Bug 1733821 - [9/9] Drive-by cleanup: add nullptr_t overload for CheckArg r=nika

Since `CheckArg`'s `aParam` is declared as `const CharT **`, it's
treated as a deduction parameter. Unfortunately, `nullptr` is of type
`nullptr_t`, and it doesn't get coerced before template argument
deduction takes place. To allow passing `nullptr`, people have been
using unwieldy constructs like `static_cast<const wchar_t**>(nullptr)`
when `aParam` isn't needed.

Centralize this by adding an overload of `CheckArg` that explicitly
takes `nullptr_t` and forwards it on to the primary implementation.
Strip out all the now-unnecessary `static_cast`s everywhere else.

No functional changes.

Differential Revision: https://phabricator.services.mozilla.com/D152327

browser/app/winlauncher/LaunchUnelevated.cpp

@@ -144,9 +144,7 @@ LauncherVoidResult LaunchUnelevated(int aArgc, wchar_t* aArgv[]) {
     // This should have already been checked, but just in case...
     EnsureBrowserCommandlineSafe(aArgc, aArgv);
 
-    if (mozilla::CheckArg(aArgc, aArgv, "osint",
-                          static_cast<const wchar_t**>(nullptr),
-                          CheckArgFlag::None)) {
+    if (mozilla::CheckArg(aArgc, aArgv, "osint", nullptr, CheckArgFlag::None)) {
       // If the command line contains -osint, we have to arrange things in a
       // particular order.
       //

browser/app/winlauncher/LauncherProcessWin.cpp

@@ -146,21 +146,16 @@ static void SetMitigationPolicies(mozilla::ProcThreadAttributes& aAttrs,
 static mozilla::LauncherFlags ProcessCmdLine(int& aArgc, wchar_t* aArgv[]) {
   mozilla::LauncherFlags result = mozilla::LauncherFlags::eNone;
 
-  if (mozilla::CheckArg(aArgc, aArgv, "wait-for-browser",
-                        static_cast<const wchar_t**>(nullptr),
+  if (mozilla::CheckArg(aArgc, aArgv, "wait-for-browser", nullptr,
                         mozilla::CheckArgFlag::RemoveArg) ==
           mozilla::ARG_FOUND ||
-      mozilla::CheckArg(aArgc, aArgv, "marionette",
-                        static_cast<const wchar_t**>(nullptr),
+      mozilla::CheckArg(aArgc, aArgv, "marionette", nullptr,
                         mozilla::CheckArgFlag::None) == mozilla::ARG_FOUND ||
-      mozilla::CheckArg(aArgc, aArgv, "backgroundtask",
-                        static_cast<const wchar_t**>(nullptr),
+      mozilla::CheckArg(aArgc, aArgv, "backgroundtask", nullptr,
                         mozilla::CheckArgFlag::None) == mozilla::ARG_FOUND ||
-      mozilla::CheckArg(aArgc, aArgv, "headless",
-                        static_cast<const wchar_t**>(nullptr),
+      mozilla::CheckArg(aArgc, aArgv, "headless", nullptr,
                         mozilla::CheckArgFlag::None) == mozilla::ARG_FOUND ||
-      mozilla::CheckArg(aArgc, aArgv, "remote-debugging-port",
-                        static_cast<const wchar_t**>(nullptr),
+      mozilla::CheckArg(aArgc, aArgv, "remote-debugging-port", nullptr,
                         mozilla::CheckArgFlag::None) == mozilla::ARG_FOUND ||
       mozilla::EnvHasValue("MOZ_AUTOMATION") ||
       mozilla::EnvHasValue("MOZ_HEADLESS")) {
@@ -220,9 +215,9 @@ static bool DoLauncherProcessChecks(int& argc, wchar_t** argv) {
     result = true;
   }
 
-  result |= mozilla::CheckArg(
-                argc, argv, "launcher", static_cast<const wchar_t**>(nullptr),
-                mozilla::CheckArgFlag::RemoveArg) == mozilla::ARG_FOUND;
+  result |=
+      mozilla::CheckArg(argc, argv, "launcher", nullptr,
+                        mozilla::CheckArgFlag::RemoveArg) == mozilla::ARG_FOUND;
 
   return result;
 }
@@ -238,8 +233,7 @@ static mozilla::Maybe<bool> RunAsLauncherProcess(int& argc, wchar_t** argv) {
 #if defined(MOZ_LAUNCHER_PROCESS)
   bool forceLauncher =
       runAsLauncher &&
-      mozilla::CheckArg(argc, argv, "force-launcher",
-                        static_cast<const wchar_t**>(nullptr),
+      mozilla::CheckArg(argc, argv, "force-launcher", nullptr,
                         mozilla::CheckArgFlag::RemoveArg) == mozilla::ARG_FOUND;
 
   mozilla::LauncherRegistryInfo::ProcessType desiredType =
@@ -279,8 +273,7 @@ Maybe<int> LauncherMain(int& argc, wchar_t* argv[],
 
   SetLauncherErrorAppData(aAppData);
 
-  if (CheckArg(argc, argv, "log-launcher-error",
-               static_cast<const wchar_t**>(nullptr),
+  if (CheckArg(argc, argv, "log-launcher-error", nullptr,
                mozilla::CheckArgFlag::RemoveArg) == ARG_FOUND) {
     SetLauncherErrorForceEventLog();
   }
@@ -288,8 +281,7 @@ Maybe<int> LauncherMain(int& argc, wchar_t* argv[],
   // return fast when we're a child process.
   // (The remainder of this function has some side effects that are
   // undesirable for content processes)
-  if (mozilla::CheckArg(argc, argv, "contentproc",
-                        static_cast<const wchar_t**>(nullptr),
+  if (mozilla::CheckArg(argc, argv, "contentproc", nullptr,
                         mozilla::CheckArgFlag::None) == mozilla::ARG_FOUND) {
     // A child process should not instantiate LauncherRegistryInfo.
     return Nothing();

toolkit/xre/CmdLineAndEnvUtils.h

@@ -212,6 +212,14 @@ inline ArgResult CheckArg(int& aArgc, CharT** aArgv, const char* aArg,
   return ar;
 }
 
+template <typename CharT>
+inline ArgResult CheckArg(int& aArgc, CharT** aArgv, const char* aArg,
+                          std::nullptr_t,
+                          CheckArgFlag aFlags = CheckArgFlag::RemoveArg) {
+  return CheckArg<CharT>(aArgc, aArgv, aArg,
+                         static_cast<const CharT**>(nullptr), aFlags);
+}
+
 namespace internal {
 // template <typename T>
 // constexpr bool IsStringRange =
@@ -248,8 +256,8 @@ inline bool EnsureCommandlineSafeImpl(int aArgc, CharT** aArgv,
 
   // If "-osint" (or the equivalent) is not present, then this is trivially
   // satisfied.
-  if (CheckArg(aArgc, aArgv, osintLit, static_cast<const CharT**>(nullptr),
-               CheckArgFlag::None) != ARG_FOUND) {
+  if (CheckArg(aArgc, aArgv, osintLit, nullptr, CheckArgFlag::None) !=
+      ARG_FOUND) {
     return true;
   }
 

toolkit/xre/SafeMode.h

@@ -39,8 +39,7 @@ inline Maybe<bool> IsSafeModeRequested(
     checkArgFlags |= CheckArgFlag::RemoveArg;
   }
 
-  ArgResult ar = CheckArg(aArgc, aArgv, "safe-mode",
-                          static_cast<const CharT**>(nullptr), checkArgFlags);
+  ArgResult ar = CheckArg(aArgc, aArgv, "safe-mode", nullptr, checkArgFlags);
   if (ar == ARG_BAD) {
     return Nothing();
   }