Limit ref() and provider() visibility in Kotlin DSL

This commit makes ref() and provider() only available from
inside the bean lambda and not from the root level of the beans DSL.

Closes gh-22177

Author: sdeleuze

spring-context/src/main/kotlin/org/springframework/context/support/BeanDefinitionDsl.kt

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2018 the original author or authors.
+ * Copyright 2002-2019 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.
@@ -83,7 +83,7 @@ open class BeanDefinitionDsl(private val init: BeanDefinitionDsl.() -> Unit,
 	internal val children = arrayListOf<BeanDefinitionDsl>()
 
 	/**
-	 * @see provider
+	 * @see BeanSupplierContext
 	 */
 	@PublishedApi
 	internal lateinit var context: GenericApplicationContext
@@ -217,7 +217,7 @@ open class BeanDefinitionDsl(private val init: BeanDefinitionDsl.() -> Unit,
 									  destroyMethodName: String? = null,
 									  description: String? = null,
 									  role: Role? = null,
-									  crossinline function: () -> T) {
+									  crossinline function: BeanSupplierContext.() -> T) {
 
 		val customizer = BeanDefinitionCustomizer { bd ->
 			scope?.let { bd.scope = scope.name.toLowerCase() }
@@ -232,29 +232,35 @@ open class BeanDefinitionDsl(private val init: BeanDefinitionDsl.() -> Unit,
 
 
 		val beanName = name ?: BeanDefinitionReaderUtils.uniqueBeanName(T::class.java.name, context);
-		context.registerBean(beanName, T::class.java, Supplier { function.invoke() }, customizer)
+		context.registerBean(beanName, T::class.java, Supplier { function.invoke(BeanSupplierContext(context)) }, customizer)
 	}
 
 	/**
-	 * Get a reference to the bean by type or type + name with the syntax
-	 * `ref<Foo>()` or `ref<Foo>("foo")`. When leveraging Kotlin type inference
-	 * it could be as short as `ref()` or `ref("foo")`.
-	 * @param name the name of the bean to retrieve
-	 * @param T type the bean must match, can be an interface or superclass
+	 * Limit access to `ref()` and `provider()` to bean supplier lambdas.
+	 * @since 5.2
 	 */
-	inline fun <reified T : Any> ref(name: String? = null) : T = when (name) {
-		null -> context.getBean(T::class.java)
-		else -> context.getBean(name, T::class.java)
-	}
+	open class BeanSupplierContext(@PublishedApi internal val context: GenericApplicationContext) {
 
+		/**
+		 * Get a reference to the bean by type or type + name with the syntax
+		 * `ref<Foo>()` or `ref<Foo>("foo")`. When leveraging Kotlin type inference
+		 * it could be as short as `ref()` or `ref("foo")`.
+		 * @param name the name of the bean to retrieve
+		 * @param T type the bean must match, can be an interface or superclass
+		 */
+		inline fun <reified T : Any> ref(name: String? = null) : T = when (name) {
+			null -> context.getBean(T::class.java)
+			else -> context.getBean(name, T::class.java)
+		}
 
-	/**
-	 * Return an provider for the specified bean, allowing for lazy on-demand retrieval
-	 * of instances, including availability and uniqueness options.
-	 * @since 5.1.1
-	 * @see org.springframework.beans.factory.BeanFactory.getBeanProvider
-	 */
-	inline fun <reified T : Any> provider() : ObjectProvider<T> = context.getBeanProvider()
+		/**
+		 * Return an provider for the specified bean, allowing for lazy on-demand retrieval
+		 * of instances, including availability and uniqueness options.
+		 * @see org.springframework.beans.factory.BeanFactory.getBeanProvider
+		 */
+		inline fun <reified T : Any> provider() : ObjectProvider<T> = context.getBeanProvider()
+
+	}
 
 	/**
 	 * Take in account bean definitions enclosed in the provided lambda only when the