Generated YAML changelogs do not contain necessary modifySql items

[SanjayVas]

I'm trying to generate an initial YAML changelog from an existing Spanner database. I find that the generated YAML doesn't contain the necessary modifySql items for things like INTERLEAVE IN PARENT or OPTIONS (allow_commit_timestamp = true).

[SanjayVas]

Likely related to #85

[olavloite]

Likely related to #85

This is indeed the same issue as #85. Interleaved tables and column options are Spanner specific features that don't really fit that well into the model of Liquibase, as they cannot really be mapped directly to a generic SQL feature. (Column options might actually be a little easier than interleaved tables)

[SanjayVas]

I believe the expectation is that changelogs should be round-trippable. That is to say that if you have DB A created from a Liquibase changelog and try to create a DB B from A with Liquibase (e.g. using generate-changelog) then B should be equivalent to A.

My concern is that the limitations of the current implementation would also mean that operations such as diff, snapshot, etc. won't work as expected. At minimum, this should be clearly documented in limitations.md. Right now, it's unclear that these operations would not work as expected. In fact, the doc seems to imply that it would work as it describes how these Spanner features can be represented in a Liquibase changelog.