[jira] [Created] (AVRO-3904) [rust] Sometimes when calculating schema compatibility the code panics but maybe it should not

["Marcos (Jira)" <ji...@apache.org>]

Marcos created AVRO-3904:
----------------------------

             Summary: [rust] Sometimes when calculating schema compatibility the code panics but maybe it should not
                 Key: AVRO-3904
                 URL: https://issues.apache.org/jira/browse/AVRO-3904
             Project: Apache Avro
          Issue Type: Improvement
            Reporter: Marcos


When calculating the *schema compatibility can read* (schema A can read or not an event written using a schema B) we expect a *true* or *false* result, but in some cases the code *panics with a message* (reason of schema not being compatible) ** which I think it should not.

Example:

{code:js}
let schema_1 = Schema::parse_str(
r#"{
    "type": "record",
    "name": "StatisticsMap",
    "fields": [
        {"name": "success", "type": {"type": "map", "values": "int"}}
    ]
}"#)?;

let schema_2 = Schema::parse_str(
    r#"{
"type": "record",
"name": "StatisticsMap",
"fields": [
    {"name": "success", "type": ["null", {"type": "map", "values": "int"}], "default": null}
]
}"#)?

assert!(SchemaCompatibility::can_read(&schema_1, &schema_2)); # true as expected


assert!(SchemaCompatibility::can_read(&schema_2, &schema_1));

The application panicked (crashed).
Message:  internal error: entered unreachable code: writers_schema should have been Schema::Map
 

{code}

PS: If the intention is to give feedback to end users when schemas are not compatible then it makes sense the panic (maybe a Result should be better?) but the feedback should be present in every time that the result is false, which is not the case.

I have a PR ready to fix this in case that we want to change the current behaviour



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