问题描述
搭建SpringBoot源码环境时，在spring-boot-test目录下启动一个子项目，Kotlin报错：
Warning:Kotlin: Language version 1.4 is experimental, there are no backwards compatibility guarantees for new language and library features
D:\springboot\spring-boot-2.2.x\spring-boot-project\spring-boot-autoconfigure\src\test\kotlin\org\springframework\boot\autoconfigure\diagnostics\analyzer\KotlinNoSuchBeanFailureAnalyzerNoKotlinReflectTests.kt
Error:(39, 41) Kotlin: 'use((T) -> R): R' is only available since Kotlin 1.3.50 and cannot be used in Kotlin 1.4
The compiler bundled to Kotlin plugin (1.3.21) is older than external compiler used for building modules:
spring-boot-autoconfigure (1.4.10)
This may cause different set of errors and warnings reported in IDE.
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问题原因
Kotlin版本问题，IDEA自带的Kotlin版本为1.3.21，而SpringBoot源码使用的Kotlin版本为1.4+。
解决方案
Kotlin版本升级
