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[FML] Replace deprecated wstring_convert with Win32 APIs - #191394
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Replaced the deprecated `std::wstring_convert` and `<codecvt>` usage in `wstring_conversion.cc` with native Win32 APIs `MultiByteToWideChar` and `WideCharToMultiByte`. This avoids the deprecation warnings and prevents potential correctness bugs (such as slash-collapsing in URLs) and performance overhead associated with `std::filesystem::path`. Added unit tests to verify that URLs are preserved during conversion.
Replaces Win32 APIs in wstring_conversion.cc with C++20 std::filesystem::path conversions.
bkonyi
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Code Review
This pull request replaces the deprecated std::wstring_convert with std::filesystem::path for UTF-8 and UTF-16 string conversions on Windows, and adds new unit tests. The review feedback notes that using std::filesystem::path for general-purpose string conversion can cause unexpected path normalization, potentially corrupting non-path strings like URLs. The reviewer suggests using native Win32 APIs (WideCharToMultiByte and MultiByteToWideChar) instead.
| #include <filesystem> | ||
| #include <string> |
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Instead of <filesystem>, we should include <windows.h> to use the native Win32 APIs WideCharToMultiByte and MultiByteToWideChar for correct and efficient string conversion.
| #include <filesystem> | |
| #include <string> | |
| #include <windows.h> | |
| #include <string> |
| std::string WideStringToUtf8(const std::wstring_view str) { | ||
| WideStringConverter converter; | ||
| return converter.to_bytes(str.data(), str.data() + str.size()); | ||
| if (str.empty()) { | ||
| return {}; | ||
| } | ||
| std::filesystem::path path(str); | ||
| std::u8string u8str = path.u8string(); | ||
| return std::string(u8str.begin(), u8str.end()); | ||
| } |
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Using std::filesystem::path for general-purpose string conversion is semantically incorrect and can lead to unexpected behavior. std::filesystem::path is designed specifically for filesystem paths and may perform path normalization (such as converting directory separators / to \ on Windows) or other path-specific validations. This can corrupt non-path strings, such as URLs (e.g., https://flutter.dev could be altered).
Since this file is Windows-specific (platform/win), we should use the standard, high-performance Win32 API WideCharToMultiByte for robust and correct UTF-8/UTF-16 conversions.
std::string WideStringToUtf8(const std::wstring_view str) {
if (str.empty()) {
return {};
}
int size_needed = WideCharToMultiByte(CP_UTF8, 0, str.data(), static_cast<int>(str.size()), NULL, 0, NULL, NULL);
if (size_needed <= 0) {
return {};
}
std::string result(size_needed, 0);
WideCharToMultiByte(CP_UTF8, 0, str.data(), static_cast<int>(str.size()), &result[0], size_needed, NULL, NULL);
return result;
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Updated to use WideCharToMultiByte.
| std::wstring Utf8ToWideString(const std::string_view str) { | ||
| WideStringConverter converter; | ||
| return converter.from_bytes(str.data(), str.data() + str.size()); | ||
| if (str.empty()) { | ||
| return {}; | ||
| } | ||
| const char8_t* start = reinterpret_cast<const char8_t*>(str.data()); | ||
| const char8_t* end = start + str.size(); | ||
| std::filesystem::path path(start, end); | ||
| return path.wstring(); | ||
| } |
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Using std::filesystem::path for general-purpose string conversion is semantically incorrect and can lead to unexpected behavior (such as path normalization or separator conversion). Since this is Windows-specific code, we should use the standard Win32 API MultiByteToWideChar.
std::wstring Utf8ToWideString(const std::string_view str) {
if (str.empty()) {
return {};
}
int size_needed = MultiByteToWideChar(CP_UTF8, 0, str.data(), static_cast<int>(str.size()), NULL, 0);
if (size_needed <= 0) {
return {};
}
std::wstring result(size_needed, 0);
MultiByteToWideChar(CP_UTF8, 0, str.data(), static_cast<int>(str.size()), &result[0], size_needed);
return result;
}There was a problem hiding this comment.
Updated to use MultiByteToWideChar.
|
So this change is technically correct, but the bot's comments are valid. Do we care if we migrate to using |
gaaclarke
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gaaclarke
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So this change is technically correct, but the bot's comments are valid. Do we care if we migrate to using
<windows.h>APIs from<codecvt>, or should we ignore these comments and just use<filesystem>for consistency?
I think we should take the bots advice here. I think there are subtle ways using paths for nonpaths could mess things up in weird ways. These functions are too generically named, someone could easily use it on accident. I poked around and I don't think there is a clean c++20 way to do this.
Thanks for digging into this, sorry it isn't as straightforward as we'd like.
…g conversion Addresses review feedback by switching to native Win32 APIs (MultiByteToWideChar and WideCharToMultiByte) instead of std::filesystem::path.
bkonyi
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Not a problem! I'd rather us get this right than just land whatever works :) |
|
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Replaces deprecated
std::wstring_convertand<codecvt>usage inengine/src/flutter/fml/platform/win/wstring_conversion.ccwith native Win32 APIsMultiByteToWideCharandWideCharToMultiByte.Changes
WideStringToUtf8: UsesWideCharToMultiBytewithCP_UTF8.Utf8ToWideString: UsesMultiByteToWideCharwithCP_UTF8.wstring_conversion_unittests.ccto verify string conversions with URLs and Unicode characters.