[obj2yaml] Refactor command line parsing

[MaskRay]

Summary

Similar to D73982 for yaml2obj.

• Hide unrelated options.
• Add an OVERVIEW: message.
• Disallow single-dash long options.

[jhenderson]

LGTM!

llvm/test/tools/obj2yaml/help.test

+## Show that help text is printed correctly when requested.
+
+# RUN: obj2yaml -h | FileCheck %s --check-prefixes=CHECK,CATEG --implicit-check-not=Options:
+# RUN: obj2yaml --help | FileCheck %s --check-prefixes=CHECK,CATEG --implicit-check-not=Options:
+# RUN: obj2yaml --help-list | FileCheck %s --implicit-check-not=Options:
+
+# CHECK: OVERVIEW: Dump a YAML description from an object file
+# CHECK: USAGE: obj2yaml{{(.exe)?}} [options] <input file>{{$}}
+# CHECK: OPTIONS:
+# CATEG: Generic Options:
+# CATEG: obj2yaml Options:

llvm/tools/obj2yaml/obj2yaml.cpp

 #include "llvm/Support/Errc.h"
 #include "llvm/Support/InitLLVM.h"
 #include "llvm/Support/ToolOutputFile.h"
 #include "llvm/Support/WithColor.h"
 
 using namespace llvm;
 using namespace llvm::object;
 
+static cl::OptionCategory Cat("obj2yaml Options");
+
 static cl::opt<std::string>
     InputFilename(cl::Positional, cl::desc("<input file>"), cl::init("-"));
 static cl::opt<std::string> OutputFilename("o", cl::desc("Output filename"),
                                            cl::value_desc("filename"),
-                                           cl::init("-"), cl::Prefix);
+                                           cl::init("-"), cl::Prefix,
+                                           cl::cat(Cat));
 static cl::bits<RawSegments> RawSegment(
     "raw-segment",
     cl::desc("Mach-O: dump the raw contents of the listed segments instead of "
              "parsing them:"),
-    cl::values(clEnumVal(data, "__DATA"), clEnumVal(linkedit, "__LINKEDIT")));
+    cl::values(clEnumVal(data, "__DATA"), clEnumVal(linkedit, "__LINKEDIT")),
+    cl::cat(Cat));
 
 static Error dumpObject(const ObjectFile &Obj, raw_ostream &OS) {
   if (Obj.isCOFF())
     return errorCodeToError(coff2yaml(OS, cast<COFFObjectFile>(Obj)));
 
   if (Obj.isXCOFF())
     return xcoff2yaml(OS, cast<XCOFFObjectFile>(Obj));
 
static void reportError(StringRef Input, Error Err) {
   logAllUnhandledErrors(std::move(Err), OS);
   OS.flush();
   errs() << "Error reading file: " << Input << ": " << ErrMsg;
   errs().flush();
 }
 
 int main(int argc, char *argv[]) {
   InitLLVM X(argc, argv);
-  cl::ParseCommandLineOptions(argc, argv);
+  cl::HideUnrelatedOptions(Cat);
+  cl::ParseCommandLineOptions(
+      argc, argv, "Dump a YAML description from an object file", nullptr,
+      nullptr, /*LongOptionsUseDoubleDash=*/true);
 
   std::error_code EC;
   std::unique_ptr<ToolOutputFile> Out(
       new ToolOutputFile(OutputFilename, EC, sys::fs::OF_None));
   if (EC) {
     WithColor::error(errs(), "obj2yaml")
         << "failed to open '" + OutputFilename + "': " + EC.message() << '\n';
     return 1;