Create a EncodingConverter class with both iconv and icu support.

llvm/CMakeLists.txt

@@ -592,6 +592,10 @@ else()
   option(LLVM_ENABLE_THREADS "Use threads if available." ON)
 endif()
 
+set(LLVM_ENABLE_ICU "OFF" CACHE STRING "Use ICU for character conversion support if available. Can be ON, OFF, or FORCE_ON")
+
+set(LLVM_ENABLE_ICONV "OFF" CACHE STRING "Use iconv for character conversion support if available. Can be ON, OFF, or FORCE_ON")
+
 set(LLVM_ENABLE_ZLIB "ON" CACHE STRING "Use zlib for compression/decompression if available. Can be ON, OFF, or FORCE_ON")
 
 set(LLVM_ENABLE_ZSTD "ON" CACHE STRING "Use zstd for compression/decompression if available. Can be ON, OFF, or FORCE_ON")

llvm/cmake/config-ix.cmake

@@ -294,6 +294,41 @@ if(LLVM_HAS_LOGF128)
   set(LLVM_HAS_LOGF128 "${HAS_LOGF128}")
 endif()
 
+if (LLVM_ENABLE_ICU STREQUAL FORCE_ON AND LLVM_ENABLE_ICONV STREQUAL FORCE_ON)
+  message(FATAL_ERROR "LLVM_ENABLE_ICU and LLVM_ENABLE_ICONV should not both be FORCE_ON")
+endif()
+
+# Check for ICU. Only allow an optional, dynamic link for ICU so we don't impact LLVM's licensing.
+if(LLVM_ENABLE_ICU AND NOT(LLVM_ENABLE_ICONV STREQUAL FORCE_ON))
+  set(LIBRARY_SUFFIXES ${CMAKE_FIND_LIBRARY_SUFFIXES})
+  set(CMAKE_FIND_LIBRARY_SUFFIXES "${CMAKE_SHARED_LIBRARY_SUFFIX}")
+  if (LLVM_ENABLE_ICU STREQUAL FORCE_ON)
+    find_package(ICU REQUIRED COMPONENTS uc i18n)
+    if (NOT ICU_FOUND)
+      message(FATAL_ERROR "Failed to configure ICU, but LLVM_ENABLE_ICU is FORCE_ON")
+    endif()
+  else()
+    find_package(ICU COMPONENTS uc i18n)
+  endif()
+  set(HAVE_ICU ${ICU_FOUND})
+  set(CMAKE_FIND_LIBRARY_SUFFIXES ${LIBRARY_SUFFIXES})
+endif()
+
+# Check for builtin iconv to avoid licensing issues.
+if(LLVM_ENABLE_ICONV AND NOT HAVE_ICU)
+  if (LLVM_ENABLE_ICONV STREQUAL FORCE_ON)
+    find_package(Iconv REQUIRED)
+    if (NOT Iconv_FOUND OR NOT Iconv_IS_BUILT_IN)
+      message(FATAL_ERROR "Failed to configure iconv, but LLVM_ENABLE_ICONV is FORCE_ON")
+    endif()
+  else()
+    find_package(Iconv)
+  endif()
+  if(Iconv_FOUND AND Iconv_IS_BUILT_IN)
+    set(HAVE_ICONV 1)
+  endif()
+endif()
+
 # function checks
 check_symbol_exists(arc4random "stdlib.h" HAVE_DECL_ARC4RANDOM)
 find_package(Backtrace)

llvm/include/llvm/Config/config.h.cmake

@@ -236,6 +236,12 @@
 /* Have host's ___chkstk_ms */
 #cmakedefine HAVE____CHKSTK_MS ${HAVE____CHKSTK_MS}
 
+/* Define if ICU library is available */
+#cmakedefine01 HAVE_ICU
+
+/* Define if iconv library is available */
+#cmakedefine01 HAVE_ICONV
+
 /* Linker version detected at compile time. */
 #cmakedefine HOST_LINK_VERSION "${HOST_LINK_VERSION}"
 

llvm/include/llvm/Support/EncodingConverter.h

@@ -0,0 +1,139 @@
+//===-- EncodingConverter.h - Encoding 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_ENCODING_CONVERTER_H
+#define LLVM_SUPPORT_ENCODING_CONVERTER_H
+
+#include "llvm/ADT/SmallString.h"
+#include "llvm/ADT/StringRef.h"
+#include "llvm/Config/config.h"
+#include "llvm/Support/ErrorOr.h"
+
+#include <string>
+#include <system_error>
+
+namespace llvm {
+
+template <typename T> class SmallVectorImpl;
+
+namespace details {
+class EncodingConverterImplBase {
+
+private:
+  /// 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 encoding is stateful, 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 convertString(StringRef Source,
+                                        SmallVectorImpl<char> &Result) = 0;
+
+  /// Resets the converter to the initial state.
+  virtual void reset() = 0;
+
+public:
+  virtual ~EncodingConverterImplBase() = default;
+
+  /// Converts a string and resets the converter to the initial state.
+  std::error_code convert(StringRef Source, SmallVectorImpl<char> &Result) {
+    auto EC = convertString(Source, Result);
+    reset();
+    return EC;
+  }
+};
+} // namespace details
+
+// Names inspired by https://wg21.link/p1885.
+enum class TextEncoding {
+  /// UTF-8 character set encoding.
+  UTF8,
+
+  /// IBM EBCDIC 1047 character set encoding.
+  IBM1047
+};
+
+/// Utility class to convert between different character encodings.
+class EncodingConverter {
+  std::unique_ptr<details::EncodingConverterImplBase> Converter;
+
+  EncodingConverter(
+      std::unique_ptr<details::EncodingConverterImplBase> Converter)
+      : Converter(std::move(Converter)) {}
+
+public:
+  /// Creates a EncodingConverter instance.
+  /// Returns std::errc::invalid_argument in case the requested conversion is
+  /// not supported.
+  /// \param[in] From the source character encoding
+  /// \param[in] To the target character encoding
+  /// \return a EncodingConverter instance or an error code
+  static ErrorOr<EncodingConverter> create(TextEncoding From, TextEncoding To);
+
+  /// Creates a EncodingConverter instance.
+  /// Returns std::errc::invalid_argument in case the requested conversion is
+  /// not supported.
+  /// \param[in] From name of the source character encoding
+  /// \param[in] To name of the target character encoding
+  /// \return a EncodingConverter instance or an error code
+  static ErrorOr<EncodingConverter> create(StringRef From, StringRef To);
+
+  EncodingConverter(const EncodingConverter &) = delete;
+  EncodingConverter &operator=(const EncodingConverter &) = delete;
+
+  EncodingConverter(EncodingConverter &&Other)
+      : Converter(std::move(Other.Converter)) {}
+
+  EncodingConverter &operator=(EncodingConverter &&Other) {
+    if (this != &Other)
+      Converter = std::move(Other.Converter);
+    return *this;
+  }
+
+  ~EncodingConverter() = default;
+
+  /// Converts a string.
+  /// \param[in] Source source string
+  /// \param[out] Result container for converted string
+  /// \return error code in case something went wrong
+  std::error_code convert(StringRef Source,
+                          SmallVectorImpl<char> &Result) const {
+    return Converter->convert(Source, Result);
+  }
+
+  ErrorOr<std::string> convert(StringRef Source) const {
+    SmallString<100> Result;
+    auto EC = Converter->convert(Source, Result);
+    if (!EC)
+      return std::string(Result);
+    return EC;
+  }
+};
+
+} // namespace llvm
+
+#endif

llvm/lib/Support/CMakeLists.txt

@@ -186,6 +186,7 @@ add_llvm_component_library(LLVMSupport
   ELFAttributes.cpp
   ELFAttrParserCompact.cpp
   ELFAttrParserExtended.cpp
+  EncodingConverter.cpp
   Error.cpp
   ErrorHandling.cpp
   ExponentialBackoff.cpp
@@ -316,6 +317,14 @@ add_llvm_component_library(LLVMSupport
   Demangle
   )
 
+# Link ICU library if it is an external library.
+if(ICU_FOUND)
+  target_link_libraries(LLVMSupport
+  PRIVATE
+  ${ICU_LIBRARIES}
+  )
+endif()
+
 set(llvm_system_libs ${system_libs})
 
 # This block is only needed for llvm-config. When we deprecate llvm-config and