Serializing Some(date) gives validation error

[ttencate]

Using avro-rs 0.11.0 because 0.12.0 won't compile for me.

use avro_rs::{Schema, Writer};
use serde::Serialize;

#[derive(Serialize)]
struct Foo {
    date: Option<i32>,
}

fn main() {
    let schema = Schema::parse_str(
        r#"{
            "type": "record",
            "name": "Foo",
            "fields": [
                {"name": "date", "type": ["null", {"type": "int", "logicalType": "date"}]}
            ]
        }"#)
        .unwrap();
    let mut writer = Writer::new(&schema, Vec::new());

    writer.append_ser(Foo { date: None }).unwrap(); // This works fine.

    writer.append_ser(Foo { date: Some(42) }).unwrap(); // This returns avro_rs::Error::Validation.
}

I think this happens because UnionSchema::find_schema only looks for a variant that matches the input type exactly:

avro-rs/src/schema.rs

Lines 343 to 349 in de6153e

	pub fn find_schema(&self, value: &types::Value) -> Option<(usize, &Schema)> {
	let type_index = &SchemaKind::from(value);
	self.variant_index
	.get(type_index)
	.copied()
	.map(|i| (i, &self.schemas[i]))
	}

That logic fails here, because the schema contains a Schema::Date variant but the incoming value is a Value::Int. Note that Value::validate handles this case correctly.

[ttencate]

I hacked around this in my fork, but my approach is probably not the best way so I doubt it's worth a PR: ttencate@1c89f55

[poros]

Thanks for reporting the bug. As for the compilation, the error should disappear if you can update your rust version.