Introduce extendable access plan for DF scans (#5855)

Building on top of some previous work, this should make using extensions
more durable in the future, allowing us to support multiple ones.

---------

Signed-off-by: Adam Gutglick <[email protected]>

Author: AdamGS

vortex-datafusion/src/persistent/access_plan.rs

@@ -0,0 +1,39 @@
+// SPDX-License-Identifier: Apache-2.0
+// SPDX-FileCopyrightText: Copyright the Vortex contributors
+
+use vortex::scan::ScanBuilder;
+use vortex::scan::Selection;
+
+/// Custom Vortex-specific information that can be provided by external indexes or other sources.
+///
+/// This is intended as a low-level interface for users building their own data systems, see the [advance index] example from the DataFusion repo for a similar usage with Parquet.
+///
+/// [advance index]: https://github.com/apache/datafusion/blob/47df535d2cd5aac5ad5a92bdc837f38e05ea0f0f/datafusion-examples/examples/data_io/parquet_advanced_index.rs
+#[derive(Default)]
+pub struct VortexAccessPlan {
+    selection: Option<Selection>,
+}
+
+impl VortexAccessPlan {
+    /// Sets a [`Selection`] for this plan.
+    pub fn with_selection(mut self, selection: Selection) -> Self {
+        self.selection = Some(selection);
+        self
+    }
+}
+
+impl VortexAccessPlan {
+    /// Apply the plan to the scan's builder.
+    pub fn apply_to_builder<A>(&self, mut scan_builder: ScanBuilder<A>) -> ScanBuilder<A>
+    where
+        A: 'static + Send,
+    {
+        let Self { selection } = self;
+
+        if let Some(selection) = selection {
+            scan_builder = scan_builder.with_selection(selection.clone());
+        }
+
+        scan_builder
+    }
+}

vortex-datafusion/src/persistent/mod.rs

@@ -2,13 +2,15 @@
 // SPDX-FileCopyrightText: Copyright the Vortex contributors
 
 //! Persistent implementation of a Vortex table provider.
+mod access_plan;
 mod cache;
 mod format;
 pub mod metrics;
 mod opener;
 mod sink;
 mod source;
 
+pub use access_plan::VortexAccessPlan;
 pub use format::VortexFormat;
 pub use format::VortexFormatFactory;
 pub use format::VortexOptions;