Bug 1766359 - Fix unreachable-code-return warnings in Windows builds. r=emilio,mhowell,nika,rkraesig

dom/system/PathUtils.cpp(77,10): error: 'return' will never be executed [-Werror,-Wunreachable-code-return]
  return false;
         ^~~~~
ipc/chromium/src/chrome/common/ipc_channel_win.cc(479,10): error: 'return' will never be executed [-Werror,-Wunreachable-code-return]
  return true;
         ^~~~
mozglue/misc/PreXULSkeletonUI.cpp(1263,10): error: 'return' will never be executed [-Werror,-Wunreachable-code-return]
  return 0;
         ^
mozglue/tests/TestPEExportSection.cpp(348,12): error: 'return' will never be executed [-Werror,-Wunreachable-code-return]
    return 0;
           ^
security/manager/ssl/OSReauthenticator.cpp(428,10): error: 'return' will never be executed [-Werror,-Wunreachable-code-return]
  return NS_OK;
         ^~~~~
toolkit/components/maintenanceservice/maintenanceservice.cpp(214,10): error: 'return' will never be executed [-Werror,-Wunreachable-code-return]
  return 0;
         ^
widget/windows/WindowsUIUtils.cpp(383,10): error: 'return' will never be executed [-Werror,-Wunreachable-code-return]
  return false;
         ^~~~~

Differential Revision: https://phabricator.services.mozilla.com/D144661

build/moz.configure/warnings.configure

@@ -65,7 +65,7 @@ check_and_add_warning("-Wno-error=tautological-type-limit-compare")
 
 # catches some dead code
 add_warning("-Wunreachable-code", when=not_clang_cl)
-check_and_add_warning("-Wunreachable-code-return", when=not_clang_cl)
+check_and_add_warning("-Wunreachable-code-return")
 
 # catches parameters that are set but not read
 # Only enable on clang because gcc reports false positives.

dom/system/PathUtils.cpp

@@ -71,10 +71,12 @@ static bool DoWindowsPathCheck() {
 #ifdef XP_WIN
 #  ifdef DEBUG
   return true;
-#  endif  // DEBUG
+#  else  // DEBUG
   return xpc::IsInAutomation();
-#endif  // XP_WIN
+#  endif  // DEBUG
+#else  // XP_WIN
   return false;
+#endif  // XP_WIN
 }
 
 /* static */

ipc/chromium/src/chrome/common/ipc_channel_win.cc

@@ -475,8 +475,6 @@ bool Channel::ChannelImpl::ProcessIncomingMessages(
 
     bytes_read = 0;  // Get more data.
   }
-
-  return true;
 }
 
 bool Channel::ChannelImpl::ProcessOutgoingMessages(

mozglue/misc/PreXULSkeletonUI.cpp

@@ -1259,8 +1259,6 @@ DWORD WINAPI AnimateSkeletonUI(void* aUnused) {
       return 0;
     }
   }
-
-  return 0;
 }
 
 LRESULT WINAPI PreXULSkeletonUIProc(HWND hWnd, UINT msg, WPARAM wParam,

mozglue/tests/TestPEExportSection.cpp

@@ -345,7 +345,6 @@ class ChildProcess final {
     for (;;) {
       ::Sleep(100);
     }
-    return 0;
   }
 
   ChildProcess(const wchar_t* aExecutable, const wchar_t* aOption,

security/manager/ssl/OSReauthenticator.cpp

@@ -424,8 +424,9 @@ static nsresult ReauthenticateUser(const nsAString& prompt,
       prefLastChanged, isAutoAdminLogonEnabled, isRequireSignonEnabled);
 #elif defined(XP_MACOSX)
   return ReauthenticateUserMacOS(prompt, reauthenticated, isBlankPassword);
-#endif  // Reauthentication is not implemented for this platform.
+#else
   return NS_OK;
+#endif  // Reauthentication is not implemented for this platform.
 }
 
 static void BackgroundReauthenticateUser(RefPtr<Promise>& aPromise,

toolkit/components/maintenanceservice/maintenanceservice.cpp

@@ -211,7 +211,6 @@ void BackupOldLogs(LPCWSTR basePath, int numLogsToKeep) {
 DWORD WINAPI EnsureProcessTerminatedThread(LPVOID) {
   Sleep(5000);
   exit(0);
-  return 0;
 }
 
 void StartTerminationThread() {

widget/windows/WindowsUIUtils.cpp

@@ -379,8 +379,9 @@ bool WindowsUIUtils::ComputeOverlayScrollbars() {
   boolean autoHide = false;
   sUiSettings->get_AutoHideScrollBars(&autoHide);
   return autoHide;
-#endif
+#else
   return false;
+#endif
 }
 
 void WindowsUIUtils::UpdateInTabletMode() {