[llvm] Create a CharSetConverter class with both iconv and icu support (PR #74516)

[Abhina Sree via llvm-commits]

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+//===-- CharSet.h - Characters set conversion class ---------------*- C++ -*-=//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+///
+/// \file
+/// This file provides a utility class to convert between different character
+/// set encodings.
+///
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_SUPPORT_CHARSET_H
+#define LLVM_SUPPORT_CHARSET_H
+
+#include "llvm/ADT/SmallString.h"
+#include "llvm/ADT/StringRef.h"
+#include "llvm/Config/config.h"
+#include "llvm/Support/ErrorOr.h"
+
+#include <functional>
+#include <string>
+#include <system_error>
+
+namespace llvm {
+
+template <typename T> class SmallVectorImpl;
+
+namespace details {
+class CharSetConverterImplBase {
+public:
+  virtual ~CharSetConverterImplBase() = default;
+
+  /// Converts a string.
+  /// \param[in] Source source string
+  /// \param[out] Result container for converted string
+  /// \return error code in case something went wrong
+  ///
+  /// The following error codes can occur, among others:
+  ///   - std::errc::argument_list_too_long: The result requires more than
+  ///     std::numeric_limits<size_t>::max() bytes.
+  ///   - std::errc::illegal_byte_sequence: The input contains an invalid
+  ///     multibyte sequence.
+  ///   - std::errc::invalid_argument: The input contains an incomplete
+  ///     multibyte sequence.
+  ///
+  /// If the destination charset is a stateful character set, the shift state
+  /// will be set to the initial state.
+  ///
+  /// In case of an error, the result string contains the successfully converted
+  /// part of the input string.
+  ///
+
+  virtual std::error_code convert(StringRef Source,
+                                  SmallVectorImpl<char> &Result) const = 0;
+};
+} // namespace details
+
+// Names inspired by https://wg21.link/p1885.
+namespace text_encoding {
+enum class id {
+  /// UTF-8 character set encoding.
+  UTF8,
+
+  /// IBM EBCDIC 1047 character set encoding.
+  IBM1047
+};
+} // end namespace text_encoding
+
+/// Utility class to convert between different character set encodings.
+class CharSetConverter {
+  std::unique_ptr<details::CharSetConverterImplBase> Converter;
+
+  CharSetConverter(std::unique_ptr<details::CharSetConverterImplBase> Converter)
+      : Converter(std::move(Converter)) {}
+
+public:
+  /// Creates a CharSetConverter instance.
+  /// \param[in] CSFrom the source character encoding
+  /// \param[in] CSTo the target character encoding
+  /// \return a CharSetConverter instance
+  static CharSetConverter create(text_encoding::id CSFrom,
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abhina-sree wrote:

This function will only get called if the conversion is supported by the ConverterEBCDIC tables which will not fail which is why we don't report errors for this specific one.

https://github.com/llvm/llvm-project/pull/74516