YT-19324: move YT provider to ydb/library/yql

This commit is formed by the following script: https://paste.yandex-team.ru/6f92e4b8-efc5-4d34-948b-15ee2accd7e7/text.
This commit has zero effect on all projects that depend on YQL.

The summary of changes:
- `yql/providers/yt -> ydb/library/yql/providers/yt `- the whole implementation of YT provider is moved into YDB code base for further export as a part of YT YQL plugin shared library;
- `yql/providers/stat/{expr_nodes,uploader} -> ydb/library/yql/providers/stat/{expr_nodes,uploader}` - a small interface without implementation and the description of stat expr nodes;
- `yql/core/extract_predicate/ut -> ydb/library/yql/core/extract_predicate/ut`;
- `yql/core/{ut,ut_common} -> ydb/library/yql/core/{ut,ut_common}`;
- `yql/core` is gone;
- `yql/library/url_preprocessing -> ydb/library/yql/core/url_preprocessing`.

**NB**: all new targets inside `ydb/` are under `IF (NOT CMAKE_EXPORT)` clause which disables them from open-source cmake generation and ya make build. They will be enabled in the subsequent commits.

1 files changed, 67 insertions, 0 deletions

diff --git a/yt/cpp/mapreduce/io/lenval_table_reader.h b/yt/cpp/mapreduce/io/lenval_table_reader.h
new file mode 100644
index 0000000000..990fe0b756
--- /dev/null
+++ b/yt/cpp/mapreduce/io/lenval_table_reader.h
@@ -0,0 +1,67 @@
+#pragma once
+
+#include "counting_raw_reader.h"
+
+#include <yt/cpp/mapreduce/interface/io.h>
+
+namespace NYT {
+
+////////////////////////////////////////////////////////////////////////////////
+
+class TLenvalTableReader
+{
+public:
+    explicit TLenvalTableReader(::TIntrusivePtr<TRawTableReader> input);
+    virtual ~TLenvalTableReader();
+
+protected:
+    bool IsValid() const;
+    void Next();
+    ui32 GetTableIndex() const;
+    ui32 GetRangeIndex() const;
+    ui64 GetRowIndex() const;
+    void NextKey();
+    TMaybe<size_t> GetReadByteCount() const;
+    bool IsEndOfStream() const;
+    bool IsRawReaderExhausted() const;
+
+    void CheckValidity() const;
+
+    bool Retry();
+
+    template <class T>
+    bool ReadInteger(T* result, bool acceptEndOfStream = false)
+    {
+        size_t count = Input_.Load(result, sizeof(T));
+        if (acceptEndOfStream && count == 0) {
+            Finished_ = true;
+            Valid_ = false;
+            return false;
+        }
+        Y_ENSURE(count == sizeof(T), "Premature end of stream");
+        return true;
+    }
+
+    virtual void SkipRow() = 0;
+
+protected:
+    NDetail::TCountingRawTableReader Input_;
+
+    bool Valid_ = true;
+    bool Finished_ = false;
+    ui32 TableIndex_ = 0;
+    TMaybe<ui64> RowIndex_;
+    TMaybe<ui32> RangeIndex_;
+    TMaybe<ui64> TabletIndex_;
+    bool IsEndOfStream_ = false;
+    bool AtStart_ = true;
+    bool RowTaken_ = true;
+    ui32 Length_ = 0;
+
+private:
+    bool PrepareRetry();
+};
+
+////////////////////////////////////////////////////////////////////////////////
+
+} // namespace NYT