Document DataSource implementations supported by DataSourceBuilder

[snicoll]

Spring Boot supports a number of DataSources using DataSourceProperties but the level of support is not the same. Some datasources have dedicated support (with fine-grained properties support) and we have a best effort support for others if the user opt-in for that explicitly using .type.

That best effort is mostly about aliasing core properties (such as mapping setUserName to setUser). In 2.4.x we only map an alias for a datasource we know about (rather than just adding such alias regardless of the type).

We should document those so that it's clear that if the user opt-in for a type, this may or may not be supported.

[tinselspoon]

Please could this also be added to the release notes? I just hit this issue and couldn't find an indication that the behaviour had changed from the upgrade notes.

[snicoll]

What issue did you hit exactly? Please also review #25263 (comment)

[tinselspoon]

It was the issue described in that linked comment in that the user -> username alias is no longer being applied (although in our case we were using a PGSimpleDataSource). Having a heads-up about this change in the release notes would be good for the folks relying on this without realising it, as it would have always "just worked" before.

[snicoll]

@tinselspoon this infrastructure is meant to be used only with the DataSource implementations that Spring Boot supports officially and PGSimpleDataSource isn't one of them. It was working so far by accident. Having said that and since we manage it I am inclined to add an explicit alias for it.

See #25363