[llvm] [Support]Look up in top-level subcommand as a fallback when looking options for a custom subcommand. (PR #71776)

[Snehasish Kumar via llvm-commits]

================
@@ -525,6 +525,74 @@ TEST(CommandLineTest, LookupFailsInWrongSubCommand) {
   EXPECT_FALSE(Errs.empty());
 }
 
+TEST(CommandLineTest, SubcommandOptions) {
+  enum LiteralOptionEnum {
+    foo,
+    bar,
+    baz,
+  };
+
+  cl::ResetCommandLineParser();
+
+  // This is a top-level option and not associated with a subcommand.
+  // A command line using subcommand should parse both subcommand options and
+  // top-level options.  A valid use case is that users of llvm command line
+  // tools should be able to specify top-level options defined in any library.
+  cl::opt<std::string> TopLevelOpt("str", cl::init("txt"),
+                                   cl::desc("A top-level option."));
+
+  StackSubCommand SC("sc", "Subcommand");
+
+  // The positional argument.
+  StackOption<std::string> PositionalOpt(
+      cl::Positional, cl::desc("positional argument test coverage"),
+      cl::sub(SC));
+  // Thel literal argument.
+  StackOption<LiteralOptionEnum> LiteralOpt(
+      cl::desc("literal argument test coverage"), cl::sub(SC), cl::init(bar),
+      cl::values(clEnumVal(foo, "foo"), clEnumVal(bar, "bar"),
+                 clEnumVal(baz, "baz")));
+  StackOption<bool> BoolOpt("enable", cl::sub(SC), cl::init(false));
+
+  std::string Errs;
+  raw_string_ostream OS(Errs);
+
+  for (const char *literalArg : {"--bar", "--foo", "--baz"}) {
+    const char *args[] = {"prog",     "sc",      "input-file",
+                          literalArg, "-enable", "--str=csv"};
+
+    // cl::ParseCommandLineOptions returns true on success. it returns false
+    // and prints errors to caller provided error stream (&OS in this setting).
+    EXPECT_TRUE(cl::ParseCommandLineOptions(6, args, StringRef(), &OS));
----------------
snehasish wrote:

This should be ASSERT_TRUE since it does not make sense to continue if we failed to parse this arg. Though note that it will fail the entire test and the rest of the tests will not be executed (which imo is fine). 

https://github.com/llvm/llvm-project/pull/71776