Redirect stdout/stderr in Windows template (#56089)

Redirects stdout/stderr in the Windows template when creating a console. This fixes the console opened when running from Visual Studio to actually show output, instead of being empty.

Fixes #53169

packages/flutter_tools/templates/app/windows.tmpl/Runner.vcxproj.filters

@@ -27,6 +27,9 @@
     <ClCompile Include="runner\flutter_window.cpp">
       <Filter>Source Files</Filter>
     </ClCompile>
+    <ClCompile Include="runner\utils.cpp">
+      <Filter>Source Files</Filter>
+    </ClCompile>
     <ClCompile Include="runner\win32_window.cpp">
       <Filter>Source Files</Filter>
     </ClCompile>
@@ -53,6 +56,9 @@
     <ClInclude Include="runner\flutter_window.h">
       <Filter>Header Files</Filter>
     </ClInclude>
+    <ClInclude Include="runner\utils.h">
+      <Filter>Header Files</Filter>
+    </ClInclude>
     <ClInclude Include="runner\win32_window.h">
       <Filter>Header Files</Filter>
     </ClInclude>

packages/flutter_tools/templates/app/windows.tmpl/Runner.vcxproj.tmpl

@@ -227,6 +227,7 @@
     <ClCompile Include="runner\main.cpp" />
     <ClCompile Include="flutter\generated_plugin_registrant.cc" />
     <ClCompile Include="runner\run_loop.cpp" />
+    <ClCompile Include="runner\utils.cpp" />
     <ClCompile Include="runner\window_configuration.cpp" />
     <ClCompile Include="runner\win32_window.cpp" />
     <ClCompile Include="runner\flutter_window.cpp" />
@@ -238,6 +239,7 @@
     <ClInclude Include="flutter\generated_plugin_registrant.h" />
     <ClInclude Include="runner\resource.h" />
     <ClInclude Include="runner\run_loop.h" />
+    <ClInclude Include="runner\utils.h" />
     <ClInclude Include="runner\win32_window.h" />
     <ClInclude Include="runner\flutter_window.h" />
     <ClInclude Include="runner\window_configuration.h" />

packages/flutter_tools/templates/app/windows.tmpl/runner/main.cpp

@@ -4,19 +4,19 @@
 
 #include "flutter_window.h"
 #include "run_loop.h"
+#include "utils.h"
 #include "window_configuration.h"
 
-int APIENTRY wWinMain(_In_ HINSTANCE instance,
-                      _In_opt_ HINSTANCE prev,
-                      _In_ wchar_t* command_line,
-                      _In_ int show_command) {
+int APIENTRY wWinMain(_In_ HINSTANCE instance, _In_opt_ HINSTANCE prev,
+                      _In_ wchar_t *command_line, _In_ int show_command) {
   // Attach to console when present (e.g., 'flutter run') or create a
   // new console when running with a debugger.
   if (!::AttachConsole(ATTACH_PARENT_PROCESS) && ::IsDebuggerPresent()) {
-    ::AllocConsole();
+    CreateAndAttachConsole();
   }
 
-  // Initialize COM, so that it is available for use in the library and/or plugins.
+  // Initialize COM, so that it is available for use in the library and/or
+  // plugins.
   ::CoInitializeEx(nullptr, COINIT_APARTMENTTHREADED);
 
   RunLoop run_loop;

packages/flutter_tools/templates/app/windows.tmpl/runner/utils.cpp

+#include "utils.h"
+
+#include <flutter_windows.h>
+#include <io.h>
+#include <stdio.h>
+#include <windows.h>
+
+#include <iostream>
+
+void CreateAndAttachConsole() {
+  if (::AllocConsole()) {
+    FILE *unused;
+    if (freopen_s(&unused, "CONOUT$", "w", stdout)) {
+      _dup2(_fileno(stdout), 1);
+    }
+    if (freopen_s(&unused, "CONOUT$", "w", stderr)) {
+      _dup2(_fileno(stdout), 2);
+    }
+    std::ios::sync_with_stdio();
+    FlutterDesktopResyncOutputStreams();
+  }
+}

packages/flutter_tools/templates/app/windows.tmpl/runner/utils.h

+#ifndef CONSOLE_UTILS_H_
+#define CONSOLE_UTILS_H_
+
+// Creates a console for the process, and redirects stdout and stderr to
+// it for both the runner and the Flutter library.
+void CreateAndAttachConsole();
+
+#endif  // CONSOLE_UTILS_H_