Bug 1569089 - Sync std handles after AttachConsole(). r=aklotz

AttachConsole() may change Win32 std handle values if Firefox is launched from
cmd.exe that makes discrepancy between Win32 and CRT. This patch synchronizes
both std handles.

Differential Revision: https://phabricator.services.mozilla.com/D51275

--HG--
extra : moz-landing-system : lando

widget/windows/WindowsConsole.cpp

@@ -10,23 +10,41 @@
 
 namespace mozilla {
 
+static void AssignStdHandle(const char* aPath, const char* aMode, FILE* aStream,
+                            DWORD aStdHandle) {
+  // Visual Studio's _fileno() returns -2 for the standard
+  // streams if they aren't associated with an output stream.
+  const int fd = _fileno(aStream);
+  if (fd == -2) {
+    freopen(aPath, aMode, aStream);
+    return;
+  }
+  if (fd < 0) {
+    return;
+  }
+
+  const HANDLE handle = reinterpret_cast<HANDLE>(_get_osfhandle(fd));
+  if (handle == INVALID_HANDLE_VALUE) {
+    return;
+  }
+
+  const HANDLE oldHandle = GetStdHandle(aStdHandle);
+  if (handle == oldHandle) {
+    return;
+  }
+
+  SetStdHandle(aStdHandle, handle);
+}
+
 // This code attaches the process to the appropriate console.
 void UseParentConsole() {
   if (AttachConsole(ATTACH_PARENT_PROCESS)) {
     // Redirect the standard streams to the existing console, but
     // only if they haven't been redirected to a valid file.
-    // Visual Studio's _fileno() returns -2 for the standard
-    // streams if they aren't associated with an output stream.
-    if (_fileno(stdout) == -2) {
-      freopen("CONOUT$", "w", stdout);
-    }
+    AssignStdHandle("CONOUT$", "w", stdout, STD_OUTPUT_HANDLE);
     // There is no CONERR$, so use CONOUT$ for stderr as well.
-    if (_fileno(stderr) == -2) {
-      freopen("CONOUT$", "w", stderr);
-    }
-    if (_fileno(stdin) == -2) {
-      freopen("CONIN$", "r", stdin);
-    }
+    AssignStdHandle("CONOUT$", "w", stderr, STD_ERROR_HANDLE);
+    AssignStdHandle("CONIN$", "r", stdin, STD_INPUT_HANDLE);
   }
 }