Part 2: propagate transform in visit_scan_files

ffi/examples/read-table/arrow.c

@@ -66,7 +66,7 @@ static GArrowRecordBatch* add_partition_columns(
     char* col = partition_cols->cols[i];
     guint pos = cols + i;
     KernelStringSlice key = { col, strlen(col) };
-    char* partition_val = get_from_map(partition_values, key, allocate_string);
+    char* partition_val = get_from_string_map(partition_values, key, allocate_string);
     print_diag(
       "  Adding partition column '%s' with value '%s' at column %u\n",
       col,

ffi/examples/read-table/read_table.c

@@ -28,7 +28,7 @@ void print_partition_info(struct EngineContext* context, const CStringMap* parti
   for (uintptr_t i = 0; i < context->partition_cols->len; i++) {
     char* col = context->partition_cols->cols[i];
     KernelStringSlice key = { col, strlen(col) };
-    char* partition_val = get_from_map(partition_values, key, allocate_string);
+    char* partition_val = get_from_string_map(partition_values, key, allocate_string);
     if (partition_val) {
       print_diag("  partition '%s' here: %s\n", col, partition_val);
       free(partition_val);
@@ -87,14 +87,15 @@ void scan_row_callback(
 void do_visit_scan_data(
   void* engine_context,
   ExclusiveEngineData* engine_data,
-  KernelBoolSlice selection_vec)
+  KernelBoolSlice selection_vec,
+  const CTransforms* transforms)
 {
   print_diag("\nScan iterator found some data to read\n  Of this data, here is "
              "a selection vector\n");
   print_selection_vector("    ", &selection_vec);
   // Ask kernel to iterate each individual file and call us back with extracted metadata
   print_diag("Asking kernel to call us back for each scan row (file to read)\n");
-  visit_scan_data(engine_data, selection_vec, engine_context, scan_row_callback);
+  visit_scan_data(engine_data, selection_vec, transforms, engine_context, scan_row_callback);
   free_bool_slice(selection_vec);
   free_engine_data(engine_data);
 }

ffi/src/scan.rs

@@ -7,7 +7,7 @@ use delta_kernel::scan::state::{visit_scan_files, DvInfo, GlobalScanState};
 use delta_kernel::scan::{Scan, ScanData};
 use delta_kernel::schema::Schema;
 use delta_kernel::snapshot::Snapshot;
-use delta_kernel::{DeltaResult, Error};
+use delta_kernel::{DeltaResult, Error, ExpressionRef};
 use delta_kernel_ffi_macros::handle_descriptor;
 use tracing::debug;
 use url::Url;
@@ -211,6 +211,7 @@ pub unsafe extern "C" fn kernel_scan_data_next(
         engine_context: NullableCvoid,
         engine_data: Handle<ExclusiveEngineData>,
         selection_vector: KernelBoolSlice,
+        transforms: &CTransforms,
     ),
 ) -> ExternResult<bool> {
     let data = unsafe { data.as_ref() };
@@ -224,15 +225,17 @@ fn kernel_scan_data_next_impl(
         engine_context: NullableCvoid,
         engine_data: Handle<ExclusiveEngineData>,
         selection_vector: KernelBoolSlice,
+        transforms: &CTransforms,
     ),
 ) -> DeltaResult<bool> {
     let mut data = data
         .data
         .lock()
         .map_err(|_| Error::generic("poisoned mutex"))?;
-    if let Some((data, sel_vec, _transforms)) = data.next().transpose()? {
+    if let Some((data, sel_vec, transforms)) = data.next().transpose()? {
         let bool_slice = KernelBoolSlice::from(sel_vec);
-        (engine_visitor)(engine_context, data.into(), bool_slice);
+        let transform_map = CTransforms { transforms };
+        (engine_visitor)(engine_context, data.into(), bool_slice, &transform_map);
         Ok(true)
     } else {
         Ok(false)
@@ -281,7 +284,7 @@ pub struct CStringMap {
 /// # Safety
 ///
 /// The engine is responsible for providing a valid [`CStringMap`] pointer and [`KernelStringSlice`]
-pub unsafe extern "C" fn get_from_map(
+pub unsafe extern "C" fn get_from_string_map(
     map: &CStringMap,
     key: KernelStringSlice,
     allocate_fn: AllocateStringFn,
@@ -293,6 +296,10 @@ pub unsafe extern "C" fn get_from_map(
         .and_then(|v| allocate_fn(kernel_string_slice!(v)))
 }
 
+pub struct CTransforms {
+    transforms: Vec<Option<ExpressionRef>>,
+}
+
 /// Get a selection vector out of a [`DvInfo`] struct
 ///
 /// # Safety
@@ -355,6 +362,7 @@ fn rust_callback(
     size: i64,
     kernel_stats: Option<delta_kernel::scan::state::Stats>,
     dv_info: DvInfo,
+    _transform: Option<ExpressionRef>,
     partition_values: HashMap<String, String>,
 ) {
     let partition_map = CStringMap {
@@ -388,6 +396,7 @@ struct ContextWrapper {
 pub unsafe extern "C" fn visit_scan_data(
     data: Handle<ExclusiveEngineData>,
     selection_vec: KernelBoolSlice,
+    transforms: &CTransforms,
     engine_context: NullableCvoid,
     callback: CScanCallback,
 ) {
@@ -398,5 +407,12 @@ pub unsafe extern "C" fn visit_scan_data(
         callback,
     };
     // TODO: return ExternResult to caller instead of panicking?
-    visit_scan_files(data, selection_vec, context_wrapper, rust_callback).unwrap();
+    visit_scan_files(
+        data,
+        selection_vec,
+        &transforms.transforms,
+        context_wrapper,
+        rust_callback,
+    )
+    .unwrap();
 }

kernel/examples/inspect-table/src/main.rs

@@ -12,7 +12,7 @@ use delta_kernel::expressions::ColumnName;
 use delta_kernel::scan::state::{DvInfo, Stats};
 use delta_kernel::scan::ScanBuilder;
 use delta_kernel::schema::{ColumnNamesAndTypes, DataType};
-use delta_kernel::{DeltaResult, Error, Table};
+use delta_kernel::{DeltaResult, Error, ExpressionRef, Table};
 
 use std::collections::HashMap;
 use std::process::ExitCode;
@@ -163,6 +163,7 @@ fn print_scan_file(
     size: i64,
     stats: Option<Stats>,
     dv_info: DvInfo,
+    transform: Option<ExpressionRef>,
     partition_values: HashMap<String, String>,
 ) {
     let num_record_str = if let Some(s) = stats {
@@ -176,6 +177,7 @@ fn print_scan_file(
               Size (bytes):\t{size}\n  \
               Num Records:\t{num_record_str}\n  \
               Has DV?:\t{}\n  \
+              Transform:\t{transform:?}\n  \
               Part Vals:\t{partition_values:?}",
         dv_info.has_vector()
     );
@@ -209,10 +211,11 @@ fn try_main() -> DeltaResult<()> {
             let scan = ScanBuilder::new(snapshot).build()?;
             let scan_data = scan.scan_data(&engine)?;
             for res in scan_data {
-                let (data, vector, _transforms) = res?;
+                let (data, vector, transforms) = res?;
                 delta_kernel::scan::state::visit_scan_files(
                     data.as_ref(),
                     &vector,
+                    &transforms,
                     (),
                     print_scan_file,
                 )?;

kernel/examples/read-table-multi-threaded/src/main.rs

@@ -15,7 +15,7 @@ use delta_kernel::engine::sync::SyncEngine;
 use delta_kernel::scan::state::{DvInfo, GlobalScanState, Stats};
 use delta_kernel::scan::transform_to_logical;
 use delta_kernel::schema::Schema;
-use delta_kernel::{DeltaResult, Engine, EngineData, FileMeta, Table};
+use delta_kernel::{DeltaResult, Engine, EngineData, ExpressionRef, FileMeta, Table};
 
 use clap::{Parser, ValueEnum};
 use url::Url;
@@ -111,6 +111,7 @@ fn send_scan_file(
     size: i64,
     _stats: Option<Stats>,
     dv_info: DvInfo,
+    _transform: Option<ExpressionRef>,
     partition_values: HashMap<String, String>,
 ) {
     let scan_file = ScanFile {
@@ -210,10 +211,11 @@ fn try_main() -> DeltaResult<()> {
     drop(record_batch_tx);
 
     for res in scan_data {
-        let (data, vector, _transforms) = res?;
+        let (data, vector, transforms) = res?;
         scan_file_tx = delta_kernel::scan::state::visit_scan_files(
             data.as_ref(),
             &vector,
+            &transforms,
             scan_file_tx,
             send_scan_file,
         )?;

kernel/src/scan/log_replay.rs

@@ -347,6 +347,7 @@ mod tests {
         size: i64,
         stats: Option<Stats>,
         _: DvInfo,
+        _: Option<ExpressionRef>,
         part_vals: HashMap<String, String>,
     ) {
         assert_eq!(

kernel/src/scan/mod.rs

@@ -304,6 +304,16 @@ pub enum ColumnType {
 /// A transform is ultimately a `Struct` expr. This holds the set of expressions that make that struct expr up
 type Transform = Vec<TransformExpr>;
 
+/// utility method making it easy to get a transform for a particular row. If the requested row is
+/// outside the range of the passed slice returns `None`, otherwise returns the element at the index
+/// of the specified row
+pub fn get_transform_for_row(
+    row: usize,
+    transforms: &[Option<ExpressionRef>],
+) -> Option<ExpressionRef> {
+    transforms.get(row).cloned().flatten()
+}
+
 /// Transforms aren't computed all at once. So static ones can just go straight to `Expression`, but
 /// things like partition columns need to filled in. This enum holds an expression that's part of a
 /// `Transform`.
@@ -463,6 +473,7 @@ impl Scan {
             size: i64,
             _: Option<Stats>,
             dv_info: DvInfo,
+            _transform: Option<ExpressionRef>,
             partition_values: HashMap<String, String>,
         ) {
             batches.push(ScanFile {
@@ -487,9 +498,15 @@ impl Scan {
         let scan_data = self.scan_data(engine.as_ref())?;
         let scan_files_iter = scan_data
             .map(|res| {
-                let (data, vec, _transforms) = res?;
+                let (data, vec, transforms) = res?;
                 let scan_files = vec![];
-                state::visit_scan_files(data.as_ref(), &vec, scan_files, scan_data_callback)
+                state::visit_scan_files(
+                    data.as_ref(),
+                    &vec,
+                    &transforms,
+                    scan_files,
+                    scan_data_callback,
+                )
             })
             // Iterator<DeltaResult<Vec<ScanFile>>> to Iterator<DeltaResult<ScanFile>>
             .flatten_ok();
@@ -816,11 +833,12 @@ pub(crate) mod test_utils {
         );
         let mut batch_count = 0;
         for res in iter {
-            let (batch, sel, _transforms) = res.unwrap();
+            let (batch, sel, transforms) = res.unwrap();
             assert_eq!(sel, expected_sel_vec);
             crate::scan::state::visit_scan_files(
                 batch.as_ref(),
                 &sel,
+                &transforms,
                 context.clone(),
                 validate_callback,
             )
@@ -1020,15 +1038,22 @@ mod tests {
             _size: i64,
             _: Option<Stats>,
             dv_info: DvInfo,
+            _transform: Option<ExpressionRef>,
             _partition_values: HashMap<String, String>,
         ) {
             paths.push(path.to_string());
             assert!(dv_info.deletion_vector.is_none());
         }
         let mut files = vec![];
         for data in scan_data {
-            let (data, vec, _transforms) = data?;
-            files = state::visit_scan_files(data.as_ref(), &vec, files, scan_data_callback)?;
+            let (data, vec, transforms) = data?;
+            files = state::visit_scan_files(
+                data.as_ref(),
+                &vec,
+                &transforms,
+                files,
+                scan_data_callback,
+            )?;
         }
         Ok(files)
     }

kernel/src/scan/state.rs

@@ -4,7 +4,9 @@ use std::collections::HashMap;
 use std::sync::LazyLock;
 
 use crate::actions::deletion_vector::deletion_treemap_to_bools;
+use crate::scan::get_transform_for_row;
 use crate::utils::require;
+use crate::ExpressionRef;
 use crate::{
     actions::{deletion_vector::DeletionVectorDescriptor, visitors::visit_deletion_vector_at},
     engine_data::{GetData, RowVisitor, TypedGetData as _},
@@ -104,6 +106,7 @@ pub type ScanCallback<T> = fn(
     size: i64,
     stats: Option<Stats>,
     dv_info: DvInfo,
+    transform: Option<ExpressionRef>,
     partition_values: HashMap<String, String>,
 );
 
@@ -138,12 +141,14 @@ pub type ScanCallback<T> = fn(
 pub fn visit_scan_files<T>(
     data: &dyn EngineData,
     selection_vector: &[bool],
+    transforms: &[Option<ExpressionRef>],
     context: T,
     callback: ScanCallback<T>,
 ) -> DeltaResult<T> {
     let mut visitor = ScanFileVisitor {
         callback,
         selection_vector,
+        transforms,
         context,
     };
     visitor.visit_rows_of(data)?;
@@ -154,6 +159,7 @@ pub fn visit_scan_files<T>(
 struct ScanFileVisitor<'a, T> {
     callback: ScanCallback<T>,
     selection_vector: &'a [bool],
+    transforms: &'a [Option<ExpressionRef>],
     context: T,
 }
 impl<T> RowVisitor for ScanFileVisitor<'_, T> {
@@ -201,6 +207,7 @@ impl<T> RowVisitor for ScanFileVisitor<'_, T> {
                     size,
                     stats,
                     dv_info,
+                    get_transform_for_row(row_index, self.transforms),
                     partition_values,
                 )
             }
@@ -214,6 +221,7 @@ mod tests {
     use std::collections::HashMap;
 
     use crate::scan::test_utils::{add_batch_simple, run_with_validate_callback};
+    use crate::ExpressionRef;
 
     use super::{DvInfo, Stats};
 
@@ -228,6 +236,7 @@ mod tests {
         size: i64,
         stats: Option<Stats>,
         dv_info: DvInfo,
+        transform: Option<ExpressionRef>,
         part_vals: HashMap<String, String>,
     ) {
         assert_eq!(
@@ -242,6 +251,7 @@ mod tests {
         assert!(dv_info.deletion_vector.is_some());
         let dv = dv_info.deletion_vector.unwrap();
         assert_eq!(dv.unique_id(), "uvBn[lx{q8@P<9BNH/isA@1");
+        assert!(transform.is_none());
         assert_eq!(context.id, 2);
     }
 

kernel/tests/read.rs

@@ -10,7 +10,7 @@ use delta_kernel::actions::deletion_vector::split_vector;
 use delta_kernel::engine::arrow_data::ArrowEngineData;
 use delta_kernel::engine::default::executor::tokio::TokioBackgroundExecutor;
 use delta_kernel::engine::default::DefaultEngine;
-use delta_kernel::expressions::{column_expr, BinaryOperator, Expression};
+use delta_kernel::expressions::{column_expr, BinaryOperator, Expression, ExpressionRef};
 use delta_kernel::scan::state::{visit_scan_files, DvInfo, Stats};
 use delta_kernel::scan::{transform_to_logical, Scan};
 use delta_kernel::schema::{DataType, Schema};
@@ -348,6 +348,7 @@ fn scan_data_callback(
     size: i64,
     _stats: Option<Stats>,
     dv_info: DvInfo,
+    _transforms: Option<ExpressionRef>,
     partition_values: HashMap<String, String>,
 ) {
     batches.push(ScanFile {
@@ -369,8 +370,14 @@ fn read_with_scan_data(
     let scan_data = scan.scan_data(engine)?;
     let mut scan_files = vec![];
     for data in scan_data {
-        let (data, vec, _transforms) = data?;
-        scan_files = visit_scan_files(data.as_ref(), &vec, scan_files, scan_data_callback)?;
+        let (data, vec, transforms) = data?;
+        scan_files = visit_scan_files(
+            data.as_ref(),
+            &vec,
+            &transforms,
+            scan_files,
+            scan_data_callback,
+        )?;
     }
 
     let mut batches = vec![];