refactor: Remove new streaming old multiscan (#21300)

crates/polars-plan/src/plans/conversion/scans.rs

@@ -131,6 +131,60 @@ pub(super) fn ipc_file_info(
     Ok((file_info, metadata))
 }
 
+#[cfg(feature = "csv")]
+pub fn isolated_csv_file_info(
+    source: ScanSourceRef,
+    file_options: &FileScanOptions,
+    csv_options: &mut CsvReadOptions,
+    _cloud_options: Option<&polars_io::cloud::CloudOptions>,
+) -> PolarsResult<FileInfo> {
+    use std::io::{Read, Seek};
+
+    use polars_io::csv::read::schema_inference::SchemaInferenceResult;
+    use polars_io::utils::get_reader_bytes;
+
+    let run_async = source.run_async();
+
+    let memslice = source.to_memslice_async_assume_latest(run_async)?;
+    let owned = &mut vec![];
+    let mut reader = std::io::Cursor::new(maybe_decompress_bytes(&memslice, owned)?);
+    if reader.read(&mut [0; 4])? < 2 && csv_options.raise_if_empty {
+        polars_bail!(NoData: "empty CSV")
+    }
+    reader.rewind()?;
+
+    let reader_bytes = get_reader_bytes(&mut reader).expect("could not mmap file");
+
+    // this needs a way to estimated bytes/rows.
+    let si_result =
+        SchemaInferenceResult::try_from_reader_bytes_and_options(&reader_bytes, csv_options)?;
+
+    csv_options.update_with_inference_result(&si_result);
+
+    let mut schema = csv_options
+        .schema
+        .clone()
+        .unwrap_or_else(|| si_result.get_inferred_schema());
+
+    let reader_schema = if let Some(rc) = &file_options.row_index {
+        let reader_schema = schema.clone();
+        let mut output_schema = (*reader_schema).clone();
+        output_schema.insert_at_index(0, rc.name.clone(), IDX_DTYPE)?;
+        schema = Arc::new(output_schema);
+        reader_schema
+    } else {
+        schema.clone()
+    };
+
+    let estimated_n_rows = si_result.get_estimated_n_rows();
+
+    Ok(FileInfo::new(
+        schema,
+        Some(Either::Right(reader_schema)),
+        (None, estimated_n_rows),
+    ))
+}
+
 #[cfg(feature = "csv")]
 pub fn csv_file_info(
     sources: &ScanSources,

crates/polars-plan/src/plans/ir/scan_sources.rs

@@ -47,21 +47,57 @@ pub enum ScanSourceRef<'a> {
 }
 
 /// A single source to scan from
-#[derive(Debug)]
+#[derive(Debug, Clone)]
 pub enum ScanSource {
-    Path(PathBuf),
-    File(File),
+    Path(Arc<Path>),
+    File(Arc<File>),
     Buffer(MemSlice),
 }
 
 impl ScanSource {
+    pub fn from_sources(sources: ScanSources) -> Result<Self, ScanSources> {
+        if sources.len() == 1 {
+            match sources {
+                ScanSources::Paths(ps) => Ok(Self::Path(ps.as_ref()[0].clone().into())),
+                ScanSources::Files(fs) => {
+                    assert_eq!(fs.len(), 1);
+                    let ptr: *const File = Arc::into_raw(fs) as *const File;
+                    // SAFETY: A [T] with length 1 can be interpreted as T
+                    let f: Arc<File> = unsafe { Arc::from_raw(ptr) };
+
+                    Ok(Self::File(f))
+                },
+                ScanSources::Buffers(bs) => Ok(Self::Buffer(bs.as_ref()[0].clone())),
+            }
+        } else {
+            Err(sources)
+        }
+    }
+
     pub fn into_sources(self) -> ScanSources {
         match self {
-            ScanSource::Path(p) => ScanSources::Paths([p].into()),
-            ScanSource::File(f) => ScanSources::Files([f].into()),
+            ScanSource::Path(p) => ScanSources::Paths([p.to_path_buf()].into()),
+            ScanSource::File(f) => {
+                let ptr: *const [File] = std::ptr::slice_from_raw_parts(Arc::into_raw(f), 1);
+                // SAFETY: A T can be interpreted as [T] with length 1.
+                let fs: Arc<[File]> = unsafe { Arc::from_raw(ptr) };
+                ScanSources::Files(fs)
+            },
             ScanSource::Buffer(m) => ScanSources::Buffers([m].into()),
         }
     }
+
+    pub fn as_scan_source_ref(&self) -> ScanSourceRef {
+        match self {
+            ScanSource::Path(path) => ScanSourceRef::Path(path.as_ref()),
+            ScanSource::File(file) => ScanSourceRef::File(file.as_ref()),
+            ScanSource::Buffer(mem_slice) => ScanSourceRef::Buffer(mem_slice),
+        }
+    }
+
+    pub fn run_async(&self) -> bool {
+        self.as_scan_source_ref().run_async()
+    }
 }
 
 /// An iterator for [`ScanSources`]
@@ -261,8 +297,15 @@ impl ScanSourceRef<'_> {
     // @TODO: I would like to remove this function eventually.
     pub fn into_owned(&self) -> PolarsResult<ScanSource> {
         Ok(match self {
-            ScanSourceRef::Path(path) => ScanSource::Path(path.to_path_buf()),
-            _ => ScanSource::Buffer(self.to_memslice()?),
+            ScanSourceRef::Path(path) => ScanSource::Path((*path).into()),
+            ScanSourceRef::File(file) => {
+                if let Ok(file) = file.try_clone() {
+                    ScanSource::File(Arc::new(file))
+                } else {
+                    ScanSource::Buffer(self.to_memslice()?)
+                }
+            },
+            ScanSourceRef::Buffer(buffer) => ScanSource::Buffer((*buffer).clone()),
         })
     }
 
@@ -335,6 +378,10 @@ impl ScanSourceRef<'_> {
             Self::Buffer(buff) => Ok(DynByteSource::from((*buff).clone())),
         }
     }
+
+    pub(crate) fn run_async(&self) -> bool {
+        matches!(self, Self::Path(p) if polars_io::is_cloud_url(p) || polars_core::config::force_async())
+    }
 }
 
 impl<'a> Iterator for ScanSourceIter<'a> {