I asked this question on the dev list, but didn't get a response here. (My original question to the dev list: https://sematext.com/opensee/m/F2svI1cI2oW1CwdmF1?subj=readers+using+writer+s+aliases+ )
It also seems this question was asked before in late 2018, but dead-ended at https://sematext.com/opensee/m/Avro/F2svI1obxDi4WGqf1?subj=Re+Alias+with+Backward+Compatibility Avro aliases are typically used by *reader* schemas to rename fields. (I.e., readers can expect "first-name" string and use an alias "firts-name" to deal with old writer's that had it mispelled in the original writer schema.) This is backwards compatibility (new readers can read old writers). However we would like to not have to update reader code to deal with new writers (ie we want *forward* compatibility with aliases). It seems that this should be easy: (old) readers could look at the new writer-defined aliases and leverage them for forward compatibility while doing schema resolution. Concrete example: my old schema expects "firts-name"; my new schema fixes this by introducing "first-name" with the "firts-name" as an alias. Instead of being obligated to update my old reader(s), couldn't the schema resolution logic notice this alias and *invert* the aliasing as it reads the data to give the old reader the field it expects? Is there a fundamental reason that this isn't part of the avro java impl, or spec documentation? Not having to coordinate updates to readers during schema evolution (field renames) would be a huge win imo.
