Report EISDIR when opening a directory on AIX

llvm/lib/Support/CommandLine.cpp

if (!Res || !Res->exists()) {
       }
       if (!EC)
         EC = llvm::errc::no_such_file_or_directory;
       return createStringError(EC, Twine("cannot not open file '") + FName +
                                        "': " + EC.message());
     }
     const llvm::vfs::Status &FileStatus = Res.get();
 
+    if (FileStatus.isDirectory()) {
+      return createStringError(std::make_error_code(std::errc::is_a_directory),
+                               Twine("cannot not open file '") + FName +
+                                   "': Is a directory");
+    }
     auto IsEquivalent =
         [FileStatus, this](const ResponseFileRecord &RFile) -> ErrorOr<bool> {
       ErrorOr<llvm::vfs::Status> RHS = FS->status(RFile.File);
       if (!RHS)
         return RHS.getError();
       return FileStatus.equivalent(*RHS);
     };
 

llvm/unittests/Support/CommandLineTest.cpp

TEST(CommandLineTest, BadResponseFile) {
   SmallVector<const char *, 2> Argv = {"clang", AFileExp.c_str()};
 
   bool Res = cl::ExpandResponseFiles(Saver, cl::TokenizeGNUCommandLine, Argv);
   ASSERT_TRUE(Res);
   ASSERT_EQ(2U, Argv.size());
   ASSERT_STREQ(Argv[0], "clang");
   ASSERT_STREQ(Argv[1], AFileExp.c_str());
 
-#if !defined(_AIX) && !defined(__MVS__)
   std::string ADirExp = std::string("@") + std::string(ADir.path());
   Argv = {"clang", ADirExp.c_str()};
   Res = cl::ExpandResponseFiles(Saver, cl::TokenizeGNUCommandLine, Argv);
   ASSERT_FALSE(Res);
   ASSERT_EQ(2U, Argv.size());
   ASSERT_STREQ(Argv[0], "clang");
   ASSERT_STREQ(Argv[1], ADirExp.c_str());
-#endif
 }
 
 TEST(CommandLineTest, SetDefaultValue) {
   cl::ResetCommandLineParser();
 
   StackOption<std::string> Opt1("opt1", cl::init("true"));
   StackOption<bool> Opt2("opt2", cl::init(true));
   cl::alias Alias("alias", llvm::cl::aliasopt(Opt2));