Decoding a ParquetScan/AvroScan physical plan panics when the feature is disabled, instead of returning an error

[adriangb]

Filed with AI assistance (Claude Code); verified against main.

Describe the bug

Decoding a physical plan that contains a ParquetScan or AvroScan node panics when datafusion-proto was built without the corresponding feature, instead of returning a DataFusionError:

PhysicalPlanType::ParquetScan(_) => {
    #[cfg(feature = "parquet")]
    {
        ParquetSource::try_from_proto(self.node(), &decode_ctx)
    }
    #[cfg(not(feature = "parquet"))]
    panic!(
        "Unable to process a Parquet PhysicalPlan when `parquet` feature is not enabled"
    )
}

The bytes being decoded here come from a peer — that is the entire point of datafusion-proto. A distributed executor built without the parquet feature will abort the process when a scheduler sends it a Parquet scan, rather than failing that one plan and staying up.

This is pre-existing behaviour that was carried over verbatim by the proto-hook migration (#24169 for Parquet, #24190 for Avro), so it is not a regression — just something worth cleaning up now that both arms have the same shape.

Expected behavior

Return an error. not_impl_err! is already the convention elsewhere in the same file for feature-gated paths, e.g.:

not_impl_err!("ParquetSink requires the `parquet` feature")

Both scan arms should follow it:

#[cfg(not(feature = "parquet"))]
not_impl_err!("Unable to process a Parquet PhysicalPlan when the `parquet` feature is not enabled")

Additional context

Sites to fix in datafusion/proto/src/physical_plan/mod.rs:

• the PhysicalPlanType::ParquetScan decode arm
• the PhysicalPlanType::AvroScan decode arm
• the same panic! inside the deprecated try_into_avro_scan_physical_plan compatibility wrapper

While there: the message reads "a Avro PhysicalPlan", which should be "an Avro PhysicalPlan".

Good first issue — the change is mechanical, but note that the arms need to keep type-checking under every combination of the parquet and avro features, so please verify with cargo check -p datafusion-proto (no features), --features parquet, --features avro, and --all-features.

Noticed while reviewing #24190. Part of the epic in #23494.

[nam2ee]

take