Proguard breaks Flyway database migration

Question

Posting this self-answered so when I break it again in a few months an answer will actually come up in google.

Simple Java project where Flyway API is used to migrate database schema. A resource directory of sql scripts following the V1__init.sql, V2__updateCustomerTable.sql convention is used to check against the schema_version metadata table and migrate if needed.

Everything works fine until the jar is proguarded. The sql scripts are definitely packed into the jar file, but they are not found:

2017-04-10 17:17:13,612 [main] DEBUG (?:?) - Validating migrations ...
2017-04-10 17:17:13,884 [main] DEBUG (?:?) - Scanning for classpath resources at 'classpath:db/migration/postgres' (Prefix: '', Suffix: '.sql')
2017-04-10 17:17:13,885 [main] DEBUG (?:?) - Determining location urls for classpath:db/migration/postgres using ClassLoader sun.misc.Launcher$AppClassLoader@8b819f ...
2017-04-10 17:17:13,885 [main] WARN  (?:?) - Unable to resolve location classpath:db/migration/postgres
2017-04-10 17:17:13,899 [main] DEBUG (?:?) - Scanning for classpath resources at 'classpath:db/migration/postgres' (Prefix: 'V', Suffix: '.sql')
2017-04-10 17:17:13,900 [main] DEBUG (?:?) - Scanning for classpath resources at 'classpath:db/migration/postgres' (Prefix: 'R', Suffix: '.sql')

An un-proguarded jar finds them with the following log messages (note that it looks in the jar file now):

2017-04-10 17:07:16,612 [main] DEBUG (?:?) - Validating migrations ...
2017-04-10 17:07:16,613 [main] DEBUG (?:?) - Scanning for classpath resources at 'classpath:db/migration/postgres' (Prefix: 'V', Suffix: '.sql')
2017-04-10 17:07:16,614 [main] DEBUG (?:?) - Scanning URL: jar:file:/C:/Dev/Sanbox/myjar.jar!/db/migration/postgres
2017-04-10 17:07:16,614 [main] DEBUG (?:?) - JBoss VFS v2 available: false
2017-04-10 17:07:16,615 [main] DEBUG (?:?) - Filtering out resource: db/migration/postgres/ (filename: )
2017-04-10 17:07:16,615 [main] DEBUG (?:?) - Found resource: db/migration/postgres/V1__init.sql
2017-04-10 17:07:16,616 [main] DEBUG (?:?) - Found resource: db/migration/postgres/V2__updateCustomerTable.sql

Answer 1

The culprit was that you need to tell proguard to leave your db/migrations directory alone (or wherever you put your migration scripts) in your config file, else flyway will not be able to find your scripts even if they seem to be in the right place in the jar. This is the line I needed in my proguard config:

-keepdirectories db/migration/**

If you change where you put your sql scripts down the road, this config will also need to be updated.