[lld-macho] Error out if we encounter a HelpHidden flag in tests

[int3]

Summary

@thakis caught a bunch of implemented flags for which HelpHidden wasn't
removed. This diff ensures that we prevent those issues going ahead.

I initially considered making %lld expand to include
-fatal_warnings, but that would've made testing for desired warnings
more awkward. Hence this approach.

[compnerd]

I still don't really like the environment variable approach to the testing.

[thakis]

I'm also not a super fan of things depending on env vars:

1. I often copy-paste the output of llvm-lit lld/tests/some-test.s -vv. LLD_IN_TEST isn't in that output but set implicitly by lit, so that means copying the env now has magically different behavior (for that reason, a whole bunch of tests in the COFF port explicitly set env LLD_IN_TESTS=1 redundantly -- but we'd have to add that to every single test)

2. This gives LLD_IN_TEST a much wider semantic meaning than it had before. Before, it's a very targeted thing for making sure we do fast exit and global exception handling and test repeats; now it affects basically anything

I think globally passing -fatal_warnings is a bit less surprising, and it's not so bad. I prootyped it in D92575 -- wdyt? (I can put in the two test.s changes you have in here if you like it.)

[int3]

Good points! I do copy-paste llvm-lit's output pretty often too...

Let's go with yours :)

lld/MachO/Driver.cpp

static void warnIfUnimplementedOption(const opt::Option &opt) {
   case OPT_grp_obsolete:
     warn("Option `" + opt.getPrefixedName() +
          "' is obsolete. Please modernize your usage.");
     break;
   case OPT_grp_ignored:
     warn("Option `" + opt.getPrefixedName() + "' is ignored.");
     break;
   default:
-    warn("Option `" + opt.getPrefixedName() +
-         "' is not yet implemented. Stay tuned...");
+    Twine msg = "Option `" + opt.getPrefixedName() +
+                "' is not yet implemented. Stay tuned...";
+    if (getenv("LLD_IN_TEST"))
+      error(msg);
+    else
+      warn(msg);
+
     break;
   }
 }
 
 static const char *getReproduceOption(opt::InputArgList &args) {
   if (auto *arg = args.getLastArg(OPT_reproduce))
     return arg->getValue();
   return getenv("LLD_REPRODUCE");

lld/test/MachO/load-commands.s

 # REQUIRES: x86
 # RUN: rm -rf %t && mkdir -p %t
 # RUN: llvm-mc -filetype=obj -triple=x86_64-apple-darwin %s -o %t/test.o
 # RUN: %lld -o %t/executable %t/test.o
-# RUN: %lld -fatal_warnings -execute -o %t/explicit-executable %t/test.o
-# RUN: %lld -fatal_warnings -bundle -o %t/bundle %t/test.o
-# RUN: %lld -fatal_warnings -dylib -o %t/dylib %t/test.o
+# RUN: %lld -execute -o %t/explicit-executable %t/test.o
+# RUN: %lld -bundle -o %t/bundle %t/test.o
+# RUN: %lld -dylib -o %t/dylib %t/test.o
 
 ## These load commands should be in every final output binary.
 # COMMON-DAG: cmd LC_DYLD_INFO_ONLY
 # COMMON-DAG: cmd LC_SYMTAB
 # COMMON-DAG: cmd LC_DYSYMTAB
 # COMMON-DAG: cmd LC_UUID
 
 ## Check for the presence of load commands that are essential for a working

lld/test/MachO/x86-64-reloc-unsigned.s

 # REQUIRES: x86
 # RUN: llvm-mc -filetype=obj -triple=x86_64-apple-darwin %s -o %t.o
 # RUN: %lld -o %t %t.o
 # RUN: llvm-objdump --macho --rebase --full-contents %t | FileCheck %s
 
-# RUN: %lld -fatal_warnings -pie -o %t-pie %t.o
+# RUN: %lld -pie -o %t-pie %t.o
 # RUN: llvm-objdump --macho --rebase %t-pie | FileCheck %s --check-prefix=PIE
-# RUN: %lld -fatal_warnings -pie -no_pie -o %t-no-pie %t.o
+# RUN: %lld -pie -no_pie -o %t-no-pie %t.o
 # RUN: llvm-objdump --macho --rebase %t-no-pie | FileCheck %s --check-prefix=NO-PIE
-# RUN: %lld -fatal_warnings -no_pie -pie -o %t-no-pie %t.o
+# RUN: %lld -no_pie -pie -o %t-no-pie %t.o
 # RUN: llvm-objdump --macho --rebase %t-no-pie | FileCheck %s --check-prefix=NO-PIE
 
 # RUN: %lld -platform_version macos 10.6.0 11.0 -o %t-pie %t.o
 # RUN: llvm-objdump --macho --rebase %t-pie | FileCheck %s --check-prefix=PIE
 # RUN: %lld -platform_version macos 10.5.0 11.0 -o %t-no-pie %t.o
 # RUN: llvm-objdump --macho --rebase %t-no-pie | FileCheck %s --check-prefix=NO-PIE
 
 # CHECK:       Contents of section __DATA,foo: