Previously, if a ConfigurationProperties had a nested type or was
extending from a type located outside the compilation unit, no
metadata discovered on the source code was available (documentation and
explicit default value, if any). This typically happens when such a type
resides in another module.
This commit introduces `@ConfigurationPropertiesSource` as a way to
annotate such type and have metadata generated for them in their own
module.
Type-metadata is generated as one file per type and is reused
transparently whenever that type is used. As for module metadata, an
additional file can be crafted manually and will be merged when the
metadata for the type is generated.
The following is an example structure with two types where one has
an additional metadata:
META-iNF/
spring/
configuration-properties/
additional/
com.example.SourceOne.json
com.example.SourceOne.json
com.example.SourceTwo.json
Those files are used only by the annotation processor and are not meant
to be public API.
See gh-18366
b3f35baed3