library/
      |__autoconfigure/
                      |__datasource/
                                   |__DataSourceAutoConfiguration.java
                                   |__PrimaryDataSourceConfiguration.java
                                   |__SecondaryDataSourceConfiguration.java
      |__datasource/
                   |__CustomRepository.java
      |
      |__datasource-spring-boot-starter/

@Configuration
@ConditionalOnBean({DataSource.class})
@ConditionalOnClass({JpaRepository.class})
public class DataSourceAutoConfiguration {

}

@Configuration
@EnableTransactionManagement
@EnableJpaRepositories(
    entityManagerFactoryRef = "entityManagerFactory",
    )
public class PrimaryDataSourceConfiguration {

    @Primary
    @Bean(name = "dataSource")
    @ConfigurationProperties(prefix = "service.datasource")
    public DataSource dataSource() {
        return DataSourceBuilder.create().build();
    }

    @Primary
    @Bean(name = "entityManagerFactory")
    public LocalContainerEntityManagerFactoryBean
        entityManagerFactory(
        EntityManagerFactoryBuilder builder,
        @Qualifier("dataSource") DataSource dataSource
        ) {
        return builder
                .dataSource(dataSource)
            .build();
    }

    @Primary
    @Bean(name = "transactionManager")
    public PlatformTransactionManager transactionManager(
        @Qualifier("entityManagerFactory") EntityManagerFactory
        entityManagerFactory
        ) {
        return new JpaTransactionManager(entityManagerFactory);
    }
}

datasource:
  hikari:
    jdbc-url: jdbc:mysql://localhost:3306/test
    username: root
    password: root
    driver-class-name: com.mysql.jdbc.Driver

Caused by: java.lang.IllegalArgumentException: dataSource or dataSourceClassName or jdbcUrl is required.
at com.zaxxer.hikari.HikariConfig.validate(HikariConfig.java:1063) ~[HikariCP-2.7.9.jar:?]