[Impeller] Convert the ImpellerC command line arguments to UTF-8 on Windows (flutter/engine#36335)

engine/src/flutter/ci/licenses_golden/licenses_flutter

@@ -335,6 +335,7 @@ FILE: ../../../flutter/fml/platform/linux/message_loop_linux.h
 FILE: ../../../flutter/fml/platform/linux/paths_linux.cc
 FILE: ../../../flutter/fml/platform/linux/timerfd.cc
 FILE: ../../../flutter/fml/platform/linux/timerfd.h
+FILE: ../../../flutter/fml/platform/posix/command_line_posix.cc
 FILE: ../../../flutter/fml/platform/posix/file_posix.cc
 FILE: ../../../flutter/fml/platform/posix/mapping_posix.cc
 FILE: ../../../flutter/fml/platform/posix/native_library_posix.cc
@@ -342,6 +343,7 @@ FILE: ../../../flutter/fml/platform/posix/paths_posix.cc
 FILE: ../../../flutter/fml/platform/posix/posix_wrappers_posix.cc
 FILE: ../../../flutter/fml/platform/posix/shared_mutex_posix.cc
 FILE: ../../../flutter/fml/platform/posix/shared_mutex_posix.h
+FILE: ../../../flutter/fml/platform/win/command_line_win.cc
 FILE: ../../../flutter/fml/platform/win/errors_win.cc
 FILE: ../../../flutter/fml/platform/win/errors_win.h
 FILE: ../../../flutter/fml/platform/win/file_win.cc

engine/src/flutter/fml/BUILD.gn

@@ -214,6 +214,7 @@ source_set("fml") {
 
   if (is_win) {
     sources += [
+      "platform/win/command_line_win.cc",
       "platform/win/errors_win.cc",
       "platform/win/errors_win.h",
       "platform/win/file_win.cc",
@@ -226,6 +227,7 @@ source_set("fml") {
     ]
   } else {
     sources += [
+      "platform/posix/command_line_posix.cc",
       "platform/posix/file_posix.cc",
       "platform/posix/mapping_posix.cc",
       "platform/posix/native_library_posix.cc",

engine/src/flutter/fml/command_line.h

@@ -38,6 +38,7 @@
 
 #include <cstddef>
 #include <initializer_list>
+#include <optional>
 #include <string>
 #include <string_view>
 #include <unordered_map>
@@ -239,6 +240,13 @@ inline CommandLine CommandLineFromInitializerList(
 // outlined at the top of this file.
 std::vector<std::string> CommandLineToArgv(const CommandLine& command_line);
 
+// Builds a |CommandLine| by obtaining the arguments of the process using host
+// platform APIs. The resulting |CommandLine| will be encoded in UTF-8.
+// Returns an empty optional if this is not supported on the host platform.
+//
+// This can be useful on platforms where argv may not be provided as UTF-8.
+std::optional<CommandLine> CommandLineFromPlatform();
+
 }  // namespace fml
 
 #endif  // LIB_FML_COMMAND_LINE_H_

engine/src/flutter/fml/platform/posix/command_line_posix.cc

@@ -0,0 +1,13 @@
+// Copyright 2013 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "flutter/fml/command_line.h"
+
+namespace fml {
+
+std::optional<CommandLine> CommandLineFromPlatform() {
+  return std::nullopt;
+}
+
+}  // namespace fml

engine/src/flutter/fml/platform/win/command_line_win.cc

@@ -0,0 +1,35 @@
+// Copyright 2013 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "flutter/fml/command_line.h"
+
+#include <windows.h>
+
+#include <Shellapi.h>
+#include <memory>
+
+namespace fml {
+
+std::optional<CommandLine> CommandLineFromPlatform() {
+  wchar_t* command_line = GetCommandLineW();
+  int unicode_argc;
+  std::unique_ptr<wchar_t*[], decltype(::LocalFree)*> unicode_argv(
+      CommandLineToArgvW(command_line, &unicode_argc), ::LocalFree);
+  if (!unicode_argv) {
+    return std::nullopt;
+  }
+  std::vector<std::string> utf8_argv;
+  for (int i = 0; i < unicode_argc; ++i) {
+    wchar_t* arg = unicode_argv[i];
+    int arg_len = WideCharToMultiByte(CP_UTF8, 0, arg, wcslen(arg), nullptr, 0,
+                                      nullptr, nullptr);
+    std::string utf8_arg(arg_len, 0);
+    WideCharToMultiByte(CP_UTF8, 0, arg, -1, utf8_arg.data(), utf8_arg.size(),
+                        nullptr, nullptr);
+    utf8_argv.push_back(std::move(utf8_arg));
+  }
+  return CommandLineFromIterators(utf8_argv.begin(), utf8_argv.end());
+}
+
+}  // namespace fml

engine/src/flutter/impeller/compiler/impellerc_main.cc

@@ -227,7 +227,9 @@ bool Main(const fml::CommandLine& command_line) {
 }  // namespace impeller
 
 int main(int argc, char const* argv[]) {
-  return impeller::compiler::Main(fml::CommandLineFromArgcArgv(argc, argv))
-             ? EXIT_SUCCESS
-             : EXIT_FAILURE;
+  std::optional<fml::CommandLine> command_line = fml::CommandLineFromPlatform();
+  if (!command_line) {
+    command_line = fml::CommandLineFromArgcArgv(argc, argv);
+  }
+  return impeller::compiler::Main(*command_line) ? EXIT_SUCCESS : EXIT_FAILURE;
 }