fix: Raise when parquet file has extra columns and no select() was done

crates/polars-io/src/parquet/read/reader.rs

@@ -83,7 +83,7 @@ impl<R: MmapBytesReader> ParquetReader<R> {
 
     /// Checks that the file contains all the columns in `projected_arrow_schema` with the same
     /// dtype, and sets the projection indices.
-    pub fn with_projected_arrow_schema(
+    pub fn with_arrow_schema_projection(
         mut self,
         first_schema: &ArrowSchema,
         projected_arrow_schema: Option<&ArrowSchema>,
@@ -96,6 +96,13 @@ impl<R: MmapBytesReader> ParquetReader<R> {
                 projected_arrow_schema,
             )?;
         } else {
+            if schema.len() > first_schema.len() {
+                polars_bail!(
+                   SchemaMismatch:
+                   "parquet file contained extra columns and no selection was given"
+                )
+            }
+
             self.projection =
                 projected_arrow_schema_to_projection_indices(schema.as_ref(), first_schema)?;
         }
@@ -292,7 +299,7 @@ impl ParquetAsyncReader {
         })
     }
 
-    pub async fn with_projected_arrow_schema(
+    pub async fn with_arrow_schema_projection(
         mut self,
         first_schema: &ArrowSchema,
         projected_arrow_schema: Option<&ArrowSchema>,
@@ -305,6 +312,13 @@ impl ParquetAsyncReader {
                 projected_arrow_schema,
             )?;
         } else {
+            if schema.len() > first_schema.len() {
+                polars_bail!(
+                   SchemaMismatch:
+                   "parquet file contained extra columns and no selection was given"
+                )
+            }
+
             self.projection =
                 projected_arrow_schema_to_projection_indices(schema.as_ref(), first_schema)?;
         }

crates/polars-mem-engine/src/executors/scan/parquet.rs

@@ -216,7 +216,7 @@ impl ParquetExec {
                             .with_slice(Some(slice))
                             .with_row_index(row_index)
                             .with_predicate(predicate.clone())
-                            .with_projected_arrow_schema(
+                            .with_arrow_schema_projection(
                                 first_schema.as_ref(),
                                 projected_arrow_schema.as_deref(),
                             )?
@@ -421,7 +421,7 @@ impl ParquetExec {
                         let df = reader
                             .with_slice(Some(slice))
                             .with_row_index(row_index)
-                            .with_projected_arrow_schema(
+                            .with_arrow_schema_projection(
                                 first_schema.as_ref(),
                                 projected_arrow_schema.as_deref(),
                             )

crates/polars-pipe/src/executors/sources/parquet.rs

@@ -131,7 +131,7 @@ impl ParquetSource {
             }
 
             let mut reader = reader
-                .with_projected_arrow_schema(
+                .with_arrow_schema_projection(
                     &self.first_schema,
                     self.projected_arrow_schema.as_deref(),
                 )?
@@ -196,7 +196,7 @@ impl ParquetSource {
                 ParquetAsyncReader::from_uri(&uri, cloud_options.as_ref(), metadata)
                     .await?
                     .with_row_index(file_options.row_index)
-                    .with_projected_arrow_schema(
+                    .with_arrow_schema_projection(
                         &self.first_schema,
                         self.projected_arrow_schema.as_deref(),
                     )

crates/polars-stream/src/nodes/parquet_source/metadata_fetch.rs

@@ -1,14 +1,14 @@
 use std::sync::Arc;
 
 use futures::StreamExt;
-use polars_error::PolarsResult;
+use polars_error::{polars_bail, PolarsResult};
 use polars_io::prelude::FileMetadata;
 use polars_io::utils::byte_source::{DynByteSource, MemSliceByteSource};
 use polars_io::utils::slice::SplitSlicePosition;
 use polars_utils::mmap::MemSlice;
 use polars_utils::pl_str::PlSmallStr;
 
-use super::metadata_utils::{ensure_metadata_has_projected_fields, read_parquet_metadata_bytes};
+use super::metadata_utils::{ensure_schema_has_projected_fields, read_parquet_metadata_bytes};
 use super::ParquetSourceNode;
 use crate::async_executor;
 use crate::async_primitives::connector::connector;
@@ -107,6 +107,15 @@ impl ParquetSourceNode {
         };
 
         let first_metadata = self.first_metadata.clone();
+        let reader_schema_len = self
+            .file_info
+            .reader_schema
+            .as_ref()
+            .unwrap()
+            .as_ref()
+            .unwrap_left()
+            .len();
+        let has_projection = self.file_options.with_columns.is_some();
 
         let process_metadata_bytes = {
             move |handle: task_handles_ext::AbortOnDropHandle<
@@ -127,10 +136,16 @@ impl ParquetSourceNode {
                         )?,
                     };
 
-                    ensure_metadata_has_projected_fields(
-                        &metadata,
-                        projected_arrow_schema.as_ref(),
-                    )?;
+                    let schema = polars_parquet::arrow::read::infer_schema(&metadata)?;
+
+                    if !has_projection && schema.len() > reader_schema_len {
+                        polars_bail!(
+                           SchemaMismatch:
+                           "parquet file contained extra columns and no selection was given"
+                        )
+                    }
+
+                    ensure_schema_has_projected_fields(&schema, projected_arrow_schema.as_ref())?;
 
                     PolarsResult::Ok((path_index, byte_source, metadata))
                 });

crates/polars-stream/src/nodes/parquet_source/metadata_utils.rs

@@ -1,6 +1,5 @@
 use polars_core::prelude::{ArrowSchema, DataType};
 use polars_error::{polars_bail, PolarsResult};
-use polars_io::prelude::FileMetadata;
 use polars_io::utils::byte_source::{ByteSource, DynByteSource};
 use polars_utils::mmap::MemSlice;
 
@@ -122,12 +121,10 @@ pub(super) async fn read_parquet_metadata_bytes(
 
 /// Ensures that a parquet file has all the necessary columns for a projection with the correct
 /// dtype. There are no ordering requirements and extra columns are permitted.
-pub(super) fn ensure_metadata_has_projected_fields(
-    metadata: &FileMetadata,
+pub(super) fn ensure_schema_has_projected_fields(
+    schema: &ArrowSchema,
     projected_fields: &ArrowSchema,
 ) -> PolarsResult<()> {
-    let schema = polars_parquet::arrow::read::infer_schema(metadata)?;
-
     for field in projected_fields.iter_values() {
         // Note: We convert to Polars-native dtypes for timezone normalization.
         let expected_dtype = DataType::from_arrow(&field.dtype, true);

py-polars/tests/unit/io/test_lazy_parquet.py

@@ -597,10 +597,11 @@ def test_parquet_unaligned_schema_read(tmp_path: Path, streaming: bool) -> None:
         pl.DataFrame({"a": [1, 2], "b": [10, 11]}),
     )
 
-    assert_frame_equal(
-        lf.collect(streaming=streaming),
-        pl.DataFrame({"a": [1, 2, 3], "b": [10, 11, 12]}),
-    )
+    with pytest.raises(
+        pl.exceptions.SchemaError,
+        match="parquet file contained extra columns and no selection was given",
+    ):
+        lf.collect(streaming=streaming)
 
 
 @pytest.mark.write_disk