Support for alter database statement

[fujin]

I have an empty Spanner database (created with Terraform) which, during creation, is creating a DDL like this:

ALTER DATABASE test SET OPTIONS (
  version_retention_period = '7d'
);

When I run the diff tool, I get an error here:

Exception in thread "main" java.lang.IllegalArgumentException: Unsupported statement type: alter_database_statement
    at com.google.cloud.solutions.spannerddl.diff.DdlDiff.separateTablesIndexesConstraints(DdlDiff.java:539)
    at com.google.cloud.solutions.spannerddl.diff.DdlDiff.build(DdlDiff.java:483)
    at com.google.cloud.solutions.spannerddl.diff.DdlDiff.main(DdlDiff.java:638)

As far as I can tell, the tool doesn't allow for a non-default version_retention_period to be set via ALTER DATABASE, as it cannot parse the ALTER DATABASE statement.

We have two potential workarounds and wanted to know your input:

• Text process the input ddl to remove the ALTER DATABASE
• Implement the alter_database_statement so parsing works, make it noop? Or actually support ALTER DATABASE settings.

[zhiwei-arbo]

jfyi for anyone looking at this, in my own fork I made it a no-op here (warn instead of throw)

It also seems possible to parse it by creating the relevant ASTXXX files, but I don't have such a use case yet