FlywayAutoConfiguration filesystem: prefix fails

[andyrbell]

Flyway locations can be prefixed with "classpath: or "filesystem:".

FlywayAutoConfiguration by default checks at least one location exists.

That check fails when using the "filesystem:" prefix due to:

java.net.MalformedURLException: unknown protocol: filesystem

which results in the following:

Caused by: java.lang.IllegalStateException: Cannot find migrations location in: [filesystem:src/main/resources/db/migration] (please add migrations or check your Flyway configuration)
    at org.springframework.util.Assert.state(Assert.java:94)
    at org.springframework.boot.autoconfigure.flyway.FlywayAutoConfiguration$FlywayConfiguration.checkLocationExists(FlywayAutoConfiguration.java:168)
    at org.springframework.boot.autoconfigure.flyway.FlywayAutoConfiguration$FlywayConfiguration.flyway(FlywayAutoConfiguration.java:152)
    at org.springframework.boot.autoconfigure.flyway.FlywayAutoConfiguration$FlywayConfiguration$$EnhancerBySpringCGLIB$$65b82c95.CGLIB$flyway$1(<generated>)
    at org.springframework.boot.autoconfigure.flyway.FlywayAutoConfiguration$FlywayConfiguration$$EnhancerBySpringCGLIB$$65b82c95$$FastClassBySpringCGLIB$$bf4a67a0.invoke(<generated>)
    at org.springframework.cglib.proxy.MethodProxy.invokeSuper(MethodProxy.java:228)
    at org.springframework.context.annotation.ConfigurationClassEnhancer$BeanMethodInterceptor.intercept(ConfigurationClassEnhancer.java:361)
    at org.springframework.boot.autoconfigure.flyway.FlywayAutoConfiguration$FlywayConfiguration$$EnhancerBySpringCGLIB$$65b82c95.flyway(<generated>)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at org.springframework.beans.factory.support.SimpleInstantiationStrategy.instantiate(SimpleInstantiationStrategy.java:154)
    ... 70 more

If the prefix is changed to "file:", the FlywayAutoConfiguration check succeeds but then Flyway throws an exception:

Caused by: org.flywaydb.core.api.FlywayException: Unknown prefix for location (should be either filesystem: or classpath:): file:src/main/resources/db/migration
    at org.flywaydb.core.api.Location.<init>(Location.java:71) ~[flyway-core-5.1.4.jar:na]
    at org.flywaydb.core.internal.util.Locations.<init>(Locations.java:46) ~[flyway-core-5.1.4.jar:na]
    at org.flywaydb.core.api.configuration.ClassicConfiguration.setLocationsAsStrings(ClassicConfiguration.java:864) ~[flyway-core-5.1.4.jar:na]
    at org.flywaydb.core.Flyway.setLocations(Flyway.java:518) ~[flyway-core-5.1.4.jar:na]
    at org.springframework.boot.autoconfigure.flyway.FlywayAutoConfiguration$SpringBootFlyway.setLocations(FlywayAutoConfiguration.java:285) ~[spring-boot-autoconfigure-2.1.0.BUILD-SNAPSHOT.jar:2.1.0.BUILD-SNAPSHOT]
    at org.springframework.boot.autoconfigure.flyway.FlywayAutoConfiguration$FlywayConfiguration.flyway(FlywayAutoConfiguration.java:175) ~[spring-boot-autoconfigure-2.1.0.BUILD-SNAPSHOT.jar:2.1.0.BUILD-SNAPSHOT]
    at org.springframework.boot.autoconfigure.flyway.FlywayAutoConfiguration$FlywayConfiguration$$EnhancerBySpringCGLIB$$ae83b85c.CGLIB$flyway$0(<generated>) ~[spring-boot-autoconfigure-2.1.0.BUILD-SNAPSHOT.jar:2.1.0.BUILD-SNAPSHOT]
    at org.springframework.boot.autoconfigure.flyway.FlywayAutoConfiguration$FlywayConfiguration$$EnhancerBySpringCGLIB$$ae83b85c$$FastClassBySpringCGLIB$$d56b3dc1.invoke(<generated>) ~[spring-boot-autoconfigure-2.1.0.BUILD-SNAPSHOT.jar:2.1.0.BUILD-SNAPSHOT]
    at org.springframework.cglib.proxy.MethodProxy.invokeSuper(MethodProxy.java:244) ~[spring-core-5.1.0.BUILD-SNAPSHOT.jar:5.1.0.BUILD-SNAPSHOT]
    at org.springframework.context.annotation.ConfigurationClassEnhancer$BeanMethodInterceptor.intercept(ConfigurationClassEnhancer.java:361) ~[spring-context-5.1.0.BUILD-SNAPSHOT.jar:5.1.0.BUILD-SNAPSHOT]
    at org.springframework.boot.autoconfigure.flyway.FlywayAutoConfiguration$FlywayConfiguration$$EnhancerBySpringCGLIB$$ae83b85c.flyway(<generated>) ~[spring-boot-autoconfigure-2.1.0.BUILD-SNAPSHOT.jar:2.1.0.BUILD-SNAPSHOT]
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_161]
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:1.8.0_161]
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_161]
    at java.lang.reflect.Method.invoke(Method.java:498) ~[na:1.8.0_161]
    at org.springframework.beans.factory.support.SimpleInstantiationStrategy.instantiate(SimpleInstantiationStrategy.java:154) ~[spring-beans-5.1.0.BUILD-SNAPSHOT.jar:5.1.0.BUILD-SNAPSHOT]
    ... 70 common frames omitted

A workaround is to disable the check:

spring.flyway.check-location=false

This repository replicates the issue: https://github.com/andyrbell/spring-boot-flyway-issue

These various issues appear relate to the same problem:

https://stackoverflow.com/questions/49572576/spring-boot-flyway-autoconfiguration
flyway/flyway#1982
#13190

[snicoll]

@andyrbell thanks for raising this and the PR. Let's continue the discussion on the latter.