[COFF] Add support for /WX

[smeenai]

Summary

link.exe supports this option to convert warnings into errors, and it's
useful to support in LLD as well.

[compnerd]

COFF/Options.td

88–89

You should move this down and use the QB multiclass instead.

[ruiu]

COFF/DriverUtils.cpp

743

nit: add parentheses on RHS.

COFF/Options.td

88–89

Yes, you can use QB instead.

[smeenai]

COFF/Options.td

88–89

QB is defined in the section for unimplemented arguments, so if anything I'd want to move QB up. However, as best as I can tell, QB doesn't allow specifying help text. We already have B, which is what I was using originally, but that only allows specifying help text for the :no part. I could extend either of those macros to accept a help text for both options or introduce a new multiclass, of course.

[ruiu]

COFF/Options.td

88–89

Makes sense. I'm fine with this.

[smeenai]

Rebase atop D39216

[ruiu]

LGTM

COFF/Config.h

struct Configuration {
   std::string OutputFile;
   std::string ImportName;
   bool ColorDiagnostics;
   bool DoGC = true;
   bool DoICF = true;
   uint64_t ErrorLimit = 20;
   bool Relocatable = true;
   bool Force = false;
+  bool FatalWarnings = false;
   bool Debug = false;
   bool WriteSymtab = true;
   unsigned DebugTypes = static_cast<unsigned>(DebugType::None);
   llvm::SmallString<128> PDBPath;
   std::vector<llvm::StringRef> Argv;
 
   // Symbols in this set are considered as live by the garbage collector.
   std::set<SymbolBody *> GCRoot;

COFF/DriverUtils.cpp

opt::InputArgList ArgParser::parse(ArrayRef<const char *> Argv) {
   // Print the real command line if response files are expanded.
   if (Args.hasArg(OPT_verbose) && Argv.size() != Vec.size()) {
     std::string Msg = "Command line:";
     for (const char *S : Vec)
       Msg += " " + std::string(S);
     message(Msg);
   }
 
+  // Handle /WX early since it converts missing argument warnings to errors.
+  Config->FatalWarnings = Args.hasFlag(OPT_WX, OPT_WX_no, false);
+
   if (MissingCount)
     fatal(Twine(Args.getArgString(MissingIndex)) + ": missing argument");
   for (auto *Arg : Args.filtered(OPT_UNKNOWN))
     warn("ignoring unknown argument: " + Arg->getSpelling());
   return Args;
 }
 
 // link.exe has an interesting feature. If LINK or _LINK_ environment

COFF/Error.cpp

void fatal(std::error_code EC, const Twine &Msg) {
   fatal(Msg + ": " + EC.message());
 }
 
 void fatal(llvm::Error &Err, const Twine &Msg) {
   fatal(errorToErrorCode(std::move(Err)), Msg);
 }
 
 void warn(const Twine &Msg) {
+  if (Config->FatalWarnings) {
+    error(Msg);
+    return;
+  }
+
   std::lock_guard<std::mutex> Lock(Mu);
   print("warning: ", raw_ostream::MAGENTA);
   *ErrorOS << Msg << "\n";
 }
 
 } // namespace coff
 } // namespace lld

COFF/Options.td

 def swaprun_cd : F<"swaprun:cd">;
 def swaprun_net : F<"swaprun:net">;
 def verbose : F<"verbose">;
 def wholearchive_flag : F<"wholearchive">;
 
 def force : F<"force">,
     HelpText<"Allow undefined symbols when creating executables">;
 def force_unresolved : F<"force:unresolved">;
+defm WX : B<"WX", "Treat warnings as errors", "Don't treat warnings as errors">;
 
 defm allowbind : B<"allowbind", "Enable DLL binding (default)",
                    "Disable DLL binding">;
 defm allowisolation : B<"allowisolation", "Enable DLL isolation (default)",
                         "Disable DLL isolation">;
 defm appcontainer : B<"appcontainer",
                       "Image can only be run in an app container",
                       "Image can run outside an app container (default)">;
 defm dynamicbase : B<"dynamicbase", "Enable ASLR (default unless /fixed)",

 def ignore : QF<"ignore">;
 def maxilksize : QF<"maxilksize">;
 def natvis : QF<"natvis">;
 def pdbaltpath : QF<"pdbaltpath">;
 def tlbid : QF<"tlbid">;
 def tlbout : QF<"tlbout">;
 def verbose_all : QF<"verbose">;
 def guardsym : QF<"guardsym">;
-
-defm wx : QB<"wx">;

test/COFF/wx.s

+# REQUIRES: x86
+
+# RUN: llvm-mc -triple=x86_64-windows-msvc -filetype=obj -o %t.obj %s
+# RUN: not lld-link /out:%t.exe /entry:main -notarealoption /WX %t.obj 2>&1 | \
+# RUN:   FileCheck -check-prefix=ERROR %s
+# RUN: not lld-link /out:%t.exe /entry:main -notarealoption /WX:NO /WX %t.obj 2>&1 | \
+# RUN:   FileCheck -check-prefix=ERROR %s
+# RUN: lld-link /out:%t.exe /entry:main -notarealoption /WX /WX:NO %t.obj 2>&1 | \
+# RUN:   FileCheck -check-prefix=WARNING %s
+
+# ERROR: error: ignoring unknown argument: -notarealoption
+# WARNING: warning: ignoring unknown argument: -notarealoption
+
+.text
+.global main
+main:
+  ret