[flang][driver] Add checks for missing option arguments

[awarzynski]

Summary

With this patch, the following invocation of the frontend driver will
return an error:

flang-new -fc1 input-file.f90 -o

Similar logic applies to other options that require arguments.

Similar checks are already available in the compiler driver, flang-new
(that's implemented in clangDriver).

[ashermancinelli]

lgtm!

flang/lib/Frontend/CompilerInvocation.cpp

bool CompilerInvocation::CreateFromArgs(CompilerInvocation &res,
 
   // Parse the arguments
   const llvm::opt::OptTable &opts = clang::driver::getDriverOptTable();
   const unsigned includedFlagsBitmask = clang::driver::options::FC1Option;
   unsigned missingArgIndex, missingArgCount;
   llvm::opt::InputArgList args = opts.ParseArgs(
       commandLineArgs, missingArgIndex, missingArgCount, includedFlagsBitmask);
 
+  // Check for missing argument error.
+  if (missingArgCount) {
+    diags.Report(clang::diag::err_drv_missing_argument)
+        << args.getArgString(missingArgIndex) << missingArgCount;
+    success = false;
+  }
+
   // Issue errors on unknown arguments
   for (const auto *a : args.filtered(clang::driver::options::OPT_UNKNOWN)) {
     auto argString = a->getAsString(args);
     std::string nearest;
     if (opts.findNearest(argString, nearest, includedFlagsBitmask) > 1)
       diags.Report(clang::diag::err_drv_unknown_argument) << argString;
     else
       diags.Report(clang::diag::err_drv_unknown_argument_with_suggestion)

flang/test/Driver/missing-arg.f90

+! Make sure that frontend driver options that require arguments are
+! correctly rejected when the argument value is missing.
+
+! REQUIRES: new-flang-driver
+
+!-----------
+! RUN lines
+!-----------
+! RUN: not %flang_fc1 -E %s -o 2>&1 | FileCheck %s
+! RUN: not %flang_fc1 -E %s -U 2>&1 | FileCheck %s
+! RUN: not %flang_fc1 -E %s -D 2>&1 | FileCheck %s
+! RUN: not %flang_fc1 -E %s -I 2>&1 | FileCheck %s
+! RUN: not %flang_fc1 -E %s -J 2>&1 | FileCheck %s
+! RUN: not %flang_fc1 -E %s -module-dir 2>&1 | FileCheck %s
+! RUN: not %flang_fc1 -E %s -module-suffix 2>&1 | FileCheck %s
+! RUN: not %flang_fc1 -E %s -fintrinsic-modules-path 2>&1 | FileCheck %s
+
+!-----------------------
+! EXPECTED OUTPUT
+!-----------------------
+! CHECK: error: argument to '-{{.*}}' is missing (expected 1 value)