AVRO-3649: Fix for union type to match default values for any innertype

[clesaec]

What is the purpose of the change

Change the logic on Union type to validate a value (default value in particular) for AVRO-3649. Instead of check value with first union inner type, try with inner type until find a match.

Verifying this change

Some test were updated.

Documentation

• Does this pull request introduce a new feature? no

[KalleOlaviNiemitalo]

Does this pull request introduce a new feature? no

It does. This would have to be documented and implemented for other languages too.

If there is a union ["string", "bytes"], and the default value is a string, then this won't know which member was meant. That may be ok for nullable fields but makes the feature a bit more complex to document.

[clesaec]

For bytes, even this code doesn't work

    Schema schemaBytes = Schema.create(Type.BYTES);
    BinaryNode validBinary = new BinaryNode("Hello".getBytes(StandardCharsets.UTF_8));
    assertTrue(schemaBytes.isValidValue(validBinary));

It it may be another issue.

For docs, indeed, text is now reviewed

For other languages, i will made other PR (otherwise, this one will be too big)

[KalleOlaviNiemitalo]

BinaryNode is documented as "Base64 encoded binary value", but Avro does not use Base64 in field default values or in JSON encoding, so I don't think Schema.isValidValue needs to support the BinaryNode type.

[clesaec]

for other languages too
This PR is for rust

[opwvhk]

One can also call fieldSchema.isNullable() here

[opwvhk]

It looks to me that these changes make any value for the null schema or a union an invalid value. What am I overlooking?

[clesaec]

static method isValidDefault (line 1650 on new version) is private, called by new virtual function "public boolean isValidValue(final Object value) {", line 1645.
This function is redefine for NULL Schema (line 1387) and for union schema (line 1248).
May be the main flaw of this PR is to keep the static isValidDefault method and not build function isValidValue for each schema type, but it also would duplicate code for STRING, BYTES, ENUM for example (See here)).