Support noarg callable references in Kotlin beans DSL

Closes gh-23395

Author: sdeleuze

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

@@ -236,6 +236,42 @@ open class BeanDefinitionDsl internal constructor (private val init: BeanDefinit
 		context.registerBean(beanName, T::class.java, Supplier { function.invoke(BeanSupplierContext(context)) }, customizer)
 	}
 
+	/**
+	 * Declare a bean definition using the given callable reference with no parameter
+	 * for obtaining a new instance.
+	 *
+	 * @param f the callable reference
+	 * @param name the name of the bean
+	 * @param scope Override the target scope of this bean, specifying a new scope name.
+	 * @param isLazyInit Set whether this bean should be lazily initialized.
+	 * @param isPrimary Set whether this bean is a primary autowire candidate.
+	 * @param isAutowireCandidate Set whether this bean is a candidate for getting
+	 * autowired into some other bean.
+	 * @param initMethodName Set the name of the initializer method
+	 * @param destroyMethodName Set the name of the destroy method
+	 * @param description Set a human-readable description of this bean definition
+	 * @param role Set the role hint for this bean definition
+	 * @see GenericApplicationContext.registerBean
+	 * @see org.springframework.beans.factory.config.BeanDefinition
+	 * @since 5.2.3
+	 */
+	inline fun <reified T: Any>
+			bean(crossinline f: () -> T,
+				 name: String? = null,
+				 scope: BeanDefinitionDsl.Scope? = null,
+				 isLazyInit: Boolean? = null,
+				 isPrimary: Boolean? = null,
+				 isAutowireCandidate: Boolean? = null,
+				 initMethodName: String? = null,
+				 destroyMethodName: String? = null,
+				 description: String? = null,
+				 role: BeanDefinitionDsl.Role? = null) {
+
+		bean(name, scope, isLazyInit, isPrimary, isAutowireCandidate, initMethodName, destroyMethodName, description, role) {
+			f.invoke()
+		}
+	}
+
 	/**
 	 * Declare a bean definition using the given callable reference with 1 parameter
 	 * autowired by type for obtaining a new instance.

spring-context/src/test/kotlin/org/springframework/context/support/BeanDefinitionDslTests.kt

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2019 the original author or authors.
+ * Copyright 2002-2020 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.
@@ -156,6 +156,7 @@ class BeanDefinitionDslTests {
 		val beans = beans {
 			bean<Bar>()
 			bean(::baz)
+			bean(::foo)
 		}
 		val context = GenericApplicationContext().apply {
 			beans.initialize(this)
@@ -205,3 +206,4 @@ class FooFoo(val name: String)
 class BarBar(val foos: Collection<Foo>)
 
 fun baz(bar: Bar) = Baz(bar)
+fun foo() = Foo()