[lld/mac] Abort link immediately on invalid -undefined argument

[thakis]

Summary

I tried -undefined suppress without -flat_namespace.
lld printed '-undefined suppress' only valid with '-flat_namespace'
followed by many many screenfuls of error messages about undefined
symbols, making the original diag hard to see.

This is probably the common case when using -undefined, so let's
just abort the link immediately when there's an invalid -undefined
arg.

[int3]

lld/MachO/Driver.cpp

1611–1612

how about changing the error() call in getUndefinedSymbolTreatment to fatal() instead? That way the motivation for the early exit is clearer + we won't accidentally apply this early exit to other error messages in the future

[thakis]

lld/MachO/Driver.cpp

1611–1612

That's a good idea, thanks. Done.

It does have the effect that -undefined bogus with -fatal_warnings no longer aborts early, while it did previously. That's probably fine.

lld/MachO/Driver.cpp

getUndefinedSymbolTreatment(const ArgList &args) {
   if (treatment == UndefinedSymbolTreatment::unknown) {
     warn(Twine("unknown -undefined TREATMENT '") + treatmentStr +
          "', defaulting to 'error'");
     treatment = UndefinedSymbolTreatment::error;
   } else if (config->namespaceKind == NamespaceKind::twolevel &&
              (treatment == UndefinedSymbolTreatment::warning ||
               treatment == UndefinedSymbolTreatment::suppress)) {
     if (treatment == UndefinedSymbolTreatment::warning)
-      error("'-undefined warning' only valid with '-flat_namespace'");
+      fatal("'-undefined warning' only valid with '-flat_namespace'");
     else
-      error("'-undefined suppress' only valid with '-flat_namespace'");
+      fatal("'-undefined suppress' only valid with '-flat_namespace'");
     treatment = UndefinedSymbolTreatment::error;
   }
   return treatment;
 }
 
 static ICFLevel getICFLevel(const ArgList &args) {
   StringRef icfLevelStr = args.getLastArgValue(OPT_icf_eq);
   auto icfLevel = StringSwitch<ICFLevel>(icfLevelStr)
#endif
 
   if (const Arg *arg =
           args.getLastArg(OPT_flat_namespace, OPT_twolevel_namespace))
     config->namespaceKind = arg->getOption().getID() == OPT_twolevel_namespace
                                 ? NamespaceKind::twolevel
                                 : NamespaceKind::flat;
 
   config->undefinedSymbolTreatment = getUndefinedSymbolTreatment(args);
 
   if (config->outputType == MH_EXECUTE)
     config->entry = symtab->addUndefined(args.getLastArgValue(OPT_e, "_main"),
                                          /*file=*/nullptr,
                                          /*isWeakRef=*/false);
 
   config->librarySearchPaths =
       getLibrarySearchPaths(args, config->systemLibraryRoots);
   config->frameworkSearchPaths =
       getFrameworkSearchPaths(args, config->systemLibraryRoots);

lld/test/MachO/treat-undef-sym.s

 # RUN: not %lld -dylib -dead_strip -undefined error -o /dev/null %t/live.o 2>&1\
 # RUN:     | FileCheck --check-prefix=ERROR %s
 # RUN: %lld -dylib -dead_strip -undefined error -o /dev/null %t/dead.o
 
 # ERROR: error: undefined symbol: _bar
 # ERROR-NEXT: >>> referenced by
 
 # INVAL-WARNING: error: '-undefined warning' only valid with '-flat_namespace'
-# INVAL-WARNING-NEXT: error: undefined symbol: _bar
+# INVAL-WARNING-NOT: error: undefined symbol: _bar
 
 # INVAL-SUPPRESS: error: '-undefined suppress' only valid with '-flat_namespace'
-# INVAL-SUPPRESS-NEXT: error: undefined symbol: _bar
+# INVAL-SUPPRESS-NOT: error: undefined symbol: _bar
 
 # WARNING: warning: undefined symbol: _bar
 # WARNING-NEXT: >>> referenced by
 
 # UNKNOWN: unknown -undefined TREATMENT 'bogus'
 # UNKNOWN-NEXT: error: undefined symbol: _bar
 # UNKNOWN-NEXT: >>> referenced by