     @Override
     public @NonNull ClassPathResourceLoader getResourceLoader() {
         if (classPathResourceLoader == null) {
@@ -346,6 +355,12 @@ public boolean isEnvironmentPropertySource() {
             }
         }
 
+        if (!beanDefinitions.isEmpty()) {
+            for (RuntimeBeanDefinition<?> beanDefinition : beanDefinitions) {
+                applicationContext.registerBeanDefinition(beanDefinition);
+            }
+        }
+
         if (!configurationIncludes.isEmpty()) {
             environment.addConfigurationIncludes(configurationIncludes.toArray(StringUtils.EMPTY_STRING_ARRAY));
         }