[lld-macho] Add support for -w

[keith]

Summary

This flag suppresses warnings produced by the linker. In ld64 this has
an interesting interaction with -fatal_warnings, it silences the
warnings but the link still fails. Instead of doing that here we still
print the warning and eagerly fail the link in case both are passed,
this seems more reasonable so users can understand why the link fails.

[MaskRay]

lld/Common/ErrorHandler.cpp

246

delete braces for one-line simple body.

lld/Common/ErrorHandler.cpp

 }
 
 void ErrorHandler::warn(const Twine &msg) {
   if (fatalWarnings) {
     error(msg);
     return;
   }
 
+  if (suppressWarnings) {
+    return;
+  }
+
   std::lock_guard<std::mutex> lock(mu);
   reportDiagnostic(getLocation(msg), Colors::MAGENTA, "warning", msg);
   sep = getSeparator(msg);
 }
 
 void ErrorHandler::error(const Twine &msg) {
   // If Visual Studio-style error message mode is enabled,
   // this particular error is printed out as two errors.

lld/MachO/DriverUtils.cpp

InputArgList MachOOptTable::parse(ArrayRef<const char *> argv) {
   // Expand response files (arguments in the form of @<filename>)
   // and then parse the argument again.
   cl::ExpandResponseFiles(saver(), cl::TokenizeGNUCommandLine, vec);
   InputArgList args = ParseArgs(vec, missingIndex, missingCount);
 
   // Handle -fatal_warnings early since it converts missing argument warnings
   // to errors.
   errorHandler().fatalWarnings = args.hasArg(OPT_fatal_warnings);
+  errorHandler().suppressWarnings = args.hasArg(OPT_w);
 
   if (missingCount)
     error(Twine(args.getArgString(missingIndex)) + ": missing argument");
 
   handleColorDiagnostics(args);
 
   for (const Arg *arg : args.filtered(OPT_UNKNOWN)) {
     std::string nearest;

lld/MachO/Options.td

def arch_errors_fatal : Flag<["-"], "arch_errors_fatal">,
     HelpText<"Escalate to errors any warnings about inputs whose architecture does not match the -arch option">,
     Group<grp_rare>;
 def e : Separate<["-"], "e">,
     MetaVarName<"<symbol>">,
     HelpText<"Make <symbol> the entry point of an executable (default is \"start\" from crt1.o)">,
     Group<grp_rare>;
 def w : Flag<["-"], "w">,
     HelpText<"Suppress all warnings">,
-    Flags<[HelpHidden]>,
     Group<grp_rare>;
 def final_output : Separate<["-"], "final_output">,
     MetaVarName<"<name>">,
     HelpText<"Specify dylib install name if -install_name is not used; used by compiler driver for multiple -arch arguments">,
     Group<grp_rare>;
 def arch_multiple : Flag<["-"], "arch_multiple">,
     HelpText<"Augment error and warning messages with the architecture name">,
     Group<grp_rare>;

lld/include/lld/Common/ErrorHandler.h

public:
 
   uint64_t errorCount = 0;
   uint64_t errorLimit = 20;
   StringRef errorLimitExceededMsg = "too many errors emitted, stopping now";
   StringRef errorHandlingScript;
   StringRef logName = "lld";
   bool exitEarly = true;
   bool fatalWarnings = false;
+  bool suppressWarnings = false;
   bool verbose = false;
   bool vsDiagnostics = false;
   bool disableOutput = false;
   std::function<void()> cleanupCallback;
 
   void error(const Twine &msg);
   void error(const Twine &msg, ErrorTag tag, ArrayRef<StringRef> args);
   [[noreturn]] void fatal(const Twine &msg);

lld/test/MachO/fatal-warnings.s

 # REQUIRES: x86
 # RUN: llvm-mc -filetype=obj -triple=x86_64-apple-darwin %s -o %t1.o
 
 # RUN: %no-fatal-warnings-lld %t1.o -o /dev/null -single_module 2>&1 \
 # RUN:     | FileCheck -check-prefix=WARNING %s
 # RUN: not %no-fatal-warnings-lld %t1.o -fatal_warnings -o /dev/null \
 # RUN:     -single_module 2>&1 | FileCheck -check-prefix=ERROR %s
 
+# RUN: %no-fatal-warnings-lld %t1.o -w -o /dev/null -single_module 2>&1 \
+# RUN:     | count 0
+# RUN: not %no-fatal-warnings-lld %t1.o -fatal_warnings -w -o /dev/null \
+# RUN:     -single_module 2>&1 \
+# RUN:     | FileCheck --check-prefix=ERROR %s
+
 # ERROR: error: Option `-single_module' is deprecated
 # WARNING: warning: Option `-single_module' is deprecated
 
 .globl _main
 _main: