move projection pushdown optimization logic to ExecutionPlan trait

datafusion/core/src/datasource/physical_plan/csv.rs

@@ -45,6 +45,9 @@ use datafusion_execution::TaskContext;
 use datafusion_physical_expr::{EquivalenceProperties, LexOrdering};
 
 use datafusion_physical_plan::execution_plan::{Boundedness, EmissionType};
+use datafusion_physical_plan::projection::{
+    all_alias_free_columns, new_projections_for_columns, ProjectionExec,
+};
 use futures::{StreamExt, TryStreamExt};
 use object_store::buffered::BufWriter;
 use object_store::{GetOptions, GetResultPayload, ObjectStore};
@@ -479,6 +482,36 @@ impl ExecutionPlan for CsvExec {
             cache: self.cache.clone(),
         }))
     }
+
+    fn try_swapping_with_projection(
+        &self,
+        projection: &ProjectionExec,
+    ) -> Result<Option<Arc<dyn ExecutionPlan>>> {
+        // If there is any non-column or alias-carrier expression, Projection should not be removed.
+        // This process can be moved into CsvExec, but it would be an overlap of their responsibility.
+        Ok(all_alias_free_columns(projection.expr()).then(|| {
+            let mut file_scan = self.base_config().clone();
+            let new_projections = new_projections_for_columns(
+                projection,
+                &file_scan
+                    .projection
+                    .unwrap_or((0..self.schema().fields().len()).collect()),
+            );
+            file_scan.projection = Some(new_projections);
+
+            Arc::new(
+                CsvExec::builder(file_scan)
+                    .with_has_header(self.has_header())
+                    .with_delimeter(self.delimiter())
+                    .with_quote(self.quote())
+                    .with_escape(self.escape())
+                    .with_comment(self.comment())
+                    .with_newlines_in_values(self.newlines_in_values())
+                    .with_file_compression_type(self.file_compression_type)
+                    .build(),
+            ) as _
+        }))
+    }
 }
 
 /// A Config for [`CsvOpener`]